Geographic variation in sexual communication in the cotton bollworm, Helicoverpa armigera

BACKGROUND: Geographic variation in male response to sex pheromone lures has been studied in the field in a number of moth species. However, only a few studies have investigated geographic variation in female calling and sex pheromone under field conditions. For an effective field implementation of sex pheromone lures, it is essential to know the local sex pheromone blend and local timing of sexual communication. We investigated the level and extent of geographic variation in the sexual communication of the important agricultural pest Helicoverpa armigera (Lepidoptera, Noctuidae) in three continents.

RESULTS: We found there is no genetic variation in the calling behavior of H. armigera. In the female sex pheromone, we found more between-population variation than within-population variation. In male response experiments, we found geographic variation as well. Strikingly, when adding the antagonistic compound Z11-16:OAc to the pheromone blend of H. armigera, significantly less males were caught in Australia and China, but not in Spain. This variation is likely not only due to local environmental conditions, such as photoperiod and temperature, but also to the presence of other closely related species with which communication interference may occur.

CONCLUSION: Finding geographic variation in both the female sexual signal and the male response in this pest calls for region-specific pheromone lures. Our study shows that the analysis of geographic variation in moth female sex pheromones as well as male responses is important for effectively monitoring pest species that occur around the globe.