RESEARCH conducted by Purdue University and the University of Illinois suggests that normal corn plants contain an active defense mechanism that averts the western corn rootworm beetle from feeding on the plants' foliage.
Identifying this mechanism could be the key to controlling western corn rootworm, a pest that causes more than $1 billion of damage annually in losses and control measure costs in the U.S.
"This opens up a whole new opportunity to understand more about the mechanism of defense in corn to control this beetle," said Gurmukh Johal, Purdue professor of botany and plant pathology. Johal and Stephen Moose of Illinois independently discovered the mutant at around the same time.
In general, adult rootworm beetles feed on the silks and pollen, while larvae chew on the roots of the normal corn plant. After close investigation, researchers discovered that western corn rootworm beetles were singularly attracted to the leaves of the corn mutant.
At five to six weeks into the growth stage, the beetles scraped away the leaf tissue from the upper epidermis of the mutant corn; the leaves were particularly vulnerable to attack due to a combination of structural and biochemical changes.
Corn plants can become completely defoliated if the beetle infestation is severe, thus resulting in significant yield loss.
In the absence of the beetle, the mutant is virtually indistinguishable from normal corn plants, which may be why it was not discovered earlier, Johal said.
In the U.S., normal practices for controlling western corn rootworm include crop rotation, transgenic corn plants and insecticides, but the increase in use of continuous corn systems has also increased rootworm resistance.
Currently, most management strategies for western corn rootworm usually focus on reducing the larvae feeding on the roots, but the discovery of the corn root worm1 (crw1) mutant could possibly provide alternative control tactics.
"In identifying the genetic pathway involved in resistance, we can develop better ways of controlling this pest without having to use insecticides," Johal said.
The mutant could be used in a "push/pull" pest management strategy, luring the beetles to a specific location where they can be controlled, explained Christian Krupke, Purdue assistant professor of entomology and co-author of the study.
"Once you can get them where you want, you can use efficient, cost-effective ways of controlling them, either by directly targeting and eliminating them or by keeping them away from your main crop," he said.
In the present study, discovering, mapping and classifying the preliminary characterization of the crw1 mutant are the first steps in making corn plants more pest resistant, but further research needs to be conducted to discover new strategies in controlling western corn rootworm in the future.
The research was published online in PLoS ONE.