Why do the toxic insecticide proteins secreted by Bacillus thuringiensis kill insects?

Explanation

Bacillus thuringiensis (Bt) is a soil borne, Gram positive bacterium. It is used to create transgenic plants having resistance to different pests. The genes having insecticidal properties in the bacterium are isolated and incorporated into plants by using advanced biotechnological methods to create Bt plants. During sporulation, many Bt strains produce crystal proteins (proteinaceous inclusions) called `delta`-endotoxins that have insecticidal action. When consumed by insect, these toxins bind to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis, leading to the death of an insect, e.g., Bt cotton, Bt tomato, soyabean, coffee, etc.