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While most models of decision-making assume that individuals assign options absolute values, animals often assess options comparatively, violating principles of economic rationality. Such 'irrational' preferences are especially common when two rewards vary along multiple dimensions of quality and a third, 'decoy' option is available. Bumblebees are models of decision-making, yet whether they are subject to decoy effects is unknown. We addressed this question using bumblebees (Bombus impatiens) choosing between flowers that varied in their nectar concentration and reward rate. We first gave bees a choice between two flower types, one higher in concentration and the other higher in reward rate. Bees were then given a choice between these flowers and either a 'concentration' or 'rate' decoy, designed to be asymmetrically dominated on each axis. The rate decoy increased bees' preference in the expected direction, while the concentration decoy did not. In a second experiment, we manipulated choices along two single reward dimensions to test whether this discrepancy was explained by differences in how concentration versus reward rate were evaluated. We found that low-concentration decoys increased bees' preference for the medium option as predicted, whereas low-rate decoys had no effect. Our results suggest that both low- and high-value flowers can influence pollinator preferences in ways previously unconsidered. [ABSTRACT FROM AUTHOR]

Novel insecticides are continuously being developed for application in response to increased legal restriction of previously developed insecticides and resistance in target insects. These novel insecticides, such as flupyradifurone (FPF), remain relatively untested on non‐target organisms, including bumblebees. Further, existing tests on honeybees tend to focus on adult mortality and thus sub‐lethal effects, such as impacts on reproductive output, are neglected, despite their importance for population‐level impacts.To address if the novel insecticide FPF has sub‐lethal effects on bumblebee reproduction and behaviour, we established microcolonies and chronically exposed them to field‐realistic concentrations over a 14‐day period.We found that exposure to FPF reduced the bumblebees' reproductive output in terms of the number of larvae produced and the mean mass of each larval instar. FPF‐treated bees also stored less sucrose and constructed fewer honeypots. However, adult bumblebee mortality was similar between control and FPF‐exposed microcolonies.Our results show that field‐realistic FPF exposure leads to increased larval mortality and/or delayed larval development, as well as reduced nectar storage, without affecting adult mortality.Policy implications. Insecticides that impair bumblebee reproduction can have long‐term population‐level consequences, even if adult bees do not experience increased mortality. Despite this fact, sub‐lethal effects, such as impacts on reproduction, are not mandatorily assessed within the regulatory process. Our findings highlight the importance of determining sub‐lethal effects of pesticides across developmental stages, as well as using pollinator species other than honeybees within the regulatory process. [ABSTRACT FROM AUTHOR]

Wild bees are crucial pollinators of flowering plants and concerns are rising about their decline associated with pesticide use. Interspecific variation in wild bee response to pesticide exposure is expected to be related to variation in their morphology, physiology, and ecology, though there are still important knowledge gaps in its understanding. Pesticide risk assessments have largely focussed on the Western honey bee sensitivity considering it protective enough for wild bees. Recently, guidelines for Bombus terrestris and Osmia bicornis testing have been developed but are not yet implemented at a global scale in pesticide risk assessments. Here, we developed and tested a new simplified method of pesticide exposure on wild bee species collected from the field in Belgium. Enough specimens of nine species survived in a laboratory setting and were exposed to oral and topical acute doses of a sulfoximine insecticide. Our results confirm significant variability among wild bee species. We show that Osmia cornuta is more sensitive to sulfoxaflor than B. terrestris, whereas Bombus hypnorum is less sensitive. We propose hypotheses on the mechanisms explaining interspecific variations in sensitivity to pesticides. Future pesticide risk assessments of wild bees will require further refinement of protocols for their controlled housing and exposure. [ABSTRACT FROM AUTHOR]

Many bees visit just one flower species during a foraging trip, i.e. they show flower constancy. Flower constancy is important for plant reproduction but it could lead to an unbalanced diet, especially in biodiversity-depleted landscapes. It is assumed that flower constancy does not reduce dietary diversity in social bees, such as honeybees or bumblebees, but this has not yet been tested. We used computer simulations to investigate the effects of flower constancy on colony diet in plant species-rich and species-poor landscapes. We also explored if communication about food sources, which is used by many social bees, further reduces forage diversity. Our simulations reveal an extensive loss of forage diversity owing to flower constancy in both species-rich and species-poor environments. Small flower-constant colonies often discovered only 30–50% of all available plant species, thereby increasing the risk of nutritional deficiencies. Communication often interacted with flower constancy to reduce forage diversity further. Finally, we found that food source clustering, but not habitat fragmentation impaired dietary diversity. These findings highlight the nutritional challenges flower-constant bees face in different landscapes and they can aid in the design of measures to increase forage diversity and improve bee nutrition in human-modified landscapes. [ABSTRACT FROM AUTHOR]

The extent to which weeds in arable land are useful to pollinators depends in part on the temporal pattern of flowering and insect flight activity. We compiled citizen science data on 54 bees and hoverflies typical of agricultural areas in southern Sweden, as well as 24 flowering weed species classified as pollinator‐friendly in the sense that they provide nectar and/or pollen to pollinators. The flight periods of the bees and hoverflies varied greatly, but there were also some consistent differences between the four groups studied. The first group to fly were the early flying solitary bees (7 species), followed by the social bees (18 species). In contrast, other solitary bees (11 species) and hoverflies (22 species) flew later in the summer. Solitary bees had the shortest flight periods, while social bees and hoverflies had longer flight periods. Flowering of weed species also varied greatly between species, with weeds classified as winter annuals (e.g., germinating in autumn) starting early together with germination generalists (species that can germinate in both autumn and spring). Summer annuals (spring germinators) and perennials started flowering about a month later. Germination generalists had a much longer flowering period than the others. Weekly pollinator records were in most cases significantly explained by weed records. Apart from early flying solitary bees, all models showed strong positive relationships. The overall best explanatory variable was the total number of weeds, with a weight assigned to each species based on its potential as a nectar/pollen source. This suggests that agricultural weeds in Sweden provide a continuous potential supply of nectar and pollen throughout the flight season of most pollinators. [ABSTRACT FROM AUTHOR]

Patterns of abundance across space and time, and intraspecific variation in body size, are two species attributes known to influence diet breadth and the structure of interaction networks. Yet, the relative influence of these attributes on diet breadth is often assumed to be equal among taxonomic groups, and the relationship between intraspecific variation in body size on interaction patterns is frequently neglected. We observed bee–flower interactions in multiple locations across Montana, USA, for two growing seasons and measured spatial and temporal patterns of abundance, along with interspecific and intraspecific variation in body size for prevalent species. We predicted that the association between spatial and temporal patterns of abundance and intraspecific variation in body size, and diet breadth, would be stronger for bumble bee compared to non-bumble bee species, because species with flexible diets and long activity periods can interact with more food items. Bumble bees had higher local abundance, occurred in many local communities, more intraspecific variation in body size, and longer phenophases compared to non-bumble bee species, but only local abundance and phenophase duration had a stronger positive association with the diet breadth of bumble bee compared to non-bumble bee species. Communities with a higher proportion of bumble bees also had higher intraspecific variation in body size at the network-level, and network-level intraspecific variation in body size was positively correlated with diet generalization. Our findings highlight that the association between species attributes and diet breadth changes depending on the taxonomic group, with implications for the structure of interaction networks. [ABSTRACT FROM AUTHOR]

The transmission of pathogens from reservoir to recipient host species, termed pathogen spillover, can profoundly impact plant, animal, and public health. However, why some pathogens lead to disease emergence in a novel species while others fail to establish or do not elicit disease is often poorly understood. There is strong evidence that deformed wing virus (DWV), an (+)ssRNA virus, spills over from its reservoir host, the honeybee Apis mellifera, into the bumblebee Bombus terrestris. However, the low impact of DWV on B. terrestris in laboratory experiments suggests host barriers to virus spread in this recipient host. To investigate potential host barriers, we followed the spread of DWV genotype B (DWV-B) through a host's body using RT-PCR after experimental transmission to bumblebees in comparison to honeybees. Inoculation was per os, mimicking food-borne transmission, or by injection into the bee's haemocoel, mimicking vector-based transmission. In honeybees, DWV-B was present in both honeybee faeces and haemolymph within 3 days of inoculation per os or by injection. In contrast, DWV-B was not detected in B. terrestris haemolymph after inoculation per os, suggesting a gut barrier that hinders DWV-B's spread through the body of a B. terrestris. DWV-B was, however, detected in B. terrestris faeces after injection and feeding, albeit at a lower abundance than that observed for A. mellifera, suggesting that B. terrestris sheds less DWV-B than A. mellifera in faeces when infected. Barriers to viral spread in B. terrestris following oral infection may limit DWV's impact on this spillover host and reduce its contribution to the community epidemiology of DWV. [ABSTRACT FROM AUTHOR]

