How and why animals choose to do what they do at any given moment is one of the fundamental questions in animal behavior. For social animals, influences on decision-making can come from both personal and social sources, and in eusocial insects like ants, bees, and wasps, the reliance on social information is taken to the extreme. Foraging bumblebees offer the perfect model in which to examine the social influences on individual decision-making because they are presented with extensive personal and social information, and when foraging they are solely focused on the task at hand. Chapter 1 reviews information use by foraging bumblebees, setting the stage for the subsequent data chapters. Chapter 2 examines how the motivation for bumblebees to feed from a known feeder is modified by the nutritive state of the colony, such that individuals in colonies with full food stores show lower motivation to feed. In addition to this behavioral result, a biochemical analysis reveals that lipid levels may be involved in the mechanism underlying this social effect. Eusocial insects are famous for collective behaviors, such as the swarming behavior of honeybees, the foraging trails of termites, and the bridge-building of ants. While the collective foraging strategy of other eusocial insects has been well-studied, it has not received attention in bumblebees. In Chapter 3 I use a behavioral experiment to reveal that bumblebees use a strategy of informed individual initiative to collectively ensure they are foraging from the best resources in the environment. In this strategy, individual bees adjust their reward expectations based on the quality of nectar stored in the nest. I followed up this experiment with a computational model to reveal that this strategy is adaptive, as it results in higher fitness than does individual search alone. This strategy is markedly different from the spatial communication of the dance language used by honeybees, who are close relatives of bumblebees. This prompted me to extend the computational model to examine the selective pressures that shape foraging strategies in social insects, including the honeybee dance language and bumblebee strategy of informed individual initiative. In Chapter 4, I present the results of simulations of this extended model, demonstrating that, although resource density influences fitness for both the dance language and informed individual initiative, colony size only matters for the dance language. This suggests that the large colony sizes of honeybees may have been important for the dance language to evolve, whereas a similar spatial communication system would not be adaptive in bumblebees, which have smaller colony sizes. Taken all together, the results in this dissertation explore how individual decision-making is shaped by the social environment in bumblebees, and the potential selective pressures that led to these behavioral strategies over evolutionary time. Bumblebees are important pollinators in both agricultural and natural ecosystems, but many species are facing declines; a more thorough understanding of their behavior is imperative to help us conserve them as the planet continues to change due to climate change and other anthropogenic influences.
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