Bark Beetles
Western Balsam Bark Beetle
Dryocoetes confusus (Swaine)

Host:  Subalpine fir (corkbark fir)

Figure 126. Figure 126. Egg gallery of western balsam bark beetle on corkbark fir. Egg galleries typically have five or more galleries radiating from a nuptial chamber.

Symptoms/Signs:  Small entrance holes and boring dust are usually difficult to detect on green standing trees, but pitch flow may be evident. Under the bark, egg galleries lightly etch the surface of the wood. Egg galleries radiate from a central nuptial chamber. Attacked trees generally turn yellow-red within a year. Needles on a beetle-killed fir may remain for more than 4 years. Adults are shiny, dark brown, cylindrical beetles about 2 to 5 mm long. The posterior end of the elytra is abruptly rounded with no spines.

Figure 127. Figure 127. Adult western balsam bark beetle. Note the "crew cut" appearance on front of beetle heads.
Figure 128a. Figure 128a. Corkbark fir mortality caused by western balsam bark beetle on the San Francisco Peaks, Arizona.
Figure 128b. Figure 128b. Corkbark fir mortality caused by western balsam bark beetle on the Sandia Mountains, New Mexico.

Biology:  Little is published on the biology of this species; however, it is thought to have a 1- to 2-year life cycle. The lower to mid bole of standing trees is usually selected for attack. This species is moderately aggressive and capable of killing older and/or weakened trees. Occasionally cut or fallen trees are attacked.

Effects:  The direct effect of successful attack is tree mortality.

Similar Insects and Diseases:  Other bark beetles attack subalpine fir, including species of Scolytus and Pseudohylesinus. They may be separated by gallery patterns and characteristics of adult beetles. Western balsam bark beetle attacks are frequently associated with fir infected by root diseases.

References:  24, 66, 116