PITYOPHTHORUS ORARIUS BRIGHT (COLEOPTERA: SCOLYTIDAE) IN A NORTHERN CALIFORNIA DOUGLAS-FIR SEED ORCHARD: EFFECT OF CLONE, TREE VIGOR, AND CONE CROP ON RATE OF ATTACK

Abstract

AbstractThe geographic range of the Douglas-fir twig beetle, Pityophthorus orarius Bright, was extended beyond the original provenance of southern British Columbia to northern California. A survey of 457 Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] trees in 1985 revealed that those with heavy cone crops were more likely to be infested by twig beetles than were those with a light crop. Furthermore, attack rates differed among clones. A second survey done in 1987 confirmed the importance of clone and cone crop in attack rate. In this survey, stressed trees were attacked at a higher rate than unstressed trees. Beetle distributions appeared clumped in both surveys, possibly because of semio-chemicals or oviposition behavior.