The Douglas-fir beetle (Dendroctonus pseudotsugae) is the principal killer of mature Douglas-fir in B.C. It usually attacks weakened or dying trees, but occasionally its populations increase to the extent that it infests and kills large numbers of healthy trees. Aerial overview surveys recorded 47,628 hectares of damage in 2015.
This beetle is most common in B.C.'s Interior. Though it can be found in coastal forests, it rarely causes the large-scale damage seen inland.
It attacks its host in early summer. The beetle usually attacks weakened trees (e.g., drought or wildfire damage) or trees blown down by windstorms. When it attacks healthy trees, it targets the largest and oldest first — those most valued as wildlife habitat, particularly for mule deer winter range.
Adult Douglas-fir beetles are dark brown to black with reddish wing covers, and are tiny (about 4.4 to 7 millimetres long). The life cycle is usually one year, and two broods may be produced.
Native to North America, this insect is found throughout the range of the Douglas-fir, its principal host.
Strategy depends on infestation size, stand susceptibility and other factors. Detection involves walkthroughs, probes and star probes (a type of ground probe). Treatment can involve sanitation harvesting, trap trees and other techniques.
Tree Species Attacked
Large diameter, mature Douglas-fir trees are attacked; also, occasionally, downed western larch. Trees are killed when the flow of food and water between roots and needles is blocked by feeding larvae and by dead sapwood cells killed by the blue-stain fungi carried by the Douglas-fir beetle adults.
Recently attacked trees are difficult to identify except for reddish brown boring dust that may accumulate on the trunk and in bark crevices. Foliage of killed trees turns from green to pale yellow-green to red by the spring of the year following the attack.