30 December 2009

2 minute read

North America

Pioneered by ARS entomologists nearly 55 years ago, the SIT is a cornerstone of eradication programmes implemented worldwide to control not only the screwworm, Cochliomyia hominivorax, but also the Mediterranean fruit fly, tsetse fly and other insect pests. By one estimate, screwworm eradication efforts today save US livestock producers at least $900 million annually in potential losses.

ARS entomologists are developing transgenic sterile, male-only screwworm flies that could eliminate the need for the expensive irradiation technique now used in screwworm control programs.

The SIT involves sterilising adult male flies with irradiation and releasing them into the wild to mate with females. Their eggs’ failure to hatch diminishes the size of the next generation. Fewer flies, in turn, mean fewer insecticide applications to protect livestock, especially those with open wounds, where screwworm larvae feed.

But irradiating screwworms is costly. Irradiated male flies are also less competitive than wild-type males. So, starting in 2004, the ARS team—entomologists Margaret Allen and Steven Skoda and geneticist Alfred Handler—began research aimed at developing genetically sterile, male-only screwworms using transformation technology first tried on Medflies, also targets of SIT-based eradication. Ms Allen is at the ARS Biological Control of Pests Research Unit> in Stoneville, Mississippi, Mr Skoda is a research leader with the ARS Livestock Insects Research Laboratory at Kerrville, Texas; and Mr Handler works at the ARS Insect Behaviour and Biocontrol Research Unit in Gainesville, Florida.

Using a genetic element called a “piggyBac transposon” as a vector, the researchers introduced a green fluorescent protein (GFP) gene into the genomes of eight screwworm strains. When viewed under ultraviolet light, the transgenic screwworms emitted a fluorescent glow, helping confirm GFP’s activation. Caged mating experiments showed transgenic male flies were as competitive as wild-type males, the team reports in the journal Medical and Veterinary Entomology.

Once male-only screwworms are developed using the same transformation method as that used for the GFP strain, the next phase would explore inducing genetic sterility in the flies, which theoretically would eliminate the need for irradiation. Their field release, however, would hinge on an environmental impact assessment and regulatory approval.

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