Abstract: This study analysed the relation between yield loss and damage levels caused by cotton aphids through the field simulated test, systematic analysis and computer analoguing technique. On the basis of nine year's study two selective models were established: Y=14.15909+11.29091X, if the grades of damage ranged from 1 to 3; Y=-12.67929+9.71252X, if the damage grades ranged from 4 to 6. The field simulated test and the farming practice on 1.5 million mu indicated that the aphid damage level of grade 1, i.e. the ratio of cotton plants with aphides in middle of costem was less than 5 per cent, could not cause yield loss, on the contrary could increase the yield by 2.9%. This result was in harmony with that of computer analogue. So the damage degree could be used as a relaxed index for control of summer cotton aphid.

Key words: Summer cotton aphid, Computer analoguing technique, Control index, Optimum models, Systematic analysis