Which bacterium is used to make the insecticidal protein in the biological pesticide Bt?

Bacillus thuringiensis is used to make the insecticidal protein in the biological pesticide Bt.

B. thuringiensis produces crystal proteins, commonly called Cry proteins, during part of its life cycle. When susceptible insect larvae consume them, the proteins are activated in the alkaline insect gut and damage the gut lining, eventually killing the larvae.

Bt preparations have been used in agriculture and forestry for decades, especially against caterpillars and some other insect groups. Genes from B. thuringiensis have also been introduced into certain genetically modified crops so the plants can produce selected insecticidal proteins themselves.

Bt is not a general-purpose poison for every insect. Its effects depend on the particular protein, insect species, exposure, and resistance. The abbreviation “Bt” refers to the bacterium or its products, while “Bti” commonly refers to a strain used against mosquito and black-fly larvae.