Analysis of thiamethoxam residue dynamics in cotton seed coating and its correlation with cotton aphid control efficiency
[Objective]Neonicotinoid insecticides can be used as seed treatments to control aphids,whiteflies and other piercing mouthparts due to their internal absorption activity and apical conduction prop-erties.To explore the correlation between pesticide residue dynamics and control effect after thiamethoxam seed treatment,so as to provide theoretical basis for its rational application.[Method]Cotton was used as the test material,and seeds were coated with different doses of 30%thiamethoxam suspension seed coating agent.While the control effect was investigated,cotton plant samples were collected,and the residue and di-gestion dynamics of thiamethoxam and its metabolite thiamethoxam in cotton plants were analyzed by liquid mass coupled method.[Result]After coating the cotton seeds with thiamethoxam,samples were collected for the first time 16 days after sowing.The residues of different doses of thiamethoxam in cotton plants ranged from 0.753 to 2.768 mg/kg,and the content of its metabolite thiamethoxam ranged from 0.278 to 0.894 mg/kg.The residues of thiamethoxam and clothianidin decreased exponentially with time.When the cotton samples were tested at 66 days after sowing,the levels of the two drugs in cotton were less than the detection limit of 0.001 mg/kg.The digestion dynamics of thiamethoxam and its metabolite clothianidin in cotton were consistent with the first-order kinetic equation.[Conclusion]Different doses of thiamethoxam seed coating can significantly reduce aphid mouth density at seedling stage,showing an obvious dose effect,and there is a strong correlation between the pesticide residue level in plants and the control effect of cotton aphid,the mechanism of action may be related to the antifeeding effect of cotton aphid after penetrating the leaves.
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