Issue No. 25, Article 5/December 7, 2007
Follow-Up on Our Annual Survey for Second-Generation European Corn Borers
Every year after we publish the results of our annual survey for second-generation European corn borers, we receive questions about the protocol we use. One of the primary questions is "Do you select non-Bt cornfields for the survey, or do you sample randomly?" We sample cornfields randomly because our overall objective is to determine the status of the population of European corn borers for a county, for a region, or for Illinois, not to determine the status of the population of European corn borers found only in non-Bt corn.
Some people have suggested that our results are not representative, but we argue the opposite. Because we select fields randomly, the percentage of corn fields that are Bt corn during any given year is represented in our samples. Bt corn is a mortality factor that affects populations of European corn borers, just as weather events, natural enemies, and insecticides are mortality factors. So the results from our survey are estimates of the average population density of European corn borers in Illinois during any given year. There is mounting evidence to indicate that the widespread planting of Bt corn has reduced the average population of European corn borers over time, and the results from our survey reflect this situation.--Kevin Steffey and Mike Gray