Downregulation of carboxylesterase gene mediates resistance to indoxacarb in Spodoptera litura

Carboxylesterases (CarEs) play a critical role in metabolic resistance to insecticides of insects. But fewer CarEs were associated with insecticide bioactivation in insects. Previous findings showed that four CarE genes were downregulated in the indoxacarb resistant populations of Spodoptera litura. In this study, qPCR verification showed that the expression of SlituCOE067 was downregulated in the resistant strains and gradually decreased after exposure to indoxacarb. Silencing of SlituCOE067 increased the cells viability of S. litura against indoxacarb, and further knockdown of SlituCOE067 reduced the sensitivity of larvae to indoxacarb. Overexpression of SlituCOE067 in transgenic fruit flies decreased the tolerance to indoxacarb. Molecular modeling and insecticide docking predicted that SlituCOE067 protein can bind tightly to indoxacarb instead of its activated product N-decarbomethoxylated metabolite (DCJW). Heterologous expression and metabolism experiment proved that recombinant SlituCOE067 can promote the activation of indoxacarb into DCJW, but cannot metabolize DCJW. These results comprehensively demonstrate that downregulation of SlituCOE067 can reduce the activation metabolism of indoxacarb and mediate the resistance of S. litura to indoxacarb. This study reveals a new mechanism of insecticide resistance caused by blocking the activation of insecticides in lepidoptera insects.