Providing foraging resources for solitary bees on farmland: current schemes for pollinators benefit a limited suite of species

Environmental ameliorations and politics in support of pollinators. Experiences from Europe: A review

At least 87% of angiosperm species require animal vectors for their reproduction, while more than two-thirds of major global food crops depend on zoogamous pollination. Pollinator insects are a wide variety of organisms that require diverse biotic and abiotic resources. Many factors have contributed to a serious decrease in the abundance of populations and diversity of pollinator species over the years. This decline is alarming, and the European Union has taken several actions aimed at counteracting it by issuing new conservation policies and standardizing the actions of member countries. In 2019, the European Green Deal was presented, aiming to restore 100% of Europe's degraded land by 2050 through financial and legislative instruments. Moreover, the Common Agricultural Policies have entailed greening measures for the conservation of habitats and beneficial species for more than 10 years. The new CAP (CAP 23-27) reinforces conservation objectives through strategic plans based on eco-schemes defined at the national level by the member countries, and some states have specifically defined eco-schemes for pollinator conservation. Here, we review the framework of EU policies, directives, and regulations, which include measures aimed at protecting pollinators in agricultural, urban, and peri-urban environments. Moreover, we reviewed the literature reporting experimental works on the environmental amelioration for pollinators, particularly those where CAP measures were implemented and evaluated, as well as studies conducted in urban areas. Among CAP measures, several experimental works have considered the sowing and management of entomophilous plants and reported results important for environmental ameliorations. Some urban, peri-urban and wasteland areas have been reported to host a considerable number of pollinators, especially wild bees, and despite the lack of specific directives, their potential to contribute to pollinator conservation could be enhanced through targeted actions, as highlighted by some studies.

Distribution of infectious and parasitic agents among three sentinel bee species across European agricultural landscapes

Infectious and parasitic agents (IPAs) and their associated diseases are major environmental stressors that jeopardize bee health, both alone and in interaction with other stressors. Their impact on pollinator communities can be assessed by studying multiple sentinel bee species. Here, we analysed the field exposure of three sentinel managed bee species (Apis mellifera, Bombus terrestris and Osmia bicornis) to 11 IPAs (six RNA viruses, two bacteria, three microsporidia). The sentinel bees were deployed at 128 sites in eight European countries adjacent to either oilseed rape fields or apple orchards during crop bloom. Adult bees of each species were sampled before their placement and after crop bloom. The IPAs were detected and quantified using a harmonised, high-throughput and semi-automatized qPCR workflow. We describe differences among bee species in IPA profiles (richness, diversity, detection frequencies, loads and their change upon field exposure, and exposure risk), with no clear patterns related to the country or focal crop. Our results suggest that the most frequent IPAs in adult bees are more appropriate for assessing the bees' IPA exposure risk. We also report positive correlations of IPA loads supporting the potential IPA transmission among sentinels, suggesting careful consideration should be taken when introducing managed pollinators in ecologically sensitive environments.

Ecological traits interact with landscape context to determine bees' pesticide risk

Widespread contamination of ecosystems with pesticides threatens non-target organisms. However, the extent to which life-history traits affect pesticide exposure and resulting risk in different landscape contexts remains poorly understood. We address this for bees across an agricultural land-use gradient based on pesticide assays of pollen and nectar collected by Apis mellifera, Bombus terrestris and Osmia bicornis, representing extensive, intermediate and limited foraging traits. We found that extensive foragers (A. mellifera) experienced the highest pesticide risk-additive toxicity-weighted concentrations. However, only intermediate (B. terrestris) and limited foragers (O. bicornis) responded to landscape context-experiencing lower pesticide risk with less agricultural land. Pesticide risk correlated among bee species and between food sources and was greatest in A. mellifera-collected pollen-useful information for future postapproval pesticide monitoring. We provide foraging trait- and landscape-dependent information on the occurrence, concentration and identity of pesticides that bees encounter to estimate pesticide risk, which is necessary for more realistic risk assessment and essential information for tracking policy goals to reduce pesticide risk.

