The Wisconsin DATCP has conducted annual surveys of European corn borer (ECB) populations in Wisconsin corn fields since the 1940’s. Using these annual ECB population data and published research (Mitchell et al. 2002, Hurley, Mitchell and Rice 2004), the long-run average percentage yield loss due to ECB in nine Wisconsin regions (crop reporting districts) is estimated (Table 1). However, because ECB populations are uncertain, the random distribution of these yield losses is also estimated to capture the uncertainty in yield losses due to ECB. These yield losses are then combined with USDANASS five-year (1999-2003) average corn yields to estimate the long-run average net benefit of Bt corn in each Wisconsin region, assuming a corn price of $2.00/bu and a technology fee of $18/bag ($7.43/ac) (Table 1).