On July 6th, 2015 we learned about

The sound of chewing makes for tastier mustard

Does sound affect plants? Some gardeners swear that playing music for your plants will help them grow, although there’s a troubling lack of consensus about what music causes what effect. For example, 70’s rock music has been labeled a blessing or a curse for a garden, depending on your source. However, a recent experiment did seem to connect a single, specific sound to changes in the plant’s chemistry— the sound of a caterpillar eating leaves.

Specific defense to specific threats

Some Arabidopsis plants, also known as Mousear Cress, were played recordings of a cabbage butterfly caterpillar eating leaves of that species, and then checked for changes in their physiology. After the recording, the plants had measurably increased the amount of mustard oil in their leaves, which is the primary defense plants in the order brassicales have against these insects. Control plants were played a recording of silence, a recording of similarly pitched insect songs, sounds of the wind, or left in actual silence, none of which triggered the same spike in insect-warding glucosinolates. This suggests that not only are the plants sensitive to sound, but they have some sense of discrimination about when to activate this extra defensive measure.

The benefits of being selective with mustard production is really a matter of managing resources. The extra effort and resources would be very draining if the plant upped the mustard oil production every time the wind blew. But waiting for feeling a bite from the caterpillar might be too late, while being sensitive to sound gives the other leaves on the plant a chance to fend off further chomping.

What other sounds count to your garden?

While cabbage butterfly caterpillars and brassicales have been in an evolutionary arms race for millions of years, there’s also a chance that this defense isn’t so narrowly focused that the plant can’t employ it against other herbivores. Or that other plants don’t use a similar concept, although without a dynamic toxin to produce it may not be a universal concept. A rose can only grow thorns so quickly, after all.

Source: Plants Listen for Hungry Caterpillars, First-of-Its-Kind Study Suggests by Emma Weissmann, National Geographic News

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