KINGSTON, R.I. – November 15, 2021 – The results of a survey of bumblebees in Rhode Island conducted by a University of Rhode Island graduate student included one species that had not been seen in more than a decade. But it also confirmed that four other species appear to have disappeared from the state.
“There had never been a bumblebee survey of Rhode Island – or a statewide survey of any kind of bee – and there are some species in the URI historical insect collection that are no longer found in the state,” said Elizabeth Varkonyi of Cranston, who led the project with URI Professor Steven Alm. “There used to be 11 species in Rhode Island, but only six of those had been seen since 2014. I wanted to get a better idea if those six were truly the only species found here now. And it turns out that we’ve added a seventh species to the list.”
Bumblebees are important pollinators of flowers and agricultural crops. Certain crops like tomatoes, peppers and blueberries require a specific kind of pollination called buzz pollination that only a few types of bees, including bumblebees, can do efficiently, Varkonyi said. During buzz pollination, bumblebees vibrate their flight muscles when they land on a flower, and that vibration causes the plants to release their pollen.
With the assistance of fellow URI graduate students Casey Johnson and Julia Vieira, Varkonyi trapped bumblebees at 54 sites around Rhode Island from 2019 to 2021 and surveyed 48 other sites with abundant flowers to record bumblebees and the flower species they were visiting. Of the 7,096 bumblebees she documented, just two species – the common eastern bumblebee (Bombus impatiens) and the brown belted bumblebee (Bombus grisecollis) – made up 82 percent of the total.
“Bombus impatiens seems to be dominant in the region, and that could be a factor contributing to our bumblebee decline – competition with this species,” Varkonyi said. “A lot of farmers purchase colonies of this species to pollinate their crops, and they might carry parasites or diseases that could be spread to wild populations of other species.”
The most notable finding in her survey was the rediscovery of a single specimen of the American bumblebee (Bombus pensylvanicus) in southern Rhode Island, a species being considered for endangered species status and that had not been documented in Rhode Island since 2009. Robin Baranowski, a field botany instructor at URI, was the first to spot the American bumblebee in August 2021.
“We were really only expecting to find the six species that we knew were here, so we couldn’t believe it when we found that seventh species,” she said.
Varkonyi also found 23 individuals of the yellow bumblebee (Bombus fervidus), another rare and declining species.
She did not, however, find any evidence of four other species that used to be found in the state – Bombus affinis, Bombus citrinus, Bombus terricola, and Bombus ternarius. While some of these four species are still found in nearby states, all appear to be declining. Some have shifted their ranges northward, perhaps due to the changing climate.
“Having a higher diversity of bumblebee species is important because we found that each species has its own floral preferences,” said Varkonyi, who will graduate next August and plans a career involving the management and conservation of habitat for pollinators. “Losing one species can negatively affect the flowers and crops it pollinates.”
The most common plants that Varkonyi found bumblebees visiting were bee balm, common St. John’s wort, yellow wild indigo and red clover. The newly rediscovered American bumblebee was found visiting bee balm, while the rare yellow bumblebee primarily visited red clover.
Varkonyi presented the results of her bumblebee survey at the annual meeting of the Entomological Society of America in Denver on Nov. 1, where her research poster won first place in the Systematics, Evolution and Biodiversity category.