According to a new paper in the journal Current Biology, honeybees may select caffeinated nectar over an uncaffeinated but otherwise equal-quality alternative. As a result, plants may be lacing their nectar with caffeine as a way to pass off sub-standard forage.
A honeybee foraging on a citrus flower, which is one of the flowers whose nectar contains caffeine. Image credit: Jon Sullivan.
“The effect of caffeine is akin to drugging, where the honeybees are tricked into valuing the forage as a higher quality than it really is. The duped pollinators forage and recruit accordingly,” said co-author Dr Roger Schürch, of the University of Sussex and the University of Bern.
“We describe a novel way in which some plants, through the action of a secondary compound like caffeine that is present in nectar, may be tricking the honeybee by securing loyal and faithful foraging and recruitment behaviors, perhaps without providing the best quality forage,” said lead author Dr Margaret Couvillon of the University of Sussex.
The scientists were aware of earlier studies that found that honeybees are better at learning and remembering particular scents when they are under the influence of caffeine. The findings suggested a role for reward pathways in the insects’ brains.
“I could not help but wonder how caffeine would affect the natural behaviors as seen in the field. The nectar of many flowering plants contains caffeine in low concentrations,” Dr Couvillon said.
The scientists tested honeybees’ responses to a sucrose solution with field-realistic doses of caffeine or without.
They found that the caffeine caused the insects to forage more and to direct their friends to the caffeinated forage more frequently using a unique behavioral technique called a ‘waggle dance.’
The caffeine quadrupled the recruitment dances of honeybees to those feeders in comparison to uncaffeinated controls. They were also more persistent about returning to sites where they’d previously found caffeinated nectar, even after the feeder had run dry.
After sipping caffeine, the insects were also less inclined to search for other resources, a behavior that could be problematic when the well runs dry.
“We were surprised at how, across the board, we saw an effect of caffeine just about everywhere we looked in foraging and recruitment, and all in the direction to make the colony more faithful to the caffeinated source compared to an equal-quality, uncaffeinated source,” Dr Schürch said.
Based on their observations of the individual bees’ behaviors, the team’s model suggests that caffeinated nectar could reduce honey production in colonies if indeed plants reduce the sweetness of their nectar.
The findings come as a reminder that the interests of plants and their pollinators don’t always align.
“It would now be interesting to find out whether plants that lace their nectar with a secondary compound like caffeine also make nectar that’s less sweet,” the scientists said.
“And caffeine isn’t the only secondary compound found in nectar.”
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Margaret J. Couvillon et al. Caffeinated Forage Tricks Honeybees into Increasing Foraging and Recruitment Behaviors. Current Biology, published online October 15, 2015; doi: 10.1016/j.cub.2015.08.052
