Hydrocarbons in the nest material of a solitary digger wasp represent a kairomone for a specialized cuckoo wasp

Abstract

Cuticular hydrocarbons (CHCs) can be found on the cuticle of insects and they primarily serve to reduce desiccation. Additionally, they constitute important cues for species, kin and nestmate recognition. In paper wasps, these CHCs can also be found on the nest material and facilitate nestmate recognition. We analysed whether the nest material of a solitary digger wasp, the European beewolf, Philanthus triangulum (Hymenoptera, Crabronidae), also contains CHCs and whether these might provide cues for the host search of a specialized cuckoo wasp (Hedychrum rutilans). Ejected nest material contained 3.6 ± 2.1 μg of CHCs/g. The composition of these nest hydrocarbons (NHCs) was very similar to the CHC composition of the cuticles of beewolf females. In particular, there were two distinct chemomorphs occurring in the European beewolf that could be unambiguously distinguished by means of the NHCs. Because of these large amounts of NHCs, females of the specialized parasitoid H. rutilans (Hymenoptera, Chrysididae) may use these NHCs as kairomones to locate and identify the host nest. Bioassays showed that females of this cuckoo wasp are able to recognize nest mounds of their host visually and are able to discriminate between host and nonhost nest material by using qustatory cues. Furthermore, in olfactometer assays, H. rutilans females stayed significantly longer in the segment supplied with an airflow that passed over beewolf nest material than in a control segment. Our results suggest that the beewolf NHCs provide important olfactory cues for a chrysidid parasitoid for host localization.