Bacillus thuringiensis produce protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein. These proteins exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to alkaline pH of the gut which solubilizes the crystals. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually cause death of insect.