Within-tree dynamics of mass attack by Dendroctonus pseudotsugae (Coleoptera : Scolytidae) on its host

The within-tree scale dynamics of mass attack by the Douglas-fir beetle, De ndroctonus pseudotsugae Hopkins, on its host were investigated and quantifi ed. Seven similarly sized Douglas-fir, Pseudotsuga menziesii (Mirb.) France (Pinaceae), infested as part of several pheromone-induced infestations, we re monitored over an entire attack season. Ninety percent of the attacks on mass-attacked toes occurred within 3 weeks of colonization; the remaining 10% occurred gradually over the remaining 7 weeks of the attack season. Ver tical attack distribution followed a Gaussian form that shifted upwards on the hole with increasing attack density. The change in attack pattern assoc iated with increasing attack density was investigated for the central verti cal portion of the bole, where most attacks occurred, and where the vertica l pattern was least variable. At low density, attacks were randomly distrib uted. As density increased, the distance between attacks decreased, eventua lly resulting in a uniform distribution.