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Bumblebees foraging for nectar favor those flowering plants which offer the best return on effort. The bees use certain floral cues to recognize these plants, such as the color and shape of its flowers, the floral pattern and its fragrance. But new research indicates that bumblebees can also detect a flower’s electric field, exhibiting a level of communication far more complex than previously understood.

Researchers at the University of Bristol’s School of Biological Sciences, led by Professor Daniel Robert, found that flowers emit patterns of electrical signals that can communicate information to the bumblebee, a valued insect pollinator. The electric fields can change within seconds in the presence of the bees, which seems to indicate a degree of interaction. These electrical signals can work in concert with the flower’s other cues to imbed its memory with the pollinating insect.

The mechanics of this communication are not fully understood. Plants usually have a negative charge because they are grounded, and bees pick up a positive charge as they fly through the air. When a bee enters the plant’s electric field, a small electric charge develops that can transmit information. The hairs on the bumblebee may help it receive these signals.

When a bee enters the plant’s electric field, a small electric charge develops that can transmit information. The hairs on the bumblebee may help it receive these signals.

Researchers created two sets of artificial flowers, filling some with sucrose and others with a substance that does not attract bees. At initial exposure, the bees visited both sets of flowers at random. But when a small electric charge was applied to the artificial blooms containing sucrose, the bees detected the field from a few centimeters away and visited the charged flowers 81 per cent of the time. The bees reverted to random behavior when the electricity was switched off.

Since flowers emit distinct electric fields which are determined by the flowers’ shape, researchers conducted tests to determine if the bees could distinguish between fields. By varying the shape of the field around artificial flowers that had the same charge, they showed that bees preferentially visited flowers with fields in concentric rings like a bulls-eye: these were visited 70 per cent of the time compared to only 30 per cent for flowers with a solid circular field.

To explore the change, if any, in the flowers’ electric field during a bee visit, researchers placed electrodes in the stems of petunias. They found that the potential energy in the field changed for several minutes. The assumption, yet unproven, is that the changed potential sends a message to the bee regarding the status of its nectar stores. The flower would benefit by communicating this information to bees since the bee would not waste energy in searching for depleted nectar, and develop a negative memory imprint of that flower. “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,” said Robert.

Researchers also presented bees with different color flowers and found that the presence of electric fields helped the bees learn to distinguish between the colors more quickly.

The electric field most likely reinforces the information given by other cues such as color, shape and floral pattern. But only the electric field has the ability to change immediately in response to bee presence and activity. This lends credence to the idea that transitory information, such as the status of pollen reserves, is provided by the flower’s electric field.

Plants and bees developed a co-dependent relationship eons ago, and it’s not surprising that intricate mechanisms have evolved to ensure their mutual benefit. Visual, olfactory and chemical cues have been identified as messaging stimuli, and this new research adds electric field information as part of the bee-flower communication package.