Unlike other rosaceous fruit crops such as apple and cherry, commercial raspberry cultivars are largely self-fertile and can set fruit in the absence of pollinators. However, their floral morphology often prevents complete self-pollaintion. Incomplete pollination yields unmarketable small or crumbly fruits. Insect visitation is therefore essential to maximizing raspberry yield. Honey bees are typically used to pollinate commercial raspberry; however, escalating prices for hive rentals coupled with increasing acreage encourage evaluation of other manageable pollinators. Bumble bees (Bombus spp.) and several mason bees (Osmia spp.) are promising raspberry pollinators. Five bee species were evaluated and compared for their single-visit pollination efficacies on raspberry. From this a pollinator effectiveness index was created and an estimation of the minimum number of visits required to maximize fruit set was calculated. This estimation was then experimentally verified. Finally, in an attempt to synchronize their brief activity period with raspberry bloom, winter management options aimed at delaying the emergence of the mason bee, O. lignaria, were investigated. All five bee species proved excellent pollinators of raspberry. None of the alternative manageable species greatly outperformed honey bees. For this reason honey bees remain the most economical and practical option for open-field raspberry pollination. The adoption of alternative manageable bees could still be justified in other production systems, such as high-tunnel or greenhouse grown raspberry, which hamper honey bees’ ability to forage effectively. The pollinator effectiveness score for honey bees suggested that as few as two visits can achieve maximum fruit set. This estimate was confirmed through experimentation on three different red raspberry cultivars. For two of these cultivars, just one visit yielded drupelet counts similar to openly-pollinated flowers. This information can be used to help refine stocking density estimates for honey bees on raspberry. Wintering bees at 0° or -3° C rather than 4° C effectively delayed emergence of O. lignaria by more than a month without any impact on post-winter performance. These results suggest winter storage at near freezing temperatures is a viable management option for the use of O. lignaria with later-blooming crops.

Social insect colonies are complex systems with emergent properties that arise from the cooperation and interaction amongst individuals within colonies. By dividing reproduction and physical labor amongst them, individuals contribute to the growth and ecological success of their colonies, a success that is greater than individuals could achieve on their own. A key characteristic of social insects is a division of labor amongst workers that is determined primarily either by age, morphology, or dominance. Social insects are considered one of the most ecologically successful groups of organisms on earth. Colony life cycles include: 1) growth, in which workers are produced, 2) reproduction, in which queens and males with reproductive capabilities are produced, and 3) senescence. In life history theory, phenotypic plasticity (i.e. a change in phenotype in response to an environmental change), allows organisms to adjust and optimize fitness in response the change in environments. Central to life history theory is the idea that traits have costs and benefits. Using an energetics framework that considers the costs and benefits of traits contributes to our understanding as to why organisms exhibit the sets of traits that they have within their ecological environments. Using the annual bumble bee Bombus impatiens, my dissertation investigates the effects of resource availability on worker production and on the relative allocation of energy towards growth and reproduction within colonies. Bumble bees have a morphological division of labor and concomitantly, they show large intra-colony size variation amongst workers. Because body size is an important life history trait, I also examined the costs and benefits of producing various sized workers. Lastly, I examined the association among worker body size, metabolic rate (a measure of maintenance costs), and lifespan.

Social insect workers can vary in terms of body size, space use, division of labor, and reproductive potential. Here, I begin to 'dissect' a social insect colony, using the bumble bee Bombus impatiens, to determine how this variation affects colony organization. I found that workers are spatially organized inside the nest and they remain at a specific distance from the colony center. Bees that feed larvae tend to remain in the center, whereas foragers are more often found on the periphery when not foraging. Smaller workers are more likely to feed larvae and incubate brood, and larger workers are more likely to fan or guard the nest. Still, workers perform multiple tasks throughout their life. The size of this task repertoire does not depend on body size or age. Furthermore, workers that remain further from the queen while inside the nest and avoid energy-expensive tasks during the ergonomic phase are more likely to reproduce by the end of the colony cycle. Inactive bees are not, however, defensive reserves. Although inactive bees increase their speed inside the nest when the nest was disturbed, they were not more likely to leave the nest (presumably to attack the simulated attacker) or switch to guarding behavior. This suggests that inactive bumble bees that remain farther from the queen may be storing fat reserves to later develop reproductive organs. Finally, I examined how within-group variation affects colony performance. I reduced variation in body size or temperature response thresholds by removing individuals from the colony with extreme phenotypes, and compared colony performance to colonies where random bees were removed. Colonies took longer to cool down the nest after bees were removed, but this effect was most striking when variation in temperature thresholds was reduced. Further, although larger bees are better at carrying items and are more likely to fan, the ability of colonies to perform undertaking behavior or thermoregulation was not affected when size variation was reduced. These studies provide evidence that (1) within-group variation affects colony organization and (2) variation among workers in their inherent tendencies to respond to stimuli positively affects colony performance.

