Bumblebees Bite Plants to Force Earlier Bloom

Scientists have just discovered bumblebees are surprisingly resourceful when they’re hungry.

(Pashalidou et al. / Science)

(CN) — Scientists have discovered a previously unknown behavior of bumblebees that — facing a scarcity of pollen — will nibble on the leaves of flowerless plants to speed up the production of flowers.

In a study published Thursday in the journal Science, scientists revealed the drastic effects of these leaf-damaging bumblebee bites that cause plant flowering to occur anywhere from two weeks to a whole month early. Although the intentional bee damage remains an enigma to be further studied for a better understanding, the results of this study prove one fact: bumblebees are powerful agents of maintenance and change in the local availability of floral resources.

“An encouraging interpretation of the new findings is that behavioral adaptations of flower-visitors can provide pollination systems with more plasticity and resilience to cope with climate change than hitherto suspected,” Lars Chittka, an ecologist and professor of sensory and behavioral ecology at the Queen Mary University of London, wrote in a related perspective. 

Bees are some of the most important pollinators we have, and it has often been said that bees are responsible for every three bites of food we eat. Although most conservation efforts are directed towards honeybees, there are over 250 known bee species that work to pollinate the local flora. The bees feed on the nectar of flowers and carry pollen from flower to flower, collecting about 25% of their body weight and bringing it back to the offspring of their colony. As they do this, they facilitate cross-pollination between plants, allowing for the necessary growth and reproduction of plants.

According to the U.S. Department of Agriculture, cross-pollination by bees is responsible for increasing our nation’s crop values each year by more than $15 billion, and they are the most effective pollinators for crops like tomatoes, squash, berries, and more. Not only do worker bees spread pollen from flower to flower while gathering nutrients, it also gets spread from the hair on their bodies to other bees in their colony as they are constantly touching one another in the hives. From there, the bees can spread the mixed pollen to other plants and allow for the increased vital plant reproduction.

Just as bees depend on flowers for nutrition, plants need the pollinators to help them reproduce. This is a perfect example of a symbiotic relationship, in which both parties mutually benefit and thrive from their ongoing interaction. It is kept in continuous balance by the timing of the emergence of hibernating insects and spring blossoms as temperatures rise and the days get longer.

Bees have been facing the threat of extinction for some time now due to habitat loss and the widespread use of pesticides, while the fragile balance of their symbiotic relationship with flowers is threatened by climate change. Multiple studies have shown that climate change has increased the frequency of extreme weather events, including temperature spikes and heat waves that can push species like the bumblebee past the limits of what it can handle. Early warming of seasonal temperatures, for example, causes the hardworking pollinators to wake up too soon before the springtime bloom — leaving them with nothing to eat.

Study co-author Foteini Pashalidou, a junior researcher at the French National Institute for Agricultural Research, and her colleagues have discovered an adaptive strategy used by these food-deprived bumblebees to manipulate the timing of a plant’s flowering. Pashalidou and the team observed the worker bees from multiple pollen-starved colonies and witnessed them using their mouthparts to cut distinctively shaped holes in the leaves of flowering plants, which resulted in them flowering significantly sooner than normal. 

One species of bee, called the alfalfa leaf cutting bee, exhibits a similar behavior. In addition to being effective pollinators, they are also known to neatly cut circular pieces of leaves from plants to construct the nests for their offspring. However, they do not eat the leaves they cut and this action has no effect on the blossoming time of springtime flowers, making this bumblebee behavior still a mystery.

The authors were not able to recreate the same scenario by mimicking the damage on their own, and could not reproduce the flower-stimulating effects, suggesting that the bees possess an unknown feature distinct to their approach.

“Understanding the molecular pathways by which one could accelerate flowering by a full month, as reported [by Pashalidou et al.], would be a horticulturalist’s dream,” Chittka wrote.

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