Cuticular Hydrocarbons

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All insects are covered with cuticular hydrocarbons which act as a desiccation barrier. There are several distinct molecule types in each species (chain lengths from C23 to C37, with differing positions of double bonds or methyl-branches). Different blends of cuticular hydrocarbons can reflect variations in age, reproductive physiology as well as genotype among individuals in all insects. In social Hymenoptera, these cuticular differences encode information that underlie the resolution of reproductive conflicts as well as nestmate recognition (Peeters & Liebig 2009). Cuticular hydrocarbons have been shown to be reliable markers of fertiliy in a number of species. The technique of solid-phase microextraction (SPME) has been used successfully to sample hydrocarbons on the cuticle of live individuals. Combined with gas chromatography, this allows the temporal monitoring of individuals in experimentally manipulated colonies (e.g. removal of egg-layers).

Long-chained hydrocarbons (HC) coating the exoskeleton are thus a chemical signature that is produced by a combination of genotype and physiology. This cuticular signature contains dual information about colony membership and fertility status, and it a challenge to identify which compounds are used for one or the other function. Colonies have a distinct odour that underlies nestmate recognition, i.e. the HC profile is perceived and assessed during encounters between individual ants, to discriminate friends or foes. Diet can also influence nestmate recognition in some species. According to the Gestalt model, all nestmates share a colonial odour as a result of homogenizing their HC profile through trophallaxis, allogrooming or passive transfer during nestmate contacts. However, as far as the various molecules that are correlated with fertility, there is no mixing. Future studies must investigate how intracolonial differences (fertility, but also age and sex) can be reconciled with a common colonial odour.

Smith (2018) found that the intraspecific variability in Formica archboldi cuticular hydrocarbon profiles is among the greatest reported for social insects and provides a unique case of how non-parasitic species can generate parasite-like chemical-mimic phenotypes.

Cuticular hydrocarbon chemistry has been examined in many species belonging to all major subfamilies. This is often combined with studies of a wide variety of behaviours involved in nestmate and/or intracolonial recognition.