Degree

Doctor of Philosophy (PhD)

Department

Entomology Department

Document Type

Dissertation

Abstract

Intensive cultivation of Bt crops in the United States has driven Helicoverpa zea to develop high levels of resistance to the insecticidal transgenes. At the same time, persistent difficulties in maintaining laboratory H. zea colonies have become a major obstacle to performing research essential for insect resistance management (IRM). Furthermore, inbreeding depression and hybrid vigor can confound estimates of fitness cost and dominance of resistance, two critical parameters for developing IRM programs. This PhD research comprises two independent studies. The first study included six trials examining the effect of five biotic factors on calling, mating, and reproduction of multiple H. zea populations. The second study consisted of four trials that quantified the fitness of 13 near‑isogenic Cry1A.105/Cry2Ab2-susceptible (SS), resistant (RR), and F1 (RS) lines (NILs) and populations with diverse genetic backgrounds when reared on Bt diet and corn leaf tissue, with the goal of evaluating how inbreeding depression and hybrid vigor confound estimates of fitness costs and dominance of resistance. Results indicate that H. zea rearing protocols can be substantially improved by incorporating V4–V6 vegetative corn plants or R1 ears during the adult reproductive phase, maintaining large adult cohort sizes (≥10 pairs per cage), and synchronizing female and male emergence within one day. Hybrid vigor in RS populations derived from RR × SS parents with distinct genetic backgrounds caused substantial underestimation of fitness costs. Combined effects of inbreeding depression and heterosis led to misclassification of resistance as overdominant on Bt diet and incompletely dominant on Bt leaf tissue, whereas analyses using NILs showed resistance to be incompletely dominant on diet and incompletely recessive on leaf tissue. This work provides practical guidance for improving laboratory maintenance of H. zea and demonstrates that ensuring comparable genetic backgrounds is essential for accurately characterizing fitness cost and dominance of Bt resistance.

Date

7-20-2026

Committee Chair

Huang, Fangneng

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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Available for download on Tuesday, July 20, 2027

Included in

Entomology Commons

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