1. External morphology of exopterygota:
The Exopterygota are all hemimetabolous insects that have wings which develop externally and do not undergo a significant metamorphosis via a pupal stage. Apart from being wingless and smaller, the nymphs (immature stages) of these species are generally quite similar in appearance to the adults.
Holometabolous insects undergo significant morphological changes during their development. The larvae (mostly grub-like) are very different in appearance to the adults and undergo metamorphosis into the adult form via a non-feeding pupal stage where the body tissues are broken down and rearranged into the adult morphology.
2. Insect Head
Labrum (1) (Upper lip)
Mandibles (2) (Jaws)
Maxillae (2) (More jaws)
Labium (1) (Lower lip)
Hypopharynx (1) (Tongue-like, bears openings of salivary ducts) Labrum-epipharynx (1) (Fleshy inner surface of labrum - sensory)
The orientation of the mouthparts on the head may differ, and they may be described as: Prognathous: projecting forward (horizontal)
Hypognathous: projecting downward
Opisthognathous: projecting obliquely or posteriorly
Compound eyes: Individual units are facets or ommatidia. 28,000 ommatidia comprise a single compound eye in dragonflies
Oellus (Ocelli), or simple eyes: small, usually a single lens
a. Aristate antennae are pouch-like with a lateral bristle. Examples: House and shore flies (order Diptera). b. Capitate antennae are abruptly clubbed at the end. Examples: Butterflies (order Lepidoptera). c. Clavate antennae are gradually clubbed at the end. Examples: Carrion beetles (order Coleoptera). Adult carrion beetles feed on decaying animal matter or maggots. d. Filiform antennae have a thread-like shape.
Examples: Ground and longhorned beetles (order Coleoptera), cockroaches (order Blattaria). e. Geniculate antennae are hinged or bent like an elbow. Examples: Bees and ants (order Hymenoptera). f. Lamellate or clubbed antennae end in nested plates. Examples: Scarab beetles (order Coleoptera). g. Moniliform have a beadlike shape. Examples: Termites (order Isoptera). h. Pectinate antennae have a comb-like shape. Examples: Fire-colored beetles and fireflies (order Coleoptera). i. Plumose antennae have a feather-like shape. Examples: Moths (order Lepidoptera) and mosquitoes (order Diptera). j. Serrate antennae have a saw-toothed shape. Examples: Click beetles (order Coleoptera). k. Setaceous antennae have a bristle-like shape. Examples: Dragonflies and damselflies (order Odonata).
4. Mandibulate or "chewing" mouthparts represent the generalized, primitive condition within the hexapods. They consist of 4 sets of appendages: the anterior labrum, followed by a pair of mandibles, then a pair of maxillae, and finally a posterior labium. The labrum, which may or may not be appendicular in origin, is a simple flap or upper lip.The mandibles are jaw-like, used for biting, grinding, and scraping. The maxilla is comprised of a basal body (cardo and stipes) and apical processes (lacinia and galea); it bears a 5-segmented maxillary palp. The labium is composed of a body (postmentum and prementum) and apical processes (glossae and paraglossae); it has a pair of 3-segmented labial palps. This basic morphology evolved to form the more specialized mouthparts used for piercing and sucking, sponging, siphoning, etc. In adult stoneflies, the mandibles are degenerate, but the other appendages are fully formed. In some aquatic Coleoptera larvae (e.g., Dytiscidae) there is a channel-like groove running the length of the mandible that functions in piercing and sucking. 5. In adult caddisflies, the apical part of the labium (“prelabium”) and hypopharynx have fused to form a short proboscis or haustellum. The...
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