Role of Parasites in the Population Dynamics of the Western Spruce Budworm (Lepidoptera: Tortricidae) in the Northwest

The relation of parasitization to mortality during the generation ( KG ) or from instar IV to adults ( KL-A ) of western spruce budworm, Choristoneura occidentalis Freeman, is examined. Parasitization of budworm larvae and pupae was studied over a wide range of densities (0.3–48.3 larvae per m2 and 0.1–22.6 pupae per m2) at sites in Washington, Oregon, Idaho, and Montana. We found that parasites contributed about 9% of the variation affecting generation change, KG , and about 24% of variation in mortality during the interval from larvae to adults, KL-A .