When bumblebees emerge from hibernation in early spring they rely on the food provided by newly blooming flowers. However, bees sometimes emerge early and find that plants are still flowerless.
Fortunately, hungry bumblebees have a strategy for when this happens.
Consuelo De Moraes at ETH Zurich and colleagues discovered that worker bumblebees can coax plants in to flowering and making pollen earlier than normal by using their mouthparts to damage the leaves of flowerless plants.
In a series of outdoor and laboratory experiments, Buff-tailed Bumblebees Bombus terrestris were more likely to bite holes in the leaves of tomato plants and black mustard plants when faced with a shortage of food. The intensity of leaf damage varied with local flower availability. Furthermore, workers of two additional Bumblebee species were also observed to damage plant leaves in the wild. The leaf damage caused the Black Mustard plants to flower 16 days earlier than usual and the Tomato plants to flower 30 days earlier.
When De Moraes and her colleagues damaged leaves themselves, they were unable to fully replicate the early flowering results. While it remains something of a mystery as to how biting holes in leaves promotes early blooming, other studies have found that plants sometimes speed up their flowering in response to stress. The results from this study suggest that Bumblebees provide additional cues to encourage early-flowering, such as injecting saliva containing chemicals into the leaves as they cause damage. “We hope to explore this in future work,” De Moraes says.
“Climate change is making spring conditions less predictable, which could disrupt the timing of the relationship between bees and flowers,” says Mark Mescher, who was also part of the study. The ability of Bumblebees to manipulate flowering times may help them to adapt to climate change, he says.
Pashalidou, F. G., Lambert, H., Peybernes, T., Mescher, M. C., De Moraes, C. M. (2020). Bumble Bees Damage Plant Leaves and Accelerate Flower Production When Pollen is Scarce. Science, 368: pp. 881-884.