A corn pest that can devastate yields may be increasing in prevalence across Illinois and other states because Bt crops are reducing predators that once kept the pest at bay. [...] Western bean cutworms, a major pest in Nebraska and Colorado, was first detected in Illinois in 2004 and has spread to 49 counties, according to Marlin Rice, an Extension entomologist at Iowa State. [...] “Our theory is that increased (use) of Bt cotton and YieldGard corn has suppressed (populations) of corn earworms, which are predators of western bean cutworms. This allows (more) bean cutworms to survive,” Rice said.