Fields trials in northern Ontario in 1990 and 1991 confirmed that survival of spruce budworm larvae (Choristoneura fumiferana (Clemens)) (Lepidoptera: Tortricidae) parasitized by Apanteles fumiferanae Viereck (Hymenoptera: Braconidae) was greater than survival of nonparasitized budworm larvae following application of Bacillus thuringiensis var. kurstaki Berliner (Bt ). Apparent parasitism by A. fumiferanae increased slightly when application of Bt was early (instar III or IV) but increased significantly when applications were later in the season (instars IV-VI). Delaying the timing of the spray conserved parasitoids while providing significant reductions in budworm densities and not compromising the primary objective of Bt application, i.e. the protection of current year foliage. The potential for long-term management of spruce budworm through the strategic integration of natural and imposed mortalities is discussed. missing