Ash Tree Yields Potent Weapons In The War On Gypsy Moths

July 24, 1996

Ash Tree yields potent weapons

CONTACT: Dale Norris, (608) 233-8334; FAX (608) 233-7432


MADISON- A ubiquitous tree that graces many city and suburban streets has given scientists an arsenal of new chemicals with which to fight the gypsy moth, one of the world's most feared defoliators.

Plumbing the chemical depths of the green ash tree, Dale Norris, a professor of entomology at the University of Wisconsin-Madison, and Ingrid Markovic, a graduate student, have extracted an array of natural chemical compounds that repel or poison gypsy moth larvae, the leaf-eating caterpillars with appetites the size of oak trees.

"Over the past 50 years, governments have spent hundreds of millions of dollars on gypsy moth research and control," said Norris. "But nobody bothered to look at the chemistry of plants that gypsy moths won't feed on."

Although the gypsy moth caterpillar will dine on any one of more than 300 different trees and shrubs, it exhibits a distinct aversion to the green ash.

"The caterpillars will starve to death before they1ll feed significantly on it," said Norris. "It is essentially immune from one of the most serious pests of plants, period."

The reason the gypsy moth turns its nose up at the green ash is because the tree deploys a layered chemical defense, and Norris believes those same chemicals can now be turned to the defense of the hundreds of species of trees and shrubs featured prominently on the insect pest's menu.

According to Norris, the green ash tree's first line of defense resides in a group of six to eight volatile chemical compounds that the gypsy moth caterpillar detects at a distance. This mix of compounds sends the caterpillar in the opposite direction. They can detect these compounds without ever touching the tree.

If, however, a gypsy moth caterpillar accidentally drops on to the leaves of the green ash and is hungry enough to nibble, the tree deploys a second group of chemical compounds that quickly inhibit eating, and a third group that, when ingested, outright poisons the caterpillar by disrupting its development.

"There is this range of chemistry, from highly volatile messengers that go out from the foliage and repulse the insect from several feet away, to relatively non-volatile compounds that deter feeding and lethally alter development and metamorphosis," Norris said.

All of these chemicals, according to Norris, appear to work at very low concentrations (a few parts per million) and offer an apparently safe and environmentally benign new weapon in the war against the gypsy moth.

Norris and Markovic, working through the Wisconsin Alumni Research Foundation (WARF), have received a patent allowance on the green ash compounds. Norris envisions their use especially in sticky, protective strips wrapped around tree trunks and shrub stems as an adjunct or alternative to the aerial spraying of the caterpillar-killing bacterium, Bacillus thuringiensis, now the most widely used agent in the fight against the pest.

A tacky barrier, impregnated with the natural chemistry of the green ash and wrapped around a tree trunk or shrub stem, would be significantly effective, said Norris, because gypsy moth caterpillars make daily migrations up and down tree trunks and stems.

Interestingly, it is as caterpillars that the gypsy moth primarily moves about the landscape, hanging from threads and using the wind to "balloon" to new locales. They can sometimes sail for great distances to new feeding grounds where they dine exclusively on foliage.

"Between the stickiness of a barrier and its green ash chemistry, we can greatly disrupt the normal movement of the larvae," Norris said. "We think we can give people a slick, safe tool to prevent this pest from denuding their valued and otherwise susceptible plants."

Terry Devitt, (608) 262-8282,

University of Wisconsin-Madison

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