Effects Of Several Insecticides And Their Mixtures On Diamondback Moth(Plutella Xylostella) And Arthropod Community In Spring Cabbage Fields

The effects of several insecticides and their mixtures on diamondback moth (Plutella xvlostella) and the arthropod community in spring cabbage fields were studied based on the methods of pesticide bioassay in laboratory and the field experiment. The main results were as follows:1 Toxicity of several insecticides to diamondback moth in laboratoryThe results of the laboratory tests showed that abamectin had hight toxic effect on diamondback moth and its LC50 was 11,9950mg/L. Clorantraniliprole had high control effect on Lepidoptera pests and its LC50 to diamondback moth was 21.0329mg/L. Chlorpyrifos had relatively low toxic effect on diamondback moth with LC50 of 458.3529mg/L because of its wide use and the development of resistance.The synergism of abamectin+clorantraniliprole mixture and abmectin+chlorpyrifos mixture to diamondback moth was explained as antagonistic action with the co-toxicity coefficient of 53.26 and 18.27 respectively. The clorantraniliprole+chlorpyrifos mixture had additive effect on diamondback moth with the co-toxicity coefficient of 101.06.2 Control effects of several insecticides on diamondback moth in cabbage fieldsThe results of field experiments showed that the control efficacy of chlorpyrifos on Plutella xylostella was not satisfactory with the control effects of 18.17%,45.77%,-13.18% and -64.55% respectively 1d,3d,7d and 14d after application. Clorantraniliprole had evident control effects on diamondback moth with the control effects of 56.22%, 82.33%,89.92% and 81.10% respectively 1d,3d,7d and 14d after application.The control efficacy of abamectin on diamondback moth was common with the highest control effect of 60.42% 3d after application.Clorantraniliprole+chlorpyrifos mixture and abamectin+clorantraniliprole mixture had satisfactory control effects on diamondback moth which had no significant difference to that of clorantraniliprole. The control efficacy of abmectin+chlorpyrifos mixture on diamondback moth reached the highest rate of 63.44% 3d after application and lost the control effect later.3 Effects of several insecticides on arthropod community in cabbage fieldsCompared with the control treatment, the diversity of arthropod community declined in chlorpyrifos treatment plots and abmectin+chlorpyrifos mixture treatment plots because of their low control effects on the major cabbage pest, diamondback moth, and negative impact on natural enemies. The abamectin treatment had no evident effect on the evenness and diversity of the arthropod community. The treatments of clorantraniliprole clorantraniliprole+ chlorpyrifos mixture and abamectin+clorantraniliprole mixture raised the evenness and diversity of arthropod community greatly and therefore raised the community stability for their excellent control effects on diamondback moth and relative safety to natural enemies.4 Effects of several insecticides on the ratio of natural enemies to insect pests of arthropod community in cabbage fieldsThe chlorpyrifos treatment had a negative impact on the ratio of natural enemies to insect pests and the ratio dropped evidently as compared with that of the control treatment. The abamectin treatment and abamectin+chlorpyrifos mixture treatment had relatively low impacts on the ratio of natural enemies to insect pests. The ratio of natural enemies to insect pests in the treatment plots of clorantraniliprole, clorantraniliprole+chlorpyrifos mixture and abamectin+clorantraniliprole mixture rised greatly as compared with that in the plots before application and the control treatment plots. These results indicated that the treatments of clorantraniliprole. clorantraniliprole+chlorpyrifos mixture and abamectin+clorantraniliprole mixture were able to protect and promote the natural control effects of natural enemies on insect pests in cabbage fields.