Abstract: Effects of chemical control on diversity of insect pests and predatory natural enemy were investigated in 8 types of cotton fields in Raoyang County, Hebei Province in 1999. The results showed that chemical control affected diversity and homogeneity indices, richness and the numbers of pests and predators in different types of cotton fields. Chemical control had a more significant effect on the diversity of predator than pest communities. The effects of chemical control differed in different types of cotton fields and in different stages of the growing cycle: the effects were more prominent in cotton monocultures or cotton-bean intercropped fields than in those with cotton-wheat intercropping, in late sown than early sown fields, and in untilled fields than tilled fields. The effect was less on the edges of intercropped cotton fields than in the middle. The insect pest community was more sensitive to chemical insecticides at the early stage of the growing cycle, while chemical control significantly influenced the insect predator community throughout the growth period of cotton plants.

Key words: cotton field, chemical control, insect pests, predatory natural enemies, community diversity