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As the honey bee and bumble bee may suffer from the same or related microbial pathogens, cross contamination from commercially reared Bombus spp. to honey bees and wild bumble bees and vice versa is a major concern. Honey bee-collected pollen to feed commercially reared Bombus spp. is a potential risk. Nosema spp. is a fungal pathogen in bees. In this study, we developed new quantitative detection tools based on the detection of RNA using a TaqMan-based RT-qPCR for Nosema ceranae and Nosema apis, with extraction controls based on the actin gene of honey bees and bumble bees, respectively. These tools were subsequently applied to study the epidemiology of N. ceranae, a main disease in honey bees. We screened gamma radiation and cold treatment sterilisation for their efficacy to kill N. ceranae spores fed in sugar water and in pollen to honey bees and bumble bees, respectively. N. ceranae infection in adult bumble bees was checked. Spores passing the inter-alimentary track were found but no infection was observed. N. ceranae spores were fed to honey bees. Their presence and multiplication were demonstrated, showing the spores were both viable and infectious. Our results indicate that N. ceranae found in honey bees cannot infect commercially reared bumble bees (Bombus terrestris) and, that gamma radiation effectively kills N. ceranae. The highly specific and sensitive molecular assays developed, were exploited to detect N. ceranae in pollen and faeces, which would allow more comprehensive epidemiological studies on this important pathogen. [ABSTRACT FROM AUTHOR]

Different pollinators exhibit different adaptability to plants. Here, we compared the performance in visiting frequency and pollination efficiency among three bee pollinators (Bombus terrestris, Apis cerana, and Apis mellifera) on greenhouse-grown northern highbush ‘Bluecrop’ blueberry plants and evaluate their effects on yield and fruit quality. Our results indicated that the duration of daily flower-visiting of B. terrestris was 24 and 64 minutes longer than that of A. cerana and A. mellifera, respectively, and the visiting time of a single flower for B. terrestris was substantially shorter than the other two bee species, and pollen deposition on the stigma from single visit by B. terrestris was twice and three times that of A. cerana and A. mellifera, respectively. The yield of individual plants pollinated by B. terrestris showed an increase of 11.4% and 20.0% compared with the plants pollinated by A. cerana and A. mellifera, respectively, with the rate of Grade I fruit (>18 mm diameter) reaching 50.8%, compared with 32.9% and 22.5% for A. cerana and A. mellifera groups, respectively. Moreover, the early-to-midseason yield of plants pollinated by B. terrestris was higher, and the ripening time was 3 to 4 days earlier. An artificial pollination experiment demonstrated that seed set of high (≈300), medium (90–110), and low (20–30) pollination amounts were 43.0%, 42.5%, and 10.5%, respectively, and the corresponding mean weights of single fruits (related to the seed number inside) were 2.8, 2.7, and 1.2 g, respectively. The highly efficient pollination of B. terrestris was attributed to its behavior of buzz-pollination. Therefore, it is preferential for pollination of ‘Bluecrop’ blueberry in the greenhouse.

A study published in the Proceedings of the Royal Society B reveals that heat waves can impair bumble bees' ability to smell flowers, which could have significant implications for both the bees' populations and the industries that rely on them. The researchers found that exposure to heat reduced the bees' antennal response to scent molecules by up to 80%. This finding suggests that the effects of heat waves on bumble bees may be long-lasting. The decline in bee populations is already a concern, and this study highlights the potential impact of climate change on these important pollinators. [Extracted from the article]

Bombus terrestris are efficient pollinators in forestry and agriculture, with higher cold tolerance than other bees. Yet, their cold tolerance mechanism remains unclear. Aquaporins (AQPs) function as cell membrane proteins facilitating rapid water flow, aiding in osmoregulation. Recent studies highlight the importance of insect AQPs in dehydration and cold stress. Comparative transcriptome analysis of B. terrestris under cold stress revealed up-regulation of four AQPs, indicating their potential role in cold tolerance. Seven AQPs—Eglp1, Eglp2, Eglp3, DRIP, PRIP, Bib, and AQP12L—have been identified in B. terrestris. These are widely expressed in various tissues, particularly in the alimentary canal and Malpighian tubules. Functional analysis of BterAQPs in the Xenopus laevis oocytes expressing system showed distinct water and glycerol selectivity, with BterDrip exhibiting the highest water permeability. Molecular modeling of BterDrip revealed six transmembrane domains, two NPA motifs, and an ar/R constriction region (Phe131, His256, Ser265, and Arg271), likely contributing to its water selectivity. Silencing BterDRIP accelerated mortality in B. terrestris under cold stress, highlighting the crucial role of BterDRIP in their cold tolerance and providing a molecular mechanism for their cold adaptation. [Display omitted] • The majority of BterAQPs are highly expressed in Malpighian tube. • BterDRIP permeates water exclusively and most efficiently. • BterDrip has conserved NPA sites and ar/R filters. • BterDrip improves the cold tolerance of Bombus terrestris. [ABSTRACT FROM AUTHOR]

A queen’s diapause is a key period of the bumble bee life cycle that enables them to survive under unfavorable conditions. During diapause, queens fast, and nutritional reserves depend on the accumulation of nutrients during the prediapause period. Temperature is one of the most important factors affecting queens’ nutrient accumulation during prediapause and nutrient consumption during diapause. Here, we used a 6-day-old mated queen of the bumble bee Bombus terrestris to evaluate the effect of temperature (10, 15, and 25 °C) and time (3, 6, and 9 days) on free water, protein, lipids, and total sugars during prediapause and at the end of 3 months of diapause. Stepwise regression analysis revealed that total sugars, free water, and lipids were much more affected by temperature than protein (p < 0.05). Lower temperature acclimation significantly increased (p < 0.05) free water and lipid accumulation by queens during prediapause. In contrast, higher temperature acclimation significantly increased (p < 0.05) protein and total sugar accumulation by queens during prediapause. The effect of temperature acclimation on the queen survival rate was not significantly different (p > 0.05) after 3 months of diapause. Moreover, lower temperature acclimation reduced protein, lipid, and total sugar consumption by queens during diapause. In conclusion, low-temperature acclimation increases queens’ lipid accumulation during prediapause and reduces the nutritional consumption of queens during diapause. Low-temperature acclimation during prediapause could benefit queens by improving cold resistance and increasing reserves of major nutrient lipids during diapause.

Microsporidia are spore-forming intracellular parasites of various invertebrates and vertebrates. Vairimorpha bombi negatively affects the fitness of bumblebees and its prevalence correlates with declining bumblebee populations. The invasive alien species Bombus terrestris colonized Japan and possibly introduced new parasites. To assess the infection prevalence of V. bombi in Japanese bumblebees and B. terrestris, we investigated V. bombi infections using PCR and microscopy. The prevalence of sporulating V. bombi infections in three Bombus s. str. species/subspecies was low, whereas that of non/low-sporulating Vairimorpha sp. infections in three Diversobombus species/subspecies was high. Invasive B. terrestris showed low prevalence of non/low-sporulating V. bombi infections and shared the same V. bombi haplotype with B. hypocrita found in Hokkaido, where B. terrestris is present, and in Honshu, where B. terrestris is absent. Although V. bombi may have been introduced with B. terrestris colonies imported from Europe, it seems to be originally distributed in Japan. Furthermore, a new Vairimorpha sp. was found in Japanese bumblebee species. V. bombi and Vairimorpha sp. showed different organ and host specificities in bumblebees. There are no reports on the specific effects of other Vairimorpha spp. on bumblebees; further studies are needed to clarify the individual characteristics of Vairimorpha spp.

