Floral Resources Research Articles

Aspects of the reproductive biology of sympatric Myrtaceae: <i>Myrceugenia euosma</i> and <i>Siphoneugena reitzii</i> in southern Brazil

Background: The Myrtaceae family represents one of the most diverse groups in South America. Yet, there are few studies on their reproductive characteristics. Among the species with limited information on their reproductive behavior are Myrceugenia euosma (O. Berg) D. Legrand and Siphoneugena reitzii D. Legrand. Questions: What are the floral attractions and resources of M. euosma and S. reitzii for pollinators? Who are the pollinators of these species? What is the predominant reproductive system in both species? Studied species: M. euosma and S. reitzii, two sympatric Myrtaceae from southern Brazil. Study site and dates: Urubici, Painel, and Rio Rufino, Santa Catarina state, southern Brazil. November 2021 - February 2022. Methods: Information was obtained on morphological aspects, anthesis time, stigmatic viability, floral resources, structures attractive to visitors, olfactory testing, observation and identification of floral visitors, and reproductive system testing. Results: The flowers of M. euosma opens between 11 am and 17 pm (- 20 pm), with full opening occurring mostly at night; S. reitzii flowers open between 4 a.m. and 6 a.m., with a highest peak by 8 a.m. Flowers of both species have receptive stigmas until senescence. Pollen is the primary floral reward and the scent coming from the anthers combined with the floral display attract native bees and Apis mellifera, legitimate pollinators of both species. The lack of fruit development in the self-pollination tests support cross reproduction in both taxa. Conclusions: Both species exhibit traits consistent with melittophily syndrome and potential self-incompatibility. These results are essential for conservation efforts.

Honey bees and bumble bees react differently to nitrogen-induced increases in floral resources

Honey bees and bumble bees react differently to nitrogen-induced increases in floral resources

Nutritional position of managed honey bees during pollination of native plants by the melissopalynology method

Pollination services are crucial for maintaining ecological stability and ensuring food security for humans. Managed honey bees, which are economically valuable and are experiencing population growth due to the increasing demand for their products, play a significant role in pollination. To produce high-quality honey, beekeepers often choose natural high meadows, characterized by high plant species richness, for their apiaries. This practice, in turn, may contribute to the pollination of native plants, as managed honey bees are likely to forage on diverse floral resources within these meadows In this study, we investigated the nutritional position of managed bees in the pollination of native plants in Iran using the melissopalynology method to determine the extent of their contribution to the pollination of native plants. Ninety-four honey samples were collected from beekeepers located in the natural pastures of two biodiversity hotspots in Iran (Zagros and Alborz). Then, plant pollens were extracted from the honey and photographed by scanning electron microscopy. In the next step, plant species were identified, and their abundance was calculated. The results showed that managed bees visited 54 plant genera, seven of which were non-native plants. Additionally, more plant species and the highest abundance of pollen were observed at altitudes ranging from 1000 to 3000 m. Therefore, beekeepers set up their hives in this altitude range to obtain high-quality honey. In general, in this study, the results of melissopalynological analysis, involving the identification of plant genera and pollen counts, revealed that managed honey bees likely contributed less than 3% to the pollination of native plant species in Iran.

Stable pollinator communities in different white clover populations suggest potential win-win scenarios for crop yield and biodiversity

