Malaria mosquitoes' secret revealed

Mutation study uncovers key to insecticide resistance.

9 May 2003

CAMILLA CARLSSON

Insecticides are used worldwide to control mosquito numbers. © WHO

A single genetic mutation could explain why disease-carrying mosquitoes become resistant to a major class of insecticides, a new study suggests.

Insecticides made from chemicals called organophosphates and carbamates are used worldwide to keep mosquitoes in check. They block a key enzyme in the insects' nervous system called acetylcholinesterase; they become paralysed and quickly die.

But mosquitoes rapidly develop resistance to organophosphates and carbamates, especially in urban areas where they are sprayed most. How this resistance evolves has been a mystery.

"For the first time we have identified the gene that encodes acetylcholinesterase," says Mylène Weill of Montpellier University II in France, who led the study. Her team then found that a single molecular difference in this gene underpins resistance to the two insecticides¹.

So far the researchers have identified the mutation in an insecticide-resistant strain of the mosquito that carries malaria, Anopheles gambiae, and in several populations of Culex pipiens, which carries the notorious West-Nile virus and other viruses that cause bird malarias.

It's an important finding, says malaria researcher Mats Wahlgren of the Karolinska Institute in Stockholm, Sweden. "It increases our understanding of this resistance mechanism and could help the development of new insecticides," he says.

Despite the potential for developing new insecticides, chemical warfare is unlikely to beat the insects, says Weill. "We must also continue to develop drugs and vaccines to keep up the fight against malaria and other infectious diseases carried by mosquitoes," she stresses.

Weill's team is now studying other insecticide-resistant mosquitoes, such as Aedes aegypti, which carries the deadly dengue and yellow fevers, to see if they share the mutation. Some agricultural pests might have the gene tweak too, allowing them to survive organophosphates and carbamates, which are also sprayed on crops.

1. Weill, M. et al. Insecticide resistance in mosquito vectors. Nature, 423, 136 - 137, (2003).