Bees enjoy caffeine, and new research suggests its appeal is so potent that plants can get away with offering pollinators a nutritionally inferior product if they lace it with something a little extra.
Pollinators and flowering plants have a symbiotic relationship. Pollinators get food in the form of nectar and plants get their pollen transported in a manner more reliable than blowing in the wind. If something happens to either, the other can be in big trouble. However, this mutual dependence doesn't mean they always look after each other's best interests.
"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 honey bee by securing loyal and faithful foraging and recruitment behaviors, perhaps without providing the best quality forage," said Dr. Margaret Couvillon of the University of Sussex in a statement.
"The effect of caffeine is akin to drugging, where the honey bees are tricked into valuing the forage as a higher quality than it really is," added colleague Dr. Roger Schürch.
Previous studies have shown that honey bees learn better when given caffeine. Couvillon wondered how this affects their behavior in the wild. She gave one group of bees a sugar solution laced with caffeine and compared their response to a control group given pure sugared water. Her findings are published in Current Biology.
Dosed-up bees returned to drink more often and put on three times as many waggle dances – as well as were more enthusiastic in dancing – to tell their hive mates about the merits of the invigorating solution. Dancing is usually associated with the discovery of particularly concentrated nectar, and the extra effort drew four times as many fellow colonists to the spiked sample.
The bees kept coming back even after the caffeine feeder was dry, like mournful visitors to a closed coffee shop. Rather than causing the bees to search more widely, the caffeine produced a group of addicts who were less interested in exploring new locations. All this may explain why 55% of plants produce caffeine.
"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," said Schürch.
Caffeine is so attractive, the authors reason, that plants that produce it can get away with having less sugar in their nectar, which in turn could lead to reduced honey production.
Couvillon adds that caffeine may not be the only chemical tool in plants' armory for fooling insects in this way. "It may be that chemistry is a popular way in which plants can get the upper hand on their pollinators," she said.
While a reduction in their vital food store is no doubt bad for bees in the wild, caffeinated honey sounds like a great marketing opportunity for apiarists.