Conservation measures or hotspots of disease transmission? Agri-environment schemes can reduce disease prevalence in pollinator communities

Insects are under pressure from agricultural intensification. To protect pollinators, conservation measures such as the EU agri-environment schemes (AES) promote planting wildflowers along fields. However, this can potentially alter disease ecology by serving as transmission hubs or by diluting infections. We tested this by measuring plant-pollinator interactions and virus infections (DWV-A, DWV-B and ABPV) across pollinator communities in agricultural landscapes over a year. AES had a direct effect on DWV-B, reducing prevalence and load in honeybees, with a tentative general dilution effect on load in early summer. DWV-A prevalence was reduced both under AES and with increasing niche overlap between competent hosts, likely via a dilution effect. By contrast, AES had no impact on ABPV, its prevalence driven by the proportion of bumblebees in the community. Epidemiological differences were also reflected in the virus phylogenies, with DWV-B showing recent rapid expansion, while DWV-A and ABPV showed slower growth rates and geographical population structure. Phylogenies indicate that all three viruses freely circulate across their host populations. Our study illustrates how complex interactions between environmental, ecological and evolutionary factors may influence wildlife disease dynamics. Supporting pollinator nutrition can mitigate the transmission of important bee diseases, providing an unexpected boost to pollinator conservation. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Non-target effects of agri-environmental schemes on solitary bees and fungi in the United Kingdom

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

Stability of crop pollinator occurrence is influenced by bee community composition

Bees provide a vital ecosystem service to agriculture by contributing to the pollination of many leading global crops. Human wellbeing depends not only on the quantity of agricultural yields, but also on the stability and resilience of crop production. Yet a broad understanding of how the diversity and composition of pollinator communities may influence crop pollination service has previously been hindered by a scarcity of standardized data. We used outputs from Bayesian occupancy detection models to examine patterns in the inter-annual occupancy dynamics of the bee pollinator communities of four contrasting crops (apples, field bean, oilseed and strawberries) in Great Britain between 1985 and 2015. We compared how the composition and species richness of different crop pollinator communities may affect the stability of crop pollinator occurrence. Across the four crops, we found that the inter-annual occupancy dynamics of the associated pollinator communities tended to be more similar in smaller communities with closely related pollinator species. Our results indicate that crop pollinator communities composed of a small number of closely related bee species show greater variance in mean occupancy compared to crops with more diverse pollinator communities. Lower variance in the occurrence of crop pollinating bee species may lead to more stable crop pollination services. Finally, whilst our results initially indicated some redundancy within most crop pollinator communities, with no, or little, increase in the variance of overall mean occupancy when species were initially removed, this was followed by a rapid acceleration in the variance of crop pollinator occurrence as each crop's bee pollinator community was increasingly depreciated. High inter-annual variations in pollination services have negative implications for crop production and food security. High bee diversity could ensure more stable and resilient crop pollination services, yet current agri-environment schemes predominantly benefit a limited suite of common species. Management may therefore benefit from targeting a wider diversity of solitary species in order to safeguard crop pollination service in the face of increasing environmental change.

From science to society: implementing effective strategies to improve wild pollinator health

Despite a substantial increase in scientific, public and political interest in pollinator health and many practical conservation efforts, incorporating initiatives across a range of scales and sectors, pollinator health continues to decline. We review existing pollinator conservation initiatives and define their common structural elements. We argue that implementing effective action for pollinators requires further scientific understanding in six key areas: (i) status and trends of pollinator populations; (ii) direct and indirect drivers of decline, including their interactions; (iii) risks and co-benefits of pollinator conservation actions for ecosystems; (iv) benefits of pollinator conservation for society; (v) the effectiveness of context-specific, tailored, actionable solutions; and (vi) integrated frameworks that explicitly link benefits and values with actions to reverse declines. We propose use of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) conceptual framework to link issues and identify critical gaps in both understanding and action for pollinators. This approach reveals the centrality of addressing the recognized indirect drivers of decline, such as patterns of global trade and demography, which are frequently overlooked in current pollinator conservation efforts. Finally, we discuss how existing and new approaches in research can support efforts to move beyond these shortcomings in pollinator conservation initiatives. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Impact of the “Farming With Alternative Pollinators” Approach on Crop Pollinator Pollen Diet