Bee populations have declined in many parts of the world, raising concerns over their conservation and the pollination services they provide. As a result of declines in agricultural areas, agri-environment schemes have been designed and implemented in order to reverse these trends. Until now, these schemes have largely focused on providing an abundance of herbaceous flowering plants which predominantly provide pollen and nectar during the summer, but flowering trees and shrubs may have been overlooked as a source of earlier-flowering resources. Using Bombus terrestris (L.) microcolonies, we investigated differences in pollen quality from eight woody and six herbaceous plant species using compositional analyses and efficacy assays. Pollen from herbaceous plants had a higher average crude protein and lipid content, but there were no differences in the protein:lipid ratio when compared to woody plants. However, when measuring amino acids directly, woody plants had a slightly higher total and essential amino acid content. Despite these minor differences, microcolonies fed on woody plant pollen produced a greater mass of larval offspring and had a lower rate of larval ejection. There was substantial variation between individual studied plant species, and whilst no individual woody plant pollen outperformed the best herbaceous pollen, they all exceeded the performance of the worst herbaceous pollen. This consistent performance suggests that woody plants may be good candidates for inclusion in bee-focused agri-environment schemes in order to provide suitable pollen resources in the early part of the season. [ABSTRACT FROM AUTHOR]

Pollinating insects provide pollination services to many crop species, including sweet cherry (Prunus avium L.), and this can be delivered by both managed and wild pollinators. Managed pollinators are often used to pollinate a range of fruit crops, but increasingly the role of wild insects is being studied. However, the importance of pollinator species depends on their relative abundance and pollination effectiveness, which depends on their foraging activity and their variability throughout the day. In this study, insect visitors of blossoms were observed in commercial sweet cherry orchards to explore abundance, diversity and pollination foraging behaviour of different insect pollinator groups throughout the day. A total of 1,174 pollinators from 31 different species were recorded visiting cherry blossoms over 2 years, of which 71.0% of total visits were by managed pollinators (western honeybee, Apis mellifera L. and buff‐tailed bumblebee, Bombus terrestris L.) compared to 29.0% by wild pollinators. On average, solitary bees visited a sweet cherry blossom for the longest duration (20.7 (±2.0 SE) seconds), whereas wild queen bumblebees visited the greatest number of flowers per minute (mean of 19.0 (±1.3 SE)). As both these pollinator groups contacted cherry stigmas more often and moved more frequently between tree rows than managed bees and hoverflies, they are more likely to facilitate cross‐pollination. The different pollinator groups also showed variation in behavioural parameters throughout the day, but less variation was recorded when all pollinator groups were considered altogether. This suggests diverse pollinator communities might be expected to provide a more stable pollination service to sweet cherry. This study demonstrates that whilst cherry blossoms were more frequently visited by managed pollinators, wild solitary bee and bumblebee behaviours are likely to be more effective at enhancing pollination in sweet cherry orchards, which, in turn, might lead to increased yields. [ABSTRACT FROM AUTHOR]

In modern agricultural production, a variety of pesticides are widely used to protect crops against pests. However, extensive residues of these pesticides in the soil, water, and pollen have negatively affected the health of nontarget organisms, especially among pollinators such as bumblebees. As an important pollinator, the bumblebee plays a vital role in agricultural production and the maintenance of ecosystem diversity. Previous research has focused on the effects of a single pesticide on pollinating insects; however, the synergistic effects of multiple agents on bumblebees have been not studied in detail. Imidacloprid, thiamethoxam, and chlorpyrifos are three of common pesticides known for severe effects on bumblebee health. It is still unknown what synergistic effects of these pesticides on pollinators. In our test, the individual and combined toxicities of chlorpyrifos, thiamethoxam, and imidacloprid to bumblebees after 48 h of oral administration were documented by the equivalent linear equation method. Our results showed that the toxicity of each single pesticide exposure, from high to low, was imidacloprid, thiamethoxam, and chlorpyrifos. All binary and ternary combinations showed synergistic or additive effects. Therefore, our research not only shows that the mixed toxicity of insecticides has a significant effect on bumblebees, but also provides scientific guidelines for assessing the safety risks to bumblebees of these three insecticide compounds. In assessing the risk to pollinating insects, the toxicity levels of laboratory experiments are much lower than the actual toxicity in the field. [ABSTRACT FROM AUTHOR]

Insect CAPA neuropeptidesare considered to affect water and ion balance by mediating the physiological metabolism activities of the Malpighian tubules. In previous studies, the CAPA‐PK analogue 1895 (2Abf‐Suc‐FGPRLamide) was reported to decrease aphid fitness when administered through microinjection or via topical application. However, a further statistically significant decrease in the fitness of aphids and an increased mortality could not be established with pairwise combinations of 1895 with other CAPA analogue. In this study, we assessed the topical application of new combinations of 1895 with five CAPA‐PVK analogues on the fitness of aphids. We found that 1895 and CAPA‐PVK analogue 2315 (ASG‐[β3L]‐VAFPRVamide) was statistically the most effective combination to control the peach potato aphid Myzus persicae nymphs via topical application, leading to 72% mortality. Additionally, the combination (1895+2315) was evaluated against a selection of beneficial insects, that is, a pollinator (Bombus terrestris) and three natural enemies (Chrysoperla carnea, Nasonia vitripennis, and Adalia bipunctata). We found no significant influence on food intake, weight increase, and survival for the pollinator and the three representative natural enemies. These results could facilitate to further establish and generate CAPA analogues as alternatives to broad spectrum and less friendly insecticides. [ABSTRACT FROM AUTHOR]

Simple Summary: Bee declines have been reported worldwide, partly due to parasite spread induced by human activities. However, bees may forage on specific floral resources to face parasite infection. Such natural resources are comparable to 'natural pharmacies' and may be favoured in bee conservation strategies. Consumption of sunflower pollen, despite being detrimental for larval development, has been recently shown to reduce the load of a widespread bumble bee gut parasite in the common eastern bumble bee. Although the underlying mechanisms remain unknown, it has been suggested that sunflower phenolamides—a family of molecules found in most flowering plants—may be responsible for such a reduction in parasite load. Here, we tested the impacts of sunflower phenolamides on healthy and infected buff-tailed bumble bees. Expectedly, sunflower pollen had harmful consequences on bumble bee development but surprisingly, it did not alter parasite load. By contrast, sunflower phenolamides had milder effects on bumble bee development but unexpectedly increased parasite load. Phenolamide effects may stem from the physiological stress they induced or the gut microbial community alteration they may have triggered. Since biological models and experimental framework differ greatly in related studies tackling plant–bee–parasite interplays, we challenged the definition of medicinal effects and questioned the way to assess them in controlled conditions. Specific floral resources may help bees to face environmental challenges such as parasite infection, as recently shown for sunflower pollen. Whereas this pollen diet is known to be unsuitable for the larval development of bumble bees, it has been shown to reduce the load of a trypanosomatid parasite (Crithidia bombi) in the bumble bee gut. Recent studies suggested it could be due to phenolamides, a group of compounds commonly found in flowering plants. We, therefore, decided to assess separately the impacts of sunflower pollen and its phenolamides on a bumble bee and its gut parasite. We fed Crithidia-infected and -uninfected microcolonies of Bombus terrestris either with a diet of willow pollen (control), a diet of sunflower pollen (natural diet) or a diet of willow pollen supplemented with sunflower phenolamides (supplemented diet). We measured several parameters at both microcolony (i.e., food collection, parasite load, brood development and stress responses) and individual (i.e., fat body content and phenotypic variation) levels. As expected, the natural diet had detrimental effects on bumble bees but surprisingly, we did not observe any reduction in parasite load, probably because of bee species-specific outcomes. The supplemented diet also induced detrimental effects but by contrast to our a priori hypothesis, it led to an increase in parasite load in infected microcolonies. We hypothesised that it could be due to physiological distress or gut microbiota alteration induced by phenolamide bioactivities. We further challenged the definition of medicinal effects and questioned the way to assess them in controlled conditions, underlining the necessity to clearly define the experimental framework in this research field. [ABSTRACT FROM AUTHOR]

