The Plants Are Listening

No, trees and other leaved plants don't really have ears, but researchers have determined that they are sensitive to the vibrations of chewing insects, growing in a defensive manner when exposed to these alarming vibrations.

A study detailing these findings was recently published in the peer-reviewed journal Oecologia.

"Plants have many ways to detect insect attack, but feeding vibrations are likely the fastest way for distant parts of the plant to perceive the attack and begin to increase their defenses," study author Rex Cocroft said in a statement.

Cocroft collaborated with Heidi Appel to conduct controlled audio and chemical analysis of plant responses to various noises and their associated vibrations.

"We found that feeding vibrations signal changes in the plant cells' metabolism, creating more defensive chemicals that can repel attacks from caterpillars," said Appel.

According to the study, when caterpillars feed on Arabidopsis - a small flowering plant related to cabbage and mustard - the resulting vibrations trigger an process that produces mustard oil - a chemical that is unappealing to caterpillars.

Astoundingly, the researchers found that plants can actually tell the difference between the sources of vibrations, even if they are at very similar frequencies - likely a precaution to avoid wasting valuable energy fighting a non-existent threat.

"What is remarkable is that the plants exposed to different vibrations, including those made by a gentle wind or different insect sounds that share some acoustic features with caterpillar feeding vibrations did not increase their chemical defenses," Cocroft said.

According to the researchers, future work will focus on how exactly these vibrations are sensed by plants in the first place, and how exactly the plants can discern the nature of a vibration's source - information that could prove very valuable to the agricultural community.

The study was published in Oecologia for July 2.