Seed coating with a neonicotinoid insecticide negatively affects wild bees.

Simple SummaryLoss of semi-natural habitats in agricultural landscapes negatively affects wild bees. These pollinators are, however, very important in agricultural landscapes as they enable the pollination of crops and wild plants. The aim of this study was thus to understand the respective roles of different wooded and herbaceous habitats in their ability to support a diversity of wild bees. We first found that wild bee communities differed between wooded and herbaceous habitats, some bee species being found in one type of habitat and not in the other. We also showed that wooded semi-natural habitats provide some species of pollen preferred by the bees. Finally, we found that in wooded habitats there are some interactions between plant and bee species that do not happen in permanent grasslands. However, the latter also plays an important role in the diversity of bees and plants, and these wooded and herbaceous habitats complement each other. Overall, our results underline the importance of maintaining a diversity of semi-natural habitats in agricultural landscapes to maintain a diversity of wild bees and thus promote the pollination of wild plants and crops.Loss of semi-natural habitats (SNH) in agricultural landscapes affects wild bees, often negatively. However, how bee communities respond varies and is still unclear. To date, few studies have used precise descriptors to understand these effects. Our aim was to understand the respective and complementary influences of different wooded and herbaceous habitats on wild bee communities. We selected thirty 500-m radius landscapes on a gradient of a percentage of wooded SNH in south-western France. At each landscape, we sampled wild bees in spring 2016 and plants in spring 2015 and 2016 at the forest edge, in a hedgerow, and in a permanent grassland. Pollen carried by the most abundant bee species was collected and identified. Using beta diversity indices, we showed that wild bee community composition differs between the three SNH types, and especially between herbaceous and wooded SNH. Based on Jacobs’ selection index, we showed that pollen of some plant species recorded in wooded SNH are preferentially selected by wild bees. Studying the impact of the loss of each SNH type on the global bee-pollen interaction network, we found that wooded SNH contributed to its resilience, enabling specific plant–bee interactions. Overall, our results underline the non-negligible contribution of wooded SNH to the diversity of wild bees in agricultural landscapes, and thus the importance of maintaining different types of SNH.

South-central Pennsylvania, framed by the great folds of the Appalachians to the north and west, by the Mason-Dixon Line to the south, and by the rise of hills that bound the lower Susquehanna River to the east, was claimed by settler-farmers of western European descent during the early and mid-eighteenth century. They utilized river and stream valleys to gain access to the fertile lowlands and rich uplands of the region, following in the steps of surveyors to mark farm boundaries with timber fences cut from the cloak of forest. The social and ecological imprint of these boundary structures has endured for hundreds of years.

Wild bees are decreasing in species diversity and populations due to human impact. The abundance of the western honey bee (Apis mellifera L.) experiences an inverse trend, enhancing competition with wild bees and the probability of microbiome exchange. Addressing this exchange, we studied the gut microbiome composition of wild and honey bees, focusing on patterns indicating honey bee influence. Three solitary wild bee species (large scabious mining bee [Andrena hattorfiana F.], grey-backed mining bee (Andrena vaga Panzer), and European orchard bee [Osmia cornuta Latreille]) as well as bumble bees as representatives of eusocial wild bees (Bombus spp. Latreille) and honey bees were sampled in the Austrian Alps. Subsequent 16S ribosomal DNA sequencing revealed the composition of the bacterial communities. The bee groups differed concerning their bacterial composition, with honey bees having the least variation among individuals and a low number of exclusive bacterial taxa and bumble bees the highest bacterial diversity. High honey bee densities corresponded with lower bacterial diversity in wild bees and a higher bacterial similarity between wild and honey bees. Some bacterial taxa were found for the first time in the studied bee groups. Furthermore, the composition of bacterial communities differed between solitary and social bees. We found the first hints that high honey bee density negatively impacts wild bees through alterations of wild bee microbiomes. Future studies should focus on understanding microbiome transmission mechanisms and their consequences for wild bees. Suggestions on how to consider wild bee fitness are indispensable in halting the biodiversity crisis.

