Temperature variation affects most biological parameters from the molecular level to community structure and dynamics. Current studies on thermal biology assess how populations vary in response to environmental temperature, which can help determine how populations differentially respond to climate change. To date, temperature fluctuation effects on endothermic poikilotherms such as the common eastern bumblebee (Bombus impatiens) are unknown even though bumblebees are the most important natural pollinators in North America. A cold-acclimation experiment with B. impatiens colonies revealed individuals acclimated to 5°C or 10°C at night did not differ in resting metabolic rate, flight metabolic rate, wingbeat frequency, or morphological measurements, compared to the control group. Moreover, an infrared camera showed that all colonies maintained maximum nest temperature consistently above 36.8°C. A latitudinal sampling of flight metabolic rate and morphological measurements of B. impatiens from four locations spanning Ontario (N 45°; W 75°) to North Carolina (N 34°; W 77°) indicated no latitudinal trend in the measured variables. This study shows that bumblebees are well equipped to face a wide range of environmental temperatures, both in the short term and long term, and can use a combination of behavioural and physiological mechanisms to regulate body and nest temperatures. These results are reassuring on the direct effects of climate change on bumblebee ecology, but further studies on the indirect effect of temperature variation on North American bumblebees are required to predict future ecosystem dynamics.

Recent studies suggest a possible correlated evolution of wing morphology, wing beat frequency, muscle biochemistry and flight metabolic rate in bees. In order to investigate the degree to which natural selection can act on these traits, an estimation of heritability was required. Commercial and laboratory reared colonies from wild caught queens were used to estimate narrow-sense (h2) and broad-sense (H2) heritability of flight metabolic rate and its associated traits in the bumblebee Bombus impatiens. h2 estimates obtained from parent-offspring regressions were not statistically significant. H2 estimates were significant for morphological traits (body mass and wing morphology) as well as whole-animal traits (flight and resting metabolic rate, wing beat frequency) in both populations. We suggest that queens have a decrease in flight performance as a result of a trade-off between flight and fecundity, explaining the lack of significance in parent-offspring regressions.

At certain stages of a bumblebee colony life cycle workers lay eggs. Not all workers reproduce, however, since many continue to forage and care for the nest. This leads to questions regarding what differentiates a reproductive worker from a non-reproductive one. It is hypothesized that a form of reproductive competition takes place, where the most behaviourally dominant worker becomes reproductively dominant. The behaviour of orphaned Bombus impatiens pairs was recorded and aggression, social interactions, egg-laying, and ovarian development were identified. Experiment 1 examined the association between aggression and egg-laying. Contrary to the hypothesis, the most aggressive worker did not lay more eggs. When the ovarian development of workers was manipulated and two workers with developed ovaries were paired (Experiment 3), they were more aggressive than pairs with discouraged ovarian development. This provides support for the supposition that aggression and reproduction are related, however, it is only partial support as worker pairs with encouraged ovarian development did not lay more eggs. Since aggression is believed to be only one part of behavioural dominance, Experiment 2 studied the association between social interactions and aggression and reproduction. Results showed that when two socially active bees were paired they were more aggressive than pairs including one or two socially inactive bumblebees. No significant difference in ovarian development between socially active pairs and socially inactive pairs was found. Brood presence was also predicted to affect reproductive control. Experiment 1 found egg-laying and aggression were more likely to co-occur in the absence of brood. Results from Experiment 2 supplemented the first experiment since the absence of brood increased rates of aggression and ovarian development in pairs. Whereas the results confirm aggression has a role in worker reproduction the findings also reveal that behavioural dominance does not equate to reproductive dominance under all conditions. The primary contributions of this thesis were the development of a method to distinguish behavioural dominance from reproductive dominance and determining their relationship under different environments (brood presence) and experimental manipulations (ovarian development). These contributions further define dominance in Bombus impatiens.

