Semester of Graduation

Spring 2020

Degree

Master of Science (MS)

Department

Entomology

Document Type

Thesis

Abstract

A seed blend refuge has been used in the U.S. Corn Belt for Bt corn insect resistance management (IRM). The fall armyworm, Spodoptera frugiperda (F.), and corn earworm, Helicoverpa zea (Boddie) are major target pests of Bt corn in the Americas. One major concern for the use of a seed blend refuge is that larval movement of insects among non-Bt and Bt plants could affect its efficacy for resistance management. To address this concern, field and greenhouse trials were conducted to determine 1) if seed blend refugia could provide comparable levels of susceptible S. frugiperda (aabb) as structured refugia and 2) if seed blends created a more favorable environment for a S. frugiperda Cry1A.105/Cry2Ab2-dual-gene heterozygous genotype (AaBb) over aabb. Live larvae and plant injury were virtually not observed on Bt plants across all planting patterns. Performance of aabb on non-Bt plants was similar between seed blends and pure non-Bt plantings, suggesting that blend refugia might be able to provide an equivalent susceptible population of S. frugiperda as structured refugia. In the greenhouse, two insect genotypes, a homozygous susceptible (aabb) and a dual-gene heterozygous (AaBb), on seed blends performed similarly, indicating that seed blends did not create more favorable conditions for AaBb over aabb in the test condition. Additionally, three caged-field trials were conducted to evaluate larval movement and survival of H. zea, in eight seed blends of Cry1Ab/Vip3A corn with 0-30% non-Bt refuge. No live larvae or kernel damages were observed on all Bt plants across all trials and planting patterns. In pure non-Bt plantings, 64.8% larvae moved away from infested ears and survived on other plants, but most larvae (86.8%) located within a distance of three plants from the central plants, and all larvae were found on the central or its adjacent rows. Larval survival and distribution were similar among seed blends with non-Bt plants in the centers, in which larvae were predominately (85.7%) located on the central plants and 100% were found on the central rows. Overall, larval recovery from central non-Bt plants in seed blends was 27.5% less than that from pure non-Bt plantings. Kernel damage levels followed similar patterns as larval survival, and recovered larvae developed similarly across treatments. The results suggest that H. zea larvae moved significantly in corn fields, and such movement can reduce susceptible insect populations hosted in seed blend refuge. Data generated from this thesis should have value in understanding larval movement behavior of H. zea in corn fields, as well as managing S. frugiperda and H. zea and evaluating if send blend refugia could be a suitable method for Bt crop resistance management.

Committee Chair

Huang, Fangneng

Available for download on Wednesday, October 14, 2020

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