Degradation Dynamics of Thiamethoxam Residues in Cotton Leaves and Evaluation of Its Control Effect on Aphis gossypii Glover

【Objective】 To study the degradation dynamic of thiamethoxam seed treatment in leaves of cotton and evaluate the control effect of thiamethoxam seed treatment on Aphis gossypii by field experiment. 【Method】 The content of thiamethoxam in cotton leaves was determined by QuEChERS UPLC MS / MS, and the control effect of thiamethoxam seed coating on cotton aphid was investigated in the field. 【Results】 The results indicated that thiamethoxam had a good linear relationship in the range from 0.01 to 0.50 mg/L,r=0.999. At three spiked levels (0.01, 0.20 and 0.50 mg/kg), the average recoveries of thiamethoxam ranged from 93.4% to 119.71%, and the relative standard deviation ranged from 0.34% to 5.18%(n=5), the limit of detection was 0.001 mg/kg. The degradation kinetic of thiamethoxam in leaves of cotton was in accord with the first-order kinetic equation, and the half-life was 3.85-4.03 d. The concentration of thiamethoxam in the bottom leaves accounted for 59.4% to 76.39% of the total concentration of each treatment, so thiamethoxam was mainly distributed in the bottom leaves. The control effect of 600 g/100kg treatment was the highest, reaching 87.90% at 30 days after germination. 【Conclusion】 Using 600 g/100kg thiamethoxam seed treatment can better control aphids in the seedling stage.