Brood densities of Douglas-fir beetle (DFB), Dendroctonus pseudotsugae Hopkins, in green trees adjoining areas burned by the 1988 Clover Mist Fire varied by site, but averaged 8 per 36 sq. in. for bark samples at all sites examined during November 1991. Brood densities were much reduced from 1990 levels, but were similar to densities found in blackened trees in fall 1989. The reduction from 1990 levels was attributed to heavy winter mortality of brood caused by prolonged extreme cold temperatures. Most brood in fall 1991 samples was present in the callow adult stage, similar to 1989 samples, and in contrast to 1990 samples when many immatures were detected. Gallery starts and total gallery length per 36 sq. in. bark sample averaged 2.3 and 23 in., respectively, indicating high attack densities and full occupancy of the food resource. About 2-3 DFB survived to fall 1991 per attacking female. Natural enemies were 10-40 times more abundant in bark samples in fall 1991 compared to fall 1990.
In the absence of severe winter temperatures, the DFB population can be expected to increase 1.5 to 3 times from 1991 to 1992. Management alternatives to reduce the impact of the DFB epidemic are discussed and prompt treatment of infested trees is recommended where feasible.
- Douglas-fir beetle,
- Dendroctonus pseudotsugae,
- forest fire
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