Date of Graduation

5-2025

Document Type

Thesis

Degree Name

Bachelor of Science in Agricultural, Food and Life Sciences

Degree Level

Undergraduate

Department

Crop, Soil and Environmental Sciences

Advisor/Mentor

Kariyat, Rupesh

Committee Member

Jones, Austin

Second Committee Member

Szalanski, Allen L.

Abstract

Drought and insect herbivory are two major stressors on high-value crops like soybean (Glycine max). However, few studies have explored how these stressors interact, despite their presence in tandem under field conditions. We investigated how drought stress and fall armyworm (Spodoptera frugiperda) caterpillar herbivory impact Magellan (drought-tolerant) and Blackhawk (drought-susceptible) soybean cultivars. The soybean plants were subject to four treatment groups (1. Drought 2. Herbivory 3. Drought + Herbivory 4. Well-Watered) during a treatment period of 7 days in a greenhouse. We then measured plant height, physiological traits, trichome density, soil moisture, and larval mass gain. Our results show that drought significantly reduced photosynthesis, transpiration, and growth (p < 0.001), and the plants experienced the most substantial effects under combined drought and herbivory. Magellan maintained more stable photosynthetic performance and gradually increased trichome density over time, while Blackhawk showed an early but inconsistent trichome response. Larval mass gain was not significant on either cultivar or treatment, but fall armyworm generally had greater mass gain on the drought-susceptible Blackhawk cultivar. These results highlight the importance of considering cultivar-specific stress responses in selecting soybean varieties that may better maintain defensive plasticity under varying climatic conditions. Our results also show how biotic and abiotic stressors in combination lead to strong physiological and defense responses in plants.

Keywords

soybean; drought stress; insect herbivory; spodoptera frugiperda; trichomes

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