The Washington Post reported, one of the main reasons, experts say, is that farmers have used herbicides on the milkweed plants that these butterflies feed on.
《华盛顿邮报》报道，专家说，主要原因之一是，农民对马利筋植物使用除草剂，而这些蝴蝶以马利筋植物为食。
Caterpillars of monarch butterflies feed exclusively on milkweed leaves.
黑脉金斑蝶的毛虫只吃马利筋的叶子。
Maize pollen is dispersed by the wind and often blows onto milkweed plants that grow near maize fields.
玉米花粉被风吹散，经常吹到生长在玉米田附近的乳草属植物上。
The specific glycosides present in milkweed differ from region to region within the monarch butterfly's range.
马利筋中的特殊糖苷在帝王蝶的范围内因地区而异。
When, in experiments, these caterpillars were fed milkweed leaves dusted with pollen from modified maize plants, they died.
在实验中，这些毛毛虫被喂食沾有转基因玉米花粉的马利筋叶子，然后它们死亡了。
Being milkweed, it sent more shoots right back up.
作为顽强的，屡败屡战的马利筋，它立刻就生发出更多的笋芽，妄图卷土重来。
The tarantula hawk wasp feeds on milkweed pollen.
一只沙漠蛛蜂正在吞食马利筋的花粉。
Overall, a monarch butterfly is no more or less striking than its host, the milkweed pod.
总的来说，帝王蝴蝶和其宿主奶草豆荚的漂亮程度是差不多的，既不多一分，也不少一分。
This is because their staple food, milkweed, is being used more and more as a garden ornament.
这是因为它们的主要食物乳草被越来越多的用于园林装饰。
one says at the Monarch Club, “Mrs Jones of Acacia Drive, Bermuda, has planted milkweed. Fancy a bit?
也许在君主蝶聚会的时候其中一只会说：“嘿，伙计们，百慕大阿卡西亚大街的琼斯夫人家刚种了乳草，有兴趣去来一口吗？”
In defending itself so thoroughly against the monarch, the milkweed became inseparable from the butterfly.
马利筋为自我保护如此认真地抵抗黑脉金斑蝶的侵袭，结果变得与蝴蝶难舍难分。
Professor Taylor is urging people in the southern United States to help the monarchs by planting milkweed .
泰勒教授呼吁在美国南部的人来帮助种植米尔克韦德的君主。
The ornamental plant of milkweed family was liken by people with its unusual of flower, its elegant of vine.
萝藦观赏植物以其花奇特；茎蔓飘逸而倍爱人们亲睐。
There they leave their eggs on milkweed plants, with the next generation of monarchs appearing a short time later.
在那里，他们留下的蛋乳草植物，在很短的时间后出现的君主下一代。
The plants bloomed in slow, honey-fragrant fireworks, and by July there was a 4-foot wall of milkweed screening a dimly remembered pond.
缓慢的，散发着蜂蜜香味的花朵如礼花般绽放，七月的时候，池塘边的4英尺高的马利筋依稀长成了一堵屏风。
Monarch caterpillars feed on any of dozens of species of milkweed plants, including some species that contain high levels of cardenolides.
帝王蝶的幼虫以很多乳草属植物为食，包括一些包含高水平强心甾的类型。
If I met a fairy, I could stay awake all night without getting tired, then sleep all morning as fairies do, curled in a silky milkweed pod.
假若仙女来了，我整晚不睡觉也不会觉得累。第二天我和仙女们一样，蜷缩在柔滑的乳草荚里睡到中午。
S. midwest. The gene crops are designed to resist herbicides and that's allowed farmers to wipe out milkweed, which is the main food source for Monarches.
基因作物可以抵抗除草剂，这样农民就可以用除草剂除掉马利筋，而马利筋是黑脉金斑蝶最主要的食物来源。
The EPA estimates that the insects face no observable harm when consuming milkweed leaves laden with up to 150 corn pollen grains per square centimeter of leaf surface.
环保署估计，即使马利筋叶片上每平方公分有高达150颗的玉米花粉，昆虫食用后也没有明显的危害。
They are poor yet have done their bit to reduce illegal logging. Americans and Canadians are much richer, and have millions of miles of roadside that could usefully be covered with milkweed.
尽管贫穷，他们却也尽己所能减少非法伐木，相比之下，美国和加拿大要富裕得多，两国还有数百万英里的道路两侧可以种上乳草，发挥作用。
They are poor yet have done their bit to reduce illegal logging. Americans and Canadians are much richer, and have millions of miles of roadside that could usefully be covered with milkweed.
尽管贫穷，他们却也尽己所能减少非法伐木，相比之下，美国和加拿大要富裕得多，两国还有数百万英里的道路两侧可以种上乳草，发挥作用。
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