Revisiting Bt maize deployment within an IPM framework offers short and long term benefits to crop producers

Bt traits are the default approach for managing key corn pests in the United States and Canada, with over 80% of acres planted expressing at least one Bt insecticidal protein. The corn rootworm has been managed this way since 2004, with little attention given to actual pest pressure or field history. As a result, rootworm resistance has developed to four Bt toxins at multiple locations. Producers incur costs, both short term (i.e. technology fees on seed) and long term (erosion of target pest susceptibility), when they use transgenic hybrids to control corn rootworms. To revisit the current approach to rootworm management using Bt traits from the standpoint of threshold-based IPM, and to determine if a change in approach is warranted, we gathered historical ratings of rootworm damage from public sector research trials, Bt planting rates, and seed costs from key production regions of North America, from 2004 to the present. Our goal was to assess the changing relationships between rootworm susceptibility, economically-damaging populations, and profitability. The analysis suggests that current corn rootworm management choices are often not well aligned with pest threat, and that most growers are incurring both short and long-term costs associated with Bt hybrid use with limited opportunity for benefit. These conclusions are somewhat dependent upon geography, because of differences in pest pressure and resistance risk between the western and eastern corn belt. However, we demonstrate that widespread implementation of a threshold-based IPM approach can offer benefits to a range of stakeholders, regardless of location.