Bumblebees are fine little gardeners, research finds

2 Juni 2020

Bumblebees are busy as bees, flitting from flower to flower and pollinating plant after plant. Turns out, though, they do even more than that: according to new research bumblebees prod some late-blooming plants into flowering earlier. They do this by biting their leaves.

Sound implausible? Maybe it does, but it isn’t.

A team of researchers at the ETH Zurich in Switzerland has found that bumblebee workers make tiny incisions in the leaves of plants that haven’t yet flowered so as to stimulate the production of new flowers. As a result, plants visited by bumblebees flower considerably earlier than those that haven’t been.

“Previous work has shown that various kinds of stress can induce plants to flower, but the role of bee-inflicted damage in accelerating flower production was unexpected,” explains Mark Mescher, a professor at the institution who was the author of a study published in the journal Science.

The insects begin to coax plants into flowering by inflicting damage on them when they can find little or no pollen naturally. “[B]umble bee workers facing pollen scarcity damage leaves of flowerless plants and thereby accelerate flower production,” the scientists write.

Some plants are especially prone to flowering earlier thanks to bumblebee bites, the researchers say. They have identified tomato plants, which can bloom up to a month earlier than they otherwise would. Mustard plants, meanwhile, flower some two weeks earlier when visited by the bees.

“The bee damage had a dramatic influence on the flowering of the plants — one that has never been described before,” observes Prof. Consuelo De Moraes, a coauthor of the study.

Why exactly plants respond in this way remains a bit of a mystery, the scientists note. Finding the precise answer will require some further research. What isn’t in doubt, however, is that bumblebees are expert little gardeners in their own way.

“Bumblebees may have found an effective method of mitigating local shortages of pollen,” De Moraes says. “Our open fields are abuzz with other pollinators, too, which may also benefit from the bumblebees’ efforts.”

All the more reason then to save bumblebees and they do need to be saved. Recently scientists have warned that bumblebees are getting decimated across much of the world as a result of climate change and pesticides.

Using long-term data for 66 bumblebee species across North America and Europe based on some 550,000 records, a team of researchers from the University of Ottawa have found that the population of bumblebees in Europe fell by 17% between two periods examined: from 1901 to 1974 and from 2000 to 2014. In North America, the figure was even more dramatic at 46%.

“Bumblebees are among the best pollinators we have in the wildlife system,” observes Peter Soroye, a researcher at the University of Ottawa who was an author of the study on the disappearance of bumblebees, which too was published in Science.

“[They’re] out for really long periods of the year in a lot of different weather conditions and they visit a really broad range of flowers,” he added. “They’re really a critical piece of these natural landscapes that we like to enjoy,”

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