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Photo: Fire ants swarming on a wooden stick. Link to photo information
Widely disliked for their venomous, painful stings, fire ants have spread across much of the southern United States. Click the image for more information about it.

First Virus to Infect Red Imported Fire Ants Discovered

By Jim Core
November 30, 2004

The first known virus to infect the destructive and costly red imported fire ant (RIFA) was recently discovered by Agricultural Research Service scientists.

RIFA, Solenopsis invicta, currently infests about 300 million acres in the United States. Although RIFA is native to South America, it thrives here because of a lack of natural enemies. Fire ants cost Americans hundreds of millions of dollars annually. The ants occasionally kill young, unprotected livestock and wildlife, and they inflict a painful sting that is sometimes deadly to humans.

Steven M. Valles, an entomologist with the ARS Center for Medical, Agricultural and Veterinary Entomology (CMAVE) in Gainesville, Fla., and colleagues at CMAVE and the ARS Horticulture and Breeding Research Laboratory in Fort Pierce, Fla., have identified a new natural enemy of RIFA.

The newly found natural agent is a virus in the Dicistroviridae family, which is related to the well-known picorna-like viruses. The entire genome has been sequenced, and studies suggest the virus, tentatively named Solenopsis invicta virus-1 (SINV-1), may be an excellent biological control agent for fire ants. Scientists use natural organisms as part of a strategy to reduce RIFA numbers without using pesticides.

A survey in Florida locations found that approximately 23 percent of RIFA nests examined were infected with SINV-1. The virus infects all fire ant castes and stages of development, and Valles was able to successfully transmit the viral infection to uninfected fire ant nests.

Brood in infected colonies died within three months during laboratory studies, but the effect of the virus on field populations is still being evaluated, according to Valles, who is in CMAVE's Imported Fire Ant and Household Insects Research Unit.

ARS researchers are currently examining SINV-1 to determine its effectiveness and potential for use as a sustainable, microbial control agent against the red imported fire ant.

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