Multi-centre laboratory study to determine discriminating concentrations for broflanilide and isocycloseram resistance monitoring in mosquitoes

Introduction Discriminating concentrations (DCs) underpin routine monitoring of insecticide susceptibility, but none had been established for broflanilide or isocycloseram, two new active ingredients entering vector control. This study aimed to establish and validate DCs in WHO bottle bioassays for monitoring susceptibility to broflanilide and isocycloseram in Anopheles gambiae s.s., An. funestus, An. stephensi , and Aedes aegypti . Methods In 2024–2025, a multi-centre study involving seven international laboratories was conducted with the support of the World Health Organization (WHO), applying the generic WHO protocol for establishing discriminating concentrations to susceptible reference strains of each species. Results The following values are recommended for adoption as DCs for broflanilide: 10 μg/bottle for An. gambiae and Ae. aegypti , 15 μg/bottle for An. funestus , and 25 μg/bottle for An. stephensi . The recommended DCs for isocycloseram are 15 μg/bottle for Ae. aegypti , 30 μg/bottle for An. gambiae , 50 μg/bottle for An. stephensi , and 60 μg/bottle for An. funestus . Discussion Based on the experience gained from conducting this study, technical recommendations are made to support the generation and analysis of DC data for insecticides in the future.