HOUSEHOLD AND STRUCTURAL INSECTS Delayed Toxicity as a Critical Factor in the Efficacy of Aqueous Baits for Controlling Argentine Ants (Hymenoptera: Formicidae)

Boric acid, imidacloprid, and thiamethoxam in sucrose aqueous baits had different delayed toxicities toworker Argentine ants,Linepithema humile (Mayr). The concentrations required toproduce anLT50 (time required toproduce 50%mortality)within 1Ð4dwere 3.63Ð0.55%boric acid, 9.2 10 3 to 7.1 10 % imidacloprid, and 3 10 4 to 2 10 % thiamethoxam. The three toxicants were not repellent. Other laboratory trials showed that 1% boric acid, 5 10 4 to 5 10 % imidacloprid, and 1 10 5 to 1 10 % thiamethoxam had delayed toxic effects, whereas 0.5% boric acid and 5 10 % imidacloprid did not. Baits that provided an LT50 between days 1 and 4 were considered to have delayed toxic effects. The utility of aqueous sucrose baits and toxicants soluble in such systems and the negative impact of fast-acting toxicants on trail following, recruitment, trophallaxis, and control of Argentine ants are discussed.