Compared to monocultures, intercropping systems offer many agronomic benefits, including higher yield stability. In this study, we assessed whether cropping systems that are beneficial for yield stability are also beneficial for pollinator communities and whether the effect is modulated by the landscape type. Using a replicated block design in one heterogeneous and one homogeneous agricultural landscape, we studied the pollinator communities in eight populations (i.e., genotypes) of white clover (Trifolium repens) grown as a monoculture or as a two-species mixture (together with perennial ryegrass, Lolium perenne) or three-species mixture (together with perennial ryegrass and chicory, Cichorium intybus). We recorded 1486 honey bees and 1254 wild pollinators belonging to 46 species. Bumble bees were the most abundant wild pollinators (49.6 %), followed by hover flies (23.4 %), and non-Bombus wild bees (21.5 %). Lepidoptera accounted for only 5.4 % of the wild pollinators. We found a higher species richness and abundance of wild pollinators in monocultures than in two-species mixtures, but white clover population did not influence pollinators. Moreover, species richness and abundance were also higher in the homogeneous landscape than in the heterogenous one. Most species were foraging on white clover. However, 18 species (39.1 %, n = 18/46) were recorded foraging on chicory and/or weeds, and ten of these wild pollinator species were never recorded on white clover. Our study highlights that diverse pollinator communities require both abundant floral resources and diverse plant communities, that their needs are not in conflict with the goal of achieving yield stability, and that the landscape type can modulate the effect of the cropping system. Moreover, the lack of pollinator preference for different white clover populations suggests that farmers can select mixtures that enhance yield stability without negatively affecting pollinator communities. Overall, these results highlight that intercropping systems comprising several plant species and plant genotypes can guarantee yield stability without compromising the pollinator community, showing that win-win situations for farmers and biodiversity are possible.

Thermal biology diversity of bee pollinators: Taxonomic, phylogenetic, and plant community‐level correlates

AbstractCommunity‐wide assembly of plant–pollinator systems depends on an intricate combination of biotic and abiotic factors, including heterogeneity among pollinators in thermal biology and responses to abiotic factors. Studies on the thermal biology of pollinators have mostly considered only one or a few species of plants or pollinators at a time, and the possible driving role of the diversity in thermal biology of pollinator asemblages at the plant community level remains largely unexplored. More specifically, it is unknown whether diversity in the thermal biology of bees, a major pollinator group worldwide, contributes to the assembly and maintenance of diverse bee communities; broadens the spectrum of possibilities available to bee‐pollinated plants; facilitates interspecific partitioning of ecological gradients across habitats, seasons, and time of day; and/or enhance plant pollination success through complementarity effects. The objectives of this study were to assess the diversity in thermal biology of the bee assemblage that pollinates plants in a Mediterranean montane area, evaluate its taxonomic and phylogenetic underpinnings, and elucidate whether there existed seasonal, daily, between‐habitat, or floral visitation correlates of bee thermal biology which could contribute to partition ecological gradients among plant and bee species. Thermal biology parameters were obtained in the laboratory (K, intrinsic warming constant) and the field (thoracic and ambient temperature at foraging site, Tth and Tair) on individual bees of a diverse sample (N = 204 bee species) comprising most bee pollinators of the regional plant community. Species‐specific thermal biology parameters were combined with quantitative field data on bee pollinators and flower visitation for the regional community of entomophilous plants (N = 292 plant species). Results revealed that the regional bee assemblage harbored considerable diversity in thermal biology features; that such diversity was mostly taxonomically, phylogenetically, and body‐size structured; and that the broad interspecific heterogeneity in thermal biology represented in the bee community as a whole eventually translated into daily, seasonal, among‐habitat, and flower visitation patterns at the plant community level. This lends support to the hypothesis that broad diversity in thermal biology of bees can enhance opportunities for bee coexistence, spatiotemporal partitioning of floral resources, and plant pollination success.

Floral resource availability declines and florivory increases along an elevation gradient in a highly biodiverse community.

Flower-visitor interactions comprise a continuum of behaviors, from mutualistic partners to antagonistic visitors. Despite being relatively frequent in natural communities, florivory remains unexplored, especially when comprising abiotic factors, spatio-temporal variations and global environmental changes. Here, we addressed the variation of florivory driven by changes in elevation and temporal flower availability. We expect decreased floral resources as elevation increases -due to environmental constraints- which may affect plant-florivore interactions. Yet, if floral resources decrease but florivores remain constant, then we may expect an increase in florivory with increasing elevation in the community. The flowering phenology of plant individuals was recorded in the Neotropical campo rupestre vegetation, in southeastern Brazil. Damages by florivores were recorded in plots at elevations ranging from 823 to 1411 m using two response variables as a proxy for florivory: the proportion of attacked flowers per plant and the proportion of petal removal on single flowers. Flower attack increased with elevation and damages were intensified in species with longer flowering periods. Conversely, longer flowering periods resulted in higher levels of petal removal when decreasing elevation. The temporal availability of flowers affected florivory, with the proportion of attacked flowers being more intense when there are less flowered individuals in the community. Petal removal on single flowers was intensified in plots with a larger number of individuals flowering, and with more species co-flowering. This study brings one of the broadest records of a commonly neglected interaction of insects feeding on floral structures, quantifying the combined effect of floral display and availability along an elevation gradient in a highly biodiverse mountaintop community. These findings contribute to filling in the gap in the understanding of florivory dynamics, focusing on a tropical mountaintop scenario facing imminent environmental changes and excessive natural resource exploitation.

