Temperature requirements for western balsam bark beetle (Dryocoetes confusus Swaine (Coleoptera: Curculionidae: Scolytinae) development in southern British Columbia

Abstract

The western balsam bark beetle, Dryocoetes confusus, is the primary biotic disturbance that is causing accelerated subalpine fir mortality in northern and high elevation forests in southern British Columbia.  B.C.’s climate has warmed dramatically over recent decades and is affecting many biological processes including those of D. confusus and its host subalpine fir.  D. confusus generally undergoes a two-year life cycle, with larvae and teneral adults each overwintering once.  To determine if it could have a univoltine life cycle, we reared D. confusus from field and laboratory-infested logs at five constant temperature regimes between 18°C and 24°C, with and without cold treatments.  In the coolest 18°C regime, development was arrested in the late larval stage indicating that an environmental cue was needed for development to proceed or not.  At temperatures higher than 21°C D. confusus displayed continuous development to teneral adult and emergence without requiring a cold period.  Our results demonstrate that D. confusus does not have an obligatory diapause, requiring 1,200 degree-days to complete development and that under warming field conditions it may be able to switch to a univoltine life cycle.  A life cycle contraction could have enormous implications to the future health of subalpine fir forests.