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Study Documents Historic Decline In Vermont Bumble Bee Population

A Yellow-banded Bumble Bee nectaring Joe-pye weed
K.P. McFarland
Vermont Center for Ecostudies
A Yellow-banded Bumble Bee nectaring Joe-pye weed

A team of researchers from the Vermont Center for Ecostudies and the University of Vermont has found that several species of bumblebees native to the state are in severe decline or appear to have vanished.
The newstudy examining 100 years of records discovered that nearly half of Vermont’s bumblebee species have vanished or are in serious decline.  Researchers engaged over 50 trained citizen scientists to gather information on more than 10,000 bumblebee encounters across the state. Center for Ecosystem Studies Conservation Biologist Kent McFarland says they compared that data to historic insect collections at Yale, Middlebury College, UVM, and other public and private collections, some dating back to 1915.   “We were surprised by how much data we could get and compare it to the present day. And that enabled us to actually see what kind of changes might have happened throughout the state over the last hundred years because the data went back that far in some of these collections.”

McFarland says they categorized their analysis into two groups — what happened to bees before the 1990’s and what happened after the 1990’s.  “We did that because the 1990’s were this sort of bellwether period in which worldwide people were really noticing declines had happened with bumblebees. And so we wanted to know did the Vermont data fit that trend. And it really did. After the 1990’s at least half of them had drastically declined. We can’t even find four of them anymore. They’ve just disappeared.”

He adds many of the bumblebees had been quite common based on the historic collections.  “For example the Rusty Patch Bumblebee looks like it probably was just a regular bumblebee in our fauna. And then the last one of those we ever found in a collection was in 1999. Lots of them in the collections and then disappears, can’t find it anywhere. And we went and tried to find it pretty much in all the historic sites that it had been found before and we couldn’t turn it up. And there’s three other species like that the same way. They really were bees that were found in these collections and then really suddenly in the 1990’s bang they’re not in the collections anymore and we can’t turn them up.”   

UVM Gund Institute for Environment Ecologist Leif Richardson wasn’t surprised that some species are in decline in Vermont but notes that not all bumblebees are disappearing.  “It’s important to understand that this study makes statements about changes in the diversity, so like the number of species of bumblebees over time, but it does not say that we’ve lost abundance of bumblebees.  But it’s clear that we’ve lost some diversity.”

Wild bumblebees are primary plant pollinators and Richardson says the loss of four species raises concerns.  “Bumble bees are diverse in their foraging habits. It’s not like you can just swap one in for another. They actually do different things when they visit flowers and there are different types of outcomes for the plants. So I think we’re right to be concerned about the loss of species diversity.”

A number of factors may be contributing to changes in bee populations including climate change, habitat loss and pesticide use. McFarland’s theory implicates other bee species.  “All four of these bumblebee species tend to be closely related in one way or another, either ecologically or genetically. And it looks like there was a catastrophic decline in them that might have related to using another species of bumblebees in greenhouses. Those bees might have passed a pathogen or a parasite into these native populations that just didn’t have any resistance to it and it really might have done some damage to their populations. But then there’s a whole ‘nother group they tend to be stable or even expanding their populations.”

The Rusty-patched Bumble Bee was last seen in Vermont in 1999. The Yellow-banded, American and Ashton Cuckoo species are also in severe decline in the state.

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