Chemical integration of Thorictus myrmecophilous beetles into Cataglyphis ant nests

Thorictus beetles of the Dermestidae are obligate myrmecophiles. To understand how these beetles are integrated into and tolerated by their host colonies, the cuticular hydrocarbon profiles of different species of the Thorictus castaneus group that are generally associated with Cataglyphis were examined. The beetles are characterized by small amounts of cuticular hydrocarbons, which render them partly chemically “insignificant”. They also have the same cuticular hydrocarbon profiles as their hosts and thus likely use chemical mimicry to evade worker hostility but, like slaves in slave-maker species, they maintain some partial chemical identity. Thorictus martinezi from Burkina Faso were immediately adopted by conspecific colonies of their host, Cataglyphis sp. aff. bicolor, but were never adopted by colonies of other species (i.e. Cataglyphis viatica and Formica selysi). Thorictus buigasi from Morocco also mimicked the chemical profile of its host, C. viatica, but, in contrast to T. martinezi, individuals were adopted by colonies of Cataglyphis velox from Spain. This result can be explained by the similarity between the hydrocarbon profiles of C. viatica and C. velox, which may facilitate adoptions. T. buigasi beetles remained in Formica selysi colonies for some time but were ultimately rejected, probably due to their very different hydrocarbon profiles. In contrast, they were sometimes adopted by Camponotus herculeanus colonies and eventually chemically matched their new hosts, probably by passive camouflage. These data suggest that Thorictus of castaneus group myrmecophily is the result of coevolution with Cataglyphis hosts and that the mimicry is plastic, such that beetles can live with different hosts if the hosts show very limited CHC differences.