Agricultural intensification and the loss of suitable habitats are drivers of insect declines. Besides the promotion of semi-natural habitats (SNH), the utilization of diversified crop rotations including flowering crops is an option to sustain pollinators. As flowering and nitrogen fixing crops, grain legumes provide several environmental benefits but are underrepresented in the EU. Since 2013 they are promoted within the greening reform of the Common Agricultural Policy (CAP). On-field biodiversity measures are often criticized, though their possible benefits for biodiversity are widely unknown. My PhD thesis aims at investigating the landscape-scale effect of conventional faba bean (Vicia faba L.) cultivation on wild bee communities, their resource utilization and their pollination services. Experiments were conducted in 1km x 1km study landscapes in Germany. For the first three chapters a paired study design was applied with one landscape of a pair comprising at least one faba bean field and the respective control landscape without grain legumes. In the first chapter we studied effects of faba bean cultivation on functional groups of wild bees. We conducted pollinator surveys at field margins of different crops in 30 study landscapes. Bumblebee densities were more than twice as high in faba bean compared to control landscapes, while non-Bombus wild bees were only driven by the amount of SNH. These results indicate that a combination of on- and off-field greening measures is necessary to conserve farmland biodiversity and we recommend that the CAP should furthermore promote both. In the second chapter we investigated the effect of two mass-flowering crops (MFC) on the functional trait composition of bee communities in SNH. Faba bean cultivation promoted bumblebees, especially long-tongued species, social bees and bees foraging on Fabaceae. High oilseed rape (OSR) covers changed wild bee community composition in favor for solitary bees. Local flower cover of SNH was the main driver of non-Bombus wild bees and wild bee species richness. Thus, different MFC promote specific functional bee groups adapted to the crop`s flower morphology. Concluding, the cultivation of functionally diverse crops, combined with a high local flower cover of SNH needs to be targeted by management practices to sustain diverse pollinator communities. In the third chapter we studied landscape and faba bean cultivation effects on the colony development and resource utilization of bumblebees (Bombus terrestris L.). The colonies` reproductive success was not influenced by landscape composition but enhanced by landscape diversity. Faba bean cultivation and pollen diversity interacted and resulted in more young queens with increasing pollen diversity in landscapes without faba bean. In addition, colonies that collected a higher pollen diversity had a reduced A. sociella depredation. Increased parasitism had a cascading negative effect on the reproductive success of bumblebees by limiting colony growth. Our study shows that high landscape diversity and diverse pollen diets can enhance the reproductive success of bumblebees. A diverse diet even mitigated depredation by wax moths. To sustain vital bumblebee populations and their pollination services, diverse and floral rich habitat types should be conserved or restored in agricultural landscapes. In the fourth chapter we investigated, how bee densities in OSR fields are affected by past and current MFC cultivation and how insect pollination affects OSR yield components. Bee densities were positively affected by past MFC covers and negatively affected by current OSR covers. Pollinator exclusion decreased seed number per pod and increased seed weight. Insect pollination interacted with the plants` pod number in shaping yields, while compensating for low pod numbers. In the fifth chapter we analyzed the effect of landscape composition on the densities of different functional bee groups and their foraging behavior in faba bean fields in 11 different landscapes. Moreover, the effect of insect pollination and of landscape composition was tested on faba bean yield components. Landscape composition affected the bees` foraging behavior in the crop. Increasing covers of faba bean and of semi-natural habitats in a landscape had a positive effect on bee densities and on faba bean yield, while oilseed rape cover had a negative effect. Our study emphasizes the importance of considering landscape management in order to maximize flowering crop yields. In conclusion, Vicia faba cultivation is an effective measure to promote wild bees, which are needed for high crop yields. Though, since benefits for pollinator groups depend on the crops` flower morphology, functional trait composition of wild bee communities can be changed in landscapes with a dominating mass-flowering crop species. Thus, landscape and local farm management should aim at increasing farmland plant diversity. The combination of a high cover and quality of semi-natural habitats as well as of diversified farming practices targeting a high spatial and temporal crop diversity is essential to conserve diverse pollinator communities and to sustain high crop yields.

