"All cold-blooded animals and a large number of warm-blooded ones spend an unexpectedly large proportion of their time doing nothing at all, or at any rate, nothing in particular." (Elton 1927) Many animals are remarkably "lazy", spending >50% of their waking hours "resting" . This is common across all taxa, ecologies, and life histories, including what are commonly considered to be highly industrious animals: the social insects (e.g., Aesop's Fable 'The Grasshopper and the Ant'). This dissertation broadly seeks to explain a phenomenon that has long been observed, but never adequately addressed, by asking: 'why are there 'lazy' ants?' First, I established that inactivity was a real and ecologically relevant phenomenon in the ant Temnothorax rugatulus by testing whether inactivity was a lab artifact. I then showed that inactive workers comprise a behaviorally distinct group of workers that are commonly overlooked in studies looking at colony function, though they typically represent at least half of the individuals within social insect colonies. I then tested a set of mutually non-exclusive hypotheses explaining inactivity in social insects: that (1) inactivity is a form of social "cheating" in which egg-laying workers selfishly invest in their own reproduction rather than contribute to colony fitness, (2) inactive workers comprise a pool of reserve workers used to mitigate the effects of fluctuations in colony workload, (3) inactivity is the result of physiological constraints on worker age such that young and old workers may less active due to inexperience/physical vulnerability, and physiological deterioration respectively, (4) inactive workers are performing an as-yet unidentified function, such as playing a role in communication and acting as food stores, or repletes, and that (5) inactive workers represent the 'slow' end of intra-nest variation in worker 'pace-of-life'. Inactivity is linked to worker age, reproduction, and a potential function as food stores for the colony. These hypotheses are not mutually exclusive, and in fact, likely form a 'syndrome' of behaviors common to inactive social insect workers. Their simultaneous contribution to worker inactivity may explain the difficulty in finding a simple answer to this deceptively simple question.

The determination of a symbiotic association as beneficial requires good assessment of the costs and benefits involved in the maintenance and transmission of these microbes across generations. In social insects, symbiotic associations are complex as they may involve a network of interactions between individual and colony that result in stable associations over evolutionary time. My goal was to investigate the roles of behavior and morphology as integrators that have enabled the benefits of harboring gut microbes to reach both adult and growing brood in a colony. To achieve this goal, I used turtle ants (Cephalotes), a group that has co-evolved with their gut microbes since the Eocene (Sanders et al. 2014) and that shows a variety of morphological and behavioral specializations likely connected to this symbiotic association. In my dissertation I present evidence that the specialized behavior and morphology of Cephalotes are indeed strongly associated with mechanisms that ensure stability of ant-gut microbe interactions over evolutionary time. In Appendix A, I show that a valve between the crop and midgut (proventriculus) of C. rohweri works as a filtration organ, capable of excluding possible pathogens from the mostly liquid diet consumed by turtle ants. In addition, the proventricular filter is also associated with the structuring of the gut microbiota, dividing it in at least two great groups: one upstream and another downstream of the proventriculus. Through behavioral observation and microscopy, we also suggest that the formation of the proventricular filter is only complete after young and sterile workers (callows) are inoculated with the core group of symbiotic bacteria. In Appendix B, I present results confirming that the compartmentalization of gut microbiota is also present in the congener C. varians. I compare these results with previously published data, defining the meta-communities of the gut microbiota, and demonstrate that the previously recognized core microbiota is composed of compartment-specific microbial communities and lineages. This compartmentalization of the gut microbiota is similar to the one found in highly specialized herbivores, both vertebrates and invertebrates. In addition, I also sampled the infrabuccal pocket, a characteristic oral cavity found in ants and that has largely been ignored in studies of gut symbiosis. Based on my results, I provide compelling evidence that hindgut microbes are inoculated into food particles trapped in the infrabuccal pocket, aiding in digestion of this substrate. Moreover, I suggest that trophallaxis olays a central role in inoculation of food and individuals, and might be responsible for the transmission of nutrients that are predicted to result from the gut bacteria metabolism. Finally, in Appendix C I characterize abdominal trophallaxis in C. rohweri to gain insight on its role in the context of symbiotic associations with gut microbes. I show that the hindgut contents, including bacteria, can be transmitted via abdominal trophallaxis. This interaction is found to occur between all combinations of major and minor workers, in addition to callows. The rate of solicitation of abdominal trophallaxis is higher when individuals are protein starved, indicating that hindgut content may also be nutritive. Using shotgun metagenomic data, we show that the microbiota present in the infrabuccal pocket (mostly hindgut bacteria) are indeed capable of re-utilizing nitrogen and synthesizing essential amino acids, in addition to breaking down plant material. We also report that oral trophallaxis is a possible route for transmission of crop-specific bacteria for callows, as this group has performed oral trophallaxis at a relatively higher rate than older workers. Put together, these results highlight the importance of nestmate interactions and gut morphology in the establishment and maintenance of symbiotic microbes in a social insect, introducing a new model for explaining the evolution and functioning of ant-gut microbe symbiosis.

