Scientists have been experimenting with playing sounds to plants since at least the 1960s, during which time they have been exposed to everything from Beethoven to Michael Jackson. Over the years, evidence that this sort of thing can have an effect has been growing. One paper, published in 2018, claimed that an Asian shrub known as the telegraph plant grew substantially larger leaves when exposed to 56 days of Buddhist music — but not if it was exposed to Western pop music or silence. Another, published last year, found that marigolds and sage plants exposed to the noise of traffic from a busy motorway suffered growth difficulty.
Plants have been evolving (进化) alongside the insects that eat them for hundreds of millions of years. With that in mind, Heidi Appel, a botanist now at the University of Houston, and Reginald Cocroft, a biologist at the University of Missouri, wondered if plants might be sensitive to the sounds made by the animals with which they most often interact. They recorded the vibrations made by certain species of caterpillars (毛毛虫) as they chewed on leaves. These vibrations are not powerful enough to produce sound waves in the air. But they are able to travel across leaves and branches, and even to neighbouring plants if their leaves touch.
They then exposed tobacco plant — the plant biologist's version of the laboratory mouse — to the recorded vibrations while no caterpillars were actually present. Later, they put real caterpillars on the plants to see if exposure had led them to prepare for an insect attack. The results were striking. Leaves that had been exposed had significantly higher levels of defensive chemicals, making them much harder for the caterpillars to eat. Leaves that had not been exposed to vibrations showed no such response. Other sorts of vibration — caused by the wind, for instance, or other insects that do not eat leaves — had no effect.
"Now speakers with the right audio files are more often being used to warn crops to act when insects are detected but not yet widespread," says Dr. Cocroft. "Unlike chemical pesticides, sound waves leave no dangerous chemicals."
