Screwworm Fly Eradication
Screw-worm, Cochliomyia hominivorax, Can Be Wiped Out
A weak link in the life cycle of the New World screwworm fly made it possible for scientists to wipe it out in the United States and Central America.
The gruesome habits of the New World screwworm fly, Cochliomyia hominivorax, make it an unwelcome insect everywhere it occurs. The parasitic and carnivorous maggots of the screwworm (often incorrectly spelled screw-worm) fly are responsible for illness and death in animals and humans alike, and it used to account for millions of dollars of lost revenues in American agriculture every year.
In the late 1930s Edward Kipling, an American entomologist, realized that C. hominivorax had a weak spot, a vulnerability that might be exploited to wipe out the fly. The female screw-worm fly mates only once—even if the mating doesn’t produce viable offspring, she will not mate again. If scientists could somehow manipulate things so that matings were unsuccessful, the screw-worm fly would disappear.
Two other scientists provided additional pieces of the puzzle. Raymond Bushland devised a way to raise screwworm flies in captivity, and Herman Muller discovered that irradiated male flies were sterile, but sterile males could still compete successfully with normal males for mates. The knowledge for an eradication program was there; all they needed was a plan and the resources to carry it out.
The first area to be tested with a screwworm fly eradication plan was southern Florida in the United States—it was warm enough there for C. hominivorax to survive the winters and spread north in the warmer months, but geographically isolated enough to be a good place for a trial run. Between 1957 and 1959 hundreds of millions of sterile male screwworm flies were released in Florida, Georgia, and Alabama. It worked. By mid 1959, there were no screwworm flies in Florida.
The next stage was an eradication program to rid Texas, Arizona, and California of the screwworm fly. This effort took longer, because it was impossible to prevent the reintroduction of the fly across the lengthy United States-Mexico border. It wasn’t until the eradication zone was dropped to the narrow Isthmus of Tehuantepec in Mexico, that C. hominivorax was successfully contained. All of the southern United States and northern Mexico were free of the fly by about 1985.
Screwworm fly eradication was so successful that it was worth continuing the effort. The US, in cooperation with Central American governments, kept pushing southward and by 1996, the screwworm fly had retreated to the Panama-Columbia border, there to be held back by the continual release of sterile male flies. Having perfected fly-rearing and eradication methods, North American specialists were also able to come to the aid of Libya when the North American screwworm was accidentally introduced there in 1988.
Read about the life cycle of Cochliomyia hominivorax .
Related content:
Sources:
Food and Agriculture Organization of the United Nations. The New World Screwworm Eradication Programme: North Africa 1988-1992. Rome: FAO, 1992.
Galvin, Thomas J., and John H. Wyss. “Screwworm Eradication Program in Central America.” Ann N Y Acad Sci. 791 (1996): 233-40.
Schmidt, Gerald D. and Larry S. Roberts. Foundations of Parasitology 6th Ed. Boston: McGraw Hill, 2000.
