Abstract: Bacillus thuringiensis (Bt) has been widely used because of its specificity for target insects, its low development cost and its environmental compatibility. Much efforts are devoted to the mechanism of its action and the enhancement of its toxicity. This paper is confined to Cry I δ-endotoxin to present the progress of studies on these points. The mode of action of δ-endotoxin includes 5 steps: solubilization, degradation, binding with receptors, intercalation and formation of pore or channel. In order to improve the toxicity of δ-endotoxin, various physical and chemical factors including plant allelochemicals are used for strengthening the solubilization, degradation of B-endotoxin, or the interaction between δ-endotoxin and insect midgut. Other means such as screening higher toxicity strains of Bt, using the feeding stimulants to increase larval ingestion, protecting δ-endotoxin from ultraviolet irradiation and cooperatinig with othermicrobes, are also proved to be effective in the potentiation of B endotoxin.

Key words: Bacillus thuringiensis, mode of action, potentiation