This dissertation explored the way in which bumblebees' visual system helps them discover their first flower. Previous studies found bees have unlearned preferences for parts of a flower, such as its colour and shape. The first study pitted two variables against each other: pattern type: sunburst or bull's eye, versus the location of the pattern: shapes appeared peripherally or centrally. We observed free-flying bees in a flight cage using Radio-Frequency Identification (RFID) tracking. The results show two distinct behavioural preferences: Pattern type predicts landing: bees prefer radial over concentric patterns, regardless of whether the radial pattern is on the perimeter or near the centre of the flower. Pattern location predicts exploration: bees were more likely to explore the inside of artificial flowers if the shapes were displayed near the centre of the flower, regardless of whether the pattern was radial or concentric. As part of the second component, we implemented a mathematical model aimed at explaining how bees come to prefer radial patterns, leafy backgrounds and symmetry. The model was based on unsupervised neural networks used to describe cognitive mechanisms. The results captured with the results of multiple behavioural experiments. The model suggests that bees choose computationally "cheaper" stimuli, those that contain less information. The third study tested the computational load hypothesis generated by the artificial neural networks. Visual properties of symmetry, and spatial frequency were tested. Studying free-flying bees in a flight cage using motion-sensitive video recordings, we found that bees preferred 4-axis symmetrical patterns in both low and high frequency displays.

At certain stages of a bumblebee colony life cycle workers lay eggs. Not all workers reproduce, however, since many continue to forage and care for the nest. This leads to questions regarding what differentiates a reproductive worker from a non-reproductive one. It is hypothesized that a form of reproductive competition takes place, where the most behaviourally dominant worker becomes reproductively dominant. The behaviour of orphaned Bombus impatiens pairs was recorded and aggression, social interactions, egg-laying, and ovarian development were identified. Experiment 1 examined the association between aggression and egg-laying. Contrary to the hypothesis, the most aggressive worker did not lay more eggs. When the ovarian development of workers was manipulated and two workers with developed ovaries were paired (Experiment 3), they were more aggressive than pairs with discouraged ovarian development. This provides support for the supposition that aggression and reproduction are related, however, it is only partial support as worker pairs with encouraged ovarian development did not lay more eggs. Since aggression is believed to be only one part of behavioural dominance, Experiment 2 studied the association between social interactions and aggression and reproduction. Results showed that when two socially active bees were paired they were more aggressive than pairs including one or two socially inactive bumblebees. No significant difference in ovarian development between socially active pairs and socially inactive pairs was found. Brood presence was also predicted to affect reproductive control. Experiment 1 found egg-laying and aggression were more likely to co-occur in the absence of brood. Results from Experiment 2 supplemented the first experiment since the absence of brood increased rates of aggression and ovarian development in pairs. Whereas the results confirm aggression has a role in worker reproduction the findings also reveal that behavioural dominance does not equate to reproductive dominance under all conditions. The primary contributions of this thesis were the development of a method to distinguish behavioural dominance from reproductive dominance and determining their relationship under different environments (brood presence) and experimental manipulations (ovarian development). These contributions further define dominance in Bombus impatiens.

This dissertation explored the way in which bumblebees' visual system helps them discover their first flower. Previous studies found bees have unlearned preferences for parts of a flower, such as its colour and shape. The first study pitted two variables against each other: pattern type: sunburst or bull's eye, versus the location of the pattern: shapes appeared peripherally or centrally. We observed free-flying bees in a flight cage using Radio-Frequency Identification (RFID) tracking. The results show two distinct behavioural preferences: Pattern type predicts landing: bees prefer radial over concentric patterns, regardless of whether the radial pattern is on the perimeter or near the centre of the flower. Pattern location predicts exploration: bees were more likely to explore the inside of artificial flowers if the shapes were displayed near the centre of the flower, regardless of whether the pattern was radial or concentric. As part of the second component, we implemented a mathematical model aimed at explaining how bees come to prefer radial patterns, leafy backgrounds and symmetry. The model was based on unsupervised neural networks used to describe cognitive mechanisms. The results captured with the results of multiple behavioural experiments. The model suggests that bees choose computationally "cheaper" stimuli, those that contain less information. The third study tested the computational load hypothesis generated by the artificial neural networks. Visual properties of symmetry, and spatial frequency were tested. Studying free-flying bees in a flight cage using motion-sensitive video recordings, we found that bees preferred 4-axis symmetrical patterns in both low and high frequency displays.

