Molecular Characterization and Insecticide Resistance Mechanisms in Culex quinquefasciatus Populations from Urban and Peri-Urban Environments in Oyo State, South West Nigeria

Insecticide resistance in Culex quinquefasciatus threatens the effectiveness of public health control programs targeting lymphatic filariasis and nuisance mosquito management in Nigerian cities. While phenotypic resistance has been documented in some cities, the molecular mechanisms underpinning resistance in Oyo State populations remain uncharacterized. This study combines bioassay profiling with molecular analysis to characterize insecticide resistance mechanisms in Cx. quinquefasciatus from urban Ibadan, peri-urban Egbeda, and a remote reference site in Oyo State. Field-collected larvae will be reared to adults and subjected to WHO bioassays with four insecticide classes. Synergist pre-exposure assays with PBO and DEF will differentiate metabolic resistance from target-site mechanisms. PCR and sequencing will screen for the Ace-1 G119S mutation (organophosphate resistance) and kdr alleles (pyrethroid resistance). Quantitative RT-PCR will measure expression levels of CYP9M10 and CYP6M7 oxidases associated with metabolic resistance. Principal component analysis will relate resistance profiles to urban ecological gradients. This research produces the first mechanistic resistance characterization for Cx. quinquefasciatus in Oyo State, providing actionable data for the Oyo State Lymphatic Filariasis Programme on insecticide rotation and resistance management strategies. Keywords: Culex quinquefasciatus, insecticide resistance, kdr mutation, metabolic resistance, Oyo State