Illustrated Guide to Pests


Spruce beetle, Dendroctonus rufipennis

The spruce beetle is a highly destructive pest of mature spruce trees and is found throughout the range of spruce in the Kamloops Region. Sporadic outbreaks have killed extensive stands of spruce in the province and usually last 5 or more years. Outbreaks often occur when beetle populations build up to high levels in downed material and move on to attack live, mature, large diameter standing spruce. The beetle prefers stands composed of more than 65% spruce occurring in well-drained creek bottoms.

Host trees: Hosts of the spruce bark beetle include Engelmann (interior), white, sitka and occasionally black spruce. Preferred host materials consist of weakened or windthrown trees, stumps and large slash. Blowdown occurs naturally, but increases along the edges of roads, utility right-of-ways, and logged areas.

Description and life cycle: The spruce beetle usually has a 2 year life cycle, but can vary from 1-3 years depending on geographic location, elevation and climatic conditions. Adults are hard, stout-bodied, cylindrical, black-reddish black insects ranging in length from 4.0-7.0mm.

In late May to early July, females initiate attack by boring into a host tree and releasing a pheromone that attracts both sexes and ensures mass attack. Eggs are laid in galleries that extend upwards from the entrance hole parallel to the grain of the wood. At first the larvae bore out horizontally in groups. When they are one third grown they then form individual mines which often intersect to form fan-shaped galleries. The brood overwinters as late instar larvae. The following spring to early summer they pupate and become adults. In late August many of these new adults bore out of the tree and crawl or drop to the base of the tree where they again bore under the bark to overwinter. Spruce beetles must overwinter once as adults prior to attacking new host trees. The overwintered adults emerge and attack fresh host material from late May to early July.

Infested trees have red brown boring dust present in bark crevices and around the base. Small pitch tubes may form where beetles attack. Woodpeckers may remove bark in search of larvae, exposing red patches on the tree. Spruce may fade a yellow-red but this is not always evident.

Last updated on January 28, 2008
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