Summary: | Previous studies have indicated widespread insecticide resistance in malaria vector populations from Cameroon. However, the intensity of this resistance and underlying mechanisms are poorly known. Therefore, we conducted three cross-sectional resistance surveys between April 2018 and October 2019, using the revised World Health Organization protocol, which includes resistance incidences and intensity assessments. Field-collected <i>Anopheles gambiae</i> s.l. populations from Nkolondom, Nkolbisson and Ekié vegetable farms in the city of Yaoundé were tested with deltamethrin, permethrin, alpha-cypermethrin and etofenprox, using 1× insecticide diagnostic concentrations for resistance incidence, then 5× and 10× concentrations for resistance intensity. Subsamples were analyzed for species identification and the detection of resistance-associated molecular markers using TaqMan® qPCR assays. In Nkolbisson, both <i>An. coluzzii</i> (96%) and <i>An. gambiae</i> s.s. (4%) were found together, whereas only <i>An. gambiae</i> s.s. was present in Nkolondom, and only <i>An. coluzzii</i> was present in Ekié. All three populations were resistant to the four insecticides (<75% mortality rates―MR1×), with intensity generally fluctuating over the time between mod-erate (<98%―MR5×; ≥98%―MR10×) and high (76–97%―MR10×). The <i>kdr</i> L995F, L995S, and N1570Y, and the <i>Ace-1</i> G280S-resistant alleles were found in <i>An. gambiae</i> from Nkolondom, at 73%, 1%, 16% and 13% frequencies, respectively, whereas only the <i>kdr</i> L995F was found in <i>An. gambiae</i> s.s. from Nkolbisson at a 50% frequency. In <i>An. coluzzii</i> from Nkolbisson and Ekié, we detected only the <i>kdr</i> L995F allele at 65% and 60% frequencies, respectively. Furthermore, expression levels of <i>Cyp6m2</i>, <i>Cyp9k1</i>, and <i>Gste2</i> metabolic genes were highly upregulated (over fivefold) in Nkolondom and Nkolbisson. Pyrethroid and etofenprox-based vector control interventions may be jeopardized in the prospected areas, due to high resistance intensity, with multiple mechanisms in <i>An. gambiae</i> s.s. and <i>An. coluzzii</i>.
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