Opportunities and threats for pollinator conservation in global towns and cities

Urban environment decreases pollinator availability, fertility, and prolongs anthesis in the field bindweed (Convolvulus arvensis Linnaeus, 1753)

Urbanization alters the natural environment, with broad negative impacts on living organisms. Urbanization can also disrupt plant-pollinator networks by reducing the abundance and diversity of invertebrates. Firstly, I investigated whether the field bindweed (Convolvulus arvensis) is an obligatory entomophilous plant because previous reports were ambiguous. Secondly, I investigated how the obligatory entomophilous plant, field bindweed, responds to urbanization by comparing the flowering duration (anthesis) and the reproductive success of field bindweeds in urban and rural populations. Unlike cross-pollinated flowers and controls, flowers experimentally prevented from pollination and self-pollinated flowers did not produce seeds, suggesting that the field bindweed is self-incompatible and obligatory entomophilous. The abundance of urban pollinators was 5-6 times lower than the abundance of rural pollinators, and flies (Diptera), beetles (Coleoptera) and moths (Lepidoptera) were significantly more negatively influenced by the urban environment than hymenopterans (Hymenoptera). Urban plants showed significantly longer anthesis duration and lower reproductive success than rural plants. Illuminance and low pollinator abundance were negatively associated with the duration of the anthesis, but relative humidity did not affect the anthesis. Prolonged duration of the anthesis may be an adaptation to pollinator scarcity because more prolonged flowering increases the likelihood of pollination. Future research should unravel whether the longer anthesis of urban flowers is determined by behavioral plasticity or by the evolutionary selection of plants with a genetically determined longer anthesis.

Neonicotinoid insecticides in well-developed agricultural cultivation areas: Seawater occurrence, spatial-seasonal variability and ecological risks

Neonicotinoids (NEOs) are widely used insecticides and have been detected in aquatic environments globally. However, little is known about NEOs contamination in the coastal environments under the terrestrial pressure of multiple planting types simultaneously. This study investigated the occurrence, spatial-seasonal variability, and ecological risks of NEOs along the coast of the Shandong Peninsula during the dry and wet seasons, where located many largest fruit, vegetable, and grain production bases in China. The concentrations of ∑NEOs in seawater were higher in wet seasons (surface: 195.46 ng/L; bottom: 14.56 ng/L) than in dry seasons (surface: 10.07 ng/L; bottom: 8.45 ng/L). During the wet seasons, NEOs peaked in the northern and eastern areas of the Shandong Peninsula, where the inland fruit planting area is located. While dry seasons had higher concentrations in Laizhou Bay, influenced by rivers from vegetable-growing areas. Grain crops, fruit, and cotton planting were major NEOs sources during wet seasons, while wheat and vegetables dominated in dry seasons. Moderate or above ecological risks appeared at 53.8% of the monitoring sites. Generally, NEOs caused high risks in the wet seasons mainly caused by Imidacloprid, and medium risk in the dry seasons caused by Clothianidin, which should be prevented and controlled in advance.

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.

Differential impacts of land-use change on multiple components of common milkweed (Asclepias syriaca) pollination success

Land-use change is one the greatest threats to biodiversity and is projected to increase in magnitude in the coming years, stressing the importance of better understanding how land-use change may affect vital ecosystem services, such as pollination. Past studies on the impact of land-use change have largely focused on only one aspect of the pollination process (e.g., pollinator composition, pollinator visitation, and pollen transfer), potentially misrepresenting the full complexity of land-use effects on pollination services. Evaluating the impacts across multiple components of the pollination process can also help pinpoint the underlying mechanisms driving land-use change effects. This study evaluates how land-use change affects multiple aspects of the pollination process in common milkweed populations, including pollinator community composition, pollinator visitation rate, pollen removal, and pollen deposition. Overall, land-use change altered floral visitor composition, with small bees having a larger presence in developed areas. Insect visitation rate and pollen removal were also higher in more developed areas, perhaps suggesting a positive impact of land-use change. However, pollen deposition did not differ between developed and undeveloped sites. Our findings highlight the complexity evaluating land-use change effects on pollination, as these likely depend on the specific aspect of pollination evaluated and on the of the intensity of disturbance. Our study stresses the importance of evaluating multiple components of the pollination process in order to fully understand overall effects and mechanisms underlying land-use change effects on this vital ecosystem service.

