Pest description and damage Adults are black and about 0.25 inch long. Larvae are white and found under the bark in straight galleries. The mountain pine beetle attacks pine trees (trunks and branches) 4 or 5 inches in diameter or larger. The adults and larvae mine the bark, weakening and girdling trees. Heavily infested trees may decline or die. Red sawdust on the bark and ground and pitching on the trunk or large branches may indicate the presence of these bark beetles. Bark beetles typically attack weakened trees. Lodgepole pine is the preferred host, but other pines also are attacked. This insect is ranked as the most destructive of the bark beetles.
Biology and life history The insects overwinter as larvae or adults under the bark of the host tree. In the spring, adults emerge, fly to a new host tree and excavate galleries in the bark. Eggs are deposited singly along the gallery on alternate sides. When the eggs hatch in a few days, the small white larvae excavate short feeding tunnels at right angles to the gallery. When fully grown, the larvae construct small pupal cells at the ends of the larval mines and then emerge as adults the next spring. One generation per year is the general rule.
Pest monitoring Look for pitch tubes and red boring dust in bark crevices and on the ground.
Healthy trees are better able to resist borer infestations, so use proper watering, fertilizing, and pruning practices. Remove heavily infested trees to protect healthy adjacent ones.