Many insects form symbioses with maternally inherited, intracellular bacteria, which can have major effects on the ecology and evolution of the insect host. Here I investigated the interaction between a global agricultural pest, Bemisia tabaci (the sweetpotato whitefly), and a Rickettsia bacterial symbiont. Rickettsia had previously been tracked sweeping through field populations of B. tabaci in the southwestern USA and had been shown to dramatically increase whitefly fitness under laboratory conditions. In contrast, the Rickettsia present in whiteflies in Israel has few observable fitness effects and is declining in frequency in field populations. I explored the population dynamics of Rickettsia in B. tabaci field populations in the USA and Israel, and assessed the genetic diversity of the Rickettsia in these populations. In laboratory experiments, there was no observable effect of Rickettsia on the heat shock or constant temperature tolerance of USA B. tabaci. Instead, whitefly genetic background appears to influence the effects of Rickettsia. Lastly, analysis of the genome sequence of Rickettsia provided insights into the mechanism of the fitness benefit and evolutionary history of the bacterium. Taken together, these integrated ecological, physiological and genomic studies provide some explanation for the contrasting and wide-ranging phenotypes associated with whitefly Rickettsia, and provide support for the hypothesis that the fitness benefit provided by Rickettsia is context dependent. The Rickettsia symbiosis exhibits geographically distinct population dynamics, is affected by whitefly genotype, and may involve manipulation of host plants and/or defense against pathogens rather than nutritional supplementation. Overall, these results highlight the important role that microbial symbionts may play in the adaptation of invasive species to changing environments.

Whirligig beetles are gregarious aquatic insects living on the water surface. They are equipped with two separate pairs of compound eyes, an upper aerial pair and a lower aquatic pair, but little is known about how their brains are organized to serve such an unusual arrangement. In the first study of this dissertation, I describe the neural organization of their primary visual centers (the optic lobes) of the larval and adult whirligig beetle Dineutus sublineatus. I show that the divided compound eyes of adult beetles supply elaborate optic lobes in the brain that are also split into an upper and a lower half, each optic lobe comprising an upper and lower lamina, an upper and lower medulla, and a partly split bilobed lobula. The exception is the fourth neuropil, the lobula plate. Studies of their development show that the lobula plate Anlagen serving the upper and lower eyes develop at different rates and thus different developmental stages. The upper lobula plate develops precociously in the larva and is thought to process information that enables subaquatic ambush hunting. During metamorphosis the upper lobula plate degenerates and is lost as are the larval stemmatal eyes supplying it. The lower lobula plate develops later, during metamorphosis, and is present in the imago where it is supplied by the lower compound retina. By analogy with dipteran lobula plates it is proposed to support subaquatic locomotory balance. In the subsequent study, I describe the neural organization of the whirligig beetle’s mushroom bodies, a pair of prominent brain centers in the forebrain that are best known for their roles in higher olfactory processing and olfactory-based learning and memory. I found that unlike other insects examined so far, the calyces of the whirligig beetle’s mushroom bodies are exclusively supplied by visual neurons from optic lobe neuropils serving the pair of upper aerial compound eyes, thereby showing a complete modality switch from olfaction to vision in this brain center. These findings, along with multiple evidence from hymenopteran insects and cockroaches, suggest that insect mushroom bodies are not merely olfactory-related but may be involved in visual tasks, such as memory of place. In the last study, I describe experiments to demonstrate that a group of D. sublineatus is able to learn their location with respect to visual cues provided from above the water line, and simultaneously establish and maintain their relative positions with each other within the group. These results provide an explanation as to how a collective, such as several hundred whirligig beetles, can maintain cohesion and remember landmarks that "anchor" the collective at a particular location in a pond or stream. Using techniques in comparative neuroanatomy, this dissertation documents visual specializations of an insect brain that has evolved to suit a unique group-living lifestyle on the water surface. In addition, the spatial learning paradigm described in the third study provides an essential assay for future lesion studies to determine if mushroom bodies are indeed required for visually mediated spatial learning and memory.

