Areawide Approach to Fire Ant Control

Progress is being made in coordinated efforts to halt the spread of imported fire ants, according to Agricultural Research Service (ARS) scientists studying this invasive pest that now inhabits more than 320 million acres in several southern states and Puerto Rico.

Fire ants cause millions of dollars in agricultural damage each year. Not only do they build large mounds that damage nearby plant roots and farm equipment, they also cause painful stings to animals and people.

ARS entomologists David Oi and Steven Valles in the agency's Center for Medical, Agricultural and Veterinary Entomology at Gainesville, Fla., are studying two parasitic microsporidia to curb fire ant populations.

In collaboration with Juan Briano at the ARS South American Biological Control Laboratory in Hurlingham, Argentina, they are testing Thelohania solenopsae. Using new genetic detection methods, they found that worker ants transfer T. solenopsae spores to the queen. This reduces the queen's egg production, so colonies die out.

Another microsporidium, Vairimorpha invictae, has successfully destroyed ant colonies. According to Oi, studies have so far shown that V. invictae doesn't infect non-fire ants or other arthropods collected in Argentina, so it may be suitable for release in the United States.

To abate the progression of fire ants across the southern United States, an areawide project is in place. Participants include USDA's Animal and Plant Health Inspection Service, state agencies and land-grant universities.

Thus far, the most successful tactic in the areawide project is the release of tiny phorid flies. These flies pursue their targets, intent on laying a single egg inside each fire ant's body. After two to three weeks, the fly maggot decapitates the ant and turns into a pupa inside the ant head. The fly that ultimately emerges repeats the process. Three phorid fly species have been established in the United States, with a fourth awaiting field release later this year.

Read more about this research in the September 2007 issue of Agricultural Research magazine.

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