Bees in the city: Findings from a scoping review and recommendations for urban planning

Over the last decades, bee biodiversity has dropped sharply due to land use change, including urbanization. To contrast this, recent research has pointed to cities as a hotspot for bees. Because of this ambiguity, a scoping review has been conducted to examine the urban characteristics that impact bees and how bees are impacted. A total of 276 articles were analyzed against landscape and local habitat characteristics. The key findings include first that natural areas are more valuable for bees since biodiversity levels are higher. Second, urban areas generally score better than agricultural and rural areas. Third, plant biodiversity positively influences bee biodiversity. Fourth, the urban environment strongly affects some bee traits and the proportion of native bees. For making cities bee friendly and bee inclusive, we recommend to maintain natural areas, connect natural areas to urban ecosystems, encourage floral abundance and diversity and increasing the size of urban green areas overall.

Bee and butterfly records indicate diversity losses in western and southern North America, but extensive knowledge gaps remain

Pollinator losses threaten ecosystems and food security, diminishing gene flow and reproductive output for ecological communities and impacting ecosystem services broadly. For four focal families of bees and butterflies, we constructed over 1400 ensemble species distribution models over two time periods for North America. Models indicated disproportionally increased richness in eastern North America over time, with decreases in richness over time in the western US and southern Mexico. To further pinpoint geographic areas of vulnerability, we mapped records of potential pollinator species of conservation concern and found high concentrations of detections in the Great Lakes region, US East Coast, and southern Canada. Finally, we estimated asymptotic diversity indices for genera known to include species that visit flowers and may carry pollen for ecoregions across two time periods. Patterns of generic diversity through time mirrored those of species-level analyses, again indicating a decline in pollinators in the western U.S. Increases in generic diversity were observed in cooler and wetter ecoregions. Overall, changes in pollinator diversity appear to reflect changes in climate, though other factors such as land use change may also explain regional shifts. While statistical methods were employed to account for unequal sampling effort across regions and time, improved monitoring efforts with rigorous sampling designs would provide a deeper understanding of pollinator communities and their responses to ongoing environmental change.

Understanding how environmental degradation, microclimate, and management shape honey production across different spatial scales

Although the abundance, survival, and pollination performance of honeybees are sensitive to changes in habitat and climate conditions, the processes by which these effects are transmitted to honey production and interact with beekeeping management are not completely understood. Climate change, habitat degradation, and beekeeping management affect honey yields, and may also interact among themselves resulting in indirect effects across spatial scales. We conducted a 2-year, multi-scale study on Chiloe Island (northern Patagonia), where we evaluated the most relevant environmental and management drivers of honey produced by stationary beekeepers. We found that the effects of microclimate, habitat, and management variables changed with the spatial scale. Among the environmental variables, minimum temperature, and cover of the invasive shrub, gorse (Ulex europaeus) had the strongest detrimental impacts on honey production at spatial scales finer than 4 km. Specialized beekeepers who adopted conventional beekeeping and had more mother colonies were more productive. Mean and minimum temperatures interacted with the percentage of mother colonies, urban cover, and beekeeping income. The gorse cover increased by the combination of high temperatures and the expansion of urban lands, while landscape attributes, such as Eucalyptus plantation cover, influenced beekeeping management. Results suggest that higher temperatures change the available forage or cause thermal stress to honeybees, while invasive shrubs are indicators of degraded habitats. Climate change and habitat degradation are two interrelated environmental phenomena whose effects on beekeeping can be mitigated through adaptive management and habitat restoration.

One hundred important questions facing plant science derived using a large language model

Artificial intelligence (AI) is advancing rapidly and continually evolving in various fields. Recently, the release of ChatGPT has sparked significant public interest. In this study, we revisit the '100 Important Questions Facing Plant Science' by leveraging ChatGPT as a valuable tool for generating thought-provoking questions relevant to plant science. These questions primarily revolve around the utilization of plants in product development, understanding plant mechanisms, plant-environment interactions, and enhancing plant traits, with an emphasis on sustainable product development. While ChatGPT may not capture certain crucial aspects highlighted by scientists, it offers valuable insights into the questions generated by experts. Our analysis demonstrates that ChatGPT can be cautiously employed as a supportive tool to facilitate, streamline, and expedite specific tasks in plant science.

