Abstract: Closely related species Helicoverpa armigera and H. assulta are two key crop pests sympatrically occurred in and around China. They use opposite ratios of cis-11-hexadecenal and cis-9-hexadecenal as their sex attractant pheromone components to maintain the interspecific reproductive isolation. Besides such difference in pheromone components, the acetate compositions in sex pheromone glands of the two species are also significantly different. In order to understand the biosynthetic mechanism resulting in the different compound compositions in pheromone glands of the two species, we topically applied unsaturated exogenous fatty alcohol and acetate precursors to the pheromone glands of H. armigera and H. assulta and monitored their conversion with gas chromatography analysis. The results showed that the gland oxidases had no substrate specificity to the exogenous cis-11hexadecenol, cis-9-hexadecenol and trans-10-hexadecenol, and therefore the corresponding erminal oxidation reaction did not affect the formation of the specific sex pheromone blend ratio in the two species. Significantly higher esterase acitivity was found in the pheromone gland of H. armigera than that in the pheromone gland of H. assulta. These discoveries would be useful to fully elucidate isolation mechanisms of the two moth species.

Key words: Helicoverpa armigera, Helicoverpa assulta, sex pheromone, oxidase, esterase