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.

Pollination, one of our ecosystem services, is considered to be in critical condition due to a worldwide reduction in pollinators and their biodiversity. As the agricultural landscape becomes more and more intense, the pollinators lose important food and living resources.     In temperate ecosystems, bumblebees (Bombus spp) are an important group of wild pollinators, and as with pollinators in general, they are declining in both abundance and richness, in Sweden as well as other countries.      The purpose of this study was to see if bumblebee species number of a location is linked to the location’s number of flowering angiosperm species in northwestern Scania when examining eight locations, and to see if gene flow existed between four chosen locations.        The result of this study suggests that it is not possible to tell from the flowering angiosperm species how many bumblebee species that will be abundant, but that it might be possible to tell the number of bumblebee individuals. With the number of bumblebee species, the abundant Fabaceae species was more important than the total number of flowering angiosperms of the location. The number of abundant Fabaceae species was strongly correlated to the bumblebee diversity index of the locations, indicating that it is a group of flowers closely linked to bumblebees.      To see if gene flow occurred between the chosen locations, mtDNA sequences were compared in neighbor joining trees. The result showed that though some tendencies of isolation existed, gene flow seemed to occur in general between the locations in that fragmented and human dominated landscape of northwestern Scania.

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Society depends on bumblebees for the ecosystem service in the pollination of crops. Bumblebee declines have been documented, mostly due to intensification of agriculture and loss of species-rich semi-natural grasslands, an important bumblebee habitat. To conserve bumblebee diversity and the ecosystem service of pollination, it is important to do analyses on multiple spatial scales to see how the intensification of agriculture affects bumblebees at a landscape level. In this study, I related abundance of bumblebees in 476 sites in southern Sweden (total abundance and abundance of declining/non-declining, long-tongued/short-tongued, and species preferring open terrain vs. forest boundaries) to amount of land use types (semi-natural grassland, arable land, forest, water and “other land use”) at 34 spatial scales (radii 100 to 40,000 m). Arable land had a negative effect on total bumblebee abundance at scales from 464 to 10,000 m and forest had a negative effect at scales from 2929 to 5412 m. Semi-natural grassland showed no clear effects – however, the partial regression coefficients were consistently negative. Arable land had a negative effect on non-declining species, long- and short-tongued species and on species preferring forest boundaries at larger scales, e.g. regions dominated by agriculture. Forest had a positive effect at smaller scales on species preferring forest boundaries and a negative effect at larger scales on species preferring open terrain and on declining species. The results suggest that arable land is a non-habitat for bumblebees and that semi-natural grassland does not affect bumblebee abundance at a landscape level.

Chemical substances are transferred between bumblebees of the species Bombus terrestris during their mating behavior. These substances are present mainly on the cuticle. The aim of this thesis was to identify and quantitatify differences in the amount of the compounds among defined groups of bumblebees - mated, non-mated and attempting to mate. Cuticular extracts were obtained by washing of the whole bumblebees bodies in hexane. These extracts were analyzed by using a two-dimensional gas chromatography with the time of fly mass spectrometr (GCxGC-TOF/MS). Cuticular hydrocarbons were identified and semi-quantified. Double bounds locations were determined in heptacosene and nonacosene. Five compounds were differed in the examined groups - β-springene, α-springene, dihydrofarnesyl-oleate, palmityl-palmitate and palmityl- palmitoleate. By comparing of the amount of these compounds differences between defined groups of bumblebees were determined. Analysis of the cutilar extracts showed that mated and non-mated bumblebees can be distinguished. Furthermore, there were statistically significant differences in the amounts of identified compounds in all defined groups of bumblebees. Key words: two-dimensional gas chromatography, Bombus terrestris, cutilar extract

