Co-baiting for spruce beetles, Dendroctonus rufipennis, and western balsam bark beetles, Dryocoetes confusus (Coleoptera: Scolytidae)

Co-baiting to contain and concentrate the spruce beetle, Dendroctonus rufipennis (Kirby), and the western balsam bark beetle, Dryocoetes confusus Swaine, was investigated at four locations in British Columbia. Two 9-ha areas were established at each location; one was baited and the other left as a control. Single "interior firs," Abies bifolia A. Murray × Abies lasiocarpa (Hook.) Nutt., or groups of two or three trees, were baited with (±)-exo-brevicomin released at 1.0 mg/24 h. "Interior spruces," Picea engelmannii Engelm. ex Parry × Picea glauca (Moench) Voss, were baited with frontalin released at 0.1, 0.6, or 2.5 mg/24 h, or at 0.6 mg/24 h with alpha-pinene, ethanol, or ethyl crotonate. Another experiment investigated possible interspecific interference between D. confusus and D. rufipennis baits. Ratios of currently attacked "green" trees to previously attacked "red" trees for both insects were significantly higher in baited than in control areas, indicating that populations were contained. Baiting, however, did not attract either insect from a zone surrounding each baited area. There was a significant increase in D. confusus attack when two trees instead of one were baited per centre, no increase in D. rufipennis attack when frontalin was released alone or with the potential adjuvants, no effect of frontalin release rates on the percentage of trees attacked by D. rufipennis, and no indication of cross-repellency between baits.