By Robert Krulwich – National Public Radio –  April 29, 2014

Over the past 20 years, scientists have found that all kinds of trees and plants like sagebrush, barley, corn, and yes, bean plants, release VOCs when they’re being invaded. It’s a plant’s way of crying out. But is anyone listening? Apparently. Because we can watch the neighbors react.

In our case, when the distress signal reaches the two bean plants on either side of our aphid-covered plant, they also emit VOCs — cries of their own. As you can see, they seem to be calling for help — that’s my fanciful way of describing what happens next.

Some bean plants pump out chemicals specifically designed to keep aphids away. Those are smelly irritants, especially noxious to invaders. But some bean plants do double duty. They pump out attractants — perfumes designed to lure in different airborne insects — in this case, wasps. Wasps are an aphid’s worst nightmare. Once they arrive, the tables are turned. The critter who was lunching now becomes lunch.

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