Activation of CncC pathway by ROS burst regulates cytochrome P450 CYP6AB12 responsible for λ-cyhalothrin tolerance in Spodoptera litura

Frequent insecticide use poses an environmental hazard and also selects for insecticide tolerance. Increased metabolic detoxification by cytochrome P450 monooxygenases (P450s) is the most common mechanism of insecticide tolerance. However, the underlying regulatory mechanisms remain unknown. We studied the midgut-specific P450 gene, CYP6AB12, associated with lambda-cyhalothrin tolerance. Its regulatory pathway was investigated in the tobacco cutworm, Spodoptera litura (Fabricius). P450 activities and CYP6AB12 transcript levels increased after lambda-cyhalothrin exposure. Inhibiting P450 activities with piperonyl butoxide and silencing CYP6AB12 by double-stranded RNA (dsRNA) injection decreased larval tolerance to lambda-cyhalothrin. lambda-Cyhalothrin exposure induced the expression of the cap 'n' collar isoform C (CncC) and muscle aponeurosis fibromatosis (Maf), increased hydrogen peroxide (H2O2) contents and elevated antioxidant enzyme activities. CncC knockdown by dsRNA feeding suppressed CYP6AB12 expression and decreased larval tolerance to lambda-cyhalothrin. In contrast, application of the CncC agonist curcumin induced CYP6AB12 expression and enhanced insecticide tolerance. Ingestion of the reactive oxygen species (ROS) scavenger N-acetylcysteine reduced H2O2 accumulation, suppressed the expression of CncC, Maf and CYP6AB12 and led to increased larval susceptibility to lambda-cyhalothrin. The results demonstrate that in S. litura, lambda-cyhalothrin induces cytochrome P450 CYP6AB12 via elicitation of the ROS burst and activation of the CncC pathway.