Although a great deal is known of how genes shape behavior, far less is known of how genes are modified to produce the meaningful differences in behavior that exist among natural populations. As an initial step towards finding natural genetic variants that influence mating behavior, we have focused on differences between two sibling species of Drosophila. D. sechellia, and D. simulans, diverged ~242,000 years ago. Crosses between the two species produce viable males and fertile females. While D. sechellia males and D. simulans females mate readily, the reciprocal cross, between D. sechellia females and D. simulans males, is rarely successful. Mate discrimination at courtship in Drosophila is believed to occur through 1) female preference for species-specific courtship songs, and 2) male preference for species-specific female contact pheromones. We tested D. simulans-D. sechellia recombinant flies in 2-choice mating assays and used a high-resolution seq-based method, Multiplexed Shotgun Genotyping (MSG) to identify regions of the genome that are associated with species-specific mate preference. In females, two large effect QTL overlie enzymes that produce the pheromone, 7,11 heptacosadiene (7,11-HD). Previous work has shown that both enzymes are expressed in D. sechellia females, but not D. simulans. Moreover, 7,11-HD is produced in D. sechellia females, but not D. simulans females, and transfer of 7,11-HD to D. simulans females has been shown to reduce courtship by D. simulans males. We are currently using tissue specific expression to test this prediction. Two different large effect QTL determine mate preference in males, and we are testing candidate genes from these regions. In contrast to previous work on interspecific mate choice and courtship, our data suggests that the genetic basis of a complex behavior can be fairly simple.