New study finds bumblebees can learn to associate new smells with their queen
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UNIVERSITY PARK -- Bumblebees are able to learn to associate new odors with their colony's queen, instead of being preprogrammed to recognize the queen's pheromones from birth, according to a new study led by researchers at Penn State.
For the study, recently published in the journal Communications Biology, the researchers treated buff-tailed bumblebee queens daily with one of two different floral scents as they built their colonies.
Later, the researchers gave these worker bees -- who grew up exposed to one of these scents as they tended to the queen -- a choice between the floral scent applied to their queen and a new, different scent they never encountered before. They found that the workers preferred the odor of the queen, which meant that they were able to learn it.
Etya Amsalem, associate professor of entomology in the College of Agricultural Sciences and lead author on the study, said the findings improve the understanding of how social behavior is regulated in insect societies.
"Insects are often thought of as 'hard-wired' animals with behavior that is largely preprogrammed and driven by instinct -- especially when it comes to chemical communication, such as worker bees recognizing a queen's pheromones," she said. "These findings demonstrate that these mechanisms are much more flexible and adaptable than previously thought."
With many insects, behavior is often guided by chemical signals called pheromones. These chemicals typically trigger innate responses -- meaning insects react appropriately without any prior experience or learning, the researchers explained.
The same assumption has long been made for social insects such as bees, ants and termites. In these societies, workers remain nonreproductive and instead care for the queen and her offspring because they respond to chemical signals produced by the queen.
"These pheromones influence both worker behavior and physiology, helping maintain the colony's social organization," Amsalem said. "However, it is still unknown how flexible these responses are and whether workers can learn and update how they perceive and respond to the queen over their lifetime."
For the study, the researchers applied one of two harmless floral scents to eight bumblebee queens as they built their colonies. Four queens were scented with a compound that smelled similar to grape popsicles, and another four were scented with a compound that smelled like anise.
"By repeatedly pairing these new scents with the queen, young workers grew up learning that the added odor was part of the queen's identity," Amsalem said.
The researchers then tested whether workers had learned to associate the new smells with their queen by placing them in a T-shaped maze and observing whether the workers walked toward the queen-associated odor in one arm of the "T" or a new odor they'd never experienced in the other arm.
They found that 74% of the time, the bees preferred the scent they had been raised to associate with their queen.
Next, the researchers wanted to see whether this learned scent could influence worker reproduction. They housed small groups of workers with either their queen-associated odor or a control odor and then measured how many eggs they laid. They repeated this twice -- the first time, the bees were simply exposed daily to the odor. The second time was the same as before, except with the addition of eggs, larvae and pupae from their colony.
When the bees were alone, without brood from their colony, odor had no effect on physiology -- the bees laid the same number of eggs in the presence of the queen-associated odor or in the presence of the control odors.
"However, when the brood was present, the smell of the queen made workers lay more eggs, which was the opposite of what we predicted," Amsalem said.
The researchers said this could potentially be because the brood may not be the right context for the odor. Since the workers learned to associate the new odor with a queen, the odor may suppress worker reproduction only when it is paired with other queen-related cues, such as the visual presence of a queen. Without such a visual cue, workers may instead be triggered to enter a "competition phase" in which they start laying their own eggs.
Moving forward, the researchers are building on the findings of this study by examining whether teaching bees to associate new odors with their queen can affect reproduction in different contexts.
Abraham Hefetz, professor emeritus at Tel Aviv University, co-authored the study.
This research was supported by the U.S. National Science Foundation under grant number IOS-1942127. This content is solely the responsibility of the authors and does not necessarily represent the official views of the funders.