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Abstract Selection of mosquito collection methods is of crucial importance to evaluate the impact of vector control tools on entomological outcomes. During a cluster randomised control trial evaluating the relative efficacy of two dual-active ingredient (a.i.) long-lasting insecticidal nets (LLINs) compared to pyrethroid-only LLINs, we assessed the performance of different mosquito collection methods: Human landing catches (HLC), Centers for Disease Control and Prevention (CDC) light traps, and pyrethrum spray catches (PSC). Anopheles mosquitoes were collected using three collection methods in 4 houses, in each of the 60 trial clusters at baseline and every quarter for 24 months using PSCs and HLCs, while CDC light traps were performed during two quarters only. Mean density of vectors collected per method per night was the highest with HLCs (15.9), followed by CDC light traps (6.8); with PSCs (1.1) collecting 10 times less mosquitoes than HLCs. All three collection methods collected fewer mosquitoes in the Interceptor G2® dual a.i. arm, compared to the other trial arms, although only HLCs and PSCs demonstrated strong evidence of this due to a greater number of collection rounds undertaken, than CDC light traps. The broadly similar results regarding the differential impact of the two dual a.i. LLINs showed by the three collection methods suggest that the more ethically acceptable, cheaper, and logistically simpler methods such as CDC light traps could be prioritised for use in large community trials for measuring the efficacy of vector control tools.

Abstract Background In Alibori and Donga, two departments of high malaria incidence of Northern Benin, pirimiphos-methyl, mixture deltamethrin + clothianidin, as well as clothianidin were used at large scale for IRS. The present study aimed to assess the residual efficacy of these products. Methods Immatures of Anopheles gambiae sensu lato (s.l.) collected in the communes of Kandi and Gogounou (Department of Alibori), Djougou and Copargo (Department of Donga) were reared until adulthood. Females aged 2–5 days were used for susceptibility tube tests following the WHO protocol. The tests were conducted with deltamethrin (0.05%), bendiocarb (0.1%), pirimiphos-methyl (0.25%) and clothianidin (2% weight per volume). For cone tests performed on cement and mud walls, the An. gambiae Kisumu susceptible strain was used. After the quality control of the IRS performed 1-week post-campaign, the evaluation of the residual activity of the different tested insecticides/mixture of insecticides was conducted on a monthly basis. Results Over the three study years, deltamethrin resistance was observed in all the communes. With bendiocarb, resistance or possible resistance was observed. In 2019 and 2020, full susceptibility to pirimiphos-methyl was observed, while possible resistance to the same product was detected in 2021 in Djougou, Gogounou and Kandi. With clothianidin, full susceptibility was observed 4–6 days post-exposure. The residual activity lasted 4–5 months for pirimiphos-methyl, and 8–10 months for clothianidin and the mixture deltamethrin + clothianidin. A slightly better efficacy of the different tested products was observed on cement walls compared to the mud walls. Conclusion Overall, An. gambiae s.l. was fully susceptible to clothianidin, while resistance/possible resistance was observed the other tested insecticides. In addition, clothianidin-based insecticides showed a better residual activity compared to pirimiphos-methyl, showing thus their ability to provide an improved and prolonged control of pyrethroid resistant vectors.

Abstract Background The selection and the spread of insecticide resistance in malaria vectors to the main classes of insecticides used in vector control tools are a major and ongoing challenge to malaria vector control programmes. This study aimed to determine the intensity of vector resistance to insecticides in three regions of Benin with different agro-ecological characteristics. Methods Larvae of Anopheles gambiae sensu lato (s.l.) were collected from September to November 2017 in different larval sites in three northern Benin communes: Parakou, Kandi and Malanville. Two to five-day-old, non-blood-fed, female mosquitoes were exposed to papers impregnated with deltamethrin, permethrin and bendiocarb at dosages of 1 × the diagnostic dose, 5 × and 10 × to determine the intensity of resistance in these vectors. Molecular frequencies of the kdr L1014F and ace-1R G119S insecticide resistance mutations and levels of detoxification enzymes were determined for mosquitoes sampled at each study site. Results Resistance to pyrethroids (permethrin and deltamethrin) was recorded in all three communes with mortality rates below 60% using the diagnostic dose (1x). The results obtained after exposure of An. gambiae to permethrin 10 × were 99% in Kandi, 98% in Malanville and 99% in Parakou. With deltamethrin 10x, mortality rates were 100% in Kandi, 96% in Malanville and 73% in Parakou. For the diagnostic dose of bendiocarb, suspected resistance was recorded in the communes of Malanville (97%) and Kandi (94%) while sensitivity was observed in Parakou (98%).Using the 10 × dose, mortality was 98% in Kandi, 100% in Malanville and 99% in Parakou. The frequencies of the kdr L1014F allele varied between 59 and 83% depending on the sites and species of the An. gambiae complex, while the frequency of the ace-1R G119S gene varied between 0 and 5%. Biochemical tests showed high levels of oxidase and esterase activity compared to the susceptible colony strain of An. gambiae sensu stricto (Kisumu strain). Conclusion Anopheles gambiae showed a generalized loss of susceptibility to permethrin and deltamethrin but also showed moderate to high intensity of resistance in different regions of Benin. This high intensity of resistance is a potential threat to the effectiveness of vector control.