“They got here in the ’30s and spread to Georgia in the ’50s,” the University of Georgia entomologist said.
The newest control strategy — pioneered in Florida — involves the introduction of tiny insects known as phorid flies, whose larvae attack, kill and decapitate fire ants.
“We’ve got the state pretty well covered,” he said. “Every county in Georgia has at least one species of the phorid, and we have 40 counties that have two species.”
The fly, native to South America where imported fire ants originated, reproduces by injecting eggs into ants. The larvae eat the ant’s brain before emerging through its head.
Scientists at the U.S. Department of Agriculture’s agriculture research center in Gainesville, Fla., spent years evaluating the program before launching widespread distribution of the flies in the state’s ant-infested northern regions. One objective was to make sure the flies would not harm existing species, including a fire ant native to the U.S.
“After all the work that went into this — trial-and-error and studies — they are beginning to see a decrease in imported fire ant density that they are attributing to the fly,” Gardner said. “We’re not at that point by any means here, but we are making progress.”
In Georgia, the release of phorid flies began in earnest around 2003 and has included about two dozen stockings, including one in Taliaferro County that occurred over a 10-day period.
Introducing the flies is a tedious process that begins with sending a team to map a series of imported fire ant mounds.
“You flag them and number each one,” Gardner said. “Then you capture some of the ants, maybe a couple hundred, and send them to Florida.”
At the USDA lab, the captive ants are exposed to phorid flies, and returned to Georgia as “parasitized” carriers of fly larvae.
“The flies lay eggs in the ants and we put the ants back in the mound,” he said. “We have to put them back in the same mound, too, or the ants there won’t accept them.”
In addition to killing the ants by injecting eggs into them, the flies also inhibit the movement and foraging ability of ant colonies. “The ants can sense the wing beat of phorid flies, and they will freeze and they will hide,” Gardner said.
The most recent Georgia survey found both phorid fly species living in Augusta-Richmond County, with just one species in nearby counties. Jenkins County was the closest area to Augusta found to have two species, he said, adding that efforts remain under way to populate the state with a third phorid fly species.
Anecdotally, fire ant populations in Georgia appear to have retreated in recent years, but the causes are linked to factors other than the predator flies.
“We’ve seen, over the last five years, a marked decrease in density of fire ants,” Gardner said. “We would like to take credit, but it’s really due to drought conditions and higher temperatures. Now that we’ve had a milder winter and some periodic rainfall, all of a sudden ants have really come back to the surface this spring.”
The long-range outcome of the phorid fly wars are difficult to predict, but scientists are optimistic that there will be positive results over time.
They also generally agree there is no way to eliminate imported fire ants altogether.
“What nature is all about is balance,” Gardner said. “We’ll never eradicate them, but we hope we can control them.”