By one estimate, screwworm eradication efforts to-day save U.S. livestock producers at least $900 million annually in potential losses.

The SIT involves sterilizing 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.

Irradiating screwworms is costly. Irradiated male flies are also less competitive than wild-type males. So, starting in 2004, the ARS team began research aimed at developing genetically sterile, male-only screwworms using transformation technology first tried on Medflies.

Using a genetic element called a "piggyBac transposon" as a vector, the research-ers 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.

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.