Agonistic Interactions Among Invasive Ant Species (Hymenoptera: Formicidae) from Two Habitats on Oahu, Hawaii

The Hawaiian Islands represent the most isolated land mass in the world, with no native ant species. To study invasive biology within two ant communities on Oahu, Hawaii we conducted laboratory bioassays to assess agonistic interactions among five introduced ant species: Leptogenys falcigera (Roger,), Camponotus variegatus (F. Smith), Anoplolepis gracilipes (F. Smith), Ochetellus glaber (Mayr), and Pheidole megacephala (Fabricius). Both individual and group assays were conducted, pairing either individual ant workers or groups of ten workers from each species. Individual assays were scored using a rating system ranging from aggressive to defensive behavior. Group assays were evaluated on the basis of ant mortality, assuming that aggression led to mortality of one or both of the species. The species with the highest and lowest levels of agonistic behavior were similar in individual and group experiments. Pheidole megacephala ranked first with the highest level of aggression in the individual assays and highest mortality in group assays. Anoplolepis gracilipes ranked second in aggressive behavior in individual assays and second in group assays. Leptogenys falcigera was the most non-responsive in individual assays, and had 100% survival in the group trials. These experimental results correspond with our field observations that P. megacephala and A. gracilipes are numerically dominant species and L. falcigera is a subdominant species on Oahu, Hawaii.