Pollinators are facing declines at a global level. One of the main factors driving this decline is insufficient access to floral resources due to habitat loss and degradation that can affect both diet generalist species as well as those with more restricted floral preferences. Here we evaluated the effect of a novel mitigation strategy in agricultural ecosystems, Farming with Alternative Pollinators (FAP) on the pollen diet of crop pollinators. The approach dedicates 25% of the cropped area to Marketable Habitat Enhancement Plants (MHEP) that attract pollinators, natural enemies of the crops, and provide farmers with income. We assessed the effect of the approach on pollen diet of faba bean (Vicia faba) and pumpkin (Cucurbita maxima) flower visitors in four different regions in Morocco during 2018 and 2019 by comparing control fields (monoculture) and FAP fields in 13 trials and 101 sites. Results from 25 wild bee species show that almost two-thirds of the species carrying or collecting pollen when visiting pumpkin flowers and half of the species carrying or collecting pollen when visiting faba bean flowers gathered this pollen from two or more host plants (i.e., MHEP, main crop, and/or wild plants) and displayed a wide dietary breadth. Pollen grains from the main crops were poorly represented on the female scopae, indicating that crops were mainly visited for nectar. Hence, crop flower visitors may require alternative pollen sources to meet their nutritional needs. The number of pollen genera collected by flower visitors and the dietary breadth of crop flower visitors did not show a significant increase in response to FAP management. Among the selected MHEP, sunflower (Helianthus annuus) was the pollen resource for pumpkin flower visitors. In faba bean, flower visitors collected pollen from coriander (Coriandrum sativum) and canola (Brassica napus). Our study sheds light on the importance of characterizing the pollen diet and the foraging behavior of crop pollinators to identify appropriate plant species that complement their food, maintain and conserve their populations.

Using DNA Metabarcoding to Identify Floral Visitation by Pollinators

The identification of floral visitation by pollinators provides an opportunity to improve our understanding of the fine-scale ecological interactions between plants and pollinators, contributing to biodiversity conservation and promoting ecosystem health. In this review, we outline the various methods which can be used to identify floral visitation, including plant-focused and insect-focused methods. We reviewed the literature covering the ways in which DNA metabarcoding has been used to answer ecological questions relating to plant use by pollinators and discuss the findings of this research. We present detailed methodological considerations for each step of the metabarcoding workflow, from sampling through to amplification, and finally bioinformatic analysis. Detailed guidance is provided to researchers for utilisation of these techniques, emphasising the importance of standardisation of methods and improving the reliability of results. Future opportunities and directions of using molecular methods to analyse plant–pollinator interactions are then discussed.

Impacts of Wildflower Interventions on Beneficial Insects in Fruit Crops: A Review

Integrated pest management (IPM) has been practiced by the fruit industry for at least 30 years. Naturally occurring beneficial insects have been encouraged to thrive alongside introduced predatory insects. However, Conservation Biological Control (CBC) and augmented biocontrol through the release of large numbers of natural enemies is normally only widely adopted when a pest has become resistant to available conventional pesticides and control has begun to break down. In addition, the incorporation of wild pollinator management, essential to fruit production, has, in the past, not been a priority but is now increasingly recognized through integrated pest and pollinator management (IPPM). This review focuses on the impacts on pest regulation and pollination services in fruit crops through the delivery of natural enemies and pollinating insects by provisioning areas of fruiting crops with floral resources. Most of the studies in this review highlighted beneficial or benign impacts of floral resource prevision to fruit crops. However, placement in the landscape and spill-over of beneficial arthropods into the crop can be influential and limiting. This review also highlights the need for longer-term ecological studies to understand the impacts of changing arthropod communities over time and the opportunity to tailor wildflower mixes to specific crops for increased pest control and pollination benefits, ultimately impacting fruit growers bottom-line with less reliance on pesticides.

