Gardeners have long known the importance of bees for pollination, but the insects can also help flowers to grow bigger and smell more fragrant, scientists have discovered.
Swiss researchers found that plants evolve differently depending on the insect pollinating them. Tests on field mustard cabbage, a close relative of oilseed rape, showed when pollinated by bumblebees, the plants grew three inches taller than with hoverflies in just nine generations. They also flowered a day earlier and had double the fragrance. When placed on ultraviolet light, they had more colours that bees can see.
"The traditional assumption is that evolution is a slow process," Professor Florian Schiestl said. "But a change in the composition of pollinator insects in natural habitats can trigger a rapid evolutionary transformation in plants."
The change happens because insects differ in their preference. 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 the emergence of new traits. Prof Schiestl said the rapid decline of bee populations could be leading to flowers that do not grow as abundantly or smell as sweet. Long term, it could reduce genetic diversity of plants, leaving them more susceptible to disease.
Purple and blue flowering plants are best because they are easier for bees to see and different species prefer different shapes of flower.
Gardeners are encouraged to leave dandelions and clover to flower for bees, and a 'messy corner' of old wood and leaves will provide shelter. Chemical pesticides should be avoided, especially those containing neonicotinoid pesticides.