Bright Sparks: Bumblebees Can Detect Electric Field Changes in Flowers

It is well known that flowers use colours and scents to attract pollinators such as bees, even using complicated patterns like the bee orchid, which attracts male bees by mimicking a female. A new study in the journal Science, however, has shown that bumblebees may also be able to detect changes in the electric fields of flowers that allow them to tell when another bee has already visited.

White-tailed bumblebee on japonica © Poppy Simon

Bumblebees and flowers have opposite electric potentials, leading to an electric field caused by the potential difference between them. The electric potential of the flower changes according to its ‘pollination status’, so it changes when a bumblebee visits. Unlike the other cues, such as scent, the electrical field changes in seconds, rather than minutes or hours, and so provide an instant cue. The team were able to show that the bees could discriminate between charged and uncharged flowers by rewarding them with sucrose at charged flowers rather than the bitter quinine at uncharged flowers.

As a control, the experiment was then carried out without the charge, and the bees were no longer able to discriminate between sucrose and quinine flowers. The study also showed that the electric field cue enhances the effectiveness of other cues, such as colour. When they combined both electric charge and colour, the bees were able to learn which flowers were rewarding quicker than when just using colour.

White-tailed bumblebee © Poppy Simon

Having discovered that the bumblebees are able to detect these changes, the team will now be looking into trying to find out how exactly the bees do it. Whereas the sensory organs for smell and vision are known, that for detecting electricity is not. There are other animals that can detect electricity, such as some fish, but it is likely to have evolved separately in bees, given the evolutionary distance between them, and so may be a completely different mechanism.

Professor Daniel Robert, an author on the paper, says that the team will also be looking into whether the phenomenon occurs in other insects. In theory other pollinators are likely to also be charged, and therefore interact with the charge of flowers, but he points out that insects such as flies and moths “cannot be trained to choose rewards, unlike bees, and therefore they are less amenable to such experiments”. Honeybees, on the other hand, can be trained like bumblebees and so may be the next guinea pigs in the Bristol group’s experiments.

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