Sex allocation, nests, and prey in the grass-carrying wasp Isodontia mexicana (Saussure) (Hymenoptera: Sphecidae)

Abstract

At six locations in Montana, Isodontia mexicana (Hymenoptera: Sphecidae) nested either in trap nests or in commercial bee boards used for alfalfa leafcutting bees. Partitions and plugs in the nests were constructed fromfragments of grass stems gathered by females, who provisioned nests containing 1-6 cells with either tree crickets (Gryllidae: Oecanthinae, Oecanthus) or katydids (Tettigoniidae: Conocephalinae, Conocephalus). The number of prey per cell, but not cell length or cell volume, was a significant predictor of offspring size. Isodontia mexicana displayed differences between the sexes typical of Sphecidae, having larger females that received more investment from their mothers, that occupied cells deeper within nests, and that emerged as adults later in the season on average than males. Finally, by taking unequal numbers of male and female prey, I. mexicana may impose sex-biased selection pressure on their prey populations.