Effect of pollen movement in mixed plantings of Bt and non-Bt corn on survival and damage of corn earworm

Seed mixture, also called RIB, has been used as a resistance management strategy for planting pyramided Bt corn in the 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. In this study, Bt protein expression, insect occurrence and development, and ear damage were evaluated in three planting patterns of seed mixtures of nonBt and Bt corn including 1) pure stand Bt corn; 2) pure stand nonBt corn; and 3) 95:5% of RIB design. CEW has no preference of egg-laying between Bt and nonBt plants. Pollen movement caused majority (e.g.90%) of the refuge kernels to express ≥one Bt protein. At the early stage, pollen movement did not significantly affect larval survival on the refuge ears, but it could delay larval development. CEW pupation rate (8.2%) on refuge ears was significantly less than that (43.0%) on ears of the pure stand nonBt corn plants. The results suggest that the usefulness of the RIB strategy may be diminished in the areas where CEW can overwinter and is a major target of Bt corn.