Pesticide thiamethoxam in seed treatment: Uptake, metabolic transformation and associated synergistic effects against wheat aphids

Precise, effective and green control plays an essential role in reducing environmental and ecosystem damage. Seed treatment has proven effective and long-lasting for target organisms, and exploring the reasons for long-term protection is important for sustainable agricultural development. This study examined the uptake and metabolism behaviour of thiamethoxam under seed treatment in wheat samples throughout the whole growth cycle, as well as the associated synergistic effects of thiamethoxam and its metabolites during the most severe period of aphid occurrence. Uptake and metabolism results showed that 41 % of thiamethoxam and its active metabolites (clothianidin and demethyl-clothianidin) accumulated mainly in flag leaves of wheat, severely harming aphids, which was significant in controlling leaf-feeding pests. Combined activity results showed that thiamethoxam, clothianidin and demethyl-clothianidin produced synergistic efficacy in controlling aphids, with cotoxicity coefficients ranging from 179.34 to 452.07. Compared with the control, thiamethoxam seed treatments at a rate of 1.5 a.i. g/kg seeds and 3.0 a.i. g/kg can significantly enhance salicylic acid (55 % and 41 %) and jasmonic acid (168 % and 125 %) concentrations and invoke changes in the concentrations of plant secondary substances, which promoted wheat resistance to aphids. Future studies cannot ignore the synergistic effects of metabolites and plant secondary substances in pest control. These results provided data support for reducing pesticide use, increasing efficiency and making more rational use of neonicotinoid insecticides.