Host specific social parasites (Psithyrus) indicate chemical recognition system in bumblebees

Semiochemicals influence many aspects of insect behavior, including interactions between parasites and their hosts. We studied the chemical recognition system of bumblebees (Bombus) by examining the cuticular hydrocarbon cues of 14 species, including five species of social parasites, known as cuckoo bees (subgenus Psithyrus). We found that bumblebees possess species-specific alkene positional isomer profiles that are stable over large geographical regions and are mimicked by three host-specific cuckoo parasites. In three host-cuckoo associations where mimicry is poor, possibly due to recent host shifts, these cuckoos produce dodecyl acetate a known chemical repellent that allows the cuckoos to invade their host colonies. Our findings indicate cuckoos use two chemical mechanisms, mimicry and repellents, to invade their hosts, and this may reflect different stages of an ongoing dynamic arms race.