Although esterase-mediated spinosad resistance has been proposed for several insects, the associated molecular mechanism remains poorly understood. In this study, we investigated the mechanism of esterase-based spinosad resistance in house flies using a susceptible strain (SSS) and a spinosad-resistant, near-isogenic line (N-SRS). Combined with the synergistic effect of DEF on spinosad in the N-SRS strain, decreased ali-esterase activity in the spinosad-resistant strain has implicated the involvement of mutant esterase in spinosad resistance in house flies. Examination of the carboxylesterase gene MdαE7 in the two strains revealed that four non-synonymous mutations (Trp251-Leu, Asp273-Glu, Ala365-Val, and Ile396-Val) may be associated with spinosad resistance in house flies. Single nucleotide polymorphism analysis further indicated a strong relationship between these four mutations and spinosad resistance. Moreover, quantitative real-time PCR revealed a female-linked MdαE7 expression pattern in the N-SRS strain, which may contribute to sex-differential spinosad resistance in house flies.
Keywords: Caboxylesterase; MdαE7; Musca domestica; Spinosad resistance.