CONTAINMENT AND CONCENTRATION OF INFESTATIONS OF THE WESTERN BALSAM BARK BEETLE, DRYOCOETES-CONFUSUS (COLEOPTERA, SCOLYTIDAE), USING THE AGGREGATION PHEROMONE EXO-BREVICOMIN

Containment and concentration of infestations of the western balsam ba rk beetle, Dryocoetes confusus Swaine, was demonstrated when (+/-)-exo -brevicomin released at 0.4 mg/24 h was applied to single subalpine fi rs, Abies lasiocarpa (Hook.) Nutt., on a 50-m grid over 9-ha blocks, o r released at 0.8 mg (24 h/tree)-1 applied to two trees at 50-m centre s over the central 4 ha of 16-ha blocks. Nearest-neighbour distance be tween red trees and newly mass-attacked trees was 24 m in the central 4 ha of baited 16-ha blocks, compared with 13.8 m in control blocks, s uggesting a movement of beetles away froin ''normal'' attack centres. Treatments with exo-brevicomin at two trees per spot concentrated 89% of newly mass-attacked trees within 10 m of baited trees, clearly indi cating the potential for semiochemical-based management of D. confusus . Within-stand distribution of attacked trees was highly aggregated (C lark-Evans test), in both treated and control blocks. The highly aggre gated pattern of attack in control blocks could have been a product of stand structure, and it is hypothesized that D. confusus plays a role in the regeneration of its host by initiating small gaps that favour subalpine fir reproduction. If so, there is potential for using semioc hemicals to manipulate D. confusus populations within a patch or selec tion logging system to maintain cover in climax subalpine forests.