Revisiting ant-plant-pollinator interactions: plant fitness depends on mutualist identity

Abstract Two species may share a mutualistic interaction if the benefits gained by the interaction outweigh the costs incurred. In this study, we tested experimentally how the identity of ants (pinned) and floral visitors of an extrafloral nectary (EFN)-bearing plant can affect plant fitness. We quantified ant activity and floral visitor visitation overlap over time, floral visitor behaviour, amount of floral resources collected, and plant fitness as influenced by the ant species identity in an EFN-bearing plant from Brazilian Cerrado savanna, Qualea multiflora (Vochysiaceae). We found that: (i) ant activity and floral visitation overlap greatly in time; (ii) floral visitors vary in their response to the presence of ants; (iii) different ant species have different impacts on floral visitors; (iv) ants affected the amount of floral resources collected by pollinators, but their levels were contingent on ant identity; and (v) plant fitness components (fruit production, seed weight, and seed size) were most strongly affected by the largest and most aggressive ant species. Our results suggest that the balance of the trade-off between the beneficial effects of ant protection against herbivorous insects and the negative consequences for plant fitness by deterring pollinators depends on the species identity of both the ants and the floral visitors to the plant.

Pre-extension Demonstration and Evaluation of Top Feeder Honeybee Feeding Technology at Wolmera Woreda, Oromia Region

To maintain optimum honeybee colony population during dearth of floral resources, feeding of honeybee colonies with supplementary feeds is important. This research activity is conducted with the main objectives to evaluate and demonstrate top feeder technology under farmers’ management and create awareness on the importance of the technology. As to the method, selection of demonstration sites and farmers was purposive due to the reason that the evaluation of the technology requires modern box hive and experience on this hive. Two demonstration sites at two Village Administrations selected and Farmers research groups were used for technology evaluation. One FRG which contain 10-15 beekeepers strengthened at each demonstration site and group apiaries of FRG members used as centers of learning and technology evaluation. At each sites, farmers, development agents and experts trained and experimental colonies established. Honeybee colony follow up and technology evaluation activities undertaken in partnership with these FRG members, development agents and experts. As to the result, by using top feeder, the beekeeper can feed many colonies in short period of time. The average time taken to feed one honeybee colony using top feeder was only 55.85 seconds where as it was 107.26 seconds using plastic bucket under farmer’s management. Moreover, feeding using top feeder also reduced honeybee colonies disturbance during time of feeding. In conclusion, technologies like top feeder that saves beekeepers time and also reduce disturbances of honeybee colony are critical for our beekeepers. Therefore, it is suggested to further pre scale up the technology in other areas

Assessing pollinator abundance and services to enhance agricultural sustainability and crop yield optimization in the Qilian Mountains

