Research shows: Insects, plants wage war

A chemical battle is waged whenever some insects feed on plants, according to University of Arkansas Division of Agriculture research conducted by an entomology graduate student.

“Our goal is to develop crop plants that are resistant to insect pests,” said Richard Musser, a Ph.D. student from Fayetteville. “This research reveals the complex mechanisms involved in plant defenses and the means insects use to suppress them.”

Musser is working toward his Ph.D. in insect physiology with a minor in plant biotechnology. His thesis research, Caterpillar Saliva Suppresses Inducible Plant Defenses, won the Plant Resistance to Insects Graduate Student Research Award from the Entomological Society of America and first place in the Ph.D. poster contest for the Gamma Sigma Delta student research competition.

Musser used tobacco plants in his study because they use nicotine, which is easy to measure, for defense. The research used corn earworm larvae. Individual caterpillars were caged on a single tobacco plant for 24 hours.

Higher nicotine levels were measured in the damaged leaves fed on by caterpillars, whose salivation was inhibited. Nicotine levels in leaves damaged by caterpillars with normal salivation were lower, indicating the insects' saliva inhibited the plant's defensive response.

“This is the first time research has demonstrated that insect saliva causes a plant to respond defensively and that the saliva actually suppresses that defense mechanism in the plant,” Musser said.

In a related study, Musser punched holes in plant leaves to simulate insect damage, then treated some of the holes with saliva extracts from the caterpillars and others with ordinary water. Corn earworm larvae were then allowed to feed on those leaves. The insects feeding on leaves treated with saliva solutions gained more weight than those feeding on leaves treated only with water.

“This demonstrates the impact a plant's defenses can have on caterpillars and how the suppressant effect of the insects' saliva can improve its ability to overcome those defenses and feed on the plant,” Musser said.

Musser expects to receive his Ph.D. from the University of Arkansas in May 2002 and is currently exploring research positions in Arkansas and Georgia.

Fred Miller is a science writer for the Arkansas Agricultural Experiment Station.

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