When the plant is stressed, it doesn’t quiet about it. I can’t hear the screams of plants. Because it is in the ultrasound range and is too high for the human ear – but for decades, scientists have been listening using special devices.
For the first time, a team of Israeli researchers documented that insects can hear and interpret the acoustic pain signals of plants.
The findings are based on records of previous research from the research group that makes tomato and tobacco plants when dehydrated, said Rya Seltzer, an entomologist and doctoral student at the Faculty of Zoology at Tel Aviv University in Israel.
“The general hypothesis is that these sounds are produced as a result of changes in the water balance of plants within the xylem,” a specialized plant cell that transports water and nutrients from the roots to the stems and leaves told CNN via email.
During periods of stress due to lack of water, air bubbles form, expanding and collapse of the xylem tissue. This series of events generates vibrations, producing click-like sounds every few seconds measured by researchers over the acoustic frequency range of approximately 20-100 kilometres. They estimated that these frequencies were heard to insects at distances up to 16 feet (about 5 meters). (Sound waves at frequencies above 20 kilometres usually exceed human hearing).
Scientists wanted to know if these ultrasound sounds were picked up by insects, so they observed Egyptian cotton lobbite worms (Spodoptera of littoralis) that place eggs on plant leaves. The research team found that these moths tend to avoid loud, stressful tomato plants. Instead, insects prefer tomato plants that are quieter and therefore in better condition, and therefore have leaves that provide a juicy diet to newly hatched larvae, according to a recent study published in the journal Elife.
“(The study) reveals an incredible new way animals can sense and respond to cues from the environment. In this case, insects pick up sounds from stressed plants. Chan, who studied chemical communication between insects and plants at the Monel Chemosensory Center in Philadelphia, was not involved in this study.
But just because moth hears and responds to sounds from dehydrated plants doesn’t mean that the plants or moth are having a conversation, Seltzer said.
“It’s important to make it clear that we observed interactions rather than communication,” she added. “It’s important to understand that plants are likely to passively produce these sounds and that they are not actively trying to communicate with insects.”
Listening and interpretation
When scientists chose tomato plants and fresh plants for female moth, moth flocked to fresh plants to lay eggs. However, the team wanted to understand whether sounds from dehydrated plants were a factor in Moth’s choice. The researchers built an arena consisting of two boxes. In one box they played a recording of the sound of plant pain, while the other box was silent.
In experiments, moths are drawn to a loud box, and scientists theorize that this is because the sound suggests that it finds living plants there. This preference disappeared when scientists became deaf and came to the conclusion that Moth was listening to plants before Moth made a choice, the study author wrote.
In another experiment, the researchers once again offered female moth a choice of two tomato plants. This time, both plants were hydrated, but one was near the speakers that played ultrasound stress sounds. Results: More moth chose quiet plants.
In a third experiment, we tested whether egg-selling females were affected by other acoustic cues, such as Moth in males, which produce ultrasound courtship clicks. Research found that when male moss calls were broadcast from one side of the arena, women “showed no significant preferences” about where to lay their eggs.
Together, these experiments told researchers that moth is aware that they hear and recognize sounds made by plants, and that they use them to determine for reproduction to determine about those plants, Seltzer said.
“Cool and amazing things”
Insects have been able to detect ultrasound sounds at least since the Eocene era (55.8 million to 33.9 million years ago). However, researchers were surprised to see MOTH recognize ultrasound signs of plant distress, Seltzer said. The female moth in the experiment had no prior experience deciphering acoustic cues from plants, as he had never laid eggs before, but not only recognized the sound of the plant, he preferred quiet plants for his first egg sales.
“It’s a really cool and amazing discovery!” said Chan. “For a long time, we’ve known plants smell when they’re in trouble, like when they’re eating bugs or thirsty. These smells help attract kind insects and scare pests,” he said.
“What’s new here is that the sound can provide additional information, like a warning signal, especially if there is no smell or it is difficult to detect the smell.”
Plant Acoustics is an area of growing interest for scientists, and preliminary research suggests that healthy works are widespread, Seltzer said. Future research can investigate the use of acoustic monitoring to understand how stress affects plant health and identify potential uses for agricultural pest control.
“I think this is just the beginning of discoveries in this field,” Seltzer said. “There are countless creatures that can be heard on these frequencies, and potentially more and more plants that we haven’t yet discovered,” she added. “This is definitely the tip of the iceberg.”
Mindy Weisberger is a science writer and media producer who appeared in Live Science, Scientific American and How It Works Magazine. She is the author of Rise of the Zombie Bugs: The Suprising Parasitic Mind Control (Hopkins Press).
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