none Females of parasitic wasp Bracon hebetor Say killed 19% of Spodoptera littoralis Boisd. 3rd instar larvae in laboratory bioassays. However, prior ingestion by the larvae with a sublethal dose of Bacillus thuringiensis ssp. entomocidus increased their mortality to 70%. On cotton plants in the greenhouse, there was some increase in mortality by the combined treatment of B. thuringiensis and Bracon hebetor, and the leaf area consumed by the surviving larvae was significantly smaller than that consumed in each of the separate treatments.