As gardeners get busy filling tubs and borders with colourful bedding plants, scientists at the Universities of Bristol and Cambridge have discovered more about what makes flowers attractive to bees rather than humans. Published today in the British Ecological Society’s journal Functional Ecology , their research reveals that Velcro-like cells on plant petals play a crucial role in helping bees grip flowers - especially when the wind gets up.
The study focuses on special cells found on the surface of petals, whose stunning structure is best seen under an electron microscope. According to lead author, Beverley Glover: "Many of our common garden flowers have beautiful conical cells if you look closely - roses have rounded conical petal cells while petunias have really long cells, giving petunia flowers an almost velvety appearance, particularly visible in the dark-coloured varieties."
Glover’s group previously discovered that when offered snapdragons with conical cells and a mutant variety without these cells, bees prefer the former because the conical cells help them grip the flower. "It’s a bit like Velcro, with the bee claws locking into the gaps between the cells," she explains.
Compared with many garden flowers, however, snapdragons have very complicated flowers; bees have to land on a vertical face and pull open a heavy lip to reach the nectar so Glover was not surprised that grip helps. But she wanted to discover how conical cells help bees visiting much simpler flowers.
"Many of our garden flowers like petunias, roses and poppies are very simple saucers with nectar in the bottom, so we wanted to find out why having conical cells to provide grip would be useful for bees landing on these flowers. We hypothesised that maybe the grip helped when the flowers blow in the wind."
Using two types of petunia, one with conical cells and a mutant line with flat cells, Glover let a group of bumblebees that had never seen petunias before forage in a large box containing both types of flower, and discovered they too preferred the conical-celled flowers.