Bt cotton plants are transgenic plants having the gene of Bacillus thuringiensis bacteria produce a toxic protein that kill insects of lepidopterons (tobacco, budworms) beetles, flies, moth etc. This toxin is actually a protein crystals which are formed in bacteria in certain phase of growth. Bacteria produced protein crystals are insoluble in bacteria and no longer harmful but when these crystals reached to the alkaline medium of larvae gut, crystals solubilised in epithelial cell and get activated. So that insecticidal protein kill the insect larvae.