Establishment and management of wildflower areas for insect pollinators in commercial orchards

Sown wildflower areas are increasingly recommended as an agri-environmental intervention measure, but evidence for their success is limited to particular insect groups or hampered by the challenges of establishing seed mixes and maintaining flower abundance over time. We conducted a replicated experiment to establish wildflower areas to support insect pollinators in apple orchards. Over three years, and across 23 commercial UK orchards with and without sown wildflowers, we conducted 828 transect surveys across various non-crop habitats. We found that the abundance of flower-visiting solitary bees, bumblebees, honeybees, and beetles was increased in sown wildflower areas, compared with existing non-crop habitats in control orchards, from the second year following floral establishment. Abundance of hoverflies and other non-syrphid flies was increased in wildflower areas from the first year. Beyond the effect of wildflower areas, solitary bee abundance was also positively related to levels of floral cover in other local habitats within orchards, but neither local nor wider landscape-scale context affected abundance of other studied insect taxa within study orchards. There was a change in plant community composition on the sown wildflower areas between years, and in patterns of flowering within and between years, showing a succession from unsown weedy species towards a dominance of sown species over time. We discuss how the successful establishment of sown wildflower areas and delivery of benefits for different insect taxa relies on appropriate and reactive management practices as a key component of any such agri-environment scheme.

Cattle grazing results in greater floral resources and pollinators than sheep grazing in low-diversity grasslands

Land-use and land-cover change associated with agriculture is one of the main drivers of biodiversity loss. In heavily modified agricultural landscapes, grazing lands may be the only areas that can provide essential resources for native grassland species. Management decisions, such as choice of livestock species, affect the extent to which grazing lands provide suitable habitat for native species such as pollinators.Our study compared how sheep versus cattle herbivory affected floral resources and butterfly abundance across low-diversity, former Conservation Reserve Program (CRP) pastures managed with patch-burn grazing.Across all years (2017-2019), flowering species richness and abundance were significantly higher in cattle pastures than sheep pastures. On average, we recorded 6.9 flowering species/transect in cattle pastures and 3.8 flowering species/transect in sheep pastures. The average floral abundance per transect was 1278 stems/transect in cattle pastures and 116 stems/transect in pastures grazed by sheep.Similarly, we observed higher butterfly species richness, diversity, and abundance in cattle than in sheep pastures. In cattle pastures, we observed an average of 75 butterflies and 6.75 species per transect, compared with an average of 52 butterflies and 3.37 species per transect in sheep pastures. However, the butterfly community composition did not significantly differ between grazing treatments likely because agricultural-tolerant, habitat generalists comprised the majority of the butterfly community. Five generalist butterflies comprised 92.3% of observations; Colias philodice was the most abundant (61% of observations). Speyeria idalia and Danaus plexippus, two butterflies of conservation concern, comprised less than 0.5% of butterfly observations.Our results, which are among the first attempt quantifying butterfly use of post-CRP fields grazed by livestock, show that increased precipitation and cattle grazing promoted higher forb abundance and richness. However, additional interventions may be needed to enhance floral resources to sustain and improve pollinator diversity in these landscapes.

Contribution of Extensive Farming Practices to the Supply of Floral Resources for Pollinators

Simple Summary

One of the causes of pollinator decline is the decreased availability of flower resources, that constitute their nutritional requirements. In particular, the intensification of agricultural practices has led to a loss of flower resources. For many years, as part of the Common Agricultural Policy and the efforts to preserve biodiversity, several Agri-Environmental Schemes (AESs) and extensive farming practices have been promoted in Europe. To assess the relative contribution of extensive farming practices such as hedgerows, organic crops and extensive grasslands, we compared pairs of agricultural landscapes in Belgium. We recorded the densities of the insect-pollinated plant species per biotope and per month, the abundance and diversity of the main visiting insects. In April, hedgerows and forest edges constituted the main nectar resources. In May, most of the nectar resources were produced by grasslands and mass-flowering crops. In June, extensive grasslands and organic crops contributed to nectar resources, contrarily to intensive agricultural elements. Extensive and diverse agricultural practices should therefore be encouraged to provide less fluctuating nectar resources on a landscape scale.

