VOA常速英语:Malaria-Control Scheme Targets Older Mosquitoes

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Despite new drugs and strategies for combating malaria, this infectious illness remains one of the world's most dangerous and deadly diseases. Now, some researchers think they have a strategy to produce a new, more environmentally friendly insecticide that targets geriatric mosquitoes.

Insecticides such as DDT were effective at controlling mosquitoes for several generations. But DDT had such toxic side-effects that it was eventually banned, despite its effectiveness.

Now, entomologist Andrew Read at Penn State University thinks the problem with insecticides such as DDT may be because people looking to control malaria have gone about it the wrong way.

"You don't need to indiscriminately kill mosquitoes to stop disease," he says. "You just need to kill the old ones."

That's because mosquitoes only live a few weeks. It takes the malaria parasite about two weeks in the mosquito to become dangerous to people. So Read says instead of trying to kill all mosquitoes, a better strategy is to target older, dangerous ones.

"The good thing about just killing the old ones is that most mosquiotoes will have done most of their reproduction before you kill them, and that means the susceptible mosquitoes will indeed continue to breed, so you still have susceptible mosquitoes, and your insecticides then just work against the old guys, removing them, and they are the dangerous ones. So under those circumstances, you don't get the evolution of insecticide-resistant mosquitoes."

He and his colleagues have been testing a kind of fungus that makes mosquitoes sick over the course of several weeks. And it eventually kills the oldest and most infectious mosquitoes.

"The name of the game is not mosquito control. It's actually malaria control," Read explains. "So if you just remove the old ones, you still have lots of young, non-dangerous mosquitoes around, but you have controlled malaria."

Read says this fungus is about 98 to 99 percent effective at killing old mosquitoes in the lab. Now he says he needs to test this fungal insecticide in villages areas where malaria is prevalent, to see whether fewer people get the disease, even if they're still getting bitten by mosquitoes.

Read's research is published in the open access journal PLoS Biology.