Transgenic corn expressing one of the three proteins active against corn rootworm usually performs significantly better than soil insecticides.

"Phone calls this fall, however, from several areas of Minnesota report unprecedented levels of corn rootworm injury to rootworm-resistant corn," says Ken Ostlie, University of Minnesota entomologist.

Before labeling injury as "unexpected," Ostlie says planting records have been checked and the corn tested to see it its expressing protein. Preliminary evidence suggests hybrids are expressing the protein, but the root injury was equivalent or even worse than in insecticide-protected refuge corn.

In these fields, Ostlie says that northern and western corn rootworms were unusually abundant in September when lodging was reported.

In the aerial view of one field, root injury averaged about 0.6 nodes gone in the four-row refuge strips where only 0.5% of the plants were lodged. In contrast in the rootworm-resistant corn, nearly 2.0 nodes were gone and 35% of the corn was lodged.

"It's too early to know the reason behind unexpected root injury," Ostlie says. "Possibilities range from unusually severe corn rootworm pressure to resistance by corn rootworms to reduced protein production in drought-stressed corn.

"Dry weather conditions early in the summer certainly favored corn rootworm survival, while midseason drought certainly stressed corn plants. Extended diapause pressure from 2007 has also been unusually heavy. Biological changes in corn rootworm populations, such as resistance, cannot be ruled out yet."