2020托福听力练习：鸡味可驱蚊防疟疾（下载）

　　In Africa's battle against malaria, two low-tech tactics—insecticides and bed nets—have done a decent job killing off mosquitoes. "But it's mainly one species that's been affected. That's a species called Anopheles gambiae, often referred to the African malaria mosquito." Rickard Ignell, a chemical ecologist at the Swedish University of Agricultural Sciences.

　　He says, despite that success, the problem is far from solved. For one, mosquitoes are developing resistance to insecticides. And two, there are many other species that can spread the disease. Including one that's common in the horn of Africa: Anopheles arabiensis.

　　Unlike the pickier gambiae, its palate is wide-ranging. Arabiensis sucks the blood of cattle, sheep, goats. But… not chickens. "Chickens like mosquitoes. So they'll actively feed on mosquitoes and other insects. So avoiding chickens could be a way of surviving, and evolving a way of smelling the chickens could be an early warning system for them."

　　And it turns out, that aversion to chickens can be used against the insects. Ignell and his colleagues isolated chemical compounds from chicken feathers, and dispensed them next to a human sleeping under a bed net—a human lure. And they found that fewer mosquitoes came round for a snack, due to the repellent chemicals. The findings appear in the Malaria Journal.

　　Ignell says this chicken cologne won't be immediately available. "Ideally the world would be like that, that we could bottle it up and send it off and they don't have to pay anything. But that's not the case usually." Luckily, there's an equally effective substitute. "We can actually reduce the number of mosquitoes indoors by just using a chicken. So that's probably the cheapest option."