To determine the optimal ratio of Bacillus thuringiensis delta-endotoxins Cry1Aa, Cry1Ac, and Cry2Aa bioinsecticide formulations, and for development of novel biopesticides based on B. thuringiensis, the toxicities of these three proteins, individually and in combinations, have been determined against the Mediterranean flour moth, Ephestia kuehniella. While B. thuringiensis crystals containing a mixture of Cry1Aa, Cry1Ac, and Cry2Aa displayed toxicity with an LC50 and LC95 of 109.7 and 463.0 ng of toxin per mg flour, respectively, when used individually or in combination, Cry1Aa, Cry1Ac, and Cry2Aa showed significantly lower activity. Thus, it is clear that synthesis of these toxins together in the wild strain is more efficient than a mixture of them.