Fundamentals of Plant Protection
COLLEGE OF NATURAL RESOURCES
Student Handout MODULE: Fundamentals of Plant Protection UNIT: Entomology
Year 1 Semester 2
Compiled by: Karma Penjore & Dr. Jamba Gyeltshen August 2009 Updated by Ugyen Yangchen March 2013
CONTENT
Introduction to entomology ........................................................................3
A Class of Distinction ................................................................................................ 3 The Dominance of Insects ......................................................................................... 4 Why are insects so successful? .................................................................................. 5 Economic importance - how do insects affect us? ..................................................... 6 Features of Arthropods .............................................................................................. 7
Classification of Insects ..............................................................................9
Insect orders ............................................................................................................... 9 Insect orders of agricultural importance .................................................................. 11
Insect morphology ....................................................................................13
Head ......................................................................................................................... 13 Antennae .............................................................................................................. 13 Eyes ...................................................................................................................... 16 Mouthparts ........................................................................................................... 16 The insect thorax ...................................................................................................... 20 Legs ...................................................................................................................... 20 Wings ................................................................................................................... 21 Abdomen and external genitalia .............................................................................. 25
Reproduction in insects .............................................................................27
How do insects find their mates? ............................................................................. 27 Types of reproduction in insects .............................................................................. 27
Insect growth and development ................................................................27
Insect life cycle ........................................................................................................ 28 Metamorphosis ......................................................................................................... 29 Insect seasonal cycles .............................................................................................. 31 Larval forms ............................................................................................................. 32 Pupal forms .............................................................................................................. 33
Insect Collection .......................................................................................35
Purpose of collecting and preserving insects ........................................................... 35 Insect collection equipment and materials ............................................................... 36 Preserving insects..................................................................................................... 40 Hard-Bodied Insects............................................................................................. 40 Soft-Bodied Insects .............................................................................................. 40
Pinning, mounting and displaying insects ................................................41
Equipment required .................................................................................................. 41 Pinning Insects ......................................................................................................... 41 Labeling Insects ....................................................................................................... 44
REFERENCE:...........................................................................................45
Entomology handout
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Introduction to entomology
Entomology is a branch of zoology that deals with the study of insects. The term is derived from the Greek word Entomon = Insects and logos = study. Agricultural Entomology deals with the study of insects that affect agriculture. There are other branches of entomology, such as medical entomology, veterinary entomology, and forensic entomology (study of insects inhabiting decomposing remains). With over one million different species inhabiting the earth, insects make up more than 80% of all described animal species and form a major component of the earth's biodiversity. They have different roles: as plant consumers and herbivores, food source for other organisms, scavengers and detritivores (feeding on decomposing organic matter), predators and parasites. Insects also directly affect human welfare by competing with us for food and transmitting diseases. However, not all insects are detrimental to us. For example, bees are used to produce honey, silkworms to produce silk and similarly numerous predatory species are used to control pests in our crops.
A Class of Distinction
Adapted from John R.Meyer, (http://www.cals.ncsu.edu/course/ent425/library/tutorials/index.html) We humans are such a self-centered species that we seldom stop to acknowledge or appreciate the importance of other living organisms in our environment. Our prowess in science and technology has given us unparalleled control over our physical environment, and as a result, we have developed an inflated view of our own importance in the web of life. Although we have learned to use tools, dam rivers, level mountains, and harness atomic power, we are still dependent on Mother Nature for the countless housekeeping chores that keep our environment stable and healthy. Indeed, we are relatively minor players in the ecological drama that continually unfolds all around us. If humans were to suddenly vanish from the planet, there would be no ecological calamity, no massive extinctions, and no tears shed for our demise. Remnants of human civilization would soon be smothered in vegetation, the forests would reclaim our cities, and life would go on without us just as it did for millions of years before our ancestors first reckoned the passage of time. Sadly, the earth would probably be better off without us. In simplest terms, life (as we know it) exists on planet earth because of a global cycle of production and consumption that hinges almost exclusively on green plants as primary producers and insects as primary consumers. These two life-forms overshadow all other multi-cellular organisms in terms of abundance and diversity. They are mutually dependant on one another for survival, and form a nucleus around which all terrestrial and fresh-water ecosystems are built. Without green plants and the organic molecules they produce through photosynthesis, all animal life would collapse from starvation. Without insects and other decomposers, green plants would quickly exhaust their nutrient supplies, dead organic matter would accumulate in putrid, rotting heaps, and many species of flowering plants would become extinct for lack of insect pollinators.
Entomology handout
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In a sense, we owe our very existence to members of the insect world -- creatures we often fear or despise. We expend considerable resources trying to eliminate these animals from every facet of our daily lives, but in fact, we could never hope to survive without them -- they make the earth habitable for us. Like tiny maids and butlers, they perform Nature's housekeeping tasks with competence and efficiency. Nothing else -- animal, vegetable, or mineral -- could ever take their place. By virtue of their diversity, their world-wide distribution, their ecological importance, and their impact on other life-forms, the insects are indeed a class of distinction.
The Dominance of Insects
Figure 1
Number of Species Entomologists estimate that over 800,000 insect species have been named and described since Carolus Linnaeus (1707-1778) founded the modern system of nomenclature (genus and species) for all plants and animals. The entire plant kingdom, by comparison, contains between 400,000 and 500,000 species. Thus, insects represent more than half (about 53%) of the 1.5 million species of living organisms known to science (Figure 1). Number of individuals Another way to look at the dominance of insects is to consider the distribution and density of individual species or populations. Because of their small size and high reproductive potential, insect populations often grow to epic proportions. A single colony of Australian termites can swell to several million individuals within an earthen mound 20-25 feet tall. A swarm of migratory locusts may contain up to 10 billion individuals, cover an area of several thousand hectares, and have a total biomass of over 30,000 metric tons. Above the arctic circle, hordes of mosquitoes Entomology handout Page 4
and black flies can make life miserable for any warm-blooded animal. In some cases, these biting flies are so abundant and persistent that large animals, such as reindeer, have been known to die from the massive loss of blood (desanguination). In the tropics, ants are the most pervasive and diverse of all animal species. Colonies of driver ants (Dorylus sp.) on the African savannah may contain 20 million individuals. Distribution A third way to assess the dominance of insects is to examine their abundance and diversity in a wide range of ecological habitats. Indeed, insects are found in virtually every terrestrial and fresh-water environment on the face of the earth. They live everywhere from mountain tops in the Himalayas to tide pools at the seashore. Dozens of eyeless species spend their entire lives in the total darkness of underground caverns. At least 40 species live on the polar ice caps of Antarctica, others exist on the surface of glaciers, or near the edge of melting snow fields. A few species can survive in hot springs where the water temperature is 50oC; others inhabit deserts where water is scarce and daytime temperatures exceed 60oC. Insects live both above and below the surface of rivers, streams, lakes, and ponds. One species of water strider makes its home among floating seaweed in the Sargasso Sea, nearly 2400 kilometers (1500 miles) from the nearest land mass. The petroleum fly (Helaeomyia petrolei), develops in pools of crude oil in the California oil fields. A related species, the brine fly (Ephydra cinera), thrives in the high salinity of Utah's Great Salt Lake. In fact, the only place on earth where insects are not plentiful is in the ocean depths. Most marine environments are filled by another successful group of arthropods, the Crustacea.
Why are insects so successful?
There are many attributes of insects that have allowed for their success and diversification. Exoskeleton -this is a marvelous structure that not only gives shape and support to the body's soft tissues, but also provides protection from attack or injury, minimizes the loss of body fluids in both arid and freshwater environments, and assures mechanical advantage to muscles for strength and agility in movement. Small size -there are many more niches for small organisms than for large organisms. For instance, one insect could live solely on and in the seeds of a specific plant. Short life cycle - this allows many generations within a given time for selection and evolution to take place. Reproductive potential - large numbers of offspring are produced to compensate the mortality due to adverse conditions. When large numbers of offspring are produced, there are also large variation in the population for natural selection and evolution to act upon. A honey bee queen lays as many as 4,000 eggs a day, and an African termite queen can lay as many as 43,000 eggs a day. Page 5
Entomology handout
Metamorphosis- Variation of life style of different stages in an insect's life (e.g. caterpillar versus butterfly) reduces competition for resources within the species. Wings-the ability to fly are relatively rare outside insects and have allowed them to colonize freely. Adaptability - A combination of large and diverse populations, high reproductive potential, and relatively short life cycles, has equipped most insects with the genetic resources to adapt quickly in the face of a changing environment. Sensory sophistication - the sensory capabilities of insects surpasses most other organisms. Adaptation of appendages - mouthparts, wings and legs have often become highly specialized.
Economic importance - how do insects affect us?
Insects affect us in different ways. Some are beneficial while some are harmful. The beneficial and detrimental effects of insects are as discussed below. Beneficial effects 1. Pollination- Insects such as honey bees, beetles and wasps aid in pollinating our crops and fruit trees. Crops in Rosaceae, Cucurbitaceae and Leguminosae are exclusively pollinated by bee. It is estimated that 80% of the commercial food crops are pollinated by honey bees. 2. 2: Bio-control agents- Some parasitic and predatory insects are excellent biocontrol agents for controlling other injurious insects. Example Encarsia formosa is an excellent bio-control agent for white flies on tomatoes and potatoes. 3. Production of products - Honey, wax, silk (from Bombyx mori), shellac (from Laccifer lacca) and cochineal (red dye widely used in cosmetics, medicinals and food products) derived from, a scale insect, Dactylopius coccus. 4. Nutrient recycling - Insects feed on dead and decaying plants, animals and animal excreta and help in recycling the nutrients. Some insects burrow into soils and improve the soil structure and texture. Examples are dung feeders and termites. 5. Source of food - over 500 species of insects are used as food by humans usually crickets, grasshoppers, beetle, wasp, butterfly larvae, bugs etc 6. Miscellaneous – Some insects are used for medicinal purpose, decoration, hobby, and pets. Detrimental effects Destruction or spoilage of food (both fresh and stored) and crops (including forests) 2. Damage to goods - leather, paper, textiles, (by beetles, cockroaches, silverfish or moths), timber (by termites and different types of borers) 3. Transmits disease in plants and animals. 4. Possess venoms and cause allergies
1.
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5. 6. 7.
Some insects are a nuisance to our well being -house flies, ants, mosquitoes Cause phobias – fear of grisly caterpillars or spiders (arachnophobia) Require use of pesticides and other poisons, which often harm other animals
Features of Arthropods
Arthropoda (from arthros = jointed, podos = foot) is the largest phylum in the Animal Kingdom. Arthropods are segmented animals which have jointed appendages. All arthropods have: All arthropods possess:
Exoskeleton - a hard protective covering around the outside of the body (divided by sutures into plates called sclerites) Segmented body Jointed limbs and jointed mouthparts - that allow extensive specialization Bilateral symmetry - whereby a central line can divide the body into two identical halves, left and right Ventral nerve cord - as opposed to a vertebrate nerve cord which is dorsal Dorsal blood pump
The Phylum Arthropoda includes the class Insecta and other classes like the Arachnida, the Chilopoda, the Diplopoda and the Crustacea. It is with these groups that the insects, especially the wingless ones, are most likely to be confused and the main characters that are used to differentiate these classes are:
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Class Arachnida (arachnids): spiders, scorpions, ticks, mites, etc. Arachnids possess:
2 body segments - cephalothorax and abdomen 8 legs 1 pair of chelicerae no antennae
University of Sydney
Class Chilopoda (centipedes) Chilipods are quick moving predators with poison glands which possess:
body flattened and multi-segmented 1 pair of legs per body segment 1 pair of antennae 1st pair of legs modified into venomous ―fangs‖
University of Sydney
Class Diplopoda (millipedes) Diplopods are slow moving vegetarians which possess:
Many body segments 2 pair of legs per body segment 1 pair of antennae
University of Sydney
Class Crustacea (crustaceans): crabs, shrimp, barnacles, sowbugs, etc. Crustaceans possess:
Two body regions – Cephalothorax and abdomen 2 pairs of antennae Varied number of legs (usually five)
University of Sydney
Class Insecta (Insects); beetles, bugs, wasps, moths, flies, etc. Insects possess:
3 body segments 6 legs 1 pair of antennae Most flying insects possess two pairs of wings
University of Sydney
Entomology handout
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Classification of Insects
All living organisms are placed into certain groups or categories for classification and identification. The seven most commonly used categories are: Kingdom- Animal Phylum - Arthropoda Class – Insecta Order – Lepidoptera (Butterflies and moths) Family - Noctuidae Genus - Helicoverpa Species – armigera The species is the basic taxonomic category and may be defined as groups of actually interbreeding natural populations which are reproductively isolated from other such groups. Closely related species are grouped together in the next higher category - the genus. Related genera make up a family and related families are grouped into orders. The scientific name of an organism consists of two words - the generic name and the specific name. This system of naming insects is called the binomial system of nomenclature.
Insect orders
Insects are among the most abundant and successful of terrestrial animals. They include about three-fourths of all described species of animals and have become adapted to a wide range of environments. No other group of living creatures has such variety of form, colour, function and habitat. The classification of insects into various orders is based on the presence or absence of wings, wing venation, the type of metamorphosis, the type of mouth parts, the characters of antennae, tarsi, etc. Thus we have: Class INSECTA
Sub-class APTERYGOTA (Wingless) There are four orders in Apterygota, viz: 1. Collembola (Springtails) 2. Diplura 3. Protura 4. *Thysanura (Silverfish)
Sub-class PTERYGOTA (Winged)
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Here, none of them are of economic importance, except silverfish, which occasionally damage book-bindings. The subclass PTERYGOTA is further divided into two groups as: PTERYGOTA
EXOPTERYGOTA
ENDOPTERYGOTA
exo=external; endo=internal In Exopterygota, the wings develop externally and the young ones are called nymphs and metamorphosis is in-complete (Hemimetabolous). The following orders are included in this division: 5. Ephemeroptera (Mayflies) 6. Odonata (Dragonflies) 7. Blattodea (Cockroaches) 8. Isoptera (Termites) 9. Mantodea (Mantids) 10. Zoraptera 11. Gryllablattodea 12. Dermaptera (Earwigs) 13. Plecoptera (Stoneflies) 14* Orthoptera (Grasshoppers, Crickets etc.) 15. Phasmatodea (Stick insects) 16. Embioptera (Web-spinners) 17. Psocoptera (Psocids, Book lice) 18. Anoplura (Sucking lice) 19. Mallophaga (Biting lice) 20* Hemiptera (Bugs) 21* Thysanoptera (Thrips) In Endopterygota, the development of wings occurs internally and transformation from larva to adult form occurs during a quiescent pupal stage. They undergo complete metamorphosis (Holometabolous). The following orders are included in this division: 22. 23. 24* 25. Megaloptera (Alder flies) Neuroptera (Lace wings, Antlions) Coleoptera (Beetles) Strepsiptera (Stylops) Page 10
Entomology handout
26. 27. 28* 29. 30* 31*
Mecoptera (Scorpion-flies) Siphonaptera (Fleas) Diptera (Flies, Mosquitoes) Trichoptera (Caddisflies) Lepidoptera (Moths, Butterflies) Hymenoptera (Wasps, Bees, Ants)
Insect orders of agricultural importance
ORTHOPTERA: Includes grasshoppers, crickets, etc. Orthopterans have chewing mouth types in both adult and immature stage. Most orthopterans have two pairs of wings, the forewings being thickened and of leathery texture are called tegmina. The hind wings are large and fanlike and are folded beneath the tegmina when not in use. They have thread-like, filiform antennae. The hind legs are usually enlarged for jumping. THYSANOPTERA: (Thrips) - Thrips are small or minute insects, and have a rasping - sucking mouth type. Many species are wingless but when wings are present, they are long, narrow and fringed with hairs. Many species of thrips are phytophagous, causing damage to a variety of plants. HEMIPTERA: Hemipterans have piercing and sucking mouth type. The fore-wings are called hemelytra and are normally held flat over the abdomen when at rest. The basal portions of these wings are hardened in texture, while the apical portions are membranous. The hind wings are membranous and folded beneath the hemelytra. They have a segmented beak which arises ventrally from the front or anterior region of the head. HOMOPTERA: They have piercing and sucking mouth parts. The fore-wings are uniformly membranous or slightly thickened and the wings are held roof-like or tentlike over their bodies when at rest. This order also includes wingless and short wing insects. Their segmented beak arises ventrally from the posterior portion of the head. The order includes aphids, hoppers, mealy bugs and scale insects. COLEOPTERA: These are the beetles characterized by having fore-wings which are thickened and hardened into elytra, which meet along the mid-lines of the dorsal surface and which are used to protect the delicate, folded hind wings. Beetles have chewing mouth types in both the immature and adult stages. This is the largest order in the animal kingdom and the group exhibits great diversity of forms and habits. Included in this order are a variety of harmful as well as beneficial insects. LEPIDOPTERA: These are the moths and butterflies. Lepidopteran larvae have chewing mouth types, while some adults have vestigial or non-functioning mouth types and do not feed. Most adults, however, have a long coiled proboscis which is used for siphoning plant nectar. They have two pairs of membranous wings and the body and appendages are clothed in broad scales. The immature stages of Lepidoptera, called caterpillars, can cause considerable damage by their feeding. Entomology handout Page 11
DIPTERA: These are the true flies, with a single pair of membranous wings, the hindwings being modified into club-shaped halteres. There is a variety of feeding habits and mouth types associated with members of this order. Adult Diptera may have sponging, lapping or piercing-sucking mouth types. Dipteran larvae are legless and have a chewing mouth type. HYMENOPTERA: This order includes sawflies, wasps, bees and ants. Larval hymenoptera generally have a chewing mouth type. Adults have chewing mouth parts but this may again be modified for specific functions. Only a few species from this order are considered to be of economic importance but the majority of them are beneficial insects
Entomology handout
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Insect morphology
Head
The head of an insect is composed of a series of segments, which are specialized for food gathering and manipulation, sensory perception, and neural integration. The head bears the eyes (compound eyes and ocelli), antennae, and mouthparts. The anterior part of the head is the frons. The anterior area below the dorsum of the head, between and behind the eyes is the vertex. The area below the compound eye, on the side of the head, is the gena. The liplike sclerite is the clypeus. The principle structures of an insect head are given in figure 1.
