[A]bout half of Vermont’s bumble bee species have disappeared or are in serious decline, which could be bad for produce farmers.
Researchers from the Vermont Center for Ecostudies and the University of Vermont’s Gund Institute combed through historical collections of bumble bees and — with the help of more than 50 citizen scientists — conducted field surveys around the state to document changes in the state’s bumble bee population. In a study published this month in the Journal of Insect Conservation, they found that four of the state’s 17 bumble bee species have disappeared in the past 100 years.
Kent McFarland, a study author who is a conservation biologist with the Vermont Center for Ecostudies, said the group was expecting to see some decline in species diversity based on similar trends researchers had documented worldwide.
But “to have almost half of the bumble bee fauna in Vermont disappear or severely decline, I was bummed out,” he added. The species that have disappeared in Vermont are: Rusty patched bumble bee, Ashton’s cuckoo bumble bee, Black-and-gold bumble bee and Fernald’s cuckoo bumble bee. Researchers found that four other bee species showed “significant” declines in population.
There’s no “smoking gun” researchers can point to for the decline in species diversity, said Leif Richardson, an ecologist with the Gund Institute who worked on the study. One possible factor is the decline in the state’s grasslands since researchers found that grasslands were home to the greatest variety of bumble bee species. Vermont’s grasslands have been converting back to forests or are being developed to the tune of roughly 1,000 acres a year, he said.
Other factors likely contributing to the decline in bumble bee diversity are climate change, new parasites and pathogens, and pesticide use, said Richardson. Conventional corn is commonly grown with seeds treated with neonicotinoids, which are systemic — “meaning the whole plant becomes toxic to herbivores” like bees, he said.
Richardson noted that the troubles plaguing bumble bees and other native bees should not be conflated with problems plaguing honey bees, like colony collapse disorder, that have garnered media attention lately.
“Interestingly, honey bees are part of the problem for bumble bees,” he said. Honey bees can spread parasites and pathogens to native bees.
Not all bumble bees have done poorly — researchers found that four closely related species in the subgenus Pyrobombus are actually more abundant, in line with a global trend. Richardson said that those bees must have some common traits, such as resistance to parasites or an ability to better survive in developed areas, that is allowing them to fare better. For instance, the common eastern bumble bee — one of the bees in that subgenus— is the bumble bee you’re mostly like to see in downtown Burlington, “foraging on flowers and planters on Church Street,” he said.
UVM’s Gund Institute has been conducting research to quantify the value of pollination for Vermont farmers. A recent study found that pollination by wild bees increases size and quantity of berries. On one farm that was particularly lacking in wild bees, researchers found that increased wild bees could have boosted berry production by $136,000.
While Richardson said that it is not yet clear that “we’ve lost the ecosystem service (of pollination) from bumble bees themselves,” the disappearance of species is troubling as plants co-evolve with particular pollinators.
“What underlies all of this is that we’ve lost some of the biodiversity,” he said. “Plants do better with different kinds of pollinators.”
Additionally, bumble bees are particularly adept at pollinating in Vermont as they have a greater tolerance for cold than many species. “It can be 40 degrees and you’ll still see bumble bees out there trying to make a living,” said McFarland.
A decrease in bee diversity has the potential for broader impacts to the natural world outside the realm of agriculture. For example, the swath of color that pops up on forest floors in the form of ephemeral wildflowers is reliant on native pollinators, said McFarland.
The bee survey is part of a broader effort by the Vermont Center for Ecostudies to catalog the state’s biodiversity. McFarland said working with trained volunteers, called “citizen scientists,” is crucial for efficiently conducting statewide surveys of flora and fauna. VCE completed similar surveys of butterflies and birds before embarking on the bee survey from 2012-2014.
The data collection led to three species to be added to the state’s endangered species list, said McFarland. He added that he is currently drafting a report to request that another bee, the American bumble bee, be added to the list. “That species used to be pretty common in the Champlain Valley, but we can’t find it anywhere now.”
While inclusion on the state’s endangered species list does not in itself afford great levels of protection, McFarland said the hope is that drawing attention to the decline in bumble bee biodiversity will catalyze a broader conservation movement similar to what happened with the common loon. The population of that iconic bird has increased from seven nesting pairs in 1983 to 97 pairs in 2017.
Planting bee friendly flowers, and not spraying them with pesticides, is one step concerned citizens can take to provide more bee habitat, said Richardson. At a larger scale, owners of grasslands can implement management strategies, like leaving sections of fields uncut each year, that could provide more flowering plants for pollinators, he said.
Banning the use of seeds treated with neonicotinoids is another step that could help native bees, said Richardson. The European Union banned that class of pesticides last year. Closer to home, Vermont lawmakers considered a ban on neonicotinoids last session that did not make it out of committee.
Another step lawmakers could take would be to ban the importation of unhealthy bee colonies into the state, said Richardson.
“We don’t allow people to bring sick horses into Vermont,” he added. “With these invertebrate livestock, honey bees and commercial bumble bees … we allow (people) to bring diseased animals into the state all they want and it is causing some of these problems.”