Bacillus thuringiensis is a soil-dwelling bacterium that targets a specific group of insects, including butterflies, moths, . Bt is safe for humans and is the most widely used environmentally-friendly bio-pesticide worldwide. 

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There are several strains of Bt and each one acts on a slightly different group of insects. For example, Bacillus thuringiensis var. kurstaki (Btk) is toxic only to larvae of the butterflies and moths (Lepidoptera), while Bacillus thuringiensis var. israelensis (Bti) kills the larvae of certain flies and mosquitoes – before they become biting adults.

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Bt kurstaki is available as either a liquid or a powder. Use it to control pests such as tomato hornworms, tent caterpillars, and webworms.

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Bt israelensis kills mosquito larva. It's available in donut-shaped chunks -- or dunks designed to be placed in ponds, bird baths, and any other places where there may be standing water. Mosquito Bits deliver it in the form of a granule that can be sprinkled on the soil in flower beds and even on lawns.