Sex-specific responses to aggregation pheromone Regulation of colonization density in the bark beetleIps paraconfusus

About equal numbers of each sex of flyingIps paraconfusus Lanier (Coleoptera: Scolytidae) were caught on traps several meters downwind from a male-infested ponderosa pine log releasing pheromone while a significantly different ratio of over four times more females than males were caught at the pheromone source. Females oriented directly to higher concentrations of colonizing males in a felled tree while males tended to land on the host in adjacent uncolonized areas. The attraction response of walking males to a 1∶1∶1 mixture of the synthetic pheromone components ispenol-ipsdienol-cis-verbenol was reduced progressively at higher concentrations while female response continued to increase. These responses may function to regulate density of colonization and limit intraspecific competition.