AMES, Iowa, March 24 -- Iowa State University issued the following news release: * * * 'Too much of a good thing': Overuse is making Bt corn less effective against rootworm AMES, Iowa - Widespread planting of corn hybrids designed to combat corn rootworm, the crop's most damaging pest in the Corn Belt, is reducing both the technology's effectiveness and some farmers' profits. The findings come from a new analysis of 12 years of field trials and seed usage data across 10 Midwestern corn-growi more PR