Abstract: Four aggregation indices I,Ca,m/m,Iδare used to analyze the spatial distribution pattern of Rhopalosiphum padi on winter wheat fields after earing. The results indicate that the distribution of aphids is in aggregative pattern during fifteen days after earing and beforeharvesting, and in uniform pattern from the fifteenth to thirtysixth day after earing. Thechange of spatial distribution pattern is related with the proportion of plants carrying aphids (q0). Their aggregative pattern is transformed into uniform one when the proportion of plants carrying aphids(q0) is more than 93%. Sample size requirements for estimating population means with fixed level of precision are also available to cereal aphids,and the pest control threshold can be estimated by the proportion of plants uncarrying aphids (p0).

Key words: Rhopalosiphum padi, Spatial distribution, Sampling technique, Wheat, terrace, agriculture, land abandonment, historical transformation