Science / Medicine : Resistance Tied to Genetic Error

A genetic accident in a single mosquito apparently led to the ability of some mosquitoes around the world to resist a class of insecticides, French researchers reported last week in the journal Nature. The finding may have important implications for programs that use insecticides to control mosquitoes that spread disease.

The study investigated why mosquitoes called Culex pipiens can often resist organophosphate insecticides. Scientists knew that the mosquito does that by overproducing substances called esterases that fend off the insecticides. This occurs in mosquitoes with an excess number of copies of esterase genes, the result of a genetic accident.

The new results suggest that such an accident occurred once and then spread through migration of mosquitoes.

The researchers studied genetic material from insecticide-resistant mosquitoes from California, Texas, Pakistan, the Congo, Egypt and the Ivory Coast. Normally, different mosquito populations show wide variation in the details of the stretch of genetic material containing the esterase gene. But the researchers found that the samples were identical, making it “highly improbable” that they had developed independently.