Western balsam bark beetle, Dryocoetes confusus Swaine (Coleoptera: Curculionidae: Scolytinae), in situ development and seasonal flight periodicity in southern British Columbia

Abstract

In situ development and seasonal flight periodicity of the western balsam bark beetle, Dryocoetes confusus Swaine, was observed in subalpine fir, Abies lasiocarpa (Hook) Nutt. stands in southern British Columbia for three years between 1998 and 2002. This study shows developmental differences of western balsam bark beetle in downed and in standing, live subalpine fir. Larval development was slower in the downed trees. Recorded daily minimum phloem temperatures were significantly lower for downed trees than for standing trees during periods of beetle development and flight. There were no significant differences in the recorded daily maximum phloem temperatures between standing and downed trees until late summer, when downed trees saw cooler daily maximum phloem temperatures. This cooler host habitat would provide fewer degree days for insect development. Three distinct larval instars were identified by head capsule measurement. There were two flights per season, the first and major flight occurring from late June to late July, and the other smaller flight occurring in late August. A combination of minimum daily phloem temperatures reaching 5° C and maximum daily phloem temperatures approaching 20° C appeared to trigger the onset of beetle flight, with flight initiated earlier in the season at lower elevations.