Bacillus thuringiensis (Bt) produces crystal proteins with insecticidal properties (ICPs) specific for certain insect pests, yet it has little or no toxicity to humans, most beneficial insects and other non-target organisms (Hofte and Whiteley, 1989; Lereclus et al. 1989, Adang, 1991). It has been shown that the basis of the specificity of Bt ICP resides mainly in one of the steps in its mode of action - its binding to specific sites in the bursh border membrane of the midgut epithelial cells.