Finding the right mating partner is crucial for all sexually reproducing species, including humans. Variation in sexual attraction between populations is hypothesized to be important in the speciation process. To determine the role of sexual attraction in speciation, genes responsible for within-species variation will need to be identified, and the level of phenotypic plasticity needs to be assessed. Moths are ideal animals to identify these factors: i) Females attract males through a well-defined species-specific sex pheromone, which is produced in a special pheromone gland. ii) We found significant geographic variation in the pheromone blend of the noctuid moth Heliothis subflexa (Hs), especially in one group of compounds with a dual function: the acetates not only enhance attraction of conspecific males but also inhibit attraction of heterospecific Heliothis virescens (Hv) males. iii) Through QTL analysis we found one major QTL, explaining 40% of the geographic variance in the acetates, and we constructed a cDNA library from the pheromone gland to generate candidate genes involved in the pheromone biosynthetic pathway. This sets the ideal stage to identify the responsible gene(s) for the acetate variation. iv) Recently, we found that Hs females change their signal when emerged in the odor of heterospecific Hv. Such phenotypic plasticity has not been explored in moth sexual communication before. Therefore, we also propose to determine the level of phenotypic plasticity in Hs sexual communication. Identifying genes (G) and the level of environmental variation (E) will give the unique opportunity to disentangle evolutionary forces shaping sexual attraction.