Reducing spruce beetle Dendroctonus rufipennis (Kirby) (Coleoptera: Curculionidae) emergence for hibernation in central British Columbia by felling infested trees

Sanitation harvesting for the removal, processing and killing of spruce beetle in infested trees the year after attack is often only partially effective because a significant percentage of beetles emerge from standing trees in the autumn and drop down to the root collar to hibernate under the bark below the duff line. When trees are harvested, these beetles are left behind in stump root collars. We hypothesized that falling of spruce beetle-infested standing trees, in the second summer (before pre-hibernation emergence of beetles), can increase the window of opportunity for sanitation harvesting and extract more beetles from the forest. Thirty Engelmann spruce that had been successfully infested by spruce beetle on a 2-year life cycle in 1995 were selected at each of two locations in the central interior of British Columbia in 1996. At each site, 10 replicates of three treatments were randomly applied. Ten spruce were felled from 29 May to 10 June (early treatment), 10 were felled on 8 August (late treatment) and the remaining 10 were left standing. In mid-August, a pair of nylon screening emergence traps were attached to all trees to capture any immature adults emerging for hibernation. Emergence traps and underlying phloem were collected in late September to early October and revealed that 48–62% of immature adults emerged for hibernation from standing trees, whereas significantly fewer (7–17%) emerged from felled trees. We conclude that, if sanitation harvesting of 2-year cycle spruce beetle-infested spruce cannot occur until the second winter, pre-harvest felling of these trees in the second year can reduce emergence for hibernation by 69–88% and allow the extraction of more beetles over a longer period.