Fig: 1 Principle parts of in insect head.
Source: http://basicentomology.ifas.ufl.edu/lab5.doc
Antennae
The antennae are the sensory organ of smell touch and hearing (auditory) in insects. It is with the help of antenna that insects are able to locate food, find their mates, detect danger, feel and find their way. The specialisation of the antenna for different functions may vary from one type of insect to the other. For e.g. antenna of houseflies have a strong sense of smell and that is why they can appear from anywhere if there is a rotten smell of meat. The shape, size and length of antenna vary so much. Cockroaches have very long antenna whereas the antenna of houseflies no matter how big in size can hardly be seen. Depending upon the shape, antenna can be filiform (thread-like), clavate (clubshaped), pectinate (comb-like), bipectinate (double comb like), plumose (feather-like), serrated (sawtooth-like), lamellate (plate-like), monoliform (bead-like), aristate (pouch-like). Antennal segments Antennae are mobile, segmented, paired appendages. The paired antennae are made up of a number of individual joints and the entire antenna typically has three main divisions: The first antennal segment (closest to the head) is called the scape, generally is larger than the other segments and is the basal stalk. The second antennal segment is called the pedicel, nearly always contains a sensory organ known as Johnston’s organ, which responds to movement of the distal part of the antennae relative to the pedicel.The remainder of the antenna is called the flagellum, is often filamentous and multi segmented.
Entomology handout
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Antennae of male insects may be more elaborate than those of the corresponding females, increasing the surface area available for detecting female sex pheromones. The basic form of antenna is filiform. In this type there are many segments that are more or less equal in size. Filiform antennae are seen in a wide variety of groups, such as Dragonflies, Grasshoppers and Crickets, Book Lice, Biting Lice, Scorpion Flies and Beetles. The length and number of joints varies much between them.
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Types of antennae:
Name
Appearance
Example(s)
Setaceous -- bristle-like
Dragonflies
Filiform -- thread-like
Ground Cockroaches
beetles
and
Moniliform -- bead-like
Termites
Serrate -- sawtoothed
Click beetles
Clavate -- gradually clubbed
Carrion beetles
Capitate -- abruptly clubbed
Butterflies
Lamellate -- nested plates
Scarab beetles
Pectinate -- comb-like
Fire-colored and Male glow-worms
beetles
Plumose -- brush-like
Mosquitoes
Geniculate -- elbowed
Weevils and Ants
Aristate -- pouch-like with lateral bristle
House flies
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Eyes
Insects have usually 2 types of eyes. The pair of big eyes that are prominently seen in most insects are known as the compound eyes. It is so named because of the fact that the eyes are made of many units of photo receptors that are each individually functioning like our human eye. These visual units that make up the compound eyes are known as ommatidia (ommatidium sing.). There may be up to 30,000 ommatidia in a compound eye. The number of ommatidium however varies from insect to insect depending upon their habit. The predatory insects have very powerful eyes which mean the number of ommatidia is very high. Insects like worker ants have very few ommatidia. This type of eye gives less resolution than the vertebrate eye, but it gives acute perception of movement which is important in flight.
Besides the compound eyes, insects do have simple eyes called ocelli, on their forehead. They are less apparent and are seen only as dark shining patches (usually 3) of epidermal cells. Higher insects have both types of eyes where as lower insects and larvae have simple eyes only. They are not as sensitive as the compound eyes but can detect the changes in the illumination or intensity of light. For example it can alert the insect if a shadow of a predator falls on it. Cut worms which are nocturnal in habit probably depend on these simple eyes.
Mouthparts
The most important way in which insects inflict losses and injury upon man and his possessions is by eating or feeding. Since insects feed in various ways, it is evident that knowledge of insect mouth parts is of prime importance in the study of entomology. The mouth part of an insect can be classified in accordance with their function. According to this scheme there are those are those intended for biting and chewing (Mandibulate) like in grasshoppers, crickets, cockroaches, lacewings and beetles; those that are primarily used for sucking liquids (Haustellate) like in stinkbugs, aphids, mosquitoes, houseflies.
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1. Mandibulate 2. Haustellate a) Stylet b) Non-stylate
Biting-chewing
Piercing-sucking Siphoning Sponging Chewing-lapping Rasping-sucking
Stylets are needle-like projections used to penetrate plant and animal tissue. The modified mandibles, maxilla, and hypopharynx form the stylets and the feeding tube. After piercing solid tissue, insects use the modified mouthparts to suck liquids from the host. 1. Madibulate type- Biting-chewing mouthpart
Source: http://www.ndsu.edu/entomology/topics/heads.htm
The main parts of this type are the (1) Labrum - an unpaired, flap-like structure hinges to its upper margin to the lower edge of the clypeus. It is located in front of (or above, depending on the direction the head points) the oral cavity and serve as an upper "lip" and moves longitudinally. (2) Mandibles (upper jaws) – is a pair of highly sclerotised, horny, usually large nonsegmented structures found immediately behind (or below) the labrum. They articulate on the distal margins of the genae. The mandibles move at right angles to the body. They are used for biting, chewing and severing food.
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(3) Maxillae - (lower jaw) is a pair of segmented structures situated immediately behind or below the mandible. The maxillae moves at right angles to the body and possess segmented palps. (4) Labium – (the lower lip) is an unpaired structure serving as a lower lip and closing the oral cavity from below or behind; it moves longitudinally and possesses a pair of segmented palps. (5) Hypopharynx - this is an unpaired structure, otherwise known as the tongue, which occupies a portion of the oral cavity; it is located more or less in the center of this space and near the base of the labium.
Fig. 11 Different parts of a mandubulate type mouth. 2. Haustellate type of mouthpart is basically a modification of the simple bitingchewing type. Haustellate mouthpart can be broken down into two subgroups: those that possess stylets and those that do not. a) Piercing-sucking type of mouthpart present in stink bugs is an example of haustellate type with stylets. Mandibles and maxillae are formed into stylets which are enclosed by the labium. Once the stylets penetrate, a secretion is injected to dissolve tissue, act as a toxin in predacious species, or as anticoagulant for mosquitoes.
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b) Siphoning type: Those without stylets are unable to pierce tissues, and therefore these insects must rely on easily accessible food sources such as nectar at the base of a flower. One example of nonstylate mouthpart is the long siphoning proboscis of butterflies and moths (Lepidoptera). When feeding the proboscis is uncoiled and extended. Nectar is sucked up into the mouth or oral cavity. The proboscis is a modified maxillae.
c) Sponging - Found in adults of specialized flies. During feeding the proboscis (modified labium) is lowered and salivary secretions are pumped onto the food. The dissolved or suspended food then moves by capillary action into the pseudotracheae (sponge) and is ingested. There may be sharp teeth on the pseudotracheae to rasp flesh and draw up blood. The labella is the fleshy distal end of the labium that functions as a sponge-like organ to sop up liquids.
d) Chewing-Lapping - Adult honeybees and bumble bees. Mouthparts are modified to utilize liquid food, honey and nectar. A central "tongue" is used to draw liquid into the body. The mandibles are not used for feeding but function to cut floral tissue to gain access to nectar, for defense, and for manipulating wax. e) Rasping-sucking – Thrips have rasping sucking type of mouthpart. (To rasp means to scrape with a coarse file). The mandibles which are asymmetrical injure the tissue and the cell sap oozing out is being sucked
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The insect thorax
The insect thorax is box-like with dorsal, ventral and lateral sclerites. The dorsal sclerites are collectively called the notum (pronotum, mesonotum, and metanotum) which may be further subdivided into an anterior scutum and a posterior scutellum. The ventral sclerites are called the sternum (prosternum, mesosternum, and metasternum). Each sternum is divided into several plates, called sternites. The lateral sclerites are called the pleuron.
The thorax is divided into three parts and from front to back; these segments are named as follows: (1) Prothorax - the first of the three (hence Pro-) and bearing the first pair of true legs; wings are never present on this portion of the thorax. The top plate of the segment, the Pronotum, is in most winged insects are rather highly specialized and is usually enlarged to some extent. (2) Mesothorax - (meso= middle) this is the middle of the three thoracic ringsegments; it bears the second pair of true legs and the first pair of wings when two pairs are present. If only one pair of wings is present, as is the case with the flies, then that single pair is located on this segment of the thorax. In other species (i.e., scale insects, the males have one pair of wings on the metathorax!). One pair of spiracles is often found on this segment. In most insects, usually no spiracles are found on the 1st or third thoracic segments. (3) Metathorax - (Meta-last) this is the third and last of the thoracic segments; it bears the third pair of true legs and the second pair of wings, when they are present. A pair of thin knobbed projections (halters) takes the place of this second pair of wings in the Diptera.
Legs
The legs, named from the anterior, are the fore, mid and hind legs. Each leg consists of four main parts - the coxa, the femur, the tibia and the tarsus (plural: tarsi) - with a small, often inconspicuous segment between the coxa and femur, called the Entomology handout Page 20
trochanter. The tarsus is collectively composed of 2 to 5 smaller tarsomeres. The last tarsomere usually has a pair of claws and often 2 or 3 tarsal pads- the arolium.
Figure: 12 parts (source: http://basicentomology.ifas.ufl.edu/lab5.)
of
insect
legs
Insect legs have been variously adapted for running, jumping, grasping, swimming or digging. An examination of insect legs can often tell much about the habits of the insect. Some of the insect leg modifications are Unmodified legs are used for walking and are called ambulatory Legs modified for running are called cursorial. Digging legs are called fossorial Swimming legs are called natatorial. Jumping legs are called saltorial. Grasping legs are called raptorial.
Wings
(Source: http://www.cals.ncsu.edu/course/ent425/tutorial/wings.html) Insects are the only invertebrates that can fly and their wings are unique among all animals. They are outgrowths of the body wall rather than modified appendages. The wings may be membranous, parchment-like, heavily sclerotized, fringed with long hairs, or covered with scales. Most insects have two pairs of wings -- one pair on the mesothorax and one pair on the metathorax (never on the prothorax). Wings serve not only as organs of flight, but also may be adapted variously as protective covers (Coleoptera and Dermaptera), thermal collectors (Lepidoptera), gyroscopic stabilizers (Diptera), sound producers (Orthoptera), or visual cues for species recognition and sexual contact (Lepidoptera). Basically, insect wings are very simple flap-like extensions of the body wall, with an upper and lower membrane between which run hollow tubes known as the veins which give rigidity and support. In most cases, a characteristic network of veins runs throughout the wing tissue. These veins are extensions of the body's circulatory system. They are filled with hemolymph and Entomology handout Page 21
contain a tracheal tube and a nerve. The venation (arrangement of veins) varies from very simple to extremely complex and is an important character in identification of many orders, families and genera. In membranous wings, the veins provide strength and reinforcement during flight. Wing shape, texture, and venation are quite distinctive among the insect taxa and therefore highly useful as aids for identification. Wings become functional only in the adult stage. Wing Venation: Costa (C) -- the leading edge of the wing Subcosta (Sc) -- second longitudinal vein (behind the costa), typically unbranched
Radius (R) -- third longitudinal vein, one to five branches reach the wing margin Media (M) -- fourth longitudinal vein, one to four branches reach the wing margin Cubitus (Cu) -- fifth longitudinal vein, one to three branches reach the wing margin Anal veins (A1, A2, A3) -- unbranched veins behind the cubitus Names of crossveins are based on their position relative to longitudinal veins: c-sc crossveins run between the costa and subcosta r crossveins run bewteen adjacent branches of the radius r-m crossveins run between the radius and media m-cu crossveins run between the media and cubitus
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Wing adapations and modifications: Insect wings have been modified in many ways; for example:
The wings of a moth are covered with minute scales which are often brightly colored. The fore wings of a beetle are hardened and form a protection (the elytra) for the membranous hind wings. Cockroaches and grasshoppers have leathery fore wings (Tegmina). Some bugs have half-leathery, half-membranous fore wings (hemelytra). In flies, (Diptera), the hind wings have become modified to form small balance organs, called halteres. Appearance Order(s)
Characteristic Elytra -- hard, sclerotized front wings that serve as protective covers for membranous hind wings Hemelytra -front wings that are leathery or parchment-like at the base and membranous near the tip Tegmina -- front wings that are completely leathery or parchment-like in texture
Coleoptera and Dermaptera
Hemiptera: Heteroptera
Orthoptera, Blattodea, and Mantodea
Halteres -- small, club-like hind wings that serve as gyroscopic stabilizers during flight
Diptera
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Fringed wings -slender front and hind wings with long fringes of hair Hairy wings -front and hind wings clothed with setae
Thysanoptera
Trichoptera
Scaly wings -front and hind wings covered with flattened setae (scales)
Lepidoptera
Hamuli -- tiny hooks on hind wing that hold front and hind wings together
Hymenoptera
Frenulum -Bristle near base of hind wing that holds front and hind wings together
Lepidoptera
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Abdomen and external genitalia
The abdomen is the third and posterior region of the insect body. The abdomen of adult insects contains no legs or wings and usually consists of 10 or 11 segments. However, in many orders, reduction has occurred or the segments are concealed or modified. Each segment of the abdomen consists of a dorsal sclerite, the tergum, and a ventral sclerite, the sternum, joined to one another laterally by a pleural membrane. In many adult insects, there is a spiracle (opening to the respiratory system) near the pleural membrane on each side of the first eight abdominal segments. At the very back of the abdomen, the anus (rear opening of the digestive system) is nestled between three protective sclerites: a dorsal epiproct and a pair of lateral paraprocts. A pair of sensory organs, the cerci, may be located near the anterior margin of the paraprocts. These structures are tactile (touch) receptors. They are usually regarded as a "primitive" trait because they are absent in the hemipteroid and holometabolous orders. Terminally the abdomen bears the external genitaliaThe insect's genital opening lies just below the anus: it is surrounded by specialized sclerites that form the external genitalia. In females, paired appendages of the eighth and ninth abdominal segment fit together to form an egg-laying mechanism called the ovipositor. A pair of cerci is also present at the end of the abdomen. These have a sensory function.