Living in a social group increases the risks of parasitism, especially in highly-related groups. In homogenous groups, with no reproductive division of labour, the impact of parasitism is unlikely to vary with host identity. Many social systems, however, do exhibit division of reproductive labour, most famously in social insects with their reproductive queens and generally infertile workers. In such systems, the impact of parasitism will differ for each group. Consequently, we predict that susceptibility to parasites will vary to reflect such differential impact. We tested this prediction using a trypanosome-bumble bee system, where Crithidia bombi infects both gynes and workers of Bombus terrestris. We studied both susceptibility to the parasite and relevant measures of the immune function. As predicted, gynes were significantly less susceptible to the parasite than workers, but while gynes and workers expressed different immune profiles, how these link to differential susceptibility remains unclear. In conclusion, our results suggest that differential selection pressures exerted by parasites may produce multiple phenotypes from a single genotype in order to maximise fitness in a social group context. Significance statement: Social insect colonies dominate terrestrial ecology, and as such are targets for parasites. How they defend themselves against such threats is a key question. Here, we show that bumble bee gynes — the reproductive individuals that overwinter and found colonies in this annual social system — are more resistant to a parasite that disproportionately affects reproductive fitness than their sister workers. Differential patterns of susceptibility may help to explain the success of these social insects. [ABSTRACT FROM AUTHOR]

Neonicotinoid insecticides are the most commonly used insecticide in the world and can have significant sub-lethal impacts on beneficial insects, including bumblebees, which are important pollinators of agricultural crops and wildflowers. This has led to bans on neonicotinoid use in the EU and has resulted in repeated calls for the agrochemical regulatory process to be modified. For example, there is increasing concern about 1) the underrepresentation of wild bees, such as bumblebees, in the regulatory process, and 2) the failure to determine how agrochemicals, such as neonicotinoids, interact with other commonly occurring environmental stressors, such as parasites. Here, we modify an OECD approved lethal dose (LD50) experimental design and coexpose bumblebees (Bombus terrestris) to the neonicotinoid thiamethoxam and the highly prevalent trypanosome parasite Crithidia bombi, in a fully crossed design. We found no difference in the LD50 of thiamethoxam on bumblebees that had or had not been inoculated with the parasite (Crithidia bombi). Furthermore, thiamethoxam dosage did not appear to influence the parasite intensity of surviving bumblebees, and there was no effect of either parasite or insecticide on sucrose consumption. The methodology used demonstrates how existing ring-tested experimental designs can be effectively modified to include other environmental stressors such as parasites. Moving forward, the regulatory process should implement methodologies that assess the interactions between agrochemicals and parasites on non-Apis bees and, in cases when this is not practical, should implement post-regulatory monitoring to better understand the real-world consequences of agrochemical use. [ABSTRACT FROM AUTHOR]

Nectar robbers are common cheaters of plant-pollinator mutualisms by making holes in flower tissues to attain floral rewards often without providing pollination service. Most studies have focused on the consequences of nectar robbing on plant reproduction, whereas the underlying drivers of spatiotemporal variation in nectar robbing have been comparatively less explored. We assessed variation in nectar robbing of Campsidium valdivianum, an endemic hummingbird-pollinated climber species from the temperate forests of Southern South America, which currently is subjected to nectar robbing by the alien short-tongued Bombus terrestris, and determined if this variation is related to characteristics of the floral neighborhood. We located plants of C. valdivianum and estimated the proportion of flowers with holes. We recorded the presence, identity and distance to the nearest bumblebee-pollinated plants with open flowers. Results showed that the proportion of robbed flowers in C. valdivianum increased almost seven times in the presence of bumblebee flowering plants in the neighborhood. No evidence was found that the proportion of robbed flowers differs between neighborhoods with Berberis darwinii only vs. B. darwinii and Cytisus scoparius, the co-flowering plant species typically visited by bumblebees during the study. Finally, the proportion of robbed flowers increased not only with the presence but also with the proximity of these bumblebee-pollinated plants. Our results suggest that floral neighborhoods attractive to bumblebees can operate as magnets, potentially increasing the intensity of nectar robbing on nearby hummingbird-pollinated species. This study provides novel insights into understanding spatio-temporal variation in nectar robbing. [ABSTRACT FROM AUTHOR]

Floral traits often display sexual dimorphism in insect‐pollinated dioecious plant species, with male individuals typically being showier than females. While this strategy is theorized to be optimal when pollinators are abundant, it might represent a risk when they become scarce, because the disproportionately high number of visits on the most attractive sex, males, might preclude efficient pollen transfer from males to females. Here, the effect of sexual dimorphism on pollination efficiency was assessed in experimental arrays of dioecious Silene dioica that were exposed to one frequent visitor of the species, Bombus terrestris, and that differed in the magnitude of sexual dimorphism for either flower number or flower size. We found that flower number dimorphism negatively affected the number of visits on female plants, on female flowers and on the number of female flowers visited after a male flower. However, flower number dimorphism had no effect on the number of pollen grains deposited per stigma, presumably because the decrease in the number of visits to female flowers was compensated by a higher number of pollen grains deposited per visit. Flower size dimorphism did not affect visitation patterns and pollen transfer in our experimental arrays. These results highlight the need to jointly study visitation patterns and pollen receipt on stigmas when exploring the effect on floral phenotypes on pollination efficiency. [ABSTRACT FROM AUTHOR]

The global movement of bees for agricultural pollination services can affect local pollinator populations via hybridization. When commercial bumblebees are of the same species but of different geographic origin, intraspecific hybridization may result in beneficial integration of new genetic variation, or alternatively may disrupt locally adapted gene complexes. However, neither the existence nor the extent of genomic introgression and evolutionary divergence between wild and commercial bumblebees is fully understood. We obtained whole‐genome sequencing data from wild and commercial Bombus terrestris collected from sites in Southern Sweden with and without long‐term use of commercially imported B. terrestris. We search for evidence of introgression, dispersal and genome‐wide differentiation in a comparative genomic analysis of wild and commercial bumblebees. Commercial B. terrestris were found in natural environments near sites where commercial bumblebees were used, as well as drifting wild B. terrestris in commercial bumblebee colonies. However, we found no evidence for widespread, recent genomic introgression of commercial B. terrestris into local wild conspecific populations. We found that wild B. terrestris had significantly higher nucleotide diversity (Nei's pi, π), while the number of segregating sites (Watterson's theta, θw) was higher in commercial B. terrestris. A highly divergent region on chromosome 11 was identified in commercial B. terrestris and found to be enriched with structural variants. The genes present in this region are involved in flight muscle contraction and structure and pathogen immune response, providing evidence for differing evolutionary processes operating in wild and commercial B. terrestris. We did not find evidence for recent introgression, suggesting that co‐occurring commercial B. terrestris have not disrupted evolutionary processes in wild B. terrestris populations. [ABSTRACT FROM AUTHOR]

