Bees can help flowers to grow bigger and smell more fragrant, scientists have discovered.

Swiss researchers found that plants evolve differently depending on the insect that is pollinating them. Tests on a type of cabbage species called field mustard, a close relative of oilseed rape, showed that when pollinated by bumblebees, the plants grew 7.5cm taller than with hoverflies in just nine generations.

They also flowered a day earlier and had double the fragrance. And when placed on ultraviolet light, they had more colours that bees can see.

"The traditional assumption is that evolution is a slow process," said Professor Florian Schiestl. "But a change in the composition of pollinator insects in natural habitats can trigger a rapid evolutionary transformation in plants."

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The change happens because insects differ in their preference for plants.

Bees like taller, more fragrant plants, so will seek out and pollinate those more often than shorter, unfragranced varieties, causing the bigger, stronger-scented plants to thrive. Flies are not as effective at pollination and so plants will self-pollinate more often, slowing down the emergence of new traits.

Schiestl said the rapid decline of bee populations could lead to flowers that do not grow as abundantly or smell as sweet. In the long term it could reduce genetic diversity of plants, leaving them more susceptible to disease.

The research was published in Nature Communications.