Seasonal Changes in Nestmate Discrimination in the Paper Wasp, Polistes metricus Say (Hymenoptera: Vespidae)

Abstract

Nestmate discrimination in the paper wasp, Polistes metricus Say (Hymenoptera: Vespidae) was examined during each stage (nesting and non-nesting phases) of the colony cycle. Resident wasps of each caste were paired with nestmates or non-nestmates of the same caste in a clear plastic box near the nest in the field and all aggressive and non-aggressive behavioral interactions initiated by the resident wasps were noted. Each wasp caste, particularly the resident foundress, workers, and males exhibited a significantly high proportion of aggressive behaviors towards non-nestmates than towards nestmates, thus demonstrating nestmate discrimination. However, the response of resident fall gynes towards nestmates and non-nestmates was not significantly different. During winter, gynes of P. metricus and P. fuscatus Fabricius were found to overwinter together in the same clusters. The overwintering gynes of P. metricus showed complete tolerance towards conspecifics (non-nestmates) and allospecifics (P. fuscatus). These findings suggest that the acceptance threshold of P. metricus shifts from being restrictive towards the beginning of the nesting phase to being permissive towards the end, which differs from previous studies on P. fuscatus, whose acceptance threshold was more restrictive during the reproductive phase than during the worker phase. However, during the non-nesting (overwintering) phase of the colony cycle, the acceptance threshold likely becomes even more permissive to an “accept-all” level in both species. These shifts in acceptance threshold follow the predictions of Reeve's (1989) conspecific acceptance threshold model, and most likely reflect the cost-benefit ratio assessment of wasps to minimize negative inclusive fitness consequences at each stage of the colony cycle.