Published on 05/22/08

Headless fire ants can't bite

By Sharon Omahen
University of Georgia

If you’ve ever been stung by a fire ant, you probably wished they’d all get sick and their heads would fall off. Agricultural scientists are working to do just that.

Scientists at the University of Georgia, the USDA-ARS in Gainesville, Fla., and other universities in the Southeast are releasing parasitic flies with the hopes of reducing the fire ant population in the South.

Didn't bring their enemies

“Fire ants came from Brazil and Argentina,” said Wayne Gardner, an entomologist with the UGA College of Agricultural and Environmental Sciences. “Unfortunately for us, they didn’t bring their 30 to 50 natural enemies with them.”

When a new species becomes an invasive pest, like the fire ant, controlling it is like “constantly playing catch up,” he said.

USDA scientists are coordinating the release of phorid flies to sites in southeastern states, including Georgia. The flies, which are smaller than gnats, come from areas in South America where fire ants are native.

“They rear the flies in their laboratory and provide them to cooperators in the individual states,” Gardner said. “The flies are then strategically introduced to sites in each state.”

Off with their heads

The female fly stings the ant and lays an egg inside her body. “It’s a painful sting,” Gardner said. “You can tell by the way the ant goes into contortions.”

The egg hatches in the ant, and the larva grows and develops inside the body. “When the larva hatches, it eats the ant from the inside out and the ant’s head falls off,” said Gardner. “It’s basically a decapitating fly, which is amazing.”

Gardner and his UGA colleagues have used natural enemies to fight insect pests for 15 years. “It’s not as easy as just finding a natural enemy of the ant and bringing it here,” he said. “It takes time and resources to go into their native range, collect and study them and get a point where we know it’s safe to introduce them here.”

The scientists are testing the effectiveness of nine species of parasitic flies. Each species attacks different size ants and at different times of day.

Cuts their appetites

“The flies definitely kill fire ants, but they actually cause more harm to fire ant populations by looking for ants to sting,” Gardner said. “The ants sense the wing beat of the adult flies, know that their enemies are in the area and quit foraging.”

When the ants stop foraging, the colony weakens.

Gardner’s team has introduced two species in at least 6 sites in central and south Georgia. They are also seeing flies spread into northern, western and southern counties from releases made in the bordering states of Tennessee, Alabama and Florida.

The researchers don’t expect the flies to solve the fire ant problem in the South. “Will we see areas that are totally devoid of fire ants?” Gardner said. “No, but we may see one mound instead of 10 in a row.”

Sharon Omahen is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.