Their focus was prompted by observations made by Jorge Zavala, a former postdoctoral researcher at Illinois and a co-author on this work. Zavala, now a visiting scholar at Illinois from the University of Buenos Aires, knew from previous research that levels of protein-degrading enzymes in the insect gut, called proteinases, rise and fall in response to chemical defenses in soybean leaves. He saw that rotation-resistant rootworms survived longer on soybeans and inflicted more damage on soybean leaves than their non-resistant peers. He also detected differences in levels of proteinases in rotation-resistant and non-resistant (wild-type) rootworms.
The new study tested these results in a broad sample of western corn rootworms from Illinois, Iowa, Nebraska and Missouri.
"We indeed found that the rotation-resistant rootworms could eat more foliage than the (non-resistant) wild type (rootworms)," Seufferheld said. "They are also able to survive a little longer on the soybean than the wild-type rootworms."
When insects feed on their leaves, soybeans ramp up production of proteinase inhibitors to combat the insects' ability to digest proteins in their leaves. The researchers hypothesized that the rotation-resistant rootworms had evolved the ability to compete a little longer in this chemical warfare with the soybeans.
Tests confirmed that rotation-resistant rootworms had higher levels of a special class of proteinases than wild-type rootworms to begin with, and that they increased production of one of these proteinases, Cathepsin-L, in response to soybean defenses. The wild-type rootworms increased levels of another proteinase, Cathepsin-B, when feeding on soybeans, the researchers found. But this enzyme appears to be ineffective against the plant's defenses.<
|Contact: Diana Yates|
University of Illinois at Urbana-Champaign