Summary1. Wild bees are one of the most important groups of pollinators in the temperate zone. Therefore, population declines have potentially negative impacts for both crop and wildflower pollination. Although heavy metal pollution is recognized to be a problem affecting large parts of the European Union, we currently lack insights into the effects of heavy metals on wild bees.2. We investigated whether heavy metal pollution is a potential threat to wild bee communities by comparing (i) species number, (ii) diversity and (iii) abundance as well as (iv) natural mortality of emerging bees along two independent gradients of heavy metal pollution, one at Olkusz (OLK), Poland and the other at Avonmouth (AVO), UK. We used standardized nesting traps to measure species richness and abundance of wild bees, and we recorded the heavy metal concentration in pollen collected by the red mason bee Osmia rufa as a measure of pollution.3. The concentration of cadmium, lead and zinc in pollen collected by bees ranged from a background level in unpolluted sites [OLK: 1·3, 43·4, 99·8 (mg kg−1); AVO: 0·8, 42·0, 56·0 (mg kg−1), respectively] to a high level on sites in the vicinity of the OLK and AVO smelters [OLK: 6·7, 277·0, 440·1 (mg kg−1); AVO: 9·3, 356·2, 592·4 (mg kg−1), respectively].4. We found that with increasing heavy metal concentration, there was a steady decrease in the number, diversity and abundance of solitary, wild bees. In the most polluted sites, traps were empty or contained single occupants, whereas in unpolluted sites, the nesting traps collected from 4 to 5 species represented by up to ten individuals. Moreover, the proportion of dead individuals of the solitary bee Megachile ligniseca increased along the heavy metal pollution gradient at OLK from 0·2 in uncontaminated sites to 0·5 in sites with a high concentration of pollution.5. Synthesis and applications. Our findings highlight the negative relationship between heavy metal pollution and populations of wild bees and suggest that increasing wild bee richness in highly contaminated areas will require special conservation strategies. These may include creating suitable nesting sites and sowing a mixture of flowering plants as well as installing artificial nests with wild bee cocoons in polluted areas. Applying protection plans to wild pollinating bee communities in heavy metal‐contaminated areas will contribute to integrated land rehabilitation to minimize the impact of pollution on the environment.

Contrasting effects of wooded and herbaceous semi-natural habitats on supporting wild bee diversity

Wild bees are the most important group of pollinators among insects. In agroecosystems, they promote successful pollination and thus ensure crop yields. In order to enhance species diversity and abundance of wild bees in farmland, it is essential to study the impact of the surrounding landscape as well as local habitat factors on the occurrence of wild bees, and identify and implement biodiversity enhancing measures. We established a national-wide monitoring program for wild bees in Austria’s main agricultural regions for the first time (project BINATS 2). This was achieved through a stratified random sampling design comprising 1,000 transects across 100 test areas. In this paper, we investigate the direct and indirect effects of local habitat and landscape factors on the richness of wild bee species, their abundance and selected functional traits (ground nesting, above-ground nesting, solitary, social and polylectic bees, Fabaceae specialists, bumblebees). Additonally, we analyse whether these effects vary between the early and late seasons using structural equation modeling (SEM). Our results show that wild bee species richness and abundance are directly positively related to flower cover and semi-natural open landscapes. Grasslands and insect pollinated crops contribute to increased local flower cover, and thereby indirectly enhance wild bee species richness and abundance. Although insect pollinated crops have a stronger positive effect on flower cover in spring compared to summer, the effect on wild bee species richness and abundance does not vary significantly throughout the season. Solitary and above-ground nesting bees are also positively influenced by the percentage of organic farming in the different test areas, while bumblebees – beside above-ground nesting wild bees – are specifically enhanced by plant diversity. In addition, bumblebees are the only group directly positively affected by insect pollinated crops. These results demonstrate the strong and complex dependency of wild bees on flowering fodder plants and semi-natural open landscapes. This highlights the risks of their decline within agricultural landscapes caused by a reduction of various landscape structures and diverse floral richness present over long periods of time. We also confirm that organic farming is a crucial factor for promoting certain wild bee traits.

