Trunk-Implanted Acephate to Protect Douglas-Fir Seed Crops on Individual Trees in Northern California

Abstract

To reduce seed and cone insect damage, 0.875 g per capsule of acephate (technical grade) was implanted into individual Douglas-fir, Pseudotsuga menziesii (Mirb.) Franko, trees on 15 April or 6 May 1985. A spacing of one capsule per 10 cm of trunk circumference was used. Neither implant treatment affected actual infestation levels of a Douglas-fir cone gall midge, Contarinia oregonensis Foote, or a Douglas-fir seed chalcid, Megastigmus spermotrophus Wachtl. Both implant treatments, however, significantly reduced the damage of a fir coneworm, Dioryctria abietivorella (Grote), and the Douglas-fir cone moth, Barhara colfaxiana (Kearfott), by at least 62%. The latter implant significantly increased the number of filled seeds per cone by 154% compared with control trees, but the difference between implant treatment dates was not significant. Interspecific interaction between reduction of damage by Lepidoptera and the increase in C. oregonensis-damaged seeds and filled seeds suggests a negative association with reduced predation.