We’ve heard it many times before: wild bumblebees are in decline. There is a host of reasons for their downward spiral – from industrial expansion to parasites – but one largely untested player in the mix is viruses on the flowers themselves, spreading from domestic honeybee populations to wild bumblebees.
"This is likely through salivary secretions or feces left behind on flowers while bees are foraging," lead author Samantha Alger, a scientist at the University of Vermont, told IFLScience. "We are working on controlled experiments to demonstrate and test this transmission route.
Two RNA viruses, in particular, were found in higher rates in wild bumblebees collected near managed bee hives than those further out: the deformed wing virus (DWV) and the black queen cell virus (BQCV). The first causes shrunken, crumpled wings in bee pupa. The second makes the queen’s pupae turn black and die. The team detected BQCV in 75.7 percent of the bumblebees tested and DWV in 9.3 percent of the population.
"Bumblebees are very important pollinators of our crops and wild flowers," said Alger. "Bumblebees (and some other species of native bees) are only capable of 'buzz pollination', which is needed to fertilize some crops such as squash and tomatoes. In this type of pollination, the foraging bee will grasp the male parts of the flower and vibrate her wing muscles to release pollen. Honey bees are not capable of buzz pollination."
The team collected bumblebees, honeybees, and flowers in Vermont, US, from seven sites with commercial honey bee apiaries within 300 meters (0.2 miles) and 12 sites with no commercial apiaries within 1 kilometer (0.6 miles). Data published on bee flight ranges for both honeybees and bumblebees indicates a flying overlap of 1 kilometer. At each field site, they placed the bees on dry ice to preserve their RNA until lab storage at 80°C (176°F).
The team also collected highly visited common flower species from each site, detecting viruses on 19 percent of flowers within apiaries. "I thought this was going to be like looking for a needle in a haystack. What are the chances that you're going to pick a flower and find a bee virus on it?" said Alger, whose study is published in PLOS One. "Finding this many was surprising."
The team did not, however, find bee viruses on flowers that were 1 kilometer from managed beehives. They note that careful monitoring and treatment of diseased honeybee colonies could help mitigate the damage from these viruses to wild bees.
"Honey bees are the most important managed pollinator of our agricultural crops and it would be difficult to grow food in the vast quantities we need in the current monoculture food system. However, if you want to 'save the bees', purchasing a honey bee colony is not the answer," said Alger.
"As livestock, honey bees need to be monitored and treated when necessary. Imagine being a farmer of cows or chickens and not treating your livestock for a parasite infestation."
"If you aren't willing to put in the work to monitor and treat your bees, you could actually be harming wild bee populations instead of helping them."