By Echo Martin
Vervet monkeys have specific alarm calls for leopards, snakes, and eagles. Blackbirds give off a high seee call when birds of prey are nearby. And plants get…gassy? Over the last 30 years research has shown that plants, much like animals, ‘scream’ at each other when being attacked by pests through the specific gasses they give off. Plants can even tell the difference between an insect bite and general tearing and adjust the signal they give off accordingly. Recent findings in John Erwin’s lab, however, indicate that these gasses do more than just warn nearby plants to be on high alert: they also call in beneficial insects.
The idea that plants communicate with one another isn’t new — it was first put forth through two studies published in 1983 on willow trees, poplars, and sugar maples. In the last 33 years more scientists have explored the nuances of whether and how plants communicate, including Erwin’s lab. Specifically, his lab has looked at the effects of methyl jasmonate (MeJA), an organic compound that plants emit to ‘tell’ surrounding plants that they are being attacked so the other plants can turn on defenses, which lessens those plants’ chances of being attacked by pests.
“We turned on all their defenses by exposing plants to small amounts of MeJA gas in the greenhouse,” says Erwin. “By doing that, all the plants in that greenhouse are on high alert and would be naturally defended against pests and we would need to use less pesticide.” The findings, which were published in the scientific journal Entomologia Experimentalis et Applicata, showed that plants exposed to MeJA actually produced more compounds that give pests indigestion.
Last year, Erwin decided to take the concept of plants communicating with one another to his Plant Production I class. The class was divided into groups; each had to develop a hypothesis about plant communication and an experiment to test it. One group submitted a proposal that caught Erwin’s interest: Do the gasses plants give off to communicate with each other also affect beneficial insects?
To find the answer the students used soybeans, aphids, and lacewings (an aphid predator). “They set up three cages with soybeans in them,” says Erwin. “Cage one, the control, was put in a greenhouse that had no aphids. Cage two we infested with aphids, and right next to it we placed the third cage.” The third cage wasn’t infested with aphids, but it was exposed to the air given off by the plant being attacked by aphids.
After being exposed to the ‘aphid air’, cage three was then moved next to the control group and lacewings were released. Students then documented where the lacewings chose to lay their eggs. Lacewings flocked to cage three, even though no aphids were physically present on the plant to attract them. Erwin comments, “We know that when plants are exposed to aphids, or any other pest, the plants near them turn on genes to help defend themselves. What this experiment suggests is that turning on those genes not only makes the plants less attractive to pests, but may make them more attractive to beneficial insects — plants are ‘calling’ to other organisms to defend them.”
The practical applications for this research are still being explored, but it has a lot of potential for use in greenhouses. “Instead of applying pesticides, we could apply attractants to allow natural beneficial pests to better focus on pest infestations,” says Erwin. Since it’s a closed system, even just a small amount of MeJA could turn on defenses in the whole greenhouse. “The goal is to reduce pesticide use, which is good for the environment and reduces costs. It’s also something organic farmers could use, because it’s a natural compound.”
And it doesn’t stop there. While Erwin’s research focuses on greenhouses, there’s potential application to field production as well — but more research is needed. As research continues, don’t be surprised to see more producers using this plant alarm system to keep their crops safe in a more natural way.