Declines in several pollinator species are due to a variety of factors, including pathogens. Incorporating pollinator-friendly plant species into wild and agricultural habitats could reduce the stress of pathogens if food sources act medicinally against pathogens. Previous research demonstrated one domesticated sunflower cultivar (Helianthus annuus) can dramatically reduce a gut pathogen (Crithidia bombi) of the common eastern bumble bee, Bombus impatiens. To ascertain the breadth of this medicinal trait, we tested whether pollen from several H. annuus cultivars and four relatives could also reduce C. bombi infections in B. impatiens. We also investigated whether timing of exposure to sunflower pollen relative to time of infection affected the strength of this medicinal trait. In all experiments, bees were infected and then fed their respective pollen diets for a week before they were dissected to assess infection. In our first experiment, all pollen from Helianthus species and relatives reduced C. bombi cell counts compared to our single species control of buckwheat (Fagopyrum esculentum). In our timing of exposure experiments, a one-time exposure to sunflower pollen present at the time of infection did not lower infection levels. In longer exposure trials, sunflower pollen suppressed C. bombi infection with a strength inversely proportional to the time between treatment and infection. Our results suggest that medicinal pollen may be widespread in the Helianthus genus and potentially throughout the Asteraceae family. Thus, these results provide insights into how strategic plantings of certain floral resources can help mediate and influences pollinator disease dynamics.

Habitat loss and climate change are major factors implicated in the decline of bumble bees worldwide. These factors may be particularly acute in regions subject to climatic extremes such as seasonal drought. Combining methods from pollinator research and phylogenetic community ecology, I investigated the impacts of seasonal drought on plant phenology and bumble bee community ecology across gradients of disturbance and soil moisture in a semi-arid ecosystem. Seasonal fluctuations in floral resources coincided with significant phylogenetic clustering in plant communities, with decreasing plant diversity observed under conditions of increasing drought stress. In the late season, modified wet areas supported higher floral resource availability and greater bumble bee abundances as compared to dry woodlands, though wetlands were also an important source of late season floral resources. Despite these local effects, however, the areal extent of natural vs modified matrix habitat accounted for the majority of variation in models explaining bumble bee abundances. Modified matrix habitat was negatively associated, and natural matrix habitat positively associated, with the occurrence of bumble bee workers in June and late-flying queens in July and August. Results provide insight into the temporal niche dynamics of entomophilous flowering plants in this system, and emphasize the importance of conserving natural habitat diversity in efforts to promote resilient plant-pollinator communities. This study also provides evidence for the local extinction of Bombus occidentalis Greene, 1858 and Bombus suckleyi Greene, 1860 from Galiano Island, BC, Canada, as well as the island’s recent colonization by Bombus vosnesenskii Radoszkowski, 1862. / Graduate

Several reports of North American bumble bee (Bombus Latreille) decline have been documented across the continent, but no study has fully assessed the geographic scope of decline. In this study I discuss the importance of Natural History Collections (NHC) in estimating historic bumble bee distributions and abundances, as well as in informing current surveys. To estimate changes in distribution and relative abundance I compare historic data assembled from a >73,000 specimen database with a contemporary 3-year survey of North American bumble bees across 382 locations in the contiguous U.S.A. Based on my results, four historically abundant bumble bees, B. affinis, B. occidentalis, B. pensylvanicus and B. terricola, have declined by 72 - 96% relative abundance across their native distribution, while B. bifarius, B. bimaculatus, B. impatiens, and B. vosnesenskii appear to be relatively stable. Finally, I provide some notes on the distribution, abundance, and frequency of Nosema bombi infections in Alaskan B. occidentalis.

No description available.

