Understanding evolutionary paradigm of knockdown resistance in mosquitoes by analyzing DNA sequence polymorphisms in voltage-gated sodium channel in Culex quinquefasciatus

The Voltage Gated Sodium Channel (VGSC) is critical for binding of different insecticides and plays a key role in insecticide resistance. The insect sodium channel consists of four homologous domains (I to IV), each containing six transmembrane segments (S1 to S6). An important mechanism of resistance to DDT and pyrethroids is termed knockdown resistance (kdr), caused by a single nucleotide polymorphism in IIS6 domain of sodium channels. We analyzed the polymorphisms, nucleotide diversity, and phylogenies in VGSC-IIS6 gene in Culex quinquefasciatus from India. We analyzed the neutral model / hypothesis to infer if natural selection is acting upon the analyzed vgsc gene. Tajima’s D, Fu and Li’s D* and F* and Fu’s Fs test were performed to determine whether the distribution of nucleotide variation within the samples was consistent with neutral model. We theorized that the evolutionary pattern of intra-population distribution of variability in vgsc gene is consistent with the neutral expectation.