Tobacco Cutworm (Spodoptera Litura) Larvae Silenced in the NADPH-Cytochrome P450 Reductase Gene Show Increased Susceptibility to Phoxim

Nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome P450 reductases (CPRs) function as redox partners of cytochrome P450 monooxygenases (P450s). CPRs and P450s in insects have been found to participate in insecticide resistance. However, the CPR of the moth Spodoptera litura has not been well characterized yet. Based on previously obtained transcriptome information, a full-length CPR cDNA of S. litura (SlCPR) was PCR-cloned. The deduced amino acid sequence contains domains and residues predicted to be essential for CPR function. Phylogenetic analysis with insect CPR amino acid sequences showed that SlCPR is closely related to CPRs of Lepidoptera. Quantitative reverse transcriptase PCR (RT-qPCR) was used to determine expression levels of SlCPR in different developmental stages and tissues of S. litura. SlCPR expression was strongest at the sixth-instar larvae stage and fifth-instar larvae showed highest expression in the midgut. Expression of SlCPR in the midgut and fat body was strongly upregulated when fifth-instar larvae were exposed to phoxim at LC(15) (4 μg/mL) and LC(50) (20 μg/mL) doses. RNA interference (RNAi) mediated silencing of SlCPR increased larval mortality by 34.6% (LC(15) dose) and 53.5% (LC(50) dose). Our results provide key information on the SlCPR gene and indicate that SlCPR expression levels in S. litura larvae influence their susceptibility to phoxim and possibly other insecticides.