Douglas-Fir Beetle

The Douglas-fir beetle (Dendroctonus pseudotsuqae Hopk.) infests and kills Douglas-fir throughout most of its range in western United States British Columbia and Mexico. Occasionally western larch trees are infested when growing among Douglas-fir under attack. Attacks in standing larch are always unsuccessful, while those in freshly felled larch are usually successful and brood emergence is equivalent to that in Douglas-fir. Douglas-fir beetles normally kill small groups of trees, but during outbreaks 100 tree groups are not uncommon (fig. 1). Losses can be devastating during periodic outbreaks, such as four that occurred in western Oregon and Washington from 1950 through 1969, during which 7.4 billion board feet of timber were killed. Outbreaks in standing trees range from 2 to 4 years. Those of longest duration coincide with periods of drought. For example, thousands of acres of Douglas-fir supported outbreaks in several western states following a drought from 1986 through 1988. In 1966, an outbreak in California killed 800 million board feet of timber and an outbreak in Idaho killed 109 million board feet of Douglas-fir between 1970 and 1973