Chemical cues in a bee kleptoparasite trigger an evasive response in a facultative eusocial orchid bee

Brood parasites often evade host detection through chemical mimicry or chemical insignificance, whereas alternative strategies such as chemical deterrence are rarely documented. We used the host-parasite model of the orchid bee Euglossa viridissima and its kleptoparasite, the megachilid Hoplostelis bivittata, to study this relationship in primitively eusocial bees. We hypothesized that H. bivittata employs a chemical strategy to enter the nest and avoid host aggression, and that response rapidity increases with chemical distance. To test this, the cuticular profiles of host and parasite were first compared, followed by bioassays analysing the response of host bees to conspecifics, the kleptoparasite and the stingless bee Melipona beecheii as a control. Bioassays involved live and frozen specimens, as well as dummies coated with parasite cuticular extracts of the different species. Notably, host E. viridissima showed aggression towards conspecifics and M. beecheii, but consistently fled from live and frozen H. bivittata, including dummies covered in the parasite's cuticular extract. We conclude that cuticular hydrocarbons in H. bivittata mediate an evasive response in its host E. viridissima, allowing nest parasitism. This is the first evidence of deterrence in a Neotropical brood-parasitic bee, expanding our understanding of chemical mediation in host-parasite arms-race interactions in orchid bees.