Parafilm method was adopted for feeding the third instar nymphs of Macrosiphum avenae on two liquid diets (20% sucrose and redistilled water). Their saliva after feeding for 24 h was collected and assayed identifying salivary enzymes and determining their activities. The results showed that pectinase, polyphenol oxidase and cellulase were identified in 20% sucrose diet; cellulase was identified in redistilled water diet; peroxidase was not identified in both diets. The activities of pectinase, polyphenol oxidase and cellulase secreted into 20% sucrose diet by 30 aphids were 2.59×10^-3 U/g, 7×10^-3 U/g and 7.89×10^-3 U/g, respectively; and cellulase activity secreted into redistilled water diet by 30 aphids was 3.68×10^-3 U/g. In the behavioral response test, the predator Coccinella septempunctata and parasitoid Aphidius avenae of M. avenae showed much preference for the volatiles in wheat seedlings treated by pectinase. It was so concluded that pectinase secreted by M. avenae play an important role in wheat plant indirect defense induced by aphid feeding.