A U.S. Department of Agriculture researcher has discovered a natural infection that he believes may one day help control the spread of fire ants.

There is no sneezing or bouts of convulsive coughs, but the cold-like virus nonetheless sickens the imported red ants. It is the first time that a virus has ever been found in the invasive pest species."It could be six months to a year, but we'd like to be able to pull (the virus) out, grow it in cells, harvest it and be able to develop some method ... so a homeowner could disperse it," said Steven Valles, an entomologist with the Agricultural Research Service Center for Medical, Agricultural and Veterinary Entomology.

The virus discovery is "just an additional control measure" in the ongoing war against fire ants, Valles said.

Each year, the imported ants cause an estimated $6 billion in agricultural damage and various expenditures, the USDA estimates. Since its accidental importation from Brazil to Florida and Alabama in the early 1900s, Solenopsis invicta has infested more than 320 million acres in 14 states across the Southeast.

Known for its painful sting, the invasive pest has been held in check in its native ranges, thanks to the prevalence of natural enemies. But because few controls followed the pest when it moved into North America, imported populations have increased nearly unchecked.

Scientists studying natural controls have reported some progress. Sanford Porter, another USDA entomologist, has unleashed an aggressive and effective killer - the South American phorid fly - to hunt and destroy the ant. About half the ant's size, the fly decapitates its prey by implanting eggs and raising its young in the ant's hollowed-out head.

Numerous Florida communities have released the fly in test operations, though it could be years before a decline in ant populations is seen, experts say.

In addition to the phorid flies, scientists are testing various species of fungus and parasites.

But the virus identified by Valles may prove one of the most promising finds in the decades-long war against the fire ant.

Discovered during experimentation with the ant's genetic sequence, Valles and colleagues from the University of Florida stumbled across material they said was commonly associated with viruses. The unintended finding then prompted further study, which eventually led to the testing of 168 nests throughout Florida.

The pattern that emerged showed fairly widespread distribution of the infection, with nearly 23 percent of all nests testing positive. The findings were reported last month in the journal Virology.

Additional work found that the virus, tentatively named S. invicta, infected all fire ant caste members and developmental stages, from eggs to queens. In laboratory analysis, infant ants in test colonies suffered 100 percent mortality within three months.

Valles said more work was needed to understand how the infection affects wild populations.

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