Social bees are frequently exposed to pesticides when foraging on nectar and pollen. Recent research has shown that pesticide exposure not only impacts social bee host health but can also alter the community structure of social bee gut microbiotas. However, most research on pesticide-bee gut microbiota interactions has been conducted in honey bees; bumble bees, native North American pollinators, have received less attention and, due to differences in their ecology, may be exposed to certain pesticides for shorter durations than honey bees. Here, we examine how exposure to the fungicide chlorothalonil for a short, field-realistic duration alters bumble bee fecal microbiotas (used as a proxy for gut microbiotas) and host performance. We expose small groups of Bombus impatiens workers (microcolonies) to field-re alistic chlorothalonil concentrations for 5 days, track changes in fecal microbiotas during the exposure period and a recovery period, and compare microcolony offspring production between treatments at the end of the experiment. We also assess the use of fecal microbiotas as a gut microbiota proxy by comparing community structures of fecal and gut microbiotas. We find that chlorothalonil exposure for a short duration does not alter bumble bee fecal microbiota structure or affect microcolony production at any concentration but that fecal and gut microbiotas differ significantly in community structure. Our results show that, at least when exposure durations are brief and unaccompanied by other stressors, bumble bee microbiotas are resilient to fungicide exposure. Additionally, our work highlights the importance of sampling gut microbiotas directly, when possible. [ABSTRACT FROM AUTHOR]

The role of visual search during bee foraging is relatively understudied compared to the choices made by bees. As bees learn about rewards, we predicted that visual search would be modified to prioritise rewarding flowers. To test this, we ran an experiment testing how bee search differs in the initial and later part of training as they learn about flowers with either higher- or lower-quality rewards. We then ran an experiment to see how this prior training with reward influences their search on a subsequent task with different flowers. We used the time spent inspecting flowers as a measure of attention and found that learning increased attention to rewards and away from unrewarding flowers. Higher quality rewards led to decreased attention to non-flower regions, but lower quality rewards did not. Prior experience of lower rewards also led to more attention to higher rewards compared to unrewarding flowers and non-flower regions. Our results suggest that flowers would elicit differences in bee search behaviour depending on the sugar content of their nectar. They also demonstrate the utility of studying visual search and have important implications for understanding the pollination ecology of flowers with different qualities of reward. Significance statement: Studies investigating how foraging bees learn about reward typically focus on the choices made by the bees. How bees deploy attention and visual search during foraging is less well studied. We analysed flight videos to characterise visual search as bees learn which flowers are rewarding. We found that learning increases the focus of bees on flower regions. We also found that the quality of the reward a flower offers influences how much bees search in non-flower areas. This means that a flower with lower reward attracts less focussed foraging compared to one with a higher reward. Since flowers do differ in floral reward, this has important implications for how focussed pollinators will be on different flowers. Our approach of looking at search behaviour and attention thus advances our understanding of the cognitive ecology of pollination. [ABSTRACT FROM AUTHOR]

Many pollinators, such as bees, hummingbirds and bats, use multi-destination routes (traplines) to exploit familiar plant resources. However, it is not clear to what extent the mechanisms underpinning trapline development and optimisation are comparable across species. Here we compared route formation, repeatability and efficiency by foragers of two social bee species, the solo foraging bumblebee Bombus terrestris and the mass foraging honey bee Apis mellifera, in the same laboratory conditions. In a simple routing task (with four artificial flowers), all bumblebees and honey bees developed a route, although honey bees were slower to do so. In a more complex routing task (with six flowers), however, only bumblebees developed a route between the 6 flowers. Honey bees took a longer time to discover all flowers and developed routes between fewer flowers. Comparing bumblebees and honey bees using the same experimental paradigm thus revealed key behavioural differences likely resulting from their contrasting collective foraging strategies. Significance statement: Pollinators face some of the most complex foraging challenge among animals: collecting small amounts of nectar from large numbers of flowers in a minimum of time. Previous studies report bees, birds and bats rely on spatial memory to develop routes optimising foraging efficiency. Here we compared this routing behaviour in two major pollinators, the buff-tailed bumblebee and the Western honey bee, in the same experimental conditions. We found that bumblebees were much faster and more efficient at visiting flowers following repeatable sequences than honey bees. This behavioural difference suggests bee cognition is shaped by their social ecology and illuminates about the known complementarity of different bee species for pollination. [ABSTRACT FROM AUTHOR]

This study explored the flower visiting behaviors and pollination abilities of mason bees (Osmia excavata Alfken (Hymenoptera: Megachilidae)), bumble bees (Bombus terrestris (Linnaeus, 1758) (Hymenoptera: Apidae)), and Italian honey bees (Apis mellifera ligustica Spinola (Hymenoptera: Apidae)) in apple orchards in early spring in Jinan (located in the central region of Shandong) and Yantai (located in the Peninsula of Shandong). We compared the pollen collection patterns, flower visiting behavior, flying speed, and effects on apple pollination of the 3 types of bees. The frequencies of flower visits were significantly higher for mason bees (12.89/min in Jinan and 10.63/min in Yantai) than bumble bees and Italian honey bees in the 2 regions. The single flower residence times were significantly higher for Italian honey bees (8.22 s in Jinan and 9.43 s in Yantai), but Italian honey bees were most affected by the climate. The 3 bees differed significantly in terms of the amount of apple pollen collected and their effects on the fruit setting rate in apples (mason bees > bumble bees > Italian honey bees). The results showed that the mason bee was the most suitable pollinating species for spring apple orchards; Bumble bees were more suitable as alternative pollinators during cloudy and low temperatures; Italian honey bees were able to take advantage of their large number of worker bees in sunny and warm weather. Compared to individual bee species, a combination of 2 or 3 species of bees might be more advantageous in dealing with complex and variable weather conditions. [ABSTRACT FROM AUTHOR]

Bumblebees are crucial for both natural ecosystems and agriculture, but their decline in distribution and abundance over the past decade is alarming. The global importance of bumblebees in natural ecosystems and agricultural food production cannot be overstated. However, the reported decline over the past decade has led to a surge of interest in understanding and addressing bumblebee population decline. Hence, we aimed to detect disruptions in the gut microbiome of male and worker bumblebees reared indoor and outdoor to assess potential resilience to environmental stress. Using the Illumina MiSeq platform for 16s rRNA amplicon sequencing, we analyzed the gut microbiome of male and worker bees that were raised indoors (designated as the IM and IW group) and those that were raised outdoors (also designated as the OM and OW group). Our results show presence of core bacteria Neisseriaceae, Orbaceae, Lactobacillaceae and Bifidobacteriaceae from indoor reared worker bees. However, a higher abundance of Bifidobacterium and absence of Fructobacillus from indoor reared worker bees was also observed. Indoor-reared male bees had lower diversity and fewer observed OTUs compared to outdoor-reared male bees. Additionally, the relative abundance of Actinobacteriota, Bacteroidota, and Firmicutes was significantly lower in indoor-reared males, while Proteobacteria was significantly increased. Despite this, we did not observe any dysbiosis in the gut microbiota of indoor-reared bumblebees when comparing the role of the gut symbionts among the groups. These results suggest that indoor-reared Bombus terrestris may be resilient to environmental stress when used as outdoor pollinators. [ABSTRACT FROM AUTHOR]

