Interspecific differences in female moth pheromones as small as a change in ratio of two components can cause complete reproductive isolation between species. However, evolutionary theory suggests that these genetic changes are selected against and may only occur as very rare events. If this is the case, females in all populations of a single species should produce an identical pheromone blend. There are some preliminary data indicating that there may be intraspecific variation in pheromones of Heliothis virescens and H. subflexa, but it is not known if this variation has a genetic basis and could eventually lead to speciation. Therefore, we determined the degree of intraspecific variation in pheromone production in these two closely related moth species due to genetic and environmental factors. We determined variation in pheromone production in lab strains as well as in field populations from different geographic regions. Moth pheromones are produced de novo every night, so that environmental factors may influence the ratio and/or production of different components. One environmental factor may be the presence of other females, e.g. when other, conspecific females are present, pheromone composition and/or calling behavior may differ from the situation where other, heterospecific females are in the vicinity. We determined whether the odor of conspecific or heterospecific females influences calling behavior and pheromone composition in both species. The results will be presented at the meeting.