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Deformed wing virus (DWV), notorious for its virulence in the western honey bee (Apis mellifera) when vectored by the ectoparasitic mite Varroa destructor, is also widespread among wild bumble bee species, presumably through spillover from honey bees. Experimental studies on the virulence of DWV in Bombus spp. have provided equivocal results and have until now been confined to bumble bees under laboratory conditions.Here, we inoculated commercially reared Bombus terrestris workers with DWV‐A through feeding or injection and introduced them into experimental colonies placed in the field, thus exposing them to the environment and associated stressors. We monitored the survival of inoculated worker bumble bees and quantified their viral load at 10 days post inoculation.Bombus terrestris workers injected with DWV‐A supported high viral loads and exhibited significantly reduced median survival compared to controls. Bumble bees inoculated by feeding had low or zero detectable viral loads while their mortality did not differ from the control group.Our results demonstrate that, although DWV‐A is pathogenic for commercial B. terrestris, the risks for individual fitness from spillover of DWV‐A during foraging on shared flowers appear limited.The findings of this experiment also highlight the necessity to address the potential context‐dependence of virulence when evaluating the impact of a pathogen in an alternative host. [ABSTRACT FROM AUTHOR]

Bee declines are an increasingly recognised problem globally. Nutritional stress due to agricultural intensification is one of the drivers of bee declines. Therefore, understanding the nutritional requirements of bees is crucial to mitigate the effects of food scarcity on bee populations.Laboratory studies evaluating nutritional effects on bumble bees often use microcolonies as a model system for effects on queenright colonies. Microcolonies consist of workers, whereby one worker will lay male‐destined unfertilized eggs. Consequently, microcolonies exclusively produce males, while queenright colonies produce (female) workers and reproductives (males and queens).A comparison between Bombus terrestris (L.) microcolonies and queenright colonies was made by feeding three diets of varying nutritional quality.The experimental diets affected most fitness parameters of microcolonies differently than those of queenright colonies. Low‐protein, largely monofloral, pollen affected queenright colony fitness by reducing colony size and increasing larval mortality, while these fitness parameters were not affected in microcolonies. High‐protein polyfloral pollen reduced larval mortality in queenright colonies but did not affect larval mortality in microcolonies. For both colony types, a similar result was obtained when assessing offspring body mass, which was reduced by the low‐quality diet and increased by the high‐quality diet.In conclusion, our results demonstrate that microcolonies are inaccurate model systems and their use can lead to erroneous conclusions in terms of effects of nutritional stress or pollen quality on bumble bees. Our results further highlight the importance of high‐quality (here high‐protein polyfloral) pollen for sustaining colony development of bumble bees. [ABSTRACT FROM AUTHOR]

As with other species linked to agricultural environments, many bumblebee species are exhibiting significant population declines.This study assesses the success of colonies of Bombus terrestris audax on farms differing in conservation inputs via agri‐environment schemes (AES).B. terrestris audax colonies were placed on farms of three treatments: Conventionally managed, AES Entry‐Level Stewardship (ELS), or AES Higher‐Level Stewardship.Colonies on AES‐compliant farms gained significantly more mass than those on conventional farms, which decreased in mass.Nests on conventional farms were also more likely to become infested by the wax moth Aphomia sociella, followed by ELS‐compliant farms.The results suggest that adopting an AES can increase bumblebee colony success through the production of larger colonies and with greater ability to combat parasite infestations. [ABSTRACT FROM AUTHOR]

