Biochemical and Molecular Analysis of Field Resistance to Spirodiclofen in Panonychus citri (McGregor)

SIMPLE SUMMARY: The citrus red mite, Panonychus citri, is one of the most destructive citrus pests worldwide. Spirodiclofen is an important chemical acaricide to control P. citri. In this study, the complete acetyl-CoA carboxylase (ACCase) gene between field spirodiclofen-resistant and laboratory-susceptible strains of P. citri were sequenced and compared based on the mode of action of spirodiclofen and the reported literature. Enzyme activity measurement and digital gene expression profile analysis were applied to identify candidate metabolic resistance genes. RT-qPCR and RNA interference (RNAi) further confirmed that the most prominent upregulated gene, CYP385C10, may be involved in the field of spirodiclofen-resistance of P. citri in China. These results provide the molecular foundation for understanding the spirodiclofen resistance in P. citri. ABSTRACT: Spirodiclofen is one of the most widely used acaricides in China. The citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae), is one of the most destructive citrus pests worldwide and has developed a high resistance to spirodiclofen. However, the molecular mechanism of spirodiclofen resistance in P. citri is still unknown. In this study, we identified a field spirodiclofen-resistant strain (DL-SC) that showed 712-fold resistance to spirodiclofen by egg bioassay compared to the susceptible strain. Target-site resistance was not detected as non-synonymous mutations were not found by amplification and sequencing of the ACCase gene of resistant and susceptible strains; in addition, the mRNA expression levels of ACCase were similar in both resistant and susceptible strains. The activity of detoxifying enzymes P450s and CCEs in the resistant strain was significantly higher than in the susceptible strain. The transcriptome expression data showed 19 xenobiotic metabolisms genes that were upregulated. Stage-specific expression profiling revealed that the most prominent upregulated gene, CYP385C10, in transcriptome data was significantly higher in resistant strains in all stages. Furthermore, functional analysis by RNAi indicated that the mortality caused by spirodiclofen was significantly increased by silencing the P450 gene CYP385C10. The current results suggest that overexpression of the P450 gene, CYP385C10, may be involved in spirodiclofen resistance in P. citri.