Insect pollinators serve a critical role in maintaining plant biodiversity and are especially susceptible to changes within their environment. To study the possible effects of seasonal variation in temperature, as well as climatic temperature increase on the plant-pollinator community, the relationship between bumblebee and flowering plant traits along an elevational gradient, representing warming-induced changes in plant community, were examined. Two hypotheses were tested; 1) if plant traits can predict visiting bumblebee proboscis length, and 2) if the relationship between plant traits and proboscis length is influenced by elevation, and the progression of the growing season. The study took place along an elevational gradient on Mt. Nuolja in Abisko National Park, Sweden. During surveys bumblebees were caught and measured. Flowers visited by captured bumblebees were collected, categorized by restrictiveness (i.e., whether or not the flower require a certain proboscis length, in order to access the nectar and pollen rewards) and floral traits measured (e.g., petal length). The results revealed that petal length was a significant predictor of bumblebee proboscis length, when taking restrictiveness into account. Furthermore, the relationship became weaker with increasing elevation for restrictive flowers but stronger for unrestrictive flowers. These findings show that trait-matching between bumblebees and flowers is an influential factor for flower selection and is affected by climatic temperature. This highlights the importance of considering individual-level traits when studying plant preference and creates a framework for assessing plant-pollinator networks. Future studies should examine additional traits that could explain the apparent size matching between unrestrictive flowers and proboscis.

Pollination syndromes refer to stereotyped floral characteristics (flower colour, shape, etc.) that are associated with a functional group of pollinators (bee, bird, etc.). The trumpet creeper Campsis radicans, endemic to the southeast and mid-west United States, has been assigned to the hummingbird-pollination syndrome, due mainly to its red, trumpet-shaped flowers. Previous studies demonstrated that the ruby-throated hummingbird Archilochus colubris is C. radicans' primary pollinator, but anecdotal data suggest various bee species may provide pollination service when hummingbirds are absent. This study characterised C. radicans nectar volume and concentration by time of day. Nectar volume was suitable for hummingbirds, but concentration was higher than typical hummingbird-pollinated plants (∼20% w/w); at ∼30% w/w, it approached the concentration expected in bee-pollinated plants (∼50% w/w). We also found substantial amounts of nectar at night. Two C. radicans populations received virtually no hummingbird visits, but the number of bees were markedly higher than in the populations previously described. Interestingly, there were no night-time visitors despite the large quantity of nocturnal nectar. Based on previously published pollen delivery per visit by various species, this study estimated that cumulative deposition by bees routinely reached pollen deposition thresholds for setting fruit in C. radicans. They are, unequivocally, the predominant pollinators in these populations, thus providing pollination service in the absence of hummingbirds. These results highlight C. radicans as a food source for native bees and add to the understanding of how floral phenotypes can facilitate pollination by disparate functional groups.

As the climate warms, Arctic bumblebee species face the loss of habitat and must deal with increased competition from southern species tracking their thermal and habitat niches north, for example Bombus terrestris. Previous studies demonstrate that bumblebees follow Bergmann’s rule, i.e., larger body sizes at higher latitudes, despite bumblebees not being considered truly ectothermic, as they can generate heat through muscular activity (i.e., beating their wings). This study seeks to confirm and understand the relationship between body size and temperature using an elevational gradient as a proxy for climate. In this study, I examined 13 plots (420-1164 m.a.s.l.) set along the 3.4 km transect up the slope of Mt. Nuolja in Abisko National Park, Sweden. For body size, I chose to use the commonly accepted proxy distance between the base of the wings (i.e., intertegular distance). For temperature, I chose the mean temperature at time of visitation. Results show that climate is a significant explanatory variable for bumblebee body size, with an overall increasing body size with increasing elevation (i.e., colder climate), although most of the variance is explained by caste, i.e., queens having a larger body size than workers. Body size also shows some correlation with day of capture, which can be explained by changes in environmental conditions (e.g., temperature, flowering plant species) during the growing season experienced by the different emerging times for the castes. Given that caste was the most useful explanatory variable for body size, future studies could look at a larger environmental gradient, for example, by sampling at multiple locations along the entire Scandes mountain range to see if the effects found are localized. Further, specific habitat and specific traits of preferred plants may also help to elucidate body-size differences between species and castes. For example, many bumblebee species’ castes emerge at a specific time of year when only certain flowering plant species in specific habitats are available. This important research would also help to illuminate whether bumblebees and the species of plants they pollinate remain synchronous as climate warming accelerates. Nevertheless, my results show an overall positive relationship between bumblebee body size and elevation, indicating that a warming climate will result in reduced body sizes among bumble bee species. Future studies will have to investigate what consequences this will have for Arctic bumblebee populations – and for the plants that rely on bumblebee visits for their pollination.

