Pollinator Communities Research Articles

Local influence of floral resource attributes on urban bumble bee foraging activity

IntroductionUrbanization diminishes the extent of uncompacted, exposed soil and the coverage of wild plant species, yet still supports diverse pollinator communities when their habitat is maintained within the built environment. Floral abundance and richness are known to influence bee foraging behavior, and these factors vary across the landscape, especially across heterogeneous urban extents. This study assesses how floral resources are distributed across the city of Madison, WI and how these factors influence the distribution of foraging bumble bees.MethodsWe conducted a systematic walking transect survey of bumble bees across Madison, WI. The resulting point location data associated with more than 5,000 non-lethally surveyed bumble bees were analyzed with regard to floral resource explanatory variables as well as underlying land use zoning on more than 700 transects. We used Moran's I correlograms to investigate spatial autocorrelation in floral resource variables and bumble bee counts, then we fitted a generalized linear model predicting transect bee counts based on floral cover, density, species richness and wild plant species richness on the distribution of foraging bees. We employed a geographically-weighted regression model to explore non-stationarity in the effects of floral resource explanatory variables across the study extent.ResultsWe found significant positive influence of flower cover, species richness, and weakly significant positive influence of wildflower species richness on foraging bee counts within the model as well as a significant positive influence of the land use zoning categorical variable. The effects of floral resource predictors on foraging bumble bees varies based on landscape context across the city.DiscussionThe results of this study show that landscapes with high cover as well as floral diversity maximize bumble bee foraging, and the positive effect of wildflower species richness stands out where floral cover and overall richness are also present. Given that urban landscapes are not homogeneous and that floral resources are not consistently distributed across the cityscape, valuable pollinator habitat should be protected, and supplemented where gaps persist.

Honey bees (Apis mellifera) modify plant-pollinator network structure, but do not alter wild species' interactions.

Honey bees (Apis mellifera) are widely used for honey production and crop pollination, raising concern for wild pollinators, as honey bees may compete with wild pollinators for floral resources. The first sign of competition, before changes appear in wild pollinator abundance or diversity, may be changes to wild pollinator interactions with plants. Such changes for a community can be measured by looking at changes to metrics of resource use overlap in plant-pollinator interaction networks. Studies of honey bee effects on plant-pollinator networks have usually not distinguished whether honey bees alter wild pollinator interactions, or if they merely alter total network structure by adding their own interactions. To test this question, we experimentally introduced honey bees to a Canadian grassland and measured plant-pollinator interactions at varying distances from the introduced hives. We found that honey bees increased the network metrics of pollinator and plant functional complementarity and decreased interaction evenness. However, in networks constructed from just wild pollinator interactions, honey bee abundance did not affect any of the metrics calculated. Thus, all network structural changes to the full network (including honey bee interactions) were due only to honey bee-plant interactions, and not to honey bees causing changes in wild pollinator-plant interactions. Given widespread and increasing use of honey bees, it is important to establish whether they affect wild pollinator communities. Our results suggest that honey bees did not alter wild pollinator foraging patterns in this system, even in a year that was drier than the 20-year average.

Pollinator competition and the structure of floral resources

The mutualism between plants and pollinators is built upon the trophic ecology of flowers and florivores. Yet the ecology of flowers‐as‐food is left implicit in most studies of plant–pollinator ecology, and it has been largely neglected in mainstream trophic ecology. This deficit is especially evident in an emerging issue of basic and applied significance: competition between pollinators for floral resources. In this synthesis, we start by exploring the notion of floral resource limitation upon which most studies concerning competition between pollinators are tacitly predicated. Both theoretical and empirical lines of evidence indicate that floral resource limitation must be understood as a complex ecological contingency; the question is not simply whether but when, where and in what regions of floral trait space resources are limiting. Based on this premise, we propose a framework for understanding floral resource availability in terms of temporal, spatial and functional structure. While this framework is conceptually intuitive, it is empirically and analytically demanding. We review existing methods for measuring and summarizing the multi‐dimensional structure of floral resources, highlight their strengths and weaknesses, and identify opportunities for future methods development. We then discuss the causal relationships linking floral resource structure to species coexistence, plant–pollinator community dynamics, and exogenous drivers like climate, land use, and episodic disturbances. In its role as both cause and effect, floral resource structure mediates the relationship between behavioral ecology, landscape ecology, and coexistence theory with respect to flowers and florivores. Establishing floral resource structure as an object of study and application will both shed light on basic questions of coexistence and guide management decisions concerning contentious issues such as the compatibility of apiculture with wild pollinator conservation and the appropriate use of floral enhancements in agri‐environment schemes.

