Sequencing and characterizing the olfactory receptors of Megacyllene caryae (Coleoptera: Cerambycidae)

Many species of longhorned beetles (Cerambycidae) rely on volatile sex and aggregation pheromones to locate mates. The chemical structures of pheromones vary across subfamilies, but within these groups many species produce similar or identical compounds. In the subfamily Cerambycinae, the chemicals 3-hydroxyhexan-2-one, 2,3-hexanediol, and 2-methyl-1-butanol have been described as pheromones of over twenty different species. We are studying the pheromone receptors of the Cerambycinae to better understand the evolution of this unusual overlap of pheromones. We sequenced an antennal transcriptome of the longhorned beetle Megacyllene caryae (Gahan), which produces in its pheromone blend the common cerambycine pheromones 2,3-hexanediol and 2-methyl-1-butanol. From these data we constructed models of 69 transcripts of putative olfactory receptors, and then characterized receptors by expressing them in vivo and measuring the response to chemicals in a voltage-clamp system. Through this method we have identified receptors for 2-methyl-1-butanol, (2S,3R)-hexanediol, and an additional pheromone 2-phenylethanol. We are now sequencing orthologs in other beetles that produce these chemicals to trace the evolution of both receptors and pheromones through the Cerambycinae.