Argentine ants, Linepithema humile, (Hymenoptera: Formicidae) in Louisiana: Ant-ant competition and treatment with insecticides

Abstract:
The Argentine ants nest in the ground and forage into hundreds of trees and houses in the area. We investigated the effect of competition between Argentine ants and red imported fire ants. When equal numbers of Argentine ants and fire ants interacted, fire ants were more successful than Argentines, which faced great mortality risk. However, when large numbers of Argentines interacted with fewer fire ants, entire colonies of fire ants were quickly decimated. We also tested several methods of controlling Argentine ants on a large scale. We tested contact insecticide barrier sprays, broadcasts of liquids and granules, and liquid and solid baits. Some of these efforts suppressed the ants for a short time, while others appeared to be ineffective. Several hypotheses were tested: contact insecticides were sprayed around the trees in conjunction with large-scale baiting to reduce ant populations; pesticide degradation or runoff was investigated by testing the soil for pesticide residue; and, ants were tested for pesticide detoxification enzymes. Contact insecticides around the trees reduced the number of ants foraging in the trees but did not eliminate. The granular bait that was broadcast combined with strategically placed liquid bait stations further reduced the population of Argentine ants. Some of the contact insecticides that were applied were not present in tested treated soil one month after treatment. Subsequent experiments provide evidence that there is a runoff. Argentine ants from Toledo Bend had 7.5 times more glutathione-S-transferase activity than ants from California, which have never been exposed to insecticides. These results may explain some of the difficulty in managing Argentine ants.