1. Bumble bees are important eusocial pollinators whose worker caste, fuelled by nectar sugar, accelerate colony growth through brood incubation, but allocating workers to nectar foraging could compromise nest thermoregulation in daytime and produce 'incubator limitation'. 2. We hypothesise that colonies in nectar‐poor habitats experience stronger incubator limitation by diverting workers from incubation to foraging, but this potential effect of habitat quality on colony fitness via task allocation is not fully understood. 3. We therefore modelled levels of nectar foraging in relation to forage richness and theoretically estimated the impact of incubator‐limitation on colony fitness. Additionally, we investigated whether live colonies of bumble bees (Bombus terrestris) responded to manipulation of their sugar supply as if incubator‐limited. 4. Model solutions for environmentally realistic scenarios showed that colonies allocate up to one third of workers to nectar foraging in order to avoid sugar starvation during sustained incubation. The incubator‐limitation that results can strongly reduce colony reproduction, but its impact depends on the temperature regime of the nesting habitat. 5. Live colonies allocated between one sixth and one third of daytime worker effort to foraging and responded to sugar supplementation as if incubator‐limited. 6. These findings suggest that forage richness and nest temperature relations could interact to affect the fitness of wild bumble bee colonies through incubator limitation. Our testable theory promises an integrative understanding of how forage quality and climate could govern the distribution and abundance of bumble bees and other eusocial insects that utilise brood incubation by their worker caste. [ABSTRACT FROM AUTHOR]

1. The ideal conditions for a parasite are typically found with its preferred host. However, prior to transmission to a naïve host and successful infection, a parasite may have to withstand extrinsic environmental conditions. Some parasites have adapted to time away from hosts, for example, by co‐opting vectors or by having drought‐resistant growth stages. However, other parasites may have no obvious adaptations to persist during prolonged transmission cycles. Consequently, the environment may detrimentally impact parasite fitness and ultimately epidemiology. 2. Here, we investigate the impact of nectar‐realistic sugar concentrations on the ability of the trypanosome parasite Crithidia bombi, which may be transmitted between conspecifics at flowers, to infect its bumblebee host Bombus terrestris and to reproduce during the infection (parasitaemia). Our results show, following 30 min exposure to our experimental nectars that as sugar concentration increases, infection prevalence and parasitaemia decrease. This is likely due to the increased osmotic stress C. bombi experiences in high sugar, aqueous environments. 3. Consequently, if C. bombi transmission is facilitated by nectar or a high‐sugar environment, it may have a negative impact on parasite fitness. [ABSTRACT FROM AUTHOR]

1. Ground‐nesting colonies of bumble bees incubate their brood at > 30 °C if floral forage provides sufficient energy and the thermogenic power of the colony can counteract cool soil conditions. To explore the basis of incubation, the thermogenic power and sugar consumption of orphaned nests of bumble bee workers (microcolonies) were investigated under laboratory conditions. 2. This study tested experimentally the effect of variation in worker number (ranging from four to 12 adults) on a microcolony's capacity to regulate brood temperature and recover from acute cold exposure. Microcolonies were provided with ad libitum sugar syrup and minimal insulation and maintained at an ambient temperature of c. 25 °C. Energy conversion efficiency was estimated by comparing sugar consumption with the power required for artificial incubation. The joint energetics of foraging and incubation were modelled in wild colonies to explore the effect of colony size and landscape quality on thermoregulation. 3. The results showed that all sizes of microcolonies regulated brood temperature at c. 31 °C under laboratory conditions, which required 96 mW of thermogenic power. It was estimated that individual workers of B. terrestris generated an incubatory power of 35 mW. The smallest microcolonies had the highest conversion efficiency (57%), apparently because few workers were required for incubation. 4. Modelling indicated that small microcolonies of three to seven adult workers have the capacity for normal brood incubation in the wild, but that the minimum viable colony size increases as floral forage becomes poorer or more distant. 5. These preliminary findings suggest the feasibility of identifying the minimum conditions (forage quality, soil temperature, and colony size) necessary for brood incubation by queenright colonies in the wild. [ABSTRACT FROM AUTHOR]

