VECTRON™ T500, a new broflanilide insecticide for indoor residual spraying, provides prolonged control of pyrethroid-resistant malaria vectors

Background: Broflanilide is a newly discovered insecticide with a novel mode of action targeting insect gamma-aminobutyric acid receptors. The efficacy of VECTRON (TM) T500, a wettable powder formulation of broflanilide, was assessed for IRS against wild pyrethroid-resistant malaria vectors in experimental huts in Benin. Methods: VECTRON (TM) T500 was evaluated at 100 mg/m(2) in mud and cement-walled experimental huts against wild pyrethroid-resistant Anopheles gambiae sensu lato (s.l.) in Cove, southern Benin, over 18 months. A direct comparison was made with Actellic (R) 300CS, a WHO-recommended micro-encapsulated formulation of pirimiphos-methyl, applied at 1000 mg/m(2). The vector population at Cove was investigated for susceptibility to broflanilide and other classes of insecticides used for vector control. Monthly wall cone bioassays were performed to assess the residual efficacy of VECTRON (TM) T500 using insecticide susceptible An. gambiae Kisumu and pyrethroid-resistant An. gambiae s.l. Cove strains. The study complied with OECD principles of good laboratory practice. Results: The vector population at Cove was resistant to pyrethroids and organochlorines but susceptible to broflanilide and pirimiphos-methyl. A total of 23,171 free-flying wild pyrethroid-resistant female An. gambiae s.l. were collected in the experimental huts over 12 months. VECTRON (TM) T500 induced 56%-60% mortality in wild vector mosquitoes in both cement and mud-walled huts. Mortality with VECTRON (TM) T500 was 62%-73% in the first three months and remained >50% for 9 months on both substrate-types. By comparison, mortality with Actellic (R) 300CS was very high in the first three months (72%-95%) but declined sharply to < 40% after 4 months. Using a non-inferiority margin defined by the World Health Organization, overall mortality achieved with VECTRON (TM) T500 was non-inferior to that observed in huts treated with Actellic (R) 300CS with both cement and mud wall substrates. Monthly in situ wall cone bioassay mortality with VECTRON (TM) T500 also remained over 80% for 18 months but dropped below 80% with Actellic (R) 300CS at 6-7 months post spraying. Conclusion: VECTRON (TM) T500 shows potential to provide substantial and prolonged control of malaria transmitted by pyrethroid-resistant mosquito vectors when applied for IRS. Its addition to the current list of WHO-approved IRS insecticides will provide a suitable option to facilitate rotation of IRS products with different modes of action.