article · Parasites & Vectors
Insecticide resistance among mosquitoes threatens global interventions against malaria and arboviral diseases. To evaluate compounds with novel physical properties or modes of action, a new World Health Organization glass bottle bioassay method was assessed across 21 laboratories worldwide. The multi-centre evaluation tested approximately 200,000 mosquitoes across seven species, including key Anopheles and Aedes vectors, against seven insecticides from five chemical classes. Researchers analysed concentration-response data to determine lethal concentrations and oviposition inhibition endpoints, measuring mortality and sterilising effects. The mean within-bioassay variability remained below 10 percent for most combinations, although greater variation was observed for transfluthrin and flupyradifurone. These findings provided the empirical basis for 17 new discriminating concentrations, validating the bioassay for global vector surveillance.
Mosquito-borne diseases such as malaria depend heavily on chemical vector control, but rising insecticide resistance jeopardises these interventions. Standardising a reliable glass bottle bioassay allows global health teams to measure mosquito susceptibility to newer insecticide classes. This capability helps public health authorities identify resistance early and select appropriate interventions, preventing operational failures in disease control programmes.
The method represents a validated, ready-for-use testing protocol designed for public health agencies, vector control programmes, and monitoring laboratories. By establishing 17 new discriminating concentrations, the bioassay enables immediate real-world monitoring of wild mosquito resistance. Agro-chemical and public health insecticide developers can use these standardised baseline assays to guide the deployment, registration testing, and post-market stewardship of new vector control formulations.
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Abstract Background The continued spread of insecticide resistance in mosquito vectors of malaria and arboviral diseases may lead to operational failure of insecticide-based interventions if resistance is not monitored and managed efficiently. This study aimed to develop and validate a new WHO glass bottle bioassay method as an alternative to the WHO standard insecticide tube test to monitor mosquito susceptibility to new public health insecticides with particular modes of action, physical properties or both. Methods A multi-centre study involving 21 laboratories worldwide generated data on the susceptibility of seven mosquito species ( Aedes aegypti , Aedes albopictus , Anopheles gambiae sensu stricto [ An. gambiae s.s.], Anopheles funestus, Anopheles stephensi, Anopheles minimus and Anopheles albimanus ) to seven public health insecticides in five classes, including pyrethroids (metofluthrin, prallethrin and transfluthrin), neonicotinoids (clothianidin), pyrroles (chlorfenapyr), juvenile hormone mimics (pyriproxyfen) and butenolides (flupyradifurone), in glass bottle assays. The data were analysed using a Bayesian binomial model to determine the concentration–response curves for each insecticide–species combination and to assess the within-bioassay variability in the susceptibility endpoints, namely the concentration that kills 50% and 99% of the test population (LC 50 and LC 99 , respectively) and the concentration that inhibits oviposition of the test population by 50% and 99% (OI 50 and OI 99 ), to measure mortality and the sterilizing effect, respectively. Results Overall, about 200,000 mosquitoes were tested with the new bottle bioassay, and LC 50 /LC 99 or OI 50 /OI 99 values were determined for all insecticides. Variation was seen between laboratories in estimates for some mosquito species–insecticide combinations, while other test results were consistent. The variation was generally greater with transfluthrin and flupyradifurone than with the other compounds tested, especially against Anopheles species. Overall, the mean within-bioassay variability in mortality and oviposition inhibition were < 10% for most mosquito species-insecticide combinations. Conclusion Our findings, based on the largest susceptibility dataset ever produced on mosquitoes, showed that the new WHO bottle bioassay is adequate for evaluating mosquito susceptibility to new and promising public health insecticides currently deployed for vector control. The datasets presented in this study have been used recently by the WHO to establish 17 new insecticide discriminating concentrations (DCs) for either Aedes spp. or Anopheles spp. The bottle bioassay and DCs can now be widely used to monitor baseline insecticide susceptibility of wild populations of vectors of malaria and Aedes- borne diseases worldwide. Graphical abstract
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DOI: 10.1186/s13071-022-05554-7
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