Abstract
Parasporal crystals of Bacillus thuringiensis Berliner were 30X as toxic to larvae of Ephestia cautella (Walker) as were spores. The toxicity of spore-crystal mixtures was predictable from the number of crystals in the mixture. Parasporal crystals were only 3X as toxic as spores to Plodia interpunctella (Hübner) larvae, and a 50:50 mixture of spores and crystals was more toxic than crystals alone.