Soil bacterium Bacillus thuringiensis (Bt) possesses is a gene family cry gene (1-40) over its plasmid, which forms an endotoxic proteins, cry protein (protein crystals) during a particular phase of its growth. These crystals contain a toxic insecticidal protein. This toxin, however does not kill the Bacillus. Actually, the Bt toxin protein exists as inactive protoxins but once an insect ingests the inactive toxin, it is converted into an active form of toxin due to the alkaline $\mathrm{pH}$ of the gut which solubilise the crystals. The activated toxin binds to the surface of midgut epithelial cells and creates pores that cause cell swelling and lysis, and eventually cause death of the insect.