1. In insect-pollinated plants, pollinator attraction is influenced by flowers (e.g. number, size) and their associated rewards (e.g. pollen, nectar). These traits can depend on plant interactions. Indeed, below-ground competition between plants can lead to a decrease in flower or reward production in insect-pollinated species. 2. Wind-pollinated plants, in particular, which are almost never studied in plant-pollinator networks, can alter insect-pollinated plants' attractiveness through competition for nutrients. The response of pollinators to such changes has never been investigated. 3. A pot experiment was carried out in which an insect-pollinated species, Echium plantagineum, was grown in binary mixture with three wind-pollinated species selected to exert a panel of competitive interactions. Below-ground competition was controlled using dividers limiting interspecific root competition. Floral traits of E. plantagineum ( i.e. flower production, floral display size, flower size and nectar production) were measured. For each species mixture, the visits ( i.e. first visit, number of visits, 10-min sequences) of Bombus terrestris individuals released in a flight cage containing two pots were followed, one with and one without below-ground competition. 4. Below-ground competition significantly affected nectar's sucrose concentration but did not influence flower and nectar production. Likewise, pollinator visits were not influenced by below-ground competition. Competitor identity significantly influenced flower and reward production of E. plantagineum, with a decrease in the presence of the most competitive wind-pollinated species. A tendency for faster flower visitation events was also detected in the presence of the least competitive competitor. This study raises new questions regarding the influence of wind-pollinated plants on plant-pollinator interactions. [ABSTRACT FROM AUTHOR]

1. Size variations in pollinator populations may modify competitive interactions among foragers. Competition among pollinators has been shown to lead to one of two contrasting behaviours: either specialisation to the most profitable plant species or generalisation to several species. When foraging, pollinators are also confronted with heterogeneity in the spatial distribution of plant resources. Because variations in both the forager density and plant spatial distribution can affect pollinator behaviour, focus was on the interactive effect of these two factors. 2. Bumble bee ( Bombus terrestris L.) individuals were trained on a focal species ( Lotus corniculatus L.) and experimentally tested whether variations in the forager density (two or six bumble bees foraging together), plant community spatial distribution (two plant species: L. corniculatus and Medicago sativa, which were either patchily or randomly distributed), and their interaction modified bumble bee foraging behaviour. 3. It was shown that when confronted with a high forager density, bumble bees focused their visits towards the most familiar species, especially when foraging under a random plant distribution. These modifications affected the fruiting of the focal plant species, with a significantly lower reproductive success under low density/patchy conditions. 4. This study demonstrates that the foraging decisions of bumble bees are influenced by variations in both the conspecific density and plant spatial distribution. Given the increasing impact of human activities on plant-pollinator communities, this raises the question of the potential implications of these results for plant communities in natural conditions when confronted with variations in the pollinator density and spatial distribution of plants. [ABSTRACT FROM AUTHOR]

1. Workers in several bee species travel to conspecific nests ('drifting'), enter them, and produce male offspring inside them, so acting as intra-specific social parasites. This adds a new dimension to bees' reproductive behaviour and spatial ecology, but the extent to which drifting occurs over field scales, i.e. at natural nest densities in field conditions, has been unclear. 2. Using the bumble bee Bombus terrestris ( Linnaeus) as a model system, we sought to determine rates of worker drifting at field scales and the frequency of potential drifter workers in wild nests. 3. A field experiment with 27 colonies showed that workers travelled to, and became accepted in, conspecific nests that were up to 60 m away, although the number of accepted drifter workers within nests fell significantly with distance. The rate at which nests were entered by drifters was relatively high and significantly exceeded the rate at which drifters became accepted. 4. Microsatellite genotyping of eight field-collected nests from Greater London, U.K., showed that a low frequency (3%) of workers were not full sisters of nestmate workers and hence were likely to have been drifter workers. 5. It is therefore concluded that workers can drift to conspecific nests over field scales and confirmed that successful drifting occurs in natural populations. Drifting appears to be a natural but low-frequency behaviour permitting B. terrestris workers to gain direct fitness. [ABSTRACT FROM AUTHOR]

