Some of the characteristics of Bt cotton are 

• long fibre and resistance of aphids

• medium yield, long fibre and resistance to beetle pests

• high yield and production of toxic protein crystals which kill dipteran pests

• high yield and resistance to bolloworms

D.

high yield and resistance to bolloworms

Bacillus thuringiensis forms crystals containing a toxic insecticidal protein. Bt toxin protein exists as an inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut, which solubilises the crystals. The activated toxin binds to the surface of midgut epithelial cells and creates pores the cause cell swelling and lysis and eventually cause the death of the insect. Specific Bt toxin genes were isolated from B. thruingiensis and incorporated into the several plants such as cotton. The toxin is coded by the gene name cry. There is a number of them, eg, the proteins encoded by the genes cry IAc a cry II Ab control the cotton bollworms, that of cry IAB control corn borers.