Evaluation of Bombus (Psithyrus) rupestris success in usurping colonies of reported host species B. pascuorum and B. sylvarum in laboratory conditions

Abstract

Identifying all the potential host species of a social parasite requires reliable data that often proves quite difficult to acquire. This is particularly true for bumblebees whose colonies are all but easy to locate in the wild, and to make matters worse, there is a low probability of finding the usurper in a nest. The parasite’s presence alone is not usually enough proof of the host species’ suitability, evidence of prior or ongoing parasite reproduction in the nest is also required. Bombus (Psithyrus) rupestris is generally considered a specialized social parasite usurping colonies of Bombus lapidarius, but several other species have been reported through the years as its hosts. Here, we tested the ability of B. rupestris to take over nests of the reported host species Bombus pascuorum and Bombus sylvarum in laboratory conditions. Results show that in the conditions provided by this study, B. rupestris did not usurp colonies of the aforementioned species, in accordance with the standing view of it being a specialized social parasite of B. lapidarius.