Bumblebee inquilinism in Bombus (Fernaldaepsithyrus) sylvestris (Hymenoptera, Apidae): behavioural and chemical analyses of host-parasite interactions

The bumblebee Bombus sylvestris is an obligate social inquiline of B. pratorum and nestinvading females are known to integrate themselves into host colonies, usually without any aggression. We investigated whether cuticular compounds could be involved in discrimination processes in common bumblebees, and whether they play a role in the social integration of inquilines in host nests. We tested nestmate recognition in B. terrestris workers, and analysed cuticular chemical profiles of hairs taken from allocolonial individuals. Bumblebees belonging to the same colony shared a common odour. Then, we investigated how B. sylvestris females integrated into colonies of natural and non-natural hosts, B. pratorum and B. terrestris, respectively. Inquiline females apparently succeeded in entering a host colony by expressing non-aggressive behaviours and had no chemical signature; subsequently, acquisition of a chemical signature similar to the host colony might facilitate their integration into the host nest.