Study finds bees can swim, pesticides disrupt ability

Honey bee. Photo credit: U.S. Fish and Wildlife Service.

This article was originally published by Capital News Service and is republished here under a syndication agreement.

by Sonja Krohn, Capital News Services

A scientist at Michigan State University and his collaborators have discovered that honey bees can swim.

That research has implications for the survival of these essential pollinators – and a cautionary lesson about the risk that pesticides may impair their ability to swim to safety.

The study conducted on the MSU campus and at a Chinese university builds on earlier research showing that bees can use their wings as hydrofoils to move on the water surface.

If a honey bee accidentally falls into a pond, that older research found it can propel itself across the surface by keeping its upper wing surfaces dry while beating them. It’s an ability that could help the insect reach the shore and increase its chance of survival.

But Zachary Huang, an associate professor of entomology at MSU, said, “That study did not examine if the behavior was indeed swimming.”

While hydrofoiling allows bees to move on the water surface, it was unknown whether their behavior was purposeful or oriented towards a particular direction.

“So I set up an arena to study bee swimming right away,” he said.

Together with his co-authors, he theorized that honey bees would prefer to swim towards dark areas in a laboratory setting, so they set up “swimming arenas” to test that idea at two locations, MSU and Guangdong Academy of Sciences in Guangzhou, China.

They replicated dark elements like tree bark or a soil bank surrounding water, the study said, to test whether “orienting to dark objects in nature would help a bee reach land to avoid drowning.”

The scientists monitored the behavior of honey bees in circular glass bowls filled with water, while generating a dark area on its surface using a light and a piece of partially black paper.

And their theory was correct: The experiment showed that the insects preferred the dark region as they moved on the water surface to reach the edge.

In other words, they proved that honey bees do, in fact, swim.

And because their swimming is directional, the study in the journal Communications Biology said, it “has ecological significance because it can increase bees’ chance of survival.”

However, the scientists also found that environmental pollution from pesticides may negatively impact this behavior.

In the experiment, bees that were fed thiamethoxam, a widely used insecticide in both the U.S. and China, no longer moved towards the dark area. Instead, they moved rather randomly across the water, made more turns and took longer to reach the edge of the bowl.

With that, Huang said, “we further showed that bee swimming will lose the directionality if poisoned” as the insecticide may reduce the bees’ motor control.

That aligns with previous research showing that similar concentrations of the insecticide adversely impacted honey bees’ ability to walk, climb and fly, the study said.

While the experiment highlights the effects of “excessive pesticide use,” Huang noted that it used a dose that is about 25 times higher than the dose normally used in practice.

MSU Extension apiculture educator Ana Heck said, “Pesticides are used in Michigan for a variety of reasons.”

Many farmers and growers use pesticides to protect crop health and produce food, but they can also be a tool for managing landscapes, for protecting native plant species and for cosmetic purposes.

“Pesticides play a role in pollinator health along with other stressors like poor or inadequate nutrition, diseases and other pests and climate change,” Heck said.

While some pesticides are “acutely toxic to bees and kill them outright,” she said others have chronic or less-than-deadly effects that can impair a bee’s behavior and make it more susceptible to other stressors.

What Huang and his co-authors showed in their experiment “is a strong example of how pesticides can have sublethal effects and impair the normal behavior or functioning of bees,” she said.

by Sara Swanson

Sara Swanson is an editor, writer and a founder of the Manchester Mirror.