Abstract: The peritrophic membrane (PM) is an invertebrate-unique semi-permeable structure secreted from midgut epitheliums.As a barrier to infection and mechanical damage,it plays an important role in protecting the midgut epithelium from pathogens,toxins,and other damaging factors.The disruptive effects of Fluorescent Brightener 28 (FB28) and Helicoverpa armigera granulovirus enhancin (En-Ha) on the peritrophic membrane of Hyphantria cunea larvae as well as their enhancing effects on the toxicity of H.cunea nucleopolyhedrovirus (HcNPV) were studied.The result of bioassay showed that FB28 and En-Ha could disrupt the structure of PM and enhance the vitality of HcNPV.The LC50 value decreased to 1.91×103 and 7.70×103 PIBs/mL,and the synergism rate were 58.12 and 14.42, respectively,after feeding diets containing FB28+HcNPV and En-Ha +HcNPV.The results of SDS-PAGE indicated that after the larvae were reared with diets containing FB28,the protein with molecular weight 60 ku disappeared and some with molecular weight 37 ku appeared;after the larvae were reared with diets containing En-Ha,the protein with molecular weight 75 ku disappeared and some with molecular weight 44.3 ku appeared.However,the disappeared protein bands recovered again after 10-24 hours,suggesting the effects of FB28 and En-Ha on PMs of H.cunea was temporary and reversible.