FACTORS AFFECTING the PERFORMANCE of BAIT TOXICANTS for ARGENTINE ANTS (HYMENOPTERA: FORMICIDAE)

Abstract:
Argentine ants, Linepithema humile (Mayr), are a major urban pest species in many countries with Mediterranean and semi-tropical climates. L. humile primarily feeds on honeydew, nectar, and other liquid sweets. Baits consisting of sucrose solutions are highly preferred. Sucrose-based liquid solutions containing imidacloprid exhibited delayed toxicity, were non-repellent, and provided good reductions of ants foraging around structures. Optimal concentrations ranged from 0.0005 to 0.005%, a 100-fold range in effective rate. Boric acid in sucrose water did not exhibit delayed toxicity. Only 0.5% to 1.0% boric acid provided slow toxicity to L. humile, the optimal range being just 2-fold. A commercial bait containing 1.0% boric acid provided statistically significant reductions, but the level of control was unacceptable. Reduced attractiveness and evaporation of water from the baits probably contributed to the reduced performance in the field. A wide range of effective concentrations is therefore desirable under field conditions.