OLFACTORY RECEPTOR CELL RESPONSES OF IPS-GRANDICOLLIS (EICHHOFF) (COLEOPTERA, SCOLYTIDAE) TO INTRASPECIFIC AND INTERSPECIFIC BEHAVIORAL CHEMICALS

Electrophysiological recordings from antennal olfactory receptor cells were obtained from Ips grandicollis. Recordings were made from olfactory receptor cells from nine regions of the antennae in response to stimulation with the semiochemicals alpha-pinene, frontalin, endo-brevicomin, verbenone, trans-verbenol, cis-verbenol, ipsdienol, and ipsenol. In many cases, up to two cells were recorded concurrently from the same location. When compared to males, females had a greater percentage of cells responsive to the primary pheromones of Dendroctonus frontalis, frontalin and trans-verbenol, and of Ips spp., ipsdienol and ipsenol. Among females, more cells responded to trans-verbenol and the Ips-produced volatiles than to host or other D. frontalis-produced compounds. Olfactory cells of males responded mostly to cis-verbenol, followed by alpha-pinene, verbenone, trans-verbenol, and endo-brevicomin. Of those cells responsive primarily to one compound, the greatest percentage were responsive to trans-verbenol in females and to verbenone in males. The response of the antennal olfactory receptor cells to semiochemicals used by male and female I. grandicollis is consistent with the presence of these compounds during the host colonization period for each sex. Our results, which show a lack of specificity in most pheromone and host odor receptor cells, is in contrast with previously published accounts of olfactory receptor cell specificity in other Ips species.