Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Plant and Soil Science

First Advisor

Yolanda H. Chen

Second Advisor

Brent L. Lockwood


In contemporary agroecosystems, insect pests encounter numerous stressors arising from both natural factors and human activities. One prevalent stressor is the repeated exposure to pesticides, which could prepare insects to endure further challenges posed by insecticides or high temperatures. Existing research suggests that the effects of multiple stressors on insect performance can be either positive or negative. However, it remains uncertain how repeated pesticide exposure affects how insects respond at both the phenotypic and genomic levels when confronted with subsequent stressors.

In this dissertation, we investigate whether selection for pesticide tolerance influences phenotypic, transcriptomic, and epigenomic responses to multiple stressors in the Colorado potato beetle (CPB), Leptinotarsa decemlineata. First, we examine how selection influences phenotypic responses to imidacloprid and high-temperature stress, both individually and in combination. By subjecting beetles to nine generations of selection for imidacloprid tolerance, we compared how selected beetles responded to imidacloprid exposure and high-temperature stress against unselected beetles. Given that behavior is a sensitive indicator of stress responses, we assessed the effects of single and combined exposure to imidacloprid and high temperatures on larval mobility and herbivory. Additionally, we monitored long-term effects, including mortality over time, development time, and female fecundity.

Next, we investigate how selection influences transcriptomic responses to single and combined imidacloprid and high-temperature stress. Specifically, we focused on identifying differentially expressed genes associated with xenobiotic and thermal tolerance, as well as cellular stress defenses. This analysis allowed us to discern whether selected and unselected beetles employ distinct strategies to cope with single and combined stressors.

Lastly, we examine how selection impacts DNA methylation patterns in response to single and combined imidacloprid and high-temperature stress in both selected and unselected beetles. We identified differentially methylated sites within stress-related genes across all treatments compared to control groups in both beetle groups. By comparing differentially methylated genes to our previous transcriptomic data, we revealed the potential role of DNA methylation in promoting the transcription of stress-related genes. Collectively, our study provides a comprehensive perspective on how the selection for insecticide tolerance shapes responses to multiple stressors in a highly resilient insect pest.



Number of Pages

329 p.

Available for download on Friday, November 08, 2024