Turning the Worms

Chemical misinformation fights rootworm infestation

Imagine a horde of tiny, ravenous worms moving through the soil, seeking lunch — and lunch is the root system of a corn plant. That's the common story of western corn rootworm in the United States. Rootworms can leave corn roots so riddled that stalks collapse or lodge, causing $1 billion in annual losses due to crop damage and control costs.

Oddly enough, western corn rootworm has a strong preference for corn roots — and almost nothing else. This singular preference piqued the curiosity of Colorado Agricultural Experiment Station researcher Louis Bjostad, who set out to learn why rootworms only eat corn and to see if there was some way to exploit this fact to stop the root-crippling onslaught.

What Bjostad discovered is an interesting process of chemical communication that takes place between corn plants and rootworms. As they grow, corn roots give off carbon dioxide. The CO 2 strongly attracts the larvae to the root systems. Then, like all youngsters, the larvae like to taste their food before they dig in.

"We found that larvae take at least one bite of the roots to see if they like them," says Bjostad.

"If the right stuff is there, they will continue to feed, causing severe damage. If it's something else, they'll move on. The right stuff is a precise mixture of.compounds that only corn roots produce. So far, we have identified a blend of 27 organic acids, monosaccharides, salts, and amino acids that occur in corn roots. We are about to conduct feeding bioassays to find out if this is the complete blend."

While identifying the products in corn roots, Bjostad unexpectedly found something that might prove useful. Corn roots produce small amounts of substances that, in high doses, actually repel the larvae. Unfortunately, the repellents are not strong enough in commercial varieties of corn to overcome the larvae's natural attraction to their favorite food.

Bjostad, a professor in the Department of Bioagricultural Sciences and Pest Management, has teamed up with other researchers to isolate and identify these natural repellents and then figure out ways to synthesize them in strong compounds that could be applied in bands around the corn seed at planting time.

Another approach Bjostad is considering is to use genetic engineering to increase production of the natural repellents in the corn roots themselves.

Bjostad says his goal is to create an integrated program of basic research on chemical communication in insects that he can use to develop new, environmentally-desirable technologies for pest control. His approach makes a lot of sense. Using naturally occurring pest deterrents instead of traditional pesticides reduces hazards to farmers who handle pest-control products. It also reduces groundwater contamination and starts a whole string of other environmental benefits that present fewer hazards to animals and beneficial insects. Developing alternative control methods also may prove extremely useful should corn rootworms someday develop resistance to insecticides now being used.

"We know many consumers now favor use of non-toxic approaches to pest control in food production," says Bjostad. "We think this research is a step in that direction."