A simple field-ready method for collecting cuticular hydrocarbons reveals tradeoffs in hydrocarbon compound production in ants (Formicidae)

Cuticular hydrocarbons (CHCs) are waxy substances on the cuticles of most insects, which protect them from microbes, desiccation, and other environmental risks. The CHCs are also used broadly in insect communication, and can be a valuable phenotype for taxonomic analyses. However, collecting CHCs in the field is often difficult because the appropriate reagents may be hard to come by, the conditions are ripe for contamination, and many solvents cannot be transported. Here, we have optimized a new method for preserving the CHC phenotype, without the use of solvents. Ants are collected alive and freeze killed, then stored using desiccating agents such as silica or drierite. The dried ants can be extracted at a later date in a controlled lab setting, which reduces the risks for contamination. Using field collected ants of three chemical types, we found no difference between freshly collected hydrocarbon extracts and ants extracted after 3 years on drierite. This new dry collection method is extremely low-tech and straight forward, while maintaining high sample quality. We recommend that any field entomologist considers adopting this new method to collect and preserve the CHC phenotype. Using these newly developed methods, we were able to collect ants throughout the Neotropics. Preliminary examination within the genus Pseudomyrmex reveals that each of the 25 examined species carries a specific set of hydrocarbons. There is weak phylogenetic signal of compound class, indicating hydrocarbon phenotypes evolve quickly. However, there seem to be trade-offs in the production of certain compound classes. Specifically, ants that carry alkadienes do not have certain methyl branched compounds common within the genus. Given the differing genetic pathways for methyl branched and unsaturated compounds, our findings suggest potential metabolic or communication tradeoffs in producing different hydrocarbon classes.