How is Bacillius thuringiensis useful in biocontrol of insect pests?

Explanation

B. thruingiensis forms protein crystals (cry protein) during a particular phase of their growth. These crystals contain toxic insecticidal protein called Bt toxin protein. This protein does not kill the bacterium because it exists as inactive protoxins. Once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the alimentary canal which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and finally cause death of the insect.
The specific genes coding for Bt toxin were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton. The choice of genes depend upon the crop and targeted pest, as most Bt toxins are insect-group specific. The toxin is coded by a gene named .cry.. There are number of cry genes. For example, the proteins encoded by the genes cry I Ac and cry II Ab control the cotton bollworms (Helicoperpa armigera) and cry IAD controls corn borer.