Abstract

Intensification of agricultural practices leads to a loss of floral resources and drives pollinator decline. Extensive agricultural practices are encouraged in Europe and contribute to the preservation of biodiversity. We compared three agricultural landscapes without extensive farming practices with three adjacent landscapes containing organic crops and extensively managed grasslands in Belgium. Nectar resource availability and plant–pollinator interactions were monitored from April to June. Flower density per plant species and plant–pollinator interactions were recorded in different landscape elements. In April, the main nectar resources were provided by linear elements such as hedgerows and forest edges. Nectar production peaked in May, driven by intensive grasslands and mass-flowering crops. Occurrence of extensive grasslands and organic crops significantly alleviated the nectar resource gap observed in June. Our results underscore the importance of maintaining landscape heterogeneity for continuous flower resources and highlight the specific role of extensive grasslands and organic crops in June.

Plant protection product residues in plant pollen and nectar: A review of current knowledge

Exposure to Plant Protection Products, PPPs, (fungicides, herbicides and insecticides) is a significant stressor for bees and other pollinators, and has recently been the focus of intensive debate and research. Specifically, exposure through contaminated pollen and nectar is considered pivotal, as it presents the highest risk of PPP exposure across all bee species. However, the actual risk that multiple PPP residues might pose to non-target species is difficult to assess due to the lack of clear evidence of their actual concentrations. To consolidate the existing knowledge of field-realistic residues detected in pollen and nectar directly collected from plants, we performed a systematic literature review of studies over the past 50 years (1968-2018). We found that pollen was the matrix most frequently evaluated and, of the compounds investigated, the majority were detected in pollen samples. Although the overall most studied category of PPPs were the neonicotinoid insecticides, the compounds with the highest median concentrations of residues in pollen were: the broad spectrum carbamate carbofuran (1400 ng/g), the fungicide and nematicide iprodione (524 ng/g), and the organophosphate insecticide dimethoate (500 ng/g). In nectar, the highest median concentration of PPP residues detected were dimethoate (1595 ng/g), chlorothalonil (76 ng/g), and the insecticide phorate (53.5 ng/g). Strong positive correlation was observed between neonicotinoid residues in pollen and nectar of cultivated plant species. The maximum concentrations of several compounds detected in nectar and pollen were estimated to exceed the LD_50s for honey bees, bumble bees and four solitary bee species, by several orders of magnitude. However, there is a paucity of information for the biggest part of the world and there is an urgent need to expand the range of compounds evaluated in PPP studies.

Beyond the Decline of Wild Bees: Optimizing Conservation Measures and Bringing Together the Actors

Wild bees are facing a global decline mostly induced by numerous human factors for the last decades. In parallel, public interest for their conservation increased considerably, namely through numerous scientific studies relayed in the media. In spite of this broad interest, a lack of knowledge and understanding of the subject is blatant and reveals a gap between awareness and understanding. While their decline is extensively studied, information on conservation measures is often scattered in the literature. We are now beyond the precautionary principle and experts are calling for effective actions to promote wild bee diversity and the enhancement of environment quality. In this review, we draw a general and up-to-date assessment of the conservation methods, as well as their efficiency and the current projects that try to fill the gaps and optimize the conservation measures. Targeting bees, we focused our attention on (i) the protection and restoration of wild bee habitats, (ii) the conservation measures in anthropogenic habitats, (iii) the implementation of human made tools, (iv) how to deal with invasive alien species, and finally (v) how to communicate efficiently and accurately. This review can be considered as a needed catalyst to implement concrete and qualitative conversation actions for bees.

Opportunities and threats for pollinator conservation in global towns and cities

Urban expansion is considered to be one of the main threats to global biodiversity yet some pollinator groups, particularly bees, can do well in urban areas. Recent studies indicate that both local and landscape-level drivers can influence urban pollinator communities, with local floral resources and the amount of impervious cover in the landscape affecting pollinator abundance, richness and community composition. Urban intensification, chemicals, climate change and increased honey bee colony densities all negatively affect urban pollinators. Maintaining good areas of habitat for pollinators, such as those found in allotments (community gardens) and domestic gardens, and improving management approaches in urban greenspace and highly urbanised areas (e.g. by increasing floral resources and nesting sites) will benefit pollinator conservation. Opportunities for pollinator conservation exist via multiple stakeholders including policymakers, urban residents, urban planners and landscape architects.

