Female-Specific Lethal Genetic Systems for use in Sterile Insect Technique (SIT): Development and Mechanism
Michael C. Delomen
Sterile insect technique (SIT) is a means of biological pest control. Sterile males are released into the environment, mates with wild females, producing no offspring. SIT is not chemical based and it is species-specific. However, it is an expensive technique. Sterilization via irradiation also sometimes affects the males’ health; such that sterile males cannot compete with wild males when seeking mates. Also, during laboratory rearing, the males may be difficult to distinguish morphologically from the females. To solve this, RIDL (release of insects carrying a dominant lethal) technique is being developed. This involves insertion of dominant lethal genes that are repressible via certain chemical substances into insects. The usual lethal genetic system is designed to be female-specific. A pest population with this kind of system can be reared in the laboratory, where the growth medium used is supplied with the repressor of the lethal genetic system. Upon reaching a desired population size, the repressor will be withdrawn from the medium, killing all females and leaving only males for SIT. These males are not sterile, but when they mate with wild females, any female offspring would inherit the lethal genetic system and die. Reduction of females would eventually lead to reproductive failure of the population. RIDL can make for easier separation of males from females during rearing. No sterilization is required; reducing expenses without reducing the reproductive ability of the released males. A system like this has been designed for Drosophila. The system involves a lethal proapoptotic gene (hid) controlled by a tetracycline-activated transactivator (tTA). The latter is then controlled by the female-specific enhancer from Drosophila yolk protein 1 (yp1). Experiments successfully show female specific lethality in flies inserted with the lethal genetic system. The technique is hypothesized to work with other insect pest species.
Sterile insect technique (SIT) is a means of biological pest control. It involves mass rearing of pests in the laboratory. Males are then irradiated to sterilize them. These sterile males are then released into the environment. They mate with wild females, producing no progeny. This reduces the population size of the pest; and with repeated releases, a pest population in a particular area can be eradicated. Males are the ones released as it is usually the female of the pest species that do damage (laying eggs on plants, acting as disease vectors).
SIT was developed by American entomologists Raymond Bushland and Edward Knipling during the 1950’s to combat screwworm infestation of North American livestock. During the 1930’s, the screwworm fly was decimating cattle herds along the American South. The larvae of these flies enter open wounds in cattle and they start eating the flesh of the animal. Bushland and Knipling hypothesized that if they could disrupt the life cycle of screwworm by sterile male release, it would reduce the impact of pesticide use (or eliminate the need for chemical pesticides entirely). Their research into this area was hampered by World War II, but was resumed in the early 1950’s. Shortly after resumption, their work succeeded in eradicating screwworm population in Sanibel Island, Florida. In 1954, they also succeeded in the island of Curacao, off the coast of Venezuela. Up to the 1990’s, their technique worked in different American states, Mexico and North Africa. This initial SIT uses males sterilized by X-ray irradiation.
Former US Secretary of Agriculture Orville Freeman has hailed SIT as “the greatest entomological achievement of the 20th century”, and for good reason. The application of SIT has resulted to near eradication in the pest species that have been targeted. Since no...
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