Response of Little Fire Ant (Hymenoptera: Formicidae) Colonies to Insect Growth Regulators and Hydramethylnon

Abstract

The little fire ant, Wasmannia auropunctata (Roger) (Hymenoptera: Formicidae), a highly successful, destructive invasive ant, is potentially the great- est ant species threat to the Pacific region. Once established, W. auropunctata is extremely difficult to control. This study was conducted to observe the effects of ant baits containing insect growth regulators (IGR) on W. auropunctata colonies during a five-month observation period. Baits containing both methoprene and hydramethylnon achieved 100% mortality by six weeks after treatment, possibly because of the metabolic inhibitor, hydramethylnon, rather than the IGR, metho- prene. The IGR pyriproxyfen-exposed queens were unable to produce worker brood or replacements at 20 weeks after treatment. In methoprene-treated colonies three distinct effects on queen fecundity were observed with either continued or cessa- tion of production of viable worker brood and worker replacements, or production of sexual brood exclusively. With its consistent interference with production of replacement workers and viable sexual brood as compared to methoprene, pyri- proxyfen shows potential to be an effective IGR for controlling W. auropunctata.