Abstract: This experiment was conducted in the Tuanchenguoyuan Apple Orchard near Fragrant Hill Park, Beijing in 1985. The white sweet clover Mclilotus albus was grown as a cover crop between the rows of apple tree. The population dynamics of natural enemies,such as Orius minutus,,Chrysopa sinica,Scolothrips, sex-macnlatus and Amblyseius pseudolongispinosus, and the arthropod pests, such as Tetranychus viennensis, were observed. After the middle of July, the ratio of T.vicnnensis to its natural enemies on the apple trees was much lower in the cover cropping orchard than in the control orchards without the cover crop. On July 12, when the population of T. vienncnsis was most significantly different between the orchards with and without cover crop, there were 2.54 active mite stages per leaf and 8.80 active mite stages per leaf in test and control orchard respectively. During the entire growing season, miticide was applied only once. Obviously.cover cropping in apple orchards should be considered as one of important methods of IPM.

Key words: Predators, Cover cropping, Tetranychus viennensis, Biological control