›› 2015, Vol. 58 ›› Issue (3): 288-296.

• RESEARCH PAPERS • Previous Articles     Next Articles

Fipronil-resistance mediated by carboxylesterases in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

REN Na-Na1,2,3, XIE Miao1,2,3,4,*, YOU Yan-Chun1,2,3,4, LI Jian-Yu1,2,3,4, CHEN Wei-Jun 1,2,3,4, CHENG Xue-Min1,2, YOU Min-Sheng1,2,3,*   

  1. (1. Institute of Applied Ecology, Fujian Agriculture and Forestry University, Fuzhou 350002, China; 2. FujianTaiwan Joint Centre for Ecological Control of Crop Pests, Fujian Agriculture and Forestry University, Fuzhou 350002, China; 3. Key Laboratory of Integrated Pest Management of Fujian and Taiwan, China Ministry of Agriculture, Fuzhou 350002, China; 4. College of Life Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China)
  • Online:2015-03-20 Published:2015-03-20

Abstract: 【Aim】 Carboxylesterases (CarEs) are one of the most important detoxification enzymes in insects, and are implicated in the metabolic resistance of many different classes of insecticides. The present study aims to investigate the mediated functions of carboxylesterases in fipronil resistance of the diamondback moth, Plutella xylostella (L.), and thus to reveal the physiological, biochemical, and molecular mechanisms of carboxylesterases in metabolic detoxification of insects. 【Methods】 Topical application was used to test the toxicity of fipronil to the susceptible population (SP) and the fipronil-resistant population (FRP) and the synergistic effect of triphenyl phosphate (TPP), a carboxylesterase inhibitor, on fipronil. The LC30and LC50 concentrations of fipronil were used to treat FRP, and the effect on the carboxylesterase activity after treatment was determined. Stage-and tissue-specific expression patterns of Pxae22 and Pxae31 were profiled by qRT-PCR. Expression levels of Pxae22 and Pxae31 and the insecticide susceptibility of the 3rd instar larvae were also examined after RNA interference (RNAi). 【Results】 The results showed that TPP decreased the resistance of the 3rd instar larvae of P. xylostella to fipronil by about six times. After treatment with the lower doses (LC30 and LC50) of fipronil, the carboxylesterase activity in the treated 3rd instar larvae of P. xylostella was significantly higher than that of the control, suggesting that the carboxylesterase activity in P. xylostella could be induced by fipronil. Developmental expression profiling of genes exhibited that Pxae22 and  Pxae31 had the highest expression levels in the 4th instar larvae. Tissue expression profiling of genes showed that Pxae22 and Pxae31 were highly expressed in the midgut of the 4th instar larvae, while lowly expressed in the head, cuticle and fat body. The expression levels of the two genes in the fipronil-resistant population were significantly higher than those in the susceptible population, respectively. The qRT-PCR analysis showed that after RNAi of Pxae22 and Pxae31, the expression of the two genes was significantly suppressed, and the sensitivity of the 3rd instar larvae of P .xylostella  to fipronil increased by 1.63 times and 1.73 times, respectively. 【Conclusion】 Carboxylesterases play important roles in metabolic detoxification of fipronil in P.xylostella. Two CarE genes, Pxae22and Pxae31,are involved in insecticide resistance, and the variation of their expression levels can directly influence the susceptibility of P. xylostella to fipronil.

Key words: Plutella xylostella;pesticide resistance, carboxylesterases, mediated resistance, expression level, RNA interference