Gut microbial communities exist in the vast majority of animals, and often form complex symbioses with their hosts that affect their host's biology in numerous ways. To date, the majority of studies of these complex interactions have focused on the nutritional benefits provided by the microbiota; however, the natural microbiota can also influence development, immunity, and the metabolism of its host. Apis mellifera, the honey bee, harbors a distinctive bacterial community that is present in individuals from distant locations around the world; however, the basis of the bee-microbiota association is unknown. This dissertation explores properties of the bacterial microbiota within bees, including its persistence of this association, mechanisms of transmission, localization through host ontogeny, and basic metabolic capabilities that define and maintain the symbiotic relationship. Apis and Bombus species (honey and bumble bees) share a distinct bacterial microbiota that is not present in other bees and wasps. Close analysis of the A. mellifera microbiota revealed consistent communities in adult worker gut organs and a general lack of bacteria in larvae. Contact between workers and with hive materials were identified as major routes of transmission for bacterial communities, showing the importance of social behavior in this association. Genomic analysis of a gut bacterium co-sequenced with the Bombus impatiens genome revealed it as a divergent lineage of Gammaproteobacteria, and deletions of conserved metabolic pathways, reduction in genome size, and its low GC content all suggest that the bacterial species has had a long association with its host.

Natural enemies provide critical population regulation of many pest species, though their effects are not commonly incorporated into agricultural management decisions. Conservation biological control is an important tool that can be implemented to minimize pest damage, but applying it requires appropriate understanding of pest and natural enemy relationships. Through experimental cotton field trials, I identified predator: prey ratios based on key arthropod predators as action thresholds of the whitefly pest Bemisia tabaci MEAM1 (Dinsdale et al. 2010; equivalent to Bemisia argentifolii Bellows et al. 1994 [Hemiptera: Aleyrodidae]), validated their efficacy, and promoted them to cotton pest managers. This dissertation begins with a multi-year field trial where whitefly and natural enemy populations were manipulated with a series of insecticidal treatments to identify key arthropod predators. The critical abundance of four key predators necessary to suppress whiteflies was estimated through predator: prey ratios. These ratios were refined for commercial pest management and developed to conform to the current whitefly IPM framework as a simple to use management-decision tool that would be readily adopted and used by pest managers. Predator: prey ratios were then validated in 1) a second field trial, 2) commercial fields in Arizona and northern Mexico and 3) historical field trials conducted from 1997-2010, where whitefly management decisions made with the standard threshold and ratios, were compared with the standard threshold alone. I found no difference in management outcomes when decisions were made with the standard threshold alone, or with predator: prey ratios in the field trial, but analysis of potential decisions on commercial farms and with historical trial data indicated that the majority of sprays could be delayed if control decisions incorporated ratio-based thresholds. Finally, an outreach program was developed and deployed to present ratios as decision-making tools for cotton pest managers that reduce uncertainty in control decisions and optimize spray outcomes. Pest managers indicated positive changes in knowledge and a gradual adoption of ratios for decision-making. The implementation of whitefly control decisions that incorporate predator: prey ratios may reduce pest managers' uncertainty in decision-making, as well as insecticide use and management costs.

