Some naturally occurring pathogens of insects have been produced and formulated as microbial insecticides. By far the most widely used microbial insecticide is Bacillus thuringiensis, sold as Dipel, Thuricide and Sok-Bt. This bacterium produces spores containing a toxin that is deadly to many lepidoptera larvae (butterfly and moth caterpillars). The toxin crystal dissolves only under the high gut pH conditions found in caterpillar digestive systems. B. t. is not toxic to mammals and has little effect on most natural enemies, so it is strongly promoted for use in IPM programs designed to preserve natural enemies.
Two other microbial insecticides are commercially available but are not used on woody ornamentals: milky spore disease for Japanese beetle larvae, and B.t.i. for mosquito larvae.