Pollen report: quantitative review of pollen crude protein concentrations offered by bee pollinated flowers in agricultural and non-agricultural landscapes

To ease nutritional stress on managed as well as native bee populations in agricultural habitats, agro-environmental protection schemes aim to provide alternative nutritional resources for bee populations during times of need. However, such efforts have so far focused on quantity (supply of flowering plants) and timing (flower-scarce periods) while ignoring the quality of the two main bee relevant flower-derived resources (pollen and nectar). As a first step to address this issue we have compiled one geographically explicit dataset focusing on pollen crude protein concentration, one measurement traditionally associated with pollen quality for bees. We attempt to provide a robust baseline for protein levels bees can collect in- (crop and weed species) and off-field (wild plants) in agricultural habitats around the globe. Using this dataset we identify crops which provide sub-optimal pollen resources in terms of crude protein concentration for bees and suggest potential plant genera that could serve as alternative resources for protein. This information could be used by scientists, regulators, bee keepers, NGOs and farmers to compare the pollen quality currently offered in alternative foraging habitats and identify opportunities to improve them. In the long run, we hope that additional markers of pollen quality will be added to the database in order to get a more complete picture of flower resources offered to bees and foster a data-informed discussion about pollinator conservation in modern agricultural landscapes.

Impact of Biotic and Abiotic Stressors on Managed and Feral Bees

Large-scale declines in bee abundance and species richness over the last decade have sounded an alarm, given the crucial pollination services that bees provide. Population dips have specifically been noted for both managed and feral bee species. The simultaneous increased cultivation of bee-dependent agricultural crops has given rise to additional concern. As a result, there has been a surge in scientific research investigating the potential stressors impacting bees. A group of environmental and anthropogenic stressors negatively impacting bees has been isolated. Habitat destruction has diminished the availability of bee floral resources and nest habitats, while massive monoculture plantings have limited bee access to a variety of pollens and nectars. The rapid spread and increased resistance buildup of various bee parasites, pathogens, and pests to current control methods are implicated in deteriorating bee health. Similarly, many pesticides that are widely applied on agricultural crops and within beehives are toxic to bees. The global distribution of honey bee colonies (including queens with attendant bees) and bumble bee colonies from crop to crop for pollination events has been linked with increased pathogen stress and increased competition with native bee species for limited resources. Climatic alterations have disrupted synchronous bee emergence with flower blooming and reduced the availability of diverse floral resources, leading to bee physiological adaptations. Interactions amongst multiple stressors have created colossal maladies hitting bees at one time, and in some cases delivering additive impacts. Initiatives including the development of wild flower plantings and assessment of pesticide toxicity to bees have been undertaken in efforts to ameliorate current bee declines. In this review, recent findings regarding the impact of these stressors on bees and strategies for mitigating them are discussed.

Pollen metabarcoding reveals broad and species-specific resource use by urban bees

Bee populations are currently undergoing severe global declines driven by the interactive effects of a number of factors. Ongoing urbanisation has the potential to exacerbate bee declines, unless steps are taken to ensure appropriate floral resources are available. Sown wildflower strips are one way in which floral resources can be provided to urban bees. However, the use of these strips by pollinators in urban environments remains little studied. Here, we employ pollen metabarcoding of the rbcL gene to compare the foraging patterns of different bee species observed using urban sown wildflower strips in July 2016, with a goal of identifying which plant species are most important for bees. We also demonstrate the use of a non-destructive method of pollen collection. Bees were found to forage on a wide variety of plant genera and families, including a diverse range of plants from outside the wildflower plots, suggesting that foragers visiting sown wildflower strips also utilize other urban habitats. Particular plants within the wildflower strips dominated metabarcoding data, particularly Papaver rhoeas and Phacelia tanacetifolia. Overall, we demonstrate that pollinators observed in sown wildflower strips use certain sown foodplants as part of a larger urban matrix.

