Sweet hum

It turns out that conversations between insects and flowers are not just a figment of the national poet's imagination

"Butterfly, butterfly, live flower,
Please come down quickly, sit on me.
Please come down quickly, matza and matza,
Covered with dew she drank."

Haim Nachman Bialik's poem "The Flower to the Butterfly", which was first published in 1922, describes a simple interaction between a butterfly and a flower, one that we have seen a lot recently following the wave of "Nymphit Hahorshef" butterflies that invaded the country, and yet - its charm has never worn off. This is evidenced by the thousands of photos that we rushed to take and distribute, as if we saw at least a unicorn and not one of the most common butterflies in the world.

What Bialik did not know is that almost 100 years after the publication of the poem, researchers from Tel Aviv University would discover that "conversations" between flowers and pollinating insects take place, and not only in the poetic world of poetry.

A conversation by candlelight

A collaboration between Prof. Lilach Hadani and Dr. Yuval Sapir from the School of Plant Sciences and between Prof. Yossi Yuval from the School of Zoology in the George S. Wise Faculty of Life Sciences, produced an extraordinary study, which proves that plants are able to hear. In the study, the response of evening primrose plants (Oenothera drummondii) to recordings of humming bees was examined.

The coastal nightshade is a perennial plant from the nightshade family, which grows in Israel in the sands along the coastal plain. The plant is named so because its flowers open at night. The flowers of the coastal nightshade are closed during the day and open only at dusk, when they are visited by butterflies that sip from the nectar at the base of the flowers and in the process also pollinate them. After pollination, the flower detaches from the upper region of the ovary, which develops as a chamber for the developing seeds.

The researchers found that the humming sounds led to a rapid increase of 20% on average in the sugar concentration in the nectar of the flowers, compared to the sugar concentration measured in plants that were exposed to other loud sounds or not exposed to sounds at all.

The results of the research prove, for the first time, that plants are able to respond efficiently and quickly to the voices of pollinators. The sounds cause vibration in the structure of the plant, and apparently motivate a process in which the flower serves as the plant's auditory organ.

Flowers hear

How did the researchers discover that the flowers are the part of the plant structure that is used to hear the hum? When the flowers of the plant were wrapped in soundproof glass and the plant was exposed to the sounds of the pollinators, no increase in the concentration of sugar in the nectar was recorded. In addition, when the plants were exposed to higher frequencies than those produced by the pollinators, there was no increase in the sugar concentration either. Which shows that the vibration in the flower structure, as well as the increased sugar secretion, are specific responses to the frequency produced by the pollinators.

According to Prof. Lilach Hadani, "The ability of plants to respond to sounds can have far-reaching effects. First, if flowers can respond to the voices of pollinators, they can invest their resources in a more precise way - to provide fine nectar exactly when the pollinators are present - and thus save resources on the part of the flowers and/or increase the reward for the pollinators. It has been observed that natural selection will act on the structure of the flower also according to its effect on the plant's ability to hear - "ear-like" flowers will have an advantage over pollinators that make sounds, such as bees or flappers. On the other hand, natural selection can also act on pollinators making sounds, and "noisy" pollinators may gain an advantage thanks to the flowers' improved response to them."

Beyond the extensive implications of the research for understanding the physiology and evolutionary development of plants and their pollinating insects, the findings point to the possibility that plants are also affected by other sounds. "If plants can hear the pollinators, it is likely that they can also hear and respond to other sounds: herbivores, climate events and perhaps also sounds resulting from human activity. It is also possible that significant noises can damage the communication between the flowers and the pollinators." Lilac summarizes.

The fascinating discovery, published in leading newspapers around the world, is another milestone in understanding the world of plants and how they communicate. The next step is to find out if and how they also speak.