Simple Summary: Research on nutritional requirements in combination with improving bee protection has recently increased because of the continuous global decline in the abundance and diversity of bees. The decline is currently attributed to several stressors, including climate change, diminishing forage resources, and pesticide use, among other factors. Industrial hemp (Cannabis sativa L.) is a new crop that is grown over a wide geographic area in the United States, providing economic and nutritional benefits to humans. However, the contribution of hemp floral resources (pollen) to bee nutrition is not well understood. We investigated the chemical composition of pollen from four industrial hemp varieties (Canda, CFX-2, Henola, and Joey) and documented the abundance and diversity of bees on the crop using two sampling methods. Results showed differences in composition among the four hemp varieties. Overall, the Joey variety was the most preferred by bees, despite expressing lower protein, amino acid, and saturated and monosaturated fatty acid content. Based on our findings, we concluded that industrial hemp pollen provides some nutritional benefits to bees. However, it is important to understand that multiple sources of pollen are needed for sustained bee survival. Apart from its economic value, industrial hemp (Cannabis sativa L.) is a prolific pollen producer, serving as a food source for bees. However, little is known regarding the extent to which varietal differences in hemp pollen chemistry influences bee preference. Here, we report the chemical profile of pollen from four hemp varieties (Canda, CFX-2, Henola, and Joey) and bee abundance and diversity, using direct visual counts and pan traps. The number and type of bees on each variety was recorded and the chemical composition (proximate analysis and mineral, amino, and fatty acid profiles) of pollen from each hemp variety was determined. During the entire sampling period, three bee types (bumble bees, honey bees, and sweat bees) were recorded, with a combined total of 1826. Among these, sweat bees and bumble bees were the most prevalent and were highest on the Joey variety. The four varieties expressed protein content ranging from 6.05% to 6.89% and the highest in Henola. Seventeen amino acids were expressed in all varieties, with leucine recording the highest content ranging from 4.00 mg/g in Canda to 4.54 mg/g in Henola. In general, Henola expressed high protein, amino acid, and saturated and monosaturated fatty acid contents and recorded significantly fewer bees compared with Joey, which had a low content of these components and a high content of polyunsaturated fatty acids. Our findings suggest that, while industrial hemp offers abundant and accessible pollen that would promote bee health and sustainability of their ecosystem services, the nutritional quality may not be adequate for bee growth and development as an exclusive pollen source. [ABSTRACT FROM AUTHOR]

Bees are prolific, vital pollinators in agricultural and natural settings, but some taxa are declining. Surveying bees is crucial to understand the needs of these taxa; however, we lack a fine‐grained understanding of assemblages associated with different sampling methods that would enable us to analyse data range‐wide.Here we examine the difference in abundance and richness of bees (bee bowls and vane traps only) and bumble bees (genus Bombus; bee bowls, blue vane traps and target netting) sampled with these methods from mixed‐grass prairie to alpine habitats in Wyoming, USA.We collected four times more bees and twice as many genera of bees in vane traps than bee bowls. Vane traps captured more individuals of abundant genera than bee bowls.Bombus species abundance did not vary between vane traps and target netting; however, richness was higher in vane traps. Bee bowls captured few Bombus species.Overall, we recommend using vane traps to sample most bees, and a combination of vane traps and target netting to collect bumble bees. We evaluated how three sampling techniques perform when surveying for wild bees, which will aid in identifying declining species as well as monitoring species of conservation concern. [ABSTRACT FROM AUTHOR]

Grassland management under local-scale results-based agri-environmental payment schemes (RBAPSs) are designed to benefit some biodiversity groups like plants. However, it is unknown if RBAPSs affect plant-pollinator interaction networks, and whether local or landscape management is more influential. Most studies focus on traditional community structure measures like richness, neglecting the impacts management may have on network structure and stability, and thereby ecosystem function. Plant species that benefit from RBAPSs could also act as key forage plants for pollinators, but this has not been investigated. We sampled networks across 23 grasslands in the West of Ireland to investigate if grassland management at local (RBAPS) and/or landscape scale (proportion of semi-natural grassland) influence network size, connectance, nestedness, linkage density and specialization of networks. Species strength analysis was used to identify key plant species for bumblebees, solitary bees, hoverflies, and butterflies. Results indicate RBAPSs benefit network size and linkage density, where species-rich grasslands supported larger networks and higher linkage densities. Networks surrounded by higher proportions of semi-natural grassland also had larger network sizes and higher linkage densities. Nestedness was greater in landscapes with high proportions of improved grassland. Key plant species differed between pollinator groups. Our results highlight that managing grasslands to promote greater plant diversity through a local scale RBAPS positively influences the structure and stability of networks, with possible implications for pollination service delivery. However, networks are also influenced by landscape management suggesting that local-scale management by itself may not be sufficient to conserve networks. We conclude that measures aimed at pollinators should include grassland management at both spatial scales where possible and to promote the establishment of key plant species to help sustain a wider range of pollinator taxa. [ABSTRACT FROM AUTHOR]

Floral scents shape plant–pollinator interactions. Although populations of the same species can vary in their floral scent, little is known about how this variation affects pollinator visitation. In this study, we compare the scents emitted by buzz-pollinated Solanum rostratum (Solanaceae) in two areas of its distribution (Mexico and USA) and investigate how these differences in scent affect pollinator preferences and attraction. We determined the variation of floral volatile compounds using hexane extraction followed by gas chromatography coupled with spectrometry. We also performed a field cage multiple-choice bioassay and a Y-tube behavioural bioassay using Bombus impatiens. We recorded 13 volatile compounds in floral extracts for plants from both ranges that varied qualitative and semi-quantitatively among populations. We found that in the field cage experiment, bumble bees visited plants from the US populations more frequently than plants from Mexican populations. However, bees showed no difference in preference between extracts from Mexican or US flowers. We conclude that although bees show differential visitation to whole plants of different regions, variation in floral extract alone does not translate into differences in preference by B. impatiens. The potential effects of variation in floral scent on the other native bee pollinators remain to be assessed. [ABSTRACT FROM AUTHOR]

The gut microbiome of bees is vital for the health of their hosts. Given the ecosystem functions performed by bees, and the declines faced by many species, it is important to improve our understanding of the amount of natural variation in the gut microbiome, the level of sharing of bacteria among co-occurring species (including between native and non-native species), and how gut communities respond to infections. We conducted 16S rRNA metabarcoding to discern the level of microbiome similarity between honey bees (Apis mellifera, N = 49) and bumble bees (Bombus spp., N = 66) in a suburban-rural landscape. We identified a total of 233 amplicon sequence variants (ASVs) and found simple gut microbiomes dominated by bacterial taxa belonging to Gilliamella, Snodgrassella, and Lactobacillus. The average number of ASVs per species ranged from 4.00-15.00 (8.79 ± 3.84, mean ± SD). Amplicon sequence variant of one bacterial species, G. apicola (ASV 1), was widely shared across honey bees and bumble bees. However, we detected another ASV of G. apicola that was either exclusive to honey bees, or represented an intra-genomic 16S rRNA haplotype variant in honey bees. Other than ASV 1, honey bees and bumble bees rarely share gut bacteria, even ones likely derived from outside environments (e.g., Rhizobium spp., Fructobacillus spp.). Honey bee bacterial microbiomes exhibited higher alpha diversity but lower beta and gamma diversities than those of bumble bees, likely a result of the former possessing larger, perennial hives. Finally, we identified pathogenic or symbiotic bacteria (G. apicola, Acinetobacter sp. and Pluralibacter sp.) that associate with Trypanosome and/or Vairimorpha infections in bees. Such insights help to determine bees' susceptibility to infections should gut microbiomes become disrupted by chemical pollutants and contribute to our understanding of what constitutes a state of dysbiosis. [ABSTRACT FROM AUTHOR]

Animals commonly exhibit a tendency to return to previously visited locations. Such tendency is manifested at different scales, for example, fidelity to a site or fidelity to a specific patch within a site. Although patch fidelity has important implications for the pollinators and the plants they visit, our understanding of patch fidelity, and the extent to which it varies among bee species, remains limited. Here, we used a mark–reobservation approach to compare patch fidelity and patch size preference between one bumble bee and one honey bee species foraging on patches of Medicago sativa L. Honey bees exhibited greater patch fidelity (76%) than bumble bees (47%); they were more likely to return to the patch where they were marked. Patch size affected the level of patch fidelity for bumble bees but not for honey bees. Bumble bees were more likely to return to larger rather than smaller patches. In addition to patch fidelity, we detected preference of bees for the larger patches. Bees visited the larger patches more often than the smaller patches. These results add patch fidelity to the already known repertoire of differences in foraging strategies between a bumble bee and a honey bee species. It also indicates how the simultaneous study of distinct species in a similar environment can reveal important previously undetected information about their behavioral ecology. Observed differences in patch fidelity and patch size preferences may have important implications for crop pollination and conservation habitat design. [ABSTRACT FROM AUTHOR]

