What links flowers, bees and electric fields?

Over three-quarters of the world’s food crops are pollinated by animals[1]. Bees alone pollinate over 120 types of fruit and vegetables[2], but how do they know which flowers have already been visited ?

Let’s start with the flower, which is the reproductive section of flowering plants, also known as angiosperms. Four parts make up the flower : sepal, petal, stamen and carpel. The number of these elements varies depending on the plant. The role of the sepal is to protect the fertile structures of the plant. In addition to assisting sepals in this role, petals play a part in attracting pollinators.

The male reproductive organs are the anther (or pollen sac) and the filament. These are collectively known as the stamen. The pistil is the name for the female organs composed of the ovary, stigma (which receives the pollen) and style (connecting the ovary to the stigma).

So, where do the bees and electric fields come in? Well, the bees are attracted to the flower in search of nectar, a surgary secretion which provides energy, and pollen, rich in protein and amino acids. As the bees gather the nectar, pollen from the stamen brushes onto the bee which it then disposes on other parts of the flower and other flowers. Static electricity plays an important role in this process. Flowers (and pollen grains), through their connection to the earth, generally have a negative charge. Bees develop a positive charge when they fly through the air and, as the bee approaches the flower, these two charges attract one another. Through this force of attraction, pollen is transferred onto the bee, weakening the electric field of the flower. This modification in the charge of the flower then indicates to other bees that the supply of nectar is low so they know to move onto another plant[3], [4]

Once pollination has taken place, the flower will then start the incredible process of transforming into the fruit.

For more information on flowers, see "What makes a flower attractive?".

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[1] https://www.usda.gov/peoples-garden/pollinators

[2] https://www.farmers.gov/blog/value-birds-and-bees

[3] Clarke, Whitney, Sutton & Robert. Detection and Learning of Floral Electric Fields by Bumblebees. Science http:/dx.doi.org/10.1126/science.1230883

[4]Clarke D, Morley E, Robert D. The bee, the flower, and the electric field: electric ecology and aerial electroreception. J Comp Physiol A Neuroethol Sens Neural Behav Physiol. 2017 Sep;203(9):737-748.