Factors influencing butterfly and bumblebee richness and abundance in gardens

Gardens are often depicted as green sanctuaries, providing refuges for wildlife displaced from the countryside due to intensive farming. While gardens have been recognized for their positive impact on biodiversity conservation, few studies have investigated the impact of pesticide usage in domestic gardens. In this study, we explored how butterfly and bumblebee populations in gardens across the UK are influenced by habitat quality, urbanisation level and pesticide use. To achieve this, we engaged with participants in Garden BirdWatch, a weekly garden wildlife recording scheme operated by the British Trust for Ornithology. Participants in the study provided data on the attributes of their garden and surrounding area and were asked to complete a questionnaire about their pesticide practices. Of the 417 gardens from which we obtained useful data, we found that 32.6 % had pesticides applied to. Urbanisation and garden quality were the main factors influencing insect populations. Butterfly richness was lower in suburban and urban gardens and butterfly abundance lower only in suburban gardens when compared to rural gardens, but this relationship did not hold for bumblebees. Abundance of butterflies and bumblebees, but not their species richness, increased with the habitat quality of gardens. Butterflies were lower in abundance and richness in more northerly gardens, which was not the case for bumblebees. Effects of pesticides were relatively weak, but butterfly richness was 7 % lower in gardens applying any pesticide. Overall, our study shows that garden butterfly and bumblebee abundance and richness are strongly influenced by both extrinsic and intrinsic factors, and that garden management can have an important positive effect on insect population.

Interaction of chlorothalonil and Varroa destructor on immature honey bees rearing in vitro

Under realistic environmental conditions, bees are often exposed to multiple stressors, especially Varroa destructor and pesticides. In this study, the effects of exposure to NOAEC of chlorothalonil during the larval stage, in the presence or absence of V. destructor, was examined in terms of survival, morphological and transcriptional changes. The interaction between chlorothalonil and V. destructor on the survival of honey bee was additive. V. destructor are the dominant factor in the interaction for survival and transcriptome alternation. The downregulation of the genes related to tissue growth and caste differentiation may directly link to the mortality of honey bees. Either chlorothalonil or V. destructor induces the irregular morphology of trophocytes and oenocytes in the fat body. In addition to irregular shapes, oenocytes in V. destructor alone and double-stressor treatment group showed altered nuclei and vacuoles in the cytoplasm. The interaction of V. destructor and chlorothalonil at the larval stage have potential adverse effects on the subsequent adult bees, with up-regulation of genes involved in lipid metabolism and detoxification/defense in fat body tissue. Our findings provide a comprehensive understanding of combinatorial effects between biotic and abiotic stressors on one of the most important pollinators, honey bees.

Insect-Mediated Pollination of Strawberries in an Urban Environment

Pollination services provided by a diversity of pollinators are critical in agriculture because they enhance the yield of many crops. However, few studies have assessed pollination services in urban agricultural systems. We performed flower-visitor observations and pollination experiments on strawberries (Fragaria × ananassa) in an urban area near Paris, France, in order to assess the effects of (i) insect-mediated pollination service and (ii) potential pollination deficit on fruit set, seed set, and fruit quality (size, weight, and malformation). Flower-visitor observations revealed that the pollinator community solely comprised unmanaged pollinators, despite the presence of beehives in the surrounding landscape. Based on the pollination experiments, we found that the pollination service mediated by wild insects improved the fruit size as a qualitative value of production, but not the fruit set. We also found no evidence of pollination deficit in our urban environment. These results suggest that the local community of wild urban pollinators is able to support strawberry crop production and thus plays an important role in providing high-quality, local, and sustainable crops in urban areas.

How can residents protect and promote pollinators? The diffusion of residential pollinator-friendly gardening

Urbanization and land use change are leading causes of declines in pollinator abundance and diversity. However, researchers in different regions of the world have found that some pollinators can thrive in urban landscapes, depending on land use practices, environmental conditions, and species traits. Residential landscapes constitute a significant portion of urban green space and thus, residents' adoption of landscape practices to promote pollinators can play a central role in addressing the global pollinator challenge. Yet, although residents' willingness and intention appear strong, adoption of pollinator-friendly gardening remains low. The present study - guided by the Diffusion of Innovations theory - aimed to build empirical understanding by surveying 1598 [State] residents on their experiences and perceptions related to pollinator-friendly gardening to determine the most salient barriers and opportunities to engagement. Key findings suggest making the practice more widely observable and reducing perceived complexity in learning to do the practice are critical to promoting adoption. This demonstrates, in practical terms, that: (1) targeted efforts to build residents' actionable knowledge about pollinator-friendly gardening may significantly reduce uncertainty and boost the likelihood of adoption; and (2) examples of active pollinator gardens need to be more widely showcased and popularized (e.g., through experiential or virtual demonstrations). We also found most residents living in homeowner associations (HOAs) believed HOA policies on pollinator-friendly gardening were restrictive or the residents were unsure whether they are allowed to practice pollinator-friendly gardening. Given these perceptions strongly associated with residents' low intent to engage in pollinator-friendly gardening, a major opportunity exists to diffuse the practice and increase adoption by working with HOAs and community leaders to become promoters of - rather than barriers to - pollinator-friendly gardening.

