Considerations for Argentine ant management

by Alder, Patricia McKeithan.

Alder, Patricia McKeithan. Considerations for Argentine ant management (Under the direction of Dr. Jules Silverman). This research project investigated various aspects of Argentine ant management in North Carolina. The effects of interspecific competition between the Argentine ant, Linepithema humile (Mayr), and a native ant species, Monomorium minimum (Buckley), on toxic bait performance were examined. In a laboratory study, we found that L. humile diminished the effects of a solid sulfluramid bait against M. minimum, while M. minimum reduced the performance of a liquid fipronil bait against Argentine ants. Argentine ants were not adversely affected by sulfluramid bait at any time, while M. minimum was not affected by fipronil bait until 14 days of exposure. In field studies, L. humile visited food stations over an entire 24-hour period, while M. minimum was only observed at food stations during daylight hours. In addition, during the afternoon hours M. minimum appeared to delay L. humile visits to food stations by ca. 30 minutes before ultimately being displaced by L. humile. We compared the variability and time associated with four monitoring methods commonly employed to detect changes in Argentine ant populations: trailing activity, ant counts at baits, sucrose consumption, and pitfall trap collections. Pitfall trapping was both the most variable and time consuming, while the variability of the remaining methods was similar. Deployment of baits required the least time per unit, however, and was therefore recommended as a monitoring tool for Argentine ant populations. Finally, three field studies were performed to evaluate various insecticides and treatment strategies for use against L. humile. In one trial, we compared the efficacy of gel bait or contact granules with that of a combination of the two applications. There were no significant reductions of Argentine ants one week following application. A combination treatment of Deltagard® granules and Maxforce® bait provided a greater, although not significant, reduction in Argentine ant populations. In a second trial, we evaluated the efficacy of two liquid baits. We found that average Argentine ant reductions following exposure to thiamethoxam bait or AdvanceTM bait did not differ. In addition, the number of Argentine ants consuming thiamethoxam bait was numerically but not significantly less than the number of ants consuming AdvanceTM bait. Finally, the effect of liquid fipronil (Termidor®) applied as a barrier around the exterior of homes infested with Argentine ants was measured in a third trial. Houses receiving Termidor® had an average Argentine ant population reduction of 41% two weeks following treatment. Those homes that served as untreated controls had a 62% reduction, a reduction greater than that of our treatment. ii