taking their tolls on
下記の文章のtaking their tolls on のtheir は、何を指していますか。Enviromental stress を指していると思いますが、その場合意味が良くわかりません。
わかる方がいらっしゃいましたら、よろしくお願いします。
Environmental stresses are taking their tolls on the insects, however, and this year's Tyler Prize for Environmental Achievement has gone to researcher May Berenbaum, who is studying solutions to the bee crisis.
＊take a toll on ～に被害［損害］を与える、～に犠牲を強いる
前後の文章
Bees play an important role in agriculture, pollinating crops and providing us with the natural sweetener, honey. Environmental stresses are taking their tolls on the insects, however, and this year's Tyler Prize for Environmental Achievement has gone to researcher May Berenbaum, who is studying solutions to the bee crisis.
出展：VOA
http://www.voanews.com/english/news/usa/Bee-Expert-Honored-with-Tyler-Environmental-Prize-121265429.html
お礼
ありがとうございました。 よく分かりました