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Bees prefer pollinating plants that offer a shot of caffeine with their nectar

Photo of: two bees, one on a flower, the other hovering nearby © | amit erez

© | amit erez

Plants serving up just the right blend of caffeine and nectar have a better chance of getting pollinated, a University of Toronto study has found, providing yet another fascinating glimpse into the secret lives of bees.

Using an elegant and efficient combination of flight cages, fake flowers and coloured dyes to mimic pollen, James Thomson of Ecology & Evolutionary Biology and genetics student Mimi Draguleasa established the Goldilocks zone for caffeine and nectar — not too much and not too little — at least as far as some bees are concerned.

Their results showed the artificial flowers that provided low-caffeine nectar received 42 per cent of all the “pollen” transferred by the North American bumblebees used in the experiment, compared to 29 per cent for caffeine-free flowers and 29 per cent for flowers with high amounts of caffeine.

Researchers have long established bees are extremely good at associating certain qualities of nectar with things like colour and scent, Thomson notes.

“So it seems pretty certain that they’re also able to do it for something like caffeine concentration,” he says of the study’s results, which were published earlier this year in the journal Anthropod-Plant Interactions.

“Mimi’s experiments certainly suggest that the bees figured out which of those flower colours was associated with the caffeine.”

Their work adds another piece to the puzzle about bees and how they interact with the plant world.

It’s only in the last decade scientists were even able to figure out the physics behind why bees can fly.

Now they are also seeing worrisome diseases and declines in commercial honeybee and wild bumblebee populations, which have been attributed to a range of factors from parasites to pesticides called neonicotinoids.

At the same time, “there are many, many other species of wild bees that are neither bumblebees nor honeybees, and we know virtually nothing about their status,” Thomson points out.

As for the business of some flowers and their best customers, namely caffeine-fixated bees, recent research has suggested low-doses of this modestly psychoactive substance strengthens their memory.

But is that what keeps the bees coming back for their favourite blends of caffeinated nectar? While their study has made the advantage for flowers quite clear, “I don’t think we have enough information yet to know what the benefit is for the bees,” says Draguleasa.

Apart from the obvious coffee plant, some citrus plants also produce caffeinated nectar. Other chemical additives are widespread. The primary value of such compounds to plants is thought to be deterrence of leaf-eating insects, and the compounds might turn up in nectar through passive leakage from other tissues. But Thomson says, “Given the fact that bees like it, and that plants benefit when they produce it, it suggests there is an adaptive role [in nectar, too].”

Bees’ positive reactions to exotic plant substances might simply reflect “pleasurable” sensations, but Thomson has been reviewing research — some of it as yet unpublished — suggesting bees may seek them out like “drug stores” for medicine.

“In terms of importance of the findings that we’ve put together, we’re looking at one facet of the bigger picture of how bees interact with these nectar constituents,” says Thomson.

“And it’s possible that bees with access to plants that produce certain chemicals with medicinal value might have some protection against diseases that other bees don’t.”

Further investigation is required, but Thomson says it is an intriguing prospect, given some research suggests bees have the ability to detoxify plant compounds that can harm other mammals.

However, he harbours no whimsical illusions about the nature of the harmony between the flowers and the bees.

“It’s a cut-throat world like everything else. Bees are out for themselves. Plants are out for themselves. And it just turns out they can use each other.”