Ars Technica reports on More problems for bees: we’ve wiped out their favorite plants.
"The scientists concluded that loss of preferred host plants is one of the main factors responsible for wild bee decline, along with body size (bigger bees need more food and are more sensitive to its loss). The variety of the bees' diet did not play nearly as large a role. The researchers played with a variant on the chicken-and-egg idea; just because bees and their favorite flowers declined in tandem the loss of the flowers did not necessarily cause the loss of the bees, as the flowers rely on the bees for pollination. So perhaps the loss of bees caused a subsequent decline in the flowers. But circumstantial evidence—the fact that these plants can be pollinated by a number of different insects, and plants pollinated by water and wind have also decreased dramatically due to agriculture—suggests that the loss of the flowers led to a loss of the bees."