Abstract: 【Aim】 This study aims to investigate the sublethal effects of spinosad on Plutella xylostella after long-term exposure to low concentration of spinosad. 【Methods】 The Sub strain of P. xylostella was continuously selected using the LC₂₅ of spinosad. The susceptibility of the 4th instar larvae of various subpopulations of P. xylostella to spinosad was assayed by leaf dip feeding method, and the change of expression level of nicotinic acetylcholine receptor (nAChR) α subunit gene in the 4th instar larvae of P. xylostella treated with low concentration of spinosad was determined by quantitative real-time PCR. 【Results】 The sensitivity of P. xylostella to spinosad decreased across generations. After selection with the LC₂₅ of spinosad for ten generations (Sub10), the Sub strain developed 2.70-fold resistance compared with the SS strain. Quantitative real-time PCR analysis indicated that the expression level of nAChR α subunit gene decreased with generations and significantly decreased by 32.04% in the Sub10 generation compared to that in the SS strain, and the expression level in the spinosad resistant strain RR (resistance ratio=17.85-fold) was only 37% of that in the SS strain. 【Conclusion】 This multi-generational study found the possible correlation between spinosad susceptibility and the expression abundance of nAChR α subunit gene in P. xylostella, and this is helpful for further understanding of spinosad resistance mechanisms in P. xylostella.  

Key words: Plutella xylostella, spinosad, insecticide resistance, nAChR, gene expression