Residual efficacy of indoor residual spraying using clothianidin (SumiShield 50WG) under experimental huts and field conditions in Senegal

Abstract

Background: In Senegal, the main vector control strategies include indoor residual spraying (IRS) and the distribution of insecticide-treated nets (ITNs). However, drugs and insecticides resistance have become a major challenge in the fight against malaria transmission. Addressing the problem of escalating resistance is vital to maintaining progress towards malaria elimination, which has stalled in recent years. New formulations belonging to the neonicotinoid class, clothianidin, have been developed and is now being used for malaria vector control through IRS.

Methods: The residual efficacy of clothianidin-treated walls was assessed monthly using WHO cone bioassays. Five houses in each of the two treated villages were evaluated, while one untreated house served as a control. In the experimental huts, a total of six huts, three in banco (mud) and three in cement, were evaluated on a monthly basis. Three cones were installed on three walls of each sprayed house at heights of 0.5 m, 1 m and 1.5 m above the ground, and three additional cones were placed in the control house. Ten female Anopheles coluzzii mosquitoes, aged between 3 and 5 days and derived from a laboratory-susceptible strain, were exposed in each cone for 30 min. After exposure, the mosquitoes were transferred to cups and mortality rates were recorded up to four days after exposure.

Results: Results demonstrate high efficacy of SumiShield 50WG on mud and cement substrates, residual activity for up to twelve months in experimental huts and eight months under field conditions. In experimental huts, the 96 h mortality rate of the susceptible mosquito strain remained at 100% throughout the study, except in months ten and twelve for mud-walled huts, and months six and ten for cement-walled huts, where mortality rates were 98.33%, 99.16%, 95.68%, and 97.52%, respectively. In the field sites of Bandafassi and Tomboronkoto, the 72 h mortality rate of the susceptible strain remained consistently at 100% over the eight-month period.

Conclusions: Clothianidin, a neonicotinoid insecticide, has not yet shown resistance in malaria vectors in Senegal. SumiShield 50WG is effective for resistance management through a rotation strategy using insecticides with different modes of action across spray cycles.

Keywords: (SumiShield 50WG); Clothianidin; Experimental huts; Field conditions; IRS; Residual efficacy; Senegal.