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Gnat-size Dive Bombers Strike Georgia Fire Ants


Photo: Scott Bauer, USDA-ARS

A dive-bombing phorid fly (center) takes aim to lay an egg behind a fire ant's head. When the egg hatches, the larva will crawl into the ant's head, which will fall off and become food for the larva.
Until the decapitating flies showed up, Buck Aultman had no way to rid his 20-acre pasture of its pox of fire ant mounds. "You can't afford to spread fire ant bait out here," he said.

But Aultman's pasture is now home to a swarm of fierce little flies that may be better than a pesticide. The Tift County farmer is taking part in a research study involving the first Georgia release of phorid flies.

About the size of gnats, phorid flies are Brazilian parasitic flies. They feed on fire ants in their reproductive cycle, said Sanford Porter, an entomologist with the U.S. Department of Agriculture's Agricultural Research Service in Gainesville, Fla.

The flies have been successfully introduced in Florida and pose no threat to people or anything else in the environment. "The only things they're attracted to are fire ants," Porter said. "For that matter, they're attracted only to imported fire ants."

Off With Their Heads!

Each female phorid fly carries about 200 eggs, Porter said. In the blink of an eye, she lays an egg right behind the head of a fire ant, releasing a deadly enzyme in the process.

In about two weeks, the egg hatches, and the small larva crawls into the head of the fire ant, which falls off -- really. The larva then feeds, grows, pupates and emerges as an adult from the cleaned-out shell of the fire ant's head. And the deadly cycle starts again.

The 7,000 flies released near Tifton could spread as far as five miles within the next year, said Wayne Gardener, an entomologist with the University of Georgia College of Agricultural and Environmental Sciences.


Photo: USDA-ARS

After eating the contents of the fire ant's head, a new adult phorid fly emerges to continue a cycle that makes fire ants scurry and humans smile.
A Boundless Buffet

For phorid flies, Georgia is a boundless buffet of fire ants. Since arriving in the United States from Brazil in the 1930s, fire ants have had no diseases or insects to hamper them. So far, their spread has been limited only by cold weather.

But scientists hope phorid flies can change that.

"Phorid flies won't kill out fire ant colonies," said Beverly Sparks, an UGA Extension Service entomologist. "They will parasitize the ants and reduce the numbers within a colony."

Sparks said the tiny dive bombers harass fire ants endlessly, too, trying to inject their egg time bombs into them. "The result is that the ants spend a lot more time in a defensive posture and less time foraging," she said. "The colony is thus weakened and hopefully less competitive with native ant species."

A Slow Process

Scientists don't know how well the flies will survive and how effectively they'll reduce fire ant numbers. They'll closely watch the fire ant mounds near the release site. "This is an expensive research project," Sparks said. "Releases of these flies cost us nearly three dollars per fly."

Since phorid flies spread only a few miles a year, their spread will require a long time unless more funds can be provided to support further releases. "We'd probably have to get local governments involved in the process," Gardner said. "Maybe even the state government."

That would be fine with Aultman. "Anything to control fire ants," he said. "I'm all for it."

(Dan Rahn is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

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