Effects Of Several Insecticides In Pieris Rapae And Natural Enemy Communities In Spring Cabbage Fields

The effects of several insecticides on cabbage caterpillar(Pieris rapae)and the predatory natural enemy community in spring cabbage fields were studied based on the methods of insecticide bioassay in laboratory and the field experiment.The main results are as follows:1 Susceptibility of Pieris rapae to several insecticides in laboratoryThe results of toxicity tests in laboratory show that cabbage caterpillar is relatively sensitive to abamectin and chlorantraniliprole with LC50 of 1.4085 mg/L and 2.9981 mg/L respectively and their susceptibility is 57.98 and 27.23 times as much as that of chlorpyrifos respectively.Among the three insecticide mixtures,cabbage caterpillar is most sensitive to abamectin+ chlorantraniliprole mixture with LC50 of 0.7882mg/L and sensitive times of 103.59 as much as that of chlorpyrifos.The mixture of abamectin+chlorantraniliprole has obvious synergistic effect on cabbage caterpillar with co-toxicity coefficient of 233.7898.According to the results of toxicity tests in laboratory and the toxicological regression line of several insecticides against cabbage caterpillar,the susceptibility of 3 instar larvae of Pieris rapae to the insecticides is in order of abamectin+chlorantraniliprole mixture > abamectin > chlorantraniliprole > chlorantraniliprole+chlorpyrifos mixture ? abamectin+ chlorpyrifos mixture >chlorpyrifos.2 Control effects of several insecticides on Pieris rapae in spring cabbage fieldsThe results of field experiments show that both abamectin and chlorantraniliprole have excellent control effects on cabbage caterpillar.The control effects of chlorpyrifos on cabbage caterpillar are significantly lower than those of abamectin and chlorantraniliprole and its persistent control effect is not satisfactory.All the three insecticide mixtures have excellent control effects on cabbage caterpillar,especially the mixture of abamectin +chlorantraniliprole and the mixture of chlorantraniliprole + chlorpyrifos have both excellent fast and persistent control effects on cabbage caterpillar.The use of the insecticide mixtures can reduce the application dosage of single insecticide,is helpful to delay the emergence and development of resistance of insect pests to insecticides and is able to control other insect pests in the meantime.They have practical value in agricultural production.3 Effects of several insecticides on natural enemy community in springcabbage fieldsThe research results show that compared with the control treatment,the treatments of chlorpyrifos,abamectin,chlorantraniliprole+ chlorpyrifos mixture and abamectin+chlorpyrifos mixture have evident negative influence on the total individuals of predatory natural enemies and the treatment of chlorpyrifos has the greatest negative impact.The treatments of chlorantraniliprole and abamectin+ chlorantraniliprole mixture are safe to natural enemies.The treatments of chlorpyrifos and abamectin have evident negative impact on the species richness of natural enemy community and the other insecticide treatments have no evident influence.All the insecticide treatments have no significant effects on the evenness of natural enemy community.The treatment of chlorpyrifos has certain negative effects on the diversity of predatory natural enemy community in spring cabbage fields while other insecticide treatments have no evident negative influence and the treatment of chlorantraniliprole has some promotive effects on the diversity of natural enemy community in spring cabbage fields.4 Effects of several insecticides on the ratio of natural enemies to insect pests of natural enemy community in spring cabbage fieldsThe research results show that compared with the control treatment,the treatment of chlorpyrifos has relatively great negative impact on the ratios of natural enemies to insect pests in spring cabbage fields and the ratio of means is only 0.59,which is related to the unsatisfactory control efficacy of chlorpyrifos on major insect pests and the negative impact on natural enemies.The treatments of abamectin and abamectin+ chlorpyrifos mixture have a little positive impact on the ratios of natural enemies to insect pests in spring cabbage fields.Compared with the control treatment,the ratios of natural enemies to insect pests in spring cabbage fields under the treatments of chlorantraniliprole,chlorantraniliprole+ chlorpyrifos mixture and abamectin+ chlorantraniliprole mixture rise greatly and this indicates that the use of chlorantraniliprole,chlorantraniliprole+chlorpyrifos mixture and abamectin+ chlorantraniliprole mixture to control the insect pests such as cabbage caterpillar etc.is helpful to protect and increase the natural control effects of natural enemies on insect pests in spring cabbage fields.