As the climate warms, Arctic bumblebee species face the loss of habitat and must deal with increased competition from southern species tracking their thermal and habitat niches north, for example Bombus terrestris. Previous studies demonstrate that bumblebees follow Bergmann’s rule, i.e., larger body sizes at higher latitudes, despite bumblebees not being considered truly ectothermic, as they can generate heat through muscular activity (i.e., beating their wings). This study seeks to confirm and understand the relationship between body size and temperature using an elevational gradient as a proxy for climate. In this study, I examined 13 plots (420-1164 m.a.s.l.) set along the 3.4 km transect up the slope of Mt. Nuolja in Abisko National Park, Sweden. For body size, I chose to use the commonly accepted proxy distance between the base of the wings (i.e., intertegular distance). For temperature, I chose the mean temperature at time of visitation. Results show that climate is a significant explanatory variable for bumblebee body size, with an overall increasing body size with increasing elevation (i.e., colder climate), although most of the variance is explained by caste, i.e., queens having a larger body size than workers. Body size also shows some correlation with day of capture, which can be explained by changes in environmental conditions (e.g., temperature, flowering plant species) during the growing season experienced by the different emerging times for the castes. Given that caste was the most useful explanatory variable for body size, future studies could look at a larger environmental gradient, for example, by sampling at multiple locations along the entire Scandes mountain range to see if the effects found are localized. Further, specific habitat and specific traits of preferred plants may also help to elucidate body-size differences between species and castes. For example, many bumblebee species’ castes emerge at a specific time of year when only certain flowering plant species in specific habitats are available. This important research would also help to illuminate whether bumblebees and the species of plants they pollinate remain synchronous as climate warming accelerates. Nevertheless, my results show an overall positive relationship between bumblebee body size and elevation, indicating that a warming climate will result in reduced body sizes among bumble bee species. Future studies will have to investigate what consequences this will have for Arctic bumblebee populations – and for the plants that rely on bumblebee visits for their pollination.

Insect pollinators serve a critical role in maintaining plant biodiversity and are especially susceptible to changes within their environment. To study the possible effects of seasonal variation in temperature, as well as climatic temperature increase on the plant-pollinator community, the relationship between bumblebee and flowering plant traits along an elevational gradient, representing warming-induced changes in plant community, were examined. Two hypotheses were tested; 1) if plant traits can predict visiting bumblebee proboscis length, and 2) if the relationship between plant traits and proboscis length is influenced by elevation, and the progression of the growing season. The study took place along an elevational gradient on Mt. Nuolja in Abisko National Park, Sweden. During surveys bumblebees were caught and measured. Flowers visited by captured bumblebees were collected, categorized by restrictiveness (i.e., whether or not the flower require a certain proboscis length, in order to access the nectar and pollen rewards) and floral traits measured (e.g., petal length). The results revealed that petal length was a significant predictor of bumblebee proboscis length, when taking restrictiveness into account. Furthermore, the relationship became weaker with increasing elevation for restrictive flowers but stronger for unrestrictive flowers. These findings show that trait-matching between bumblebees and flowers is an influential factor for flower selection and is affected by climatic temperature. This highlights the importance of considering individual-level traits when studying plant preference and creates a framework for assessing plant-pollinator networks. Future studies should examine additional traits that could explain the apparent size matching between unrestrictive flowers and proboscis.