Indoor residual spraying of experimental huts in Cameroon highlights the potential of Fludora® Fusion to control wild pyrethroid-resistant malaria vectors

Abstract

<title>Abstract</title> Elevated resistance to pyrethroids has led to the introduction of novel insecticides including neonicotinoids. However, the efficacy of these new control products could be impacted by cross-resistance mechanisms from metabolic resistance to pyrethroids. In this study, after evaluating the resistance to clothianidin and mixture of clothianidin+deltamethrin in the lab using CDC bottle assays, the efficacy of the new IRS formulation Fludora^® Fusion IRS was tested in the experimental huts against wild free-flying pyrethroid-resistant <italic>Anopheles funestus</italic> in Elende and field <italic>An. gambiae</italic> from Nkolondom, Cameroon. Additionally, cone tests were performed on the wall of treated huts each month to evaluate the residual efficacy of the sprayed products. Furthermore, the L1014F-kdr target site mutation and the L119F-GSTe2 mediated metabolic resistance to pyrethroids were genotyped on a subset of mosquitoes from the EHT to assess the potential cross-resistance. All Anopheles species tested were fully susceptible to clothianidin and clothianidin+deltamethrin mixture in CDC bottle assay while resistance was noted to deltamethrin. Accordingly, Fludora^® Fusion and clothianidin induced significantly higher mortality rates in EHT than deltamethrin with mortality rates of 62.83%, 64.42% and 42.42% against free flying <italic>An. funestus </italic>from Elende. However, lower mortality rates were recorded against <italic>An. gambiae</italic> from Nkolondom (mortality rates 50%, 45.56% and 26.68%). <italic>In-situ</italic> cone test on the wall showed a high residual efficacy of Fludora^® Fusion and clothianidin on the susceptible strain KISUMU (&gt;12 months) and moderately on the highly pyrethroid-resistant <italic>An. gambiae</italic> strain from Nkolondom (6 months). Interestingly, no association was observed between the L119F-GSTe2 mutation and the ability of mosquitoes to survive exposure to Fludora^® Fusion, whereas a trend was observed with the L1014F-kdr mutation. This study highlights that Fludora^® Fusion, has good potential of controlling pyrethroid-resistance mosquitoes with prolonged residual efficacy. This could be therefore an appropriate tool for vector control in several malaria endemic regions.