Various flowers

left: Geranium magnificum; center: Gerbera hybrida; right: Clematis armandii

showing a composite of immediately before and after application of charged powder paint.

The pattern of powder deposition reveals the shape of the electric field.
Image by Dominic Clarke and Daniel Robert



Flowers' methods of communicating are at least as sophisticated as any devised by an advertising agency, according to a new study, published today in Science Express by researchers from the University of Bristol.


However, for any advert to be successful, it has to reach, and be perceived by, its target audience. The research shows for the first time that pollinators such as bumblebees are able to find and distinguish electric signals given out by flowers.


Flowers often produce bright colors, patterns and enticing fragrances to attract their pollinators.


Researchers at Bristol's School of Biological Sciences, led by Professor Daniel Robert, found that flowers also have their equivalent of a neon sign - patterns of electrical signals that can communicate information to the insect pollinator. These electrical signals can work in concert with the flower’s other attractive signals and enhance floral advertising power.


Plants are usually charged negatively and emit weak electric fields. On their side, bees acquire a positive charge as they fly through the air. No spark is produced as a charged bee approaches a charged flower, but a small electric force builds up that can potentially convey information.


By placing electrodes in the stems of petunias, the researchers showed that when a bee lands, the flower’s potential changes and remains so for several minutes. Could this be a way by which flowers tell bees another bee has recently been visiting?


To their surprise, the researchers discovered that bumblebees can detect and distinguish between different floral electric fields.


Also, the researchers found that when bees were given a learning test, they were faster at learning the difference between two colors when electric signals were also available.


How then do bees detect electric fields?  This is not yet known, although the researchers speculate that hairy bumblebees bristle up under the electrostatic force, just like one’s hair in front of an old television screen.


The discovery of such electric detection has opened up a whole new understanding of insect perception and flower communication.


Dr. Heather Whitney, a co-author of the study said:

"This novel communication channel reveals how flowers can potentially inform their pollinators about the honest status of their precious nectar and pollen reserves."

Professor Robert said:

“The last thing a flower wants is to attract a bee and then fail to provide nectar: a lesson in honest advertising since bees are good learners and would soon lose interest in such an unrewarding flower.


"The co-evolution between flowers and bees has a long and beneficial history, so perhaps it's not entirely surprising that we are still discovering today how remarkably sophisticated their communication is."

The research was supported by the Leverhulme Trust.





'Detection and learning of floral electric fields by bumblebees' (Science DOI: 10.1126/science.1230883) by Dominic Clarke, Heather Whitney, Gregory Sutton and Daniel Robert in Science Express










Bumblebees Sense...

Flowers' Electric Fields
by Ben Aviss

21 February 2013
from BBCNature Website




Beyond the naked eye:

differences in electric signals provide bees with information about a flower

Bumblebees (Bombus terrestris) can detect flowers' electric fields, scientists have discovered.

Results indicate floral electric fields improve the bees' ability to discriminate between different flowers. When used with visual signals, electrical cues can enhance the bee's memory of floral rewards.

Researchers suggest this method of signaling provides rapid and dynamic communication between plants and pollinators. The findings are published in the online journal Science Express.

Flowering plants reward pollinators with nectar and pollen in return for their assistance in the flowers' sexual reproduction.


Brilliant bees and fantastic flowers


Flowers attract pollinators using cues such as bright colors, patterns and enticing fragrances but this study suggests the importance of electrostatic information as an additional cue for the first time.

"Of course it has existed for a long time but this is a new way we can look at the interactions between bees and flowers," said Prof Daniel Robert of the University of Bristol.


"This doesn't throw away any of the previous work on cues that flowers are using, it adds another layer on top of that."

Prof Robert and his team were studying the mechanism of pollen transfer between flowers via an insect pollinator.

"What the pollen needs to 'know' is when to 'jump' onto the 'vehicle' - the bee - and when to get off it. So it's a selective adhesion type of question," Prof Robert told BBC Nature.



Electric attraction

The team's investigation highlighted the possible importance of electrostatic forces.


This is the tip of the iceberg,

there's so much more that we haven't seen yet”
Prof Daniel Robert University of Bristol


"We looked at [existing] literature and realized that the bees were being positively charged when they fly around, and that flowers have a negative potential.

"There's always this electrical bias around. As a sensory biologist, suddenly I thought: can the bees sense that?" Prof Robert said.

Dominic Clarke, one of the lead authors, designed "fake" electric flowers in a laboratory "flying arena" to prove that electric fields are important floral cues.

Electric flowers with a positive charge offered a sucrose reward while those without offered a bitter quinine solution. Bumblebees were allowed 50 visits in the flying arena and the last 10 visits showed the bees had learnt to tell the difference between the flowers.



Bumblebee in laboratory flying arena

Eliminating other variables in the bee 'flying arena'

When the electric field was turned off,

"the bee goes back to selecting at random because it hasn't got a way to tell the difference between them any more," commented Mr Clarke.


"That's how we know it was the electric field that they were learning."

"Animals are just constantly surprising us as to how good their senses are. More and more we're starting to see that nature's senses are almost as good as they could possibly be," Mr Clarke told BBC Nature.

Prof Robert summed up:

"We know they can detect these electrostatic fields… this is the tip of the iceberg, there's so much more that we haven't seen yet."