Implementing IPM in crop management simultaneously improves the health of managed bees and enhances the diversity of wild pollinator communities

Impacts of insecticide use on the health of wild and managed pollinators have been difficult to accurately quantify in the field. Existing designs tend to focus on single crops, even though highly mobile bees routinely forage across crop boundaries. We created fields of pollinator-dependent watermelon surrounded by corn, regionally important crops in the Midwestern US. These fields were paired at multiple sites in 2017–2020 with the only difference being pest management regimes: a standard set of conventional management (CM) practices vs. an integrated pest management (IPM) system that uses scouting and pest thresholds to determine if/when insecticides are used. Between these two systems we compared the performance (e.g., growth, survival) of managed pollinators—honey bees (Apis mellifera), bumble bees (Bombus impatiens)—along with the abundance and diversity of wild pollinators. Compared to CM fields, IPM led to higher growth and lower mortality of managed bees, while also increasing the abundance (+ 147%) and richness (+ 128%) of wild pollinator species, and lower concentrations of neonicotinoids in the hive material of both managed bees. By replicating realistic changes to pest management, this experiment provides one of the first demonstrations whereby tangible improvements to pollinator health and crop visitation result from IPM implementation in agriculture.

Effects of forest management on native bee biodiversity under the tallest trees in the world

AbstractIt is not clear if mature secondary growth coniferous forests can support similar pollinator communities as old growth coniferous forests, or how active management (e.g., retention forestry) in mature secondary growth forests may affect pollinator communities. We compare the native bee community and plant‐bee interaction networks of old growth, naturally regenerating and actively managed (retention forestry) mature secondary growth forests of similar stand age. Old growth forests had a higher bee species richness and Shannon's diversity index, but not Simpson's diversity index, than both actively managed and naturally regenerating mature secondary forests. Forest type (old‐growth, naturally regenerating mature secondary growth, and actively managed mature secondary growth) had a significant effect on bee community composition. Redwood forest bee‐plant interaction networks were small in size and had lower complexity than expected and few connector species. While studies suggest that small‐scale timber harvest may increase bee biodiversity in the short‐term in other coniferous forest habitats, our study suggests that there may be long‐term negative effects of clear‐cutting that lower bee biodiversity in mature secondary growth forests as compared to mature old‐growth forests.

Phenology and foraging bias contribute to sex-specific foraging patterns in the rare declining butterfly Argynnis idalia idalia.

Variation in pollinator foraging behavior can influence pollination effectiveness, community diversity, and plant-pollinator network structure. Although effects of interspecific variation have been widely documented, studies of intraspecific variation in pollinator foraging are relatively rare. Sex-specific differences in resource use are a strong potential source of intraspecific variation, especially in species where the phenology of males and females differ. Differences may arise from encountering different flowering communities, sex-specific traits, nutritional requirements, or a combination of these factors. We evaluated sex-specific foraging patterns in the eastern regal fritillary butterfly (Argynnis idalia idalia), leveraging a 21-year floral visitation dataset. Because A. i. idalia is protandrous, we determined whether foraging differences were due to divergent phenology by comparing visitation patterns between the entire season with restricted periods of male-female overlap. We quantified nectar carbohydrate and amino acid contents of the most visited plant species and compared those visited more frequently by males versus females. We demonstrate significant differences in visitation patterns between male and female A. i. idalia over two decades. Females visit a greater diversity of species, while dissimilarity in foraging patterns between sexes is persistent and comparable to differences between species. While differences are diminished or absent in some years during periods of male-female overlap, remaining signatures of foraging dissimilarity during implicate mechanisms other than phenology. Nectar of plants visited more by females had greater concentrations of total carbohydrates, glucose, and fructose and individual amino acids than male-associated plants. Further work can test whether nutritional differences are a cause of visitation patterns or consequence, reflecting seasonal shifts in the nutritional landscape encountered by male and female A. i. idalia. We highlight the importance of considering sex-specific foraging patterns when studying interaction networks, and in making conservation management decisions for this at-risk butterfly and other species exhibiting strong intraspecific variation.

