From Ars Technica:
Bees are disappearing—that much is certain. What's unclear is why. Pathogens and pesticides have been posited as potential causes, as has the loss of bees' preferred floral resources. This last reason has intuitive appeal: wildflowers are disappearing because of agriculture, and bees rely on the pollen and nectar in flowers, so the loss of flowers should be causing the loss of bees.
But a demonstration of this seemingly simple idea has been hard to come by. Different species of bees rely on different plants—the bee species that are disappearing have never been analyzed in terms of taste for the plants that are disappearing to see if they match up. And, once the bees or plants are gone, it's hard to figure out what relationship (if any) they might have had. Pesky details.
Researchers in the Netherlands have gotten around this problem by examining museum specimens of bees to figure out which bees like which flowers. They've demonstrated that the bee species that have declined are in fact those that like the pollen from flower species that have also declined.
The Netherlands was an appropriate place for this work because, in addition to conveniently being where the researchers live, it is (according to them) "one of the most human-modified and intensively farmed countries in the world." As a result, bees in the country have lost eighty percent of their habitat over the course of the twentieth century.
Bees are pickier in choosing their source of pollen, which supplies them with protein and minerals, than in choosing their source of nectar, which provides them with energy. Thus, the ecologists who designed this study looked at the pollen loads in the bodies of bees collected before 1950—before agriculture intensified and bee populations plummeted. This is important because by now, when both bee and floral populations have been declining for decades, bee species may be reduced to eating from plants that are not really their faves.
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