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

Seed mixture, also called RIB, has been used as a strategy to provide refuge insect populations for planting pyramided Bt corn in the U.S. Corn Belt. However, the RIB strategy has not been approved in the south region of the U.S., where Bt cotton is also planted. A major concern in implementing RIB is cross-pollination of corn hybrids that can cause Bt proteins to be present in refuge corn kernels in seed mix plantings. The Bt protein contamination in RIB could negatively affect refuge insects, especially for the species that mainly feed on ears such as the corn earworm (CEW), Helicoverpa zea (Boddie). Our previous studies have shown that the currently used 95: 5% (Bt: non-Bt seeds) RIB was not effective for providing refuge population of CEW. In this study, Bt protein expression, insect survival and development were evaluated in five 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; 3) 90: 10% RIB planting; 4) 80: 20% RIB planting; and 5) 70: 30% RIB planting. Cross-pollination in the three RIBs caused ≥90% of refuge kernels to express ≥ one Bt proteins. On refuge ears, 16.1 and 18.1% of neonates developed to the adult stage in the 90: 10% and 80: 20% RIBs, respectively, which were significantly less than the survivorship (31.4%) on ears of the pure non-Bt plantings. However, 26.0% neonates in the 70: 30% RIB developed to adults, which was not significantly different from the value observed in the pure non-Bt planting. Results from this study suggest that a greater (e.g. 30%) refuge size might be effective to provide refuge populations of CEW for resistance management.