Biology
One or more species of bark beetle attack virtually all trees in the Pacific Northwest. Most bark beetles are secondary pests, attacking trees already stressed from other causes. However, one particular group, the terpentine beetles, attack the collar area of some conifers, and are considered primary pests. Bark beetles measure from 1/8" to 1/4" long, and may appear cylindrically-shaped, and shiny brown or black with a somewhat reddish tint. Adults, larvae, or pupae overwinter under bark. Adult beetles emerge in the spring (around May), leaving tiny "shotholes" in the bark. Some have more than one emergence period. Adults feed on bark, occasionally girdling and killing entire trees. After feeding, the adult beetle lays eggs in galleries under the bark of branches, trunks, or in branch crotches of diseased or weakened trees. Adults will also lay eggs in recently cut wood when the bark is intact. The adult galleries are typically arranged parallel to the grain of the wood, while the larvae make secondary galleries more or less perpendicular to the main gallery. Beetles emerging from trees will seek out and infest other trees. The beetles must be present in sufficient numbers to overcome the resistance of the host tree. Trees attacked by bark beetles rarely survive. Uniform, single-species stands of older trees are particularly susceptible.
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