The invasive Souther fire ant likely came from fewer than a dozen stowaways that landed in Mobile, Ala., in the mid-1930s, says a University of Georgia researcher.

Using a bit of genetic sleuthing, Kenneth Ross, an entomologist with the UGA College of Agricultural Environmental Sciences, tracked the lineage of this notorious Southern pest. What he found surprised him.

"Most didn't make it over on the boat," Ross says. "When we look at the area around Mobile, the most probable number of queens is seven, eight, nine and at the minimum six."

Ross worked to determine the number of queen ant colonizers with his former student DeWayne Shoemaker, who now works at the U.S. Department of Agriculture Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla.

They also used the genetic markers to pinpoint where the invasive fire ants, known scientifically as Solenopsis invicta, originated.

Formosa, in northeast Argentina, looks to be the source population."In textbooks, they were saying Brazil, but those ants look nothing genetically like the ones we have here," he says.

The Argentine queens set out on their journey accidentally, either in soil or by landing on boats after their spring mating flight.

By tracing the U.S. fire ant population back to Argentina, scientists can determine how fast and how far other fire ant colonies can grow. Currently, Solenopsis invicta fire ants cover most of the central part of South America.

This information, Ross says, can help with the development of effective management practices based on the biology of an invasive species. It can help researchers predict other species' invasive potential, too.

Since moving out of Alabama, the Argentine fire ants have spread like wildfire. Georgia got its first colonies in the 1950s. On their own, the ants have traveled as far north as North Carolina and as far west as Texas. With a little help, such as in nursery pots and soil, they have travelled as far as California.

Five years ago, they landed in China, stowing away from the United States.

"The fire ants are hopscotching along," he says. Solenopsis invicta is also found in Australia and the Philippines.

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