Dr. Galen Dively, a Professor Emeritus in the Department of Entomology at the University of Maryland, has become a leading figure in the effort to monitor and mitigate resistance development to genetically modified Bt corn, primarily addressing the very destructive corn earworm. At this week’s colloquium, Dr. Dively presented on his work designing a new approach for monitoring insect resistance in Bt corn, as well as how this approach is changing the way genetically modified crop technologies are regulated by the EPA.
Using paired sentinel plots of Bt sweet corn varieties and their corresponding non-Bt isolines, Dr. Dively is able to measure “practical resistance” by showing actual declines in the ability of these different varieties to control insect pests in the field. Dr. Dively has created a sentinel plot monitoring network spanning 23 US states and 3 Canadian provinces (Figure 1). By measuring the total damage per ear and other metrics, Dr. Dively has documented increasing resistance in the corn earworm population to a number of commonly expressed Cry proteins. Corn expressing the Cry1Ab protein, for example, contained around 81% less damage than non-Bt corn when first introduced. By 2020, however, corn expressing this protein contained only 6% less damage than the non-Bt isoline, indicating significant resistance development in the corn earworm population (Figure 2). Similar reductions in field efficacy were seen in other Cry proteins monitored as well.