Abstract: From April of 1989 to April of 1990, the effects of two kinds of pyreth-roid on the insect community (including spiders) were studied combining withthe work of controlling the pest Dendrolimus punctatus conducted by QianshanCounty, Anhui Province. The results indicate that the species in the commu-nity is more abundent during the period of the pest's outbreaks but the evenessand diversity index of the community are lower than those of the communityof the control plots. After the pest was effectively controlled by the insectici-des, the pest was difficult to return to a high population density; though thespecies in the community was less abundent at this time, the diversity index was higher because the eveness had incresed greatly; each kind of measure-ment index for community shows a similar change tendency with that of thecontrol plots. Chemical control not only decreased the pest's population den-sity but also killed a lot of natural enemies of the community. But the effectsof insecticides on different groups of natural enemies (beneficial insectsand spiders) were different. Beneficial insects were greatly affected by insec-ticides, and the species and individuals in this group decreased rapidly afterchemical control; spiders were little affected and showed great resistance to the insecticides. Beneficial insects are more dependent on the population den-sity of the pest than spiders in both species and individuals.

Key words: Chemical control, Denarolimus punctatus, insect community, Beneficial insects, Spiders