While feeding, foragers can alter their environment. Such alteration constitutes ecological niche construction (ENC) if it enables future benefits for the constructor and conspecific individuals. The environmental modification may also affect non‐constructing, bystander species, especially if they share resources with constructor species. If so, ENC could confer the constructor species a competitive advantage by both enhancing its foraging returns and reducing those of bystander species.Expectations – (E1) ENC frequency should vary positively with the recent and current density of the constructor species, and (E2) constructors should use modifications disproportionately. In contrast, bystanders should (E3) experience intensified competition for the affected resource, and (E4) exhibit diverse, possibly mitigating, responses to ENC, depending on opportunity and relative benefits.We investigated these expectations in Argentina for competition for Fuchsia magellanica nectar between an invasive bumble bee Bombus terrestris (terr: putative constructor), which often bites holes at the bases of floral tubes to rob nectar, and native B. dahlbomii (dahl: bystander), which normally accesses Fuchsia nectar through the flower mouth (front visits). Robbing holes constitute ENC, as they persist until the 7‐day flowers wilt. The dynamics of the incidence of robbed flowers, abundance of both bees and the number and types of their flower visits (front or robbing) were characterised by alternate‐day surveys of plants during 2.5 months.After initially accessing Fuchsia nectar via front visits, terr switched to robbing and its abundance on Fuchsia increased 20‐fold within 10 days (E2). Correspondingly, the incidence of robbed flowers varied positively with recent and past terr abundance (E1). In contrast, dahl abundance remained low and varied negatively with the incidence of robbed flowers (E3). When terr ceased visiting Fuchsia, dahl abundance increased sixfold within 10 days (E3), possibly because many dahl previously had avoided competition with terr by feeding on other plant species (E4). While terr was present, dahl on Fuchsia used front visits (tolerance) or used existing robbing holes (adoption: E4). The diverse dahl responses suggest partial compensation for competition with terr.ENC alters competitive asymmetry, favouring constructor species. However, bystander responses can partially offset this advantage, perhaps facilitating coexistence. [ABSTRACT FROM AUTHOR]

Free-living organisms face multiple stressors in their habitats, and habitat quality often affects development and life history traits. Increasing pressures of agricultural intensification have been shown to influence diversity and abundance of insect pollinators, and it may affect their elemental composition as well. We compared reproductive success, body concentration of carbon (C) and nitrogen (N), and C/N ratio, each considered as indicators of stress, in the buff-tailed bumblebee (Bombus terrestris). Bumblebee hives were placed in oilseed rape fields and semi-natural old apple orchards. Flowering season in oilseed rape fields was longer than that in apple orchards. Reproductive output was significantly higher in oilseed rape fields than in apple orchards, while the C/N ratio of queens and workers, an indicator of physiological stress, was lower in apple orchards, where bumblebees had significantly higher body N concentration. We concluded that a more productive habitat, oilseed rape fields, offers bumblebees more opportunities to increase their fitness than a more natural habitat, old apple orchards, which was achieved at the expense of physiological stress, evidenced as a significantly higher C/N ratio observed in bumblebees inhabiting oilseed rape fields. [ABSTRACT FROM AUTHOR]

The buff-tailed bumblebee Bombus terrestris presents two distinct colony phenotypes in which some colonies already start producing males very early in the season, while others switch to producing sexuals much later in the season, and specialize mainly in the production of virgin queens. Despite having been extensively investigated in the past, the mechanisms underlying these two distinct phenotypes remain poorly understood. Here we use a combination of behavioral and genetic data to demonstrate that early switchers are in fact diploid male producing colonies, while late switchers produced normal, haploid males. Hence, at a proximate level, early switching to male production was caused by queens mating with males that by chance carried the same sex allele. These patterns were not the result of strong inbreeding within the study population, as the average inbreeding coefficient was very low and in fact slightly negative (−0.11). Moreover, an effect of inbreeding was further excluded because hybrids produced by crossing two distinct outbred populations also produced diploid males in early switching colonies. Finally, we found that diploid males only emerged after a first cohort of workers was produced, while we would have expected diploid males to be produced simultaneously with workers in a 50:50 ratio. We demonstrate that adult diploid males had a distinct cuticular hydrocarbon profile and propose that queens likely cull diploid males during early colony development to reduce the cost of diploid male production.

Bee populations are facing numerous stressors globally, including environmental pollution by trace metals and metalloids. Understanding whether bees can detect and avoid these pollutants in their food is pivotal, as avoidance abilities may mitigate their exposure to xenobiotics. While these pollutants are known to induce sublethal effects in bees, such as disrupting physiological mechanisms, their potential impacts on locomotive abilities, fat metabolism, and reproductive physiology remain poorly understood. In this study, utilising workers of the buff-tailed bumble bee and two prevalent trace metals, namely cadmium and copper, we aimed to address these knowledge gaps for field-realistic concentrations. Our findings reveal that workers did not reject field-realistic concentrations of cadmium and copper in sucrose solutions. Moreover, they did not reject lethal concentrations of cadmium, although they rejected lethal concentrations of copper. Additionally, we observed no significant effects of field-realistic concentrations of these metals on the walking and flying activities of workers, nor on their fat metabolism and reproductive physiology. Overall, our results suggest that bumble bees may not avoid cadmium and copper at environmental concentrations, but ingestion of these metals in natural settings may not adversely affect locomotive abilities, fat metabolism, or reproductive physiology. However, given the conservative nature of our study, we still recommend future research to employ higher concentrations over longer durations to mimic conditions in heavily polluted areas (i.e., mine surrounding). Furthermore, investigations should ascertain whether field-realistic concentrations of metals exert no impact on bee larvae., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Bumblebees are crucial pollinators, providing essential ecosystem services and global food production. The success of pollination services relies on the interaction between sensory organs and the environment. The antenna functions as a versatile multi-sensory organ, pivotal in mediating chemosensory/olfactory information, and governs adaptive responses to environmental changes. Despite an increasing number of RNA-sequencing studies on insect antenna, comprehensive antennal transcriptome studies at the different life stages were not elucidated systematically. Here, we quantified the expression profile and dynamics of coding/microRNA genes of larval head and antennal tissues from early- and late-stage pupa to the adult of Bombus terrestris as suitable model organism among pollinators. We further performed Pearson correlation analyses on the gene expression profiles of the antennal transcriptome from larval head tissue to adult stages, exploring both positive and negative expression trends. The positively correlated coding genes were primarily enriched in sensory perception of chemical stimuli, ion transport, transmembrane transport processes and olfactory receptor activity. Negatively correlated genes were mainly enriched in organic substance biosynthesis and regulatory mechanisms underlying larval body patterning and the formation of juvenile antennal structures. As post-transcriptional regulators, miR-1000-5p, miR-13b-3p, miR-263-5p and miR-252-5p showed positive correlations, whereas miR-315-5p, miR-92b-3p, miR-137-3p, miR-11-3p and miR-10-3p exhibited negative correlations in antennal tissue. Notably, based on the inverse expression relationship, positively and negatively correlated microRNA (miRNA)-mRNA target pairs revealed that differentially expressed miRNAs predictively targeted genes involved in antennal development, shaping antennal structures and regulating antenna-specific functions. Our data serve as a foundation for understanding stage-specific antennal transcriptomes and large-scale comparative analysis of transcriptomes in different insects., (© 2024 The Authors. Insect Molecular Biology published by John Wiley & Sons Ltd on behalf of Royal Entomological Society.)

