Plants Know The Rhythm Of The Caterpillar's Creep

According to new research, plants can actually hear the sounds of insects chewing. A University of Missouri study is the first work to report that plants can recognize the sound of a predator through the vibrations of their leaves. To learn more, Robert Siegel speaks with Heidi Appel, senior research scientist in the Bond Life Sciences Center at the University of Missouri.

ROBERT SIEGEL, HOST:

The idea that plants respond, and even benefit from sound, is a popular one that's prompted many studies. So if you read poetry to your tomatoes, can they hear you? That's a good question. What about the chewing of a hungry caterpillar?

(SOUNDBITE OF CATERPILLAR VIBRATION)

SIEGEL: Well, that one we do know the answer to, and the answer is, yes. This recording, and the research showing that plants respond to it, come from the University of Missouri. It's the first study to suggest that plants can recognize the sound of a predator through vibrations on their leaves. To explain how that conclusion was reached, we're joined by Heidi Appel. She and Rex Cocroft did this research. She's a senior research scientist in the College of Agriculture, Food and Natural Resources, at the University Missouri. Welcome to the program.

HEIDI APPEL: Thank you, pleasure to be here.

SIEGEL: And how did you conduct a study with the leaves and the caterpillars?

APPEL: Well, the first thing we had to do was record the kinds of vibrations that caterpillars make on leaves when they're feeding. And these vibrations are very subtle - you can't actually see them. The leaves are moving like one ten-thousandth of an inch. But you can record those very delicate movements with a cold laser. So we were able to play back those vibrations to the plants in the absence of the caterpillars and then afterwards, challenge the plants with insects and measure their chemical response.

SIEGEL: And the chemical response was different if - if they'd been exposed to these vibrations beforehand?

APPEL: Yes, they made many more mustard oils, which are these insect repellents. And we also in a second experiment measured anthocyanins, which are things that give flowers their color, red wine its lovely hue, and provide the health benefits to chocolate. And those defenses too were increased in plants after attack, if the plant had received the vibrations beforehand.

SIEGEL: So what you're saying is that a plant that has experienced, what sounded like the harassment of a caterpillar, responds differently than an inexperienced plant.

APPEL: That's correct. And in our second experiment, we really wanted to tackle the question, is this ability to detect the vibrations ever important - because a plant of course is exposed to all kinds of help vibrations outdoors. So, in this second experiment we played back vibrations caused by a gentle wind on the leaves and also vibrations from a common insect in the plant's habitat, a tree-hopper. And neither of those vibrations stimulated the chemical defense.

SIEGEL: What plant was it that you used?

APPEL: We started with arabidopsis thaliana, which is the lab rat of the plant world. It's very useful to us because it has a completely sequenced genome and a lot of other genetic resources.

SIEGEL: And what we call it in English?

APPEL: Thale cress.

SIEGEL: It's a kind of cress.

>>APPEL Yeah, mustard. It's related to the water cress - you know, we love to eat. And that - those mustard oils are what make the water cress tasty to us.

SIEGEL: Heidi Appel, thank you very much for talking with us.

APPEL: Thank you, Robert. It's been my pleasure.

SIEGEL: Heidi Appel is a senior research scientist in the Bond Life Sciences Center at the University of Missouri. She spoke to us about the study that she and Rex Cocroft have published, showing that plants respond to insects chewing. It was published last week in the journal "Oecologia."

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