The red imported fire ant (Solenopsis invicta) can be controlled through baits, which workers carry back to the colony, thereby spreading the active ingredient that inhibits the ability of colony’s queen to produce eggs. Standard ant baits, however, break down in moist conditions. A new water-resistant bait shows promise. (Photo credit: USDA APHIS PPQ – Imported Fire Ant Station, Bugwood.org)

The red imported fire ant (Solenopsis invicta) and the little fire ant (Wasmannia auropunctata) are just two species of invasive ants that have thrived since their introduction to the U.S. The former has spread through much of the southeastern United States, while the latter has become widespread on the Big Island of Hawaii. In both locales, however, moisture in the environment means existing bait control methods have limitations.

Baits for fire ants have mostly gone unchanged since they were first developed in the 1960s—half a century ago—despite the significant drawback that the typical bait carrier breaks down in wet conditions. However, a new ant bait formulation that is water-resistant offers promise, say researchers with the United States Department of Agriculture’s Agricultural Research Service (USDA-ARS). Their comparison study is published today in the Journal of Economic Entomology.

A team led by Robert K. Vander Meer, Ph.D., at the USDA-ARS Center for Medical, Agricultural, and Veterinary Entomology in the Imported Fire Ant and Household Insects Research Unit conducted an experiment that deployed existing ant baits and water-resistant baits in closely matched wet conditions. Both baits carry an active ingredient that inhibits the ability of an ant colony’s queen to produce eggs. At the end of the 13-week test period, half of the red imported fire ant colonies exposed to standard bait were no longer producing worker ants, while none of the colonies exposed to the water-resistant bait were producing workers.

Vander Meer says the experiment was designed carefully to ensure that similar-sized ant colonies were compared and that they were exposed to baits under the same moisture and temperature conditions. “If you’re comparing two formulations of the same insecticide, at the same rates, then you have to control variables as much as you can, or else you’re not going to be able to show significant differences between the two,” he says. “We were very happily surprised.”

The water-resistant, or hydrophobic, ant bait, Erasant, is produced in Taiwan, by Chung Hsi Chemical Plant Ltd. The company has a U.S. patent, but the bait is not currently available in the United States.

“Our objective is to ultimately provide better control tools to the public for the control of pest ants and, in particular, the fire ant. Ideally, we would like to see this appear as a product at some time in the future here in the U.S., because I think it could be very useful in terms of providing a very good control method that is not affected by the heavy moisture that we deal with in the southeast,” says Vander Meer.

USDA-ARS is conducting further testing of the water-resistant ant bait, in irrigated plant environments in California and Florida as well as tropical areas such as Hawaii.