Abstract: Population dynamics of natural enemies and effects on Aphis citricola Vander Goot in apple orchards were analyzed through systematic scouting and cage tests to support the rational use of ground vegetation in management of A. citricola. The analysis results showed that the ground vegetation affected the population of natural enemies in apple orchards. Densities of predators and parasitoids were significantly higher in grass-growing orchards than in natural grass orchards and clear cultivation orchards. Direct scouting showed no significant difference in the ratio of natural enemies to A. citricola between different apple orchards, while investigation using yellow sticky traps showed significantly higher ratios of natural enemies to A. citricola in grass-growing orchards than in the natural grass orchards and clear cultivation orchards, which was 2.2 times and 21.88 times more, respectively. Cage tests indicated no difference in the relative growth rates of A. citricola between the open treatment and the treatment caged on the 15^th days after trial. But A. citricola increased more in clear cultivation orchards than in grass-growing orchards and natural grass orchards. The biocontrol services index of natural enemies to A. citricola was not significantly different between the three treatment orchards. These results provide evidence that grass-growing in apple orchards can significantly increase the density of natural enemies and the ratio of enemies to A. citricola and plays an important role in pest management.

Key words: apple orchards, Aphis citricola, orchard grass, control