Efficacy of the Insecticide Formulation SumiShield® 50WG for Malaria Vector Control in Experimental Huts in Madagascar

Indoor residual insecticide spraying and the distribution of insecticide-treated nets have undoubtedly led to a significant reduction in the global malaria burden. However, insecticide resistance poses a threat to the effectiveness of these recommended control methods. In the present study, the aim was to determine the efficacy of SumiShield® 50WG (Sumitomo Chemical Co. Ltd., Tokyo, Japan), an insecticide containing clothianidin, a neonicotinoid, in controlling malaria vectors in Madagascar. The study was conducted over 9 months after the initial spraying in experimental huts made with walls coated using different substrates, and both wild anopheline mosquitoes and an Anopheles arabiensis (An. arabiensis) insecticide-susceptible laboratory strain were used. Mortality in wild mosquitoes remained above the WHO threshold of 80.0% for up to 8 months post-spray, when assessed up to 96 hours after capture, depending on the type of wall surface. SumiShield 50WG did not induce exophily or inhibit blood-feeding in wild mosquitoes because no significant differences were observed between treated and control huts regarding the rates of exophily and blood-fed mosquitoes. In An. arabiensis, the WHO mortality threshold was also met for up to 8 months post-spray when assessed up to 96 hours after exposure. However, during the ninth month, this threshold was not achieved, even when mortality was assessed up to 120 hours after exposure. The residual efficacy of the formulation, which lasts up to 8 months, is sufficient to cover the malaria transmission season in most endemic areas of Madagascar.