HOUSEHOLD AND STRUCTURAL INSECTS Horizontal Transfer of Insecticides in Laboratory Colonies of the Argentine Ant (Hymenoptera: Formicidae)

Five insecticides used by urban pest management professionals for ant control and threeexperimental insecticideswere tested todeterminewhether these insecticideswerehorizontally transferred among individuals in colonies of Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae). Antswere exposed to insecticide-treated sand for 1min and then placed in a colony of untreated ants. Ants exposed to 20 and 40 ppm Þpronil readily transferred the insecticide to other individuals in the colony, resulting in high mortality. Most of the transfer and subsequent mortality occurred within 4 d after exposure to treated ants. The other insecticides were not transferred, and ants exhibited mortality rates similar to that of the controls. Experiments in large foraging arenas demonstrated that necrophoresis was an important behavior facilitating the horizontal transfer of Þpronil. When ants contacted contaminated corpses in the process of removing them to refuse piles, they received a lethal dose of Þpronil and subsequently died. Fipronil-contaminated dead ants that were placed in the vicinity of the nest resulted in signiÞcantly highermortality thandid corpses placed in a distant foraging arena (30 cm away).Most of the dead ants accumulated in the vicinity of the nest rather than in the foraging arena, workers retrieving dead ants to refuse piles from the foraging arena. The position effect of insecticide-contaminated corpses relative to the nest and its implication for Argentine ant control are discussed.