Background: To understand mechanisms of adaptation and plasticity of pollinators and other insects a better understanding of diversity and function of their key symbionts is required. Commensalibacter is a genus of acetic acid bacterial symbionts in the gut of honey bees and other insect species, yet little information is available on the diversity and function of Commensalibacter bacteria. In the present study, whole-genome sequences of 12 Commensalibacter isolates from bumble bees, butterflies, Asian hornets and rowan berries were determined, and publicly available genome assemblies of 14 Commensalibacter strains were used in a phylogenomic and comparative genomic analysis. Results: The phylogenomic analysis revealed that the 26 Commensalibacter isolates represented four species, i.e. Commensalibacter intestini and three novel species for which we propose the names Commensalibacter melissae sp. nov., Commensalibacter communis sp. nov. and Commensalibacter papalotli sp. nov. Comparative genomic analysis revealed that the four Commensalibacter species had similar genetic pathways for central metabolism characterized by a complete tricarboxylic acid cycle and pentose phosphate pathway, but their genomes differed in size, G + C content, amino acid metabolism and carbohydrate-utilizing enzymes. The reduced genome size, the large number of species-specific gene clusters, and the small number of gene clusters shared between C. melissae and other Commensalibacter species suggested a unique evolutionary process in C. melissae, the Western honey bee symbiont. Conclusion: The genus Commensalibacter is a widely distributed insect symbiont that consists of multiple species, each contributing in a species specific manner to the physiology of the holobiont host. [ABSTRACT FROM AUTHOR]

The ontogeny of nectar robbing by pollinators is not well understood. In this study, we investigated the interplay of pre-existing biases and experience in the expression of nectar-robbing behavior by common eastern bumble bee (Bombus impatiens) workers. Flower-naïve bees were released individually into an arena containing six live Tecoma stans flowers in one of two treatments. One treatment consisted of open flowers bearing a single artificial slit, allowing the bee to rob or enter legitimately for nectar, while the other consisted of flowers bearing slits, whose corollas were plugged with cotton, requiring the bee to rob for nectar. A subset of bees was tested twice, once on each treatment; the order of treatments was balanced across bees. Results showed that first attempts by flower-naïve bees were biased nearly absolutely towards legitimate visitation regardless of flower treatment. Most bees in both treatment groups robbed over the course of a trial, but plugged flowers were robbed significantly more. Previous experience affected robbing frequency on subsequent visits, suggestive of learning; bees induced to rob on plugged flowers tended to continue to rob even when legitimate access was restored. We speculate that the initial bias towards legitimate visits is due to the flower corolla's distinctive odor and nectar guides, to which bees respond innately. Bees nevertheless readily learn to rob, particularly when it is the only option for extracting nectar. Our findings support the view that studies of cognition are essential to understanding the pattern of cooperation and conflict in plant-pollinator mutualism. Significance statement: Nectar-robbing behavior is widely observed among pollinators in nature. Unlike visitation of flowers through the floral entrance, nectar robbing often does not transfer pollen. However, despite the importance of nectar robbing on plant fitness, little is known about the ontogeny of nectar-robbing behavior. In this study, we found that naïve Bombus impatiens workers strongly preferred legitimate visits over nectar robbing on their first visits to live flowers. However, bees quickly switched to nectar robbing when nectar could not be accessed legitimately and continued robbing even when legitimate access is restored. Our results suggest that flowers may take advantage of their pollinators' innate responses for their own or mutual gain, but also that pollinators can overcome this manipulation through learning. [ABSTRACT FROM AUTHOR]

Insect population decline has been reported worldwide, including those of pollinators important for ecosystem services. Therefore, conservation actions which rely on available rigorous species distribution data are necessary to protect biodiversity. Niche modeling is an appropriate approach to distribution maps, but when it comes to bumble bees, few studies have been performed in South America. We modeled ecological niches of nine Colombian Bombus species with MAXENT 3.4 software using bioclimatic variables available from WorldClim. This resulted in maps for each species that show the potential distribution area at the present time. Modeled species maps accurately represent potential niches according to the description of bioclimatic conditions in the species' habitat. We grouped the species into three clusters based on our results, as well as on distributional information from literature on the topic: High Mountain, Mid-Mountain and inter-Andean, and the Amazon and Eastern Plains Basin. Niche modeling depicted bumble bee species' distribution in Colombia, the results of which can serve as a useful tool for conservation policies in the country. [ABSTRACT FROM AUTHOR]

Simple Summary: Why do plants have showy flowers? Clearly, many plant species must attract pollinators and have floral adaptations for this. However, some flowers attract insects without showy petals. This suggests that a key function of showy visual signals is to attract naïve, first-time pollinator visitors. This is similar to how a restaurant with a large sign and showy visual signals may be especially important in gaining first-time visits when competing with other establishments or plants. Customers or pollinators will know if the first visit is rewarding and use this to decide whether to revisit. First, they must visit. Most flowers and restaurants would benefit from more visitors. Restaurants usually have empty tables, and many flowers are pollen limited in their reproduction. Here, we manipulated the ray petals of inflorescences of two garden flowers to test the hypothesis that the role of showy visual signals is to attract naïve visitors. On their first inflorescence visit to both species, naïve honey bees and bumble bees were more likely to visit intact inflorescences, than those with ray petals removed. However, by the tenth consecutive inflorescence, bees showed no preference. A positive correlation was observed between the visitation of inflorescences with no petals and the inflorescence number on both study plants, for both bees. These results strongly suggest that a key function of showy petals is to attract naïve, first-time visitors. Flower evolution includes a range of questions concerning the function of showy morphological features such as petals. Despite extensive research on the role of petals in attracting pollinators, there has been little experimental testing of their importance in attracting naïve versus experienced flower-visitors. In an exploratory field study, we manipulated the ray petals of inflorescences of two garden flowers, Rudbeckia hirta and Helenium autumnale, to test the hypothesis that these showy structures primarily function to attract first-time, naïve, visitors. On their first inflorescence visit to both species, naïve honey bees and bumble bees were more likely to visit intact inflorescences, than those with ray petals removed. However, by the tenth consecutive inflorescence on the same visit to the flower patch, test insects showed no preference. A positive correlation was observed between the visitation of inflorescences with zero petals and inflorescence number on both study plants, for both bees. These results suggest that a key function of showy petals is to attract naïve, first-time visitors. Similar to how a restaurant attracts diners with a large sign, showy signals may be vital to enticing first-time visitors when competing with other establishments or plants for customers or pollinators. We hope the findings of this exploratory study will stimulate further work in this area. [ABSTRACT FROM AUTHOR]

The low number of pollinating insects is the limiting factor for entomophilous plants in the north, and the situation is exacerbated by a short growing season and often unfavorable weather conditions for their life. The paper presents the results of studying the complex of pollinators of the specialized melittophilic species Veronica spicata at the northern limit of its distribution. It is shown that the structure of this complex is determined by the structural features of V. spicata flowers, the latitudinal position, and the differentiation of ecological niches of the species in the north. Unlike other parts of the range, where solitary bees play an important role in the pollination of V. spicata, this function in the north is performed by representatives of the genus Bombus Latr. (Hymenoptera, Apidae). Considering the level of species diversity and population structure, the pollinator complex of V. spicata is based on short proboscis species of bumblebees: Bombus lucorum s.l., B. jonellus, B. pratorum, B. sporadicus, and medium proboscis B. pascuorum. In accordance with the differentiation of ecological niches of V. spicata in the north, differences in the structure of the pollinator complex and foraging strategies of bumblebees were revealed. [ABSTRACT FROM AUTHOR]

