Social and environmental olfactory signals mediate insect behavioral ecology and evolution

Odors are essential in mediating insect reproductive behavior. Environmental odors help insects locate suitable feeding or egg-laying sites and avoid suboptimal hosts or dangerous habitats. Sex pheromones, on the other hand, are responsible for mate finding and elicit courtship and mating. Although pheromones elicit stereotypical behaviors on their own, they are embedded in a background of environmental odors in nature. Using the cotton leafworm, Spodoptera littoralis, and the common fruit fly, Drosophila melanogaster, I studied the effect of blending environmentally relevant odors with pheromones on insect behavior. For the cotton leafworm, we first developed an attractive cotton volatile blend. We next used this blend to determine the physiological effect of DMNT, a strong behavioral antagonist, on the cotton leafworm olfactory system. I then blended the individual volatiles and volatile blends with an incomplete and complete pheromone. The combination of cotton volatiles and the complete pheromone elicits attraction. Deviations from this optimum, either by changing the pheromone composition or the cotton volatile blend strongly reduces male S. littoralis attraction. I then used the fruit fly to study the effect of food (vinegar) and habitat (yeast) volatiles on fly attraction towards pheromones. Starvation affects attraction towards a blend of vinegar and a male produced pheromone in a sexually dimorphic way. We next describe a novel female fruit fly pheromone and the odorant receptor involved in its perception. Finally, we show that vinegar and yeast volatiles interact in a different manner with male and female produced pheromones, suggesting that although vinegar is a good feeding cue, even in the presence of pheromones, it is not an appropriate mate finding cue. My findings suggest that pheromones and host volatiles function as a single unit that mediates insect behavior, rather than as individual components. As such the olfactory cues that mediate mate finding in insects are under both natural and sexual selection simultaneously, which has strong implications for insect speciation and evolution