We investigated the effect of feeding by the western conifer-seed bug, Leptoglossus occidentalis Heidemann, on seed production in developing cones of coastal Douglas-fir, Pseudostuga menziesii (Mirb.) Franco, with respect to seed bug life stage and sex (nymphs, adult females, and adult males) and timing of feeding (early, mid-, and late season cone development). Feeding by females on caged cones for a 2-wk period during late season cone development reduced the proportion of full seeds in cones by ≈70% compared with caged control cones. There was no significant difference among nymphs, adult females, and adult males with respect to the proportion of empty or partially fed-upon seeds produced during the same feeding period. Feeding by nymphs for 2 wk early in the season resulted in a threefold increase in the number of unextractable seeds fused to cones compared with the control. Weight measurements of harvested seeds indicated that radiography is an accurate tool to distinguish among Douglas-fir seeds that have sustained light, moderate, or severe damage. Determining the full impact of L. occidentalis on conifer seed production will require the development of a reliable method to distinguish between naturally aborted seeds and seeds emptied through feeding by seed bugs.