DEVELOPMENT AND EVALUATION OF TRANSGENIC INSECT STRAINS FOR GENETIC CONTROL PROGRAMS

One the greatest accomplishments of the USDA in the 20th century was the eradication of the New World screwworm (NWS) fly from all of North and Central America. NWS females lay their eggs in open wounds or a natural orifice. The hatched larvae then feed on the animal's living tissue. Animals with severe screwworm infestations may die if untreated. NWS was eradicated using the sterile insect technique, which involved the mass rearing of NWS, sterilization by irradiation and distribution of sterile flies over the targeted area. Currently, sterile NWS are released in a ' buffer zone' in southern Panama to prevent re-infestation from South America. Transgenic 'male-only' NWS offer the potential of more efficient genetic suppression, reduced diet costs, higher plant capacity, improved monitoring and reduced risk should (in the very unlikely event) any NWS that escape the plant. Transgenic NWS lines have been obtained carrying a single-component tetracycline-repressible female-lethal system. Females die at the pupal stage. These strains will be further evaluated for characteristics that influence production such fertility and fecundity. Additional experiments that will provide data needed for a risk-benefit analysis by regulators (e.g. outcrossing potential, longevity). A two-component female-specific embryo lethal genetic system is also being developed at North Carolina State University. The most efficient gene system will be sent to Panama for evaluation in NWS. The most promising strains carrying the early lethal system will be selected for additional experiments to obtain data for a potential field release.Drosophila suzukii (commonly called spotted wing Drosophila or SWD) is a serious pest of berries and other soft fruits that has recently invaded the West and East coasts of the United States. Female SWD use their highly developed serrated ovipositor to pierce the skin of soft fruits and lay their eggs inside the fruit. Unlike the larger native fruit flies (e.g. blueberry maggot) that have only one generation a year, SWD has a short generation time and multiple generations per year. Thus it is potentially a much more serious pest. Any fruit that contain developing SWD larvae (maggots) can cause an entire shipment to be rejected. Growers are currently using broad spectrum insecticides to protect fruit from damage caused by SWD. We are developing transgenic SWD 'male-only' strains that could be used for genetic suppression programs. Similar to the NWS strains, female SWD will die unless tetracycline is added to the diet. A male-only release is significantly more effective in suppressing a population than releasing both sexes.