Now There’s Proof: Bumblebees Make Bigger Plants

Bumblebee pollinating mustard plant/ Photo: University of Zurich (UZH)

In recent years, there’s been a lot of buzz about pollinators, especially the fuzzy yellow and black kind. Now comes news that bumblebees not only help plants propagate, but they also have a positive effect on their size, fragrance and color. It’s all part of an experiment by researchers at the University of Zurich that proves bees do it bigger and better.

Of course, we all know by now that pollinators are essential for plant reproduction. But the recent study undertaken by biologists from the University of Zurich (UZH) found that plants change in significant ways depending on the pollinator. Specifically, those plants pollinated by bumblebees are larger in size, more fragrant and have brighter color. Needless to say, this has big implications for the plant world.

Bee covered in pollen

THE EXPERIMENT

For their experiment, UZH professor Florian Schiestl and doctoral student Daniel Gervasi chose a common field weed called Brassica rapa, also known as field mustard. Field mustard is the origin of many cultivars including canola, turnip and bok choy.

Field mustard

The researchers divided the plants into three groups. They allowed the first to be pollinated by bumblebees, the second by hover flies and the third by hand. They then followed the field mustard for nine generations. At the end of that period, they analyzed what, if any, had been the pollinators’ effects.

(A word on hover flies. Hover flies may look like bees or wasps, but they are actually flies with black and orange markings. They’re important pollinators whose larvae love to feed on aphids.)

A hover fly

THE RESULTS

Not to disparage the hover flies, but after just nine generations, they simply couldn’t keep up with the bumblebees. In contrast to the plants pollinated by the bees, those pollinated by the hover flies were smaller and their flowers were less fragrant. As a result, the flowers were forced to self-pollinate to make up for the flies’ lower efficiency.

Plants pollinated by bumblebees (left) and hover flies (right) Photo: UZH

WHY THIS IS IMPORTANT

It’s well-known that different pollinators have preferences for different plants. Still, the dramatic changes in the test plants after just nine generations came as a surprise to the researchers. Most evolutionary changes occur over a much longer period of time.

UZH professor Schiestl drew the following conclusion:

A change in the composition of pollinator insects in natural habitats can trigger a rapid evolutionary transformation in plants.

Before we jump all over the hover fly, let’s remember that all pollinators are good. What this study shows us, however, is that some are better than others. The fact that bumblebees are threatened could have a direct impact on our agriculture, not to mention our garden plants as they are forced to make the necessary adaptations.

This is of particular concern given the recent decline in bumblebee populations due to pesticides and other environmental factors. With less bees available, plants such as field mustard might be forced to rely more and more on other, less effective pollinators like hover flies. The result will be weaker flower fragrances and increased self-pollination.

Yet one more reason to get busy saving the bees.