Mountain Pine Beetles

Quick Facts About Mountain Pine Beetles in Colorado

  • 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. The typical treatment window is from mid-May to late July.

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 attacked.

During early stages of an outbreak, attacks are limited largely to trees in poor health, such those 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 Treatment

There is no treatment to "cure" trees that have been infested by mountain pine beetles. The only solution is to cut down the trees and treat the logs to kill off any beetles that are still present.

However, it is possible to treat healthy trees that have not yet been attacked. This preventive insecticide is sprayed on pines to stop beetles from feeding and laying eggs, effectively stopping infestation in treated trees.

Call us at 303-674-8733 to learn more about mountain pine beetle treatment.

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 major 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 Identification is Easiest in Winter

Pitch tubes caused by Mountain Pine Beetle

The best time to check for mountain pine beetle infestation 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 you see this bluish-gray color under the bark, the tree(s) must be removed. Not doing so will allow the beetle to spread rapidly, not only to other trees on your property but to trees throughout the entire area.

The Certified Arborists at LAM Tree Service are available in winter (and all year round) to inspect your property for beetles. We charge an hourly fee for this service.


If you'd rather try to identify these destructive pests yourself (and to see how we do it when we're called to evaluate pines on your property), check out the brief video below. In it, Ryan Reed (owner of LAM Tree Service) shows you how to remove the bark and points out the beetle galleries beneath.