Fire Ants Vulnerable to Microscopic Organism

STEPHENVILLE, Texas, May 10, 2004 (ENS) - Texas A&M University entomologists have found a microorganism that kills imported red fire ants, but they are reluctant to set it loose in U.S. fire ant colonies.

A protozoa that is deadly to the stinging ants, the microorganism has been found to exist in fire ant colonies in 120 of the 157 Texas counties where the invasive ants have been found.

The protozoa may not eradicate the fire ants but it has the potential of changing them from aggressive pests into pests that are less competitive with native species, said Dr. Forrest Mitchell, entomologist with the Texas Agricultural Experiment Station at Stephenville. He conducted the survey of Texas fire ant colonies to identify those infected with the protozoa.

Once a colony is infected, the protozoa debilitates the queen, the workers and even the larvae. The disease shortens their the ants' life spans and raises the mortality of sexual females.

There are several native species of U.S. domestic fire ants, but their stings are slight compared to those of the red imported fire ant, which was accidentally introduced to the United States in the 1930s.

Because it lacks natural predators here, the red imported fire ant has spread to all or portions of Florida, Georgia, South Carolina, Tennessee, Alabama, Mississippi, Arkansas, Texas and Oklahoma. The species has become very abundant, displacing many native ant species.

Scientists have long known that in South America one of the pest's natural enemies is Thelohania solenopsae, a microscopic organism related to the amoeba.

"It infects about 25 percent of the ants down there. It is one of the natural pathogens, but the degree of its importance is hard to access," Mitchell said.

The scientific community has been cautious about introducing the protozoa in the United States, however, not knowing what effect it might have on the native ant species, such as harvester, carpenter and leaf-cutting ants, Mitchell said.

Because of these fears, studies of the South American protozoa were done in labs under controlled conditions. Then in 1998, a U.S. Department of Agriculture entomologist found an fire ant colony near Thorndale infested with the protozoa.

"Later, tests showed that the DNA of the Thorndale strain differed from the South American strain," Mitchell said.

A survey of Texas imported fire ant colonies conducted by Mitchell shows the protozoa has occurred naturally, without human intervention.

But Mitchell is not rushing into a decision to introduce the protozoa more widely into the United States. If the protozoa is native to North America, then its further introduction will not likely harm the native ant population. They are already adapted to it. "If it's not native, helping it spread might not be a wise thing to do," Mitchell said.