Mortality of pupae ofApanteles fumiferanaeViereck andA. morrisi(Mason) that parasitize the jack pine budworm(Choristoneura pinusFreeman) was studied in the field for three years. Estimated mortality inflicted by hyperparasites, predators, and unknown sources was 63.9 and 58.2% in two successive years at one site. Hyperparasitism by various species varied both temporally and spatially in various microhabitats in jack pine stands. Mortality caused by one hyperparasite,Pteromalus phycidisAshmead, was dependent on local variation in density ofApantelesspp. pupae. The intensity of the density-dependent response was most evident when data were grouped by crown levels, and was reduced for larger or smaller habitat units.