1. Experimental studies of multihost parasite dynamics are scarce. Understanding the transmission dynamics of parasites in these systems is a key task in developing better models of parasite evolution and to make more accurate predictions of disease dynamics. 2. Bumblebee species ( Bombus spp.) host the trypanosomatid parasite, Crithidia bombi. Its transmission in the field occurs through the shared use of flowers. Flowers are a perfect scenario for inter-taxa transmission of diseases because they are used by a wide range of animals. 3. Honey bees host a poorly studied trypanosomatid, Crithidia mellificae. In this study, five questions have been experimentally addressed: (a) Can C. bombi infect honey bees? (b) Can C. mellificae infect bumblebees? (c) Can the honey bee act as a vector for C. bombi? (d) Are C. bombi cells present in honey-bee faeces? (e) Does C. bombi have an effect on the mortality of honey bees after ingestion? 4. While both parasites were found to be specific to their hosts at the genus level, results suggest that honey bees may play a role in the epidemiology of C. bombi transmission. [ABSTRACT FROM AUTHOR]

1. The study tested the hypotheses that bumblebees have shorter foraging trips in environments that provide abundant resources than in environments that provide sparse resources, and that shorter foraging trips translate into greater colony growth. 2. Six even-aged Bombus terrestris colonies were established in contrasting resource environments. Three colonies had access to abundant resources ( Phacelia tanacetifolia fields with high flower densities), and three colonies were placed in an environment with sparse resources (scattered semi-natural habitats with food plants at lower densities). 3. A total of 870 foraging trips of 220 marked B. terrestris foragers were observed using automated camcorder recordings. 4. The duration of foraging trips was shorter in environments with abundant resources (66 ± 4.6 min) than in environments with sparse resources (82 ± 3.7 min). Within 34 days colonies that had access to abundant resources gained significantly more weight (129 ± 40 g) than colonies foraging on sparse resources (19 ± 7 g). 5. Thus, the spatial distribution and quality of resources at landscape level affected the duration of foraging trips and the colony growth. It was concluded that future conservation schemes need to improve the spatial and temporal availability of resources in agricultural landscapes to counteract the ongoing decline of bumblebees. [ABSTRACT FROM AUTHOR]

Abstract. 1. Visitation by the key pollinator, Bombus terrestris , was implicated in inducible flower colour change in Lupinus pilosus . Behaviour at the flower and rate of visitation by these bumble bees had specific effects; exclusion of this flower visitor led to retarded onset, and reduced rate, of colour change. 2. The foraging behaviour of B. terrestris was influenced by floral colour change in L. pilosus . Choice of pre-change flowers was greater than random in relation to the proportion of colour phases available within the plant population. 3. Levels of floral manipulation that mimicked the flower handling characteristics of visiting bumble bees confirmed that triggering of the pollen release mechanism is necessary for the instigation of colour change. 4. Moreover, this study suggests that, in L. pilosus , an aspect of pollination (pollen deposition by bees and/or subsequent pollen tube growth within the style) is linked with colour change and may act as the trigger for such change. [ABSTRACT FROM AUTHOR]

Abstract 1. Senescence in workers of social insects is a particularly intriguing life-history trait as the future fitness of workers relies primarily on age-dependent survival rate. The pattern of senescence of immune defence traits was investigated under laboratory conditions in workers of two bumble bees: Bombus terrestris and B. lucorum . 2. In both species, there was a significant decrease with age in the ability to encapsulate a foreign object (a global measure of the efficiency of immune systems). This pattern of senescence was observed in all colonies in B. terrestris (seven) and B. lucorum (eight) assayed, even though, for the latter, there was some heterogeneity among colonies. 3. In B. terrestris , two other measures of immune defence were taken: the relative percentage of fat body in the abdomen and the concentration of haemocytes (the immune defence cells). The quantity of fat body increased only slightly with age and there was no effect for the concentration of haemocytes. Interestingly, the concentration of haemocytes decreased strongly after an encapsulation response, regardless of the age of workers. 4. The importance of the senescence pattern observed for the immune defence traits is discussed in the context of the social biology of workers. [ABSTRACT FROM AUTHOR]