We apply Antweiler’s (2001) double-nested unbalanced panel data model to estimate a western corn rootworm damage function using data from field trials in Illinois and Nebraska. Results imply that expected yield losses for a one unit difference in the node injury scale are 16.4%. Estimated random year and state effects are statistically significant, as is the estimated random experimental effect. The experimental effect is relatively large indicating the tremendous variability in yield losses at the small scale for plots with the same node injury scale measure of root damage. Using the estimated pest damage function to assess the value of Bt corn for farmers in Nebraska and Illinois, we find that, with a mean yield of 200 bu/ac, a yield CV of 25%, a corn price of $3.50/bu, and a Bt corn technology fee of $16/ac, the value of Bt corn for farmers is $173.35/ac and $156.14/ac under very high and high pest pressure respectively.