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Insect Taste Buds Target Of Control Method

March 30, 1998

Dallas, Texas -- Insects are probably more finicky than cats when it comes to their diets, so a Penn State insect toxicologist is targeting their taste buds in an effort to protect crops.

Dr. Christopher A. Mullin, professor of insect toxicology in Penn State's College of Agricultural Sciences, is working with corn rootworm to develop better methods of controlling this insect. Corn rootworm is the primary pest of corn in the United States. While its larva does most of the damage, this occurs beneath the ground and it is easier to target the adult beetle.

"Most pesticides are neurotoxins and must make it past all of the insect's defenses before they can effect the central nervous system," says Mullin. "Usually, hundreds of times more pesticide must be applied outside the insect so that a lethal dose can arrive at the proper location inside the insect."

To circumvent this problem, Mullin is looking at insect taste buds because they are a direct connection between the central nervous system and the outside. Insects are also specialty feeders, targeting one or two plant types as their primary food and starving if those plants are unavailable. Taste is very critical to insects.

Mullin does not know what insects perceive as taste, but he does know that chemicals considered sweet-tasting by humans are chemicals that stimulate feeding and, for the most part, chemicals that humans consider bitter-tasting put the beetles off their food.

One exception is cucurbitacin, an extremely bitter chemical found in the fruit skins and roots of squashes and other cucurbits. Adult beetles will feed on anything coated with cucurbitacin to the exclusion of other foods. Farmers currently mix ground-up squash rinds with pesticides to get the insects to ingest the pesticides.

"But purified cucurbitacins are too toxic to use and too water soluble to remain on the tiny pollen-like spheres suggested as a delivery method," Mullin told attendees today (March 30) at the spring meeting of the American Chemical Society in Dallas, Texas. "We are using three-dimensional chemical modeling to create structural templates of stimulatory and antifeedant chemicals."

Finding the structural similarities between chemicals that stimulate feeding or between antifeedant chemicals will allow researchers to pinpoint the physical characteristics of the molecular shape needed to stimulate the neurons in the taste buds. A search of chemical libraries for potentially useful chemicals could then identify candidate substances that might also be less water soluble than those that are already known. It may also allow researchers to design chemicals specifically to stimulate or suppress feeding behavior.

Although chemicals that stimulate feeding behavior can be used to convince insects to consume poisons, Mullin would rather find a chemical that depresses feeding to the point of starvation. Corn rootworm beetles must feed to reproduce.

"While humans have thousands of taste buds, insects generally have four taste buds with four hairs per taste bud, or about 16 neurons," says Mullin. "Corn rootworm beetles have slightly more neurons."

The Penn State scientist is looking for a chemical that so overwhelms the taste bud neurons that they shut down, and because there are so few neurons, the insects would be incapable of perceiving their food and starve. This could be done either by a chemical, like cucurbitacin that is so attractive that they will feed exclusively on it, or by a powerful antifeedant.
Vicki Fong (814) 865-9481 (office) (814) 238-1221 (home) vyf1@psu.eduEDITORS: Dr. Mullin may be reached at (814) 863-4437 or

Penn State

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