In males, the genital opening is usually enclosed in a tube-like aedeagus which enters the female's body during copulation (like a penis). The external genitalia may also include other sclerites (e.g. subgenital plate, claspers, styli, etc.) that facilitate mating or egg-laying. The structure of these genital sclerites differs from species to species to the extent that it usually prevents inter-species hybridization and also serves as a valuable identification tool for insect taxonomists. Other abdominal structures may also be present in some insects. These include:
Pincers -- In Dermaptera (earwigs), the cerci are heavily sclerotized and forceps-like. They are used mostly for defense, but also during courtship, and sometimes to help in folding the wings. Median caudal filament -- a thread-like projection arising from the center of the last abdominal segment (between the cerci). This structure is found only in "primitive" orders (e.g. Diplura, Thysanura, Ephemeroptera). Cornicles -- paired secretory structures located dorsally on the abdomen of aphids. The cornicles produce substances that repel predators or elicit caregiving behavior by symbiotic ants.
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Abdominal prolegs -- fleshy, locomotory appendages found only in the larvae of certain orders (notably Lepidoptera, but also Mecoptera and some Hymenoptera). Sting -- a modified ovipositor, found only in the females of aculeate Hymenoptera (ants, bees, and predatory wasps). Abdominal gills -- respiratory organs found in the nymphs (naiads) of certain aquatic insects. In Ephemeroptera (mayflies), paired gills are located along the sides of each abdominal segment; in Odonata (damselflies), the gills are attached to the end of the abdomen. Furcula -- the "springtail" jumping organ found in Collembola on the ventral side of the fifth abdominal segment. A clasp (the tenaculum) on the third abdominal segment holds the springtail in its "cocked" position. Collophore -- a fleshy, peg-like structure found in Collembola on the ventral side of the first abdominal segment. It appears to maintain homeostasis by regulating absorption of water from the environment.
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Reproduction in insects
How do insects find their mates?
Insects use different ways in order to attract their mating partners. Insects use sound (Example crickets, grasshoppers and cicadas), smell (Moths), colour (Moths and butterflies) and pheromones (Moths). Pheromone is a chemical which is produced by living organisms that transmits message to other members of the same species.
Types of reproduction in insects
Reproduction in insects can take a wide variety of forms, often very complex. Some can switch their type of reproduction during their life cycle based on environmental triggers. Others reproduce the same way throughout their life history. The basic theme and some of the variations are described below. Sexual reproduction: The standard model for reproduction is where males and females occur throughout the life cycle, and each produces a germ cell (egg and sperm, respectively). The male inseminates the female during mating. The female often stores sperm in special pouches in her abdomen called spermathecae (singular, spermatheca). The eggs are fertilized within the female's body, producing an embryo. Eggs are deposited on a host. They hatch and develop into either male or female offspring. Parthenogenesis: This is asexual reproduction, where eggs grow and develop without fertilization. There are several variations of parthenogenesis. Arrhenotokous parthenogenesis is where unfertilized eggs produce only males. In deuterotokous parthenogenesis, both males and females are produced from unfertilized eggs. In thelyotokous reproduction, unfertilized eggs produce only females. Viviparity: Most insects deposit eggs that hatch into nymphs or larvae, a process called oviparity, but some insects bear living young. A common example is aphids, which are viviparous during part of their life cycle. A variation is ovoviviparity, where eggs are held within the female's body, where they hatch, and the young are born live. Polyembryony: This is where two or more embryos develop from a single egg, as in the parasitic Hymenoptera, such as braconid, encyrtid, and dryinid wasps.
Insect growth and development
Definitions1 Chrysalis - a butterfly pupa, not enclosed in a cocoon, a pupa without a protective cover. Cocoon - a case formed partly or wholly of silk secreted by the larva and in which pupation occurs, a protective cover.
1
http://www.ndsu.nodak.edu/entomology/topics/growth.htm
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Instar Larva
Molting Nymph Pupa
Stage
- form of an insect between successive molts, the first instar being the stage between emerging from the egg and the first molt. - (pl. larvae) immature stage between the egg and pupa in insects with complete metamorphosis or, sometimes, between egg and adult in insects with incomplete metamorphosis. - the acting of shedding the cuticle or insect skin, shedding of the exoskeleton . - immature stage of insects with incomplete metamorphosis. - (pl. pupae) the third, inactive stage of insects with complete metamorphosis, the transition stage between the larval and adult stages. Usually non-mobile. - any definite period in the development of an insect, e.g.. the egg stage, nymphal or larval stage, pupal stage, adult stage. The number of nymphal or larval stages is variable.
Insect life cycle
Life cycle is the chain of biological events that occurs during the lifetime of an individual insect. The cycle usually begins with deposition of egg and ends with egg lying by the adult. Egg: Eggs come in many shapes, sizes, and colors. They might be deposited on or in the ground, the roots, the stems, the leaves, or the flowers. When the eggs hatch the new insect is called a larva. The plural of larva is larvae. Larva: The larva seldom looks like the adult it will become. Some common larval forms are the maggot, grub worm, nymph and caterpillar. As the larva grows it must shed its old skin from time to time. This is called molting or ecdysis. From hatching to the first molt the larva is said to be in its 1st instar stage. After molting the first time the larva enters its second instar stage, and so on (fig. 13). Different insects have different numbers of instars, but eventually the larva is fully grown and ready to pupate.
Fig.13 Stages in development of an insect to adult insect
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Pupa: The pupa is the life stage between larva and adult. In this stage the insect does not feed, and is in a quiescent state. Most pupae are found hidden and protected habitats. Some usually construct some kind of shelter (cocoon) to pupate in. This "cocoon" might be made from soil particles, silk, chewed seeds, chewed plant material, ground litter, or combinations. After pupation the adult emerges to mate and to lay eggs. The figure below illustrates the life cycle of a fly.
Figure: 14. An example of insect life cycle showing complete metamorphosis (Source: http://www.ndsu.nodak.edu/entomology/topics/growth.htm)
Metamorphosis
The majority of insects start life in the form of a fertilized egg laid by a female on plants or in the ground. After hatching of the egg the developing young one undergoes a series of changes in size and structure before becoming adult. Each time an insect makes a change into the next growth stage, it has to molt (shed) its skin. After each molt, the insect becomes a little larger and somewhat different in form until it reaches the adult stage. After it reaches the adult stage, it does not molt or grow any more. To the series of changes which takes place in the life history of an insect the term metamorphosis has been applied. There are four kinds of metamorphosis, complete (butterflies), gradual (grasshoppers), incomplete (dragonflies) and no metamorphosis (Silverfish). The exact style of metamorphosis is not the same for all insects, but insects in the same order have the same style of metamorphosis. Ametabolous development: Some orders of insects are said to have no metamorphosis (Ametabolous development) because there is little or no difference in appearance between the young stages and the adult except for size (Fig.14). The Entomology handout Page 29
no-metamorphosis model is found in primitively wingless insects (Subclass Apterygota). Suitable examples are primitive insects such as silverfish (Thysanura).
Fig. 15 typical development of an aterygote insect with no metamorphosis Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Gradual metamorphosis (Paurometabolous development): The life cycle of insects with gradual metamorphosis have three life stages (Fig. 16): egg, nymph and adult. Nymphs resemble the adult except that their body parts are out of proportion with each other, and they do not have fully developed wings and external genetalia. With each molt, the nymphs gradually develop wings and take on the body proportions of an adult. Nymphs have the same type of mouthparts as the adult, and they both feed on the same kind of food.
Fig.16 The life cycle of a plant bug. Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Incomplete metamorphosis (Hemimetabolous development) is somewhat like gradual metamorphosis and also has three life stages: egg, naiads and adult. However, the adult insect with incomplete metamorphosis lays its eggs in or near Entomology handout Page 30
water and the naiads develop in water. The adults are flying insects that live out of water. Naiads and adults therefore do not eat the same kind of food. Naiads have chewing mouthparts, but the adults have differently shaped chewing mouthparts or no functional mouthparts. The naiad and the adult usually differ a lot in appearance although the naiads gradually develop wings. Complete metamorphosis (Holometabolous development): It has four distinct form stages: egg, larvae, pupa and adult (Fig.17). The larval stages do not look like the adult at all, and they are often worm-like. Larvae often have different mouthparts and food habits than the adult, and they often live in places different from the adult. Larvae molt several times and get a little larger with each molt, but there is no gradual development of wings or other adult characteristics. When a fully grown larva molts, it changes into a pupa. The pupa usually does not eat or move around much, but a lot of internal changes take place. When the pupa has made all its internal changes, its skin splits and the fully formed adult emerges. Most insects with complete metamorphosis are winged in the adult stage. The adults do not molt or grow any more. Little flies or beetles, for instance, do not grow to become larger. Flies (Diptera), beetles (Coleoptera), wasps (Hymenoptera) and butterflies (Lepidoptera), have holometabolic life cycles.
Fig. 17 Complete metamorphosis Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Insect seasonal cycles
The progression of one or more life cycles occurring during a 1-year period is termed as the insect seasonal cycles. Seasonal cycles are very important to the survival of the insects because most environments of which insects are part of undergo annual colds. Therefore, to achieve success, insects have evolved ways to time their activities to take advantage on environmental resources and avoid unfavorable extremes. Entomology handout Page 31
Knowledge of patterns in seasonal cycles and the timing of important biological events relative to environmental cycles are crucial when attempting to reduce pest damage. Seasonal cycle can be grouped according to the number of generations that occur in a year; this number is referred to as a population’s voltinity. Voltinity types are univoltine, multivoltine, and delayed voltine.
Larval forms
The larval form is highly variable in insects, but there are similarities in the general structure to permit a classification of type that is useful in describing their appearance. (1) Campodeiform larvae have a flattened body with long legs, usually with filaments on the end of the abdomen. Larvae of diving beetles in the family Dytiscidae and many other beetles, Neuroptera, and Trichoptera are typical examples. (2) Carabiform larvae are similar to the campodeiform type, but the legs are shorter and filaments are lacking on the end of the body. They receive their name from the larvae of carabid beetles. Chrysomelid beetle larvae are of the same type. (3) Eruciform larvae (Polypod larvae) are cylindrical; they have a well-formed head, 3 pair of sclerotised and jointed thoracic legs, and fleshy abdominal prolegs. However, several species representing the various orders of insects do not have such distinguishing features. Larvae of Lepidoptera and sawflies are typical (4) Scarabaeiform larvae (Oligopod larvae) are C-shaped, have a well developed head, and usually possess thoracic legs but lack prolegs. The type is named after larvae of scarabaeid beetles (dung beetles, May beetles) and is also represented by the larvae of weevils and furniture beetles. (5) Elateriform larvae are cylindrical, smooth, and relatively tough-skinned larvae with short legs. They are named after larvae of elaterid or click beetles (wireworms). Larvae in the beetle family Tenebrionidae also have this appearance. (6) Platyform larvae are broad and flat with legs short or absent. This type is not common, but examples are found among larvae of some syrphid flies, certain caterpillars, and blister beetles. (7) Vermiform or wormlike larvae (Apod larvae) are cylindrical and elongate, without appendages of locomotion. This form is represented by the larvae of higher Diptera (maggots), some woodboring beetles, fleas, and higher Hymenoptera, including the honey bee.
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Appearance
Larval Type
Common Name
Description
Examples
Eruciform
Caterpillar
Body cylindrical with Moths short thoracic legs and 2and 10 pairs of fleshy butterflies abdominal prolegs Elongated, flattened body Lady with prominent antennae beetle, and/or cerci. Thoracic legs lacewing adapted for running Body robust and "C"shaped with no abdominal prolegs and short thoracic legs June beetle, dung beetle
Campodeifo rm
Crawler
Scarabaeifor m
White grub
Elateriform
Wireworm
Body long, smooth, and Click cylindrical with hard beetle, exoskeleton and very Flour short thoracic legs beetle Body fleshy, worm-like. House fly, No head capsule or flesh fly walking legs
Vermiform
Maggot
Pupal forms
Pupal forms may be classified by means of the appearance of developing appendages. (1) In obtect pupae the appendages are close to the body, held there by a tight-fitting outer envelope. They appear almost to be glued to the body proper. Pupae of this type are found in Lepidoptera and many Coleoptera, as well as the less advanced Diptera. The obtect pupa of butterflies is a common example. (2) Exarate pupae refer to those species that undergoes complete metamorphosis where their appendages (antennae, legs, and wings) appear to be free from the body and abdomen is movable. The bees and wasps of the Hymenoptera and beetles of Coleoptera are common examples. (3) Co-arctate pupae are represented by those that use the exuviae (cast exoskeketon) of the last larval instar as the container or place for pupal development. In this instance, neither the outline nor the actual structures are visible. The flies are examples of this type of pupation.
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Pupae can be grouped into one of three categories based on physical appearance: Appearance Pupal Type Common Name Description Examples
Obtect
Chrysalis
Developing appendages (antennae, wings, legs, etc.) held tightly against the body by Butterflies a shell-like casing. Often found and moths enclosed within a silken cocoon. All developing appendages Beetles, free and visible externally Lacewings Body encased within the hard exoskeleton of the next-to-last Flies larval instar
Exarate
None
Coarctate Puparium
Additional information on Exarate pupa is available in this website: http://www.entomology.umn.edu/museum/projects/Interactive_Keys/Intro_tutorial/GLOSSA RY/Exarate%20pupa.html Coarctate pupa and larva information: http://mothphotographersgroup.msstate.edu/MothTalkDownload/MothTalk020.htm
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Insect Collection
Purpose of collecting and preserving insects
There must be a purpose for collecting insects. Some of the reasons for collecting and preserving insects are: 1. For studying the insect biology, lifecycle and biodiversity Because of the damage inflicted by pest species, increased knowledge of these organisms has the potential to save lives and money. Insects are collected for studying the details and gaining a better understanding of their biology and life cycles. Insects are sometimes collected for recording the biodiversity. Extension agents will come across several species of pests in their geogs. For better understanding of the pest biology and lifecycle, they must make an effort to identify the pest. As the first step towards identification, proper collection, setting and preservation of the pest species is a must. 2. For identification( species determination) a) Newly detected insects Correct identification (knowing the scientific name) of a newly detected pest or disease vector is the key to all known information about the morphology, behaviour and life history, and the potential threat to human welfare. Insects are collected for species determination so that it is convenient for finding out more information. b) Small insects that are difficult to identify The behaviour of insects can be observed most easily in their natural environments. However, many species, especially the smaller ones, must be collected and properly preserved before they can be identified. Because correct identification seldom is easy, it is important that specimens be preserved in the best condition possible. Therefore preservation is highly important. c) Pest outbreak reports During pest outbreaks in the geogs, extension agents need to report to their superiors on the type of pest that is responsible for the outbreak. It is very useful to collect the pest and submit to the concerned authorities for identification. Such collections submitted for identification need to be well set and preserved. Therefore extension agents need to have the required skills of setting and preserving pest specimens. 3. Insect collection for future reference In a geog extension centre, insect pests must be collected, identified and preserved for the purpose of educating farmers (farmer trainings) on crop pest identification. A good reference collection is a valuable resource for the extension agent. It makes future identification efforts less cumbersome. In a geog extension centre, it is of utmost importance to maintain a reference collection of pest species for all the crops grown in the locality. 4. Insect collection as a hobby. There are people who love to collect insects and preserve them just for the love of it. Moths and butterflies are collected for their beautiful colour and wing patterns. Entomology handout Page 35
Some larva are collected for their giant size and weird body ornamentations. Some giant beetles are collected and sold as pets. Why insects have to be adequately set, preserved and correctly labelled? The identification of a particular insect usually requires examination of minute details of its anatomy with the aid of a hand lens or microscope. Some specimens may require dissection or even study with the electron microscope. If these details on a specimen are concealed, missing, or destroyed because of improper handling or preservation, identification is made difficult or impossible, and information about the species to which it belongs cannot be made available. Therefore, adequate preservation and proper labelling of specimens are essential to their identification. What is the relevance of the knowledge and skill of insect collection and preservation in the field of agriculture extension? For diagnostic purpose: Correct identification or species determination is the key to all known knowledge and information about the pest in question. To 2be able to correctly identify insect pests, the morphological features of the collected specimens should neither be concealed, nor destroyed. If extension agents need to send the specimens for identification by the entomologists, they need to send a specimen that is well set, preserved and packaged. Such skills can be learnt through practice. Building a reference collection for the geog extension centre: If there is a reference collection at the geog extension centre, it is not just helpful to you for using as farmers training aid but more importantly, the person who is going to relieve you upon your transfer will have great benefits. Learning the skills of collecting and preserving insects would help you to build your own reference collection at the geog extension centre.
