There are about 500 species of bark beetles (Coleoptera: Curculionidae: Scolytinae) in the United States (Wood 1982). A number of them are important disturbance agents in forested ecosystems, occasionally creating large tracts of dead trees. One eruptive species is the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, which utilizes Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, as its primary host throughout most of the tree's range. The Douglas-fir beetle is univoltine with brood adults and larvae overwintering (Schmitz and Gibson 1996). The insect prefers to attack large diameter trees in high density stands often exhibiting reduced growth (Furniss et al. 1981; Negrón 1998; Negrón et al. 1999).