Impact of corn rootworm (Diabrotica spp.)- active Bt hybrids on beetle emergence

Knowledge of corn rootworm (Diabrotica spp.) emergence patterns is critical to the success of Insect Resistance Management (IRM) plans.  Research indicates that beetle emergence patterns are altered by exposure to corn rootworm-active Bt (Bt-RW) corn, but little comparative data exist between events. This study examines the impact of Bt-RW hybrids (containing single and pyramided events) on beetle emergence.  Specifically, we hoped to quantify these shifts in beetle emergence, from calendar and thermal unit perspectives, and its prospective implications for random mating, the cornerstone of refuge-based IRM plans.  On-farm experiments utilized all available events, with or without a tefluthrin overlay, in a randomized complete block design replicated across years.  In each study, cut-plant emergence cages were used to monitor adult emergence over the entire period with collections occurring every 2-3 days.  Existing thermal unit models were evaluated for their fit to the data from refuge hybrids.  Emergence delays were assessed for respective events and compared.  Delays were observed with exposure to each transgenic events but the extent of the delay varied among events, least for mCry3A, intermediate for Cry34/35 Ab1, and longest for Cry3Bb1. Implications of these results for IRM success, monitoring corn rootworm populations, and adult management will be discussed.