A common substance produced by fungi and other organisms has been found in the saliva of caterpillars and helps to suppress the toxins that plants produce when chewed on by insects, according to a team of entomologists. "The saliva of herbivorous insects has been overlooked as a factor in overcoming host defenses," the researchers report in today's issue of Nature. "Our results show that glucose oxidase, one of the principal components of Helicoverpa Zea saliva, is responsible for suppressing induced resistance in (tobacco)." Investigation of the caterpillar commonly known as corn earworm by a team of Penn State and University of Arkansas entomologists aimed at isolating the substance in caterpillar saliva that suppressed expression of defensive mechanisms in leaves. These defensive mechanisms include production of nicotine -- a neural toxin, and digestive protease inhibitors -- which interfere with caterpillar digestion. "Initially it was thought that caterpillar saliva contained only compounds that triggered the plant's defense mechanisms," says Dr. Gary W. Felton, head and professor of entomology at Penn State. "Rather than inducing defense mechanisms as we supposed, the saliva inhibits production of the harmful chemicals and actually weakens the defenses of the plant."

Felton, working with Richard O. Musser, the lead author on this paper and Sue M. Hum-Musser, graduate students at University of Arkansas; Herb Eichenseer, University of Arkansas post doctoral fellow now at Pioneer Seed Company, Gary Ervin, postdoctoral fellow now at Mississippi State University; and J. Brad Murphy, professor of horticulture, University of Arkansas; and Michelle Peiffer, research assistant, Penn State, identified glucose oxidase as an active ingredient of caterpillar saliva. Glucose oxidase converts the simple sugar glucose into gluconic acid and hydrogen peroxide.

"While glucose oxidase is produced in many biologic systems and glucose oxidase extracted from fung
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Contact: A'ndrea Elyse Messer
aem1@psu.edu
814-865-9481
Penn State
10-Apr-2002

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