In nature, pollinators must navigate fields of resources presenting a variety of features, differing in shape, size, colour, etc. Foraging on a flower by flower basis is slow and maladaptive. Instead foragers must be able to differentiate between rewarding and unrewarding floral species while also generalizing learned information between flowers of the same species. The ability to categorize stimuli occurs on several levels of abstraction, laid out by Herrnstein (1990). In order to categorize objects, animals must first be able differentiate between them without memorizing each stimulus separately. Consequently, objects can be grouped by physical characteristics through perceptual categorization, or, on a more abstract scale, by the function they serve to the animal. This thesis explores the bees’ ability to categorize flowers, following the levels of categorization to answer two questions: Can bees form categories? And how abstract can their categorization become? There has been limited investigation previously in categorization in bees, and no research done on invertebrates addresses categorization beyond physical features. The bees’ ability to form categories was evaluated with four experiments of preference: 1) similar-but-different judgements; 2) perceptual categorization; 3) simple and mediated generalization; and 4) functional relevance. Results show firstly that bees can generalize characteristics within flower species, but also differentiate individual flowers. Secondly, bees can form perceptual categories, and while they rely on physical floral features for categorization, bees also demonstrated preliminary abilities for functional generalization as well. These results provide an explanation to natural foraging techniques adopted by the bees. The adaptive nature of categorization allows foragers to find resources more efficiently and better prepare in changing environments.

Pollination by insects is of great importance for the global food production. There is a specific need for pollination by bees in greenhouses and tunnel cultivations to increase the quantity, quality and market value of the crops. Imported bee colonies from central Europe are used for pollination of Swedish crops and have a great economic importance but are also a threat to wild Swedish bees by posing a risk of pathogen transmission between the bee species. The aim of this study was to investigate how imported bees affect the prevalence of pathogens amongst wild bees.  Analysis was performed on 236 wild bees collected in near proximity to tunnel cultivation, greenhouse cultivation and collected from two control landscapes. The abdomen of the bees was used to extract RNA/DNA for further detection and quantification of ten pathogens using qPCR. The proportion of infected bees within each group was calculated based on the results from the qPCR analysis. A two-proportion z-test was used to determine whether the difference in pathogen prevalence between the four groups was of statistically significant at α = 0.05. The results show that there was no significant difference when comparing the presence of all pathogens between bees in the test groups and the bees in the control groups (p= 0,29- 0,33). However, the prevalence of three viruses was significantly higher among bees collected in the near proximity of a greenhouse compared with bees collected from the near proximity of a tunnel cultivation (p< 0,003). For Slow bee paralysis virus the prevalence was 2,5 times higher and for Deformed wing virus and Black queen cell virus the prevalence was 3,5 and 1,3 times higher among bees collected near a greenhouses compared to near a tunnel cultivation.

