Mentally “exhausted” honey bees—petroleum exhaust makes bees learn slower and forget faster

Featured Image Caption: Scent pollution could disrupt the relationship between honey bees and flowers by impairing bees’ ability to learn and remember floral scents. (Source: Myriams-Fotos via Pixabay)

Reference: Leonard, R.J., V. Vergoz, N. Proschogo, C. McArthur, and D.F. Hochuli. 2019. “Petrol exhaust pollution impairs honey bee learning and memory.” Oikos 128:264-273. DOI: 10.1111/oik.05405

Stop and smell the… exhaust fumes?

There’s a reason most of us don’t roll down the car window while we’re waiting behind an idling diesel truck in traffic. No one likes to choke on exhaust fumes—the sharp sting in your nose, the burn in your throat. It’s gross. But you’ve probably never worried about how highway exhaust affects your ability to think, learn, and remember. If you were a honey bee, though, it might be time to worry.

Exhaust is not only a nuisance to humans, it has negative effects on the cognitive abilities of bees. (Source: Kim Hansen via Flickr)

Honeybees eat nectar from flowers, and rely on airborne chemical compounds – we’ll just call them smells – to locate and identify the flowers that provide their food. It doesn’t take a scientist to figure out that exhaust fumes can mask and overshadow other, subtler smells. Let’s go back to our traffic jam—if you were lucky enough to be stuck in traffic on a road meandering through fields of wild flowers, would you smell more flowers or more exhaust fumes?

On the other hand, what it undoubtedly does take a scientist to do is conduct an “appetitive olfactory conditioning” experiment to figure out how exhaust fumes affect the brains and sense experiences of honey bees. A group of researchers at the University of Syndey, Australia was up to the task. They transported dozens of honey bees to their lab, kept them snug and stationary in bee harnesses, and closely observed their responses to different scent combinations.

The science of scents

Bees can learn, like the rest of us, from associating sensory cues with rewards. When they approach a flower, smell its scent, and drink its nectar, bees learn to associate the floral scent with a food source. They not only learn this, but remember it, and identify that scent as a feeding cue in the future.

Bees find flowers by tracking their scents, and learn to associate those scents with nectar feeding; pollutants that make this smell can interfere with bees’ ability to learn and remember these important foraging cues. (Source: OlinEJ via needpix)

The researcher team tested the effect of exhaust pollution on this cycle of learning and memory by exposing bees to scents produced by flowers with and without the secret ingredient of exhaust (which, in this case, was captured from the vent of a generator). The scientists discovered that when bees smell flower compounds in the presence of exhaust they take longer to learn the flower cue and also forget it sooner. This evidence suggests that exhaust fumes swamp out floral scents, so that bees experience the same “masking” or “overshadowing” effects that are also familiar to humans.

Inhaling pollutants could be more than just a nuisance to bees. The function of bees as pollinators is critical to human food systems as well as the life cycles of a vast swath of plant species. This study prompts a host of unanswered questions: if exhaust has these negative cognitive effects on bees, how will their partnership with flowers be affected as a result? What about other pollinators exposed to exhaust fumes? Or or the forms of pollution? The authors argue that the exposure of pollinators to pollution is likely to increase, and understanding the consequences of pollution exposure is an important direction for future work.


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Kara Cromwell

I recently finished my PhD in Ecology at the University of Wisconsin-Madison, focused on environmental drivers of disease in high-altitude streams. Beyond the science of parasites, I am interested in how people perceive the creepy, crawly and less charismatic elements of biodiversity, and I try to find creative ways to communicate about nature's unseemly side. I now live in Missoula, MT where I act as a consultant and communicator focused on making ecology research accessible and meaningful to community stakeholders.

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