Sustained mangrove reproduction despite major turnover in pollinator community composition at expanding range edge.

How well plants reproduce near their geographic range edge can determine whether distributions will shift in response to changing climate. Reproduction at the range edge can be limiting if pollinator scarcity leads to pollen limitation, or if abiotic stressors affect allocation to reproduction. For many animal-pollinated plants with expanding ranges, the mechanisms by which they have overcome these barriers are poorly understood. In this study, we examined plant-pollinator interactions hypothesized to impact reproduction of the black mangrove, Avicennia germinans, which is expanding northward in coastal Florida, USA. We monitored insects visiting A. germinans populations varying in proximity to the geographic range edge, measured the pollen loads of the most common insect taxa and pollen receipt by A. germinans stigmas, and quantified flower and propagule production. We found that despite an 84 % decline in median floral visits by insects at northernmost versus southernmost sites, range-edge pollen receipt remained high. Notably, local floral visitor assemblages exhibited substantial turnover along the study's latitudinal gradient, with large-bodied bees and hover flies increasingly common at northern sites. We also observed elevated flower production in northern populations and higher per capita reproductive output at the range edge. Furthermore, mean propagule mass in northern populations was 18 % larger than that from the southernmost populations. These findings reveal no erosion of fecundity in A. germinans populations at range limits, allowing rapid expansion of mangrove cover in the region. These results also illustrate that substantial turnover in the assemblage of flower-visiting insects can occur at an expanding range edge without altering pollen receipt.

Within-bloom shift in abundance of a wild pollinator mediates pollen deposition rates to blueberry

Intra-seasonal variation in abiotic and biotic conditions can have profound consequences for pollinator community compositions and foraging movement, with flow-on effects upon pollination services. Yet, few studies have related such variations to pollination services in crop systems. In a cultivated highbush blueberry system with two primary pollinators — the managed European honey bee and a wild stingless bee species — we investigated how pollinator abundances, bee foraging behaviour, and con- and heterospecific stigmatic pollen loads changed over early, mid, and late blueberry blooming. Both con- and heterospecific stigmatic pollen loads declined following early bloom. This shift was associated with a decline in the abundance of stingless bees, whereas the abundance of honey bees only declined during late bloom. Simultaneously, honey bees were more likely to forage for blueberry pollen, and stigmatic pollen loads, relative to bee abundance, increased during late bloom. Although mixed pollen loads were common on pollinator bodies, especially on pollen foraging honey bees, heterospecific pollen deposition on blueberry stigmas was low. Given the similar effectiveness of honey bees and stingless bees as pollinators of blueberries, we contend that the observed seasonal variation in pollen deposition is likely caused by the decline in stingless bee abundances, as honey bees were not able to fully compensate for the loss of stingless bees during late bloom. Greater consideration of seasonal heterogeneity of pollinator abundance and behaviour, as part of pollination management plans, may aid in ensuring high pollination services throughout the entirety of crop bloom.

Community context mediates effects of pollinator loss on seed production

AbstractA critical goal for ecologists is understanding how ongoing local and global species losses will affect ecosystem functions and services. Diversity–functioning relationships, which are well‐characterized in primary producer communities, are much less consistently predictable for ecosystem functions involving two or more trophic levels, particularly in situations where multiple species in one trophic level impact functional outcomes at another trophic level. This is particularly relevant to pollination functioning, given ongoing pollinator declines and the value of understanding pollination functioning for single plant species like crops or threatened plants. We used spatially replicated, controlled single‐pollinator‐species removal experiments to assess how changes in bumble bee species richness impacted the production of fertilized seeds in a perennial herb—Delphinium barbeyi—in the Rocky Mountains of Colorado, USA. To improve predictability, we also assessed how traits and abundances in the plant and bumble bee communities were related to D. barbeyi reproductive success. We hypothesized that trait‐matching between pollinator proboscis length and D. barbeyi's nectar spurs would produce a greater number of fertilized seeds, while morphological similarity within the floral community would dilute pollination services. We found that the effects of pollinator removal differed depending on the behavioral patterns of pollinators and compositional features of the plant and pollinator communities. While pollinator floral fidelity generally increased D. barbeyi seed production, that positive effect was primarily evident when more than half of the Bombus community was experimentally removed. Similarly, communities comprising primarily long‐tongued bees were most beneficial to D. barbeyi seed production in tandem with a strong removal. Finally, we observed contrasting effects of morphological similarity in the plant community, with evidence of both competition and facilitation among plants. These results offer an example of the complex dynamics underlying ecosystem function in multitrophic systems and demonstrate that community context can impact diversity–functioning relationships between trophic levels.

