AGGREGATION PHEROMONE OF PITYOGENES KNECHTELI AND SEMIOCHEMICAL-BASEDINTERACTIONS WITH 3 OTHER BARK BEETLES

Gas chromatographic-electroantennographic detection and GC-mass spectr ometric analyses of volatile extracts from male and female Pityogenes knechteli Swaine identified hexanol, (+/-)-ipsdienol, and (S)-(-)-ipse nol as male-produced candidate pheromone components. In a lodgepole pi ne, Pinus contorta var. latifolia Engelmann, forest in the southern in terior of British Columbia, multiple-funnel traps baited with (+/-)-ip sdienol alone, (S)-(-)-ipsenol alone, or both caught 60%, 6%, and 23%, respectively, of all P. knechteli trapped; unbaited traps caught the remaining 11%. In another field trapping experiment, (S)-(+)-ipsdienol was as attractive as (+)-ipsdienol, and (R)-(-)-ipsdienol was behavio rally benign. (S)-(+)-Ipsdienol is thus concluded to be the principal aggregation pheromone component of P. knechteli. At low release rates, hexanol increased attraction of beetles to (+/-)-ipsdienol, or to (+/ -)-ipsidienol plus (S)-(-)-ipsenol, but at high release rates hexanol decreased attraction, suggesting a role in preventing overpopulation i n the host tree. On the basis of laboratory bioassays in which walking beetles were attracted to (S)-(-)-ipsenol, we hypothesize that (S)-(- )-ipsenol serves as a short-range attractant for P. knechteli. Three s ympatric scolytids were also captured in field experiments as follows: the pine engraver, Ips pini (Say), to its pheromone (+/-)-ipsdienol; I. latidens LeConte to its pheromone (S)-(-)-ipsenol; and I. mexicanus (Hopkins), for which the pheromone is unknown, to (S)-(-)-ipsenol wit h (+/-)-ipsdienol. Although all four species attack lodgepole pine, we have never observed I. latidens or I. mexicanus attacking the same ho sts at P. knechteli or I. pini. These results suggest that ipsenol and ipsdienol serve as synomones involved in promoting aggregation on the host tree, maintaining species-specific communication, and thus contr ibuting to resource partitioning and reduced competition among the fou r species.