Pollinators provide important ecosystem services for crop production and food security. With the development of agricultural economy and the increasing intensity of land-use, a large number of natural or semi-natural habitats have been converted to croplands. Landscape homogenization and intensive management lead to the decline of wild bee diversity and threaten the sustainable agricultural production. In this study, we investigated the effects of landscape complexity (proportion of semi-natural habitats), local management practices (local flowering plant diversity and soil total nitrogen), and their interactions on diversity of bee pollinators in apple orchard in Changping District, Beijing. A total of 8642 bee individuals were captured, including 5125 honey bees and 3517 wild bees from 5 families, 14 genera, and 49 species. The optimal landscape scale for the response of bee diversity to landscape complexity and local management intensity was 500 m. Within 500 m radius of the site, the abundance of overall bees and wild bees significantly increased with increasing proportion of semi-natural habitats. The landscape complexity interacting with local flowering plant diversity significantly affected the richness of overall bee and wild bee. When the proportion of semi-natural habitats surrounding the apple orchards was low (≤29.9%), we found a positive effect of flowering plant diversity on the richness of overall bee and wild bee, whereas a reversed trend was found when the proportion of semi-natural habitats surrounding the apple orchards was high (>29.9%). In addition, the abundance of honey bees significantly increased with the increase of local flowering plant diversity and soil total nitrogen. The soil total nitrogen interacting with local flowering plant diversity significantly affected the honey bee abundance. At low levels of soil total nitrogen (≤1.9 g·kg-1), there was a positive effect of flowering plant diversity on honey bee abundance; whereas this trend was reversed at high levels of soil total nitrogen (>1.9 g·kg-1). Increasing the proportion of semi-natural habitats in agricultural landscape was beneficial to the increase of wild bee abundance, and flowering plant diversity could promote bee diversity but depending on landscape scale (proportion of semi-natural habitats) and local scale (nitrogen application). Therefore, multi-scale factors should be considered to develop conservation strategies to maintain the diversity of wild bees in agricultural landscape. Maintaining a higher proportion of cultivated land as much as possible is still a long-term requirement for production, while maintaining intermediate landscape complexity, increasing the diversity of flowering plants on the ground, and reducing the application of nitrogen fertilizer would be effective ways to promote the diversity of pollinating bees in apple orchards.

Effects of arsenic and selenium pollution on wild bee communities in the agricultural landscapes

The study of bee species present in agricultural landscapes is necessary to identify potential crop pollina-tors and promote the ecosystem services they provide. Bee community studies are the first step to know the bee species in a given area, as well as their abundance and activity periods. The aim of this research was to identify bee species as potential pollinators of onion crops in a xeric area of Argentina (San Juan province). Specimens were captured with elevated pan traps during flowering of onion crops, and the bee community was characterized by functional traits such as body size, nesting biology, and sociality. Additionally, we stud-ied the period of activity for each species in relation to the peak of onion blossom. Traps collected a total of 1,765 individuals and 55 species/morphospecies of bees were identified, reporting 21 new records for San Juan province. The most abundant species were Apis mellifera L. and two species of Lasioglossum (Dialic-tus) Robertson. The bee community was characterized by a great richness of species of small and very small size, with a preference for nesting below ground and solitary behavior. Among wild bees, genus La-sioglossum Curtis showed a high diversity (richness and abundance) during onion flowering. Future studies are needed to determine their contribution to the pollination of this crop. In this study, we highlight the diver-sity of wild bees present during onion flowering in a xeric environment and its importance for future ecolog-ical, conservation, and pollination studies.