Indirect interactions between pollinators drive interaction rewiring through space

AbstractIn recent years, an extended body of literature has focused on the importance of either temporal or spatial dynamics in shaping the structure of interacting plant and pollinator communities. This improvement from a previously static and aggregated perspective has allowed us to understand many of the ecological processes that shape community assembly. However, fewer are the studies that have simultaneously focused on spatial and temporal dynamics, and even fewer are those that collect data across different habitat types to assess the generality of their findings. Here, we used a dataset collected weekly throughout the full flowering season for two consecutive years and within two contrasting habitat types in N and SW Spain: a mountain grassland area and the understory of sparse pine forests. We evaluated species and interaction persistence through space and time, pollinator fidelity, and turnover patterns in interaction composition while providing a potential mechanistic explanation for the patterns observed. Our results show that although species generalization does not explain species or interaction persistence, moderately generalist species are those showing the greatest fidelity to the subset of plant species they visit through space and time. Further, we find that interaction turnover through time is mostly driven by changes in species composition, while through space it is mostly driven by interaction rewiring resulting from indirect competitive interactions between pollinator species. Our results help to shed light on the potential mechanisms driving community assembly patterns beyond niche or neutral processes by adding within‐trophic‐level interactions that can modify pollinator preferences.

Pollinators differ in their contribution to the male fitness of a self-incompatible composite.

Reproductive fitness in plants is often determined by the quantity and quality of pollen transferred by pollinators. However, many fitness studies measure only female fitness or rely on proxies for male fitness. Here we assessed how five bee taxon groups affect male fitness in a prairie plant by quantifying pollen removal, visitation, and siring success using paternity assignments and a unique pollinator visitation experiment. In Echinacea angustifolia, we measured per-visit pollen removal for each pollinator taxon and estimated the number of pollen grains needed for successful ovule fertilization. Additionally, we directly measured pollinator influence on siring by allowing only one bee taxon to visit each pollen-donor plant, while open-pollinated plants acted as unrestricted pollen recipients. We genotyped the resulting offspring, assigned paternity, and used aster statistical models to quantify siring success. Siring success of pollen-donor plants differed among the five pollinator groups. Nongrooming male bees were associated with increased siring success. Bees from all taxa removed most of the flowering head's pollen in one visit. However, coneflower-specialist bee Andrena helianthiformis removed the most pollen per visit. Female fitness and proxy measures of male fitness, such as pollinator visitation and pollen removal, did not align with our direct quantifications of male fitness. Our results illustrate the need for more studies to directly quantify male fitness, and we caution against using male fitness proxy measures. In addition, conservation efforts that preserve a diverse pollinator community can benefit plants in fragmented landscapes.

Evaluation of Afidopyropen Toxicity at Environmentally Relevant Doses to the Asian Honeybee (Apis cerana) Using Physiological and Transcriptome Analysis.

Afidopyropen is a novel biogenic pesticide widely applied to control sap-feeding pests, and a few studies have evaluated the side effects of afidopyropen on pollinators, excluding the Asian honeybee. Thus, we estimated the physiological influences of afidopyropen in Apis cerana, which could cause significant death and nutritional deficiency in bees after continuous dietary intake (14 days) at the field recommended dose. Moreover, we found afidopyropen ingestion-induced changes in the activity of detoxification enzymes (AChE, GR, CarE) and expression of genes critical for the central nervous system and chemosensory function in the antennae, brain, midgut, and malpighian tubule of exposed bees. However, there was no evidence that there was a long-term impact on foraging activity when observing foragers treated with apfidopyropen as newly emerged workers. Overall, our study provides vital information to improve bee health, which will improve outcomes for beekeepers, increase pollination services, and strengthen pollinator communities.

