Chemical convergence between a guild of facultative myrmecophilous caterpillars and host plants

Ants exert a strong selective pressure on herbivorous insects, although some caterpillars can live in symbiosis with them using chemical defensive strategies. We investigated the adaptive resemblance of cuticular hydrocarbons (CHCs) in multitrophic systems involving a guild of facultative myrmecophilous caterpillar species (Lepidoptera: Lycaenidae), tending ants (Hymenoptera: Formicidae) and host plants from three families. We hypothesized that the CHCs of the caterpillars would resemble those of their host plants (chemical camouflage). We analyzed CHCs using gas chromatography/mass spectrometry. Morisita’s similarity index (SI) was used to compare CHC profiles of caterpillar species with different types of ant associations (commensal or mutualistic), ants and host plants. We found strong convergence between caterpillars’ CHCs and plants, especially for commensal species that do not provide secretion rewards for ants. Moreover, we found unexpected chemical convergence among mutualistic caterpillar species that offer nectar reward secretions to ants. These results show that the studied caterpillars acquire CHCs through their diet and that they vary according to host plant species and type of ant association (commensalism or mutualism). This ‘chemical camouflage’ of myrmecophilous caterpillars may have arisen as a defensive strategy allowing coexistence with ants on plants, whereas ‘chemical conspicuousness’ may have evolved in the context of honest signaling between true mutualistic partners. We suggest the existence of both Müllerian and Batesian chemical mimicry rings among myrmecophilous caterpillar species. Cuticular chemical mixtures can play a key adaptive role in decreasing ant attacks and increasing caterpillar survival in multimodal systems. Graphical abstract Chemical camouflage can be a defensive strategy of myrmecophilous caterpillars against ants. ‘Chemical conspicuousness’ is proposed as a new strategy mediated by cuticular hydrocarbons in myrmecophilous caterpillars. Chemical mimicry rings can occur between myrmecophilous caterpillars and especially between mutualistic species that produce nectar rewards for ants.