Nest Architecture, Prey, and Body Size in the Grass-Carrying Wasp, Isodontia auripes, at two sites in New York (Hymenoptera: Sphecidae)

Abstract: Isodontia auripes [Fernald] females nested in fourteen 12-mm diameter artificial trap nests at two locations in New York State (Geneseo and Rensselaerville). We report broods of up to 14 pupae in a single chamber with an average of 5.8 pupae per chamber (previously reported range 2 - 6 pupae/chamber). Nest architecture, with plugs of finely shredded, packed grass and coarse, wound grass stems, was similar to other reports of I. auripes nests, except that only one nest contained a grass partition on the back wall of the chamber (in a case where mud-nesting wasps had preceded I. auripes). All prey items that could be identified to species were either the non-native drumming katydid, Meconema thalassinum [DeGeer], or the narrow-winged tree cricket, Oecanthus niveus [DeGeer]; M. thalassinum accounted for 71% of identified prey and is a new prey record for this wasp. Nests contained an estimated average of 11 prey per pupa, with a strongly female-biased prey sex ratio. The 116 collected pupae suffered from high pre-emergence mortality (65.5%), mostly due to the presence of parasitic flies and chalcid wasps in many nests. Adult females were larger than males in body mass and head width but did not differ in emergence time. Both male and female wasps could be found within single brood chambers, though the population was male-biased (2.4:1) and individual nests strongly favored one sex. In general, pupal cases closest to the nest entrance within a chamber were smaller than those found furthest away, suggesting size-related fitness impacts for offspring based on the order of egg laying.