I dagsläget importeras omkring 4600 humlebon årligen från Europa till Sverige för att öka produktionen av grönsaker och då framförallt tomater. Sverige har i dagsläget ingen egen produktion av humlor men bolaget Svenska Humlor AB ämnar att starta en försäljning under 2021. Att humlorna är svenskuppfödda och närda på svensk pollen är en ny produkt på marknaden som kan medföra nya intressen och intressekonflikter från olika aktörsperspektiv. Syftet med denna studie är att skapa en ögonblicksbild av åsikter som finns kring att starta en inhemsk försäljning av humlor av arten Bombus terrestris. Vidare är ett mål är att utreda hur en framtida svensk humleproduktion kan utformas och hur det kan relatera till hållbar utveckling. Studien kopplar till FN:s Agenda 2030 och målet att bevara biodiversitet och ekosystem. Humlor påverkas av klimatförändringar och flyttar därför till nya områden. Vidare hotas vissa humlearter av antropogen påverkan av landskapen. Humlornas pollinering möjliggör större skördar, som i sin tur bidrar till en ökad matproduktion som också är en målsättning i Agenda 2030. Humlesamhällen föds därför upp och placeras i jordbrukarnas odlingar.  Studien berör både för- och nackdelar med en potentiell svensk produktion av humlor. Intervjuer genomfördes med fyra för ämnet viktiga aktörer; humleuppfödare, jordbrukare, myndighet och akademi. De har ombetts diskutera de största styrkorna, svagheterna, möjligheterna och hoten med att införa svenska humlor som en ny produkt. Dessa åsikter presenteras i SWOT-diagram. SWOT är en metod för att analysera en organisation eller verksamhet där argument delas in efter styrkor (S), svagheter (W) möjligheter (O) och hot (T). Intervjuerna och SWOT-analysen struktureras med fyra huvudteman: ekonomi, teknik, ekologi och övrigt. En litteraturstudie utfördes för att få fördjupade kunskaper i ämnet inför intervjuerna. Litteraturen användes också för att styrka vissa fakta som påståtts av intervjupersonerna. I studien analyseras och diskuteras de huvudämnen som lyftes av de olika aktörerna, för att skapa en bild av vad en framtida svensk humleproduktion kan innebära.  Det framkommer bland annat att det kan vara fördelaktigt att producera svenska humlor jämfört med att importera, då det minskar risken att föra in sjukdomar som kan drabba de vilda pollinerarna. De importerade humlorna från Europa är av en annan underart än de svenska vilda humlorna, varför svenskuppfödda humlor även har mindre påverkan på den vilda genetiken. Vidare lyfts att även fler insekter kan vara relevanta för kommersiell pollinering. Andra diskussionspunkter är bland annat hur ny lagstiftning kan påverka svensk humleuppfödning, möjligheter till lönsamhet, svensk självförsörjningsgrad, inavel i uppfödningen, jämförelser med norsk humleuppfödning, återanvändning av material samt samhällsopinion kring att ha humlor som ett produktionsdjur. Studien avser att samla åsikter kring temat i en uppstartsfas av svensk humleuppfödning, för att kunna användas som diskussionsunderlag och ligga till grund för framtida studier. / Sweden imports around 4600 bumblebee colonies per year from Europe to increase the production of vegetables, primarily tomatoes. Sweden currently lacks a domestic bumblebee rearer, however the company Svenska Humlor AB plans to start selling colonies by 2021. Swedish bumblebees reared on swedish pollen is a new type of product that opens a whole new market. This can cause new undocumented interests and conflicts from different actor’s perspectives. The objective of this study is to portray a current view of opinions regarding a domestic market for bumblebees of the species Bombus terrestris. Furthermore, the study aims to investigate the future of Swedish bumblebee rearing and how it relates to sustainable development. The study integrates the United Nations’ Agenda 2030 Sustainable Development Goals since it includes conservation of biodiversity and ecosystems. Bumblebees are affected by climate change and therefore migrate to new areas. In addition, anthropogenic influence of the landscapes affects their functions. A great advantage is that bumblebee pollination contributes to food production which is included in the Agenda 2030, since bumblebee pollination increases the harvest. Hence, bumblebee colonies are bred and placed in the plantations.  The study covers advantages and disadvantages regarding a potential start-up of swedish reared bumblebees. To achieve this, interviews were conducted with four different actors; a bumblebee rearer, a farmer, authority and academy. They were asked to discuss the greatest strengths, weaknesses, opportunities and threats regarding a Swedish domestic bumblebee rearing. These opinions are presented in SWOT-diagrams, which is a method used to analyse an organisation or business model where strengths (S), weaknesses (W), opportunities (O) and threats (T) are identified and discussed. The interviews and SWOT-analysis are structured around four main themes; economy, technology, ecology and other. Additional literature was also used to strengthen facts that were brought up by the interviewees. The study aims to discuss the main themes raised by the different actors in relation to literature to create a picture of a future Swedish production.  During the interviews it was discussed that Swedish bumblebees might be beneficial in comparison to imported bumblebees as they lower the risk of spreading pathogens to wild pollinators. The imported bumblebees from Europe are of a different sub-species than the indigenous bumblebees. Due to this the Swedish bred bumblebees affect the native genetics less than their imported counterparts. It was also noted that other insects could be used as pollinators in the future. Other points of discussion related to a future Swedish bumblebee rearing were: new regulations, profitability, Swedish self-sufficiency, reusable materials for nests, inbreeding and opinions regarding the usage of bumblebees in production. The study provides opinions regarding these topics which are meant to be used for discussion as well as in future work.

