Conspecific kleptoparasitism in Pacific cicada killers, Sphecius convallis (Hymenoptera : Crabronidae): Partially provisioned nest cells are appropriated in situ by other females

Cicada killers are large crabronid wasps which mass provision their eggs with one or more paralyzed cicadas placed in nest cells connected to a burrow; if more than one cicada is used, the burrow and nest cell are left open by the wasp as she forages for successive cicadas. Female cicada killers often enter nest burrows of other females for up to an hour and are frequently evicted by the resident female if she is present. We used trap nests to test the hypothesis that such visits might result in the in situ kleptoparasitism of an open nest cell containing a paralyzed cicada put in place by the burrow’s owner at a breeding aggregation of Pacific cicada killers in Ruby, Arizona. To document conspecific kleptoparasitism of prey cicadas and of the nest cells in which they were placed, we used sand-filled trap nests baited with one freshly paralyzed cicada in a simulated nest cell at the bottom of the trap nest’s burrow. Of 29 such trap nests placed in the ground for 24 h in the breeding aggregation, 13 (45%) were appropriated by female cicada killers that laid an egg on the cicada and closed the nest cell by back-filling an average of 32 cm of the burrow. This result suggests that conspecific kleptoparasitism occurs at a high rate in this population; low cicada availability at the site and intense avian kleptoparasitism of cicada killers returning to their burrows heavily laden with cicada prey are likely causes of this behavior.