In insect-pollinated plants, the foraging behavior of pollinators affects their pattern of movement. If distinct bee species vary in their foraging behaviors, different models may best describe their movement. In this study, we quantified and compared the fine scale movement of three bee species foraging on patches of Medicago sativa. Bee movement was described using distances and directions traveled between consecutive racemes. Bumble bees and honey bees traveled shorter distances after visiting many flowers on a raceme, while the distance traveled by leafcutting bees was independent of flower number. Transition matrices and vectors were calculated for bumble bees and honey bees to reflect their directionality of movement within foraging bouts; leafcutting bees were as likely to move in any direction. Bee species varied in their foraging behaviors, and for each bee species, we tested four movement models that differed in how distances and directions were selected, and identified the model that best explained the movement data. The fine-scale, within-patch movement of bees could not always be explained by a random movement model, and a general model of movement could not be applied to all bee species. [ABSTRACT FROM AUTHOR]

Bumble bees are important pollinators in temperate forested regions where fire is a driving force for habitat change, and thus understanding how these insects respond to fire is critical. Previous work has shown bees are often positively affected by the postfire environment, with burned sites supporting greater bee abundance and diversity, and increased floral resources. The extent to which fire impacts variation in bumblebee site occupancy is not well‐understood, especially in higher latitude regions with dense, primarily coniferous forests. Occupancy models are powerful tools for biodiversity analyses, as they separately estimate occupancy probability (likelihood that a species is present at a particular location) and detection probability (likelihood of observing a species when it is present). Using these models, we tested whether bumblebee site occupancy is higher in burned locations as a result of the increase in canopy openness, floral species richness, and floral abundance. We quantified the impact of fire, and associated habitat changes, on bumblebee species' occupancy in an area with high wildfire frequency in British Columbia, Canada. The burn status of a site was the only significant predictor for determining bumblebee occurrence (with burned sites having higher occupancy); floral resource availability and canopy openness only impacted detection probability (roughly, sample bias). These findings highlight the importance of controlling for the influence of habitat on species detection in pollinator studies and suggest that fire in this system changes the habitat for bumble bees in positive ways that extend beyond our measurements of differences in floral resources and canopy cover. [ABSTRACT FROM AUTHOR]

Woodlands can play an important role in supporting bee abundance and diversity in agricultural landscapes. However, in temperate‐region studies, the canopy is rarely sampled, and our understanding of its contribution is limited.To explore this, we sampled bees in late spring with blue vane traps in the understory (n = 30) and crowns of mature Quercus robur (n = 35) at the exposed southern edges and in the interiors (ca. 25–75 m from woodland edges) of 15 woodland sites across an English agricultural landscape.A significant proportion of bee abundance and diversity was found in the canopy: canopy‐trap catches were estimated to be a third as large as understory‐trap catches, and 23 of the 29 sampled species were present in the canopy. Of the seven most common species sampled, four were equally abundant in woodland edge and interior traps; three were more abundant in understory traps, and a single species—Bombus lapidarius—was more abundant in canopy traps. The sex ratio of the most abundant species, B. pratorum, was female‐skewed in the canopy. Additionally, the presence of nearby Acer pseudoplatanus trees in flower greatly increased canopy‐trap catches in woodland interiors.These results suggest that both the woodland canopy and understory have a significant role to play in supporting farmland bee communities; they indicate the importance of nectar‐producing trees in woodland interiors, opening avenues for canopy‐based management; and they demonstrate that a diverse bee community has the potential to exploit canopy floral resources. [ABSTRACT FROM AUTHOR]

Historic pollination networks are important to understand interactions between different plant and pollinator species, as well as to differentiate between causes and consequences of present insect population decline. Natural history collections in museums store biological proxy data, which is used to reconstruct historic pollination networks of bumble bees. Four bumble bee species (Bombus terrestris, B. ruderatus, B. hortorum and B. subterraneus) were introduced to Aotearoa New Zealand in 1885 specifically for pollination purposes. Pollen samples were collected from museum specimens of three of the four NZ species of bumble bee (excluding B. subterraneus) collected between 1954 and 1972 from 56 locations across the South Island, New Zealand. The most common plants identified on all three bumble bee species were Calluna vulgaris (heather), Ulex (gorse), Cytisus (broom), and Trifolium repens (white clover). However, all three bumble bee species also carried pollen from several native plants (e.g. Arthropodium, Weinmannia, Plagianthus, Quintinia, Veronica, Melicytus) and potentially had been involved in the pollination of these species. This study adds new plant species known to be foraged upon by bumble bees in Aotearoa New Zealand. Further studies on pollination networks in New Zealand will help us understand any changes in host plant preferences over time and after the time period covered by this study. [ABSTRACT FROM AUTHOR]

Bumble bees are key pollinators with some species reared in captivity at a commercial scale, but with significant evidence of population declines and with alarming predictions of substantial impacts under climate change scenarios. While studies on the thermal biology of temperate bumble bees are still limited, they are entirely absent from the tropics where the effects of climate change are expected to be greater. Herein, we test whether bees' thermal tolerance decreases with elevation and whether the stable optimal conditions used in laboratory‐reared colonies reduces their thermal tolerance. We assessed changes in the lower (CTMin) and upper (CTMax) critical thermal limits of four species at two elevations (2600 and 3600 m) in the Colombian Andes, examined the effect of body size, and evaluated the thermal tolerance of wild‐caught and laboratory‐reared individuals of Bombus pauloensis. We also compiled information on bumble bees' thermal limits and assessed potential predictors for broadscale patterns of variation. We found that CTMin decreased with increasing elevation, while CTMax was similar between elevations. CTMax was slightly higher (0.84°C) in laboratory‐reared than in wild‐caught bees while CTMin was similar, and CTMin decreased with increasing body size while CTMax did not. Latitude is a good predictor for CTMin while annual mean temperature, maximum and minimum temperatures of the warmest and coldest months are good predictors for both CTMin and CTMax. The stronger response in CTMin with increasing elevation, and similar CTMax, supports Brett's heat‐invariant hypothesis, which has been documented in other taxa. Andean bumble bees appear to be about as heat tolerant as those from temperate areas, suggesting that other aspects besides temperature (e.g., water balance) might be more determinant environmental factors for these species. Laboratory‐reared colonies are adequate surrogates for addressing questions on thermal tolerance and global warming impacts. [ABSTRACT FROM AUTHOR]

Agri-environmental schemes (AES) are used to enhance pollinator diversity on agricultural farms within the UK. Though the impacts of these schemes on archetypal pollinator species such as the bumblebee (Bombus) and honeybee (Apis) are well-studied, the effects on non-target bee species like solitary bees, in the same environment, are generally lacking. One goal of AES is to alter floral provision and taxonomic composition of plant communities to provide better forage for pollinators, however, this may potentially impact other ecological communities such as fungal diversity associated with plant-bee communities. Fungi are integral in these bee communities as they can impact bee species both beneficially and detrimentally. We test the hypothesis that alteration of the environment through provision of novel plant communities has non-target effects on the fungi associated with solitary bee communities. We analyse fungal diversity and ecological networks formed between fungi and solitary bees present on 15 agricultural farms in the UK using samples from brood cells. The farms were allocated to two categories, low and high management, which differ in the number of agri-environmental measures implemented. Using internal transcribed spacer metabarcoding, we identified 456 fungal taxa that interact with solitary bees. Of these, 202 (approximately 44%) could be assigned to functional groups, the majority being pathotrophic and saprotrophic species. A large proportion was Ascosphaeraceae, a family of bee-specialist fungi. We considered the connectance, nestedness, modularity, nestedness overlap and decreasing fill, linkage density and fungal generality of the farms' bee–fungi ecological networks. We found no difference in the structure of bee–fungi ecological networks between low and high management farms, suggesting floral provision by AES has no significant impact on interactions between these two taxonomic groups. However, bee emergence was lower on the low management farms compared to high management, suggesting some limited non-target effects of AES. This study characterizes the fungal community associated with solitary bees and provides evidence that floral provision through AES does not impact fungal interactions. [ABSTRACT FROM AUTHOR]

