Analyses of the enantiomeric composition of ipsdienol produced by individual male pine engravers, Ips pini (Say), from six populations in British Columbia, support the hypothesis that New York and Idaho races of this species hybridize in southeastern British Columbia. Production profiles, expressed as frequency distributions of (+):(-) ipsdienol ratios [= ratio of (S)-(+)-ipsdienol to (R)-(-)-ipsdienol], were bimodal for four western British Columbia populations. The (+):(-) ratios ranged from 63:37 to 71:29, consistent with those previously found for the New York race. The profile for a southeastern population from Radium, British Columbia, was intermediate between those for the four western British Columbia populations and that from one population in Kimberley, British Columbia, just south of Radium. Males in the Kimberley population produce predominantly (R)-(-)-ipsdienol, typical of California and Idaho males. Response profiles of different individuals of I. pini, determined by captures of beetles in multiple-funnel traps baited with ipsdienol of 11 different(+):(-) ratios, were not consistent with production profiles. Populations in Williams Lake and Princeton, in western British Columbia, and Radium, in southeastern British Columbia, had response profiles with maximal attraction to ipsdienol over a broad range of (+):(-) ratios, falling off as enantiomeric purity was approached at either end of the spectrum. This type of response profile is consistent with that for the New York race, which has been shown to respond optimally to (+):(-) ratios ranging from 40:60 to 70:30. The response profile of the Kimberley population gradually declined from maximal attraction to ipsdienol with a (+):(-) ratio of 2:98 to the lowest response at a (+):(-) ratio of 98:2. The attraction of I. pini to chemical stimuli in California is interrupted by ipsdienol with a (+):(-) ratio > 5:95, a pheromone of a host competitor, the California five-spined ips, Ips paraconfusus Lanier. We hypothesize that the Idaho race, which does not compete with I. paraconfusus due to geographical separation, is characterized by a Kimberley-type enantiomeric response profile, intermediate between those of the New York and California races.
