The dreaded fire ant may have finally met its match.
B lamed for everything from starting fires to ravaging crops, delivering painful multiple bites and decimating wildlife, imported red fire ants — Solenopsis invicta — are the ants from hell. In little more than 70 years, they've become the scourge of the South, infesting more than 260 million acres from Texas to Florida and causing damage in the uncounted millions.
They've been battled with everything from grits and boiling water to the most sophisticated of chemical baits, but they've lived to bite again.
Now, however, the seemingly indestructible pests from South America may have met their match in a microscopic organism that deals a knock-out punch to their colonies, which can teem with as many as 200,000 insects.
"This may prove to be the great leveler," said Forrest Mitchell, an entomologist studying the protozoan Thelohania solenopsae at Texas A&M University's research and extension center in Stephenville.
Mitchell said early research suggests the organism, which naturally infects the ants both in South America and the United States, may prove an effective, economical weapon against infestations on farms and rangeland. While chemical baits are effective against the ants in urban settings, he said, they are far too costly for widespread agricultural use.
The protozoan has been found in red fire ant nests in 126 of 157 infested Texas counties. Their heaviest concentration was in Hamilton and Lampasas counties in the center of the state. Few were found in East Texas, and none in Harris County.
Closely related to a protozoan that infects roughly a fourth of fire ant nests in South America, Thelohania solenopsae was first found in the United States six years ago. U.S. Department of Agriculture scientists discovered the organism in Florida, then later identified it in ant nests in Texas.
Intrigued by the USDA findings, Mitchell and his colleagues began testing Texas fire ants for the protozoan in 2002. "We finally finished in 2003," he said, "and we've been hammering away at it ever since."
Scientists are uncertain how the protozoan came to the United States, how it spreads or how it infects individual ants within a nest. What is apparent, though, is that once established in an ant colony, it decimates the population.
"From studies I've read, it's apparent that they cause a chronic, debilitating disease," Mitchell said. "The ants are less able to reproduce. ... I don't have scientific proof, but in some colonies that were heavily infected with the protozoan, I had a hard time finding ants." When he dug into the nests, he said, the surviving ants fled rather than attacked.
"If the colonies are infested with the protozoan, I consider them dead," Mitchell said.
The organism naturally spreads from nest to nest, and Mitchell said he and his colleagues are puzzled why it hasn't moved extensively into East Texas.
"Where it hasn't spread naturally, there's a reason," he said. "Maybe it just hasn't had a chance to spread. Maybe the ants are healthier and more resistant. Maybe there are more single-queen colonies (a type of nest less commonly infected than those with multiple queens)."
Mitchell suspects East Texas' heavy rainfall may deter the organism's spread.