Synthetic chemicals have largely been responsible for accomplishing the task but the agricultural industry has more recently started a biological warfare campaign against insects with an organism known as Bacillus thuringiensis, or the Bt toxin. What is Bacillus thuringiensis? Bacillus thuringiensis (Bt) is a bacteria that produces proteins which are toxic to insects. Bt’s extreme toxicity comes at no surprise. It’s in the same family of bacteria as B. anthracis, which causes anthrax, and B. cereus, which causes food poisoning. What is Bt Used For?