A fundamental question in biology is how animals efficiently locate and use diverse resources. Pollinators foraging on flowers are one of our most thoroughly studied examples of generalist foraging behavior and cognition. Individual pollinators typically specialize on a subset of flowering species available to them. Specialization by nectar-foraging pollinators is often the consequence of learned or innate preferences for floral display traits such as color, pattern, and scent. Pollinators must also typically learn to extract nectar from each floral type. By specializing, pollinators reduce costs associated with learning and forgetting nectar extraction routines. Specialization also benefits the plant by enhancing conspecific pollen transfer. Yet nectar is not the only floral reward. The pollen of hundreds of thousands of plant species is collected by pollinators such as bees, beetles, and flies. In fact, solitary and social bees must collect both pollen and nectar to survive. However, much of the vast literature on bee foraging behavior concerns the collection of nectar. This research investigated mechanisms by which generalist bumblebees (Bombus impatiens) specialize on diverse floral resources. Most foragers in a colony were reward generalists over their lifetime, but specialized daily on either pollen or nectar collection. Lifetime patterns of pollen collection were associated with interindividual differences in sensory morphology. Pollen-foraging bumblebees had weak innate preferences, but learned strong preferences for pollen-only plant species, with preferences mediated primarily by anther properties. The anthers provided indirect cues of concealed pollen, and bees learned to prefer properties of the anthers to select potentially rewarding flowers. While learning was involved in the formation of floral preferences by pollen foragers, pollen extraction behavior relied little on learning. Specifically, floral sonication, which is used by bees to extract concealed pollen, was modified only modestly with experience. Furthermore, bees foraged efficiently for pollen from diverse floral resources without relying on instrumental (associative) learning. Efficient foraging involved switching between two distinct motor routines: floral sonication and scrabbling. Switching was regulated by two ubiquitous floral cues: chemical anther cues eliciting sonication and mechanical pollen cues suppressing it (and eliciting scrabbling). I discuss how mechanisms of floral specialization by generalist pollen-foraging bees could drive floral trait evolution.

Animals in general vary immensely in body size, which greatly affects their morphology, physiology, survival, and nutritional requirements. The nervous system is also affected by variation in body size, which, in turn, shapes the perception of environmental stimuli and the behavior of animals. Comparative studies of vertebrates suggest that larger brains and their integrative centers comprise more and generally larger neurons (Jerison, 1973; Kaas, 2000), but much less is known about brain - body size relations in invertebrates. Closely related social bee species are well suited to study correlations between body size and brain composition. Different honey bee species vary in body size yet differ little in their ecological requirements and behavior and bumble bees feature a large range of body sizes even within a single colony.

All organisms live in environments that are variable across space and time. Variation in selection across these environments may lead to the evolution of generalist genotypes that express phenotypic plasticity, in which one genotype can alter their phenotype (e.g., morphology, behavior, physiology) to match changes in environmental conditions, so that they may survive across a range of environments. In many egg-laying organisms that lack parental care, choosing an oviposition site is critical. The egg is an immobile stage of an animal's life cycle and mothers must balance a complex set of risks in deciding where to place their eggs. Because many biotic and abiotic factors are sources of selection on offspring survival, there is an advantage for females to evolve strategies in oviposition site selection to improve survival. This dissertation focuses on phenotypic plasticity in an offspring protection strategy that is triggered by natural enemies. In the seed beetle Mimosestes amicus (Coleoptera: Chrysomelidae: Bruchinae), females lay eggs on the outside of seed pods of legume trees and beetle larvae bore into and develop in the limited and discrete tissue of the seed. While most eggs are laid singly, I documented that beetle females superimpose eggs atop each other ("egg stacking") in response to the presence of egg parasitoids or parasitized eggs. In my first chapter, I investigated whether egg stacking is a strategy for protecting eggs from parasitism. In my second chapter, I examined female responses to variation in the number and dispersion of parasitized eggs on seed pods. Lastly, I investigated whether the intensity of stacking was affected by egg limitation (the risk of depleting her eggs before utilizing all hosts) or time limitation (losing reproductive ability or dying before laying all of her eggs). This study is unique in that it extends life history theory on egg and time costs to explain variation in egg protection behavior. The insights gained from this dissertation provide a foundation upon which we can examine how interactions among trophic levels impact the behavioral decisions made by insects that allow them to increase offspring survival.