| The English grain aphid Sitobion avenae (Fabricius) (Homoptera: Aphididae) is an important pest on wheat in North China. Its growth, development and reproduction were influenced directly by the nutrition component and its percentage in wheat. The sort and percentage of amino acid in wheat play a critical role in resistance to aphids. But, at present, the mechanisms of resistance of AA were not understood very well so that the hypotheses which are supported consistently are absent. In this paper, we studied the function and mechanism of AA in wheat resistance to the aphid by using all chemically defined diet. After having made experiments primarily, we designed 54 protocols with orthogonality of chemically defined diet and provided to S. avenae in laboratory in order to gain some optimum prescriptions. Those protocols were composed of different assemblages of 22 AA, cholesterin and micro-saltine in 3 levels. At the same time, symbiotic bacteria in bodies of aphids are another factor that can impact on its growth and reproduction and was analyzed in our study.The results in our studies as follows: 1. Among those protocols, two prescriptions, which accorded with the nutritional and reproductive growth of wheat, were match with the nutritional requirement in growth and reproduction stage of S. avenae. 2. The results showed that there were 10 AA which were more necessary for the survival of S. avenae, including Glu,Met,Asp,Gly,Pro,Ile,His,Leu,Ser,Phe. The reproduction of aphids was influenced more severely by following 10 AA: Met, Gln, Pro, Asn, Glu, Lys, Arg, MgCl2.6H2O, Ser, Cyss. But the growth of aphids was affected by following 10 AA: Met, Gln, Ser, Asn, Arg, Pro, MgCl2.6H2O, Gly, Glu, cholesterin.3. The result of experiments which symbiotic bacteria in aphids' bodies were wiped off showed that aposymbiotic S. avenae had significant lower reproductivities than aphids in control. The bacteria had an obvious impact on aphids' reproductivities. Moreover, the results also showed the bacteria affected the efficacy of resistance to aphids of wheat.On the other hand, aposymbiotic S. avenae had a higher livability than that of aphids in control, which suggested that symbiotic bacteria make against survival of aphids. When feed on different varieties of wheat, survival rates aposymbiotic S. avenae as well as in control were different, except that on the variety KOK. Otherwise, resistance of wheat was lower to aphids in treatment than to ones in control, which suggested that expression of resistance to aphids was affected by the symbiotic bacteria in aphids' bodies. 4. Survival of aphids feed on chemically defined diet was significant lower than that of control, which suggested that the symbiotic bacteria in aphids could synthesize some nutrition and provide part to their hosts – aphids.All of the components in chemically defined diet could not completely match with the nutritional requirement of aphids in all of their lives. Further studies on superior protocol of chemically defined diet needed in following days. The detailed interactions between symbiotic bacteria, aphids and wheat are the key questions that needed be understood very well, and the mechanisms of those interactions needed further studies.
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