Organisms living in seasonal environments are exposed to different environmental conditions as they transition from one life stage to the next across their life cycle. How different life stages respond to these varying conditions, and the extent to which different life stages are linked, are fundamental components of the ecology of an organism. Nevertheless, the influence of abiotic and biotic factors on different parts of an organism's life cycle is often not accounted for, which limits our understanding of the ecological consequences of environmental change.We investigated the relative importance of climate conditions, food availability, and previous life‐stage abundance in an assemblage of seven wild bumble bee species, asking: how do these three factors directly influence bee abundance at each life stage? To do so, we used a 7‐year dataset where we monitored climate conditions, floral resources, and abundances of bees in each life stage across the active colony life cycle in a highly seasonal subalpine ecosystem in the Colorado Rocky Mountains, USA.Bee abundance at different life stages responded to abiotic and biotic conditions in a broadly consistent manner across the seven species: the survival and recruitment stage of the life cycle (overwintered queens) responded negatively to longer winters; the growth stage (workers) responded positively to floral resource availability; and the reproductive stage (males) was positively related to the abundance of the previous life stage (workers). Most species also exhibited some idiosyncratic responses.Our long‐term examination of annual bumble bees reveals a general set of responses in the abundance of each life stage to climate conditions, floral resource availability, and previous life stage. Across species, these three factors each directly influenced a distinct life stage, illustrating how their relative importance can shift throughout the life cycle. The life‐cycle approach that we have taken highlights that important details about demography can be overlooked without considering life‐stage‐specific responses. Ultimately, it is these life‐stage‐specific responses that shape population outcomes, not only for animal pollinators but also for many organisms living in seasonal environments. [ABSTRACT FROM AUTHOR]

Body size is arguably one of the most important traits influencing the physiology and ecology of animals. Shifts in animal body size have been observed in response to climate change, including in bumble bees (Bombus spp. [Hymenoptera: Apidae]). Bumble bee size shifts have occurred concurrently with the precipitous population declines of several species, which appear to be related, in part, to their size. Body size variation is central to the ecology of bumble bees, from their social organization to the pollination services they provide to plants. If bumble bee size is shifted or constrained, there may be consequences for the pollination services they provide and for our ability to predict their responses to global change. Yet, there are still many aspects of the breadth and role of bumble bee body size variation that require more study. To this end, we review the current evidence of the ecological drivers of size variation in bumble bees and the consequences of that variation on bumble bee fitness, foraging, and species interactions. In total we review: (1) the proximate determinants and physiological consequences of size variation in bumble bees; (2) the environmental drivers and ecological consequences of size variation; and (3) synthesize our understanding of size variation in predicting how bumble bees will respond to future changes in climate and land use. As global change intensifies, a better understanding of the factors influencing the size distributions of bumble bees, and the consequences of those distributions, will allow us to better predict future responses of these pollinators. [ABSTRACT FROM AUTHOR]

Bees are important pollinators in wild and agricultural ecosystems, and understanding the factors driving their global declines is key to maintaining these pollination services. Learning, which has been a focus of previous ecotoxicological studies in bees, may play a key role in driving colony fitness. Here we move beyond the standard single-stressor approach to ask how multiple stressors, an agrochemical (sulfoxaflor, a relatively new insecticide) and a parasite (Crithidia bombi, a prevalent gut parasite of bumblebees), impact learning in the bumblebee Bombus terrestris. We developed a modified version of the classic proboscis extension reflex assay to assess the combined effects of acute oral sulfoxaflor exposure and infection by C. bombi on olfactory learning of bumblebee workers. We found no evidence that either sulfoxaflor, C. bombi, or their combination had any significant effect on bumblebee olfactory learning, despite their known negative impacts on other aspects of bumblebee health. This suggests that losses in cognitive ability, as measured here, are unlikely to explain the impacts of sulfoxaflor and its interactions with other stressors on bumblebees. Our novel methodology provides a model system within which to test interactive effects of other key stressors on bee health. [ABSTRACT FROM AUTHOR]

Establishing protocols to sample and monitor bees is critical as pollinators decline. Bees are collected using passive and active methods, but choosing which method and how many samples to collect is challenging.We collected bees in pan traps, vane traps and target netting (bumble bees only) at 96 locations across Wyoming from the sagebrush steppe to mountain meadows. We used power analysis to estimate the number of samples needed to detect a change in bee and bumble bee abundance and richness across elevations (1120–3308 m).Vane traps and pan traps required a similar number of samples to detect a change in the abundance and richness of bees; however, vane traps caught four times more bees and 97% of genera compared to pan traps.Vane traps required far fewer samples to detect changes in the abundance and richness of bumble bees compared to target netting. Pan traps caught so few bumble bees that we do not recommend using them.We recommend using seven to nine vane traps to monitor the abundance and richness of bees and bumble bees, and supplementing bumble bee monitoring with target netting when possible. [ABSTRACT FROM AUTHOR]

Supporting biodiversity in agricultural landscapes is key from both a conservation and ecosystem services perspective. Planting flower margins along crop field edges is one of the most established approaches to try and improve habitat and resources for insect pollinators on farms. Whilst there is growing evidence that these margins can result in increased pollinator abundance and diversity on farms in the short-term, there is little data looking at how these margins perform over longer periods. This study looked at the utilization of pollinator-friendly margins over time in an agricultural landscape in Hungary. 'Operation Pollinator' seed mixes with 12 species, were used at 96 farms in Hungary from 2010 to 2018. Insect pollinators were recorded on the sown flower margins and control margins (with naturally occurring vegetation) using walked transects. Repeated sampling of the margins was done over several years so that data was collected on margins from 0 (planted that season) to 7 years old. The abundance of pollinators in the Operation Pollinator flower margins was greater than in control margins for all groups recorded (honey bees, bumble bees, mining bees, trap-nesting bees, hoverflies and Lepidoptera). The biggest relative increase in abundance was in honey bees (768% increase in average abundance in the flower margin compared to the control across all observations), with mining (566%) and bumble bees (414%) showing the next largest increases. The abundance of bumble bees, trap-nesting bees and Lepidoptera in the margins did not vary with the age of the margin. Honey bees, mining bees and hoverflies all decreased in abundance with increasing margin age, as did flower abundance. The results suggest that for some pollinator groups, regardless of age, flower margins provide important resources in the agricultural landscape. However, this is not universally true and for certain pollinator groups, some re-sowing of the margins may be needed to sustain longer-term benefits. [ABSTRACT FROM AUTHOR]

Bee memory has been well characterized in laboratory experiments, but its relevance for foraging in an ecological context is less well studied. A new study shows that short-term memory in bumble bees correlates with springtime foraging efficiency, when floral resources are abundant, but not with summer foraging efficiency, when resources are scarce. [ABSTRACT FROM AUTHOR]

A fundamental question in pollination ecology is how pollinators affect the evolution of different floral forms. Yet functional effects of shifts in floral form for plant and pollinator are frequently unclear. For instance, flowers that conceal pollen within tube-like anthers that are spread apart and move freely (free architecture) or are tightly joined together (joined architecture) have evolved independently across diverse plant families and are geographically widespread. Surprisingly, how their bee pollinators affect the function of both architectures remains unknown. We hypothesised that bee body size would affect foraging success and pollination differently for free and joined anther architectures. Therefore, we modified the anther architecture of a single plant species (Solanum elaeagnifolium) and used a single species of generalist bumble bee (Bombus impatiens), which varies greatly in body size. We found that on free anther architecture, larger bees were better pollinators. More pollen on their bodies was available for pollination and they deposited more pollen on stigmas. Conversely, on joined anther architecture, smaller bees were better pollinators. They collected less pollen into their pollen baskets, had more pollen on their bodies available for pollination, and deposited more pollen on stigmas. While we also found modest evidence that plants benefit more from joined versus free anther architecture, further investigation will likely reveal this also depends on pollinator traits. We discuss potential mechanisms by which pollinator size and anther architecture interact and implications for floral evolution. [ABSTRACT FROM AUTHOR]

