Hungry bumble bees make plants flower early by cutting holes in their leaves - Science Magazine

A hungry bumble bee cuts a hole in a leaf, stimulating the plant to flower early.

When bumble bee queens emerge from hibernation, they need to gather pollen and nectar to start their new colonies.

Now, researchers have discovered the bees have a way to order some fast food: They nibble holes in leaves, spurring plants to blossom weeks ahead of schedule.

Researchers at ETH Zürich chanced upon the discovery when they noticed curious bite marks on leaves while studying how bees respond to plant odors.

They had added bumble bees to a research greenhouse and observed them cutting holes in the shape of half-moons.

Nor did they appear to be taking any part of the leaves back to their colonies.

A key observation—that bumble bees from colonies with less food were more avidly damaging the leaves—suggested another goal.

The researchers wondered whether the damage triggered the plants to flower sooner, providing pollen to the hungry pollinators.

Ten plants were put in mesh bags with bumble bees that hadn’t eaten any pollen for 3 days; they proceeded to nibble five to 10 holes in each plant.

On average, those plants flowered after 17 days; undamaged plants that had not been exposed to bumble bees took an average of 33 days, the researchers report today in Science.

Hunger seems to be driving the bees: Another lab experiment showed that pollen-deprived bumble bees cut about four times as many holes as bumble bees that were fully fed.

When the researchers put potted plants and a colony of bees on a roof at the ETH Zürich campus in early spring, before flowers were blooming, the bumble bees cut holes in the leaves.

To find out whether the leaf damage alone triggers the plants to flower sooner, the researchers cut similar-size holes in leaves.

Those plants flowered earlier than controls, but not as early as the ones bitten by bumble bees.

What initial benefit, for example, would damaging leaves have brought to the bees.

Finally, to help their own colony (rather than distant ones), bees would need to keep their nibbling close to home.