Bt cotton was the first genetically modified plant in India, which produces an insecticide to combat bollworms.
Bt toxin is commonly used to produce insecticide-resistant GM crops that can kill certain insects such as dipterans, coleopterans, and lepidopterans.
Bt toxin gene called the cry gene has been isolated from the bacterium, Bacillus thuriengiensis and introduced into the cotton, corn, rice, potato, tomato and soyabean plants, where it encodes for a toxin, that protects the crop from insects such as bollworms and corn borers. There are a number of such genes for instance, the proteins encoded by gene cryIAc and cryIIAb controls cotton bollworm and that of cryIAb controls corn borer.
This toxin exists in an inactive form called protoxins, but the inactive form gets converted into an active form in the alkaline pH of the insect gut, that solubilizes the crystals. This activated form of toxin binds to the midgut epithelial cells and create pores that causes death of the insect.