Different chemical coatings used on mosquito nets can affect how well they perform, which means that nets should be assessed on more than just their insecticide content alone, new research shows.

Insecticide-treated nets remain one of the most important tools in malaria prevention. They act both as a physical barrier and as an insecticidal surface that kills or disables mosquitoes before they can transmit the parasite.

A study led by Liverpool School of Tropical Medicine developed a new evaluation platform combining chemical analysis, surface imaging and mosquito behavioral tracking to test the performance of insecticide-treated nets made with and without insecticide binder containing per- and polyfluoroalkyl substances (PFAS).

PFAS-based coatings are a group of synthetic fluorinated chemicals that have been valued for stability and performance in a range of sectors. However, their environmental persistence and potential health risks have made their removal an important priority.
Against this background, the study asked whether replacing these coating materials affects how well nets perform, particularly against malaria mosquitoes from sub-Saharan Africa, where insecticide resistance is already widespread.

Published in Science Advances, the case study found that, although nets without PFAS coatings met specifications for deltamethrin pyrethroid insecticide content, removing PFAS altered how well a net worked. Crucially, the effect varied across mosquito populations and levels of insecticide resistance. The clearest differences were seen in resistant strains, whereas the impact was small or not significant in the susceptible strain.

The findings indicate that efficacy is shaped not only by how much insecticide is present, but also by how it is presented on the fiber surface and how readily it is transferred to the mosquito. The researchers found that PFAS-based coatings possessed smaller, more evenly distributed, deltamethrin particulates, while PFAS-free coatings showed larger, coarser and less evenly distributed particulates. These surface differences were linked to changes in mosquito behaviour, including reduced irritancy and reduced knockdown in resistant strains, showing that coating chemistry can alter insecticide bioavailability and ultimately net performance.

The researchers argue that this case study shows insecticide content alone does not fully explain how a net performs. They suggest that evaluation of insecticide-treated nets should not just consider bulk chemical content, but a more integrated framework combining conventional bioassays with surface chemistry, imaging, and behavioral analysis. This approach could strengthen product development, regulatory evaluation and post-market surveillance by detecting meaningful performance differences that standard testing may miss.

Dr Hanafy Ismail, lead author and Group Leader of the Chemical Biology Group, Department of Vector Biology, Liverpool School of Tropical Medicine, said: “Malaria kills hundreds of thousands of people each year, and insecticide-treated nets remain one of the most effective and affordable tools we have against the disease. At the same time, the environmental rationale for moving away from persistent fluorinated chemicals is real and should not be ignored. Environmental sustainability and malaria control must move forward together.

“Our findings show that chemical compliance is not the same thing as biological performance. What matters is how the insecticide is presented on the fibre surface, how bioavailable it is to the mosquito, and how mosquitoes respond on contact. As malaria control tools evolve, we need integrated evaluation systems that can detect meaningful performance shifts early and help ensure that environmentally sustainable products remain effective for the communities that depend on them.”

Prof. Rasmita Raval, co-corresponding author from the University of Liverpool, said: “This study shows that surface chemistry is not a minor formulation detail. Two nets can contain similar amounts of insecticide yet behave very differently at the point of mosquito contact. By linking surface presentation to mosquito response, we can better understand how to design formulations that are both environmentally responsible and biologically effective.”