Uptake of quercetin reduces larval sensitivity to lambda-cyhalothrin in Helicoverpa armigera

Quercetin, one of the most abundant dietary flavonoids, is widely present in nature. In this study, the effects of quercetin ingestion on Helicoverpa armigera larvae growth and its sensitivity to lambda-cyhalothrin were assessed. The median lethal concentration (LC50) value of lambda-cyhalothrin to quercetin-fed H. armigera larvae was 2.39-fold higher than the control, suggesting a reduced sensitivity to lambda-cyhalothrin. Piperonyl butoxide (PBO) treatment effectively synergized lambda-cyhalothrin efficacy in quercetin-fed H. armigera larvae with a synergistic ratio of 2.36. Moreover, the growth of H. armigera larvae was inhibited by the quercetin uptake. To understand the reduced sensitivity to lambda-cyhalothrin, we measured the enzymatic activity of cytochrome P450 monooxygenases (P450s), as well as transcriptional responses of three P450s genes in quercetin-fed H. armigera larvae. We found that cytochrome P450 monooxygenases involved in the observed lambda-cyhalothrin tolerance in quercetin-fed H. armigera. After fed on quercetin for 48 h, 7-ethoxycoumarin-O-deethylase (ECOD) activity was significantly elevated in quercetin-fed H. armigera larvae; meanwhile, the expression level of CYP6B6, CYP6B8 and CYP321A1 was up-regulated. In conclusion, P450s played a crucial role in the metabolic adaptation of H. armigera larvae to its host plant's secondary metabolites as well as synthetic insecticides. The reduced lambda-cyhalothrin sensitivity in quercetin-fed H. armigera larvae suggested that previous exposure to the host plant-derived quercetin is likely to compromise the efficacy of pyrethroid insecticides.