| The cereal aphid is one of the most important cereal insect pests of field crops in Jiangsu. and in many other parts of China. Our study indicated the three main kinds of wheat aphids including Rhopalosiphum padi Linnaeus, Sitobion avenae Fabricius and Schizaphis graminum Rondani were predominant aphids in Jiangsu Province. The occurrence of natural population of three aphids had some differences depended largely on the species of wheat aphid, weather factors and so forth. Investigation showed that the proportion of population density of three kinds of aphids (bird-cherry aphid, wheat aphid, green-bug) was 81.46%, 17.32%, 2.22% in 2002, respectively; and was 68.31%, 27.53%, 4.16% in 2003, respectively. Studies also showed that temperature, raining, natural enemies were three important effect factors on the their population dynamics. Some natural enemies of the wheat aphid were Harmonia axyridis Pallas, Propylea japonila Thunberg, Coccinella septempunctata L, A. avenea Halidag, Chrysotoxum spp., Chrysopidae spp., Eriganictium griminicola Sundvall, Lycosa pseudoannulata Boes et Str. and so on and the main predominant predators controlling the wheat aphids were H. axyridis, P. Japonila and C. septempunctata; But, the controlling effects of some other predators such as A. avenea, Syrphus corollas were the second. Two years study conducted that the average proportion of four main natural enemies (H. axyridis , P. japonila, C. septempunctaia, C. spp.) were 48.68%, 25.18%. 7.17%, 4.21%, respectively. Furthermore, an interestingly following phenomenon appeared on their population density, occurrence stage between cereal aphids and its natural enemies based on the investigation.The mathematical prey-models were established by using the method of rotational combined design of square orthogonal regression between three kinds of natural enemies:P. japonila (x1), H. axyridis (x2), 5. corollae (x3) and two aphids:R. padi (x4). 5. avenae (x5). The prey-models of survival rates of R. padi aphids (Y4) and S. avenae (Y5) were as followings:Y4=0.32510-0.09852x,-0.06249x2-0.01563x3+0.09556x4-0.0065 Ix5+0.01236x,2-0.00328x22 +0.00194x32+0.01183x42-0.00328x52-0.00391xix2-0.03906x1X3+0.00585x]X4-0.02149x,X5 -0.01368x2X3+0.00781x2X4-0.01563x2X5+0.00781x3X4-0.01953x3X5+0.00586x4X5 (I)Y5=0.32309-0.07768xr0.05165x2-0.01781x3+0.01693x4+0.04792x5+0.01276x12-0.00807x22 -0.0026x32+0.02578x42-0.00911x52+0.00001xiX2-0.03907x1X3-0.00781x1x4-0.00196x1X5-0.00781x2X3+0.01563x2X4-0.01758x2X5+0.01563x3X4-0.01368x3X5-0.00586x4X5 (II)These two models can reflect the relationship between the survival rates of aphid and their natural enemies in terms of our experiments. The results pointed out an influence order of predators impacting the survival rates of bird-cherry aphid. They were H. axyridis > itself density > P. japonila > S. corollae and wheat aphid, which were H. axyridis > P. japonila > itself density > S. corollae. Meanwhile, the interaction among three natural enemies and between two wheat aphids was analyzed. An optimal proportion of the three predators in the multi-predators prey system were preliminarily established. To R. padi, the optimal proportion of five species of insect was 1: 1: 1: 2: 10 and to S. avenae, which was 1: 1: 1: 6: 2.Artificial honeydew was used as aphid's honeydew to imitate the effect on the wheat yield and qualities in the three wheat different growth stages including booting stage, earring period and milking stage. The results showed that agronomic characteristic, the content of starch, wet gluten and protein were much lower than those no-damage wheat in the three wheat stages according to the difference of concentrations of artificial honeydew. It also showed that the wheat had somewhat super-compensative function after infestation, In the booting stage, the maximal lost rate of agronomic characteristic, the content of starch, wet gluten and protein was 39.09%, 17.22%. 18.79%, 45.5%, respectively; In earring period, which was 41.79%, 8.26%, 14.83% and 39.26%. In milking stage, which was 47...
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