Effect of pollen movement on survival and development of corn earworm in seed blended conditions of non-Bt and pyramided Bt corn

Seed mixture, also called RIB, has been used as a strategy to provide refuge insect populations for planting pyramided Bt corn in the North U.S. Corn Belt. One of the major concerns for the RIB strategy is the pollen movement, which may reduce susceptible refuge populations, especially for the species that mainly feed on ears such as the corn earworm (CEW), Helicoverpa zea (Boddie). In this study, Bt protein expression, insect occurrence, development, and ear damage were evaluated in three planting patterns of seed mixtures of non-Bt corn and Bt corn containing Genuity^® SmartStax^TM traits: 1) pure stand Bt corn; 2) pure stand non-Bt corn; and 3) RIB planting. Pollen movement caused majority (~90%) of the refuge kernels to express ≥one Bt protein. At the early larval stage, pollen movement did not significantly affect larval survival on the refuge ears, but it could delay larval development. Pupation rate (neonate-to-pupa, 8.2%) of CEW feeding on refuge ears in RIB was significantly less than that (43.0%) feeding on ears of the pure stand non-Bt corn plants. The results suggest that the RIB planting may not be able to provide sufficient refuge populations for resistance management in the areas where CEW can overwinter and is a major target of Bt corn.