SPECIFICITY OF RESPONSE TO PHEROMONES IN THE GENUS Ips (COLEOPTERA: SCOLYTIDAE)

Seventeen species of Ips were laboratory or field tested for the specificity of their response to male-produced aggregating pheromones. In the laboratory, some species appeared not to differentiate among their own pheromones and those of closely related species, whether the pheromones were bioassayed individually or in direct competition. Other species showed strong preference for their own pheromones in competition with those of closely related species, even though they had demonstrated strong attraction to pheromones of the related species, Cross-responsiveness among I. confusus, I. montanus, and I. paraconfusus, and between I. mexicanus and I. concinnus, was confirmed in field tests. Moreover, wild I. paraconfuaus females entered the nuptial chambers of males of I. montanus and I. confusus but not those of the more distantly related I. mexicanus. It is hypothesized that specificity of response to aggregating pheromone is important in the maintenance of reproductive isolation among sympatric Ips. as and that the lack of specificity among closely related species enforces the parapatric distributions characteristic of these species.