Pachycondyla (=Brachyponera) Predation on Reticulitermes virginicus and Competition with Aphaenogaster rudis.

Abstract

Invasive ant species have general diet and nest requirements, which facilitate their establishment in novel habitats and their dominance over many native ants. The Asian needle ant, Pachycondyla (=Brachyponera) chinensis, native throughout Australasia was introduced to the Southeastern United States where it has become established in woodland habitats, nests in close proximity to and consumes subterranean termites (Rhinotermitidae). We illustrate that P. chinensis do not occur in habitats lacking Rhinotermitidae and suggest that subterranean termites are critical for P. chinensis success in new habitats. We demonstrate that P. chinensis is a general termite feeder, retrieving Reticulitermes virginicus five times more often than other potential prey near P. chinensis colonies. Odors produced by R. virginicus workers, as well as other potential prey, attract P. chinensis. Furthermore, P. chinensis occupy R. virginicus nests in the lab and field and display behaviors that facilitate capture of R. virginicus workers and soldiers. Termites are an abundant, high quality, renewable food supply, in many ways similar to the hemipteran honeydew exploited by most other invasive ant species. We conclude that the behavior of P. chinensis in the presence of termites increases their competitive abilities in natural areas where they have been introduced. Aphaenogaster rudis (complex) worker abundance is strongly negatively correlated with P. chinensis worker abundance, suggesting that the latter species competitively displaces the former. We examined the competitive ability of P. chinensis to better understand the mechanisms that may, in part, be responsible for the displacement of A. rudis (complex) nests by P. chinensis colonies. Pachycondyla chinensis dominated A. rudis (complex) workers in direct worker-worker and whole colony interactions, whereby most A. rudis (complex) are killed by P. chinensis workers. Furthermore, while both A. rudis (complex) and P. chinensis nests co-occur with and prey upon subterranean termites (Reticulitermes spp.), P. chinensis foragers discover nests, kill, and retrieve workers and soldiers of R. virginicus more quickly than A. rudis (complex) foragers. We demonstrated that termite defense systems such as soldier ratio and wood barriers have little if any hindering effects on P. chinensis forager ability to prey on termites. Pachycondyla. chinensis appear to be the better termite predator. However, P. chinensis competitive ability is enhanced in the presence of termites. When P. chinensis workers discover A. rudis workers foraging they kill them. When P. chinensis workers encounter an A. rudis nest, they kill them. Termites affect the interaction between P. chinensis and A. rudis workers by increasing the number of ant forager interactions.