Malaria mosquitoes' secret revealed - mutation study uncovers
key to insecticide resistance
June 18, 2003
A new study suggests a single genetic mutation could explain
why disease- carrying mosquitoes become resistant to a major
class of insecticides it was reported in Nature News magazine
on 9 May 2003.
 Insecticides
that are used worldwide to control mosquito numbers are made
from chemicals called organophosphates and carbamates. They
act by blocking a key enzyme in the insects' nervous system
called acetylcholinesterase (ACH), which paralyses the insect
and kills it.The problem until now has been the rapid resistance
developed by mosquitoes to organophosphate and carbamate based
insecticides, especially in urban areas where they are sprayed
most. It has been a mystery how this resistance evolves.
In an exciting development a team in France managed to identify
the gene that encodes for ACH and then went onto find that
a single molecular difference in this gene underpins resistance
to the two insecticides.
"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.
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.
But 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. Insects
will continue to evolve and develop means of evading efforts
at control.
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 a similar genetic mutation
allowing them to survive organophosphates and carbamates,
which are also sprayed on crops.
References:
Weill, M. et al. Insecticide resistance in mosquito vectors.
Nature, 423, 136 - 137, (2003).
Source : Nature
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