Insects possess a highly developed sense of smell and live, as far as they are concerned, in a world dominated by odors. The evolution of olfactory preference is at the very basis of the enormous niche differentiation and adaptive radiation in insects. Paradoxically, the proximate mechanisms underlying the evolution of olfactory preference are elusive. I propose to take up this issue using the simple olfactory subcircuitry of moth pheromone communication. Here I propose to study the evolutionary neuroethology of the European corn borer. Despite the pest status, the species has a polymorphism of pheromone preference. Two strains exist which produce and respond to opposite ratios of the two pheromone components. I recently discovered that this saltatory shift in pheromone preference is located in the antenna. Most likely this single gene mediated shift in preference is caused by a swap of pheromone receptors in sensory neurons. The swap reverses the preference for the ratio of the two pheromone components, and supports the coexistence of two strains. Using a multidisciplinary approach involving molecular biology, physiology and immunocytochemistry, I will elucidate the mechanisms that underles this swap. The research will unveil mechanisms underpinning evolution of pheromone preference. These are at the very basis of adaptive radiation, race formation and biodiversity.