an Baldwin works in a lab anyone could love: a large blackened burn area high on a steep slope in the Great Basin Desert of southwestern Utah. Here a distant mountain range shimmers blue and lavender, the nearer craggy cliffs of Veyo Ridge hover in red, and the curves of the desert hills are dotted green by Joshua trees and scrub. Baldwin, a biologist and the director of the Molecular Ecology Department at the Max Planck Institute for Chemical Ecology in Jena, Germany, has stationed his equipment here to launch a new study of how plants defend themselves—a question he has pursued for 20 years.
Above: Ian Baldwin and his team set up equipment in the Utah desert to monitor wild tobacco's chemical defenses against enemies like caterpillars (shown below). Baldwin had not expected to detect any effects. "The fact that it worked was an amazing surprise," he says. "I turned from a skeptic to a believer. The nice thing about research is you can prove yourself wrong."
He and his colleagues are using chemical sensors to investigate plant communications: cries for help, invitations, even warnings, each in the form of odor molecules that float past human noses unnoticed.
The harder biologists look for these signals, the more they find. They have already discovered that plants can send chemical cues to repel insect enemies, as well as signals that attract allies—other insects that are pleased to eat the insects eating the plant. But that is only the start of a more complex scenario, for Baldwin and others have also found that nearby plants can listen in to this conversation and gear up their own defenses.
Some of the most complex studies came out of these controlled environments. In 1988 Marcel Dicke and his colleagues at Wageningen University in the Netherlands offered evidence that plants under insect attack could enlist help from the enemies of their enemies. Dicke found that when spider mites attack lima bean plants, the plants release a chemical SOS that attracts another mite that preys on the spider mite. Mechanically damaged plants do not produce the cues; most likely, only elicitors in the saliva of the insect can trigger the plant to produce the right molecules. "Today," Dicke says, "the scientific community agrees that plants talking to their bodyguards is likely to be a characteristic of most, if not all, plant species." Even the gingko—a species that has been around for 150 million years—can communicate chemically with insects, he adds.