Fire Ants: A Look at New and Old Approaches to Control

An experimental insect growth regulator (IGR) reduced fire ant field populations by up to 79 percent after six weeks—making it a prime candidate for controlling the pest.

The red imported fire ant (Solenopsis invicta), a major pest from South America, is now established on 275 million acres in 11 southern states and Puerto Rico.

The IGR teflubenzuron blocks the ant’s ability to make chitin, the tough material that forms the ant’s outer shell. In field tests, fire ants eating bait containing teflubenzuron were reduced by up to 86 percent after 13 weeks and up to 91 percent after 17 weeks. After four weeks, colonies had no brood (immature offspring). The highest teflubenzuron level used in the study was 0.045 percent—22 times lower than levels of commercially available baits. Other studies at the same ARS lab found that:

• Bacteria that kill other insect pests won’t work against fire ants. Scientists fed Bacillus thuringiensis and two other bacteria to fire ants, then dissected the ants to see if the microorganisms passed into their digestive systems. They did not. The ants have a filter that admits only liquids and particles smaller than the bacteria.

• Boric acid should be reconsidered as a control for fire ants. Previous research indicated boric acid was ineffective. But that may be because the boric-acid concentrations were too high: they either repelled the worker fire ants or killed the ants before they could carry baited food into the nest. New research suggests boric acid may be an effective slow-release toxicant at low concentrations. In a lab study, scientists fed worker fire ants sugar water containing boric acid at concentrations of up to 1 percent. The ants lived to carry the bait into the colony, and after six weeks worker ants and brood were reduced 90 percent.

Scientific contact: David F. Williams (teflubenzuron and boric acid), Center for Medical, Agricultural and Veterinary Entomology, Agricultural Research Service, USDA,Gainesville, FL, e-mail dwilliams@gainesville.usda.ufl.edu; and Albert H. Undeen (bacteria), USDA-ARS Center for Medical, Agricultural and Veterinary Entomology Research, Gainesville, Florida, phone (352) 374-5903