ContextPollination services are critical to crop production and human livelihoods, linking natural ecosystems directly to agricultural production systems. However, pollination services and pollinators are under constant threat from land-use changes and various other environmental pressures. ObjectiveIn this study, employing a case study of the entire Qilian Mountains in northwest China, the distribution of nectar sources in different land use types in the study area was determined through field survey and literature. MethodsBased on 1990–2020 land use data, crop yield data, crop prices, pollinating bee species and nectar plants data. We used the Gross Ecological Product (GEP) accounting and InVEST model of pollination services and assessed the status and trends of pollination services, the risks posed by land use changes and environmental pressures, and suggested potential solutions for mitigating identified risks. Results and conclusionsThe results of the study showed that (1) nectar sources and nesting areas' potential distribution closely correlates with land use types; (2) the Pollinator abundance index (PAI) is above 0.30, a high level, and the Pollination potential index (PPI) is between 0.15 and 0.30, a medium level, with both indices generally increasing over the past 40 years; (3) Human economic activities and land management policies had the most significant impact on pollination services, with 15.57 % and 14.02 %, respectively. Climate change (temperature, precipitation, extreme events) and invasive alien species had relatively minor impacts, accounting for 0.14 % and 0.15 %, respectively. (4) The Qilian Mountains will face a new risk, whether monoculture or the expansion of pollinator-dependent crops could lead to habitat homogenization issues, potentially affecting pollinator abundance and diversity. SignificanceWe recommend that future plans emphasize the provision of pollinator nesting resources along with floral resources, restoration of semi-natural and natural habitats adjacent to crops, adjustment of cropping patterns, and implementation of agricultural diversification, which will help to ensure pollinator diversity and sustainability of agroecosystem pollination services.

Spatial Modeling of Insect Pollination Services in Fragmented Landscapes.

Pollination mapping and modeling have opened new avenues for comprehending the intricate interactions between pollinators, their habitats, and the plants they pollinate. While the Lonsdorf model has been extensively employed in pollination mapping within previous studies, its conceptualization of bee movement in agricultural landscapes presents notable limitations. Consequently, a gap exists in exploring the effects of forest fragmentation on pollination once these constraints are addressed. In this study, our objective is to model pollination dynamics in fragmented forest landscapes using a modified version of the Lonsdorf model, which operates as a distance-based model. Initially, we generated several simulated agricultural landscapes, incorporating forested and agricultural habitats with varying forest proportions ranging from 10% to 50%, along with a range of fragmentation degrees from low to high. Subsequently, employing the modified Lonsdorf model, we evaluated the nesting suitability and consequent pollination supply capacity across these diverse scenarios. We found that as the degree of forest fragmentation increases, resulting in smaller and more isolated patches with less aggregation, the pollination services within landscapes tend to become enhanced. In conclusion, our research suggests that landscapes exhibiting fragmented forest patch patterns generally display greater nesting suitability due to increased floral resources in their vicinity. These findings highlight the importance of employing varied models for pollination mapping, as modifications to the Lonsdorf model yield distinct outcomes compared to studies using the original version.

Tracking Existing Factors Directly Affecting the Reproduction of Bumblebees: Current Knowledge.

Bumblebees are primary social insects and a vital class of pollinating insects. Their distinctive reproductive mode is characterized by the independent initiation and construction of the nest by the queen and the subsequent production of sufficient workers, males, and gynes following colony development. After successful mating, the queen transitions to the first phase of its annual life cycle. The reproductive processes are directly influenced by environmental factors, including floral resources and pesticides. Moreover, the reproductive level is regulated by biological factors, particularly the role of workers, who participate in egg laying and pass on their genetic material to the next generation of queens. Successful reproduction can only be achieved by maintaining colony development under natural or artificial breeding conditions. Consequently, understanding the known factors that influence bumblebee reproduction is essential for developing conservation strategies for wild bumblebees and for successfully breeding diverse bumblebee species. Breeding various bumblebee species is crucial for in-depth research into known factors and for further exploration of other potential factors, which will also help to meet the demand for pollination in agricultural facilities globally.

Consequences of intraspecific competition for floral resources in heterogeneous landscapes for eusocial bees

Agricultural intensification is widely recognised as a primary driver of pollinator loss, but the success of land-management actions designed to remediate its impact is often mixed. Payments to farmers to increase habitat connectivity or the availability of floral and nesting resources may only result in short-term gains or even unintended consequences. The reasons may lie in changes to interaction networks or competition intensity that remain poorly understood. Models of pollination service typically implicitly assume pollinator population dynamics are regulated by nest-site availability, even though empirical evidence suggests nest-site occupancy is likely at least in part dependent on floral resource availability. To investigate the consequences of competition for floral resources in coarse-grained agricultural landscapes we extended an established model for bees combining optimal foraging and population dynamics, to include new functions for floral resource depletion and realistic colony dynamics. We find that intra-specific competition occurs late in the season forcing bees to forage underutilised sites situated further towards their foraging range limits. A lower rate of energy acquisition ultimately limits the size of the colony peak and delays its timing. Consequently, competition for floral resources can limit population size and distribution while at the same time contributing to a more stable and efficacious pollination service. Although competition was not found to be important in nest-site establishment success, the effect of a hunger gap early in the season on nest-site occupancy indirectly influences competition later in the season leading to complex outcomes.

