Plant Talk

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Plants under insect attack can release chemicals either through the air or from their roots, to alert nearby, related plants to danger. That allows the sister plants to build up their protections before the attackers get to them.

Plants can’t run away, but they do have power: they react to human touch and to breezes; they have self-healing mechanisms, too. Many can raise their temperatures sharply, to attract pollinators, as skunk cabbage does. One tropical plant that flowers for a single night heats by 20 degrees, so area pollinators know that “it’s tonight or never.”

Recently Science News, without which my life would be dull indeed, announced that plants in the wild, as well as those they’d already worked with in the lab, can send out chemical “calls” to bug-predators to fly in and kill pests.

A couple of German scientists visiting Utah learned that wild tobacco releases certain chemicals when insects start chewing on it. The chemicals attract whole troops of bugs that prey on the pest-bugs. The men pointed out that this was the first time science had discovered the specific signaling chemicals that attract pest-killers to wild plants.

Other scientists were not surprised that in farmers’ fields plants would signal to their neighbors – because, after all, thousands of the same species are all planted together. Just one of what Science News calls a “bodyguard” plant could protect a whole area of uniform plants threatened by the same pests. Researchers did wonder how it could benefit an isolated wild plant to issue signals when it was surrounded by bare sand or by unrelated plants.

Wouldn’t that make it unlikely the necessary predator would be in the area?

However, some predators aren’t that fussy.

Most of the predator-insects that were attracted to a chemical were specific killers seeking specific prey. Would predators that liked a variety of pest insects respond to a call designed to attract a particular predator? How could researchers find out? After all, there are a lot more of the generalists than of the fussy eaters, so it’s an important bit of information.

The two German-based researchers, Andr¿ Kessler and Ian T. Baldwin, did some tests. Here’s one: they covered each outdoor plant with a simple apparatus that measured the scent an attacked plant gave off by capturing its chemical releases. Flea beetles, hawkmoth caterpillars, and mature insects triggered a batch of chemical signals from the plants. The plants used six different chemicals. The researchers treated the plants with one of these at a time. They glued hawkmoth eggs under the plant leaves and watched: several of the chemicals attracted predatory insects, including one common bug, Geocoris pallens, that destroyed 95 percent of the hawkmoth eggs. They later discovered that a cocktail of chemicals from plants even reduced egg-laying by hawkmoths.

This is Ruth Page, talking with you about one more astonishing accomplishment of plants that occurs, invisibly, in our environment.

–Ruth Page is a writer, former editor of a weekly newspaper and a national gardening magazine.

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