Animal survival is dependent on the capacity to effectively find and consume nutritious food resources and avoid harmful components that may be present in food. This fundamental process operates at multiple scales in all animal species. At the organismal scale, for example, nutritional state impacts whether an individual is motivated to consume or reject food (Dethier, 1976). The goal of this dissertation research was to establish a foundation for studying feeding and foraging in bumble bees at the scales of the organism, colony, insect-plant interactions, and the environment. Although bumble bee feeding and foraging behavior have been previously studied at most of these scales, there are several substantial gaps in our knowledge that this dissertation addresses. To address these gaps, I first identified taste-related genes in Bombus impatiens and characterized the tissues in which these genes are expressed. I then examined how feeding and food-collection tasks are organized amongst workers in bumble bee colonies. Next, I tested whether pollen nutrients drive floral resource visitation in wild bumble bees. Finally, I examined what bumble bee species are present across several ecoregions in California. Together, this work provides a foundation to study the ecology and evolution of feeding and foraging in bumble bees.

Non-thermal plasmas, at their most ideal, are well understood; the realistic non-thermal plasma, that which is utilized across nearly all semi-conductor related industries as well as extensively in academia, remains thoroughly lacking that understanding, specifically, the non-thermal plasmas which synthesize and/or contain particulate matter, so-called dusty plasmas. This work addresses the marked difficulty in probing such discharges, presenting a design which results in a much more forgiving and simple system to probe and investigate—one which contains solely conductive dust and inert gases. This work studies potential conductive dust candidates and subsequent synthesis methods that adhere to these restrictions, resulting in a separate non-thermal plasma technique for the synthesis and injection of graphitic nanoparticles, as well as the inert gas, into the probed discharge. This work presents a home-built Langmuir probe capable of comprehensive measurements of the electron energy distribution function and important plasma parameters, with no measured degradation caused by a build-up of graphitic nanoparticles on the probe surface. This work confirms that the presence of dust leads to a decrease in electron density and, thus, an increase in the average electron temperature. Finally, this work studies the phenomenon of nanoparticle trapping, presents the first direct measurement of the particle floating potential in a dusty plasma, and represents a step towards understanding the incredibly complex effect of plasma-dust interactions.

This dissertation presents a deep dive into the behavior and physiology of spring queen bumble bees. Bumble bee queens emerge from diapause and initiate new nests independently in spring. As they lay eggs and subsequently rear offspring to adulthood, queens undergo a dramatic transition from a solitary, to subsocial, to eusocial lifestyle, which presents a unique opportunity to investigate phenotypic plasticity and life history transitions. This colony founding stage of their life cycle may also represent a particularly important demographic for bumble bee populations, many of which are experiencing dramatic declines. An improved understanding of this life stage may help inform conservation strategies and predict bumble bee responses to a changing world.viii In this dissertation, I investigate behavioral and physiological plasticity in bumble bee queens across the spring colony founding stage. In Chapter One, I show that queen ovary development and nest searching and occupation occur simultaneously, which may enable rapid nest initiation. In Chapter Two, I show that the emergence of workers in incipient nests increases queen survival and reproduction, suggesting that the timing of early worker emergence in the nest likely impacts queen fitness, colony developmental trajectories, and ultimately nesting success. In Chapter Three, I show that queens respond to the emergence of workers in young nests by performing fewer brood care and food collection tasks, suggesting that queen maternal care behavior is tightly regulated by the number of helpers in the nest. And finally, in Chapter Four, I show that wild queens spend most of each day foraging via short, frequent trips, which highlights the heightened demands placed on early season queens. Collectively, this work has yielded three major insights into spring queen bumble bee biology. First, it suggests that queens are highly plastic in the incipient stages of colony founding and have the capacity to change dynamically in response to social and environmental fluctuations. Second, it suggests that starting nests earlier in the season may be advantageous for bumble bees. Lastly, it underlines the importance of conservation interventions that support the early nesting period and facilitate the production and maintenance of workers in incipient nests.

Bumble bees (genus Bombus) are an important group of bees that perform many complex behaviors and provide vital ecosystem services through plant pollination. Bumble bees, along with many other pollinators, face a variety of stressors in their environment that can lead to global population declines. A deeper understanding of bumble bee molecular biology and physiology is necessary to fill the gap in our understanding of how bumble bees can be impacted by environmental stressors and can elucidate mechanisms underlying some of the responses seen in the current literature. In this dissertation, I explore how molecular mechanisms can be influenced by external stressors, such as neonicotinoid pesticides, and starvation. I also investigate the molecular mechanisms that are involved in bumble bee foraging behavioral states, of which pollination is byproduct. Bumble bee foraging behaviors are essential for the maintenance of our ecosystems as well as their own survival. Yet environmental stressors threaten the efficiency or performance of these foraging behaviors. In order to understand how bumble bee foraging behavioral states are impacted by environmental stressors, we must understand what drives these specific behaviors. Within this dissertation, each chapter explores a different facet of bumble bee molecular and metabolic biology, with the intent to fill the gap in our comprehensive understanding of the effects, or potential effects, of external factors on different aspects of bumble bee fitness. Chapter One explores the effects of both neonicotinoid pesticide exposure and starvation stress on bumble bee energy metabolism. Chapter Two focuses on investigating the molecular mechanisms associated with foraging behavioral states in wild bumble bees. Chapter Three explores how rearing history impacts offspring starvation resilience and further examines the metabolic mechanisms that are involved in enforcing starvation resistance.