Researchers Seek Control for Fire Ants

Wayne Gardner lay on the ground and used tweezers to pluck tiny white larvae from a fire ant mound. While he worked, angry ants swarmed and attacked him with excruciating bites and stings.

The South American pests are known for their aggressive behavior, nasty stings and huge mounds that have appeared around the South since fire ants were somehow imported here in the 1930s.

Researchers have abandoned hope of eradicating fire ants, but Gardner and other scientists are trying to control the pests by using natural enemies imported from their native habitat. These include a disease that reduces the queen’s egg production and a fly that can decapitate fire ants.

Fire ants are believed to have been carried from South America aboard ships docking at Gulf ports like Mobile, Ala. With no natural enemies, they have spread to more than 300 million acres in 12 Southern states and Puerto Rico. In recent years, they have shown up in California and New Mexico.

Their aggressive behavior and prolific breeding have enabled them to displace many native ants that can’t compete for food.

Fire ants attack viciously when their colonies are disturbed, posing a particular threat to small children and the elderly, who may not react quickly enough to avoid multiple stings. They can also cause potholes by undermining roads and can foul electrical contacts.

Some farmers like them because they kill other crop pests, but most people consider them a nuisance.

Gardner was wearing surgical gloves, but a few fire ants reached his unprotected wrists and zapped the entomologist with their brutal sting, which can be fatal for about 1% of the population who are allergic to the venom.

“They bite and sting you at the same time,” Gardner said. “They’re giving you a double whammy.”

Gardner shook his hand and rubbed his painful wrist but continued to delicately remove the larvae, which are about the size of the period at the end of this sentence. When a mound is disturbed, worker ants try to carry the larvae to safety.

He placed the larvae in small plastic containers for examination at the university’s Georgia Experiment Station in Griffin.

“We’re looking more at fire-ant management than eradication,” Gardner said. “We’re trying to establish a balance that already exists in South America.”

The University of Georgia research is being coordinated by the U.S. Department of Agriculture’s Imported Fire Ants and Household Insects Research Unit in Gainesville, Fla. Some of its scientists--and researchers--are trying to determine which of several natural enemies works best.

The USDA has a team in Argentina that assists in studying South American insects, including those that attack fire ants. Any of the insects introduced into the United States have to go through a quarantine process to make sure they pose no threat to native species.

“Right now it’s still early,” said David Oi, an entomologist with the USDA’s Agricultural Research Service. “We’re trying to see which ones work best. We have lab data to show they work well. Now we see how they work in the field.”

Gardner’s team is monitoring 15 fire-ant mounds in a cow pasture east of Tifton, an agricultural town about 100 miles south of Macon. Last October there were 25 mounds. Five colonies were exposed to the disease. Since then a couple of colonies are weaker, one gradually disappeared and some colonies may have moved.

Much more research will be needed to prove that the pathogen, known as Thelohania solenopsae, caused the decline, Gardner said.

Every two months, Gardner’s team plots the mounds on a map and digs into them to remove larvae. Back in Griffin, they perform lab tests to determine whether the larvae are infected.

“This disease does not spread like a cold or flu,” Gardner said. “They don’t sneeze on one another. The only way this is spread is from an infected queen to the eggs, which turn into workers or perhaps another queen.”

Another natural enemy that shows promise is the phorid fly, which lays its egg inside the ant. The egg becomes a larva that travels to the ant’s head, releasing an enzyme that causes the ant’s head to fall off.

“We’ve got to increase the number of factors that are working against the fire ant naturally,” Gardner said. “When it came out of its environment, none of its natural enemies came with it.”