Insect collection equipment and materials
The basic equipment necessary for field collecting is an insect net, one or more storage boxes, pins, pinning blocks, spreading boards, light and pitfall traps, killing jars, killing and preserving chemicals, several vials of assorted sizes, plastic bags and assorted containers. 1. Killing jars: Insects must be killed before pinning and mounting. Killing jars are used as a sort of ―small scale fumigation‖ to kill collected insects as rapidly as possible, using a liquid fumigant or killing agent (ethyl acetate) that produces a toxic atmosphere that the insect cannot breathe.
2
David L. Keith and Tiffany Heng-Moss. Collecting insects. Retrieved Aug 18, 2009, from http://entomology.unl.edu/tmh/ent115/labs/collecting.htm
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When placed in the killing jar, insects often close their spiracles, but eventually they must open them. The process may take several minutes for smaller insects or up to a half hour or more for larger specimens. Because large, hard-bodied insects such as beetles die slowly and may damage other insects placed in the same killing jar, you will need more than one jar. It is possible to make suitable killing jars with nearly any glass jar used for jam or jelly and baby food jars are especially handy. In the bottom of each jar, place about 1 to 1 1/2 inches of absorbent material, such as cotton, shredded newspaper, Plaster of Paris or sawdust. If Plaster of Paris is used, pour it about 1 inch deep and allow it to dry for at least 48 hours before use. With paper-or fiber-filled jars, cut a cardboard circle just slightly larger than the inside diameter of the jar and push it into the opening against the plaster in the bottom. Attach a label that says POISON to each jar and store the jars out of reach of children (or irresponsible adults) until you are ready to go collecting.
If a killing jar is not available, freezing is another way to kill insects. Simply place your specimens in a plastic bag or small jar and put them in the freezer for an hour or two. Do not handle them again until they are thawed or legs and antennae may break. Insects, like food, left too long in the freezer for several days or weeks will desiccate and remain dry and stiff, even when thawed. If pinned when dry, these insects will break during handling and wings, especially of Lepidoptera, will be impossible to spread. Pinching the thorax of large butterflies or moths before placing them in the killing jar will prevent them from flopping around and damaging the wings. Squeeze them for 20-30 seconds between thumb and index finger and put them in the killing jar. This procedure stuns the insects so they do not flutter once inside the jar. Remove butterflies and moths from the killing jar fairly soon so their wings do not become soaked with killing agent.
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2. Relaxing jars: We recognize that while insects should be pinned on the same day they were collected, this is not always possible. So before pinning these specimens left in the killing jar or freezer too long, to restore their flexibility, it is necessary to ―relax‖ them. By placing them in a relaxing jar at high humidity for a few days we can restore their flexibility enough to allow pinning without damage to the specimens. A relaxing jar can be made by placing some absorbent material such as newspaper, sand or cotton in the bottom of a glass jar and cut a blotting paper disk to fit tightly inside. Moisten the material with water and add a drop or two of ethyl acetate, phenol or laundry beach to prevent mold. Place insects on the paper, close the jar tightly and let it sit for about 2-3 days. Check the jar. If the insects are flexible, mount them immediately. If the specimens are still too stiff, keep them in the relaxer for a few more days, but watch them carefully. Insects will mold and decompose if held in the relaxer too long. 3. Collecting Net (Aerial nets and sweep nets): Basically, a collecting net is composed of some sort of net bag made of cloth or fine mesh that is attached to a wire hoop, which is affixed to a wooden or metal pole. Aerial nets typically have net bags that are composed entirely of some type of meshed material and often have a lightweight handle. Aerial net bags are usually white in color, but black net bags are also available. They are most useful for catching select insects that may be flying through the air or perched on something (such as dragonflies, butterflies, bees, or wasps). Aerial nets with larger hoops are better for collecting large and fast moving insects such as dragonflies and butterflies, while those with small hoops are better for bees, flies, wasps, and other smaller insects.
Sweep nets are usually made of a heavy material (such as canvas) that can be dragged through dense vegetation without being damaged. They usually have heavier handles than those on sweep nets as well. Sweep nets are used to sweep through vegetation to collect random insects not easily seen. These nets are sometimes referred to as ―beating‖ nets 4. Aspirator: The aspirator is a suction device for collecting small insects which are difficult (or hazardous) to capture with the fingers or with an insect net. Basically, it consists of a large glass or plastic vial, a length of flexible rubber tubing, some rigid plastic or metal tubing and a rubber stopper with 2 holes cut in it to receiving the tubing. A small piece of cheesecloth or fine metal screen serves to seal the suction tube on the inside so that insects are not sucked into the mouth. To collect small insect the long tube is placed beside the insect and sucked sharply by mouth from the shorter rubber tube.
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5. Light traps: Many types of insects are attracted to light and can be captured there by hand. A light trap offers the advantage that it will continue to trap specimens without being constantly watched by the collector. Insects are quite sensitive to different types of light; therefore, more of certain types can be captured with ―black‖ (or ultraviolet) light as opposed to the regular ―white‖ light given off by most standard light bulbs. The difference in attractiveness of the two types of light is due to the wave lengths produced by the two kinds of bulbs. Black light consists mainly of the shorter wave lengths which are more attractive to night-flying moths, flies and beetles. White light bulbs (producing mostly longer wave lengths) attract some moths and other insects, but not as many as a black light.
6. Pitfall traps: A pitfall trap will catch many ground beetles and other insects that live on or in the soil. It consists of a trap can that is buried in the soil, level with the rim so that insects attracted to it will fall in. Once inside, it is difficult for them to get out. Attractive bait in the bottom will increase the drawing power of the trap. Use pieces of spoiled fruit, vegetables, excrement or meat. Cover the trap with a board placed on small stones so insects can crawl under it and into the can. This arrangement will protect the trap from wind and rain, but allow access to the insects you want to catch. It will also help to hold insects inside the trap once they are caught.
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Preserving insects
Hard-Bodied Insects Since insects have a hard shell or exoskeleton and all of the soft parts are on the inside, they tend to keep rather well after drying, even for long periods of time. Only a small amount of maintenance is necessary to keep them in good condition. Soft-Bodied Insects Many types of insects, including aphids, springtails, thrips, mayflies or silverfish, are soft-bodied and cannot be pinned successfully. The same is true of many immature insects such as caterpillars, beetle and wasp larvae and others. If placed on pins, most soft-bodied insects will shrivel or decompose. Such insects must be preserved in liquids in rubber-stoppered glass vials. However, prior to preserving soft-bodied specimens for the long term, their color must be ―fixed‖ or they may fade in some cases or blacken in others. The ―fixing‖ process prevents, reduces or delays color change.
For the long term, insects are preserved in ethyl alcohol, usually of about 70 percent concentration (70% alcohol, 30% water). However, it must be remembered that alcohol is a dehydrator and removes water from the specimens preserved in it. These problems can be largely prevented in either of two ways. The best way is to ―fix‖ the insect tissues and color by killing the specimens in boiling water. For smaller specimens, simply dip them in boiling water for about 30 seconds and then transfer them to 70 percent alcohol. Use more extended periods for large-bodied insects. Specially designed and constructed container ―Schmidt Boxes‖, are required for long term insect storage. Such boxes have tightly fittng lids which help prevent entry of scavenger insects which feed on dead insect specimens. Wooden boxes can be used for temporary storage of pinned insect specimens. The bottom of wooden boxes can be lined with styrofoam material or cardboard to receive and hold the insect pins. While wooden boxes are fine for temporary storage, they are poor over long periods of time. For extended storage and for display, tighter containers are essential. Add naphthalene crystals, placing them into a small container in one corner of each display box to prevent damage to your specimens.
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Pinning, mounting and displaying insects3
Equipment required Insect Pins. Special pins are needed to pin insects. They come in several sizes from 000 through 7, the size of the pin increasing with each number. Number 3 insect pins are the best for most purposes.
Fig. 1. Insect pins
Fig. 2. Pinning block
Fig. 3 Pinning block (cross-section)
Pinning Block: Larger insects should be mounted using a wooden pinning block (Fig b & C), a simple piece of equipment. A very small hole is bored almost through the bottom in the middle of each step. A simpler pinning block can be made by drilling three holes—1, 3/4, and 1/2 inch deep—into a small wooden block. Proper use of a pinning block will result in an attractive collection with the insect, collection and identification labels in uniform position. Note the dimensions of a pinning block in the drawing below. Spreading Board: Mounting butterflies and moths is a special technique that requires a spreading board to do an attractive job. The spreading board is usually made of soft pine with a piece of cork underneath the center groove to receive insect pins.
Fig 4. Spreading board
Pinning Insects
The preferred way to display and study adult insects is to pin them into display boxes using special insect pins. The pins are pushed through the thorax of the insects while they are still fresh and the legs and antennae are placed in a natural position. This allows the specimens to be handled and studied without damaging them. In pinning insects always use special insect mounting pins that are specially treated to resist rusting. Insect pins vary in size from 000 to number 7. The latter is the largest in diameter. Numbers 2 and 3 usually work the best for the amateur collector. A good
3
David L. Keith and Tiffany Heng-Moss. Collecting insects. Retrieved Aug 18, 2009, from http://entomology.unl.edu/tmh/ent115/labs/collecting.htm.
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rule is to pin the insect slightly to the right side of the middle and down through the area where the middle pair of legs is attached. Styrofoam is an excellent base for positioning the legs so they will dry in the correct position. There is a slight variation in the pinning of the different kinds of insects. The proper way to pin an insect depends on the type of insect that you have collected. The following diagram below illustrates the proper way to pin various orders of insects. Note that the pin is usually just slightly to the right of the midline of the insect. Specimens should also be level and squarely mounted on the pin as shown.
All insects must be pinned so that they are straight on the pins. Do not tilt the specimens on the pin. The height of the specimen on the pin will depend somewhat on the size of the insect; however, always keep the distances from the top of the insect’s body to the head of the pin the same. Usually 1/3 of the pin should be above the upper surface of the insect; this will allow enough room to permit handling specimens without actually touching them. Specimens should be handled carefully to keep all legs and antennae. A small amount of time spent positioning the legs and antennae will dress up the collection. Very small insects (less than 3/16 inch) should either be pinned with micro-pin or glued on their right sides to tiny paper triangles. The latter procedure is called pointing. When pointing, first push a regular insect pin (No. 2 or 3) through the butt end of the triangle. Bend the tip of the paper triangle slightly downward with a forceps and touch it to a tiny drop of glue or clear fingernail polish. Pick up the small insect carefully with forceps and mount it by touching it on its thorax (right side) to the drop of glue. Adjust the insect so that it remains squarely in position, and then allow the glue to dry.
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Standard methods of pinning some of the insect orders are as follows: 1. Orthoptera: pin through back of thorax to right of midline (Pic no). for display purpose, one pair of wings may be spread as shown, but many orthopterists prefer to leave wings folded because of limited space in most large collections. 2. Hymenoptera and Diptera: pin through thorax between or a little behind base of forewings and to right of midline. So that no characters on body are obscured, legs should be pushed down and away from thorax, and wings turned upward or sidewise from body. Wings of most Diptera will flip upward if specimen is laid on its back before pinning and pressure is applied simultaneously to base of each wing with pair of blunt forceps. Wings should be straightened by gentle brushing with a camel’s hair brush dipped in 70 percent alcohol. For hymenoptera wings, Peterson’s XA mixture (xylene and ethanol, equal parts by volume) is recommended. 3. Coleoptera: pin through right wings cover near base such that the pin exits through the metathorax (between the middle and hind legs). Do not spread wings. 4. Heteroptera: pin through triangular scutellum to right of midline. Do not spread wings. 5. Odonata: pin through middle of thorax at thickest point or just behind base of forewings. Spread wings as described for butterfly and moths. 6. Lepidoptera: when pinning and spreading a butterfly or moth, before you begin to work, cut several thin strips of paper about 1/4" wide and 8"-10" long. Once these are ready, pick up the insect by the thorax and carefully push a pin through the middle of the thorax. Adjust the position of the butterfly on the pin and make sure that it is level, both on the sides and in both front and back. Adjust the width of the groove in the spreading board to be just slightly wider than the body of the butterfly. Push the pin into the slot of your spreading board until the bases of the wings are just level with the top of the two side pieces.
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Slip a paper strip between the wings (if they are upright) and use it to force the wings on one side down into position. Pin the ends of the paper down to hold the wings loosely in place. Do the same with the wings on the other side, also pinning the ends of the paper down. Now take another insect pin or needle and slip the point through the leading edge of the right forewing (there is a strong vein just at the front edge of each wing) near its attachment to the thorax. Be careful not to tear the wing. Loosen the forward end of the paper strip and gradually bring the forewing up into final position. Pin the wing down with a paper strip. Repeat this procedure with the forewing on the other side. Using the same technique, bring both hindwings into proper position and fasten all four wings firmly with the paper strips. Note carefully that the rear edge of the two forewings should make a perfectly straight line across the back. The hindwings should be pinned so that the rear edge is held just slightly away from the abdomen. Position antennae with pins and if the abdomen has drooped, prop it up with pins so that it dries in a natural position. Allow specimens to dry for several days before you remove the pins.
Labelling Insects
A collection has little value unless each insect is properly and accurately labeled. Labeling must be done as soon as possible after collecting, pinning and mounting or vital information may be lost. Their precise collection locations, habitats, and data on plants on which they were found are important documentation. During preparation and mounting, specimens should bear temporary labels with this information, and any time sample is subdivided, the label must be copied so that every specimen continues to be accompanied by the data. The top label should have the place from where the insect was collected, the collection date and the name of the collector (Fig. 19). The lower label should show the Order name of the insect. Many entomologists place another label beneath the collection label which gives the host plant, habitat or other pertinent information.
Fig. 19 Essential information on an insect label
The paper used for making labels should be heavy enough for labels to remain flat and not to rotate loosely round the pin. The surface of the paper should be smooth enough to write on with a fine pen (Linen ledger paper, 100% rag and 36 pound weight). Labels made from poor quality paper become yellow and brittle with age, tend to curl, disintegrate in liquid preservatives. Entomology handout Page 44
The good grade India ink is preferred that is permanent and will not run when labels are placed in liquid preservative jars. India ink is not always available when collecting in field. However, labels written with a firm hand and with a moderately soft lead pencil are satisfactory. Do not use ballpoint pens or hard lead pencils for labels placed in liquids; the writing soon fades and become illegible.
Care of collection
Pinned specimens are best kept in insect drawers with unit trays to place the pinned specimens. The bottom of unit trays is made of polyethylene and plastazote foam which makes easier to place the pinned specimens in unit trays. To keep specimens away from the museum pests, place naphthalene balls inside the wooden boxes (temporary storage) and in unit trays during storage. In moist and warm climates, mold, a kind of fungus readily attacks and grows on insect specimens. Once a specimen has become moldy, nothing can be done to restore it. If there is few hyphae of mold present on a specimen, they may be removed with forceps or brush. The specimen should be dried in a warm oven. Keeping specimens in dry place will prevent mold.
