Chemical communication among plants, herbivores, and their natural enemies: Dr. Consuelo DeMoraes
Mobilizing Defenses
It sounds more like science fiction than science: A caterpillar chews on a cotton leaf. The cotton plant, in response to the caterpillar’s attack, produces and releases an odor—a blend of chemical compounds—that attracts a species of wasp that is a natural enemy of the caterpillar. The wasp detects the odor and follows it to the cotton plant, where it stings the caterpillar, injecting an egg into it. Later, what emerges from the caterpillar’s cocoon is not a moth but a new wasp. The plant has effectively intercepted the caterpillar’s attack by calling on the wasp.
This scenario, depicting a plant “calling in its friends,” is not sci-fi; rather, it is an example of chemical ecology in action. The study of chemical ecology holds promise for developing pest-management strategies that could reduce the use pesticides, in turn enhancing grower profitability, food safety, and environmental quality. In addition, understanding these plant-insect interactions could help us to develop “sentinel plants” that could detect and alert us to explosives, harmful chemicals, or bioterror agents.
The College of Agricultural Sciences is fortunate to have some of the world’s foremost chemical ecologists on its faculty. For instance, entomologist Consuelo De Moraes has shown that plants produce different signals in response to the different caterpillar species that feed on them and thus attract the appropriate natural enemies. “Plants are not just saying, ‘Yes, I am damaged,’ they are providing specific information about who is damaging them. It is a really intricate system,” says De Moraes.
While most plant studies in the lab and in the field are conducted during the day, De Moraes and her colleagues at Penn State also have made an important nighttime discovery: tobacco plants release different volatiles at night than they do in daylight. “We actually thought volatiles were released only during the day,” says De Moraes. “So this discovery of nocturnal odors came as a surprise.” De Moraes and colleague Mark Mescher determined that tobacco plants being attacked by caterpillars release chemicals at night that repel night-flying moths searching for places to lay their eggs. The blend of odors released at night deters female moths from laying eggs on those plants.
“The plant sends out a chemical signal to the moth to stay away,” says Mescher. “These odors are the plant’s way of defending itself at night.” For a female moth, identifying a plant already crawling with caterpillars has several advantages. She can help her offspring avoid competition from other caterpillars and steer clear of besieged plants that will have already mobilized chemical defenses, making them less palatable and attracting natural enemies of the caterpillars.
Learn more about chemical ecology research:
http://www.chemicalecology.psu.edu/
