Identification of multiple mutations on the voltage-gated sodium channel gene of house flies, Musca domestica

Target site insensitivity resulting from point mutations within the sodium channel of the insect nervous system is one of the most important mechanisms of pyrethroid resistance in insects. In this study, with the Illumina RNA-Seq method, the full lengths of the house fly (Musca domestica) para-orthologous voltage gated sodium channel (Vsscl) gene were successfully isolated from the insecticide-resistant strain (ALHF), insecticide-susceptible strain (aabys) and five homozygous autosomal combination offspring lines (A2345, A1345, A1245, A1235, A1234), which were generated via genetic reciprocal crosses of ALHF and aabys strains. Each of these homozygous lines confers a different level of resistance to pyrethroid insecticides. Through a systematic analysis of comparing nucleotide polymorphisms in the entire sodium channel genes of all these house fly strains, four nonsynonymous mutations(L1014F, R1940G, T2030A,G2053A) and 12 synonymous mutations(L125, A448, P617, D707, Y772, N967, D1268, A1798, R1886, F1893, L1894, I1954) were identified in resistant strains. The co-existence of all these mutations, both nonsynomymous and synonymous mutations, were found to be responsible for the high levels of resistance. Comparison of the entire sodium channel sequences among the autosomal combination offspring lines and parental strains (ALHF, aabys) further revealed the potent inheritance of these mutations in the offspring and confirmed the genetic linkage of sodium channel gene in house flies.