Reference:
1. http://bugs.bio.usyd.edu.au/learning/resources/Entomology/introduction.html 2. Insect external morphology. (n.d.). Available http://basicentomology.ifas.ufl.edu/lab5 (Accessed 11 June 2008) 3. Keith, David L. and Heng-Moss, Tiffany. (n.d.). Collecting insects. Available http://entomology.unl.edu/tmh/ent115/labs/collecting.htm (Accessed 17 July 2008) 4. K-State Research and Extension, 4-H Entomology , Electronic Document 5. Meyer JR (2009). General Entomology. North Carolina State University. Available http://www.cals.ncsu.edu/course/ent425/library/tutorials/index.html (Accessed 1 September 2009) 6. Pedigo, Larry. P. (2002). Entomology and pest management. (4th ed.). Printice Hall of India. New-Delhi. 7. Pinning and Labeling insect for Kansas 4 – H Entomology. Available http://ag.udel.edu/extension/4h/projects/pdf/insectpinning.pdf (Accessed 1 September 2009) 8. Robinson, D.H. (2001). Entomology principles and practices. Agrobios (India). Jodhpur. 9. Schauff, M. E. (n.d). Collecting and preserving insects and mites: techniques and tools. Washington, DC. 10. University of Sydney. (2004). Importance of entomology. Available http://bugs.bio.usyd.edu.au/Entomology/importance/importance.html (Accessed 21 July 2008)
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Student Handout MODULE: Fundamentals of Plant Protection UNIT: Entomology
Year 1 Semester 2
Compiled by: Karma Penjore & Dr. Jamba Gyeltshen August 2009 Updated by Ugyen Yangchen March 2013
CONTENT
Introduction to entomology ........................................................................3
A Class of Distinction ................................................................................................ 3 The Dominance of Insects ......................................................................................... 4 Why are insects so successful? .................................................................................. 5 Economic importance - how do insects affect us? ..................................................... 6 Features of Arthropods .............................................................................................. 7
Classification of Insects ..............................................................................9
Insect orders ............................................................................................................... 9 Insect orders of agricultural importance .................................................................. 11
Insect morphology ....................................................................................13
Head ......................................................................................................................... 13 Antennae .............................................................................................................. 13 Eyes ...................................................................................................................... 16 Mouthparts ........................................................................................................... 16 The insect thorax ...................................................................................................... 20 Legs ...................................................................................................................... 20 Wings ................................................................................................................... 21 Abdomen and external genitalia .............................................................................. 25
Reproduction in insects .............................................................................27
How do insects find their mates? ............................................................................. 27 Types of reproduction in insects .............................................................................. 27
Insect growth and development ................................................................27
Insect life cycle ........................................................................................................ 28 Metamorphosis ......................................................................................................... 29 Insect seasonal cycles .............................................................................................. 31 Larval forms ............................................................................................................. 32 Pupal forms .............................................................................................................. 33
Insect Collection .......................................................................................35
Purpose of collecting and preserving insects ........................................................... 35 Insect collection equipment and materials ............................................................... 36 Preserving insects..................................................................................................... 40 Hard-Bodied Insects............................................................................................. 40 Soft-Bodied Insects .............................................................................................. 40
Pinning, mounting and displaying insects ................................................41
Equipment required .................................................................................................. 41 Pinning Insects ......................................................................................................... 41 Labeling Insects ....................................................................................................... 44
REFERENCE:...........................................................................................45
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Introduction to entomology
Entomology is a branch of zoology that deals with the study of insects. The term is derived from the Greek word Entomon = Insects and logos = study. Agricultural Entomology deals with the study of insects that affect agriculture. There are other branches of entomology, such as medical entomology, veterinary entomology, and forensic entomology (study of insects inhabiting decomposing remains). With over one million different species inhabiting the earth, insects make up more than 80% of all described animal species and form a major component of the earth's biodiversity. They have different roles: as plant consumers and herbivores, food source for other organisms, scavengers and detritivores (feeding on decomposing organic matter), predators and parasites. Insects also directly affect human welfare by competing with us for food and transmitting diseases. However, not all insects are detrimental to us. For example, bees are used to produce honey, silkworms to produce silk and similarly numerous predatory species are used to control pests in our crops.
A Class of Distinction
Adapted from John R.Meyer, (http://www.cals.ncsu.edu/course/ent425/library/tutorials/index.html) We humans are such a self-centered species that we seldom stop to acknowledge or appreciate the importance of other living organisms in our environment. Our prowess in science and technology has given us unparalleled control over our physical environment, and as a result, we have developed an inflated view of our own importance in the web of life. Although we have learned to use tools, dam rivers, level mountains, and harness atomic power, we are still dependent on Mother Nature for the countless housekeeping chores that keep our environment stable and healthy. Indeed, we are relatively minor players in the ecological drama that continually unfolds all around us. If humans were to suddenly vanish from the planet, there would be no ecological calamity, no massive extinctions, and no tears shed for our demise. Remnants of human civilization would soon be smothered in vegetation, the forests would reclaim our cities, and life would go on without us just as it did for millions of years before our ancestors first reckoned the passage of time. Sadly, the earth would probably be better off without us. In simplest terms, life (as we know it) exists on planet earth because of a global cycle of production and consumption that hinges almost exclusively on green plants as primary producers and insects as primary consumers. These two life-forms overshadow all other multi-cellular organisms in terms of abundance and diversity. They are mutually dependant on one another for survival, and form a nucleus around which all terrestrial and fresh-water ecosystems are built. Without green plants and the organic molecules they produce through photosynthesis, all animal life would collapse from starvation. Without insects and other decomposers, green plants would quickly exhaust their nutrient supplies, dead organic matter would accumulate in putrid, rotting heaps, and many species of flowering plants would become extinct for lack of insect pollinators.
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In a sense, we owe our very existence to members of the insect world -- creatures we often fear or despise. We expend considerable resources trying to eliminate these animals from every facet of our daily lives, but in fact, we could never hope to survive without them -- they make the earth habitable for us. Like tiny maids and butlers, they perform Nature's housekeeping tasks with competence and efficiency. Nothing else -- animal, vegetable, or mineral -- could ever take their place. By virtue of their diversity, their world-wide distribution, their ecological importance, and their impact on other life-forms, the insects are indeed a class of distinction.
The Dominance of Insects
Figure 1
Number of Species Entomologists estimate that over 800,000 insect species have been named and described since Carolus Linnaeus (1707-1778) founded the modern system of nomenclature (genus and species) for all plants and animals. The entire plant kingdom, by comparison, contains between 400,000 and 500,000 species. Thus, insects represent more than half (about 53%) of the 1.5 million species of living organisms known to science (Figure 1). Number of individuals Another way to look at the dominance of insects is to consider the distribution and density of individual species or populations. Because of their small size and high reproductive potential, insect populations often grow to epic proportions. A single colony of Australian termites can swell to several million individuals within an earthen mound 20-25 feet tall. A swarm of migratory locusts may contain up to 10 billion individuals, cover an area of several thousand hectares, and have a total biomass of over 30,000 metric tons. Above the arctic circle, hordes of mosquitoes Entomology handout Page 4
and black flies can make life miserable for any warm-blooded animal. In some cases, these biting flies are so abundant and persistent that large animals, such as reindeer, have been known to die from the massive loss of blood (desanguination). In the tropics, ants are the most pervasive and diverse of all animal species. Colonies of driver ants (Dorylus sp.) on the African savannah may contain 20 million individuals. Distribution A third way to assess the dominance of insects is to examine their abundance and diversity in a wide range of ecological habitats. Indeed, insects are found in virtually every terrestrial and fresh-water environment on the face of the earth. They live everywhere from mountain tops in the Himalayas to tide pools at the seashore. Dozens of eyeless species spend their entire lives in the total darkness of underground caverns. At least 40 species live on the polar ice caps of Antarctica, others exist on the surface of glaciers, or near the edge of melting snow fields. A few species can survive in hot springs where the water temperature is 50oC; others inhabit deserts where water is scarce and daytime temperatures exceed 60oC. Insects live both above and below the surface of rivers, streams, lakes, and ponds. One species of water strider makes its home among floating seaweed in the Sargasso Sea, nearly 2400 kilometers (1500 miles) from the nearest land mass. The petroleum fly (Helaeomyia petrolei), develops in pools of crude oil in the California oil fields. A related species, the brine fly (Ephydra cinera), thrives in the high salinity of Utah's Great Salt Lake. In fact, the only place on earth where insects are not plentiful is in the ocean depths. Most marine environments are filled by another successful group of arthropods, the Crustacea.
Why are insects so successful?
There are many attributes of insects that have allowed for their success and diversification. Exoskeleton -this is a marvelous structure that not only gives shape and support to the body's soft tissues, but also provides protection from attack or injury, minimizes the loss of body fluids in both arid and freshwater environments, and assures mechanical advantage to muscles for strength and agility in movement. Small size -there are many more niches for small organisms than for large organisms. For instance, one insect could live solely on and in the seeds of a specific plant. Short life cycle - this allows many generations within a given time for selection and evolution to take place. Reproductive potential - large numbers of offspring are produced to compensate the mortality due to adverse conditions. When large numbers of offspring are produced, there are also large variation in the population for natural selection and evolution to act upon. A honey bee queen lays as many as 4,000 eggs a day, and an African termite queen can lay as many as 43,000 eggs a day. Page 5
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Metamorphosis- Variation of life style of different stages in an insect's life (e.g. caterpillar versus butterfly) reduces competition for resources within the species. Wings-the ability to fly are relatively rare outside insects and have allowed them to colonize freely. Adaptability - A combination of large and diverse populations, high reproductive potential, and relatively short life cycles, has equipped most insects with the genetic resources to adapt quickly in the face of a changing environment. Sensory sophistication - the sensory capabilities of insects surpasses most other organisms. Adaptation of appendages - mouthparts, wings and legs have often become highly specialized.
Economic importance - how do insects affect us?
Insects affect us in different ways. Some are beneficial while some are harmful. The beneficial and detrimental effects of insects are as discussed below. Beneficial effects 1. Pollination- Insects such as honey bees, beetles and wasps aid in pollinating our crops and fruit trees. Crops in Rosaceae, Cucurbitaceae and Leguminosae are exclusively pollinated by bee. It is estimated that 80% of the commercial food crops are pollinated by honey bees. 2. 2: Bio-control agents- Some parasitic and predatory insects are excellent biocontrol agents for controlling other injurious insects. Example Encarsia formosa is an excellent bio-control agent for white flies on tomatoes and potatoes. 3. Production of products - Honey, wax, silk (from Bombyx mori), shellac (from Laccifer lacca) and cochineal (red dye widely used in cosmetics, medicinals and food products) derived from, a scale insect, Dactylopius coccus. 4. Nutrient recycling - Insects feed on dead and decaying plants, animals and animal excreta and help in recycling the nutrients. Some insects burrow into soils and improve the soil structure and texture. Examples are dung feeders and termites. 5. Source of food - over 500 species of insects are used as food by humans usually crickets, grasshoppers, beetle, wasp, butterfly larvae, bugs etc 6. Miscellaneous – Some insects are used for medicinal purpose, decoration, hobby, and pets. Detrimental effects Destruction or spoilage of food (both fresh and stored) and crops (including forests) 2. Damage to goods - leather, paper, textiles, (by beetles, cockroaches, silverfish or moths), timber (by termites and different types of borers) 3. Transmits disease in plants and animals. 4. Possess venoms and cause allergies
1.
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5. 6. 7.
Some insects are a nuisance to our well being -house flies, ants, mosquitoes Cause phobias – fear of grisly caterpillars or spiders (arachnophobia) Require use of pesticides and other poisons, which often harm other animals
Features of Arthropods
Arthropoda (from arthros = jointed, podos = foot) is the largest phylum in the Animal Kingdom. Arthropods are segmented animals which have jointed appendages. All arthropods have: All arthropods possess:
Exoskeleton - a hard protective covering around the outside of the body (divided by sutures into plates called sclerites) Segmented body Jointed limbs and jointed mouthparts - that allow extensive specialization Bilateral symmetry - whereby a central line can divide the body into two identical halves, left and right Ventral nerve cord - as opposed to a vertebrate nerve cord which is dorsal Dorsal blood pump
The Phylum Arthropoda includes the class Insecta and other classes like the Arachnida, the Chilopoda, the Diplopoda and the Crustacea. It is with these groups that the insects, especially the wingless ones, are most likely to be confused and the main characters that are used to differentiate these classes are:
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Class Arachnida (arachnids): spiders, scorpions, ticks, mites, etc. Arachnids possess:
2 body segments - cephalothorax and abdomen 8 legs 1 pair of chelicerae no antennae
University of Sydney
Class Chilopoda (centipedes) Chilipods are quick moving predators with poison glands which possess:
body flattened and multi-segmented 1 pair of legs per body segment 1 pair of antennae 1st pair of legs modified into venomous ―fangs‖
University of Sydney
Class Diplopoda (millipedes) Diplopods are slow moving vegetarians which possess:
Many body segments 2 pair of legs per body segment 1 pair of antennae
University of Sydney
Class Crustacea (crustaceans): crabs, shrimp, barnacles, sowbugs, etc. Crustaceans possess:
Two body regions – Cephalothorax and abdomen 2 pairs of antennae Varied number of legs (usually five)
University of Sydney
Class Insecta (Insects); beetles, bugs, wasps, moths, flies, etc. Insects possess:
3 body segments 6 legs 1 pair of antennae Most flying insects possess two pairs of wings
University of Sydney
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Classification of Insects
All living organisms are placed into certain groups or categories for classification and identification. The seven most commonly used categories are: Kingdom- Animal Phylum - Arthropoda Class – Insecta Order – Lepidoptera (Butterflies and moths) Family - Noctuidae Genus - Helicoverpa Species – armigera The species is the basic taxonomic category and may be defined as groups of actually interbreeding natural populations which are reproductively isolated from other such groups. Closely related species are grouped together in the next higher category - the genus. Related genera make up a family and related families are grouped into orders. The scientific name of an organism consists of two words - the generic name and the specific name. This system of naming insects is called the binomial system of nomenclature.
Insect orders
Insects are among the most abundant and successful of terrestrial animals. They include about three-fourths of all described species of animals and have become adapted to a wide range of environments. No other group of living creatures has such variety of form, colour, function and habitat. The classification of insects into various orders is based on the presence or absence of wings, wing venation, the type of metamorphosis, the type of mouth parts, the characters of antennae, tarsi, etc. Thus we have: Class INSECTA
Sub-class APTERYGOTA (Wingless) There are four orders in Apterygota, viz: 1. Collembola (Springtails) 2. Diplura 3. Protura 4. *Thysanura (Silverfish)
Sub-class PTERYGOTA (Winged)
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Here, none of them are of economic importance, except silverfish, which occasionally damage book-bindings. The subclass PTERYGOTA is further divided into two groups as: PTERYGOTA
EXOPTERYGOTA
ENDOPTERYGOTA
exo=external; endo=internal In Exopterygota, the wings develop externally and the young ones are called nymphs and metamorphosis is in-complete (Hemimetabolous). The following orders are included in this division: 5. Ephemeroptera (Mayflies) 6. Odonata (Dragonflies) 7. Blattodea (Cockroaches) 8. Isoptera (Termites) 9. Mantodea (Mantids) 10. Zoraptera 11. Gryllablattodea 12. Dermaptera (Earwigs) 13. Plecoptera (Stoneflies) 14* Orthoptera (Grasshoppers, Crickets etc.) 15. Phasmatodea (Stick insects) 16. Embioptera (Web-spinners) 17. Psocoptera (Psocids, Book lice) 18. Anoplura (Sucking lice) 19. Mallophaga (Biting lice) 20* Hemiptera (Bugs) 21* Thysanoptera (Thrips) In Endopterygota, the development of wings occurs internally and transformation from larva to adult form occurs during a quiescent pupal stage. They undergo complete metamorphosis (Holometabolous). The following orders are included in this division: 22. 23. 24* 25. Megaloptera (Alder flies) Neuroptera (Lace wings, Antlions) Coleoptera (Beetles) Strepsiptera (Stylops) Page 10
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26. 27. 28* 29. 30* 31*
Mecoptera (Scorpion-flies) Siphonaptera (Fleas) Diptera (Flies, Mosquitoes) Trichoptera (Caddisflies) Lepidoptera (Moths, Butterflies) Hymenoptera (Wasps, Bees, Ants)
Insect orders of agricultural importance
ORTHOPTERA: Includes grasshoppers, crickets, etc. Orthopterans have chewing mouth types in both adult and immature stage. Most orthopterans have two pairs of wings, the forewings being thickened and of leathery texture are called tegmina. The hind wings are large and fanlike and are folded beneath the tegmina when not in use. They have thread-like, filiform antennae. The hind legs are usually enlarged for jumping. THYSANOPTERA: (Thrips) - Thrips are small or minute insects, and have a rasping - sucking mouth type. Many species are wingless but when wings are present, they are long, narrow and fringed with hairs. Many species of thrips are phytophagous, causing damage to a variety of plants. HEMIPTERA: Hemipterans have piercing and sucking mouth type. The fore-wings are called hemelytra and are normally held flat over the abdomen when at rest. The basal portions of these wings are hardened in texture, while the apical portions are membranous. The hind wings are membranous and folded beneath the hemelytra. They have a segmented beak which arises ventrally from the front or anterior region of the head. HOMOPTERA: They have piercing and sucking mouth parts. The fore-wings are uniformly membranous or slightly thickened and the wings are held roof-like or tentlike over their bodies when at rest. This order also includes wingless and short wing insects. Their segmented beak arises ventrally from the posterior portion of the head. The order includes aphids, hoppers, mealy bugs and scale insects. COLEOPTERA: These are the beetles characterized by having fore-wings which are thickened and hardened into elytra, which meet along the mid-lines of the dorsal surface and which are used to protect the delicate, folded hind wings. Beetles have chewing mouth types in both the immature and adult stages. This is the largest order in the animal kingdom and the group exhibits great diversity of forms and habits. Included in this order are a variety of harmful as well as beneficial insects. LEPIDOPTERA: These are the moths and butterflies. Lepidopteran larvae have chewing mouth types, while some adults have vestigial or non-functioning mouth types and do not feed. Most adults, however, have a long coiled proboscis which is used for siphoning plant nectar. They have two pairs of membranous wings and the body and appendages are clothed in broad scales. The immature stages of Lepidoptera, called caterpillars, can cause considerable damage by their feeding. Entomology handout Page 11
DIPTERA: These are the true flies, with a single pair of membranous wings, the hindwings being modified into club-shaped halteres. There is a variety of feeding habits and mouth types associated with members of this order. Adult Diptera may have sponging, lapping or piercing-sucking mouth types. Dipteran larvae are legless and have a chewing mouth type. HYMENOPTERA: This order includes sawflies, wasps, bees and ants. Larval hymenoptera generally have a chewing mouth type. Adults have chewing mouth parts but this may again be modified for specific functions. Only a few species from this order are considered to be of economic importance but the majority of them are beneficial insects
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Insect morphology
Head
The head of an insect is composed of a series of segments, which are specialized for food gathering and manipulation, sensory perception, and neural integration. The head bears the eyes (compound eyes and ocelli), antennae, and mouthparts. The anterior part of the head is the frons. The anterior area below the dorsum of the head, between and behind the eyes is the vertex. The area below the compound eye, on the side of the head, is the gena. The liplike sclerite is the clypeus. The principle structures of an insect head are given in figure 1.
