Abstract: Fluorescent brightener 28 is used as an influencing factor to study the mechanism of M2R on the peritrophic membrane (PM) of Loxostege sticticalis larvae. The environmental scanning electron microscopy and biochemical technique were employed to analyze the morphological structure and the protein profiles of the PM of L. sticticalis larvae treated by M2R, and the disruptive effect of M2R on the PM and its synergistic effect on Bt virulence were studied. The results indicated that there were many types of PM proteins. Separation of PM proteins by SDS-PAGE showed that there were at least 19 polypeptides with molecular weight less than 94 kD. The chitin binding proteins （CBP） content of PM could be influenced when the larvae were fed with 1.0% M2R. The surface of the normal PM was smooth and wrinkled without pores or slits while the surface of the treated PM had pores and slits. Although M2R did not affect the larval growth, it could enhance the sensitivity of larvae to Bt infection, shorten the killing time and reduce the application dose of Bt. These results suggest that the M2R could damage the PM of the larvae, and thus increase the control effect of Bt.

Key words: Loxostege sticticalis, fluorescent brightener 28, peritrophic membrane, Bacillus thuringiensis, synergistic activity, environmental scanning electron microscopy