2020托福听力练习：花蜜有助于蜜蜂健康（下载）

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　　Home-based bird watchers might have mixed up a batch of nectar to attract the feathered objects of their affection.

　　It's pretty easy—just mix sugar and water.

　　But the real stuff is a lot more complex—nearly all nectars are laced with amino acids, and some contain alkaloids, like nicotine and caffeine.

　　What's the plants' motivation for producing such chemicals? "

　　It's possible that this is an antimicrobial adaptation of plants—that they're toxifying their nectar to protect it from spoilage by yeast or other microbes."

　　Leif Richardson, an ecologist at the University of Vermont.

　　He says the compounds might also be a chemical defense.

　　"Maybe the compounds are deterrent to nectar robbers, who take nectar without pollinating."

　　And yes, "nectar robbing is indeed a thing."

　　But Richardson and his colleagues have come up with yet another function for nectar's chemicals: as medicine for bees.

　　They found compounds in the nectar of wild tobacco, linden, and white turtlehead flowers that cut the numbers of a common gut parasite in bumblebees by as much as 80 percent.

　　The results are in the journal Proceedings of the Royal Society B.

　　The big unanswered question here is whether bees might actually self-medicate when they're sick.

　　Preliminary work suggests they do.

　　And if that notion holds true, farmers and home gardeners alike could boost bee health—simply by growing plants that serve up the right medicine.