Fig: 1 Principle parts of in insect head.
Source: http://basicentomology.ifas.ufl.edu/lab5.doc
Antennae
The antennae are the sensory organ of smell touch and hearing (auditory) in insects. It is with the help of antenna that insects are able to locate food, find their mates, detect danger, feel and find their way. The specialisation of the antenna for different functions may vary from one type of insect to the other. For e.g. antenna of houseflies have a strong sense of smell and that is why they can appear from anywhere if there is a rotten smell of meat. The shape, size and length of antenna vary so much. Cockroaches have very long antenna whereas the antenna of houseflies no matter how big in size can hardly be seen. Depending upon the shape, antenna can be filiform (thread-like), clavate (clubshaped), pectinate (comb-like), bipectinate (double comb like), plumose (feather-like), serrated (sawtooth-like), lamellate (plate-like), monoliform (bead-like), aristate (pouch-like). Antennal segments Antennae are mobile, segmented, paired appendages. The paired antennae are made up of a number of individual joints and the entire antenna typically has three main divisions: The first antennal segment (closest to the head) is called the scape, generally is larger than the other segments and is the basal stalk. The second antennal segment is called the pedicel, nearly always contains a sensory organ known as Johnston’s organ, which responds to movement of the distal part of the antennae relative to the pedicel.The remainder of the antenna is called the flagellum, is often filamentous and multi segmented.
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Antennae of male insects may be more elaborate than those of the corresponding females, increasing the surface area available for detecting female sex pheromones. The basic form of antenna is filiform. In this type there are many segments that are more or less equal in size. Filiform antennae are seen in a wide variety of groups, such as Dragonflies, Grasshoppers and Crickets, Book Lice, Biting Lice, Scorpion Flies and Beetles. The length and number of joints varies much between them.
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Types of antennae:
Name
Appearance
Example(s)
Setaceous -- bristle-like
Dragonflies
Filiform -- thread-like
Ground Cockroaches
beetles
and
Moniliform -- bead-like
Termites
Serrate -- sawtoothed
Click beetles
Clavate -- gradually clubbed
Carrion beetles
Capitate -- abruptly clubbed
Butterflies
Lamellate -- nested plates
Scarab beetles
Pectinate -- comb-like
Fire-colored and Male glow-worms
beetles
Plumose -- brush-like
Mosquitoes
Geniculate -- elbowed
Weevils and Ants
Aristate -- pouch-like with lateral bristle
House flies
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Eyes
Insects have usually 2 types of eyes. The pair of big eyes that are prominently seen in most insects are known as the compound eyes. It is so named because of the fact that the eyes are made of many units of photo receptors that are each individually functioning like our human eye. These visual units that make up the compound eyes are known as ommatidia (ommatidium sing.). There may be up to 30,000 ommatidia in a compound eye. The number of ommatidium however varies from insect to insect depending upon their habit. The predatory insects have very powerful eyes which mean the number of ommatidia is very high. Insects like worker ants have very few ommatidia. This type of eye gives less resolution than the vertebrate eye, but it gives acute perception of movement which is important in flight.
Besides the compound eyes, insects do have simple eyes called ocelli, on their forehead. They are less apparent and are seen only as dark shining patches (usually 3) of epidermal cells. Higher insects have both types of eyes where as lower insects and larvae have simple eyes only. They are not as sensitive as the compound eyes but can detect the changes in the illumination or intensity of light. For example it can alert the insect if a shadow of a predator falls on it. Cut worms which are nocturnal in habit probably depend on these simple eyes.
Mouthparts
The most important way in which insects inflict losses and injury upon man and his possessions is by eating or feeding. Since insects feed in various ways, it is evident that knowledge of insect mouth parts is of prime importance in the study of entomology. The mouth part of an insect can be classified in accordance with their function. According to this scheme there are those are those intended for biting and chewing (Mandibulate) like in grasshoppers, crickets, cockroaches, lacewings and beetles; those that are primarily used for sucking liquids (Haustellate) like in stinkbugs, aphids, mosquitoes, houseflies.
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1. Mandibulate 2. Haustellate a) Stylet b) Non-stylate
Biting-chewing
Piercing-sucking Siphoning Sponging Chewing-lapping Rasping-sucking
Stylets are needle-like projections used to penetrate plant and animal tissue. The modified mandibles, maxilla, and hypopharynx form the stylets and the feeding tube. After piercing solid tissue, insects use the modified mouthparts to suck liquids from the host. 1. Madibulate type- Biting-chewing mouthpart
Source: http://www.ndsu.edu/entomology/topics/heads.htm
The main parts of this type are the (1) Labrum - an unpaired, flap-like structure hinges to its upper margin to the lower edge of the clypeus. It is located in front of (or above, depending on the direction the head points) the oral cavity and serve as an upper "lip" and moves longitudinally. (2) Mandibles (upper jaws) – is a pair of highly sclerotised, horny, usually large nonsegmented structures found immediately behind (or below) the labrum. They articulate on the distal margins of the genae. The mandibles move at right angles to the body. They are used for biting, chewing and severing food.
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(3) Maxillae - (lower jaw) is a pair of segmented structures situated immediately behind or below the mandible. The maxillae moves at right angles to the body and possess segmented palps. (4) Labium – (the lower lip) is an unpaired structure serving as a lower lip and closing the oral cavity from below or behind; it moves longitudinally and possesses a pair of segmented palps. (5) Hypopharynx - this is an unpaired structure, otherwise known as the tongue, which occupies a portion of the oral cavity; it is located more or less in the center of this space and near the base of the labium.
Fig. 11 Different parts of a mandubulate type mouth. 2. Haustellate type of mouthpart is basically a modification of the simple bitingchewing type. Haustellate mouthpart can be broken down into two subgroups: those that possess stylets and those that do not. a) Piercing-sucking type of mouthpart present in stink bugs is an example of haustellate type with stylets. Mandibles and maxillae are formed into stylets which are enclosed by the labium. Once the stylets penetrate, a secretion is injected to dissolve tissue, act as a toxin in predacious species, or as anticoagulant for mosquitoes.
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b) Siphoning type: Those without stylets are unable to pierce tissues, and therefore these insects must rely on easily accessible food sources such as nectar at the base of a flower. One example of nonstylate mouthpart is the long siphoning proboscis of butterflies and moths (Lepidoptera). When feeding the proboscis is uncoiled and extended. Nectar is sucked up into the mouth or oral cavity. The proboscis is a modified maxillae.
c) Sponging - Found in adults of specialized flies. During feeding the proboscis (modified labium) is lowered and salivary secretions are pumped onto the food. The dissolved or suspended food then moves by capillary action into the pseudotracheae (sponge) and is ingested. There may be sharp teeth on the pseudotracheae to rasp flesh and draw up blood. The labella is the fleshy distal end of the labium that functions as a sponge-like organ to sop up liquids.
d) Chewing-Lapping - Adult honeybees and bumble bees. Mouthparts are modified to utilize liquid food, honey and nectar. A central "tongue" is used to draw liquid into the body. The mandibles are not used for feeding but function to cut floral tissue to gain access to nectar, for defense, and for manipulating wax. e) Rasping-sucking – Thrips have rasping sucking type of mouthpart. (To rasp means to scrape with a coarse file). The mandibles which are asymmetrical injure the tissue and the cell sap oozing out is being sucked
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The insect thorax
The insect thorax is box-like with dorsal, ventral and lateral sclerites. The dorsal sclerites are collectively called the notum (pronotum, mesonotum, and metanotum) which may be further subdivided into an anterior scutum and a posterior scutellum. The ventral sclerites are called the sternum (prosternum, mesosternum, and metasternum). Each sternum is divided into several plates, called sternites. The lateral sclerites are called the pleuron.
The thorax is divided into three parts and from front to back; these segments are named as follows: (1) Prothorax - the first of the three (hence Pro-) and bearing the first pair of true legs; wings are never present on this portion of the thorax. The top plate of the segment, the Pronotum, is in most winged insects are rather highly specialized and is usually enlarged to some extent. (2) Mesothorax - (meso= middle) this is the middle of the three thoracic ringsegments; it bears the second pair of true legs and the first pair of wings when two pairs are present. If only one pair of wings is present, as is the case with the flies, then that single pair is located on this segment of the thorax. In other species (i.e., scale insects, the males have one pair of wings on the metathorax!). One pair of spiracles is often found on this segment. In most insects, usually no spiracles are found on the 1st or third thoracic segments. (3) Metathorax - (Meta-last) this is the third and last of the thoracic segments; it bears the third pair of true legs and the second pair of wings, when they are present. A pair of thin knobbed projections (halters) takes the place of this second pair of wings in the Diptera.
Legs
The legs, named from the anterior, are the fore, mid and hind legs. Each leg consists of four main parts - the coxa, the femur, the tibia and the tarsus (plural: tarsi) - with a small, often inconspicuous segment between the coxa and femur, called the Entomology handout Page 20
trochanter. The tarsus is collectively composed of 2 to 5 smaller tarsomeres. The last tarsomere usually has a pair of claws and often 2 or 3 tarsal pads- the arolium.
Figure: 12 parts (source: http://basicentomology.ifas.ufl.edu/lab5.)
of
insect
legs
Insect legs have been variously adapted for running, jumping, grasping, swimming or digging. An examination of insect legs can often tell much about the habits of the insect. Some of the insect leg modifications are Unmodified legs are used for walking and are called ambulatory Legs modified for running are called cursorial. Digging legs are called fossorial Swimming legs are called natatorial. Jumping legs are called saltorial. Grasping legs are called raptorial.
Wings
(Source: http://www.cals.ncsu.edu/course/ent425/tutorial/wings.html) Insects are the only invertebrates that can fly and their wings are unique among all animals. They are outgrowths of the body wall rather than modified appendages. The wings may be membranous, parchment-like, heavily sclerotized, fringed with long hairs, or covered with scales. Most insects have two pairs of wings -- one pair on the mesothorax and one pair on the metathorax (never on the prothorax). Wings serve not only as organs of flight, but also may be adapted variously as protective covers (Coleoptera and Dermaptera), thermal collectors (Lepidoptera), gyroscopic stabilizers (Diptera), sound producers (Orthoptera), or visual cues for species recognition and sexual contact (Lepidoptera). Basically, insect wings are very simple flap-like extensions of the body wall, with an upper and lower membrane between which run hollow tubes known as the veins which give rigidity and support. In most cases, a characteristic network of veins runs throughout the wing tissue. These veins are extensions of the body's circulatory system. They are filled with hemolymph and Entomology handout Page 21
contain a tracheal tube and a nerve. The venation (arrangement of veins) varies from very simple to extremely complex and is an important character in identification of many orders, families and genera. In membranous wings, the veins provide strength and reinforcement during flight. Wing shape, texture, and venation are quite distinctive among the insect taxa and therefore highly useful as aids for identification. Wings become functional only in the adult stage. Wing Venation: Costa (C) -- the leading edge of the wing Subcosta (Sc) -- second longitudinal vein (behind the costa), typically unbranched
Radius (R) -- third longitudinal vein, one to five branches reach the wing margin Media (M) -- fourth longitudinal vein, one to four branches reach the wing margin Cubitus (Cu) -- fifth longitudinal vein, one to three branches reach the wing margin Anal veins (A1, A2, A3) -- unbranched veins behind the cubitus Names of crossveins are based on their position relative to longitudinal veins: c-sc crossveins run between the costa and subcosta r crossveins run bewteen adjacent branches of the radius r-m crossveins run between the radius and media m-cu crossveins run between the media and cubitus
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Wing adapations and modifications: Insect wings have been modified in many ways; for example:
The wings of a moth are covered with minute scales which are often brightly colored. The fore wings of a beetle are hardened and form a protection (the elytra) for the membranous hind wings. Cockroaches and grasshoppers have leathery fore wings (Tegmina). Some bugs have half-leathery, half-membranous fore wings (hemelytra). In flies, (Diptera), the hind wings have become modified to form small balance organs, called halteres. Appearance Order(s)
Characteristic Elytra -- hard, sclerotized front wings that serve as protective covers for membranous hind wings Hemelytra -front wings that are leathery or parchment-like at the base and membranous near the tip Tegmina -- front wings that are completely leathery or parchment-like in texture
Coleoptera and Dermaptera
Hemiptera: Heteroptera
Orthoptera, Blattodea, and Mantodea
Halteres -- small, club-like hind wings that serve as gyroscopic stabilizers during flight
Diptera
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Fringed wings -slender front and hind wings with long fringes of hair Hairy wings -front and hind wings clothed with setae
Thysanoptera
Trichoptera
Scaly wings -front and hind wings covered with flattened setae (scales)
Lepidoptera
Hamuli -- tiny hooks on hind wing that hold front and hind wings together
Hymenoptera
Frenulum -Bristle near base of hind wing that holds front and hind wings together
Lepidoptera
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Abdomen and external genitalia
The abdomen is the third and posterior region of the insect body. The abdomen of adult insects contains no legs or wings and usually consists of 10 or 11 segments. However, in many orders, reduction has occurred or the segments are concealed or modified. Each segment of the abdomen consists of a dorsal sclerite, the tergum, and a ventral sclerite, the sternum, joined to one another laterally by a pleural membrane. In many adult insects, there is a spiracle (opening to the respiratory system) near the pleural membrane on each side of the first eight abdominal segments. At the very back of the abdomen, the anus (rear opening of the digestive system) is nestled between three protective sclerites: a dorsal epiproct and a pair of lateral paraprocts. A pair of sensory organs, the cerci, may be located near the anterior margin of the paraprocts. These structures are tactile (touch) receptors. They are usually regarded as a "primitive" trait because they are absent in the hemipteroid and holometabolous orders. Terminally the abdomen bears the external genitaliaThe insect's genital opening lies just below the anus: it is surrounded by specialized sclerites that form the external genitalia. In females, paired appendages of the eighth and ninth abdominal segment fit together to form an egg-laying mechanism called the ovipositor. A pair of cerci is also present at the end of the abdomen. These have a sensory function.
