An end to evolution?: An Anopheles stephensi mosquito feeds on a human host. This species spreads malaria from Egypt to China.
Credit: Wikimedia/CDC
SYDNEY: Scientists have proposed a new weapon in the battle against malaria: insecticides that mosquitoes can't develop resistance to.
The new strategy could halt the rise of resistant strains by targeting older mosquitoes after they've laid eggs, but before they can pass on the parasite.
"Late-life insecticides will be useful for much, much longer than conventional insecticides," said lead author Andrew Read, an entomologist at Pennsylvania State University in University Park, USA. "Maybe even forever."
Problem of resistance
Each year, malaria kills over one million people worldwide. Current attempts to control its spread involve spraying insecticide on the walls of houses and bednets.
Existing compounds kill mosquitoes indiscriminately and strike all ages, though. In areas where insecticides are heavily used, many of the mosquitoes that live long enough to lay eggs are highly resistant to them.
"The insecticides work by killing the insects or denying them the human blood they use to make eggs. This imposes an enormous selection in favour of insecticide-resistant mosquitoes," he said.
In their paper, published in the journal PLoS Biology today, the researchers propose a strategy which eradicates the problem, not the insect. "Unlike in agriculture [where insects are the issue], the aim here is disease control, not necessarily insect control," they said.
They noted that mosquitoes lay several batches of eggs while the malaria parasite is still developing, before it moves to the salivary glands of mature mosquitoes to be transmitted.
Highly targeted
"If, instead of killing indiscriminately, insecticides killed just old – and ideally old infectious – mosquitoes, then the evolution of resistant mosquitoes would be really slowed, or would never occur at all," said Read.
The team created a mathematical model of malaria transmission to find out just how successful a late-life-acting insecticide might be. The model parameters were based on mosquito and parasite life cycles, and malaria transmission in four hotspots - three in Africa and one in Papua New Guinea.
They found that resistance spread much more slowly using the new treatments compared with conventional chemicals. If there is a fitness cost – such as less offspring because energy is being diverted to detoxification – to having resistance, then resistance in the population might not spread at all.
