Temporal Evaluation of Insecticide Resistance in Populations of the Major Arboviral Vector Aedes Aegypti from Northern Nigeria

SIMPLE SUMMARY: Outbreaks of dengue and yellow fever are fast becoming normal in Nigeria. Transmitted by mosquito vectors, Aedes aegypti and/or Aedes albopictus, control of these arboviral diseases depends largely on control of the above vectors. This requires knowledge of the identity/composition and insecticide resistance profile of the vector species—knowledge which is inadequate across Nigeria. In this study we characterised two populations of Aedes aegypti from north-western Nigeria (BUK/Kano and Pantami). Bioassays with Kano larvae suggest resistance to temephos (an important insecticide for larval control) is low but increasing, while deltamethrin resistance is high, and increased 6-fold between 2018 and 2019, and 11-fold by 2020. Adult bioassays established high pyrethroid resistance (the bed net insecticides) and extreme resistance to DDT (an indoor residual spraying insecticide). Bioassays with piperonylbutoxide and diethylmaleate (synergists which block activity of the enzymes that confer insecticide resistance) resulted in significant recovery of mortalities, implicating CYP450s and GSTs—enzymes which confer pyrethroid and DDT resistance, respectively. Tests with pyrethroid-containing bed net, PermaNet(®) 3.0 (side panels) revealed high resistance, in contrast to the areas also containing piperonylbutoxide (PermaNet(®) 3.0, roof panel). These findings highlight the challenges associated with the control of this arboviral vector of public health importance in Nigeria. ABSTRACT: To support evidence-based control measures, two Nigerian Aedes populations (BUK and Pantami) were characterised. Larval bioassay using temephos and deltamethrin revealed a significant increase in deltamethrin resistance, with LC(50) of 0.018mg/L (resistance ratio compared to New Orleans, RR = 2.250) in 2018 increasing ~6-fold, by 2019 (LC(50) = 0.100mg/L, RR = 12.5), and ~11-fold in 2020 (LC(50) = 0.198mg/L, RR = 24.750). For the median deltamethrin concentration (0.05mg/L), a gradual decrease in mortality was observed, from 50.6% in 2018, to 44.9% in 2019, and 34.2% in 2020. Extremely high DDT resistance was observed, with <3% mortalities and LT(50)s of 352.87 min, 369.19 min and 406.94 min in 2018, 2019 and 2020, respectively. Significant temporal increase in resistance was observed towards ƛ-cyhalothrin (a type II pyrethroid) over three years. Synergist bioassays with diethylmaleate and piperonylbutoxide significantly recovered DDT and ƛ-cyhalothrin susceptibility respectively, implicating glutathione S-transferases and CYP450s. Cone bioassays revealed increased resistance to the PermaNet(®) 3.0, side panels (mortalities of 94% in 2018, 66.4% in 2019, and 73.6% in 2020), while full susceptibility was obtained with the roof of PermaNet(®) 3.0. The F1534C kdr mutation occurred in low frequency, with significant correlation between heterozygote genotypes and DDT resistance. This temporal increase in resistance is a major challenge for control of this vector of public health importance.