The findings, published in the journal Oecologia could be useful for agriculture, say the study investigators, Heidi Appel, a senior research scientist in the Division of Plant Sciences, and Rex Cocroft, a professor in the Division of Biological Sciences, both at the University of Missouri (MU).
Dr. Appel says while previous studies have shown plants are capable of responding to acoustic energy - including music - theirs is the first to show they can "respond to an ecologically relevant vibration," and that these vibrations signal "changes in the plant cells' metabolism, creating more defensive chemicals that can repel attacks from caterpillars."
Laser beam measured caterpillar chewing vibrations
For the study, the researchers used caterpillars of the small white butterfly Pieris rapae and the flowering plant Arabidopsis thaliana. The plant is a member of the mustard or cabbage family Brassicaceae and is widely used as a model organism in biomedical research.
The researchers placed caterpillars on a plant and measured the vibrations they made when they chewed the leaves.
The researchers placed the caterpillars on the plant and measured the vibrations they made when they chewed the leaves.
The method most researchers use to detect vibrations use a contact microphone. But in this case, the microphone sensor would have been too heavy for the small leaves of Arabidopsis, so the team used a different approach based on a laser and a piece of reflective tape stuck to the leaf surface. The laser beam bounces off the tape, and the amount of deflection is then used as a measure of the amount of vibration in the leaf, minimizing contact with the leaf itself.
The researchers were also able to play the output of the laser through a speaker, so human ears could hear the noises made as the caterpillars chewed the leaves.
Then, in a separate stage of the study, the researchers played the recordings to one set of plants, and played only silence to another set.
Plants exposed to feeding vibrations produced more mustard oils against the caterpillars
When they then placed caterpillars on both sets of plants, they found the plants that had previously been exposed to recordings of the caterpillars chewing, produced more mustard oils, compounds that caterpillars find unappealing.
Prof. Cocroft says: "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."
Play the video below to find out more about the team's research:
He and Dr. Appel conclude this suggests the plants are able to distinguish vibrations made by feeding from those that come from other sources in their environment.
The pair now plans to look at how the plants sense the vibrations, which features of the signals are important, and how they integrate the vibrations with other information to generate their anti-pest defenses.
Dr. Appel says the caterpillars crawl away when they sense the chemical defense, so perhaps vibrations could be used to boost plant defenses. She suggests such applications could be useful in agriculture, and also:
"This research also opens the window of plant behavior a little wider, showing that plants have many of the same responses to outside influences that animals do, even though the responses look different."
The study was funded by the National Science Foundation.
In 2010, Medical News Today learned of a similar example when scientists in the Netherlands reported how people appear to have antiviral plant defenses. They found that in addition to known antiviral agents such as antibodies and interferons, humans also seem to have an immune system component that is like the type of "RNA silencing" that plants use to defend against virus attack.