Effects Of Several Bioinsecticides On The Arthropod Community In Cabbage Fields

Based on the field experiments and systematic field investigation, the effects of several bioinsecticides, Aolv No.1, abamectin and Bt on the arthropod community in cabbage fields were studied in this paper. The main results were as follows:1 Effects of several bioinsecticides on major dominant insect pests in cabbage fields The results of systematic investigation showed that there were 21 species of arthropods in spring cabbage fields, including 9 species of insect pests and 12 species of predatory enemies. The major dominant insect pests were Pieris rapae and Lipaphis erysimi. The three kinds of bioinsecticides had significant control effects on Pieris rapae and Lipaphis erysimi. During the period of investigation, the total populations of Pieris rapae and Lipaphis erysimi were only 26A%,20.9% and 21.8% of that of check plot in Aolv No.1, abamectin and Bt treatment plots respectively.There were 23 species of arthropods in autumn cabbage fields, including 10 species of insect pests and 13 species of predatory enemies. The major dominant insect pests were Prodenia litura and Lipaphis erysimi. The three kinds of bioinsecticides had evident control effects on Prodenia litura and Lipaphis erysimi in early period of the treatments, but the population of Prodenia litura rose rapidly in the late period of the investigation. Durind the period of investigation, the total populations of Prodenia litura and Lipaphis erysimi were 81%,86% and 92% of that of check plot in Aolv No.1, abamectin and Bt treatment plots respectively.2 Effects of several bioinsecticides on major characteristic indices of arthropod communities in cabbage fieldsThe research results showed that the three kinds of bioinsecticides of Aolv No.1, abamectin and Bt had evidnt effects on the total individuals of arthropod communities in spring cabbage fields. The populations of insect pests decreased greatly and the populations of natural enemies also decreased in some extent. There were relatively little effects of the three kinds of bioinsecticides on the richness, evenness and diversity of the community. The three kinds of bioinsecticides also had evident effects on the total individuals of arthropod communities in autumn cabbage fields, but the degrees of the effects were lower than those in spring cabbage fields and there were no evident effects on richness, evenness and diversity of the community.3 Effects of several bioinsecticides on the ratio of natural enemies to insect pests in cabbage fields The research results showed that the three kinds of bioinsecticides of Aolv No.1, abamectin and Bt had sertain effects on the ratio of natural enemies to insect pests in spring cabbage fields. The ratio of natural enemies to insect pests was higher in the bioinsecticide treatment plots than that in check plots. The effects of the three kinds of bioinsecticides on the ratio of natural enemies to insect pests in autumn cabbage fields were relatively great. The ratio of natural enemies to insect pests rose greatly after the bioinsecticide treatments,but decreased rapidly in the late growth period of autumn cabbage with the rapid rise of Prodenia litura population. Overall, the treatments of the three tested bioinsecticides were able to raise the ratio of natural enemies to insect pests and were halpful to protect and enhance the natural control effects of natural enemies on insect pests in cabbage fields.