Over 80% of wild angiosperms are reliant upon animal pollination for fruit and seed set and bees and other insects provide a vital pollination service to around a third of the crops we produce. Habitat loss, climate change and disease spread all threaten pollinator populations, with local declines and range contractions in honeybees and bumblebees leading to concerns that crop production may suffer as a result of pollinator shortages. Whilst agriculture and wildlife are often presented as being at odds with one another, the relationship between farmers growing pollination dependent crops, and the bees and insects that service them could be mutualistic. Flowering crops planted by farmers can provide an important source of forage to wild bees, whilst in return wild bees can contribute to ensuring farmers achieve adequate yields of marketable crops. The potential of this mutualistic relationship can be maximised by farmers by adopting management practices that reduce harm to, and enhance the wellbeing of, the wild bees around their farm. A group of common pesticides (neonicotinoids) used by farmers have recently been linked to pollinator ill health. Sub-lethal effects resulting from exposure to the neonicotinoid imidacloprid have been reported in honeybees and bumblebees, with bumblebee reproductive success found to diminish as a result of exposure to field realistic doses of this agrochemical. Here, the mechanism behind the reduced queen production in bumblebee colonies is suggested, with bees exposed to imidacloprid showing reduced efficiency in foraging for pollen. Farmers dependent upon pollinating insects for crop production can opt to avoid the use of pesticides known to harm these insects, however future studies are needed to identify safer alternatives that can be use in their place. Farmers can choose to increase the number of bees at their farms by utilising domesticated honeybees and purchasing commercially reared bumblebees. The use of these pollinators can ensure a minimum number of bees in the vicinity of a crop, and facilitate the production of crops at times when wild bee numbers are low. Concerns have been raised, however, regarding the use of commercially reared bees, mostly in regard to pathogen and parasite transmission, but also in respect to the possibility of outcompeting native species. Here the frequency and severity of attacks on commercial Bombus terrestris colonies, by the wax moth, an understudied bumblebee pest, are examined. Wax moths were found to infest almost half of the bumblebee nests deployed at fruit farms, with around a third of infestations resulting in nest destruction. Farmers investing in commercial bees will want to reduce the impact of harmful pests that may result in a reduced pollination service being delivered. Wax moth infestation rates at the study farms using commercial bees were high and the potential of a ‘spill- back’ effect on wild bees was examined. No evidence was found to suggest that nests in close proximity to these farms were any more or less likely to suffer from an attack than nests situated further away. Nest size was found to be the most significant predictor of an infestation, with larger nests more prone to wax moth attacks. Whilst farmers can utilise domesticated and commercially reared bees, relying on one source of pollination is inherently risky, and the most robust service will likely be provided by a range of pollinators. As well as reducing the use of chemicals known to harm beneficial insects, farmers can improve the habitat around their farms to help encourage and sustain wild pollinator populations. Sowing flower strips has been found to increase the abundance and diversity of pollinating insects, however, studies linking the use of these strips to crop production are lacking. Here we demonstrate for the first time that sowing small flower strips, adjacent to strawberry crops serviced by both wild and managed bees, can increase the overall number of pollinators foraging on the crop. This thesis contributes to our understanding of the implications of farm management decisions on pollinator health. It provides experimentally based evidence to guide farmers in making informed decisions regarding the future of crop pollination services and highlights the need for an integrated approach to managing pollination services for sustainability.