Abstract: The authors of the paper studied in 1980-1988 the growth and decline trends of aphid (M. avenae F. ) and the relationship between the number of the aphid per 100 stems and the weight loss rate of 1000 kernels. The results showed that (1) The growthand decline of the aphid population presented a double-peak type. The highest peak was on the occasion of milking stage of the wheat plant n summer. Therefore this stage is the key for the aphid control; (2) The aphid population at early and middle milking stages was significantly correlated with the weight loss rates per 1000 kernels at early and middle milking stages. The correlation coefficients were 0.9648 and 0.9554. The regression equations are as follows:y₁ =0.010383x₁ -0.871208±3.07and y₂ =0.008019x₂ +0.182175±1.69; (3) Based on the present production level of wheat, the wheat price and the level of cost for the aphid control in Hebei, the economic threshold for the aphid population would be 600 and 650 at early and middle milking stages respectively.

Key words: Macrosiphum avenue Fabr., Growth and decline trends of aphid, Economic threshold