Cuticular pheromones and water balance in the house fly, Musca domestica

Epicuticular lipids serve two major roles in insects. Their waterproofing properties are crucial to survival in terrestrial environments, and they serve as contact pheromones in a wide array of taxa. Both functions may be affected by the physical properties of the surface lipids. This provides the opportunity for natural selection on water conservation, mediated by lipid phase behavior, to interact with and perhaps conflict with sexual selection on communication and mate recognition. We used the common house fly, Musca domestica, as a model for these interacting selective forces. Male house flies preferred female models treated with a high melting-point lipid mixture, suggesting that sexual and natural selection may both act to favor longer-chain, more saturated hydrocarbons. However, higher melting points did not result in lower rates of water loss. We propose a working model in which phase separation between the unsaturated female pheromone and saturated hydrocarbons results in areas of melted, pheromone-rich lipids and regional variation in cuticular permeability.