To study biological activity and insecticidal mechanism of Bacillus thuringiensis( Bt) Cry2 Aa toxin,the insecticidal activity of commercial Cry2 Aa toxin against Plutella xylostella was determined by the leaf dipping method,and its paraffin embedded sections were used to perform immunohistochemical analysis. In addition,the binding curve of Cry2 Aa toxin with brush border membrane vesicle( BBMV) of P. xylostella was determined by ELISA method. Finally,the binding proteins in BBMV with Cry2 Aa were separate...