The objective of this study was to evaluate the residual efficacy of large-scale indoor spraying of pirimiphos-methyl, a combination of deltamethrin and clothianidin, and clothianidin in Alibori and Tonga, malaria-endemic areas in northern Benin.
Over the three-year study period, resistance to deltamethrin was observed in all communities. Resistance or potential emergence of resistance was observed to benzodiazepine. Full susceptibility to pirimiphos-methyl was observed in 2019 and 2020, while possible resistance to the same drug was identified in Djugu, Gogonu, and Kandy in 2021. Full susceptibility to clothianidin was observed 4–6 days after exposure. Residual activity of pirimiphos-methyl persisted for 4–5 months, while residual activity of clothianidin and a mixture of deltamethrin and clothianidin persisted for 8–10 months. The efficacy of the various products tested was slightly higher on cement walls than on clay walls.
Overall, Anopheles gambiae SL were fully susceptible to clothianidin but demonstrated resistance/possible resistance to other insecticides tested. Furthermore, the residual activity of clothianidin-based insecticides was superior to that of pirimiphos-methyl, demonstrating their ability to effectively and sustainably control pyrethroid-resistant vectors.
For WHO tube and cone susceptibility testing, local populations of Anopheles gambiae sensu lato (sl) and a susceptible strain of Anophoeles gambiae (Kisumu) from different IRS communities were used, respectively.
Pyrifos-methyl capsule suspension is an insecticide prequalified by the World Health Organization for indoor spraying systems . Pyrifos-methyl 300 CS is an organophosphorus insecticide with a recommended dose of 1.0 g active ingredient (AI)/m² for the control of malaria vectors. Pyrifos-methyl acts on acetylcholinesterase, causing the accumulation of acetylcholine in the synaptic cleft when acetylcholine receptors are open, thereby blocking the transmission of nerve impulses and causing paralysis and death of insects.
The use of insecticides with new modes of action, such as clothianidin, can facilitate the effective and sustainable control of pyrethroid-resistant malaria vectors. These insecticides can also help manage insecticide resistance, avoiding overreliance on the four traditional neurotoxic insecticides commonly used in public health. Furthermore, combining these insecticides with insecticides with other modes of action can also slow the development of resistance.
The susceptibility of Anopheles gambiae complex to clothianidin was only assessed in 2021, prior to the publication of WHO guidelines, using a protocol optimized by Sumitomo Chemical (SCC).WHO guidelines on susceptibility testing procedures for each prequalified insecticide were published, allowing the WHO collaborating institution Universiti Sains Malaysia in Malaysia to prepare insecticide-impregnated papers at various doses and make them available to research centers.[31] Only in 2021 did WHO publish guidelines on susceptibility testing to clothianidin.
Whatman paper was cut into pieces 12 cm wide and 15 cm long, impregnated with 13.2 mg of the active ingredient clothianidin and used for testing within 24 hours of impregnation .
The susceptibility status of the studied mosquito population was determined in accordance with WHO criteria :
Four parameters were studied: the susceptibility level of the local Anopheles gambiae population to the insecticide, the knockdown effect or immediate mortality within 30 minutes, delayed mortality and residual efficacy .
The data used and/or analyzed during this study are available from the corresponding author upon reasonable request.
Post time: Sep-22-2025