Nature of Induced Attacks by the Black Hills Beetle, Dendroctonus ponderosae (Coleoptera: Scolytidae)

Attractants of Dendroctonus ponderosae Hopkins, made by attaching infested bolts to green trees or forcing attacks on such trees under screen cages, provided a means to study how the beetle attacks trees and stands. Attractant trees were always infested first; first attacks occurred below 8 ft, and generally below 4 ft. Initial attacks on adjacent trees, which occurred during the mass attack, appeared slightly higher on the trees but not higher than 10 ft. Subsequent attacks occurred below and above the initial attacks, with the mean height increasing with time. Trees became infested at progressively greater distances from the attractant center. Infested trees were significantly larger than green trees within the radius of infestation. The greatest number of attacks was recorded at the end of the 4 PM to 6 AM period.