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Fire ant killing protozoa found in 120 Texas counties

10.05.2004

If imported fire ants dreamed – and who knows if they do or don’t – then a tiny protozoa could be their worst nightmare.

Even better news: Texas A&M University System entomologists have completed a survey that detected the protozoa in fire ant colonies in approximately 120 of the 157 Texas counties where they have been found.

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.

The tiny microorganism may not eradicate the fire ants but it has the potential of changing it from a highly aggressive pest into one much less competitive with native species, said Dr. Forrest Mitchell, entomologist with the Texas Agricultural Experiment Station at Stephenville.

Now that the survey is complete, the next step is to grow the protozoa on culture mediums. If culturing is successful, the research might eventually yield a product that would introduce the protozoa into fire ant mounds in the form of a bait. Alternately, infected fire ants might be introduced into areas where the protozoa is not present.

But there are a lot of questions to be answered and problems to be solved first.

The first question, Mitchell said, is where did the protozoans come from?

Though there are several native species of fire ant, their stings pale compared to their more aggressive cousin, 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 one of the pest’s natural enemies in South America 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 extremely 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, an 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.

The Texas A&M survey shows the protozoa has occurred naturally, without human intervention. Questions still remain, however, before Mitchell is comfortable with the idea of helping the protozoa propagate. It could be that the protozoa was in North America all along, just waiting for the fire ant to be introduced as a host? Or, was the protozoa itself an emigre, hitching into the country with the South America fire ants? If it was an emigre, did the protozoa evolve so its DNA now looks different from that of the South American strain?

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.

These are crucial questions because ants play a critical role in the ecological balance. The predatory types kill and eat many other insects, both harmful and beneficial. Though small individually, collectively ants can make a huge impact. Worldwide, a figure for ants comprising 15 percent of all terrestrial animal biomass is not out of line.

"No one really knows for sure what percentage ants constitute of the animal biomass. But one thing is for certain. If you really want to disrupt the ecosystem, disrupt the ants," Mitchell said.