Michigan State University researchers discover a decline in bumble bee populations across the state.
The research, published in the current issue of Ecology, shows that half of the bumble bee species studied have declined by more than 50%.
The Spartan study compares species from across the state with samples as far back as the 1880s.
Researchers investigated the kinds of plants each bumble bee species visited by removing pollen from the specimens. Bumble bees carry their pollen on their back legs, and this can be removed and identified under a microscope, even over a century after the bee was alive.
“Species that declined collected pollen from fewer species of plants and seem to have a narrower range of plants they visit for pollen,” said Thomas Wood, MSU entomology researcher and lead author of the study. “In contrast, the stable species visit a much wider variety of plants. This suggests that picky eaters are less able to switch if a favorite plant isn’t available.”
While many scientists focus on the decline of honey bees, relatively few study bumble bees.
“Bumble bees are important pollinators of plants across natural habitats, where they help support the seeds and berries that birds and other animals depend on,” said Wood. “They also are effective pollinators of many fruits and vegetables that are important for healthy human diets.”
For example, blueberries are a leading Michigan fruit crop where bumble bees are highly efficient pollinators.
“Many of Michigan’s key crops depend on them. In fact, about 50 percent of cherry pollination is carried out by wild bees,” said Wood.
Wood’s team compared 12 different bumble bee species across the state’s 83 counties to find some of the biggest declines of 65 to 100 percent in the yellow bumble bee (65%), yellow banded bumble bee (71%), American bumble bee (98%) and rusty patched bumble bee (100%).
Even though the study focused on Michigan, its findings hold lessons for other regions around the globe, and some of them are positive. A couple of success stories include the common eastern bumble bee which increased by 31% and the brown belted bumble bee which increased by 10%.
The next phase of the research will try to understand why bumble bee species with narrow diets do not show diet flexibility.
“Most of the declining bumble bee species in Michigan fly in the summer, feeding on prairie plants and other flowers of open countryside,” Wood said. “Fewer types of plants flower in summer compared to the spring. We also know that prairies have been lost over the last century so summer bumble bees may have been hit twice due to a loss of their preferred habitat and a reduced ability to adapt to this change.”
This research was funded in part by the USDA National Institute for Food and Agriculture, through the Great Lakes Great Bees project.