There's no way to wipe out fire ants permanently, so it's more economic to work on keeping infestations manageable, a Texas entomologist says.

"We're still hoping for a magic bullet," said Bastiaan "Bart" Drees of Texas A&M University's agricultural extension service.He said the best hope for fire ant control appears to be in using fungi and insects that prey on fire ants in South America, the ants' original home.

Florida researchers have patented one kind of South American fungi for use against fire ants, but it is likely to be years before enough organisms are available to keep down the numbers of fire ants, he said while in town to speak to the Entomological Society of America.

When fire ants showed up in this country in the 1920s, farmers tried to wipe them out with chemicals, Drees said. DDT and similar chemicals kept the numbers down only temporarily, and killed or threatened many animals higher up the food chain.

The chemicals also eradicated many of the native ants now recognized as the best defense against fire ants. "They competed with fire ants for resources. And they mated with fire ant queens," he said.

The safer pesticides now available offer only a one-year respite and are too expensive to spread on every field, he said.

"The cheapest chemicals are $10 per acre per year. That may not provide an economic return," said Drees. "So . . . the management goal becomes to solve the problems caused by ants without necessarily eliminating the fire ant from the ecosystem."

Fire ants can be helpful, too, Drees said. "The ants feed on pests that eat cotton - the boll weevil, the fleahopper, boll worms. They reduce the need for chemical treatment of those pests."

And although fire ants attack calves during birth, they also eat pests that live on cattle, such as the lone star tick, horn flies, house flies and stable flies. "Instead of treating a 600-acre cattle ranch, people are just treating the calving pasture," Drees said.