A new video is the first to document how Varroa mites, which are linked with massive die-offs of honey bees, jump from flowers to attach themselves to bees.
The mites infest nursery cells in honey bee nests and feed on developing bees while also transferring deadly viruses.
The mites are known to readily spread through both managed and wild colonies. In managed colonies, Varroa mites are thought to spread by riding on bees when they rob weak colonies or drift between hives. But widely spaced wild colonies also suffer from mite infestations, even though wild bees rarely venture into other hives.
Scientists suspected that mites could attach themselves to bees when they visit flowers, but the idea hadn’t been confirmed yet.
“No one has ever shown that bees flying naturally and freely, arriving at flowers and then leaving as they wished, presented a large enough opportunity for Varroa mites to make these jumps,” says David Peck, first author of the study published in PLOS ONE.
Peck is a graduate student in the lab of Thomas Seeley, a biology professor at Cornell University and the study’s senior author. Michael Smith, a graduate student in Seeley’s lab, is a coauthor.
How they caught the mites on video
To test whether mites could travel from flowers to bees, the researchers took colonies of honey bees to the Adirondack mountains in upstate New York, where there are very few wildflowers, so the bees’ foraging could be controlled.
They placed mites on feeders of sugar water and on potted flowers and observed the mites detect bees and deftly navigate their way onto the bees’ backs.
“A noteworthy result that we didn’t originally expect was that once the mites get onto the bees, they show some pretty sophisticated behaviors to avoid getting groomed off,” Peck says.
They quickly climbed onto the top of a leg or onto the very center of a bee’s back, where the bee could not reach. Eventually, when mites reach a hive, they reproduce in nursery cells in honey bee nests and feed on larval bees.
Shipping flowers—and mites—around the world
The findings offer evidence of another mode of transmission of mites to bees, which is important for better understanding the disease risks Varroa mites present and for preventing colony deaths.
But the results also raise concern about shipping cut flowers and spreading Varroa mites to areas where they do not exist, such as Australia.
“If a mite could jump from a flower onto a bee that tried to visit one of these flowers at an open-air flower market, the result could be disastrous,” Peck says, adding that stricter safeguards for shipping flowers should be considered. These could include spraying flowers, refrigeration or limiting shipments to flowers raised in secure greenhouses.
Next steps for this research will be to better understand mite behaviors on flowers, such as how often and under what circumstances they end up on flowers.
Source: Cornell University