Abstract
The citrus red mite, Panonychus citri (McGregor), is a major citrus pest with a worldwide distribution and an extensive record of pesticide resistance. However, the underlying molecular mechanism associated with fenpropathrin resistance in this species have not yet been reported. In this study, synergist triphenyl phosphate (TPP) dramatically increased the toxicity of fenpropathrin, suggesting involvement of carboxylesterases (CarEs) in the metabolic detoxification of this insecticide. The subsequent spatiotemporal expression pattern analysis of PcE1, PcE7 and PcE9 showed that three CarEs genes were all over-expressed after insecticide exposure and higher transcripts levels were observed in different field resistant strains of P. citri. Heterologous expression combined with 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetra-zolium bromide (MTT) cytotoxicity assay in Spodoptera frugiperda (Sf9) cells revealed that PcE1-, PcE7- or PcE9-expressing cells showed significantly higher cytoprotective capability than parental Sf9 cells against fenpropathrin, demonstrating that PcEs probably detoxify fenpropathrin. Moreover, gene silencing through the method of leaf-mediated dsRNA feeding followed by insecticide bioassay increased the mortalities of fenpropathrin-treated mites by 31% (PcE1), 27% (PcE7) and 22% (PcE9), respectively, after individual PcE gene dsRNA treatment. In conclusion, this study provides evidence that PcE1, PcE7 and PcE9 are functional genes mediated in fenpropathrin resistance in P. citri and enrich molecular understanding of CarEs during the resistance development of the mite.
Highlights
The citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae), is one of the most important citrus pests responsible for significant economic losses [1,2]
To investigate the effect of esterases on resistance of P. citri against the insecticide fenpropathrin, the synergist triphenyl phosphate (TPP) was used here and the mite of Beibei (BB) population was chosen for bioassay (Table 1)
After the application of TPP, the LC50 decreased from 4.339 mg/L to 1.405 mg/L and the synergism fold amounted to 3.09, suggesting that CarEs played a crucial role in detoxification process of P. citri to fenpropathrin
Summary
The citrus red mite, Panonychus citri (McGregor) (Acari: Tetranychidae), is one of the most important citrus pests responsible for significant economic losses [1,2]. It feeds on more than 112 different plant species [3]. As one of the most crucial metabolic detoxification systems in insects, CarEs have been shown to be associated with development of resistance to many insecticides including pyrethroids through gene amplification, improvement of mRNA stability and point mutation [19,21]. The reverse genetic study through the method of leaf-mediated dsRNA feeding was applied to explore the link between the CarE genes and pyrethroids resistance in P. citri
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