Cross-species transmission of a pathogen from a reservoir to a recipient host species, spillover, can have major impacts on biodiversity, domestic species and human health. Deformed wing virus (DWV) is a panzootic RNA virus in honeybees that is causal in their elevated colony losses, and several correlative field studies have suggested spillover of DWV from managed honeybees to wild bee species such as bumblebees. Yet unequivocal demonstration of DWV spillover is lacking, while spillback, the transmission of DWV from a recipient back to the reservoir host, is rarely considered. Here, we show in fully crossed laboratory experiments that the transmission of DWV (genotype A) from honeybees to bumblebees occurs readily, yet we neither detected viral transmission from bumblebees to honeybees nor onward transmission from experimentally infected to uninoculated bumblebees. Our results support the potential for viral spillover from honeybees to other bee species in the field when robbing resources from heterospecific nests or when visiting the same flowers. They also underscore the importance of studies on the virulence of DWV in wild bee species so as to evaluate viral impact on individual and population fitness as well as viral adaption to new host species. [ABSTRACT FROM AUTHOR]

The bumblebee Bombus terrestris L. (Hymenoptera: Apidae) is an effective pollinator of both wild and cultivated plants and essential for the pollination of various important greenhouse crops. Because of its sex determination mechanism, homozygosity of the complementary sex determination (csd) locus due to inbreeding causes fertilized eggs to develop into diploid males, which represent a serious disadvantage for the colonies as their presence decreases colony growth and survival. The identification of diploid males is thus important from both ecological and economic points of view. In the present study, we applied the geometric morphometrics method on wing shape and size of B. terrestris diploid and haploid males at overall and intra‐colony levels to investigate wing changes between the two groups. We found that changes in wing shape concerned almost all cells investigated and male diploidy resulted in a narrower and slightly longer configuration. In addition, diploid male wings presented a very high variation both in size and shape, likely due to sub‐optimal temperature of incubation and food availability during their larval development. This strong variation of diploid male wings makes the ploidy discrimination by wing geometric morphometrics inaccurate based on small reference samples at the intra‐colony level even with allometric data correction, whereas it is accurate (precision >90%) at the overall level, in which sample size is high enough (i.e., 500 individuals). Therefore, our results indicated the need to create a large dataset to allow the analysis of few samples, as is the case with studies of wild bumblebee populations, small rearing companies, or preserved museum specimens. For this reason, we provide a large database of B. terrestris wing Procrustes coordinates (500 samples) to the bumblebee scientific community for use in the analysis of the determination of diploid male individuals. [ABSTRACT FROM AUTHOR]

Gray mold caused by Botrytis cinerea is a common postharvest disease in strawberries, reducing shelf life considerably. We investigated the potential of the yeast-like biocontrol fungus Aureobasidium pullulans (AP-SLU6) vectored by bumblebees (Bombus terrestris) in the Flying Doctors® system to inhibit the pathogen and increase the shelf life of harvested strawberries (cultivar Sonata). Using bumblebees as vectors of various biocontrol agents is becoming increasingly popular, but any potentially negative effects on bee performance have been understudied. Our results show that, over the 4-week period of the trial, the performance and activity of the bees were not negatively affected by A. pullulans. The bees successfully picked up the powder formulation; then, they carried and deposited it on the flowers. The vectoring of the biocontrol agent significantly reduced gray mold development on the harvested fruits by 45% and increased shelf life by 100% in comparison with control treatments. This suggests that the biocontrol fungus applied during flowering successfully reduced Botrytis infection and thus, effectively protected the fruits from gray mold. In addition, the bee-vectored application of the biocontrol agent was found to be significantly more effective than spray application because the latter may temporarily increase humidity around the flower, thereby creating a suitable environment for the pathogen to thrive. In summary, our study demonstrates that A. pullulans vectored by bumblebees can decrease gray mold infection and improve the shelf life of strawberries without adversely affecting the bees, thus providing a basis for the sustainable and efficient control of gray mold on strawberry. [ABSTRACT FROM AUTHOR]

Environmental changes threaten insect pollinators, creating risks for agriculture and ecosystem stability. Despite their importance, we know little about how wild insects respond to environmental pressures. To understand the genomic bases of adaptation in an ecologically important pollinator, we analyzed genomes of Bombus terrestris bumblebees collected across Great Britain. We reveal extensive genetic diversity within this population, and strong signatures of recent adaptation throughout the genome affecting key processes including neurobiology and wing development. We also discover unusual features of the genome, including a region containing 53 genes that lacks genetic diversity in many bee species, and a horizontal gene transfer from a Wolbachia bacteria. Overall, the genetic diversity we observe and how it is distributed throughout the genome and the population should support the resilience of this important pollinator species to ongoing and future selective pressures. Applying our approach to more species should help understand how they can differ in their adaptive potential, and to develop conservation strategies for those most at risk. [ABSTRACT FROM AUTHOR]

Identifying which behavioural strategies maximize individual fitness is a key objective in ecology. Organisms are known to adapt their foraging behaviour to their environment in response to abiotic and biotic constraints, such as the distribution of resources or the presence of competitors. For instance, bees are known to avoid recently visited flowers and thus focus their foraging on more rewarding patches. Whether other flower‐visiting insects adapt their foraging behaviour in response to exploitative competition for floral resources remains unknown. Here, we asked if a predatory hoverfly Episyrphus balteatus and a parasitoid Aphidius colemani 1) are physiologically impacted by flower resource limitation following exploitation of flowers by a competitor (either the bumblebee Bombus terrestris or E. balteatus); 2) have the ability to discriminate flowers that were previously exploited by a competitor; and 3) modify their foraging behaviour accordingly. Episyrphus balteatus and A. colemani individuals foraging on previously exploited flowers were found to be less concentrated in sugar compounds, especially in fructose and glucose, suggesting that previously exploited flowers contained less available sugars. Nevertheless, individuals did not avoid previously exploited patches in the choice experiment. On the contrary, E. balteatus females preferentially landed on inflorescences that had previously been exploited by conspecifics (but not by B. terrestris), while A. colemani did not show preferences between inflorescences. However, female hoverflies spent more time feeding on unexploited patches, suggesting that exploited patches were resource limited. To our knowledge, this study provides the first evidence of the use of social cues among E. balteatus individuals in food foraging strategies. It also shows that even insects with tiny nectar requirements, such as parasitoids, can suffer from heavy exploitative competition. Such results may have applied consequences for the understanding of natural enemy conservation, in particular in agroecosystems where competition with honeybees may be important. [ABSTRACT FROM AUTHOR]

It is not uncommon for one or a few species, and their interactions, to have disproportionate effects on other species in ecological communities. Such keystone interactions might affect how communities respond to the invasion of non‐native species by preventing or inhibiting the establishment, spread or impact of non‐native species.We explore whether a keystone mutualism among a hummingbird–mistletoe–marsupial promotes ecological resistance to an invasive pollinator, the bumblebee Bombus terrestris, by comparing data collected at sites prior to bumblebee invasion to data collected 11 years after the invasion in sites with and without the keystone mutualism.We built pollination networks and focused on network motifs, regarded as building blocks of networks, to identify the central pollinators and estimate the change in their interactions after invasion of B. terrestris. We also estimated the interaction rewiring across the season in post‐invasion networks and tested it as a possible mechanism explaining how the keystone mutualism increased ecological resistance to invasion.We found two times more species in post‐invasion sites with the keystone mutualism than in post‐invasion sites without the keystone mutualism. Moreover, we found that invasive bumblebee reduced the strength and interaction niche of the five central pollinator species while increasing its own strength and interaction niche, suggesting a replacement of interactions. Also, we found that the keystone mutualism promoted resistance to B. terrestris invasion by reducing its negative impacts on central species. In the presence of the keystone mutualism, central species had three times more direct interactions than in sites without this keystone mutualism. The higher interaction rewiring, after invasion of B. terrestris, in sites with the keystone mutualism indicates greater chances of central pollinators to form new interactions and reduces their competence for resources with the non‐native bumblebee.Our results demonstrate that a keystone mutualism can enhance community resistance against the impacts of a non‐native invasive pollinator by increasing species diversity and promoting interaction rewiring in the community. This study suggests that the conservation of mutualisms, especially those considered keystone, could be essential for long‐term preservation of natural communities under current and future impacts of global change. [ABSTRACT FROM AUTHOR]

