Effects Of Several Insecticides On Sogatella Furcifera And Arthropod Community In Middle-season Rice Fields

The effects of several insecticides on white-backed planthopper(Sogatella furcifera)and the arthropod community in middle-season rice 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 white-backed planthopper to several insecticides in laboratoryThe results of toxicity tests in laboratory showed that white-backed planthoppers were relatively sensitive to abamectin and pymetrozine with LC50 of 0.3391 mg/L and 0.8960mg/L respectively and less sensitive to chlorpyrifos with LC50 of 4.7147 mg/L.The mixtures of abamectin + chlorpyrifos,pymetrozine + chlorpyrifos and abamectin +pymetrozine all had obvious synergistic effects on white-backed planthoppers with co-toxicity coefficient of 312.05,194.46 and 177.90 respectively,among which the synergistic effect of abamectin + chlorpyrifos mixture was the best.According to the toxicological regression line of several insecticides against white-backed planthoppers,the susceptibility of 3 instar larvae of white-backed planthoppers to the insecticides was in order of abamectin ? abamectin + pymetrozine mixture > pymetrozine ? abamectin +chlorpyrifos mixture?pymetrozine + chlorpyrifos mixture>chlorpyrifos.2 Control effects of several insecticides on white-backed planthoppers in middle-season rice fieldsThe results of field experiments showed that the control efficacy of abamectin on white-backed planthoppers was not satisfactory with the control effects of 63.33%(1d after application)and 59.52%(3d after application)respectively and the continue decline and short period of control effects.Pymetrozine worked relatively slow but had satisfactory long period control efficacy with the control effects of 90.94%(7d after application)and89.94%(14d after application)respectively and they were significantly higher than those of other insecticide treatments.Chlorpyrifos had certain control efficacy on white-backed planthoppers with the control effects of 76.78%,89.52%,75.79% and 23.77% of 1d,3d,7d,and 14 d after application and was able to control other insect pests in the same time.The control effect of abamectin + chlorpyrifos mixture of 1d after application on white-backed planthoppers was 89.07% and it was significantly higher than those of other insecticide treatments,but the persistent control effect of the mixture was still notsatisfactory although a little better compared with single abamectin treatment.The mixture of pymetrozine+ chlorpyrifos had relatively high control efficacy on white-backed planthoppers with the control effects of 72%(1d after application)and 65.26%(3d after application)respectively and they were significantly higher than those of single pymetrozine treatment.The control effect of pymetrozine + chlorpyrifos mixture of 7d after application had not significant difference with that of single pymetrozine treatment.The mixture of abamectin + pymetrozine also had quite good control efficacy on white-backed planthoppers with the control effects of 71.78% and 80.19% of 1d and 7d after application respectively,and they were significantly higher than those of single abamectin treatment and single pymetrozine treatment.In the meantime,the mixture of abamectin + pymetrozine had relatively high persistent control efficacy on white-backed planthoppers with the control effects of 79.01%(7d after application)and 68.21%(14d after application)respectively.In summary,both the mixture of pymetrozine + chlorpyrifos and the mixture of abamectin + pymetrozine had fast as well as persistent control effects on white-backed planthoppers.3 Effects of several insecticides on the arthropod community in middle-season rice fields3.1 Effects of several insecticides on the main characteristic indices of the arthropod community in middle-season rice fieldsThe results showed that all the insecticide treatments had some influence on the species richness of arthropod community in middle-season rice fields.Compared with the control treatment,the ratios of means were between 0.71 and 0.79.Among the insecticide treatments,chlorpyrifos treatment had the greatest effect on the species richness and its mean of richness was 11.6 while others were between 12.6 and 13.0 with little difference each other.All the insecticide treatments except abamectin had some promotive effects on the evenness of arthropod community in middle-season rice fields and the ratios of means were between 1.18 and 1.50 compared with the control treatment.Among the insecticide treatments,chlorpyrifos treatment and pymetrozine + chlorpyrifos mixture treatment had the greatest promotive effects on the evenness,and abamectin + pymetrozine mixture treatment and pymetrozine treatment were the next.All the insecticide treatments except abamectin had some positive effects on the means of diversity of arthropod community in middle-season rice fields and among the insecticide treatments,pymetrozine + chlorpyrifos mixture treatment and chlorpyrifos treatment had the greatest promotive effects,andabamectin + pymetrozine mixture treatment and pymetrozine treatment were the next.3.2 Effects of several insecticides on the ratio of natural enemies to insect pests of the arthropod community in middle-season rice fieldsThe results showed that the ratios of natural enemies to insect pests of middle-season rice fields of control treatment were in rising trend in time sequence.This indicated that the natural control effects of natural enemies on insect pests increased constantly along with the decrease of the dominant insect pest,white-backed planthopper population and the rise of natural enemy populations.Compared with the control treatment,the abamectin treatment had a little negative impact on the ratio of natural enemies to insect pests of middle-season rice fields,which was related to the unsatisfactory control efficacy of abamectin on white-backed planthoppers and the negative impact on natural enemies.All the other insecticide treatments had certain positive impacts on the ratio of natural enemies to insect pests of middle-season rice fields,among which pymetrozine,pymetrozine +chlorpyrifos mixture and chlorpyrifos had relatively great impacts.Especially,pymetrozine treatment not only had excellent control effect on white-backed planthoppers,but also was relatively safe to natural enemies.The average value of the ratio of natural enemies to insect pests of middle-season rice fields under pymetrozine treatment was 5.12 times as much as that of control treatment and this indicated that the use of pymetrozine to control white-backed planthoppers was helpful to protect and increase the natural control effects of natural enemies on insect pests in middle-season rice fields.