Spatiotemporal trends in floral visitation and interaction networks reveal shifting niches for bats in a Neotropical savanna.

Flower-vising bats are important components of tropical pollinator communities, yet little is known about the structure of their pollination networks and how resource availability through time (seasons) and space (habitat heterogeneity) affects the extent to which bats interact with plants within a community-wide context. This information is key for the conservation of threatened nectarivore species, such as the Cerrado-endemic Lonchophylla dekeyseri, for which data on its specialization on floral-resources is scarce. Within a seasonal and heterogeneous savanna in the central Brazilian Cerrado, we performed a year-round assessment of an inclusive assemblage of flower-visiting bats (both nectarivores and other guilds that can also feed on nectar) within a savanna-edge-forest gradient, the phenological trends and spatial distribution of bat and their resource plants, and the resultant temporal and spatial interaction networks between bats and plants in order to associate network structure to resource availability. Clear spatiotemporal trends emerged in the community. Nectarivores dominated the flower-visiting niche outside forests and were prolific floral visitors, resulting in networks with lower specialization and modularity. These bats diverged into savanna foragers active during the wet season and the wet-dry transition, and edge foragers active mostly during the dry season. The latter group encompassed L. dekeyseri, which visited mostly Bauhinia species. Frugivores took over as main floral visitors within forests, as well as during peak dry season, when fewer fruits were available, resulting in more specialized and modular networks. Our work shows that the turnover of floral resources across seasons and vegetation types has a defining role in bat-plant interactions and relates to network structure, as bat trophic guilds interact with plants in distinct habitats and times of the year. Frugivores dominate the flower-visiting niche in certain temporal and spatial subsets of the network, which calls for the inclusion of this guild in future studies. Moreover, the high visitation to Bauhinia species by L. dekeyseri during the dry season might reduce competition with other nectarivores and is relevant to the management of the species, although more data is needed on its resource consumption on a larger time frame and across its geographic range.

Impact of landscape configuration and composition on pollinator communities across different European biogeographic regions

IntroductionHeterogeneity in composition and spatial configuration of landscape elements support diversity and abundance of flower-visiting insects, but this is likely dependent on taxonomic group, spatial scale, weather and climatic conditions, and is particularly impacted by agricultural intensification. Here, we analyzed the impacts of both aspects of landscape heterogeneity and the role of climatic and weather conditions on pollinating insect communities in two economically important mass-flowering crops across Europe.MethodsUsing a standardized approach, we collected data on the abundance of five insect groups (honey bees, bumble bees, other bees, hover flies and butterflies) in eight oilseed rape and eight apple orchard sites (in crops and adjacent crop margins), across eight European countries (128 sites in total) encompassing four biogeographic regions, and quantified habitat heterogeneity by calculating relevant landscape metrics for composition (proportion and diversity of land-use types) and configuration (the aggregation and isolation of land-use patches).ResultsWe found that flower-visiting insects responded to landscape and climate parameters in taxon- and crop-specific ways. For example, landscape diversity was positively correlated with honey bee and solitary bee abundance in oilseed rape fields, and hover fly abundance in apple orchards. In apple sites, the total abundance of all pollinators, and particularly bumble bees and solitary bees, decreased with an increasing proportion of orchards in the surrounding landscape. In oilseed rape sites, less-intensively managed habitats (i.e., woodland, grassland, meadows, and hedgerows) positively influenced all pollinators, particularly bumble bees and butterflies. Additionally, our data showed that daily and annual temperature, as well as annual precipitation and precipitation seasonality, affects the abundance of flower-visiting insects, although, again, these impacts appeared to be taxon- or crop-specific.DiscussionThus, in the context of global change, our findings emphasize the importance of understanding the role of taxon-specific responses to both changes in land use and climate, to ensure continued delivery of pollination services to pollinator-dependent crops.

