May 21, 2020 - Science

Bees can force plants to flower by biting them

A bumblebee worker damaging a plant leaf.

A bumblebee worker damaging a plant leaf. Photo: Hannier Pulido, De Moraes and Mescher Laboratories

For tens of millions of years, bees and flowers have evolved together. Flowering provides bees with food, and pollination gives plants a means of reproduction.

What's new: Bumblebee workers appear to be able to control that synchronized symbiosis by damaging the leaves of plants, according to a new study in the journal Science.

What they did: In a set of experiments in the lab and outside, Foteini Pashalidou, Harriet Lambert and their colleagues at ETH Zürich found pollen-starved B. terrestris bees bit holes in leaves, but well-fed bees did not.

  • In another experiment, they placed bees deprived of pollen in mesh cages with either tomato or black mustard plants. They found the speed of flowering increased (one month ahead of schedule for tomatoes and two weeks for black mustard plants).

It's unclear how bees learned this biting behavior and why plants respond by flowering.

  • The researchers compared bites by bees and those made with razors, and they found the damage from bees sped flowering up more than that done mechanically.
  • One possibility is that as bees bite the plant, they inject chemicals that speed up flowering.
"If so, scientists might realize a horticulturist’s dream by deciphering the molecular pathways through which flowering can be accelerated by a full month."
— Lars Chittka of Queen Mary University of London wrote in an accompanying paper

The big picture: Climate change is threatening the timing of the relationship between plants and bees, and it risks starving bees that are emerging early from hibernation.

  • Bee-inflicted damage may provide resilience to the important relationship between flowering and pollination that is under threat, the authors write.
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