UC Riverside

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.