Does the Difference in the Aggregation-Sex Pheromone Release Pattern Between Monochamus alternatus Hope (Coleoptera: Cerambycidae) and Monochamus saltuarius Gebler Ensure Reproductive Isolation in the Cohabitation Area?

In our study, we analyzed diel, daily, and weekly pheromone emission patterns to determine whether pheromone release pattern may facilate reproductive isolation between two species that use the same aggregation-sex pheromone, namely Monochamus alternatus Hope (Coleoptera: Cerambycidae) and Monochamus saltuarius Gebler, (Coleoptera: Cerambycidae) in areas where they are sympatric. The daily emission of monochamol by males of both species showed irregular but constant patterns, with M. saltuarius males releasing the pheromone earlier than their M. alternatus counterparts after cuticular sclerotization. The first emission of the pheromone occurred, on average, 10.6 and 5 days after sclerotization for M. alternatus and M. saltuarius, respectively. Weekly patterns of monochamol emission showed a peak in the 3rd week after adult eclosion for both species. Monochamus saltuarius released more pheromone than M. alternatus from 13:00 to 19:00 during three different time periods throughout the day. Both species continuously released pheromones both before and after copulation. Monochamus saltuarius displayed mating behavior by mounting and attempting copulation with a glass rod coated with the female extract of M. saltuarius, while they showed no response to the female extract of M. alternatus. In contrast, male M. alternatus adults did not distinguish conspecifics through substances present on the surface of females. These findings enhance our understanding of the strategies employed to avoid interspecific competition between these two species in cohabitation areas.