Efficacy Of Pymetrozine·Dimehypo On Major Rice Pests And Its Residual Dynamics In Paddy Fields

Pymetrozine·dimhypo 0.5%BRG is a new compound insecticide developed by the Pesticide Laboratory of Jiangxi Agricultural University.On the basis of previous work,the efficacy of pymetrozine·dimhypo 0.5%BRG on main rice pests and its influence to the growth and decline of natural enemy spiders were investigated in paddy field,and the constant and residue analysis methods for determination of this preparation were developed.The dissipation dynamics of the preparation in rice and environment were determined.The results are as follows:1.Pymetrozine·dimhypo 0.5%BRG at 1125-1500 g/hm² applied before transplantation rice had good efficacy on Chilo suppressalis,Cnaphalocrocis medinalis and rice hopper（Nilaparvata lugens and Sogatella furcifera）,which were 68.09%⁸1.80%for protecting seeding and 66.67%⁸6.41%for killing insects on Chilo suppressalis in 45 days after treatment,68.09%-80.80%for protecting leaf and68.67%-81.24%for killing insects on Cnaphalocrocis medinalis,and more than 90%on rice hopper（Nilaparvata lugens and Sogatella furcifera）in 60 days after treatment.The killing rate of pymetrozine·dimhypo 0.5%BRG at 750-1500 g/hm² on natural enemy spider was 30.52%-35.50%30 days after treatment,and 22.13%-25.40%45 days after treatment,and the density of spiders returned to the blank control level 75 days after the treatment.2.In the constant analysis of pymetrozine·dimhypo mixture,the simultaneous determination of pymetrozine and dimehypo in the samples was conducted with Zorbax Eclipse XDB-C18 column as fix phase,the mixture solution of acetonitrile,water and phosphate buffer（4∶86∶10,by vol）as mobile phase by HPLC and UV detector at 242nm.The results were quantitated by external standard method.The linear correlation coefficients for pymetrozine and dimehypo were 0.9999 and 0.9998,the standard deviations were 0.0008 and 0.0014,the variation coefficients were 0.76%and 0.35%,and the average recoveries were 99.59%and 99.23%,respectively.The limit of detection for pymetrozine of this method was 2.0×10^-10 g in the residue analysis.The limit of quantification（LOQ）was 2.5×10^-33 mg/L in paddy water,3.25×10^-3 mg/kg in soil,and5.0×10^-33 mg/kg in rice plant.The limit of detection for dimhypo of this method was 2.0×10^-10 g.The limit of quantification（LOQ）was 1.0×10^-33 mg/L in paddy water,5.0×10^-3mg/kg in soil,and 10.0×10^-33 mg/kg in rice plant.The average recoveries of pymetrozine ranged from 84.69%to 95.88%with the relative standard deviations（RSD）of 1.36-9.52while fortifiled concentrations of pymetrozine in paddy water,soil,rice plant,rice hull and husk rice were 0.02-1.0 mg/kg.The average recovery ranged from 82.58%to 100.22%with RSD of 2.76%⁸.62%while fortifiled concentrations of dimehypo in soil,rice plant,rice husk and rice were 0.02-1.0 mg/kg.3.The contents of pymetrozine·and dimhypo in paddy water and rice plants were lower first and then higher then lower after pymetrozine·dimhypo 0.5%BRG at1125-1500 g/hm²（the highest recommended dosage）applied one time before transplantation rice.The initial concentrations of pymetrozine in early and late rice soils were 11.34 mg/kg and 11.25 mg/kg,respectively,and the kinetic equation of disipation was y=12.341e^-0.0245x（R²=0.9645）and y=12.196e^-0.0292x（R²=0.9566）,and the half-life of T_1/2was 32.49 days and 26.50 days,respectively.The initial concentrations of dimhypo in early and late rice soils were 45.78 mg/kg and 46.20 mg/kg,respectively,and the kinetic equation of disipation was y=46.560e^-0.0322x（R²=0.9902）and y=45.598e^-0.0387x（R²=0.9858）,and the half-life of T_1/2 was 22.05 d and 17.57 d,respectively.The final residue of pymetrozine was 0.156-0.192 mg/kg,and the final residue of dimhypo was 0.563-0.816mg/kg in early and late rice.