The impetus for this study was the discovery that male fly pheromone primes the defenses of its host plant against herbivory. The ability of plants to "eavesdrop" on the sexual communication of their herbivores has never before been demonstrated and may create novel three-way interactions among male flies, female flies, and their host plants. This project explores how male pheromone mediates male attractiveness and how defense responses by the host plant correlate with female choice. Ultimately, I hope to understand how the plant affects the fitness of male pheromone production and female choice and how these interactions might hasten or hinder reproductive isolation among populations.