Flower strip networks offer promising long term effects on pollinator species richness in intensively cultivated agricultural areas

Background

Intensively cultivated agricultural landscapes often suffer from substantial pollinator losses, which may be leading to decreasing pollination services for crops and wild flowering plants. Conservation measures that are easy to implement and accepted by farmers are needed to halt a further loss of pollinators in large areas under intensive agricultural management. Here we report the results of a replicated long-term study involving networks of mostly perennial flower strips covering 10% of a conventionally managed agricultural landscape in southwestern Germany.

Results

We demonstrate the considerable success of these measures for wild bee and butterfly species richness over an observation period of 5 years. Overall species richness of bees and butterflies but also the numbers of specialist bee species clearly increased in the ecological enhancement areas as compared to the control areas without ecological enhancement measures. A three to five-fold increase in species richness was found after more than 2 years of enhancement of the areas with flower strips. Oligolectic bee species increased significantly only after the third year.

Conclusions

In our long-term field experiment we used a large variety of seed mixtures and temporal variation in seeding time, ensured continuity of the flower-strips by using perennial seed mixtures and distributed the measures over c. 10% of the landscape. This led to an increase in pollinator abundance, suggesting that these measures may be instrumental for the successful support of pollinators. These measures may ensure the availability of a network of diverse habitats and foraging resources for pollinators throughout the year, as well as nesting sites for many species. The measures are applied in-field and are suitable for application in areas under intensive agriculture. We propose that flower strip networks should be implemented much more in the upcoming CAP (common agricultural policy) reform in the European Union and promoted more by advisory services for farmers.

Electronic supplementary material

The online version of this article (10.1186/s12898-018-0210-z) contains supplementary material, which is available to authorized users.

Limited phenological and dietary overlap between bee communities in spring flowering crops and herbaceous enhancements

Wild bee populations have undergone declines in recent years across much of the Western world, and these declines have the potential to limit yield in pollination-dependent crops. Highbush blueberry, Vaccinium corymbosum, and tart cherry, Prunus cerasus, are spring-blooming crops that rely on the movement of pollen by bees and other insects for pollination. Wild bee populations can be increased on farmland by providing floral resources, but whether the addition of these plants translates into increased pollinator density on crop flowers has not been documented in most cropping systems. To determine the importance of providing additional floral resources for wild bee pollinator communities, we selected blueberry fields and tart cherry orchards with and without herbaceous floral enhancements in western Michigan, USA. The bee communities visiting crop flowers, enhancements and control grassy field margins were sampled over a 5-yr period. In addition, the pollen diets of the most abundant wild bee crop pollinators were quantified across Michigan to better understand their foraging niches and to identify potentially important alternative host plants. The presence of floral enhancements did not increase the abundance of wild bees on either blueberry or cherry flowers during bloom. The bee community visiting blueberry was evenly composed of short-season bees that fly only during the spring and long-season bees that fly in both spring and summer. In contrast, the bee community visiting cherry was dominated by short-season spring bees. The majority of pollen collected by the wild bee communities visiting blueberry and cherry was from spring-flowering woody plants, with limited use of the herbaceous enhancements. Enhancements attracted greater abundance and species richness of bees compared to control areas, including twice as many floral specialists. Conserving summer-flying, grassland-associated bees is an appropriate goal for pollinator conservation programs. However, herbaceous enhancements may not provide adequate resources for the wild bees that pollinate spring-flowering crops. This study demonstrates that an examination of the pollen collected by wild bees across their flight periods can identify plant species to help them persist in intensively managed landscapes.

Flower preferences and pollen transport networks for cavity-nesting solitary bees: Implications for the design of agri-environment schemes