Honey bees (Apis mellifera L.) are important agricultural pollinators, and there is increasing demand for forage habitat for managed colonies. However, there is also evidence that pasturing honey bee colonies within natural landscapes may negatively affect wild bees through resource competition.To assess resource competition between managed honey bees and wild bees, we conducted repeated, short‐term deployments of honey bee colonies within Florida forests coinciding with seasonal wildflower bloom, and compared wild bee foraging with and without honey bee colonies present over multiple seasons.We recorded over 2000 bee visits including 196 pairwise bee–plant interactions. Deploying honey bee colonies was associated with a reduction in wild bee foraging rates, and honey bee and wild bee foraging rates were significantly, negatively correlated. Honey bees disproportionately visited resources with high floral density. Honey bee foraging preferences differed significantly from genera with small‐bodied (Lasioglossum, Perdita, Augochlorella), and/or specialist species (Perdita, Andrena), as well as with Megachile, but overlapped with genera including larger‐bodied (Bombus, Habropoda, Osmia, Xylocopa) and/or generalist species (Bombus, Xylocopa, Agapostemon). Deploying honey bee colonies did not significantly affect plant–pollinator network metrics.These results illustrate that short‐term honey bee colony deployment can negatively affect wild bee foraging and that competition may be greater for certain genera, particularly larger‐bodied bees or those with generalist diets though less for smaller‐bodied and/or specialist bees. Our short‐term, low‐density deployment treatments may have precluded significant effects on network metrics and likely underestimate the effects of typical higher density and longer‐term honey bee deployment. [ABSTRACT FROM AUTHOR]

Despite widespread recognition of the need for long‐term monitoring of pollinator abundances and pollination service provision, such studies are exceedingly rare.In this study, we assess changes in bee visitation and net capture rates for 73 species visiting watermelon crop flowers at 19 farms in the mid‐Atlantic region of the United States from 2005 to 2012.Over the 8 years, we found a 58% decline in wild bee visitation to crop flowers, but no significant change in honey bee visitation rate. Most types of wild bees showed similar declines in both the visitation and the net capture data; bumble bees, however, declined by 56% in the visitation data but showed no change in net capture rates. Trends in pollination services, that is, estimated pollen deposition, largely followed the trends in visitation and net capture rates.While we detected large and significant declines in wild bees when using generalised linear mixed models (GLMMs), permutation analyses that account for non‐directional variation in abundance were non‐significant, demonstrating the challenge of identifying and describing trends in highly variable populations.As far as we are aware, this article represents one of fewer than 10 published time‐series (defined as >5 years of data) studies of changes in bee abundance, and one of only two such studies conducted in an agricultural setting. More such studies are needed in order to understand the magnitude of bee decline and its ramifications for crop pollination. [ABSTRACT FROM AUTHOR]

Assuming that some wild bee populations are resource limited [[56]], the possible competition with early arriving bumble bees (as well as honey bees) may imply that some native bees need to work harder and invest more time and energy in order to collect the proteins (i.e., pollen) needed for provisioning their offspring. Bumble bees visited both pollen- and nectar-rewarding flowers earlier than the wild bees, and the pollen-rewarding flowers earlier than the carpenter bees, but with no significant difference compared to the honey bee for both type of flowers (Table 4). Bumble bees (and to lesser extent honey bees) arrive to pollen-rewarding flowers earlier in the morning and have the opportunity to deplete pollen rewards before the later arrival of the local wild bees ( I Xylocopa i and other wild bee taxa). [Extracted from the article]

Wild bees form diverse communities that pollinate plants in both native and agricultural ecosystems making them both ecologically and economically important. The growing evidence of bee declines has sparked increased interest in monitoring bee community and population dynamics using standardized methods. Here, we studied the dynamics of bee biodiversity within and across years by monitoring wild bees adjacent to four apple orchard locations in Southern Pennsylvania, USA. We collected bees using passive Blue Vane traps continuously from April to October for 6 years (2014–2019) amassing over 26,000 bees representing 144 species. We quantified total abundance, richness, diversity, composition, and phylogenetic structure. There were large seasonal changes in all measures of biodiversity with month explaining an average of 72% of the variation in our models. Changes over time were less dramatic with years explaining an average of 44% of the variation in biodiversity metrics. We found declines in all measures of biodiversity especially in the last 3 years, though additional years of sampling are needed to say if changes over time are part of a larger trend. Analyses of population dynamics over time for the 40 most abundant species indicate that about one third of species showed at least some evidence for declines in abundance. Bee family explained variation in species‐level seasonal patterns but we found no consistent family‐level patterns in declines, though bumble bees and sweat bees were groups that declined the most. Overall, our results show that season‐wide standardized sampling across multiple years can reveal nuanced patterns in bee biodiversity, phenological patterns of bees, and population trends over time of many co‐occurring species. These datasets could be used to quantify the relative effects that different aspects of environmental change have on bee communities and to help identify species of conservation concern. [ABSTRACT FROM AUTHOR]

The spread of parasites is one of the primary drivers of population decline of both managed and wild bees. Several bee parasites are transmitted by the shared use of flowers, turning floral resources into potential disease hotspots. However, we know little about how floral morphology and floral species identity affect different steps of the transmission process. Here, we used the gut parasite Crithidia bombi and its primary host, bumble bees (Bombus spp.), to examine whether floral traits or species identity better predict three basic steps of parasite transmission on flowers: feces deposition on flowers, survival of the parasite on flowers, and acquisition by a new host. We also identified which traits and/or species were most strongly associated with each step in the transmission process. We found that both trait‐ and species‐based models fit the data on deposition of feces and survival of C. bombi on flowers, but that species‐based models provided a better fit compared with trait‐based ones. However, trait‐based models were better at predicting the acquisition of C. bombi on flowers. Although different species tended to support higher fecal deposition or parasite survival, we found that floral shape provided explanatory power for each of the transmission steps. When we assessed overall transmission potential, floral shape had the largest explanatory effect, with wider, shorter flowers promoting higher transmission. Taken together, our results highlight the importance of flower species identity and floral traits in disease transmission dynamics of bee parasites, and floral shape as an important predictor of overall transmission potential. Identifying traits associated with transmission potential may help us create seed mix that presents lower parasite transmission risk for bees for use in pollinator habitat. [ABSTRACT FROM AUTHOR]

Long‐term variation in the population density of introduced honey bees (Apis mellifera) has been shown to be associated with variations in floral traits in alpine lotus (Saussurea nigrescens). However, it remains to be determined whether a high density of honey bees affects the abundance of nectariferous plants and the species richness and abundance of native bumble bees. We predicted that a high density of introduced honey bees lasting three decades would decrease the species richness and abundance of native bumble bees but increase the abundance of honey bee host plant species. Here, field experiments were conducted to examine the diversity of nectariferous plants and native bumble bees along the typical gradients of honey bee density (high density of honey bees close to the apiary and low density of honey bees distant from the apiary). We investigated nectariferous plant abundance, floral and seed traits, and bumble bee species richness and abundance at sites with either high or low honey bee densities in an alpine meadow. Our results demonstrate that an increased population of introduced honey bees is associated with increased host plant abundance and flower/capitulum number per plant but decreased nectar volume per flower, seed mass, and species richness and abundance of native bumble bees. The bumble bee visitation rate was positively correlated with nectar volume per flower at sites close to and far from apiaries. The honey bee visitation rate was positively correlated with flower/capitulum number per plant at sites close to apiaries and nectar volume per flower at sites far from apiaries. Seed mass was negatively correlated with nectariferous plant abundance. Our findings show that introduced honey bees decrease the species richness and abundance of native bumble bees, attributed to an evolutionarily decrease in nectar resources among honey bee host plant species, but increase the abundance of nectariferous plants, attributed to the production of many small seeds by plants. This suggests that long‐term high‐density beekeeping affects the biodiversity of honey bee host plants and native bumble bees. Our results provide new insights into the mechanisms of maintaining the biodiversity of nectariferous plants and native bumble bees. [ABSTRACT FROM AUTHOR]

Several agri-environment schemes aim to improve pollinator diversity and abundance, including the sowing of wildflower areas. These seed mixes are often either low in floral diversity and target few pollinator species (mainly social bees), or high in floral diversity but with limited evidence of good establishment of the component species. In order to support a greater diversity of wild bees in farmland, we need more diverse seed mixes, containing species shown to support a wide diversity of insect pollinators, with good establishment and long flowering periods. Here we trialled two typical seed mixes, a low-diversity Fabaceae-heavy mix (FAB) and a more diverse wildflower mix (WF), against two novel wildflower mixes, one based on literature sources (LT), and one based on first-hand surveys of pollinator attraction to flowers growing on a wildflower farm (WB). Both new mixes were focussed on plants attractive to wild bee species. Replicated field plots were set up on two farms and monitored over three years. Our novel wildflower mixes had higher floral diversity and abundance than the FAB mix, and began flowering earlier, reaching their floral peak before the FAB mix, potentially providing forage for a broader range of pollinators or those with earlier flight seasons. The high floral abundance in LT and WB was driven by annuals in the first year, and then multiple perennials in the second and third year. We identified five perennials from four families (Daucus carota, Leucanthemum vulgare, Geranium pyrenaicum, Lotus corniculatus and Trifolium hybridum) that established well on both farms, are known to be attractive to a diversity of bee species, and thus could be considered as providing a more taxonomically diverse base for creating future mixes. However, the mixes provided few floral resources in April (needed by early-flying wild bees), and more research is required in this area. [ABSTRACT FROM AUTHOR]