Highbush blueberry yields are dependent on pollination by bees, and introduction of managed honey bees is the primary strategy used for pollination of this crop. Complementary pollination services are also provided by wild bees, yet highbush blueberry is increasingly grown in regions outside its native range where wild bee communities may be less adapted to the crop and growers may still be testing appropriate honey bee stocking densities. To contrast crop pollination in native and non-native production regions, we sampled commercial ‘Bluecrop’ blueberry fields in British Columbia and Michigan with grower-selected honey bee stocking rates (0–39.5 hives per ha) to compare bee visitors to blueberry flowers, pollination and yield deficits, and how those vary with local- and landscape-scale factors. Observed and Chao-1 estimated species richness, as well as Shannon diversity of wild bees visiting blueberries were significantly higher in Michigan where the crop is within its native range. The regional bee communities were also significantly different, with Michigan farms having greater dissimilarity than British Columbia. Blueberry fields in British Columbia had fewer visits by honey bees than those in Michigan, irrespective of stocking rate, and they also had lower berry weights and a significant pollination deficit. In British Columbia, pollination service increased with abundance of wild bumble bees, whereas in Michigan the abundance of honey bees was the primary predictor of pollination. The proportion of semi-natural habitat at local and landscape scales was positively correlated with wild bee abundance in both regions. Wild bee abundance declined significantly with distance from natural borders in Michigan, but not in British Columbia where large-bodied bumble bees dominated the wild bee community. Our results highlight the varying dependence of crop production on different types of bees and reveal that strategies for pollination improvement in the same crop can vary greatly across production regions.

Pollination is one of the most important processes in terrestrial ecosystems. This free nature service depends on a homogeneous distribution and sufficient density of flower-visiting insects, mainly wild bees and managed honey bees. Habitat destruction and habitat fragmentation and intensive land-use led to species loss on multiple trophic levels.The aim of this work was to answer the question whether pollination is still sufficiently ensured by wild bees and honey bees in intensively managed agricultural landscapes. For this, it was necessary to quantify local honey bee abundance and wild bee species composition and density in relation to landscape structure at different spatial scales. Thus it was tested, how solitary wild bees, social bumble bees and honey bees interact with the surrounding landscape (chapter 4). Furthermore, the influence of possible pollination limitation due to low densities of flower-visiting bees on yield of oilseed rape was studied in dependence of the surrounding landscape (chapter 5). Finally, the effect of different pollination vectors on oilseed rape was measured to quantify the relative importance of bee pollination and wind pollination for fruit set. The spatial distribution and density of managed honey bees was measured using Geographical Information Systems, for the district of Göttingen (Germany). In Germany, in a period of twelve years (1989 2000), the total number of managed honey bees decreased by 26% representing a loss of about 260.000 honey bee locations. Bee diseases and the high percentage of old beekeepers led to this situation. In conclusion, the current situation of beekeeping in the district of Göttingen has reached a critical level. The conservation of wild pollinator and the support of beekeeping must be a central topic to ensure pollination services for agricultural crops. If not, a full-coverage pollination by honey bees cannot be guaranteed.An aim of this study was the analysis of the effects of landscape context and the influence of the percentage of semi-natural habitats on species composition of trap-nesting wild bee communities a gradient of structurally poor to structurally rich landscapes. An increasing proportion of the semi-natural habitats in the surrounding landscape had no positive effect on species diversity at any spatial scale. In contrast, an increasing proportion of rapecrop fields influenced the number of brood cells per nest and the total nest number of Osmia rufa (Hymenoptera: Apidae) at small spatial scales. In conclusion, all studied agricultural landscapes only supported relatively low numbers of solitary bees and wasps.Bee visitation is necessary for pollination. To analyse the value of the degree of flower-visiting bees we analysed, if an increasing diversity and density of flower-visiting bees may have positive effects on the yield of oilseed rape (Brassica napus L. ssp. oleifera (Metzg.), Brassicaceae). Flower visitor observations indicated significantly increased seed set per flower with increasing honey bee densities, whereas the abundance of flower-visiting wild bees had no measurable effect on yields of oilseed rape. Bee visitation had no effect on real yield (g/m²), probably as a result of the high compensatory-growth ability of oilseed rape and variation in cultivation methods or local soil conditions between the landscapes. In contrast, rape yield was positively related to a higher percentage of rape crop fields in the surrounding landscape, possibly due to higher pollen densities in the air and enhanced wind pollination.Summarizing this study, species richness and abundance of solitary wild bees depends on landscape context and habitat composition. Species diversity and abundance of flower-visiting bees increase with higher percentage of semi-natural habitats in the surrounding landscape. Generally, habitat fragmentation and destruction of ecologically valuable habitats can cause decreasing bee diversity (solitary wild bees, social bumble bees and honey bees). Pollination as a free nature service depends on a high pollinator density and may result in a higher fruit set and yield thus confirming the economical importance of pollination. In conclusion, a further loss of pollinators must be avoided to protect most wild plant species and to ensure high yields of insect-pollinated cultivated plants.

