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September 19, 2006
Also appeared in print September 25, 2006, p. 15


Individual Insects Make Signature Venoms

Walking stick study hints at chemical biodiversity in these insects

Ivan Amato

DEFENSIVE FRAMEWORK Stereoisomers of this 10-carbon dolichodial structure give punch to defensive sprays emitted by some walking stick insects.

It's safe to say that not many people have milked the insects known as walking sticks for the defensive secretions the insects spray when threatened. Now, milkers in Gainesville, Fla., have used nuclear magnetic resonance spectroscopy to discover that the secretions of individual walking sticks are chemically distinct. "Single-insect variability of venom demonstrates the potential variability of chemical biodiversity at the level of individual animals," the researchers say.

Walking sticks would never have perambulated into Arthur S. Edison's laboratory at the University of Florida's McKnight Brain Institute were it not for graduate student Aaron T. Dossey, an amateur entomologist who roams the Florida landscape collecting insects, including walking sticks. Dossey has repeatedly been on the business end of the insects??? chemical weaponry, which is extremely noxious to the nose and eyes.

In a joint effort involving the National High Magnetic Field Laboratory and others, Edison's lab recently christened a compact and uniquely sensitive NMR probe designed for analyzing natural products, including proteins and metabolites, which often are available in only minuscule quantities. "The walking stick became a test case," Edison says, noting that when the venom was first characterized more than 40 years ago, "it took thousands of milkings." The Florida researchers report their findings in ACS Chemical Biology (2006, 1, 511).


STICK IT TO 'EM Walking stick insects like this one can lash out at predators with noxious chemical sprays emitted from a gland behind the head.


MILK THAT HURTS With a pipette, scientists collect a microliter of defensive chemicals from a walking stick insect.

"Eavesdropping on the chemical communication of single insects is a major breakthrough," says Thomas Eisner, a professor emeritus of chemical ecology at Cornell University. He recalls donning what looked like chemical warfare apparel in the early 1960s when he and colleagues studied walking stick chemicals. "It's awful to get sprayed," he says.

By gingerly prodding insects' secretory ducts with a pipette, the Florida researchers can elicit about a microliter of a whitish fluid. They used their NMR probe and other conventional analytical techniques to examine the secretions of Anisomorpha buprestoides individuals. They found that each insect contains a mix of stereoisomers of a 10-carbon chemical framework, which the researchers refer to as dolichodial. Stereoisomers of this framework have previously been found by Eisner and others in various specimens, including walking sticks, ants, and a plant in the mint family.

The single-insect sample size in the new study revealed previously hidden details of walking stick defensive chemistry. Most notably, the researchers could discern that each walking stick produces a different ratio of dolichodial stereoisomers.

"This shows you what happens with 40 years of NMR progress," comments Jerrold Meinwald, a professor emeritus of chemistry at Cornell University who worked with Eisner decades ago in some of the first studies of walking stick defensive sprays. ???We are moving toward the ability to listen in on the chemical phone conversations??? that are going on invisibly between the world's creatures all of the time, Eisner adds.??

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2010 American Chemical Society