Fir engraver damage in western Washington

Abstract

The fir engraver beetle (Scolytus ventralis) can cause significant damage and mortality to conifers in the Abies genus in western Washington. This small insect bores below the bark of trees and feeds on the sugar-rich phloem. In the process, they also cause severe damage to the cambium, the tissue responsible for annual diameter growth. If enough beetles feed on the tree, they will eventually girdle its circumference, cutting off nutrient flow and causing the tree to die. While this beetle is capable of killing trees, in western Washington it behaves as a secondary agent. This means it typically can only establish itself in trees dealing with a preexisting stressor, such as drought or a root disease. When trees are under significant stress, they are less able to defend themselves. Because of this, severe drought conditions in western Washington often correlate with a spike in fir engraver beetle populations. Since climate models predict hotter, drier summers in the coastal northwest, fir engraver damage and mortality may become more commonplace in the years to come