Crithidia bombi is a trypanosomatid parasite that infects several species of bumble bees (Bombus spp.), by adhering to their intestinal tract. Crithidia bombi infection impairs learning and reduces survival of workers and the fitness of overwintering queens. Although there is extensive research on the ecology of this host-pathogen system, we understand far less about the mechanisms that mediate internal infection dynamics. Crithidia bombi infects hosts by attaching to the hindgut via the flagellum, and one previous study found that a nectar secondary compound removed the flagellum, preventing attachment. However, approaches that allow more detailed observation of parasite attachment and growth would allow us to better understand factors mediating this host-pathogen relationship. We established techniques for genetic manipulation and visualization of cultured C. bombi. Using constructs established for Crithidia fasciculata, we successfully generated C. bombi cells expressing ectopic fluorescent transgenes using two different selectable markers. To our knowledge, this is the first genetic modification of this species. We also introduced constructs that label the mitochondrion and nucleus of the parasite, showing that subcellular targeting signals can function across parasite species to highlight specific organelles. Finally, we visualized fluorescently tagged parasites in vitro in both their swimming and attached forms, and in vivo in bumble bee (Bombus impatiens) hosts. Expanding our cell and molecular toolkit for C. bombi will help us better understand how factors such as host diet, immune system, and physiology mediate outcomes of infection by these common parasites. [Display omitted] • First described method for genetic modification of the bee parasite Crithidia bombi. • Ectopic transgenes can be introduced using multiple selectable markers. • Cytoplasmic and organelle markers can be visualized in swimming and attached developmental forms. • Simplified method for culture adaptation of parasites from bees for subsequent modification. • Imaging of fluorescent C. bombi parasites in vivo in the bumble bee Bombus impatiens. [ABSTRACT FROM AUTHOR]

Bees play an important role in agriculture and ecology, and their pollination efficiency is essential to the economic profitability of farms. The drastic decrease in bee populations witnessed over the last decade has attracted great attention to automated remote beehive monitoring research, with beehive acoustics analysis emerging as a prominent field. In this paper, we review the existing literature on bee acoustics analysis and report on the articles published between January 2012 and December 2021. Five categories are explored in further detail, including the origin of the articles, their study goal, experimental setup, audio analysis methodology, and reproducibility. Highlights and limitations in each of these categories are presented and discussed. We conclude with a set of recommendations for future studies, with suggestions ranging from bee species characterization, to recording and testing setup descriptions, to making data and codes available to help advance this new multidisciplinary field. [ABSTRACT FROM AUTHOR]

Urbanization is associated with increases in impervious land cover, which alters the distribution of resources available to wildlife and concentrates activity in unbuilt spaces such as parks and gardens. How resource shifts alter the dynamics of parasite and pathogen transmission has not been addressed for many important species in urban systems. We focus on urban gardens, resource‐rich "islands" within the urban matrix, to examine how the availability of floral resources at local and landscape scales influences the prevalence of six RNA viruses and three parasites in honey bees and bumble bees. Because parasites and pathogens are transmitted at flowers between visitors, we expected that floral abundance would concentrate bees within gardens, amplifying infection rates in pollinators, unless increases in floral resources would enhance bee diversity enough to dilute transmission. We found that garden size and flowering perennial plant abundance had a positive, direct effect on parasite and pathogen richness in bumble bees, suggesting that resource provisioning amplifies transmission. We also found that parasitism rates in honey bees were positively associated with parasites and pathogens in bumble bees, suggesting spillover between species. Encouragingly, we found evidence that management may mitigate parasitism through indirect effects: garden size had a positive impact on bee diversity, which in turn was negatively associated with parasite and pathogen richness in bumble bees. Unexpectedly, we observed that that parasite and pathogen richness in honey bees had no significant predictors, highlighting the complexity of comparing transmission dynamics between species. Although floral resources provide bees with food, we suggest more research on the tradeoffs between resource provisioning and disease transmission to implement conservation plantings in changing landscapes. [ABSTRACT FROM AUTHOR]

With growing urbanization, it is becoming increasingly important to design cities in a manner that sustains and enhances biodiversity and ecosystem services. Native bees are critical pollinators that have experienced substantive declines over the past several decades. These declines have captured the attention of the public, particularly urbanites, prompting a large interest in protecting pollinators and their habitats in cities across North America and Europe. Unfortunately, we currently lack research about specific features of urban environments that can enhance the fitness of pollinators. We carried out an intensive study of Bombus impatiens, the Common Eastern Bumblebee, in the city of Toronto (Canada's largest city), to better understand landscape parameters that provide high‐quality habitat for this species and likely other generalist bees. We divided the city into 270 grid cells and sampled a large number of worker bees, which were then genotyped at twelve hypervariable microsatellite loci. The genetic data allowed us to quantify the effective number of colonies and foraging distance for bumblebees in our study area. We then asked how the city's landscape and human population demography and income are associated with the availability of high‐quality habitat for B. impatiens. Several aspects of Toronto's landscape influenced colony density and foraging range. Urbanization had a clear effect on both colony density and foraging distance of workers. On the other hand, functional (i.e., not cosmetic) green space was often associated with higher quality habitats for bumblebees. Our study suggests several planning strategies to enhance habitat quality for bumblebees and other pollinators in cities. [ABSTRACT FROM AUTHOR]

Bumble bees (genus Bombus) are important pollinators with more than 260 species found worldwide, many of which are in decline. Twenty‐five species occur in California with the highest species abundance and diversity found in coastal, northern, and montane regions. No recent studies have examined California bumble bee diversity across large spatial scales nor explored contemporary community composition patterns across the state. To fill these gaps, we collected 1740 bumble bee individuals, representing 17 species from 17 sites (~100 bees per site) in California, using an assemblage monitoring framework. This framework is intended to provide an accurate estimate of relative abundance of more common species without negatively impacting populations through overcollection. Our sites were distributed across six ecoregions, with an emphasis on those that historically hosted high bumble bee diversity. We compared bumble bee composition among these sites to provide a snapshot of California bumble bee biodiversity in a single year. Overall, the assemblage monitoring framework that we employed successfully captured estimated relative abundance of species for most sites, but not all. This shortcoming suggests that bumble bee biodiversity monitoring in California might require multiple monitoring approaches, including greater depth of sampling in some regions, given the variable patterns in bumble bee abundance and richness throughout the state. Our study sheds light on the current status of bumble bee diversity in California, identifies some areas where greater sampling effort and conservation action should be focused in the future, and performs the first assessment of an assembly monitoring framework for bumble bee communities in the state. [ABSTRACT FROM AUTHOR]

Bahiagrass (Paspalum notatum Flüggé; Poaceae) is primarily a pasture grass in the southern US. It is also lawn grass found in residential settings, public parks, and planted in golf courses. Bahiagrass is principally wind-pollinated, but the pollination contribution of insect pollinators is not documented. A survey was conducted on bahiagrass patches in central Georgia, USA, to determine the visitation of foraging pollinators. The results showed that European honey bees, bumblebees, and sweat bees forage on bahiagrass spikelets. Of the total bees observed, 10.6% (n = 94) were foraging on bahiagrass, compared to 46.8% on white clover, 27.7% on dandelion, and 14.8% on buckhorn plantain. This is the first report showing bee foraging on bahiagrass. The results suggest that bahiagrass spikelets may be a supplemental resource for bees and essential for bee conservation programs in rural and suburban areas. More research is warranted to determine how bahiagrass spikelets play a role in meeting the nutritional needs of bees to help sustain their colony and provide pollination service. [ABSTRACT FROM AUTHOR]