Pyrethroid and Etofenprox Resistance in and from Vegetable Farms in Yaoundé, Cameroon: Dynamics, Intensity and Molecular Basis.

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 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 (96%) and s.s. (4%) were found together, whereas only s.s. was present in Nkolondom, and only 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 L995F, L995S, and N1570Y, and the G280S-resistant alleles were found in from Nkolondom, at 73%, 1%, 16% and 13% frequencies, respectively, whereas only the L995F was found in s.s. from Nkolbisson at a 50% frequency. In from Nkolbisson and Ekié, we detected only the L995F allele at 65% and 60% frequencies, respectively. Furthermore, expression levels of , , and 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 s.s. and .