Bumble bees (bombus spp.) are significant pollinators of many plants, and are particularly attracted to mass-flowering crops such as Oilseed Rape (Brassica Napus), which they cross-pollinate. B. napus is both wind and insect-pollinated, and whilst it has been found that wind is its most significant pollen vector, the influence of bumble bee pollination could be non-trivial when bee densities are large. Therefore, the assessment of pollinator-mediated cross-pollination events could be important when considering containment strategies of genetically modified (GM) crops, such as GM varieties of B. napus, but requires a landscape-scale understanding of pollinator movements, which is currently unknown for bumble bees. I developed an in silico model, entitled HARVEST, which simulates the foraging and consequential inter-patch movements of bumble bees. The model is based on principles from Reinforcement Learning and Individual Based Modelling, and uses a Linear Operator Learning Rule to guide agent learning. The model incoproates one or more agents, or bees, that learn by ‘trial-and-error’, with a gradual preference shown for patch choice actions that provide increased rewards. To validate the model, I verified its ability to replicate certain iconic patterns of bee-mediated gene flow, and assessed its accuracy in predicting the flower visits and inter-patch movement frequencies of real bees in a small-scale system. The model successfully replicated the iconic patterns, but failed to accurately predict outputs from the real system. It did, however, qualitatively replicate the high levels of inter-patch traffic found in the real small-scale system, and its quantitative discrepancies could likely be explained by inaccurate parameterisations. I also found that HARVEST bees are extremely efficient foragers, which agrees with evidence of powerful learning capabilities and risk-aversion in real bumble bees. When applying the model to the landscape-scale, HARVEST predicts that overall levels of bee-mediated gene flow are extremely low. Nonetheless, I identified an effective containment strategy in which a ‘shield’ comprised of sacrificed crops is placed between GM and conventional crop populations. This strategy could be useful for scenarios in which the tolerance for GM seed set is exceptionally low.

Bumble bees and other wild pollinators are crucial to the support of both natural and agricultural ecosystems. However, unprecedented declines of pollinator populations have been observed all over the world, raising concerns of a looming threat to both the human food supply, as well as sustainability of the biodiversity in local ecological niches. Though declines are well described, the cause behind these still evades scientists. Proposed contributors include anthropogenic-mediated environmental stress, including application of xenobiotics for pest control, and increase of pathogen diversity and abundance due to the shipment of infection human-managed colonies. This research examined these theories and attempted to quantify the threats they may pose. Through development of a chronic, oral toxicity experiment, susceptibility of all Bombus impatiens castes to clothianidin exposure was examined. This exposed a substantial increase in vulnerability of male bumble bees to realistic concentrations of neonicotinoid pesticides, highlighting the crucial need to examine all members of wild bumble bee life cycles before determining pesticide regulations. Additionally, sublethal effects on fitness-related foraging behaviors in Bombus impatiens were examined through development of a voluntary task switching assay. The results of this experiment suggest humoral immune stimulation, through pathogenic infection, leads to significant impairment of cognitive flexibility. Taken together, this data suggests that pesticides and pathogens are capable of causing severe detrimental effects, both lethally and sublethally, in wild bumble bees. I hope this data will eventually contribute to reassessment of environmental regulations and establishment of effective conservation strategies in order to sustain the critical populations of wild bumble bees.

Det här arbetet handlar om tambins inverkan på naturligt förekommande pollinatörer. Min frågeställning berör: tillgången på näring, hälsotillståndet och populationsnivån hos naturligt förekommande pollinatörer i förhållande till tambins närvaro. Det som framkommit av den här litteraturstudien är att introducerade tambin leder till att naturligt förekommande pollinatörer minskar i antal kring bikuporna, en del arter söker föda på andra blommor eller senare på dygnet än tidigare. Den minskade tillgången på föda som denna konkurrens innebär har en negativ inverkan på humlors kroppsstorlek och därmed deras överlevnad. Samt att tambin kan föra över patogener så som varroakvalster, nosemasjuka och deformed wing virus till humlor vilket leder till minskad livslängd och sämre fortplantning. / This study is about the impact of honeybees on native pollinators. My questions concerns: availability of food, the health and population level of native pollinators in relation to the presence of honeybees. What has emerged from this literature review is that the introduction of honeybees lead to a decline in numbers of bee and bumblebee pollinators in proximity of the hives and also alters their behaviour, some species choose to forage on other flowers, or later in the day than before honeybees where introduced. The reduced availability of food that this competition induces has a negative impact on the size of bumblebees body’s and thus their survival. What was also discovered was that honeybees can transfer pathogens such as varroa mites, the microsporidium Nosema ceranae and deformed wing virus to bumblebees, leading to reduced life expectancy and poor propagation.