Abstract: To approach the effects of Aphis gossypii’s initial density on the population process of this aphid, two initial densities (1 and 20 aphids per leaf) were installed in a cotton field under open and nylon net-closed conditions, and the population dynamics of A. gossypii was monitored. At the initial density 20 aphids per leaf, the peak value of the population was larger, with no significant difference between open and nylon netclosed conditions, and the peak period occurred earlier, and advanced under open condition. Under nylon net-closed condition, the population with the initial density 20 aphids per leaf collapsed more rapidly. At the early stage of the population process, the population growth rate was higher at the initial density 1 aphid per leaf, and the population increased more rapidly under open condition. In the peak period and collapse period of the population, no significant differences were observed in the population growth rate at the two initial densities. The proportion of alate aphids was larger at the initial density 20 aphids per leaf, but no significant difference was found between open and nylon netclosed conditions.

Key words: Leymus chinensis, Clonal growth, Clonal architecture, Ecotype, Divergent type