Bumblebees create the electrical change to stimulate flowers to release sweet scents, suggests a new study from the University of Bristol. This charge helps pollen stick to them and signifies their presence in the flower they visit.
The electrical charge created by the bumblebee must be around 120 picoCoulombs (PC. However, this is a minimal charge, but 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 release more scent markedly.
Lead author Dr. Clara Montgomery said, “Flowers have a limited supply of these scents, so it makes sense they only release them when their pollinators are around. 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.”
For the study, scientists used specially constructed foraging arenas. They then measure the electrical charge carried by each bee and the amount of the attractive main chemical, benzaldehyde, released by the flowers in response to visits by bees.
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 touched with either a grounded metal rod or an electrically charged nylon ball.
Flowers visited by free-flying bumblebees exhibited a significant increase in volatile production. By contrast, flowers touched with an electrically grounded metal rod did not show such increases.
When the electrical charge equivalent to about five bee visits touched the flower, the scent emissions from petunia flowers were significantly increased again.
Dr. Montgomery said, “Pollinators have long been known to carry positive electric charges, but this is the first demonstration of plants using this to their advantage.”
“Frequent visits by charged pollinators to a flower would cause charge to build up, which might exceed a threshold for scent release. The 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.”
Project leader, Professor Daniel Robert from the University of Bristol, said: “This discovery unveils a previously unknown type of interaction between insects and plants, a world of elusive electric cues, that we humans cannot detect.”
- Montgomery, C., Vuts, J., Woodcock, C.M. et al. Bumblebee electric charge stimulates floral volatile emissions in Petunia integrifolia but not in Antirrhinum majus. Sci Nat 108, 44 (2021). DOI: 10.1007/s00114-021-01740-2