Forests in Germany are occupied with roads, paths, and trails with a density of 5.03 km/km². Their construction and maintenance create a network of verges promoting flowering plants. Whether these verges are visited by bees, which factors are determining their abundance, diversity, and composition, and which flowering resources are used is unknown. We selected 13 verges in the Black Forest (Germany), sweep-netted wild bees along transects, calculated the flowering area of all herbs, and measured the area (hectares) of grassland within 1 km around the transects. To evaluate the resource use of a common bumblebee species, we analyzed the pollen load of common carder bees (Bombus pascuorum) using microscopes. The abundance and diversity of wild bees was positively related to flowering area. With an increasing area of grassland, the abundance of ubiquitous species increased. Wild bee community composition was driven by flowering area. Common carder bees collected pollen from several flower resources but mainly used few species, such as the common hemp nettle (Galeopsis tetrahit L.). As the flowering area influenced wild bee abundance, diversity, and composition, we suggest creating road verges that favor the occurrence of native flowering plants to support wild bees in forest ecosystems.Study Implications: Forest road verges generally have higher light availability than the forest interior and therefore have higher availability of flowering plants. Although the importance of verges for wild bee conservation in agricultural landscapes is known, forest road verges are understudied. Our study demonstrates that forest road verges are important habitats for many ubiquitous bees and that the flowering area on these verges is the key determinant for the abundance and diversity of wild bees. Therefore, creating road verges that favor the occurrence of native flowering plants is key to support bees on these verges.

Loss of habitat area and diversity poses a threat to communities of wild pollinators and flowering plants in agricultural landscapes. Pollinators, such as wild bees, and insect‐pollinated plants are two groups of organisms that closely interact. Nevertheless, it is still not clear how species richness and functional diversity, in terms of pollination‐relevant traits, of these two groups influence each other and how they respond to land use change. In the present study, we used data from 24 agricultural landscapes in seven European countries to investigate the effect of landscape composition and habitat richness on species richness and functional diversity of wild bees and insect‐pollinated plants. We characterized the relationships between the diversity of bees and flowering plants and identified indirect effects of landscape on bees and plants mediated by these relationships. We found that increasing cover of arable land negatively affected flowering plant species richness, while increasing habitat richness positively affected the species richness and functional diversity of bees. In contrast, the functional diversity of insect‐pollinated plants (when corrected for species richness) was unaffected by landscape composition, and habitat richness showed little relation to bee functional diversity. We additionally found that bee species richness positively affected plant species richness and that bee functional diversity was positively affected by both species richness and functional diversity of plants. The relationships between flowering plant and bee diversity were modulated by indirect effects of landscape characteristics on the biotic communities. In conclusion, our findings demonstrate that landscape properties affect plant and bee communities in both direct and indirect ways. The interconnection between the diversities of wild bees and insect‐pollinated plants increases the risk for parallel declines, extinctions, and functional depletion. Our study highlights the necessity of considering the interplay between interacting species groups when assessing the response of entire communities to land use changes.

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