Esterase-mediated spinosad resistance in house flies Musca domestica (Diptera: Muscidae)

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 Md alpha E7 in the two strains revealed that four non-synonymous mutations (Trp(251)-Leu, Asp(273)-Glu, Ala(365)-Val, and Ile(396)-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 Md alpha E7 expression pattern in the N-SRS strain, which may contribute to sex-differential spinosad resistance in house flies.