Cuticular Hydrocarbons in Myrmecophiles are a Mechanism of Symbiotic Entrenchment

The velvety tree ant, Liometopum occidentale, hosts three myrmecophilous rove beetles, Sceptobius lativentris, Platyusa sonomae, and Liometoxenus newtonarum. The three beetles independently evolved to mimic the nestmate recognition pheromones of L. occidentale with varying degrees of accuracy. The accuracy of the mimicry determines the degree of integration of the beetles into nests of their host; P. sonomae achieves the least accurate mimicry and is located at the nest periphery, whereas S. lativentris employs the most accurate mimicry and has access to the entirety of the ant nest and its resources. The accuracy of the mimicry was found to be dependent on the mechanism by which it is achieved. P. sonomae synthesizes the pheromone blend de novo and S. lativentris acquires the pheromones from the host ant. The approach taken by S. lativentris is significant, because the class of chemicals used as nestmate recognition pheromones in ants play a more primary role, forming a desiccation barrier that coats the surface of all insects. In the transition into the nests of its hosts, which occurs after the pupal developmental stage, S. lativentris permanently shuts off its production of these anti-desiccation compounds, opting instead to steal them from its host. This high-fidelity mimicry comes at a cost. S. lativentris is locked into an obligate and irreversible dependence on L. occidentale, dying within a day away from its host ant.