Covering the Foothills & Mountains West of Denver

Mountain Pine Beetles

Quick Facts About Mountain Pine Beetles

  • Mountain pine beetle is the most important insect pest of Colorado's pine forests. Pine beetles kill large numbers of trees annually during outbreaks.
  • Trees that are not growing vigorously due to old age, crowding, poor growing conditions, drought, fire or mechanical damage, root disease and other causes are most likely to be attacked.
  • For a long-term remedy, thin susceptible stands with emphasis on leaving well-spaced healthy trees.
  • For short term controls, spray, burn, and peel attacked trees to kill the beetles. Preventive insecticide sprays can protect green, unattacked trees.

Mountain Pine Beetle larvae under the bark of a Ponderosa pine

About the Mountain Pine Beetle

Mountain pine beetle, Dendroctonus ponderosae, is an insect native to the forests of western North America. Previously called the Black Hills beetle or Rocky Mountain pine beetle, periodic outbreaks of the insect can result in losses of millions of trees.

Outbreaks develop irrespective of property lines, being equally evident in wilderness areas, mountain subdivisions, and back yards. Even windbreak or landscape pines many miles from the mountains can succumb to beetles imported in infested firewood.

How to Identify Pine Beetles

Mountain pine beetles develop in pines, particularly ponderosa, lodgepole, Scots (Scotch), and limber pine. Bristlecone and pinyon pine are less commonly attached.

During early stages of an outbreak, attacks are limited largely to trees under stress from injury, poor site conditions, fire damage, overcrowding, root disease, or old age. However, as beetle populations increase, mountain pine beetle attacks may involve most trees in the outbreak area.

A related insect, the Douglas-fir beetle (Dendroctonus pseudotsugae), occasionally damages Douglas-fir.

Pitch tube forming on Ponderosa pine

Most often, outbreaks are associated with previous injury by western spruce budworm. The spruce beetle (Dendroctonus rufipennis) is a pest of Engelmann and blue spruce in Colorado. Injured pines also can be attacked by the red turpentine beetle (Dendroctonus valens).

Mountain pine beetles, and other bark beetles in the genus Dendroctonus, can be separated from other bark beetles by the shape of the hind wing cover. In side view, it is gradually curved. The wing cover of Ips or engraver beetles, another common group of bark beetles attacking conifers, is sharply spined. In Scolytus beetles, such as the shothole borers and European elm bark beetle, the area under the wing cover (abdomen) is indented.

Mountain Pine Beetle Update

When treating pine beetle infested logs, the most common treatment has always involved the use of the insecticide "Lindane." Sometimes the logs are covered with plastic as well. Since the last beetle outbreak on the 1970's, Lindane has been banned in most forms. Because of this, and to be more environmentally friendly, we now use a solar treatment on infested logs as outlined by the U.S. Forest Service.

Pine Beetle Winter Identification

Pitch tubes caused by Mountain Pine Beetle

The best time to check for Pine Beetle attack is in winter. Check for "pitch tubes" on the trunks of your trees. If you see pitch tubes, cut a piece of bark off and see if the wood under the bark is discolored bluish-gray. If so, the tree(s) need to be removed. LAM Tree Service is available in winter to inspect your property for beetles. We charge an hourly fee for this service.


To help you identify these destructive pests (and to see how we do it when we're called to evaluate pines on your property), check out this brief video of Ryan Reed removing the bark and pointing out beetle galleries.