Abstract: Significant decrease in pheromone titer of female H. assulta occurred 1 h following mating, and the pheromone titer remained low until 72 h after mating. The results of pheromonostatic bioassay showed that the pheromonostatic factors existed mainly in the male accessory gland. There was no significant difference in pheromonostatic activity among extracts prepared from accessory glands of various dayage males. However the pheromonostatic activity of male accessory gland extract was affected by the phase of photoperiod, as the accessory gland extracts from the males in scotophase showed a high activity, while from those in photophase had no activity. The pheromone titers of females injected with accessory gland extracts from males at various hours in scotophase had no significant difference. There was a dose response relationship of pheromonostatic activity of male accessory gland extract, and 0.2ME (male equivalent) was the minimum dose required for effective inhibition. After injection of PBAN (Pheromone Biosynthesis Activating Nuropeptide) extract, the sex pheromone production in mated females was restored. This result suggests that the decrease of pheromone titer of mated female is due to the lack of PBAN in the sex pheromone glands.

Key words: Helicoverpa assulta, sex pheromone, male accessory gland, mating factor