The latest findings are part of on-going research to control the red imported fire ant (Solenopsis invicta), which was accidentally introduced into the United States from South America in 1929. It inflicts painful stings to humans and causes ecological damage by out-competing native ants, especially at construction sites and other areas where the soil is disturbed.

David Williams, who heads ARS fire ant research at the Center for Medical and Veterinary Entomology (CMAVE) in Gainesville, Fla., is searching for potential viruses and other biological controls against the fire ant. One of these is a parasitic ant from Argentina and Brazil, Solenopsis daguerrei, which Williams and colleagues are studying under quarantine at Gainesville.

This parasitic ant drains the colony's strength. Studies found that mound densities were reduced by 33 percent in fire ant colonies with the parasitic ant, and the number of fire ant queens was reduced by 47 percent in parasitized colonies.

Another potential bio-control is the pathogen Thelohania solenopsae, discovered by CMAVE scientists in the United States in 1996. The single-cell protozoan parasite from South America reduces the queen's weight, causing her to lay fewer eggs. Entomologist David Oi has discovered a new spore type of T. solenopsae that could lead to better ways to transmit the pathogen into colonies.

Insect Pathologist Roberto Pereira recently discovered a disease he named yellow head disease, thought to be caused by a protozoan from the genus Mattesia. The protozoan was present in 34 percent of sites and eight percent of nests studied in Florida. Its potential as a bio-control is still being investigated.

ARS is the U.S. Department of Agriculture's chief scientific research agency.