In laboratory experiments adults and nymphs of the western conifer seed bug, Leptoglossus occidentalis Heidemann, were allowed to feed on mature seeds of Douglas-fir, Pseudotsuga menziesii (Mirbel) Franco. Weight-loss measurements and scanning electron microscopy provided strong supporting evidence for the use of simple radiographic diagnosis as a method of classifying feeding damage to seeds into four categories: light (greater than two thirds of seed contents remaining), moderate (one third to two thirds of seed contents remaining), severe (less than one third of seed contents remaining), and extreme (seed empty). Scanning electron micrographs showed the apparent depletion of lipid and protein storage reserves which was verified by quantitative analyses that showed significant loss of lipid and buffer-insoluble (crystalloid) storage protein from seeds in all damage categories. The amount of buffer-soluble (matrix) protein was reduced in seeds from the severe and extreme damage categories. The increase in buffer-soluble protein observed in lightly damaged seeds was likely due to the solubilization of crystalloid storage protein, as a result of its breakdown into smaller peptides. Our results suggest that through the action of both lipases and proteases, L. occidentalis can have a serious impact on the major storage reserves of conifer seeds. Moreover, our data suggest that L. occidentalis feeds in a different manner than the laceration and flushing method found in other seed-feeding Hemiptera.