Western Balsam bark beetle, dryocoetes confusus Swaine : impact and semiochemical-based management

Aerial and ground surveys disclosed approximately 28,800 ha of infestation by the western balsam bark beetle, Dryocoetes confusus Swaine, in mature forests of subalpine fir, Abies lasiocarpa (Hook.) Nutt. In north-central British Columbia. D. confusus caused mortality was estimated to be 1 m3/ha/yr, primarily concentrated on the largest and most valuable trees. Mortality was marginally within BC Forest Service acceptable loss estimates. Field experiments demonstrated that D. confusus responded optimally to 8-unit multiple funnel traps baited with mixtures of (+)- and (-) exo-brevicomin. exo-Brevicomin released at 0.8 mg/24 h induced mass attack on 80% of baited trees. Baiting of more than one tree in a spot increased attack intensity on baited trees. Within-stand seasonal flight patterns of D. confusus were monitored for three years in north-central British Columbia using multiple funnel traps baited with (±)-exo-brevicomin. There were two major flight periods per year, the first commencing in mid- to late June, and the second in mid- to late August. The second flight was composed primarily of females, probably reemerged parent adults. Very little flight occurred at temperatures < 15o C. Traps placed 6 m above ground caught four times as many beetles as traps placed 2 m above ground. Containment and concentration of D. confuses infestations was demonstrated when exo-brevicomin released at 0.4 mg/24 h was applied to trees on a 50 m grid over nine ha blocks, or released at 0.8 mg/24 h/tree and applied to two trees at each 50 m centre over the central four ha of 16 ha blocks. Within-stand distribution of attacked trees was highly aggregated (Clark-Evans test). Treatments with exo-brevicomin at two trees/spot concentrated 89 % of newly mass attacked trees within 10 m of baited trees. Laboratory and field experiments demonstrated that (+)-endo brevicomin is an antiaggregation pheromone for D. confusus, and that the (-) enantiomer was benign. (+) endo-Brevicomin prevented attack on subalpine fir trees baited with exo-brevicomin, while (±)-endo brevicomin reduced attack on felled trees by up to 93 %. Infestations in 1 ha blocks of standing forests treated at 10 m centres with (±)-endo-brevicomin decreased by 30%, even when four trees at 50 m centres were baited with (±)-exo-brevicomin.