Urban bee functional groups response to landscape context in the Southeastern US

We investigated the influence of landscape cover on urban bee community functional groups. We observed a diversity of functional groups across primarily forested and primarily urban sites, however particular species were favored by forest/urban spaces. Results point to the importance of further investigating the nuance of land use impacts on pollinator communities, and in particular demonstrates the merit of investigating landscape heterogeneity. Conservation of forest remnants in urban environments can positively impact wild bees across multiple functional groups.

Floral scent and pollination of the invasive plant Coreopsis lanceolata in Japan

The invasive plant Coreopsis lanceolata threatens ecosystems in Japan by competing for resources with native plants. This species is self-incompatible and requires pollinator agents for seed production; however, it is known to produce many seeds. Here, we document the pollination biology and plant-pollinator interactions that facilitate seed production of C. lanceolata in the introduced range. Results revealed that C. lanceolata attracted a wide array of floral visitors comprising 60 species from 20 families. Although most floral visitors could be potential pollinators, the functional groups of halictid bees appeared to be the most important pollinators of C. lanceolata in terms of visitation frequency and the ability to carry pollen. The floral scent emission of C. lanceolata consists predominantly of monoterpenes, sesquiterpenes, and benzenoids. Furthermore, the mean seed set was nearly 30% of the ovule mean. Our study confirmed that in the introduced range in Japan, C. lanceolata is integrated into the local pollinator community, especially with the functional group of halictid bees involved in the reproductive success.

Evaluating remnant vegetation management practices adjacent to apple orchards to support native bee pollinators

SummaryMaintenance of a diverse pollinator community helps ensure resilience in pollination services. Fragments of woody and grassy vegetation in the vicinity of croplands have been shown to encourage the presence of crop‐pollinating bees. However, to date, little attention has been given to the management practices that may enhance the presence of bees in such fragments. We investigated how the maintenance of remnant forest fragments adjacent to apple orchards in South Australia affects floral resources and native bee communities. The fragments had been subject to either (a) fire (assessments three years post‐burn), (b) cattle grazing under trees and (c) low maintenance management (>20 years not grazed or burnt). Plant communities were sampled along transects in plots. Bee communities were sampled using hand netting. We fitted generalised linear mixed models to investigate differences in plant and bee diversity between treatments and to elucidate the effect of plant diversity on bee diversity. We compared plant and bee community composition among treatments using non‐metric multidimensional scaling and conducted network analysis to measure the robustness of plant‐pollinator interactions to the removal of species. Both floral resource abundance and bee diversity were higher in burnt and low‐maintenance fragments than in grazed fragments. Bee species richness was positively associated with plant species richness. The species richness of bees that visit apple flowers was positively associated with flower abundance but not with floral species richness. Plant‐pollinator networks in grazed sites had fewer links per species and a higher proportion of realised links than those under other management practices. However, the resilience of pollinator networks did not differ significantly between management practices. Thus, controlled burns or low‐maintenance management of forest fragments appear to be the most suitable landscape management practices to support apple pollinating bees. Burning requires consideration of additional ecological consequences, such as the conservation of fire‐sensitive species and specialist woodland fauna. Cattle grazing adjacent to orchards results in simplified bee communities and pollination networks and is not recommended if pollination services are required for adjacent land uses. This information can benefit orchardist as well as managers of fragments of native vegetation adjacent to orchard crops.

B.Y.O. Bees: Managing wild bee biodiversity in urban greenspaces.

As cities become more populated and the density of urban development increases, local biodiversity is threatened. Urban greenspaces have the capacity to preserve pollinator biodiversity, but the quality of support they provide depends on greenspace landscape attributes, including the availability of pollinator habitat and foraging resources. Wild native bees provide important pollination services to urban ecosystems, yet relatively little is known about how urban landscape management influences pollinator community composition and diversity. Our study explores how wild bee communities are affected by greenspace and landscape-level features like pollinator management practices, in urban greenspaces in and around Appleton Wisconsin: a mid-sized urban community spanning more than 100 sq. km. We sampled and identified native bees periodically between late-May 2017 and mid-September of 2018 using standardized arrays of pan traps at 15 sites around the city. We classified greenspaces based on their level of development (urban or suburban) and whether they were managed or unmanaged for increasing wild pollinator diversity. We quantified floral species diversity, floral color diversity, tree species diversity, and proximity of sites to open water for each site and used remotely sensed satellite data from both the USGS National Land Cover Database (NLCD) and the Normalized Difference Vegetation Index (NDVI). All variables were tested as potential correlates of wild bee abundance and species richness. Active pollinator management sites supported higher levels of bee abundance and richness. Notably, active greenspace management (e.g. planting native wildflowers) was a stronger correlate of bee abundance and richness than greenspace size and other landscape-level attributes. Within-greenspace attributes such as floral diversity, tree diversity, and proximity to open water contributed positively to both bee abundance and richness. Based on these findings, we suggest that urban greenspaces may be managed more efficiently and cost-effectively by focusing resources on active management by planting wildflowers, removing invasive species, creating nesting habitat, and providing water resources, rather than simply expanding in area.

