The electrical charge created by visiting bumblebees stimulates some flowers to release more of their sweet-smelling scent, scientists have found.
This is the first time a plant has been shown to use the presence of pollinators as a cue to emit more of its attractive perfume – increasing its chances of being visited.
While pollen is likely to stick to bees while they fly, researchers have discovered that the tiny electrical charge can also signal their presence to the flowers.
Clara Montgomery, the lead author of this article, suggested that the trait may have evolved in plants to maximize the effectiveness and attractive chemicals they release.
“Flowers have a limited supply of these scents, so it makes sense they only release them when their pollinators are around,” she said.
“Essentially, it is only worth advertising when you know you have an audience. Other cues they might use, such as daylight or temperature, can be unreliable, as it might also be windy or raining, which would reduce pollinator presence.
“These scents are also used by insects that want to eat or lay eggs on the plant, so increasing their chances of only attracting pollinators is vital.”
Researchers from Cardiff University and Rothamsted Research at the University of Bristol carried out the research.
The electrical charge on a bumblebee – somewhere in the region of 120 picoCoulombs (pC) – is incredibly small but the team found a charge of 600 pC, or about the same as five bee visits, was enough to induce a species of violet petunia, Petunia integrifolia, to markedly release more scent.
The team used specially designed foraging arenas to measure the electric charge carried by each bee and the amount of the main attraction chemical, benzaldehyde released by the flowers upon bee visits.
To help distinguish between a flower’s response to the mechanical stimulus of a bee landing and the electrical stimulus, scent release was also measured in a subset of petunias that were touched with either a grounded metal rod or an electrically charged nylon ball.
Volatile production increased significantly in flowers that were visited by free-flying bees. These increases were not seen in flowers touched with an electricly grounded metal rod.
When touched with the electrically charged ball, with a charge equivalent to about five bee visits, the scent emissions from petunia flowers were significantly increased again – roughly doubling the average volume of scent.
Although pollinators are known to have positive electric charges for a long time, this is the first evidence that plants can use this advantage.
“Frequent visits by charged pollinators to a flower would cause charge to build up, which might exceed a threshold for scent release,” Dr Montgomery said.
“Charge could therefore provide a useful indicator of how many pollinators are in the area, allowing the plant to assess the real time potential for pollen dispersal.
“Current understanding of the electric charges carried by different insect species is very low and the influence of electric fields on all biological systems is often poorly understood and hard to quantify.”
– The study, Bumblebee electric charge stimulates floral volatile emissions in Petunia integrifolia but not in Antirrhinum majus, is published in the journal The Science of Nature.