Do Sphecodes cuckoo bees use chemical insignificance to invade the nests of their social Lasioglossum bee hosts?

Brood parasites need to overcome host detection in order to exploit their target resource. Nest invasion by brood parasites is possibly enabled either by chemical mimicry (innate odour match with host), camouflage (acquired odour match with host) and/or chemical insignificance (odour reduction). We analysed which of these strategies may be used by the cuckoo bees Sphecodes monilicornis and S. puncticeps to sneak into the nests of their social Lasioglossum bee hosts. In staged dyadic encounters, the host bee workers interacted much more rarely towards S. monilicornis than towards nestmates, suggesting that the host bee may weakly detect this cuckoo bee in the nest. Cuticular hydrocarbon (CHC) profiles of S. monilicornis included about 30–50% of compounds found on host bees, possessed exclusively linear alkanes, a class known to be generally less important in nestmate recognition, and lacked exclusive compounds. S. monilicornis may thus avoid recognition by hosts through chemical insignificance. On the other hand, S. puncticeps has a more complex CHC profile including several exclusive methyl-branched alkanes, though no alkenes. This cuckoo bee species does not seem to use either chemical mimicry or insignificance to invade host nests. However, only a large comparative study may elucidate the evolution of CHC adaptations in Sphecodes to their hosts’ template.