Doctor of Philosophy (PhD)



Document Type



The fall armyworm (FAW), Spodoptera frugiperda, and corn earworm (CEW), Helicoverpa zea, are two target pests of pyramided Bt corn in the U.S. This study determined the susceptibility of the two pests to pyramided Bt corn and evaluated if a 95:5% seed mixture of Bt and non-Bt corn was an appropriate approach for providing refuge populations of CEW for resistance management. Firstly, susceptibility of 150 F2 two-parent families to three common pyramided Bt corn traits was examined using 7-day leaf tissue bioassays and whole plant tests. A few families survived the 7-day leaf tissue bioassays but progeny of the survivors from the leaf tissue bioassays could not survive in the whole plant tests, suggesting that the pyramided Bt corn products were effective against FAW. Secondly, occurrence and damage of CEW in three planting patterns of non-Bt and Bt corn plants containing SmartStaxTM and VipteraTM 3111 traits were evaluated in the fields. The studies showed that both Bt corn products were highly effective against CEW in both pure stand and mixed plantings. Relative to pure non-Bt corn plantings, larval occurrence at the early stages (3-4 instars) in a mixed planting of 96% Bt and 4% of non-Bt corn were similar, but the larval development was delayed. Finally, intensity of Bt protein contamination and its associated impacts on CEW populations in a mixed planting of 95% Bt and 5% non-Bt corn were assessed with the SmartStaxTM traits. The results of field and laboratory studies showed that cross-pollinations in the mixed planting caused majority (> 90%) of the refuge kernels to express ≥ one Bt protein, and the intensive Bt protein contamination in the refuge ears reduced neonate-to-adult survivorship of CEW to only 4.6%, a reduction of 88.1% relative to the larvae feeding on ears of pure non-Bt corn plantings. The results suggest that the 95:5% seed mixed approach cannot provide adequate refuge populations for CEW. Data generated from this study should provide useful information for developing appropriate resistance management strategies for the sustainable use of the Bt corn technology as a pest management tool.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Huang, Fangneng



Included in

Entomology Commons