In males, the genital opening is usually enclosed in a tube-like aedeagus which enters the female's body during copulation (like a penis). The external genitalia may also include other sclerites (e.g. subgenital plate, claspers, styli, etc.) that facilitate mating or egg-laying. The structure of these genital sclerites differs from species to species to the extent that it usually prevents inter-species hybridization and also serves as a valuable identification tool for insect taxonomists. Other abdominal structures may also be present in some insects. These include:
Pincers -- In Dermaptera (earwigs), the cerci are heavily sclerotized and forceps-like. They are used mostly for defense, but also during courtship, and sometimes to help in folding the wings. Median caudal filament -- a thread-like projection arising from the center of the last abdominal segment (between the cerci). This structure is found only in "primitive" orders (e.g. Diplura, Thysanura, Ephemeroptera). Cornicles -- paired secretory structures located dorsally on the abdomen of aphids. The cornicles produce substances that repel predators or elicit caregiving behavior by symbiotic ants.
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Abdominal prolegs -- fleshy, locomotory appendages found only in the larvae of certain orders (notably Lepidoptera, but also Mecoptera and some Hymenoptera). Sting -- a modified ovipositor, found only in the females of aculeate Hymenoptera (ants, bees, and predatory wasps). Abdominal gills -- respiratory organs found in the nymphs (naiads) of certain aquatic insects. In Ephemeroptera (mayflies), paired gills are located along the sides of each abdominal segment; in Odonata (damselflies), the gills are attached to the end of the abdomen. Furcula -- the "springtail" jumping organ found in Collembola on the ventral side of the fifth abdominal segment. A clasp (the tenaculum) on the third abdominal segment holds the springtail in its "cocked" position. Collophore -- a fleshy, peg-like structure found in Collembola on the ventral side of the first abdominal segment. It appears to maintain homeostasis by regulating absorption of water from the environment.
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Reproduction in insects
How do insects find their mates?
Insects use different ways in order to attract their mating partners. Insects use sound (Example crickets, grasshoppers and cicadas), smell (Moths), colour (Moths and butterflies) and pheromones (Moths). Pheromone is a chemical which is produced by living organisms that transmits message to other members of the same species.
Types of reproduction in insects
Reproduction in insects can take a wide variety of forms, often very complex. Some can switch their type of reproduction during their life cycle based on environmental triggers. Others reproduce the same way throughout their life history. The basic theme and some of the variations are described below. Sexual reproduction: The standard model for reproduction is where males and females occur throughout the life cycle, and each produces a germ cell (egg and sperm, respectively). The male inseminates the female during mating. The female often stores sperm in special pouches in her abdomen called spermathecae (singular, spermatheca). The eggs are fertilized within the female's body, producing an embryo. Eggs are deposited on a host. They hatch and develop into either male or female offspring. Parthenogenesis: This is asexual reproduction, where eggs grow and develop without fertilization. There are several variations of parthenogenesis. Arrhenotokous parthenogenesis is where unfertilized eggs produce only males. In deuterotokous parthenogenesis, both males and females are produced from unfertilized eggs. In thelyotokous reproduction, unfertilized eggs produce only females. Viviparity: Most insects deposit eggs that hatch into nymphs or larvae, a process called oviparity, but some insects bear living young. A common example is aphids, which are viviparous during part of their life cycle. A variation is ovoviviparity, where eggs are held within the female's body, where they hatch, and the young are born live. Polyembryony: This is where two or more embryos develop from a single egg, as in the parasitic Hymenoptera, such as braconid, encyrtid, and dryinid wasps.
Insect growth and development
Definitions1 Chrysalis - a butterfly pupa, not enclosed in a cocoon, a pupa without a protective cover. Cocoon - a case formed partly or wholly of silk secreted by the larva and in which pupation occurs, a protective cover.
1
http://www.ndsu.nodak.edu/entomology/topics/growth.htm
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Instar Larva
Molting Nymph Pupa
Stage
- form of an insect between successive molts, the first instar being the stage between emerging from the egg and the first molt. - (pl. larvae) immature stage between the egg and pupa in insects with complete metamorphosis or, sometimes, between egg and adult in insects with incomplete metamorphosis. - the acting of shedding the cuticle or insect skin, shedding of the exoskeleton . - immature stage of insects with incomplete metamorphosis. - (pl. pupae) the third, inactive stage of insects with complete metamorphosis, the transition stage between the larval and adult stages. Usually non-mobile. - any definite period in the development of an insect, e.g.. the egg stage, nymphal or larval stage, pupal stage, adult stage. The number of nymphal or larval stages is variable.
Insect life cycle
Life cycle is the chain of biological events that occurs during the lifetime of an individual insect. The cycle usually begins with deposition of egg and ends with egg lying by the adult. Egg: Eggs come in many shapes, sizes, and colors. They might be deposited on or in the ground, the roots, the stems, the leaves, or the flowers. When the eggs hatch the new insect is called a larva. The plural of larva is larvae. Larva: The larva seldom looks like the adult it will become. Some common larval forms are the maggot, grub worm, nymph and caterpillar. As the larva grows it must shed its old skin from time to time. This is called molting or ecdysis. From hatching to the first molt the larva is said to be in its 1st instar stage. After molting the first time the larva enters its second instar stage, and so on (fig. 13). Different insects have different numbers of instars, but eventually the larva is fully grown and ready to pupate.
Fig.13 Stages in development of an insect to adult insect
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Pupa: The pupa is the life stage between larva and adult. In this stage the insect does not feed, and is in a quiescent state. Most pupae are found hidden and protected habitats. Some usually construct some kind of shelter (cocoon) to pupate in. This "cocoon" might be made from soil particles, silk, chewed seeds, chewed plant material, ground litter, or combinations. After pupation the adult emerges to mate and to lay eggs. The figure below illustrates the life cycle of a fly.
Figure: 14. An example of insect life cycle showing complete metamorphosis (Source: http://www.ndsu.nodak.edu/entomology/topics/growth.htm)
Metamorphosis
The majority of insects start life in the form of a fertilized egg laid by a female on plants or in the ground. After hatching of the egg the developing young one undergoes a series of changes in size and structure before becoming adult. Each time an insect makes a change into the next growth stage, it has to molt (shed) its skin. After each molt, the insect becomes a little larger and somewhat different in form until it reaches the adult stage. After it reaches the adult stage, it does not molt or grow any more. To the series of changes which takes place in the life history of an insect the term metamorphosis has been applied. There are four kinds of metamorphosis, complete (butterflies), gradual (grasshoppers), incomplete (dragonflies) and no metamorphosis (Silverfish). The exact style of metamorphosis is not the same for all insects, but insects in the same order have the same style of metamorphosis. Ametabolous development: Some orders of insects are said to have no metamorphosis (Ametabolous development) because there is little or no difference in appearance between the young stages and the adult except for size (Fig.14). The Entomology handout Page 29
no-metamorphosis model is found in primitively wingless insects (Subclass Apterygota). Suitable examples are primitive insects such as silverfish (Thysanura).
Fig. 15 typical development of an aterygote insect with no metamorphosis Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Gradual metamorphosis (Paurometabolous development): The life cycle of insects with gradual metamorphosis have three life stages (Fig. 16): egg, nymph and adult. Nymphs resemble the adult except that their body parts are out of proportion with each other, and they do not have fully developed wings and external genetalia. With each molt, the nymphs gradually develop wings and take on the body proportions of an adult. Nymphs have the same type of mouthparts as the adult, and they both feed on the same kind of food.
Fig.16 The life cycle of a plant bug. Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Incomplete metamorphosis (Hemimetabolous development) is somewhat like gradual metamorphosis and also has three life stages: egg, naiads and adult. However, the adult insect with incomplete metamorphosis lays its eggs in or near Entomology handout Page 30
water and the naiads develop in water. The adults are flying insects that live out of water. Naiads and adults therefore do not eat the same kind of food. Naiads have chewing mouthparts, but the adults have differently shaped chewing mouthparts or no functional mouthparts. The naiad and the adult usually differ a lot in appearance although the naiads gradually develop wings. Complete metamorphosis (Holometabolous development): It has four distinct form stages: egg, larvae, pupa and adult (Fig.17). The larval stages do not look like the adult at all, and they are often worm-like. Larvae often have different mouthparts and food habits than the adult, and they often live in places different from the adult. Larvae molt several times and get a little larger with each molt, but there is no gradual development of wings or other adult characteristics. When a fully grown larva molts, it changes into a pupa. The pupa usually does not eat or move around much, but a lot of internal changes take place. When the pupa has made all its internal changes, its skin splits and the fully formed adult emerges. Most insects with complete metamorphosis are winged in the adult stage. The adults do not molt or grow any more. Little flies or beetles, for instance, do not grow to become larger. Flies (Diptera), beetles (Coleoptera), wasps (Hymenoptera) and butterflies (Lepidoptera), have holometabolic life cycles.
Fig. 17 Complete metamorphosis Source: http://www.cals.ncsu.edu/course/ent525/trans.html
Insect seasonal cycles
The progression of one or more life cycles occurring during a 1-year period is termed as the insect seasonal cycles. Seasonal cycles are very important to the survival of the insects because most environments of which insects are part of undergo annual colds. Therefore, to achieve success, insects have evolved ways to time their activities to take advantage on environmental resources and avoid unfavorable extremes. Entomology handout Page 31
Knowledge of patterns in seasonal cycles and the timing of important biological events relative to environmental cycles are crucial when attempting to reduce pest damage. Seasonal cycle can be grouped according to the number of generations that occur in a year; this number is referred to as a population’s voltinity. Voltinity types are univoltine, multivoltine, and delayed voltine.
Larval forms
The larval form is highly variable in insects, but there are similarities in the general structure to permit a classification of type that is useful in describing their appearance. (1) Campodeiform larvae have a flattened body with long legs, usually with filaments on the end of the abdomen. Larvae of diving beetles in the family Dytiscidae and many other beetles, Neuroptera, and Trichoptera are typical examples. (2) Carabiform larvae are similar to the campodeiform type, but the legs are shorter and filaments are lacking on the end of the body. They receive their name from the larvae of carabid beetles. Chrysomelid beetle larvae are of the same type. (3) Eruciform larvae (Polypod larvae) are cylindrical; they have a well-formed head, 3 pair of sclerotised and jointed thoracic legs, and fleshy abdominal prolegs. However, several species representing the various orders of insects do not have such distinguishing features. Larvae of Lepidoptera and sawflies are typical (4) Scarabaeiform larvae (Oligopod larvae) are C-shaped, have a well developed head, and usually possess thoracic legs but lack prolegs. The type is named after larvae of scarabaeid beetles (dung beetles, May beetles) and is also represented by the larvae of weevils and furniture beetles. (5) Elateriform larvae are cylindrical, smooth, and relatively tough-skinned larvae with short legs. They are named after larvae of elaterid or click beetles (wireworms). Larvae in the beetle family Tenebrionidae also have this appearance. (6) Platyform larvae are broad and flat with legs short or absent. This type is not common, but examples are found among larvae of some syrphid flies, certain caterpillars, and blister beetles. (7) Vermiform or wormlike larvae (Apod larvae) are cylindrical and elongate, without appendages of locomotion. This form is represented by the larvae of higher Diptera (maggots), some woodboring beetles, fleas, and higher Hymenoptera, including the honey bee.
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Appearance
Larval Type
Common Name
Description
Examples
Eruciform
Caterpillar
Body cylindrical with Moths short thoracic legs and 2and 10 pairs of fleshy butterflies abdominal prolegs Elongated, flattened body Lady with prominent antennae beetle, and/or cerci. Thoracic legs lacewing adapted for running Body robust and "C"shaped with no abdominal prolegs and short thoracic legs June beetle, dung beetle
Campodeifo rm
Crawler
Scarabaeifor m
White grub
Elateriform
Wireworm
Body long, smooth, and Click cylindrical with hard beetle, exoskeleton and very Flour short thoracic legs beetle Body fleshy, worm-like. House fly, No head capsule or flesh fly walking legs
Vermiform
Maggot
Pupal forms
Pupal forms may be classified by means of the appearance of developing appendages. (1) In obtect pupae the appendages are close to the body, held there by a tight-fitting outer envelope. They appear almost to be glued to the body proper. Pupae of this type are found in Lepidoptera and many Coleoptera, as well as the less advanced Diptera. The obtect pupa of butterflies is a common example. (2) Exarate pupae refer to those species that undergoes complete metamorphosis where their appendages (antennae, legs, and wings) appear to be free from the body and abdomen is movable. The bees and wasps of the Hymenoptera and beetles of Coleoptera are common examples. (3) Co-arctate pupae are represented by those that use the exuviae (cast exoskeketon) of the last larval instar as the container or place for pupal development. In this instance, neither the outline nor the actual structures are visible. The flies are examples of this type of pupation.
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Pupae can be grouped into one of three categories based on physical appearance: Appearance Pupal Type Common Name Description Examples
Obtect
Chrysalis
Developing appendages (antennae, wings, legs, etc.) held tightly against the body by Butterflies a shell-like casing. Often found and moths enclosed within a silken cocoon. All developing appendages Beetles, free and visible externally Lacewings Body encased within the hard exoskeleton of the next-to-last Flies larval instar
Exarate
None
Coarctate Puparium
Additional information on Exarate pupa is available in this website: http://www.entomology.umn.edu/museum/projects/Interactive_Keys/Intro_tutorial/GLOSSA RY/Exarate%20pupa.html Coarctate pupa and larva information: http://mothphotographersgroup.msstate.edu/MothTalkDownload/MothTalk020.htm
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Insect Collection
Purpose of collecting and preserving insects
There must be a purpose for collecting insects. Some of the reasons for collecting and preserving insects are: 1. For studying the insect biology, lifecycle and biodiversity Because of the damage inflicted by pest species, increased knowledge of these organisms has the potential to save lives and money. Insects are collected for studying the details and gaining a better understanding of their biology and life cycles. Insects are sometimes collected for recording the biodiversity. Extension agents will come across several species of pests in their geogs. For better understanding of the pest biology and lifecycle, they must make an effort to identify the pest. As the first step towards identification, proper collection, setting and preservation of the pest species is a must. 2. For identification( species determination) a) Newly detected insects Correct identification (knowing the scientific name) of a newly detected pest or disease vector is the key to all known information about the morphology, behaviour and life history, and the potential threat to human welfare. Insects are collected for species determination so that it is convenient for finding out more information. b) Small insects that are difficult to identify The behaviour of insects can be observed most easily in their natural environments. However, many species, especially the smaller ones, must be collected and properly preserved before they can be identified. Because correct identification seldom is easy, it is important that specimens be preserved in the best condition possible. Therefore preservation is highly important. c) Pest outbreak reports During pest outbreaks in the geogs, extension agents need to report to their superiors on the type of pest that is responsible for the outbreak. It is very useful to collect the pest and submit to the concerned authorities for identification. Such collections submitted for identification need to be well set and preserved. Therefore extension agents need to have the required skills of setting and preserving pest specimens. 3. Insect collection for future reference In a geog extension centre, insect pests must be collected, identified and preserved for the purpose of educating farmers (farmer trainings) on crop pest identification. A good reference collection is a valuable resource for the extension agent. It makes future identification efforts less cumbersome. In a geog extension centre, it is of utmost importance to maintain a reference collection of pest species for all the crops grown in the locality. 4. Insect collection as a hobby. There are people who love to collect insects and preserve them just for the love of it. Moths and butterflies are collected for their beautiful colour and wing patterns. Entomology handout Page 35
Some larva are collected for their giant size and weird body ornamentations. Some giant beetles are collected and sold as pets. Why insects have to be adequately set, preserved and correctly labelled? The identification of a particular insect usually requires examination of minute details of its anatomy with the aid of a hand lens or microscope. Some specimens may require dissection or even study with the electron microscope. If these details on a specimen are concealed, missing, or destroyed because of improper handling or preservation, identification is made difficult or impossible, and information about the species to which it belongs cannot be made available. Therefore, adequate preservation and proper labelling of specimens are essential to their identification. What is the relevance of the knowledge and skill of insect collection and preservation in the field of agriculture extension? For diagnostic purpose: Correct identification or species determination is the key to all known knowledge and information about the pest in question. To 2be able to correctly identify insect pests, the morphological features of the collected specimens should neither be concealed, nor destroyed. If extension agents need to send the specimens for identification by the entomologists, they need to send a specimen that is well set, preserved and packaged. Such skills can be learnt through practice. Building a reference collection for the geog extension centre: If there is a reference collection at the geog extension centre, it is not just helpful to you for using as farmers training aid but more importantly, the person who is going to relieve you upon your transfer will have great benefits. Learning the skills of collecting and preserving insects would help you to build your own reference collection at the geog extension centre.
