University news

Scientists have discovered the first cases of Anopheles funestus mosquitoes genetically mutating to develop a resistance to a type of insecticide called DDT.

The discovery of ‘knock-down resistance’ (kdr) – a major insecticide resistance mechanism in insect pests – is the first time such a mutation has been documented in this species, which is a major vector for malaria transmission in Eastern and Southern Africa.

The study – published in Molecular Ecology and led by the University of Glasgow and the Ifakara Health Institute in Tanzania– shows that the mutation the researchers found is closely associated with resistance to DDT, a banned but historically pervasive insecticide.

The mutation's emergence may be linked to widespread contamination and historic stockpiles of DDT, a banned insecticide no longer in use but which continues to affect the environment.

The discovery of the knock-down resistance (kdr) mutation was found while the researchers were conducting whole-genome sequencing across multiple mosquito populations in Tanzania in order to better understand genetic variation in Anopheles funestus populations. When the researchers observed the unexpected resistance to DDT within one population, further analysis revealed the resistance to be linked with novel kdr mutations.

After identifying the resistant population, the researchers made the discovery that the collection of this species had been from a region near a large, historical DDT stockpile. This finding suggests that prolonged environmental contamination may have exerted selective pressure on the mosquitoes, driving the emergence of this resistance.

Currently, chemical insecticides are central to the control of agricultural pests and disease vectors, such as mosquitoes. The control of Anopheles mosquitoes through the distribution of over 2.9 billion insecticide-treated bed nets (ITNs) has helped avert an estimated 633 million cases of malaria, a disease that still kills 600,000 yearly. However, the widespread use of insecticides for agricultural pest and disease vector control also has detrimental consequences, including direct lethal and sub-lethal effects on human and animal health. A key obstacle to sustainable malaria control is the evolutionary arms race between mosquitoes and insecticide-based mosquito control.

Joel Odero, the lead author and PhD student at the University of Glasgow School of Biodiversity, One Health and Veterinary Medicine, and research scientist at Ifakara Health Institute said: “Our discovery raises concerns for the effectiveness of current malaria control methods, which rely heavily on insecticides. Understanding the development of insecticide resistance is key to combating malaria, a disease that kills hundreds of thousands of people annually, mostly in Africa.

“The research highlights how environmental legacies such as DDT pollution can shape modern public health challenges. The emergence of new resistance mechanisms could threaten decades of progress made in reducing malaria transmission and mortality.”

Dr Francesco Baldini, University of Glasgow School of Biodiversity, One Health and Veterinary Medicine, said: “Our discovery sheds light on the far-reaching and unintended consequences of historical insecticide use, highlighting how past environmental contamination can shape the evolution of vector populations and impact current public health interventions.”

Fredros Okumu, University of Glasgow and Ifakara Health Institute, added: “An urgent follow-up study is required to monitor the evolution of vector DDT resistance and determine whether this type of resistance could occur in other insecticide families which are currently being rolled out in products across the African continent.”

The paper, ‘Discovery of knock-down resistance in the major African malaria vector Anopheles funestus,’ is published in Molecular Ecology.

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Enquiries: ali.howard@glasgow.ac.uk or elizabeth.mcmeekin@glasgow.ac.uk

 

First published: 8 October 2024