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New Study Sheds Light on Plants’ Nighttime Defense

By Jim Core
March 28, 2001

Agricultural Research Service scientists and cooperators have gained new insights into how plants defend themselves against insect attacks at night, according to findings published in the March 29 issue of Nature.

James H. Tumlinson, III, and other researchers at the ARS Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Fla., originally discovered that when beet armyworm caterpillars chew on plants, the plants produce chemical aromas that lure a wasp--a natural enemy of the caterpillars--to attack the crop pests. They subsequently isolated, identified and artificially produced a chemical found in the saliva of the caterpillars that prompts corn seedlings to produce the wasp-attracting chemical aromas.

They soon recognized that different caterpillar species elicit plants to produce specific chemical aromas that appeal to natural enemies of the very same caterpillar species. In effect, scientists have discovered that a caterpillar triggers its own doom mechanism.

More recent findings by ARS entomologists Consuelo M. De Moraes and Tumlinson, along with Mark C. Mescher of the University of Georgia, shed light on the role of chemical cues in a host plant’s nighttime defenses.

Little attention has been given to nighttime volatile response by plants and its effects on the behavior of nocturnal herbivores, according to De Moraes, perhaps because it has been assumed that herbivore-induced chemicals occur mainly during the day.

However, the authors found that tobacco plants (used only as a laboratory tool) release herbivore-induced plant chemicals during both day and night and that several volatile compounds are released predominantly at night. These chemicals were found to be highly repellant to female moths searching for sites to deposit their eggs. If the moths sense a chemical aroma, it indicates the crop is already larvae infested, and they find another, safer location for their offspring to develop.

ARS scientists will conduct further studies that could help plant breeders develop new crop varieties with enhanced defense systems.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.

Scientific contact: Consuelo M. De Moraes, ARS Center for Medical, Agricultural and Veterinary Entomology, Gainesville, Fla., phone (352) 374-5712, fax, (352) 374-5707,

More on Tumlinson's research on chemical volatiles.

Signal-Sending Plants Identify Their Attackers

Scientists to Caterpillar Pests: Chew on This

Scientists Identify Chemical That Triggers Plant "SOS" Call

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