Effect of Crop Management on Root Injury, Adult Abundance, and Susceptibility to Bt Toxins on Western Corn Rootworm

The western corn rootworm, Diabrotica virgifera virgifera LeConte, is a major pest of corn production.  One management strategy available to farmers is corn that produces toxins derived from Bacillus thuringiensis (Bt) that target corn rootworm. However, field-evolved resistance to Bt corn has already developed in some populations of western corn rootworm.  We asked whether cropping practices related to rootworm management affect root injury and adult rootworm abundance.  In 2013, four types of cornfields (24 in total) were identified: 1) cornfields with a history of crop rotation, 2) cornfields in continuous corn production, 3) cornfields with a history of injury to Bt corn from rootworm, and 4) cornfields reported by farmers with suspected injury from rootworm.  Root injury was measured by rating 12 roots from each cornfield and adult rootworm abundance was measured throughout August using sticky traps. Cornfields with a history of crop rotation, continuous cornfields, and cornfields with a history of injury to Bt corn generally had lower root injury (0.27, 0.53, and 0.23 average root injury, respectfully) and lower peak adult abundances (4.1, 7.9, and 3.7 rootworm/ sticky trap/day, respectfully) than farmer-reported cornfields.  Cornfields reported by farmers were characterized by severe root injury (1.44 average root injury) and extreme peak adult abundances (22.2 rootworm/ sticky trap/day).  In 2014, we will test the progeny of adults captured from 2013 cornfields and assess their susceptibility to Bt toxins.  Understanding how management practices influence rootworm populations and the development of Bt resistance can help inform insect resistance management policies.