Contextualization: lulo is a promising fruit of high demand in the markets due to its excellent organoleptic properties, as well as an important source of vitamins and minerals. Knowledge gap: in the last ten years, multiple investigations have been carried out about the ecophysiology of the lulo plant, without a previous literature review of this. Purpose: collect general aspects of the lulo crop, including the main agronomic requirements and ecophysiological aspects for sustainable production. Methodology: the research was based on a methodical and orderly review of the most relevant studies published in different databases. Results and conclusions: lulo plants grows between 1,900 and 2,200 m. a. s. l. in Colombia with temperatures of 15 to 24 °C. It requires between 1,500 to 2,500 mm of precipitation per year. It appears like a shortday plant, which exhibits its best development in shady places with relative humidity close to 80 %. The most efficient pollination method is carried out by bumblebees (Bombus terrestris and Bombus sp.) through vibrations. The net photosynthesis of the lulo plants varies from 5.52 to 34.03 pmol CO2 m-2 s-1 at 398 and 460 days after transplanting, while the maximum efficiency of photosystem II (FV/Fm) in the lulo crop oscillates between 0.55 and 0.65 for plants without and with foliar nitrogen application. The values of a, b, and total chlorophyll, for lulo plants, are higher in plants in the transplant stage than in production, due to the reduced photosynthetic area. High concentrations of nitrogen (N) (greater than 110 mg L-1) lead to better yield and a larger leaf area. The lulo plant begins its production between eight and 12 months after being transplanted and average yields of 8.5 t ha-1 have been reported. The development and growth of lulo fruits have a simple sigmoid logistic model. The lulo fruits in harvest time can reach up to 209 g, with firmness of 58 N and values of 13,6 °Brix and 56.2, 10.8 and 46.8 for the luminosity (L*), chroma a* and chorma b* color parameters, respectively. [ABSTRACT FROM AUTHOR]

Climate change and increasing average temperatures are now affecting most ecosystems. Social insects such as bumblebees are especially impacted because these changes create spatial, temporal and morphological mismatches that could impede their ability to find food resources and mate. However, few studies have assessed how the colony and life cycle are affected when temperatures rise above optimal rearing temperature. It has become imperative to understand how heat stress affects the life history traits of insect pollinators as well as how changes in life history interact with other traits like morphology. For example, a decrease in the number of foraging workers could be balanced by producing larger workers, able to forage at longer distances and gather more resources. Here, we investigated the impact of temperature on colony production and body size in the bumblebee Bombus terrestris. Colonies were exposed to two temperatures: 25 °C, which is around the optimal temperature for larval development and 33 °C, which is slightly above the set-point that is considered stressful for bumblebees. Although the production of males and workers wasn't significantly affected by these different temperatures, queen production and reproductive investment were much higher for colonies placed in 33 °C than in 25 °C. We also found that, in agreement with the temperature-size rule, workers were significantly smaller in the higher temperature. The decrease in worker body size could affect resource collection and pollination if their foraging distance and the quantity of food they are taking back to the colony decreases. While in our controlled conditions the bumblebees were fed ad libitum, the decrease of resource collection in field conditions could prevent colonies from producing as many queens as in our study. Together with the decrease of worker body size, our results suggest that elevated temperatures could ultimately have a negative impact on bumblebee colony fitness. Indeed, smaller workers are known to have weaker flight performance which could affect foraging performance and consequently colony development. [ABSTRACT FROM AUTHOR]

Bombus terrestris dalmatinus is naturally common in many countries, including Turkey, and is also used commercially for the pollination of greenhouse plants. Intensive commercial production and international trade in many countries are considered as reasons for the disappearance of some natural populations. Hybridization of native bumble bees with those produced commercially, but having escaped from greenhouses and colonization of these commercial bees in natural habitats are cause for concern. In order to assess this concern, B. t. dalmatinus workers were collected from twelve different populations: five commercial producers, three surrounding greenhouse centers, three natural areas at least 30 km away from greenhouses, and one more recent greenhouse zone in Antalya, Turkey. The genetic variations and relationships among the twelve populations were estimated using SNP haplotypes determined in mitochondrial COI and CytB. Twenty and sixteen haplotypes were obtained for COI and CytB, respectively. A single haplotype, H1, was widespread with a high frequency in all individuals for both genes. Individuals collected from around greenhouse centers and commercial companies had more common haplotypes. The genetic variations of intra-populations were higher than the interpopulations in both COI (65.41%>34.59%) and CytB (72.47%>27.53%). The natural and commercial populations were genetically more distant from each other considering Fst values. However, samples from near the greenhouses had a higher similarity with the commercially produced samples, while the natural populations far away from greenhouses still retained their genetic distinctiveness. [ABSTRACT FROM AUTHOR]

A personal narrative is presented which explores the author's experience of Letters from Spain, have encountered a great many species of Hymenoptera since came to live here over twenty years ago.

During buzz pollination, bees use vibrations to remove pollen from flowers. Vibrations at the natural frequency of pollen-carrying stamens are amplified through resonance, resulting in higher amplitude vibrations. Because pollen release depends on vibration amplitude, bees could increase pollen removal by vibrating at the natural frequency of stamens. However, few studies have characterized the natural frequencies of stamens and compared them to the frequencies of buzz-pollinating bees. We use laser Doppler vibrometry to characterize natural frequencies of stamens of six morphologically diverse, buzz-pollinated, heterantherous Solanum taxa and compare the frequency of bumblebee buzzes produced on two Solanum spp. with different natural frequencies. We found that stamen morphology and plant identity explain variation in their natural frequency. The natural frequencies of the stamens in the studied Solanum taxa fell between 45 and 295 Hz; in five out of six taxa the frequencies were < 190 Hz, which only partly overlaps floral vibrations of buzz-pollinating bees. We show that captive bumblebees produce vibrations at a frequency of 345 Hz and do not change their floral vibrations to match the natural frequency of the visited flowers. Our results suggest that pollen release induced by vibrating stamens at their natural frequencies might only play a role in a subset of buzz pollination interactions. [ABSTRACT FROM AUTHOR]

The performance of Bombus terrestris micro-colonies fed five diets differing in pollen species composition and level of nine essential amino acids (EAA; leucine, lysine, valine, arginine, isoleucine, phenylalanine, threonine, histidine, methionine) was assessed for 37 days by recording total biomass gain, nest building initiation, brood production (eggs, small and large larvae, pupae, drones), nectar, and pollen collection. Stronger colony performance was linked to higher amino acid levels but no consistent differences in biomass gain were recorded between mono- and poly-species diets. Poorest performance occurred in micro-colonies offered pure oilseed rape (OSR) pollen which contained the lowest EAA levels. Reduced micro-colony development (delayed nest initiation and lower brood production) was related to OSR proportion in the diet and lower EAA levels. Results are discussed in relation to selection of plant species in the design of habitats to promote bee populations. [ABSTRACT FROM AUTHOR]

Epitranscriptomics is an emerging field of investigation dedicated to the study of post‐transcriptional RNA modifications. RNA methylations regulate RNA metabolism and processing, including changes in response to environmental cues. Although RNA modifications are conserved from bacteria to eukaryotes, there is little evidence of an epitranscriptomic pathway in insects. Here we identified genes related to RNA m6A (N6‐methyladenine) and m5C (5‐methylcytosine) methylation machinery in seven bee genomes (Apis mellifera, Melipona quadrifasciata, Frieseomelitta varia, Eufriesea mexicana, Bombus terrestris, Megachile rotundata and Dufourea novaeangliae). In A. mellifera, we validated the expression of methyltransferase genes and found that the global levels of m6A and m5C measured in the fat body and brain of adult workers differ significantly. Also, m6A levels were differed significantly mainly between the fourth larval instar of queens and workers. Moreover, we found a conserved m5C site in the honeybee 28S rRNA. Taken together, we confirm the existence of epitranscriptomic machinery acting in bees and open avenues for future investigations on RNA epigenetics in a wide spectrum of hymenopteran species. [ABSTRACT FROM AUTHOR]