Consistent generalization of plant-hummingbird networks despite increasing vegetation cover across a tropical urban landscape

Human activities, particularly urbanization, profoundly impact ecosystems often resulting in biotic homogenization. Whether or not urban landscapes can sustain diverse pollinator and plant communities is an important question to be addressed. Here, we investigated the influence of urbanization on plant-hummingbird interaction networks in a large tropical city, Belo Horizonte, Brazil. We recorded 13198 legitimate interactions between seven hummingbirds and 57 plant species across 12 local networks. Urban landscapes exhibited predominantly generalized networks, maintaining this pattern across varying vegetation cover and floral resource abundance. Although some functionally specialized hummingbirds with long bills were recorded performing more specialized interactions, urban environments did not generally support specialized networks. Nevertheless, network specialization did increase with the proportion of native nectar plants, emphasizing their importance for maintaining some specialized interactions. Furthermore, we observed a positive effect of plant richness, but not of flower abundance, on hummingbird abundance, indicating that it is not only the amount of flowers, but the diversity of floral resources that may be a key factor in maintaining hummingbirds. Therefore, promoting a diverse assemblage of native plants in urban green areas is crucial for sustainable pollinator communities. Our study highlights that while a biodiverse urban landscape will require careful urban vegetation planning considering both floral resource diversity and availability, vegetation cover per se may not be sufficient to mitigate the negative impacts of urbanization. Maintaining a diverse vegetation with different life forms, flowering phenology, and especially of native plants across the urban landscape is needed to create welcoming spaces for pollinators.

Successful pollinator seed mixes include low grass density and high forb richness across a range of total seeding densities

Pollinator habitat restorations and enhancements are an important approach to mitigate pollinator declines due to habitat loss and other stressors. Foraging resources can be provided by wildflower plantings grown from seed mixes composed of pollinator‐friendly plant species. Despite clear evidence on the benefits of such plantings for bees and other pollinators, there is limited knowledge on how variation in multiple seed mix design parameters affects floral resources over time. Such information is crucial to improve the effectiveness of different habitat applications and to potentially lower seed costs, which remain an impediment to adoption. We conducted an incomplete factorial field experiment to test the impacts of density, diversity, and forb:grass ratio of seed mixes on floral resource availability and phenological coverage of the resulting plantings. We quantified floral area and phenological coverage over the whole blooming season for three consecutive years in replicated plots of wildflower mixes in two regions of the U.S.A, Northern California's Central Valley and Midwestern Tallgrass Prairie. When different seed densities were fully replicated (e.g. within high forb:grass seed ratios in Minnesota, or forb‐only seedings in California), seeding density had no further impact on floral area and floral phenological coverage.

Integrated vegetation management within electrical transmission landscapes promotes floral resource and flower-visiting insect diversity.

Electrical transmission rights-of-way are ubiquitous and critical infrastructure across the landscape. Active vegetation management of these rights-of-way, a necessity to deliver electricity more safely, maintains these landscape features as stages of early successional habitat, a rarity in many regions, making these areas viable movement corridors for many taxa. The goals of this study were to (i) evaluate the effects of different electrical transmission landscape management practices on flowering plant and flower-visiting insect diversity parameters and (ii) generate conservation management inferences for these landscapes. In this study we tested the impact of three vegetation management levels across 18 electrical transmission sites. We evaluated the effects of treatment on bloom abundance and species richness as well as flower-visiting insect abundance and family richness. We identified 76541 flowers/inflorescences across 456 transects, including 188 species in 56 plant families. Additionally, we obtained data on 11361 flower-visitoring insects representing 33 families from 2376 pan trap sets. High vegetation management favored the reduction of coarse woody debris in the sites and harbored the highest level of abundance and richness of both floral resources and flower-visiting insects. We discuss that we can align social and ecological values of rights-of-way, ensuring their sustainability by applying regular and targeted integrated vegetation management. Thus, we can use rights-of-way landscapes not only as an effective management strategy for the delivery of essential human services, but also to provide conservation benefits for wild pollinators.

