The effects of crop rotation and Bt corn on root injury and adult abundance of western corn Rrotworm

The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is a major pest of corn.  Farmers have several management options available to manage WCR injury to corn, including crop rotation, conventional insecticides, and genetically modified corn producing toxins derived from Bacillus thuringiensis (Bt).  However, WCR populations have evolved resistance to several management strategies, especially to those tactics that are repeatedly deployed.  We asked whether cropping practices related to WCR management affected root injury and adult WCR abundance.  In 2013 and 2014, four types of cornfields 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, and 4) cornfields reported by farmers with greater than expected injury to Bt corn.  Root injury was measured by rating 12 roots from each cornfield and adult WCR 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 and lower peak adult abundances than cornfields suspected of having greater than expected injury to Bt corn.  Cornfields suspected of having greater than expected injury were characterized by greater root injury and higher adult WCR abundance.  We observed that where crop rotation was absent and/or WCR management strategies were static cornfields were at greater risk of root injury and increased WCR populations.  Understanding how management practices influence WCR populations is a crucial component of preventing WCR injury to corn.