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Nematode Dupes House Flies

Could this be the Trojan horse of biocontrol?

A parasitic nematode that deceives houseflies into spreading nematode offspring instead of fly eggs could become a classical biological control agent, according to Agricultural Research Service scientist Christopher J. Geden.

An entomologist with ARS' Center for Medical, Agricultural, and Veterinary Entomology's Mosquito and Fly Research Unit in Gainesville, Florida, Geden is evaluating this new discovery.

The nematode, Paraiotonchium muscadomesticae, has so far been found only in Serra Talhada, a small town in northeastern Brazil. University of Florida graduate student Reginald R. Coler is credited with the discovery.

How does such trickery work? A female nematode penetrates a host fly's larval cuticle and waits for the larva to metamorphose into an adult. When the adult fly emerges, the female nematode goes through a burst of reproductive activity, producing up to 40,000 young nematodes inside the fly.

"These young parasites invade and damage the fly's ovaries, causing parasitic castration--a relatively uncommon phenomenon," says Geden.

About 15 days after the nematode's initial penetration, the female fly attempts to deposit eggs into her favorite nesting material--usually moist manure. Instead of laying her own eggs, the female fly is unaware she is actually unloading thousands of young nematodes! These new nematodes mate, after which the males die and the females begin searching for more fly hosts to parasitize. The process then repeats.

In lab studies using modest application rates, nematodes reduced house fly numbers by about 90 percent. ARS is keeping under quarantine at Gainesville the only colony of the nematode outside its native Brazil. Geden has studies under way to determine the safety of releasing the nematode and the likelihood of its survival in a typical farm setting. He is also standardizing rearing procedures so that large quantities of infected flies can be easily and economically produced.

Geden says, "In the United States, house flies pose serious legal problems for farmers because of public health, sanitation, and nuisance concerns. The poultry industry alone spends over $30 million per year on insecticides for fly control. This nematode could bring about an overall reduction in house fly populations."--By Tara Weaver, Agricultural Research Service Information Staff.

Christopher J. Geden is in the USDA-ARS Mosquito and Fly Research Unit, 1600 SW 23rd Dr., Gainesville, FL 32604; phone (352) 374-5919, fax (352) 374-5922.

"Nematode Dupes House Flies" was published in the September 1998 issue of Agricultural Research magazine. Click here to see this issue's table of contents.