Cuticular hydrocarbon profiles in velvet ants (Hymenoptera: Mutillidae) are highly complex and do not chemically mimic their hosts

Abstract

Although recognition using cuticular chemistry is important for host–parasite interactions within aculeate Hymenoptera, cuticular hydrocarbon (CHC) profiles of only a few host–parasite pairs were characterized and compared. One largely neglected family in this context is the Mutillidae (velvet ants), whose species are ectoparasitoids of bees and wasps. In our study, we characterized and compared the CHC profiles of five species of Mutillidae and seven host species. The CHC profile of velvet ants differed among species and included large proportions of n-alkanes and methyl-branched alkanes. Alkenes were much less abundant in the CHC profiles of three species of velvet ants compared with their hosts, while the other two species possess a much lower abundance of methyl-branched alkanes than their hosts. Both the number of peaks and compound diversity were generally higher in velvet ants compared with their hosts. Thus, CHC profiles of parasitoids did not show signs of mimicry when compared with their hosts. In dyadic encounters between one species of velvet ant and its host bee species, the parasitoid mainly avoided interacting, while aggression by the host was rare. Our results suggest that velvet ants did not evolve chemical mimicry, perhaps in accordance with their wide host spectrum which would limit chemical specialization. However, the reduction of alkenes in social bee-attacking species and the reduction of methyl-branched alkanes in social wasp-attacking species may favour host nest invasion, since these two CHC classes are known to be important in nestmate recognition for social bees and wasps, respectively. A larger, phylogeny-corrected comparison of Mutillidae and hosts may help clarifying the evolution of the CHC profile of these parasitoids.