Baseline susceptibility of Anopheles gambiae to clothianidin in northern Ghana

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Abstract Background: Clothianidin, an insecticide with a novel mode of action, has been deployed in the annual indoor residual spraying programme in northern Ghana since March 2021. To inform pragmatic management strategies and guide future studies, baseline data on local Anopheles gambiae s.l susceptibility to the clothianidin insecticide were collected in Kpasolgu, a village in the Northern region, Ghana.Methods: Phenotypic susceptibility of Anopheles mosquitoes to clothianidin was determined using the WHO insecticide resistance monitoring bioassay. The WHO cone bioassay was conducted on mud and cement walls sprayed with Sumishield 50 WG (with clothianidin active ingredient). Mortality rates were observed up to 168 hours. Species of the An. gambiae complex present in the area and the detection of insecticide target-site mutations (kdr and Ace-1) were determined by PCR. Results: The WHO susceptibility bioassay revealed a delayed killing effect of clothianidin. Mosquitoes exposed to the cone bioassays for five minutes died 120 hours after exposure. Slightly higher mortalities were observed in mosquitoes exposed to clothianidin-treated cement wall surfaces than mosquitoes exposed to mud wall surfaces. The kdr target-site mutation L1014F occurred at very high frequencies (0.89-0.94) across all vector species identified whereas the Ace-1 mutation occurred at moderate levels (0.32-0.44). An. gambiae s.s was the most abundant species observed at 63% whereas An. arabiensis was the least observed at 9%.Conclusions: An. gambiae s.l. mosquitoes in northern Ghana were susceptible to clothianidin. They harbored kdr and ace-1 mutations at high frequencies.

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