Insect collection equipment and materials
The basic equipment necessary for field collecting is an insect net, one or more storage boxes, pins, pinning blocks, spreading boards, light and pitfall traps, killing jars, killing and preserving chemicals, several vials of assorted sizes, plastic bags and assorted containers. 1. Killing jars: Insects must be killed before pinning and mounting. Killing jars are used as a sort of ―small scale fumigation‖ to kill collected insects as rapidly as possible, using a liquid fumigant or killing agent (ethyl acetate) that produces a toxic atmosphere that the insect cannot breathe.
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David L. Keith and Tiffany Heng-Moss. Collecting insects. Retrieved Aug 18, 2009, from http://entomology.unl.edu/tmh/ent115/labs/collecting.htm
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When placed in the killing jar, insects often close their spiracles, but eventually they must open them. The process may take several minutes for smaller insects or up to a half hour or more for larger specimens. Because large, hard-bodied insects such as beetles die slowly and may damage other insects placed in the same killing jar, you will need more than one jar. It is possible to make suitable killing jars with nearly any glass jar used for jam or jelly and baby food jars are especially handy. In the bottom of each jar, place about 1 to 1 1/2 inches of absorbent material, such as cotton, shredded newspaper, Plaster of Paris or sawdust. If Plaster of Paris is used, pour it about 1 inch deep and allow it to dry for at least 48 hours before use. With paper-or fiber-filled jars, cut a cardboard circle just slightly larger than the inside diameter of the jar and push it into the opening against the plaster in the bottom. Attach a label that says POISON to each jar and store the jars out of reach of children (or irresponsible adults) until you are ready to go collecting.
If a killing jar is not available, freezing is another way to kill insects. Simply place your specimens in a plastic bag or small jar and put them in the freezer for an hour or two. Do not handle them again until they are thawed or legs and antennae may break. Insects, like food, left too long in the freezer for several days or weeks will desiccate and remain dry and stiff, even when thawed. If pinned when dry, these insects will break during handling and wings, especially of Lepidoptera, will be impossible to spread. Pinching the thorax of large butterflies or moths before placing them in the killing jar will prevent them from flopping around and damaging the wings. Squeeze them for 20-30 seconds between thumb and index finger and put them in the killing jar. This procedure stuns the insects so they do not flutter once inside the jar. Remove butterflies and moths from the killing jar fairly soon so their wings do not become soaked with killing agent.
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2. Relaxing jars: We recognize that while insects should be pinned on the same day they were collected, this is not always possible. So before pinning these specimens left in the killing jar or freezer too long, to restore their flexibility, it is necessary to ―relax‖ them. By placing them in a relaxing jar at high humidity for a few days we can restore their flexibility enough to allow pinning without damage to the specimens. A relaxing jar can be made by placing some absorbent material such as newspaper, sand or cotton in the bottom of a glass jar and cut a blotting paper disk to fit tightly inside. Moisten the material with water and add a drop or two of ethyl acetate, phenol or laundry beach to prevent mold. Place insects on the paper, close the jar tightly and let it sit for about 2-3 days. Check the jar. If the insects are flexible, mount them immediately. If the specimens are still too stiff, keep them in the relaxer for a few more days, but watch them carefully. Insects will mold and decompose if held in the relaxer too long. 3. Collecting Net (Aerial nets and sweep nets): Basically, a collecting net is composed of some sort of net bag made of cloth or fine mesh that is attached to a wire hoop, which is affixed to a wooden or metal pole. Aerial nets typically have net bags that are composed entirely of some type of meshed material and often have a lightweight handle. Aerial net bags are usually white in color, but black net bags are also available. They are most useful for catching select insects that may be flying through the air or perched on something (such as dragonflies, butterflies, bees, or wasps). Aerial nets with larger hoops are better for collecting large and fast moving insects such as dragonflies and butterflies, while those with small hoops are better for bees, flies, wasps, and other smaller insects.
Sweep nets are usually made of a heavy material (such as canvas) that can be dragged through dense vegetation without being damaged. They usually have heavier handles than those on sweep nets as well. Sweep nets are used to sweep through vegetation to collect random insects not easily seen. These nets are sometimes referred to as ―beating‖ nets 4. Aspirator: The aspirator is a suction device for collecting small insects which are difficult (or hazardous) to capture with the fingers or with an insect net. Basically, it consists of a large glass or plastic vial, a length of flexible rubber tubing, some rigid plastic or metal tubing and a rubber stopper with 2 holes cut in it to receiving the tubing. A small piece of cheesecloth or fine metal screen serves to seal the suction tube on the inside so that insects are not sucked into the mouth. To collect small insect the long tube is placed beside the insect and sucked sharply by mouth from the shorter rubber tube.
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5. Light traps: Many types of insects are attracted to light and can be captured there by hand. A light trap offers the advantage that it will continue to trap specimens without being constantly watched by the collector. Insects are quite sensitive to different types of light; therefore, more of certain types can be captured with ―black‖ (or ultraviolet) light as opposed to the regular ―white‖ light given off by most standard light bulbs. The difference in attractiveness of the two types of light is due to the wave lengths produced by the two kinds of bulbs. Black light consists mainly of the shorter wave lengths which are more attractive to night-flying moths, flies and beetles. White light bulbs (producing mostly longer wave lengths) attract some moths and other insects, but not as many as a black light.
6. Pitfall traps: A pitfall trap will catch many ground beetles and other insects that live on or in the soil. It consists of a trap can that is buried in the soil, level with the rim so that insects attracted to it will fall in. Once inside, it is difficult for them to get out. Attractive bait in the bottom will increase the drawing power of the trap. Use pieces of spoiled fruit, vegetables, excrement or meat. Cover the trap with a board placed on small stones so insects can crawl under it and into the can. This arrangement will protect the trap from wind and rain, but allow access to the insects you want to catch. It will also help to hold insects inside the trap once they are caught.
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Preserving insects
Hard-Bodied Insects Since insects have a hard shell or exoskeleton and all of the soft parts are on the inside, they tend to keep rather well after drying, even for long periods of time. Only a small amount of maintenance is necessary to keep them in good condition. Soft-Bodied Insects Many types of insects, including aphids, springtails, thrips, mayflies or silverfish, are soft-bodied and cannot be pinned successfully. The same is true of many immature insects such as caterpillars, beetle and wasp larvae and others. If placed on pins, most soft-bodied insects will shrivel or decompose. Such insects must be preserved in liquids in rubber-stoppered glass vials. However, prior to preserving soft-bodied specimens for the long term, their color must be ―fixed‖ or they may fade in some cases or blacken in others. The ―fixing‖ process prevents, reduces or delays color change.
For the long term, insects are preserved in ethyl alcohol, usually of about 70 percent concentration (70% alcohol, 30% water). However, it must be remembered that alcohol is a dehydrator and removes water from the specimens preserved in it. These problems can be largely prevented in either of two ways. The best way is to ―fix‖ the insect tissues and color by killing the specimens in boiling water. For smaller specimens, simply dip them in boiling water for about 30 seconds and then transfer them to 70 percent alcohol. Use more extended periods for large-bodied insects. Specially designed and constructed container ―Schmidt Boxes‖, are required for long term insect storage. Such boxes have tightly fittng lids which help prevent entry of scavenger insects which feed on dead insect specimens. Wooden boxes can be used for temporary storage of pinned insect specimens. The bottom of wooden boxes can be lined with styrofoam material or cardboard to receive and hold the insect pins. While wooden boxes are fine for temporary storage, they are poor over long periods of time. For extended storage and for display, tighter containers are essential. Add naphthalene crystals, placing them into a small container in one corner of each display box to prevent damage to your specimens.
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Pinning, mounting and displaying insects3
Equipment required Insect Pins. Special pins are needed to pin insects. They come in several sizes from 000 through 7, the size of the pin increasing with each number. Number 3 insect pins are the best for most purposes.
Fig. 1. Insect pins
Fig. 2. Pinning block
Fig. 3 Pinning block (cross-section)
Pinning Block: Larger insects should be mounted using a wooden pinning block (Fig b & C), a simple piece of equipment. A very small hole is bored almost through the bottom in the middle of each step. A simpler pinning block can be made by drilling three holes—1, 3/4, and 1/2 inch deep—into a small wooden block. Proper use of a pinning block will result in an attractive collection with the insect, collection and identification labels in uniform position. Note the dimensions of a pinning block in the drawing below. Spreading Board: Mounting butterflies and moths is a special technique that requires a spreading board to do an attractive job. The spreading board is usually made of soft pine with a piece of cork underneath the center groove to receive insect pins.
Fig 4. Spreading board
Pinning Insects
The preferred way to display and study adult insects is to pin them into display boxes using special insect pins. The pins are pushed through the thorax of the insects while they are still fresh and the legs and antennae are placed in a natural position. This allows the specimens to be handled and studied without damaging them. In pinning insects always use special insect mounting pins that are specially treated to resist rusting. Insect pins vary in size from 000 to number 7. The latter is the largest in diameter. Numbers 2 and 3 usually work the best for the amateur collector. A good
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David L. Keith and Tiffany Heng-Moss. Collecting insects. Retrieved Aug 18, 2009, from http://entomology.unl.edu/tmh/ent115/labs/collecting.htm.
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rule is to pin the insect slightly to the right side of the middle and down through the area where the middle pair of legs is attached. Styrofoam is an excellent base for positioning the legs so they will dry in the correct position. There is a slight variation in the pinning of the different kinds of insects. The proper way to pin an insect depends on the type of insect that you have collected. The following diagram below illustrates the proper way to pin various orders of insects. Note that the pin is usually just slightly to the right of the midline of the insect. Specimens should also be level and squarely mounted on the pin as shown.
All insects must be pinned so that they are straight on the pins. Do not tilt the specimens on the pin. The height of the specimen on the pin will depend somewhat on the size of the insect; however, always keep the distances from the top of the insect’s body to the head of the pin the same. Usually 1/3 of the pin should be above the upper surface of the insect; this will allow enough room to permit handling specimens without actually touching them. Specimens should be handled carefully to keep all legs and antennae. A small amount of time spent positioning the legs and antennae will dress up the collection. Very small insects (less than 3/16 inch) should either be pinned with micro-pin or glued on their right sides to tiny paper triangles. The latter procedure is called pointing. When pointing, first push a regular insect pin (No. 2 or 3) through the butt end of the triangle. Bend the tip of the paper triangle slightly downward with a forceps and touch it to a tiny drop of glue or clear fingernail polish. Pick up the small insect carefully with forceps and mount it by touching it on its thorax (right side) to the drop of glue. Adjust the insect so that it remains squarely in position, and then allow the glue to dry.
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Standard methods of pinning some of the insect orders are as follows: 1. Orthoptera: pin through back of thorax to right of midline (Pic no). for display purpose, one pair of wings may be spread as shown, but many orthopterists prefer to leave wings folded because of limited space in most large collections. 2. Hymenoptera and Diptera: pin through thorax between or a little behind base of forewings and to right of midline. So that no characters on body are obscured, legs should be pushed down and away from thorax, and wings turned upward or sidewise from body. Wings of most Diptera will flip upward if specimen is laid on its back before pinning and pressure is applied simultaneously to base of each wing with pair of blunt forceps. Wings should be straightened by gentle brushing with a camel’s hair brush dipped in 70 percent alcohol. For hymenoptera wings, Peterson’s XA mixture (xylene and ethanol, equal parts by volume) is recommended. 3. Coleoptera: pin through right wings cover near base such that the pin exits through the metathorax (between the middle and hind legs). Do not spread wings. 4. Heteroptera: pin through triangular scutellum to right of midline. Do not spread wings. 5. Odonata: pin through middle of thorax at thickest point or just behind base of forewings. Spread wings as described for butterfly and moths. 6. Lepidoptera: when pinning and spreading a butterfly or moth, before you begin to work, cut several thin strips of paper about 1/4" wide and 8"-10" long. Once these are ready, pick up the insect by the thorax and carefully push a pin through the middle of the thorax. Adjust the position of the butterfly on the pin and make sure that it is level, both on the sides and in both front and back. Adjust the width of the groove in the spreading board to be just slightly wider than the body of the butterfly. Push the pin into the slot of your spreading board until the bases of the wings are just level with the top of the two side pieces.
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Slip a paper strip between the wings (if they are upright) and use it to force the wings on one side down into position. Pin the ends of the paper down to hold the wings loosely in place. Do the same with the wings on the other side, also pinning the ends of the paper down. Now take another insect pin or needle and slip the point through the leading edge of the right forewing (there is a strong vein just at the front edge of each wing) near its attachment to the thorax. Be careful not to tear the wing. Loosen the forward end of the paper strip and gradually bring the forewing up into final position. Pin the wing down with a paper strip. Repeat this procedure with the forewing on the other side. Using the same technique, bring both hindwings into proper position and fasten all four wings firmly with the paper strips. Note carefully that the rear edge of the two forewings should make a perfectly straight line across the back. The hindwings should be pinned so that the rear edge is held just slightly away from the abdomen. Position antennae with pins and if the abdomen has drooped, prop it up with pins so that it dries in a natural position. Allow specimens to dry for several days before you remove the pins.
Labelling Insects
A collection has little value unless each insect is properly and accurately labeled. Labeling must be done as soon as possible after collecting, pinning and mounting or vital information may be lost. Their precise collection locations, habitats, and data on plants on which they were found are important documentation. During preparation and mounting, specimens should bear temporary labels with this information, and any time sample is subdivided, the label must be copied so that every specimen continues to be accompanied by the data. The top label should have the place from where the insect was collected, the collection date and the name of the collector (Fig. 19). The lower label should show the Order name of the insect. Many entomologists place another label beneath the collection label which gives the host plant, habitat or other pertinent information.
Fig. 19 Essential information on an insect label
The paper used for making labels should be heavy enough for labels to remain flat and not to rotate loosely round the pin. The surface of the paper should be smooth enough to write on with a fine pen (Linen ledger paper, 100% rag and 36 pound weight). Labels made from poor quality paper become yellow and brittle with age, tend to curl, disintegrate in liquid preservatives. Entomology handout Page 44
The good grade India ink is preferred that is permanent and will not run when labels are placed in liquid preservative jars. India ink is not always available when collecting in field. However, labels written with a firm hand and with a moderately soft lead pencil are satisfactory. Do not use ballpoint pens or hard lead pencils for labels placed in liquids; the writing soon fades and become illegible.
Care of collection
Pinned specimens are best kept in insect drawers with unit trays to place the pinned specimens. The bottom of unit trays is made of polyethylene and plastazote foam which makes easier to place the pinned specimens in unit trays. To keep specimens away from the museum pests, place naphthalene balls inside the wooden boxes (temporary storage) and in unit trays during storage. In moist and warm climates, mold, a kind of fungus readily attacks and grows on insect specimens. Once a specimen has become moldy, nothing can be done to restore it. If there is few hyphae of mold present on a specimen, they may be removed with forceps or brush. The specimen should be dried in a warm oven. Keeping specimens in dry place will prevent mold.
Reference:
1. http://bugs.bio.usyd.edu.au/learning/resources/Entomology/introduction.html 2. Insect external morphology. (n.d.). Available http://basicentomology.ifas.ufl.edu/lab5 (Accessed 11 June 2008) 3. Keith, David L. and Heng-Moss, Tiffany. (n.d.). Collecting insects. Available http://entomology.unl.edu/tmh/ent115/labs/collecting.htm (Accessed 17 July 2008) 4. K-State Research and Extension, 4-H Entomology , Electronic Document 5. Meyer JR (2009). General Entomology. North Carolina State University. Available http://www.cals.ncsu.edu/course/ent425/library/tutorials/index.html (Accessed 1 September 2009) 6. Pedigo, Larry. P. (2002). Entomology and pest management. (4th ed.). Printice Hall of India. New-Delhi. 7. Pinning and Labeling insect for Kansas 4 – H Entomology. Available http://ag.udel.edu/extension/4h/projects/pdf/insectpinning.pdf (Accessed 1 September 2009) 8. Robinson, D.H. (2001). Entomology principles and practices. Agrobios (India). Jodhpur. 9. Schauff, M. E. (n.d). Collecting and preserving insects and mites: techniques and tools. Washington, DC. 10. University of Sydney. (2004). Importance of entomology. Available http://bugs.bio.usyd.edu.au/Entomology/importance/importance.html (Accessed 21 July 2008)
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