The three major pheromone components found in gland extracts of both rice and corn strain Spodoptera frugiperda virgin females were Z9-14:Ac, Z11-16:Ac and Z7-12:Ac, However, both the concentrations and relative proportions of the compounds varied significantly between strains as a function of female age and the time during the scotophase that the glands were extracted. The concentration of Z9-14:Ac found in the glands of hybrid females, coming from corn × rice and rice × corn crosses differed significantly, but in both cases did not differ significantly from that of maternal line females. The results suggest that synthesis is controlled, at least in part, by the W chromosome. Given the intraspecific variability reported in other species of Lepidoptera, both with respect to female pheromone production and male responsiveness, it would appear rather unlikely that these differences alone would be sufficient to ensure reproductive isolation of the two strains.