Mycobiota in the brood cells of the European beewolf, Philanthus triangulum (Hymenoptera: Crabronidae)

Abstract

Mass provisioning insects have to cope with microbial spoilage of their food supplies. As their fitness is directly linked to the availability of high quality food for their offspring, they have evolved various mechanisms for preserving these resources. The European beewolf, Philanthus triangulum, uses several mechanisms to not only preserve the food for their larvae, paralyzed workers of the European honeybee, Apis mellifera, but also protect the larvae that develop on the stored food. To assess the spectrum of fungi that pose a threat to beewolf brood cells, we manipulated brood cells by removing the insect defenses. We monitored the subsequent fungal infestations that would have been prevented by the beewolf defense mechanisms and isolated and identified the mold fungi. The cosmopolitan and highly competitive species of Aspergillus, in particular A. flavus, dominated the mold in beewolf brood cells. All other infestations could also be attributed to generalist mold fungi that are commonly found in soil and also on insects. Our findings indicate that beewolf brood cells can be colonized by a broad range of opportunistic soil mold fungi. Thus, it seems highly adaptive that beewolves employ general, broad spectrum defense mechanisms.