Douglas-fir beetle-infested Douglas-fir trees were partially caged to determine the emergence period and beetle production. Beetles began emerging in April, but emergence peaked between 10 and 26 June. In 1987 and 1988 beetle emergence averaged 20 or more per sq. ft. of bark. Annual growth of the infested trees showed a decline prior to the beetle outbreak followed by an increase during the outbreak.
Lessard, E. D. and Schmid, J. M.
"Emergence, attack densities, and host relationships for the Douglas-fir beetle (Dendroctonus pseudotsugae Hopkins) in northern Colorado,"
Great Basin Naturalist: Vol. 50
, Article 7.
Available at: http://scholarsarchive.byu.edu/gbn/vol50/iss4/7