Clear and present danger

Natural History, March, 2004 by Stephan Reebs

When insects munch on plants, some of the munchees call 9-1-1. The way the plants do that is to make chemicals that waft through the air, beckoning to predators. And when the predators arrive on the scene, they grab the plant-eaters for their own dinner. Now Stefano Colazza, an entomologist at the University of Palermo in Italy, and his colleagues have shown that some bean plants don't wait for the munchers to start munching.

Plant-eating insects often start life as eggs deposited on leaves. In the bean plants Colazza studied, just a few leaves covered with a herbivore's eggs cause the entire plant to produce chemical attractants; those signals lure insects that then lay their own eggs inside the eggs of the herbivore. Some trees are known to take similar preventive measures, but they react to damage inflicted to their leaves during egg laying--not, as the bean plants do, to the eggs themselves. ("Insect oviposition induces volatile emission in herbaceous plants that attracts egg parasitoids," Journal of Experimental Biology 207:47-53, January 1,2004)