Small–scale sympatric digger wasps Oxybelus argentatus and Oxybelus trispinosus segregate activity, hunt for different prey, and diverge in nesting behaviour

The behavioural ecology of Oxybelus argentatus Curtis and Oxybelus trispinosus Fabricius was investigated in a shared nesting area in Northern Italy. Females of the two species nested in bare, sandy soil and dug unicellular (O. trispinosus) or multicellular (O. argentatus) nests. Digging and provisioning activities were temporally well segregated across the day in O. argentatus, while they widely overlapped in O. trispinosus. O. trispinosus, differently from O. argentatus, never closed its nest nor performed any cleaning of the burrowed material which accumulated into a mound around the nest entrance. Females of O. argentatus hunted almost only the therevid fly Thereva fulva Meigen for its larvae, while O. trispinosus collected many species of Calliphoridae and one species of Sarcophagidae. Females of both species, however, collected only male prey. Many of the aforementioned differences may limit the competition between these two, closely related, small-scale sympatric species. Paralysed flies were taken to the nest impaled on the sting (O. argentatus) or mostly using the mid and forelegs (O. trispinosus). This difference in prey-carrying seems to reflect the different morphology of the sting, with O. argentatus having lancets shorter than the stylet (possibly increasing the efficiency of prey impaling) and O. trispinosus having lancets long as the stylet. After a literature survey of the other 23 species of the genus, a comparative review of nesting and foraging ecology of the genus is also presented