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Plants' Answer to Bug Attack: Call a Predator

Botany: A new study shows that some types of vegetation, when being eaten by an insect, emit a chemical signal that attracts help from further up the food chain.

March 25, 2001|WILL DUNHAM | REUTERS

WASHINGTON — Just as some cars are equipped with alarms that can alert police when 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 shows 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 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 harnessing plants' defensive systems could have positive applications for agriculture.

He said crops could be engineered to give off chemical signals as a way to provide more environmentally friendly pest control.

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