Quantifying the impact of an invasive Hornet on Bombus terrestris Colonies

The invasive hornet Vespa velutina nigrithorax is considered a proliferating threat to pollinators in Europe and Asia. While the impact of this species on managed honey bees is well-documented, effects upon other pollinator populations remain poorly understood. Nonetheless, dietary analyses indicate that the hornets consume a diversity of prey, fuelling concerns for at-risk taxa. Here, we quantify the impact of V. velutina upon standardised commercially-reared colonies of the European bumblebee, Bombus terrestris terrestris. Using a landscape-scale experimental design, we deploy colonies across a gradient of local V. velutina densities, utilising automated tracking to non-invasively observe bee and hornet behaviour, and quantify subsequent effects upon colony outcomes. Our results demonstrate that hornets frequently hunt at B. terrestris colonies, being preferentially attracted to those with high foraging traffic, and engaging in repeated-yet entirely unsuccessful-predation attempts at nest entrances. Notably however, we show that B. terrestris colony weights are negatively associated with local V. velutina densities, indicating potential indirect effects upon colony growth. Taken together, these findings provide the first empirical insight into impacts on bumblebees at the colony level, and inform future mitigation efforts for wild and managed pollinators.

The effects of urbanization on pollinators and pollination: A meta-analysis

Urbanization is increasing worldwide, with major impacts on biodiversity, species interactions and ecosystem functioning. Pollination is an ecosystem function vital for terrestrial ecosystems and food security; however, the processes underlying the patterns of pollinator diversity and the ecosystem services they provide in cities have seldom been quantified. Here, we perform a comprehensive meta-analysis of 133 studies examining the effects of urbanization on pollinators and pollination. Our results confirm the widespread negative impacts of urbanization on pollinator richness and abundance, with Lepidoptera being the most affected group. Furthermore, pollinator responses were found to be trait-specific, with below-ground nesting and solitary Hymenoptera, and spring flyers more severely affected by urbanization. Meanwhile, cities promote non-native pollinators, which may exacerbate conservation risks to native species. Surprisingly, despite the negative effects of urbanization on pollinator diversity, pollination service measured as seed set is enhanced in non-tropical cities likely due to abundant generalists and managed pollinators therein. We emphasize that the richness of local flowering plants could mitigate the negative impacts of urbanization on pollinator diversity. Overall, the results demonstrate the varying magnitudes of multiple moderators on urban pollinators and pollination services and could help guide conservation actions for biodiversity and ecosystem function for a sustainable future.

Native fauna interact differently with native and alien trees in a tropical megacity

The negative effects of invasive alien plant species on natural ecosystems are well known. However, in rapidly growing cities, alien plants can provide native fauna with resources otherwise lost due to the biotic homogenization, which is common to urban ecosystems. Interactions of native fauna with alien flora have thus far focused largely on invertebrate pollinators in temperate cities in the northern hemisphere. Cities in tropical areas, however, are larger and are growing more rapidly, and host a variety of vertebrate pollinators. Understanding how birds and mammals interact with native and alien flora in these megacities could improve management of urban ecosystems in highly biodiverse regions while limiting invasion potential. Therefore, here we investigate whether native diurnal birds and mammals interact differently with native versus alien trees in Bengaluru, India where historical planting has led to an abundance of alien tree species. We find that tree origin alone was not an important predictor for bird species richness and abundance, but taller native trees with large floral display sizes were more species rich than alien trees of similar floral displays. As expected from their shared evolutionary history, nectarivorous birds fed from native trees more often in a manner that could facilitate pollination, but engaged in nectar theft more often with alien trees. Squirrels (the mammal observed most frequently to interact with flowers) were more likely, however, to depredate flowers of native trees. Our results suggest alien trees can be an important resource for fauna in expanding urban areas, and that nectar theft by birds could reduce the seed set of alien trees.