Floral foraging resources are valuable for pollinator conservation on farmland, and their provision is encouraged by agri-environment schemes in many countries. Across Europe, wildflower seed mixtures are widely sown on farmland to encourage pollinators, but the extent to which key pollinator groups such as solitary bees exploit and benefit from these resources is unclear. We used high-throughput sequencing of 164 pollen samples extracted from the brood cells of six common cavity-nesting solitary bee species (Osmia bicornis, Osmia caerulescens, Megachile versicolor, Megachile ligniseca, Megachile centuncularis and Hylaeus confusus) which are widely distributed across the UK and Europe. We documented their pollen use across 19 farms in southern England, UK, revealing their forage plants and examining the structure of their pollen transport networks. Of the 32 plant species included currently in sown wildflower mixes, 15 were recorded as present within close foraging range of the bees on the study farms, but only Ranunculus acris L. was identified within the pollen samples. Rosa canina L. was the most commonly found of the 23 plant species identified in the pollen samples, suggesting that, in addition to providing a nesting resource for Megachile leafcutter bees, it may be an important forage plant for these species. Higher levels of connectance and nestedness were characteristic of pollen transport networks on farms with abundant floral resources, which may increase resilience to species loss. Our data suggest that plant species promoted currently by agri-environment schemes are not optimal for solitary bee foraging. If a diverse community of pollinators is to be supported on UK and European farmland, additional species such as R. canina should be encouraged to meet the foraging requirements of solitary bees.

Monocultural sowing in mesocosms decreases the species richness of weeds and invertebrates and critically reduces the fitness of the endangered European hamster

Intensive cereal monoculture is currently the main cause of biodiversity decline in Europe. However, it is difficult to disentangle the effects of intensive monoculture (e.g. pesticide use, mechanical ploughing and reduced protective cover), let alone evaluate how far the reduction of crop diversity affects biodiversity. It remains unclear to which extent the consequent decrease in food resources affects farmland biodiversity, and particularly vertebrate species. We therefore designed this study in mesocosms to investigate the effects of monoculture crops (organic wheat or corn seeds) and mixed crops (a combination of organic wheat, corn, sunflower and alfalfa seeds) on (1) the species richness of weeds and invertebrates and (2) the reproductive success of the European hamster (Cricetus cricetus), a critically endangered umbrella species of European farmlands. We found a negative impact of organic monoculture crops on plant and invertebrate species richness, with values respectively 38% and 28% lower than those obtained for mixed organic crops. The reproductive success of hamsters was reduced by 82% in monoculture mesocosms. These results highlight that monoculture per se can be detrimental for farmland biodiversity (i.e. from plants to vertebrates), even before taking into account the use of pesticide and mechanization. We believe that future research should further consider how food reduction in agroecosystems affects farmland wildlife, including vertebrates. Moreover, we argue that conservation actions must focus on restoring plant diversity on farmland to reverse the observed trend in farmland wildlife decline.

Connecting Earth observation to high-throughput biodiversity data

Understandably, given the fast pace of biodiversity loss, there is much interest in using Earth observation technology to track biodiversity, ecosystem functions and ecosystem services. However, because most biodiversity is invisible to Earth observation, indicators based on Earth observation could be misleading and reduce the effectiveness of nature conservation and even unintentionally decrease conservation effort. We describe an approach that combines automated recording devices, high-throughput DNA sequencing and modern ecological modelling to extract much more of the information available in Earth observation data. This approach is achievable now, offering efficient and near-real-time monitoring of management impacts on biodiversity and its functions and services.

Ecological intensification to mitigate impacts of conventional intensive land use on pollinators and pollination

Worldwide, human appropriation of ecosystems is disrupting plant–pollinator communities and pollination function through habitat conversion and landscape homogenisation. Conversion to agriculture is destroying and degrading semi‐natural ecosystems while conventional land‐use intensification (e.g. industrial management of large‐scale monocultures with high chemical inputs) homogenises landscape structure and quality. Together, these anthropogenic processes reduce the connectivity of populations and erode floral and nesting resources to undermine pollinator abundance and diversity, and ultimately pollination services. Ecological intensification of agriculture represents a strategic alternative to ameliorate these drivers of pollinator decline while supporting sustainable food production, by promoting biodiversity beneficial to agricultural production through management practices such as intercropping, crop rotations, farm‐level diversification and reduced agrochemical use. We critically evaluate its potential to address and reverse the land use and management trends currently degrading pollinator communities and potentially causing widespread pollination deficits. We find that many of the practices that constitute ecological intensification can contribute to mitigating the drivers of pollinator decline. Our findings support ecological intensification as a solution to pollinator declines, and we discuss ways to promote it in agricultural policy and practice.