The WHO regularly provides updated information on methods for monitoring insecticide resistance in arthropod vectors of disease, such as mosquitoes and sandflies. Recently the WHO commissioned a multi-center study to determine the discriminating concentrations of two new insecticides for indoor residual spraying: isocycloseram and broflanilide (Praulins et al., preprint, https://www.biorxiv.org/cgi/content/short/2026.05.22.726487v1).
The discriminating concentrations and test conditions are displayed below.
Table 1 - Summary of insecticide discriminating concentrations for Aedes species for WHO bottle bioassays (bottle drying time 24hr; mosquito exposure time 1h; holding/recording time 24hr)
| Insecticides | Species | Discriminating concentration (µg/bottle) | Solvent/ surfactant |
| Broflanilide | Ae. aegypti | 10 | Acetone and MERO at 1500ppm |
| Isocycloseram | Ae. aegypti | 15 | Acetone and MERO at 1500ppm |
Table 2 - Summary of insecticide discriminating concentrations for Anopheles species for WHO bottle bioassays (bottle drying time 24hr; mosquito exposure time 1h; holding/recording time 24hr)
| Insecticides | Species | Discriminating concentration (µg/bottle) | Solvent/ surfactant |
| Broflanilide | An. gambiae | 10 | Acetone and MERO at 800ppm |
| An. funestus | 15 | ||
| An. stephensi | 25 | ||
| Isocycloseram | An. gambiae | 30 | Acetone and MERO at 800ppm |
| An. funestus | 60 | ||
| An. stephensi | 50 |
Furthermore, in a technical consultation held in 2024 (WHO 2025), a definition of chlorfenapyr susceptibility was discussed, as this was not entirely clear in the Manual for monitoring insecticide resistance in mosquito vectors and selecting appropriate interventions (WHO 2022).
Susceptibility to chlorfenapyr will be confirmed when mortality is ≥ 98% in one bioassay, with mortality in the susceptible sample being ≥ 98% in each test at the same time point.
These updates will be added to a future update of the Manual for monitoring insecticide resistance in mosquito vectors and selecting appropriate interventions
References
Praulins G, Mechan F, Harvey G, Brooke B, Corbel V, Duchon S, Kaiser M, Moore S, Mpelepele AB, Oliver S, Singh H Stevenson J, Fotso Toguem YG, Verna V, Wondji C, Lees RS. Multi-centre laboratory study to determine discriminating concentrations of broflanilide and isocycloseram for resistance monitoring in mosquitoes. Manuscript submitted.
WHO. 2022. Manual for monitoring insecticide resistance in mosquito vectors and selecting appropriate interventions.
WHO. 2025. Quality of conduct and interpretation of insecticide susceptibility in bioassays using new insecticides for vector control. Meeting report, 24 September 2024.