Electric Shock is Bad News for Fire Ants

Shocking fire ants with electricity stimulates release of an attractant that lures ant- attacking Brazilian phorid flies to the ants, according to Agricultural Research Service scientists. Fire ants infest 300 million acres in the southern United States. Electric shock won't be an ant-control measure. But the scientists think the finding might help them speed laboratory production of flies for outdoor release against the ants.

Phorid flies are natural enemies of red imported fire ants in South America. ARS scientists brought the flies to this country and released them to help reduce U.S. fire ant populations. Since that 1997 release, the flies have survived three winters in Gainesville, Fla., where their numbers and distribution have expanded rapidly.

Researchers at ARS’ Center for Medical, Agricultural and Veterinary Entomology in Gainesville were looking into why ants are attracted to electrical devices. The scientists discovered that fire ants walking across an electrically energized grid release a natural chemical that attracts phorid flies as well as other fire ants. This chemical draws a six-fold increase in the number of flies attacking the ants.

Once a parasitic phorid fly locates an ant, it swoops down on the ant, pierces its body, and deposits an egg inside the ant. The egg hatches into a larva within a day or two. The larva then moves into the ant’s head, causing the head to fall off. The larva completes its development in the ant’s head. Electrical stimulation helps increase production of parasitized ants in the laboratory, which in turn increases the number of phorid flies available for release into fire ant field populations.

The scientists are trying to isolate the specific chemical ants release when shocked with electricity. This information will help scientists rear phorid flies in the laboratory, monitor natural fly populations and their effectiveness in reducing fire ant populations.

ARS is the U.S. Department of Agriculture’s principal research agency.

Scientific contact: Robert K. Vander Meer and Sanford Porter, Imported Fire Ant and Household Insects Research Unit, ARS Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Fla., phone (352) 374-5914, fax (352) 374-5818, bobvm@nervm.nerdc.ufl.edu, sdp@nervm.nerdc.ufl.edu.