In the early 1980s, plant to plant communication was a controversial topic of research because well, suggesting plants can talk is rather absurd, right? Apparently not. According to Prof. Andre Kessler, ecology and evolutionary biology, plants issue chemical warnings that help their colonies survive pest attacks.
“At my Ph.D., we were already looking for volatile compound emissions. These are emitted in response to some sort of damage. In most cases, it is in response to herbivore damage. Feeding insect herbivores alter the plant’s metabolism and as part of the change the plant simply smells different,” Kessler said.
These volatile emissions vary depending on the type of insect and act as chemical messages for other insects and plants to decode. Insects such as lark beetles are attracted to damaged plants, sensing an abundance of food. In contrast, moths and butterflies are often repelled by those plants, viewing them as decaying matter.
The insect-specific cocktail of volatile emissions can also be interpreted by other organisms. Predators that feed on these herbivores may use the information to find their prey. The damaged plant “calls for help” and indirectly kills off its antagonist.
Kessler hoped to build on these observations to understand how plant to plant communication via these chemical messages affected the distribution of herbivores.
Past research on the communication between sagebrush and tobacco provided important clues. When sagebrush is attacked by a herbivore, it releases volatile emissions to alert other sagebrush plants. However, nearby wild tobacco plants also pick up on these communications.
“Then those wild tobacco plants induce their own resistance and become more resistant to herbivores without actually having the herbivore,” Kessler said. “So [the researchers] suggested that this plant is eavesdropping on the damaged plant’s signals and using it to predict an incoming herbivore. They pretty much use the information from the neighbouring plant without actually investing in it.”
According to Kessler, it seems counterintuitive that the sagebrush should put so much effort in releasing chemicals to protect its own species when that only really allows wild tobacco to reap the benefits. Kessler’s experiments on goldenrod plants and beetle larvae, though, help piece together the puzzle.
“When [beetle larvae] damage a plant, the plant metabolism changes dramatically; so dramatically that these bugs move away and this is unusual. Normally, an insect that is attacking a plant first stays with the plant,” Kessler said.
This points to a smart technique of distributing herbivore damage across nearby plants. Once a goldenrod is damaged, it releases volatile compounds which neighbouring plants respond to by changing their own metabolism.
“The neighbouring goldenrod overreacts to the warning already, so the volatile compounds are already induced when the larvae arrive at the neighbouring plant which makes the larvae move two steps further. This results in an over-dispersal of herbivory within the plant population, reducing the damage to individual plants,” Kessler said.
This has massive implications in novel pest-control techniques, especially in famine-hit countries where traditional genetically-engineered crops and insecticide sprays have not worked. Biological control methods work more rapidly, more efficiently and more sustainably, guaranteeing a higher crop yield.