The western corn rootworm is the most significant insect pest of corn in Illinois. Evidence for this reality includes the continued adoption of stacked Bt hybrids that express toxins for managing this insect. Since the first rootworm Bt hybrid was commercialized in 2003 (YieldGard RW), the use of stacked Bt hybrids has increased significantly in Illinois (from 1% to 52% of corn acres planted; USDA Economic Research Service, 2010).While this insect remains an important pest, populations seemed to decline in many parts of Illinois in 2009 and 2010.Wetter-thannormal springs were likely a contributing factor. Total rainfall from April through June (17 inches in 2009; 14 inches in 2010) was higher than the 10-year average of the preceding decade (11 inches, 1999 - 2008; Midwest Regional Climate Center, 2011).Wet soil conditions, especially between larval hatch and establishment on corn roots (late May through mid-June), inhibit larval movement and increase western corn rootworm mortality (Mac-Donald and Ellis, 1990).
Another possible contributor to the recent decline in populations of western corn rootworms is the large-scale increased use of Bt hybrids for management - a similar phenomenon has been observed for the European corn borer. Surveys carried out by the Insect Management and Insecticide Evaluation Program for European corn borers indicate that populations have decreased substantially since Bt hybrids for managing this insect were commercialized in 1996 (Gray, 2011). However, the life histories of western corn rootworms and European corn borers and the Bt hybrids for managing them differ, and more information is needed before determining the reasons for population decline.We are initiating a statewide survey for western corn rootworms in 2011. Data from this and past surveys will be helpful in determining how populations of this important insect pest are changing.
In April 2011, Dow AgroSciences and Monsanto received approval from the Environmental Protection Agency for the commercial release of their refuge-in-thebag (RIB) concept, which contains a blend of 95% Bt seed along with a 5% refuge component (non-Bt seed). The blends are being marketed as Refuge Advanced by Dow AgroSciences and as Genuity SmartStax RIB Complete by Monsanto. These products target a wide range of aboveground and belowground insect pests, including the western corn rootworm. To date, the two offer the smallest refuge requirement for RIB products and are likely to be popular among corn producers for their convenience. Our program is conducting trials in 2011 to evaluate the efficacy of these new RIB products as well as soil insecticides and other Bt hybrids for managing western corn rootworms.We look forward to sharing results from our research at Agronomy Day, through newsletter articles at The Bulletin, and in our annual report, On Target.
Gray, M.E. 2011. "Relevance of traditional integrated pest management (IPM) strategies for commercial corn producers in a transgenic agroecosystem: A bygone era?" Journal of Agricultural and Food Chemistry 59: 5852-5858.
MacDonald, P.J., and C.R. Ellis. 1990. "Survival time of unfed, first-instar western corn rootworm (Coleoptera: Chrysomelidae) and the effects of soil type, moisture, and compaction on their mobility in soil." Environmental Entomology 19: 666-671.
Monsanto. 2011. Monsanto completes U.S. regulatory registration for Genuity® SmartStax® RIB Complete™. monsanto.mediaroom.com.
Midwest Regional Climate Center. 2011. Monthly climate data between April, 1999, and June, 2010, for Urbana, IL. mrcc.isws.illinois.edu.
USDA Economic Research Service. 2010. Adoption of genetically engineered crops in the U.S. www.ers.usda.gov/data /biotechcrops.
Ronald E. Estes
Senior Research Specialist in Agriculture
Nicholas A. Tinsley
Visiting Research Specialist in Agriculture