Taxon‐specific response of natural enemies to different flower strip mixtures

Abstract Flower strips are a prominent agri‐environmental scheme with the central objective to promote biodiversity and maintain associated ecosystem services. The promotion of natural enemies by increasing resource availability through flower strips is a promising approach for integrated pest management. In a 3‐year field study, two annual and two perennial flower strip mixtures, as well as a grass mixture, were tested regarding their attractiveness for natural enemies at three different study sites in Germany. Natural enemies were sampled annually in nine sampling rounds at a 10‐day rhythm using sweep netting and pitfall traps. To assess available floral resources, we estimated the species‐specific flower cover and classified species into flower types. Flower strip mixtures differed in their attractiveness to natural enemies. Treatment effects on arthropod activity density were most pronounced in the second and third year. Overall, perennial were more attractive than annual flower strip mixtures for most natural enemies, however, the response to flower strip mixtures varied significantly among taxa. For example, perennial flower strips showed a two‐ to fourfold increase of plant‐dwelling spider and parasitoid wasp activity density as well as higher numbers of juvenile stages of predatory bugs and rove beetles compared to annual flower strips. In contrast, annual flower strip mixtures showed the highest attractiveness for ground beetles. Moreover, different natural enemy taxa were associated with varying flower strip characteristics such as flower type proportion, herbivore availability and plant species richness. Synthesis and applications. We found taxon‐specific responses of natural enemies to different flower strips, which provide guidance for the floral composition of flower strips in order to maximize their effectiveness for natural pest control. We suggest the use of perennial mixtures with high proportion of flower heads (Asteraceae) and disk flowers (esp. Apiaceae, Rubiaceae, Brassicaceae) in particular, but also flag blossoms (Fabaceae) as these flower types were positively associated with several natural enemy groups. However, since we found mixed responses to flower types, specific flower strip composition will ultimately depends on its objective.

Food contamination with fipronil alters gene expression associated with foraging in Africanized honey bees.

Taking into consideration that bees can be contaminated by pesticides through the ingestion of contaminated floral resources, we can utilize genetic techniques to assess effects that are scarcely observed in behavioral studies. This study aimed to investigate the genetic effects of ingesting lethal and sublethal doses of the insecticide fipronil in foraging honey bees during two periods of acute exposure. Bees were exposed to fipronil through contaminated honey syrup at two dosages (LD50 = 0.19 µg/bee; LD50/100 = 0.0019 µg/bee) and for two durations (1 and 4 h). Following exposure, we measured syrup consumption per bee, analyzed the transcriptome of bee brain tissue, and identified differentially expressed genes (DEGs), categorizing them functionally based on gene ontology (GO). The results revealed a significant genetic response in honey bees after exposure to fipronil, regardless of the dosage used. Fipronil affected various metabolic, transport, and cellular regulation pathways, as well as detoxification processes and xenobiotic substance detection. Additionally, the downregulation of several DEGs belonging to the olfactory-binding protein (OBP) family was observed, suggesting potential physiological alterations in bees that may lead to disoriented behaviors and reduced foraging efficiency.

