WASHINGTON â Entomologists at federal laboratories in Florida say they have discovered a virus that is lethal to the hated red imported fire ant. It might be possible to use the virus as soon as a year from now to develop a way of controlling the insect without pesticides, the researchers said. Fire ants, known for their painful sting and large mounds, have spread relentlessly since they were accidentally imported into Mobile, Ala., from South America in the 1930s. The Agriculture Department estimates that more than 300 million acres in 14 states across the South are infested by the imported ants. Each year, the ants cause an estimated $6 billion in agricultural damage and various expenditures, the department estimates. Steven Valles, an entomologist at the U.S. Agriculture Department's Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla., said researchers stumbled onto the germ, which turned out to be distantly related to viruses that cause the common cold in human beings. Valles said scientists at the department's Horticulture and Breeding Research Laboratory in Fort Pierce, Fla., were analyzing fire ant genes recently when a computer they were using detected a strange sequence that didn't appear to be part of the normal ant genome. An international "library" of genetic material showed that the DNA fragment was part of a virus, he said. "That little piece of gene gave us a handhold that we used to find the virus in the wild," Valles said. About 23 percent of ant colonies are naturally infected with the virus, he said. The researchers dug up several entire colonies, some with the virus and some without, and moved them into a laboratory. "Within two or three months all the colonies that had the virus were dead, and the colonies without it were not," he said.