Mosquitoes carrying malaria are evolving resistance to insecticides faster than new chemicals can be developed, putting millions at greater risk of the deadly disease. Malaria kills over 600,000 people annually, and since World War II, insecticides have been a key tool in controlling the Anopheles mosquitoes that spread the Plasmodium parasite.
However, a new study by evolutionary geneticists reveals that mosquitoes are rapidly developing counterstrategies. In the mid-1990s, most African Anopheles were susceptible to pyrethroid insecticides, which are used in bed nets and indoor spraying. These methods prevented over half a billion malaria cases between 2000 and 2015. Today, mosquitoes from Ghana to Malawi can survive insecticide concentrations ten times the previously lethal dose, and some populations show resistance to all four main insecticide classes.
The research also examined Anopheles darlingi, the main malaria vector in South America. Analysis of over 1,000 genomes from 16 locations across the continent found extremely high genetic diversity—more than 20 times that of humans—enabling rapid adaptation. While earlier studies did not find target-site resistance, the new study detected resistance evolving through increased activity of P450 enzymes that break down insecticides. The same cluster of P450 genes has changed independently at least seven times across South America since insecticide use began in the mid-20th century.
In French Guiana, a different set of P450 genes shows similar evolutionary patterns. The findings highlight the challenge of staying ahead in the evolutionary arms race, as mosquitoes' vast gene pools make them far more adaptable than larger animals like birds, which were unable to evolve resistance to DDT.
