Palatability of Baits Containing (S)-Methoprene to Wasmannia auropunctata (Hymenoptera: Formicidae)

Abstract

Wasmannia auropunctata Roger (Hymenoptera: Formicidae), little fire ant, is recognized as a serious pest ant species that affects agriculture, homes, gardens, and natural ecosystems in Hawaii, USA, and elsewhere. Anecdotal evidence suggests that insecticidal baits containing (S)-methoprene are not effective against this species. We examined whether W. auropunctata is repelled by bait formulations containing this compound and whether the addition of torula yeast (Candida utilis Lodder; Saccharomycetales: Saccharomycetaceae) increased palatability of these baits. Wasmannia auropunctata was found to be repelled by (S)-methoprene concentrations as low as 0.25% regardless of formulation. The addition of torula yeast (3% by weight) significantly increased worker recruitment to baits with and without (S)-methoprene. Our results indicate bait formulations using (S)-methoprene are likely to offer poor efficacy against Wasmannia auropunctata without the addition of a feeding stimulant such as torula yeast due to repellency of the active ingredient.