Environmental microplastics (MPs) have been linked with increased insecticide resistance in anopheles gambiae s.s. – a primary mosquito species responsible for spreading malaria.

A recent study, published on PLOS One, uncovered this alarming connection, showing that microplastics can worsen insecticide resistance in Anopheles gambiae s.s.. by increasing their resistance. Scientists in the study, hailing from Tanzania and the UK, warn that this discovery could further make malaria control efforts more challenging.

“Our study has demonstrated the potential for microplastics to adversely affect Anopheles gambiae s.s. by increasing their resistance to insecticides,” the scientists noted. “Therefore, MPs in larval breeding sites could be contributing to the development of insecticide resistance in these important malaria vectors, which is a significant concern for environmental control programmes,” they explained.

Larval adaptation to microplastic exposure

The scientists found that exposing mosquito larvae to PET microplastics significantly reduced their survival rates and prolonged their development time. However, after several generations, the larvae adapted to these conditions, showing increased survival and faster development.

Microplastics reduce insecticide efficacy

Additionally, larvae exposed to microplastics mixed with insecticides showed higher survival rates compared to those exposed to insecticides alone, with resistance increasing over six generations. This reduced efficacy of insecticide was linked to MPs absorbing insecticides, reducing their concentration in the environment.

Heightened tolerance in adult mosquitoes

The study discovered that adult mosquitoes exposed to MPs during their larval stages also displayed heightened insecticide tolerance. This resistance became stronger over generations due to genetic and biochemical adaptations, including the overexpression of stress mediator proteins.

Urgent call for field studies, pollution reduction

In light of these findings, the scientists underscore the urgency of conducting field studies and reducing microplastic pollution to preserve the effectiveness of malaria control strategies. 

“This is the first study demonstrating the selection of insecticide tolerance in adult mosquitoes after consecutive generations of larval exposures to varying concentrations of MPs. Therefore, field-scale studies are now urgently required to quantify whether larval insecticides are less effective at controlling mosquitoes in breeding sites commonly polluted with MPs,” the scientists wrote.

As MPs become more prevalent in mosquito breeding sites, they could accelerate the development of insecticide resistance in mosquito populations, posing significant challenges for vector control programs.

Ifakara scientist among key contributors

Ifakara Health Institute scientist Mgeni Mohamed Tambwe was among the contributors to the study. The research was led by Dativa Shilla from the University of Dar es Salaam (UDSM), Tanzania, and Richard Quilliam from the University of Stirling, UK. Other contributors included Deokary Joseph Matiya and Nyanda Laini Nyamandito, both from UDSM.

Read the publication here: https://journals.plos.org/plosone/article/authors?id=10.1371/journal.pone.0315042