The effect ofLygus hesperusKnight feeding on Douglas-fir seedlings was measured in seedlings representing two elevation zones, for each of two seed zones, for each of two seedling age classes in a forest nursery during 1984. Damage frequency and height reduction both indicated significant effects of seed source. Examination of seedling distance from the nursery's west boundary with an alfalfa field (a major source ofL. hesperusin the nursery) indicated a significant effect of proximity to alternate hosts. These results suggest that seedling susceptibility to damage byL. hesperusis a function of seedling condition and location within the vegetation matrix.