Imagine that just hearing the buzzing sound of bees makes flowers produce sweeter nectar.

Lilach Hadany, a Tel Aviv University researcher and evolutionary theoretician, wondered if sound was something that only animals could sense, or if plants could hear too.

This hypothesis was recently tested with some experiments and suggests that plants can hear, at least in one case. This provides them with a very real advantage.

Hadany and her team studied evening primrose (Oenothera drummondii) because it has a long bloom time and produces measurable quantities of nectar. It also grows wild and is easily accessible in Tel Aviv on beaches and in parks.

Results showed that within minutes of sensing vibrations emanating from the wings of pollinators, the plants increased the concentration of sugar in their nectar for a short period of time.

This implies that it is the flowers themselves that act as ears. They tune out sounds like the wind and pick up on the specific frequencies of a bee's wings.

In the lab, the team subjected the primroses to five sound treatments. Silence, recordings of a honeybee from four inches away, and computer-generated sounds in low, medium, and high frequencies.

Plants exposed to the silent treatment, medium frequency (34 to 35 kilohertz) and high frequency (158 to 160 kilohertz) had no noticeable increases in nectar sugar concentrations.

In contrast, plants exposed to bee sounds (0.2 to 0.5 kilohertz) and low frequency sounds (0.05 to 1 kilohertz) increased their sugar concentration from between 12 and 17 percent to 20 percent within 3 minutes of being exposed to the sounds.

They theorize that the sweeter treat for pollinators results in an increased chance of successful cross-pollination, as it draws in more insects.  

The team was surprised by the results, but then repeated the test in various situations and seasons, indoors and out, so they are confident in these findings.

Blossoms come in a variety of shapes and sizes, with many, like evening primrose, being concave or bowl-shaped. They are perfect for receiving and amplifying sound waves, like a satellite dish.

This unrelated 2:07-minute video by Peter Del is a lovely short "bees and flowers" video:



Hadany and her co-author Marine Veits put the evening primrose flowers under a laser vibrometer machine, which measures minute movements. They then compared the flowers’ vibrations to the results of each sound treatment. The vibrations of the flowers match up with the wavelengths of the bee recording.

They ran tests on flowers with one or more missing petals. Those flowers failed to resonate with either of the low frequency sounds. This confirmed that the flower was the responsible structure.

Why does the evening primrose make its nectar so much sweeter? Bees are known to be able to detect changes in sugar concentration as small as 1 to 3 percent.

Hadany says that since flowers are unable to move around, utilizing this sense of sound is important to their survival. She calls this entirely new field of scientific research phytoacoustics.

Veits hopes that the results of this study will lead to the understanding that it doesn’t always take a traditional sense organ to perceive the world. Hearing is not only for ears.

In an entirely different part of the world, and with different researchers, more information has unfolded.

We now know that flowers can sense a bee nearby and release a burst of perfume to attract more. As it turns out, it was previously unknown that bees release a tiny electrical charge when they come into contact with petals.

Experts think this helps them carry more pollen, making them more effective pollinators.  

Dr Clara Montgomery from the University of Bristol found that soon after contact, the plant expels extra perfume. She explained that it makes sense that flowers only release these scents when their pollinators are nearby since they have limited supplies of these scents.

The electrical charge on a bumblebee is just 120 picoCoulombs (pC). It took 600 pC, or five visits in experiments for a violet petunia to be triggered to emit an extra dose of its precious aromatic payload. 

The researchers used nylon balls that were charged with electricity to conduct the experiment rather than actual bees. Flowers touched by the substitute bees jettisoned twice as much perfume as normal. Those contacted by a non-charged object were unaffected. 

Too many visits by charged pollinators to a flower would cause the charge to build up and could exceed a threshold for scent release and be a useful indicator of how many pollinators are in the area. The plant could then assess the potential for pollen dispersal.

There is little understanding so far of the electrical charges carried by different insects, and the influence of electric fields on biological systems.

There will surely be more information coming forth in this exciting new field of research in the near future. In the meantime, we can only be in awe of the intelligence in flowers, bees, and in nature in general.