Date of Award


Document Type

Campus Access Thesis

Degree Name

Master of Science (MS)



First Advisor

Mayra Cadorin Vidal

Second Advisor

Robert Stevenson

Third Advisor

Brook Moyers


Organisms respond to stressors related to climate change in many ways. Two common climate change related stressors experienced by most insect herbivores are changes in temperature and increased plant C:N ratio due to elevated CO2 concentrations. To investigate how diet C:N impacts the potential morphological response to temperature, we used Manduca sexta caterpillars reared at different combinations of temperatures and diet C:N ratio, and measured pupal mass and development time (performance metrics), color morphology and heat absorption. We specifically used a full-factorial design to test the combination of two temperature treatments (27 and 18 °C), and two artificial diets with different amounts of protein, and conducted the experiment in two trials using caterpillars from different genetic lineages. A high temperature treatment (27 °C) had a positive impact on caterpillars’ performance, whereas high C:N ratio was related to lower performance. Using a fitness metric that considers both pupal mass and development time, we found a positive effect of both higher temperature and nitrogen-rich diet. We found evidence for caterpillars reared at cooler temperatures being darker and heating up faster than caterpillars reared at a high temperature, but this pattern was not consistent across trials. Additionally, we found that diet affected coloration of caterpillars when measured by mean luminance, in which caterpillars fed a nitrogen-rich diet were darker. A direct correlation between darkness and heat absorption was only seen for caterpillars reared at the low temperature, nitrogen-rich treatment. Our results suggest a clear consistent effect of temperature on performance, and of diet on performance and color morphology, but a highly variable effect of temperature and diet on heat absorption. Global warming and CO2-related changes in plant quality could be associated with changes in insect herbivore performance and coloration, whereas the effect of these stressors on heat absorption can be more variable.


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