The correct option is D Boll worms
B. thuringiensis is an insecticidal bacterium, which is used worldwide for controlling important plant pests including caterpillars of butterflies and moths, mosquito larvae, and simuliid black flies that cause river blindness in African strains. The vegetative cells contain the insecticidal protein toxin known as endotoxins. These are of two types - Cryo-endotoxins and Cytolytic endotoxins.These cryoendotoxins are most effective in managing the bollworm in Cotton.