Genetic Variation in the Strongly Canalized Sex Pheromone Communication System of the European Corn Borer, Ostrinia nubilalis Hübner (Lepidoptera; Pyralidae)

The major difference in pheromone production between the so-called E and Z strains of the European corn borer Ostrinia nubilalis is controlled by two alleles at a single autosomal locus. E-strain females produce an (E)-11-tetradecenyl acetate pheromone with 1–3% of the Z isomer, whereas Z-strain females produce the opposite blend. In laboratory-reared insects we found that F1 females produced, on average, a 71:29 E/Z ratio, but the distribution was clearly bimodal. The variability in pheromone blend produced by heterozygous females could be explained by the existence of two different alleles in the Z strain which in combination with the E-strain allele for the major production locus cause the production of a component mixture either high or low in the E isomer. In addition, evidence was found for an independently inherited factor, existing in the E strain, with a dominant effect on the amount of E isomer produced by females homozygous for Z-alleles at the major production locus. Thus, the low variability normally found in the pheromone mixture produced by O. nubilulic and other moth females may, by canalization, hide a considerable amount of underlying genetic variation.