Different effects of local and landscape context on pollen foraging decisions by two managed orchard pollinators, Osmia cornuta and Bombus terrestris

Populations of managed pollinators are often introduced in agricultural fields to increase pollination levels. Ideally, managed pollinators should show a strong affinity for the target crop, which depends on innate preferences, but also on the availability of alternative co-blooming flower resources. In this study we compared pollen collection in Osmia cornuta and Bombus terrestris populations introduced in orchards, and we analysed how it is affected by local and landscape floral context. Based on pollen preferences and foraging rates of the two species, we expected O. cornuta to collect more fruit tree pollen than B. terrestris and to be less influenced by landscape factors. We sampled 16 orchards of various fruit tree species (almonds, apricots, cherries, apples). In each orchard, we characterized local flower availability and landscape composition, and identified pollen samples from 20 to 30 individuals of each pollinator species. O. cornuta collected a greater proportion of fruit tree pollen than B. terrestris (92% vs 81%), irrespective of the availability of alternative flower resources at the local and landscape levels. The diversity of pollen collected by B. terrestris increased with the availability of alternative flower resources, both at the local and landscape levels, suggesting that some of the foraging by this species took place away from the target orchard. Our results demonstrate that wild flowers do not compete with fruit tree flowers for O. cornuta visitation. Therefore, the use of managed O. cornuta populations to supplement pollination services in orchards is compatible with the implementation of agri-environmental measures (flower strips, ecological focus areas) to promote wild pollinator communities.

Inoculum source dependent effects of ericoid, mycorrhizal fungi on flowering and reproductive success in highbush blueberry (Vaccinium corymbosum).

Most terrestrial angiosperms form mutualisms with both mycorrhizal fungi and animal pollinators. Yet, the effects of mycorrhizae on pollinator behavior and plant reproduction are unknown for most species, and whether the source or type of mycorrhizal fungi affects reproductive success has rarely been examined. We examined whether inoculating highbush blueberry (Vaccinium corymbosum; Ericaceae) with ericoid mycorrhizal fungi enhanced investment in flowering and attractiveness to pollinators, and thus reduced their levels of pollen limitation over that of non-inoculated plants. We also examined the degree to which pollen limitation was dependent on inoculation source and the surrounding pollinator community context. Three-year-old saplings of Vaccinium corymbosum 'Bluecrop' or highbush blueberry (Ericaceae) were inoculated with a) ericoid mycorrhizal fungi within soil of the rhizosphere of plants growing at a local blueberry farm, b) a commercially available ericoid inoculant, c) both the local soils and commercial inoculum, or d) were not inoculated and served as controls. They were grown for one year in pots in a common garden and, in the following year, were moved to six farms in central Vermont that were known from prior studies to differ in pollinator abundance and diversity. We conducted a hand pollination experiment at each farm to examine if inoculation or pollinator abundance (i.e., farm context) affected reproductive success. Plants treated with all types of inoculums were more likely to flower, and produced more inflorescence buds than non-inoculated plants in 2018. However, in 2019, plants in the combination inoculum treatment, alone, produced more inflorescence buds than those in the other treatments. Neither the source of inoculum nor hand pollination affected fruit set (the proportion of flowers setting fruit), or fruit sugar content. Hand pollination, but not inoculation, increased berry mass and the average number of seeds produced/berry. Our results add to the growing body of evidence that mycorrhizal fungi can affect reproductive traits of their hosts but that the effects of mycorrhizal fungi depend on the mycorrhizal symbionts.