Bacillus Thuringiensis (Bt) is a soil-dwelling bacterium that occurs naturally in the environment. It produces Crytoxins that are lethal to specific insects so it is useful in pest control. Bt is used to control mosquitoes and some other flying insects, beetles, certain types of worms, and caterpillars. Bt can be applied on a variety of crops, trees, shrubs, and gardens. Bacillus Thuringiensis is the key ingredient in products such as Bonide Thuricide and Mosquito Dunks.