WITHIN-TREE DYNAMICS OF MASS ATTACK BY DENDROCTONUS PSEUDOTSUGAE (COLEOPTERA: SCOLYTIDAE) ON ITS HOST

Abstract

AbstractThe within-tree scale dynamics of mass attack by the Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, on its host were investigated and quantified. Seven similarly sized Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco (Pinaceae), infested as part of several pheromone-induced infestations, were monitored over an entire attack season. Ninety percent of the attacks on mass-attacked trees occurred within 3 weeks of colonization; the remaining 10% occurred gradually over the remaining 7 weeks of the attack season. Vertical attack distribution followed a Gaussian form that shifted upwards on the bole with increasing attack density. The change in attack pattern associated with increasing attack density was investigated for the central vertical portion of the bole, where most attacks occurred, and where the vertical pattern was least variable. At low density, attacks were randomly distributed. As density increased, the distance between attacks decreased, eventually resulting in a uniform distribution.