Bumblebees Use Temperature Patterns to Choose Flowers, Says New Study

A wide range of flowers produce not just signals that we can see and smell, but also ones that are invisible such as heat. According to new research from the University of Bristol, UK, bumblebees can use these temperature patterns as a cue to recognize flowers and make informed foraging choices based upon them.

Floral temperature patterns are a hidden signal to bumblebees and other pollinators that, together with other cues like color and scent, attracts them to the flowers and helps them locate any reward, like nectar. This image shows floral temperature patterns from a rock rose. Image credit: University of Bristol.

Bees experience the world in a different way to humans. The plants that they visit exploit the bee’s senses to make sure that a searching bee can easily find, handle and pollinate flowers.

For example, bumblebees can learn to choose between flowers that are different temperatures, using heat as a way of identifying the best flowers.

Some wild flowers are warmer than others when they grow in their natural environment.

“Recent advances in technology mean that scientists are now able to take a more detailed look at flower temperature than ever before,” said lead author Dr. Heather Whitney from the University of Bristol’s School of Biological Sciences and colleagues.

“We used this technology to look at 118 species of plant, including daisies, rockroses and poppies.”

The majority of flowers examined by the team had complex patterns of heat across their petals, echoing the colorful patterns that we see with our own eyes.

On average these patterns were 4-5 degrees Celsius warmer than the rest of the flower, although the patterns could be as much as 11 degrees Celsius warmer.

Dr. Whitney and co-authors made artificial flowers that copied these heat patterns, but did not include the corresponding color patterns.

While these artificial flowers look identical to human eyes, and we are not able to tell them apart, it is a different case for foraging bumblebees.

Bumblebees were found to be able to use these patterns to distinguish between different flowers and the rewards that they provide.

“The presence of multiple cues on flowers is known to enhance the ability of bees to forage efficiently, so maximizing the amount of food they can take back to sustain the rest of their colony,” Dr. Whitney said.

“Climate change might have additional previously unexpected impacts on bee-flower interactions by disrupting these hidden heat patterns.”

The findings are published in the journal eLife.

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Michael J.M. Harrap et al. 2017. The diversity of floral temperature patterns, and their use by pollinators. eLife 6: e31262; doi: 10.7554/eLife.31262