Spatial heterogeneity of fire and flooding patterns can support higher diversity of floral functional traits in an indigenous‐managed landscape

AbstractIn tropical wetlands, in addition to flooding, fire also contributes to the structure of biodiversity across environmental gradients. In fire‐prone ecosystems, flower‐rich fire refuges can be maintained by a seasonal patch‐burning mosaic. Here, we evaluate how a set of floral traits that influence and are related to the pollination systems of tree and non‐tree species varies in response to spatial patterns of fire frequency in a landscape with floodable and flood‐free areas. We classified the sampled species according to flower size, color, shape, symmetry, floral resource, type of pollination units, flowering duration, and anthesis time and compared them between floodable and flood‐free areas with high, moderate, or low fire frequency. We analyzed the functional richness in response to landscape metrics related to spatial patterns of fire frequency. The composition of floral traits of non‐tree species was stable, while tree species differed among fire frequency classes, especially in floodable areas. Many floral traits of tree species are ecological indicators, especially in floodable areas with high fire frequency. In contrast, among non‐tree species, only floral tissues as resources for pollinator were related to flood‐free areas with moderate/high fire frequency. The floral functional richness of the tree species positively linked with the modified Simpson diversity index, and for both trees and non‐trees, it negatively associated with the homogenization of the fire frequency (e.g., connectance based on probability that two adjacent sites belong to the same fire frequency class was negatively related to the functional richness of floral traits). These results demonstrate that homogenization of fire frequency in the landscape decreases the functional richness. Patches with different combinations of fire frequency and flood regime can support a shared set of floral traits besides those specifically related to a particular regime. The spatial heterogeneity of fire and flood patterns in wetlands needs to be preserved to support a higher diversity of pollination systems mediated by functional complementarity between the flowers of the tree and non‐tree species.

The role of landscape factors in shaping bumble bee pathogen loads across regions of the eastern Nearctic

Abstract Pathogens and parasites are drivers of declines in bumble bees. Their levels can be influenced by numerous abiotic and biotic factors, thus managing disease in these bees requires understanding the relative impact of these factors on pathogen loads. We evaluated loads of black queen cell virus (BQCV) and deformed wing virus in bumble bees (Bombus impatiens) and honey bees (Apis mellifera), and loads of parasites Vairimorpha bombi and Crithidia bombi in B. impatiens, from sites varying in habitat type and quality across North Carolina, USA. Pathogen loads were assessed against metrics for land cover, floral quality, bee diversity and weather. Results were compared against similar data from Pennsylvania, USA, and other landscape studies on bumble bees in North America. Spatial variation in pathogen loads was lower in bumble bees in North Carolina than in Pennsylvania, which reduced the power to detect landscape effects. For example, Crithidia was fairly ubiquitous and Vairimorpha was not detected. Data from both states revealed that developed land and honey bees were most consistently positively correlated with viral loads, especially for BQCV, whereas forest and nesting habitat availability were often negatively correlated with loads. Multivariate models only supported a positive relationship between summer floral resources and BQCV loads in North Carolina bumble bees. Together with the broader literature, these data indicate that levels of developed land and honey bees are most associated with increased pathogen loads while floral availability and bee community composition show more context‐dependent effects.

Intraspecific and interspecific resource partitioning between bumblebee workers and males related to nectar quantity and quality.

Bumblebees are important pollinators for many natural and agricultural systems in temperate regions. Interspecific and intraspecific variation in floral resource preferences have been proposed to influence bumblebee community structure. In particular, sexual dimorphism is a major source of intraspecific niche variation. Although interspecific resource partitioning is well studied, few studies have explored the intraspecific dynamics between workers and males. Here, we report a study on a total of 11528 workers and 2220 males of 14 bumblebee species recorded over 5years in the Hengduan Mountains of Southwest China. We first compared the potential for interspecific and intraspecific competition between workers and males using visitation records and resource partitioning indices (overlap index). We then evaluated the influence of nectar traits on flower preference, including nectar volume and the levels of hexose, sucrose and 10 essential amino acids (EAAs). We found that the niche overlap between intraspecific workers and males was higher than that between different species, and temporal overlap alone did not strongly determine diet overlap. Males of most species preferred flowers with high levels of EAAs and hexose, whereas workers of some species preferred flowers with high nectar volume and sucrose levels. This study suggests that there is floral resource partitioning among bumblebee species, and between workers and males, which may play a key role in alleviating interspecific and intraspecific competition. These findings also provide a useful guide for which kinds of plants might be most valuable for bumblebees, especially the understudied males, in this biodiversity hotspot.