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

Co-baiting to contain and concentrate the spruce beetle, Dendroctonus rufip ennis (Kirby), and the western balsam bark beetle, Dryocoetes confusus Swai ne, 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 c ontrol. Single "interior firs," Abies bifolia A. Murray x 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 E ngelm. ex Parry x Picea glauca (Moench) Voss, were baited with frontalin re leased at 0.1, 0.6, or 2.5 mg/24 h, or at 0.6 mg/24 h with alpha-pinene, et hanol, or ethyl crotonate. Another experiment investigated possible intersp ecific interference between D. confusus and D. rufipennis baits. Ratios of currently attacked "green" trees to previously attacked "red" trees for bot h insects were significantly higher in baited than in control areas, indica ting that populations were contained. Baiting, however, did not attract eit her insect from a zone surrounding each baited area. There was a significan t 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 rate s on the percentage of trees attacked by D. rufipennis, and no indication o f cross-repellency between baits.