Larvae of the almond moth, Ephestia cautella (Walker), were highly susceptible to Bacillus thuringiensis Berliner in their diet if exposure began during the 1st stadium; they were less susceptible if exposure began dunng the later stadia. Larvae of the Indianmeal moth, Plodia interpunctella (Hübner), also were highly susceptible if exposure began during the 1st or 2nd stadium, but only the last (4th) stadium showed low susceptibility. B. thuringiensis caused a large increase in the development time of E. cautella larvae but caused little increase in that of P. interpunctella . The bacterium had no discernible effect on the sex ratio or reproductive capacity of moths that developed from surviving larvae.