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Native to western North America, this wood boring insect has been responsible for significant losses of alpine fir (estimated in the millions of cubic metres). The range of this insect overlays that of its primary host, alpine fir, stretching as far south as Arizona and New Mexico and east to Alberta. It will also occasionally attack amabilis fir with rare instances of attacks on white spruce and Engelmann spruce. Males are attracted to a primary chemical attractant produced by the living tree. They then proceed to bore nuptial chambers beneath the bark and release a secondary attractant, drawing the females to the chambers. The greater percentage of the damage caused by this insect actually results from the introduction of a closely associated lesion-causing fungus, blue stain (Ceratocystis dryocoetidis), carried on the beetle. Although initial beetle attacks are usually pitched out by the tree, successful introduction of the fungus into the phloem facilitates subsequent beetle attacks. Once introduced, this fungus causes coalescing lesions that can girdle and eventually kill the tree, even without further beetle attack.

Points of interest

• from 1956 to 1965, this was the most destructive insect pest in the province of British Columbia
• ground detection of attack by this insect is difficult due to the lack of obvious pitch tubes as seen with other bark beetles
• females usually lay three broods within 1 year
• development from egg to adult generally takes 2 years
• average of mature larval or full-grown length is 3–4 mm

References

Garbutt, R. 1992. Western Balsam Bark Beetle. Forestry Canada, Pacific Forestry Centre, Victoria, B.C. Forest Pest Leaflet 64. 4 p.