Wildflower plantings are an important mitigation tool within agri-environmental schemes to counter insect decline in resource-scarce agricultural landscapes. Effectiveness of wildflower plantings for insect conservation is typically studied at the community or species level. It is the individual, however, that is subject to changing abiotic and biotic conditions, not the species per se. Accordingly, functional traits of individuals, i.e., the intraspecific functional diversity within species, likely mediate responses to wildflower resources and landscape context. Here we focused on the ecologically and economically important wild insect pollinator Bombus terrestris to study its intraspecific functional diversity and plant-pollinator individual interactions in wildflower plantings. We found considerable trait variation among flower-visiting B. terrestris workers. Locally, this variation could be attributed to flowering plant traits, with larger workers visiting larger inflorescences and individuals with longer tongues preferentially feeding on zygomorphic but not radially symmetrical flowers. In addition, wildflower plantings with high floral abundance attracted individuals with larger pollen baskets. At the landscape scale, increasing proportion of arable land resulted in smaller B. terrestris individuals in wildflower plantings, and a decrease in the overall size diversity of workers. These findings highlight the so far little considered role of intraspecific variation in functional traits of wild pollinators, which can mediate the trait-matching between plants and pollinator individuals. Landscape simplification from agriculture threatens intraspecific pollinator diversity, with potential harmful effects for pollinator fitness and plant reproduction. Tailored wildflower plantings can thus serve as an important tool to increase intraspecific variation in simplified landscapes. When designing seed mixtures for these plantings, high complementarity in plant traits is key for promoting high intraspecific trait diversity of bumblebees and potentially of other associated insect species. [ABSTRACT FROM AUTHOR]

Given that pollinators usually visit flowers for hidden rewards, they need to rely on floral traits that indicate reward status ("honest signals"). However, the relationship between pollination, honest signals, and floral rewards is little documented in natural conditions. The Scotch broom (Cytisus scoparius) is an invasive shrub with polymorphism in the color of its flowers that can be yellow, orange, or red. In three areas dominated by the Scotch broom, we described the abundance of the floral morphs and estimated bumblebee (Bombus terrestris) visitation rate. We examined whether bumblebee visitation to the floral morphs was related to pollen reward. We collected flowers and classified their stamens according to their function: reward or pollen export. Then, we measured anther size and estimated pollen quantity. The yellow morph was more abundant and more visited by bumblebees than the orange and red morphs. The yellow flowers did indeed offer more pollen than the other morphs and this occurred only for rewarding anthers, suggesting that bumblebees could use yellow color as an honest signal to visit the most rewarding flowers. We discuss whether innate and/or learned preferences of bumblebees can explain why the yellow morph is more visited, pollinated, and abundant, while the other morphs are maintained at a lower frequency. This is one of the few field works that shows that variation in intra-specific floral traits is associated with variation in floral reward and pollinator visitation rate, helping to understand the foraging preferences of pollinators and the coexistence of floral morphs in nature. Clinical trials registration: Not applicable. [ABSTRACT FROM AUTHOR]

In bumble bee colonies, pollen is the only protein source for larval feeding and its shortage causes a distress in larval development. Adult bumble bees need pollen for the development of glands and the reproductive system. In bumble bee rearing, honey bee collected pollen is used as the main protein source, either as fresh-frozen or dried pellets, and pollen provisioning is the most problematic and expensive aspect of mass rearing. In honey bee breeding, pollen substitutes are used during the period of food shortage or to stimulate colony strength. We tested different protein diets (five commercial pollen substitutes and two natural protein sources) for the maintenance of bumble bee colonies in captivity. We further mixed Feedbee®, one of the substitutes that gave the best results, with different amounts of pollen to evaluate the optimal amount needed for the whole colony development. Although none of the pure protein diets alone were adequate, diets with a 1 to 1 and 1 to 3 ratio of Feedbee to pollen were both suitable for colony development and queen production. The colony consumed between 2 and 4 g per day of the Feedbee mixed diets, corresponding to a protein consumption of 0.75–0.85 g day−1. Nevertheless, the consumption rate of the pure pollen showed that a mean amount of protein between 0.4 and 0.5 g day−1 was enough to allow colony development indicating the suitability of Feedbee mixed diets.

Abstract Co‐occurrence of closely related species is often explained through resource partitioning, where key morphological or life‐history traits evolve under strong divergent selection. In bumble bees (genus Bombus), differences in tongue lengths, nest sites, and several life‐history traits are the principal factors in resource partitioning. However, the buff‐tailed and white‐tailed bumble bee (Bombus terrestris and B. lucorum respectively) are very similar in morphology and life history, but their ranges nevertheless partly overlap, raising the question how they are ecologically divergent. What little is known about the environmental factors determining their distributions stems from studies in Central and Western Europe, but even less information is available about their distributions in Eastern Europe, where different subspecies occur. Here, we aimed to disentangle the broad habitat requirements and associated distributions of these species in Romania and Bulgaria. First, we genetically identified sampled individuals from many sites across the study area. We then not only computed species distributions based on presence‐only data, but also expanded on these models using relative abundance data. We found that B. terrestris is a more generalist species than previously thought, but that B. lucorum is restricted to forested areas with colder and wetter climates, which in our study area are primarily found at higher elevations. Both vegetation parameters such as annual mean Leaf Area Index and canopy height, as well as climatic conditions, were important in explaining their distributions. Although our models based on presence‐only data suggest a large overlap in their respective distributions, results on their relative abundance suggest that the two species replace one another across an environmental gradient correlated to elevation. The inclusion of abundance enhances our understanding of the distribution of these species, supporting the emerging recognition of the importance of abundance data in species distribution modeling.

The study investigated the potential impact of the insecticide chlorantraniliprole (Coragen® brand) on the bumble bee (Bombus terrestris L.) under semi-field conditions in Phacelia tanacetifolia in Germany based on ringtest protocols from the ICPPR Non-Apis workshops (2016 and 2017). The P. tanacetifolia crop was grown in soil treated with the predicted 20-year plateau concentration of chlorantraniliprole in the top 20 cm of soil (equivalent to a predicted 20-year plateau concentration of 0.088 mg a.s./kg). Additionally, two chlorantraniliprole applications at 60 g a.s./ha were made in the chlorantraniliprole treatments (T1 and T2). In T1 both applications took place before P. tanacetifolia flowering at BBCH 51-55 and BBCH 55-59. In T2 one application was conducted before P. tanacetifolia flowering at BBCH 55-59 and one application during P. tanacetifolia flowering and during daily bee flight at BBCH 61-62. The application in the control (C) and reference item treatment (R) (400 g dimethoate a.s./ha) was carried out during full P. tanacetifolia flowering and bumble bee flight. The bumble bee colonies were exposed to the treated flowering P. tanacetifolia crop for 20 days in the tunnels and afterwards the colonies were kept on a monitoring site. The results of this study indicate no significant differences between the chlorantraniliprole treatment groups T1 and T2 and the control regarding all parameters assessed (i.e. mortality in the colonies and in the tunnels, flight activity at the hive entrance, hive weight development, condition of the colonies and production of young queens and males). Overall, no effects of chlorantraniliprole on bumble bee B. terrestris colonies including queen/male production, adult and larval survival and forager flight activity were found.

