Researchers have found that a single genetic mutation causes resistance to DDT and pyrethroids (an insecticide class used in mosquito nets).
The researchers, led by Dr Charles Wondji, used a wide range of methods to narrow down how the resistance works, finding a single mutation in the GSTe2 gene, which makes insects break down DDT so it's no longer toxic.
They have also shown that this gene makes insects resistant to pyrethroids raising the concern that GSTe2 gene could protect mosquitoes against the major insecticides used in public health.
Charles Wondji said that they found a population of mosquitoes fully resistant to DDT (no mortality when they were treated with DDT) but also to pyrethroids.
They took mosquitoes from Pahou in Benin, which were resistant to DDT and pyrethroids, and mosquitoes from a laboratory fully susceptible strain and did a genome wide comparison study. They identified the GSTe2 gene as being upregulated - producing a lot of protein - in Benin mosquitoes.
They found that a single mutation (L119F) changed a non-resistant version of the GSTe2 gene to a DDT resistant version.
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They designed a DNA-based diagnostic test for this type of resistance (metabolic resistance) and confirmed that this mutation was found in mosquitoes from other areas of the world with DDT resistance but was completely absent in regions without. X-ray crystallography of the protein coded by the gene illustrated exactly how the mutation conferred resistance, by opening up the 'active site' where DDT molecules bind to the protein, so more can be broken down.
The research has been published in the journal Genome Biology.