Description:
Douglas-fir beetle, Dendroctonus pseudotsugae Hopk., has caused
extensive tree mortality in the North Fork Clearwater River drainage
since 1971. In 1974, survey estimates indicated a continued decline
in the infestation. Average group size decreased from a high of 158
trees per group in 1971 to 17 in 1974. Average area occupied by each
group declined from a high of 4.1 acres per group in 1972 to 0.65
acre in 1974. Attack densities decreased; however, brood-to-parent
ratios increased. Natural enemies are having a limited impact on
population densities. Availability of susceptible host material
may be the primary limiting factor on increased infestation
potential. Continued salvage logging of infested trees and
susceptible stands is encouraged.