Bumblebees (Bombus terrestris) are exposed daily to Plant Protection Products through their foraging and feeding activities. Through all possible means of contact with pesticides, consumption through sugarwater is the most severe. In the present study, lethal and sublethal effects of the consumption of sugarwater solutions with the pesticides Sivanto WG (flupyradifuron), Exalt SC (spinetoram) and Oikos EC (azadirachtin) were studied using a sequential dilution testing scheme of 1/1 and 1/10 of the maximum field recommended concentration (MFRC). For the weekly assessment, parameters such as the survival of the mother queen, of workers and drones, the formation of gynes, and the weight and volume of the colonies were recorded. Moreover, by the end of the colony’s life, the total number of formed workers/drones, the number of newborn gynes and queen brood were also recorded. The IOBC side-effect classes for laboratory trials were applied in order for the results to be categorized and conclusions made. Both tested concentrations of Sivanto WG (flupyradifuron) were slightly harmful for queen, worker and drone populations, Exalt SC (spinetoram) was harmful at 1/1 dilution but only slightly harmful at the 1/10 dilution, and both concentrations of Oikos EC (azadirachtin) were slightly harmful for workers and drones but toxic for queens at both dilutions

Bacillus thuringiensis subsp. aizawai, a widely used biological plant protection product, was tested on buff-tailed bumblebee Bombus terrestris, using an updated laboratory method on full standardized R&D colonies. The maximum field recommended concentration (MFRC) was applied through topical, oral pollen and oral sugar water treatment. Parameters such as survival of the mother queen and workers, formation of gynes, weight and volume of the colonies were recorded during the study, while the total number of formed workers/drones, the number of newborn gynes and queen brood were taken also at the end of the colonies’ life. For the evaluation of the results the data were calculated and categorized according to the IOBC side-effect classes, used for laboratory trials. According to the results, no toxic effect was recorded for all parameters taken from the bumblebee colonies when they were exposed to B. thuringiensis aizawai GC91.

Heatwaves are increasingly common globally and are known to have detrimental impacts on animal morphology and behaviour. These impacts can be severe, especially if heatwaves occur during development, even on animals that can regulate the temperature of their developing young. The onset and duration of heatwaves are stochastic and therefore may affect all or only part of development. In the heterothermic bumblebee Bombus terrestris, elevated temperatures over the entirety of development cause morphological changes in adults, despite their capability to regulate brood temperature. However, the effects of heatwaves that occur during a short period of development are unclear. We test the impact of elevated developmental temperature during the latter fraction of development on the behaviour and morphology of adult worker B. terrestris. We show that exposure to elevated temperature over a portion of late development is sufficient to impair the initial behavioural responses of workers to various sensory stimuli. Despite this, exposure to elevated temperatures during a period of development did not have any significant impact on body or organ size. The negative effect of elevated developmental temperatures was independent of the exposure time, which lasted from 11–20 days at the end of the workers’ developmental period. Thus, heat stress in bumblebees can manifest without morphological indicators and impair critical behavioural responses to relevant sensory stimuli, even if only present for a short period of time at the end of development. This has important implications for our understanding of deleterious climactic events and how we measure indicators of stress in pollinators.

Strawberries are popular fruits around the world, and their yield and fruit quality rely on pollination by honey bees and bumblebee colonies. Both bee species have their own advantages in strawberry pollination. This study investigates the characteristic of strawberry (Fragaria × ananassa ‘Red Face’) flower volatiles and their effects on bee pollinators by (1) detecting the volatile compounds of strawberry flowers by polydimethylsiloxane (PDMS) combined gas chromatography-mass spectrometry (GC-MS), (2) determining whether Bombus terrestris or Apis mellifera showed antennae responses to certain compounds of strawberry flower volatiles by an electroantennography test (EAG), and (3) testing whether these compounds could elicit a corresponding behavioral response in bees. The results showed that (1) there were 38 chemical compounds in ‘Red Face’ volatiles with 7 types, most of which were known to be generally emitted by flowers but also have some compounds that have not been reported in strawberry flowers; (2) B. terrestris and A. mellifera had strong EAG responses to several compounds, respectively, especially to ethyl benzoate, (Z)-3-hexenyl propionate, (Z)-3-hexenyl acetate, benzeneacetaldehyde and melonal; and (3) both bee species showed significant avoidance behaviors to four tested compounds, especially the B. terrestris. Flower volatiles of strawberry ‘Red face’ were different from other strawberry varieties that have been reported; some of these electrophysiologically active compounds could cause antennal potential responses in bees, as well as behavioral responses. Our study supports the idea that strawberry flower volatiles are one of the factors influencing bee foraging decisions and provides a reference for formulating more reasonable bee pollination to improve strawberry fruit quality.

Sulfoximines, the next generation systemic insecticides developed to replace neonicotinoids, have been shown to negatively impact pollinator development and reproduction. However, field-realistic studies on sulfoximines are few and consequences on pollination services unexplored. Moreover, the impacts of other agrochemicals such as fungicides, and their combined effects with insecticides remain poorly investigated. Here, we show in a full factorial semi-field experiment that spray applications of both the product Closer containing the insecticide sulfoxaflor and the product Amistar containing the fungicide azoxystrobin, negatively affected the individual foraging performance of bumblebees (Bombus terrestris). Insecticide exposure further reduced colony growth and size whereas fungicide exposure decreased pollen deposition. We found indications for resource limitation that might have exacerbated pesticide effects on bumblebee colonies. Our work demonstrates that field-realistic exposure to sulfoxaflor can adversely impact bumblebees and that applications before bloom may be insufficient as a mitigation measure to prevent its negative impacts on pollinators. Moreover, fungicide use during bloom could reduce bumblebee foraging performance and pollination services.

Global climate change disrupts key ecological processes and biotic interactions. The recent increase in heatwave frequency and severity prompts the evaluation of physiological processes that ensure the maintenance of vital ecosystem services such as pollination. We used experimental heatwaves to determine how high temperatures affect the bumblebees' ability to detect floral scents. Heatwaves induced strong reductions in antennal responses to floral scents in both tested bumblebee species ( Bombus terrestris and Bombus pascuorum ). These reductions were generally stronger in workers than in males. Bumblebees showed no consistent pattern of recovery 24 h after heat events. Our results suggest that the projected increased frequency and severity of heatwaves may jeopardize bumblebee-mediated pollination services by disrupting the chemical communication between plants and pollinators. The reduced chemosensitivity can decrease the bumblebees' abilities to locate food sources and lead to declines in colonies and populations.

The interaction between bees and flowering plants is mediated by floral cues that enable bees to find foraging plants. We tested floral cue preferences among three common wild bee species: Lasioglossum villosulum , Osmia bicornis , and Bombus terrestris . Preferences are well studied in eusocial bees but almost unknown in solitary or non-eusocial generalist bee species. Using standardized artificial flowers altered in single cues, we tested preferences for color hue, achromatic contrast, scent complexity, corolla size, and flower depth. We found common attractive cues among all tested bees. Intensively colored flowers and large floral displays were highly attractive. No preferences were observed in scent complexity experiments, and the number of volatiles did not influence the behavior of bees. Differing preferences were found for color hue. The specific behaviors were probably influenced by foraging experience and depended on the flower choice preferences of the tested bee species. In experiments testing different flower depths of reward presentation, the bees chose flat flowers that afforded low energy costs. The results reveal that generalist wild bee species other than well-studied honeybees and bumblebees show strong preferences for distinct floral cues to find potential host plants. The diverse preferences of wild bees ensure the pollination of various flowering plants.

Bumblebees are important pollinators in agricultural ecosystems, but their abundance is declining globally. There is an urgent need to protect bumblebee health and their pollination services. Bumblebees possess specialized gut microbiota with potential to be used as probiotics to help defend at-risk bumblebee populations. However, evidence for probiotic benefits on bumblebees is lacking. Here, we evaluated how supplementation with Lactobacillus melliventris isolated from bumblebee gut affected the colony development of Bombus terrestris. This native strain colonized robustly and persisted long-term in bumblebees, leading to a significantly higher quality of offspring. Subsequently, the tyrosine pathway was upregulated in the brain and fat body, while the Wnt and mTOR pathways of the gut were downregulated. Notably, the field experiment in the greenhouse revealed the supplementation of L. melliventris led to a 2.5-fold increase in the bumblebee survival rate and a more than 10% increase in the number of flowers visited, indicating a better health condition and pollination ability in field conditions. Our study represents a first screening for the potential use of the native gut member, L. melliventris, as probiotic strains in hive supplement for bumblebee breeding, which may be a practical approach to improve immunity and hive health., (© 2023 Institute of Zoology, Chinese Academy of Sciences.)