Plants in Distress Send SOS to Friendly Bugs
Just as some cars are equipped with alarms that can alert police that a bad guy is on the prowl, some plants emit their own chemical cry for help when they are being munched by a hungry bug, researchers say.
A new study has shown for the first time that plants in the wild, when attacked by a herbivorous bug, release a plume of chemicals that signal insects that like to eat the marauder that a juicy meal is at hand.
The finding not only sheds light on how plants defend themselves, but it provides potential strategies for environmentally friendly pest management in agriculture, said Ian Baldwin, director of the Max Planck Institute for Chemical Ecology in Jena, Germany, who spearheaded the research.
The researchers found that when a species of wild tobacco plant (Nicotiana attenuata) that is indigenous to the Great Basin Desert of the southwestern United States gets damaged by a herbivore such as a hawkmoth larva, also known as a hornworm, it releases a mixture of chemical compounds into the air. Baldwin compared it to the perfume Chanel No. 5, designed to attract predators of the insect, rather than human, variety.
The chemicals function as a signal to help predatory bugs find their prey--the hawkmoth larva--and eat it or its eggs, Baldwin said, while also deterring adult moths from laying their eggs. The findings appeared in the journal Science.
“Think of it as a car alarm,” Baldwin said in a telephone interview. “What does your car alarm do for you? Somebody breaks into the window of the car and wants to steal your CD player. When the car alarm goes off, it does two things. It sends off a signal that hopefully the nearby police might pick up on. But it also gives a signal that says to the burglar, ‘We know you’re here.’ ”
Baldwin noted, however, that police generally won’t “come eat your burglar.” He added that despite a cute anthropomorphic analogy, the reality is that “it’s not as if the plant knows necessarily that there are predators out there. There’s no conscious signaling to a particular predator.” The mechanism likely evolved with plants emitting a “nasty chemical defense” that insect predators then used as a marker for a good meal.
A plant’s chemical cry for help had been observed by researchers in the past in the laboratory and agricultural settings, but never before in the wild. The finding suggests that the “indirect defense” mechanism of emitting chemicals that attract crawly predators is used by many plants.
“From the laboratory, it’s known that tobacco, corn, lima beans, tomatoes, cucumbers, oil seed rape--a whole bunch of different species--give off these signals when they’re attacked by larvae [caterpillars]. So it’s a phenomenon that probably occurs in many, many different plants,” Baldwin said.
Baldwin said that harnessing plants’ defensive systems could have positive applications for agriculture.
“Let’s think a little bit about what we do in agriculture now,” he said. “We’ve bred all these great plants that have incredibly high yields that are basically defenseless.”
He said scientists have genetically engineered toxins back into crops to help their defenses, or simply spray crops with chemicals. Baldwin noted that insect pests can rapidly develop resistance to both methods.
Baldwin said crops could be engineered to give off chemical signals as a way to provide more environmentally friendly pest control. But farmers would have to be careful not to harm the “good” insects--the ones that the plants’ chemical signals would attract to eat the leaf-snacking interlopers.
“You have to have a crop management procedure that allows for those predators to be there,” he said. “But the predators that we found in Utah, these are little guys that live on the ground, in the soil. There’s no difficulty for them being in a crop situation. You can’t hose down the crop with an indiscriminate insecticide that kills all insects. That would take care of your predators too.”
