Bumblebee numbers dwindling, and one study points to picky diets

The next step will be to research why some bumblebee species are more finicky eaters than others.

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Bonnie Burton
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MSU entomologist Thomas Wood 

Michigan State University

It seems honey bees get all the buzzworthy headlines these days due to their declining numbers, but challenges faced by the humble bumblebee are getting some serious attention too.

In a study conducted by Michigan State University and published in Ecology: Ecological Society of America on Tuesday, scientists researched the diets of 12 bumblebee species to try to determine if their eating habits could be contributing to their dwindling numbers.  

The study compared current distributions of bumblebee species across Michigan, from the modern-day bumblebee to museum specimens dating back as far as the 1880s. 

The research shows that half of the bumblebee species studied have declined by more than 50 percent. This isn't too surprising considering that in 2017, the rusty patched bumblebee was the first bumblebee in the United States to be listed as endangered

In addition to the rusty patched bumblebee, other species, such as the American bumblebee, the yellow banded bumblebee and the yellow bumblebee, are also facing startling population declines.

But while some scientists think possible causes of the bumblebees' decline include disease, parasites and pesticides, this new study suggests the bumblebees' lower population numbers could stem from picky diets.

"Species that declined collected pollen from fewer species of plants and seem to have a narrower range of plants they visit for pollen," Thomas Wood, MSU entomology postdoctoral researcher and lead author of the study, said in a statement. "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."

The study did find that not all bumblebee species have dire population numbers. The common eastern bumblebee and the brown belted bumblebee are two examples of more stable bumblebee species that have actually seen their numbers increase.   

The next step in the research will attempt to understand why bumblebee species with narrow diets don't change their plant preferences to better survive.

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