Figure 1

Damage caused by Balsam Fir Beetles.

Figure 2
Adult Beetle

The western balsam bark beetle is the most conspicuous of a complex of pests which are responsible for high amounts of tree mortality in sub-alpine fir stands throughout Colorado.

Hosts. - Sub-alpine fir., Engelmann spruce, and lodgepole pine may be attacked.

Damage. - Low populations maintain themselves in trees weakened by old age and root disease, storm-damaged trees, or slash. During periods of drought or other environmental stress, infestations can build and spread to less-susceptible stands. Groups of 100 to 1,000 trees, generally of larger diameters, may be killed. An estimated 35 percent of sub-alpine fir mortality is due directly to attack by beetles.

Life history. – The Western Balsam Fir Beetle probably has a 2-year life cycle in much ofSummit and Eagle Counties. They probably overwinter as larvae under the bark the first year, continue development during spring and early summer, and overwinter the second year as nearly mature adults. Males bore into the phloem, excavate a nuptial chamber and mate with several females. Egg galleries radiate from the central nuptial chamber in a random pattern. Larvae extend their mines from the main egg galleries until freezing weather, then become dormant..

Identification. – Unlike the mountain pine beetle that leaves a popcorn shaped pitch tube the Western Balsam Fir Beetles are identified by long dribbles of yellow pitch.  , Entrance holes and boring dust on the bark may be visible. Attacked trees generally turn yellowish-red within a year. Adults are shiny, dark brown, cylindrical beetles ranging from 3.4 to 4.3 mm long. Their thorax is evenly convex above; their posterior is abruptly rounded and without spines. The front of their head is covered with distinct bristles. Females have a denser patch of these 'hairs' than do males.

Management. - To keep beetle populations in control the best approach is to minimize broodwood by destroying slash and trees removed for construction. Weakened and beetle-infested trees or windthrown should be removed and the wood treated by peeling, chipping, burning or hauled to a safe location.