Bumblebees Bite Plants to Make Them Flower Early

May 22, 2020

Bumblebees aren’t merely bumbling around our gardens. They’re actively assessing the plants, determining which flowers have the most nectar and pollen, and leaving behind scent marks that tell them which blooms they’ve already visited.
Now, a new study reveals that bumblebees force plants to flower by making tiny incisions in their leaves—a discovery that has stunned bee scientists.

“Wow! was my first reaction,” says Neal Williams, a bee biologist at the University of California, Davis. “Then I wondered, how did we miss this? How could no one have seen it before?”

Consuelo De Moraes, a chemical ecologist at the Swiss Federal Institute of Technology in Zurich, had the same reaction when one of her students, Foteini Pashalidou, noticed buff-tailed bumblebees making tiny incisions in the leaves of their greenhouse plants. The insects didn’t seem to be carrying off the bits of leaves to their nests or ingesting them.

Suspecting the bees were inducing the plants to flower, the team set up a series of experiments. The results show that when pollen sources are scarce, such as in a greenhouse or during early spring, bumblebees can force plants to bloom up to a month earlier than usual.

The research is promising for two reasons. For one, it strongly suggests bumblebees manipulate flowers, a particularly useful skill as warming temperatures worldwide are causing the pollinators to emerge before plants have bloomed. The insects depend nearly exclusively on pollen for food for themselves and their larvae in the early spring.

It’s also a potential boost for the human food supply: If agriculturalists can coax their crops to flower early, it could increase food production of some plants.

Master gardeners

For the study, De Moraes, Pashalidou—the study’s lead author—and colleagues placed flowerless tomato and black mustard plants in mesh cages with pollen-deprived buff-tailed bumblebee colonies. They then removed the plants after worker bees made five to 10 holes in their leaves.

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