Insect-pollinators and their interactions with plants differ in disturbed and semi-natural areas: Tanzania's Southern Highlands case study

Due to inadequate insect-pollinator data, particularly in sub-Saharan African countries like Tanzania, it is difficult to manage and protect these species in disturbed and semi-natural areas. Field surveys were conducted to assess insect-pollinator abundance and diversity and their interactions with plants in disturbed and semi-natural areas in Tanzania's Southern Highlands using pan traps, sweep netting, transect counts, and timed observations techniques. We found that species diversity and richness of insect-pollinators were high in semi-natural areas, and there was 14.29% more abundance than in disturbed areas. The highest plant-pollinator interactions were recorded in semi-natural areas. In these areas, the total number of visits by Hymenoptera was more than three times that of Coleoptera, while that of Lepidoptera and Diptera was more than 237 and 12 times, respectively. Hymenoptera pollinators had twice the total number of visits of Lepidoptera, and threefold of Coleoptera, and five times more visits than Diptera in disturbed habitats. Although disturbed areas had fewer insect-pollinators and fewer plant-insect-pollinator interactions, our findings indicate that both disturbed and semi-natural areas are potential habitats for insect-pollinators. The study revealed that the over-dominant species Apis mellifera could influence diversity indices and network-level metrics in the study areas. When A. mellifera was excluded from the analysis, the number of interactions differed significantly between insect orders in the study areas. Also, Diptera pollinators interacted with the most flowering plants in both study areas compared to Hymenopterans. Though A. mellifera was excluded in the analysis, we found a high number of species in semi-natural areas compared to disturbed areas. Conclusively, we recommend that more studies be conducted in these areas across sub-Saharan Africa to unveil their potential for protecting insect-pollinators and how ongoing anthropogenic changes threaten them.

Plant growers' environmental consciousness may not be enough to mitigate pollinator declines: a questionnaire-based case study in Hungary

BACKGROUND

Pesticides are one of the most important anthropogenic-related stressors. In times of global pollinator decline, the role of integrated farming and urban gardens in supporting wild pollinators is becoming increasingly important. We circulated an online questionnaire to survey plant protection practices among Hungarian farmers and garden owners with a particular emphasis on pollinator protection.

RESULTS

We found that plant growers rely heavily on pesticide use, and pesticides are used widely in otherwise pollinator-friendly gardens. Whether pesticide use practices were driven by expert opinion and respondent gender were the best predictors of pesticide use. Although most respondents supported pollinators, pesticides are also used widely among home garden owners, which can pose a non-evident ecological trap for pollinator populations in the gardens.

CONCLUSION

Special attention should be paid to implementing measures to reduce pesticide use not only in farmland, but also in home gardens. Environmental education and financial support through agroecological schemes could efficiently promote the transition away from pesticide use. However, whereas farmers can be encouraged to reduce pesticide use mostly by expert advice, garden owners are likely to rely on more conventional information channels. The attitudes of Hungarian plant growers can provide an insight into pesticide use practices of Central and Eastern European countries, but similar surveys are needed across Europe for a complete understanding of broad-scale processes. This work lays the foundations for similar studies that can inform and facilitate the transformation to pesticide-free farming and gardening. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Informing policy and practice on insect pollinator declines: Tensions between conservation and animal welfare

Climate change, agricultural intensification, and other anthropogenic ecosystem challenges have caused declines in the diversity and abundance of insect pollinators. In response to these declines, entomologists have called for greater attention to insect pollinator conservation. Conservation primarily aims to protect groups of non-human animals—populations or species—with only secondary concern for the welfare of individual animals. While conservation and animal welfare goals are sometimes aligned, they often are not. And because animal welfare comes second, it tends to be sacrificed when in tension with conversation priorities. Consider, for example, lethal sampling to monitor many pollinator populations. Growing evidence suggests that the welfare of individual insect pollinators may be morally significant, particularly in the Hymenoptera and Diptera. Considering insect welfare in conservation practices and policies presents many challenges as, in the face of rapid, anthropogenic change, it may be impossible to avoid harming individual animals while promoting diverse populations. We suggest some practical, implementable strategies that can allow for more robust integration of animal welfare goals into insect pollinator conservation. By following these strategies, entomologists may be able to find policies and practices that promote the health of ecosystems and the individual animals within them.

Low resource availability drives feeding niche partitioning between wild bees and honeybees in a European city

Cities are socioecological systems that filter and select species, therefore establishing unique species assemblages and biotic interactions. Urban ecosystems can host richer wild bee communities than highly intensified agricultural areas, specifically in resource-rich urban green spaces such as allotments and family gardens. At the same time, urban beekeeping has boomed in many European cities, raising concerns that the fast addition of a large number of managed bees could deplete the existing floral resources, triggering competition between wild bees and honeybees. Here, we studied the interplay between resource availability and the number of honeybees at local and landscape scales and how this relationship influences wild bee diversity. We collected wild bees and honeybees in a pollination experiment using four standardized plant species with distinct floral morphologies. We performed the experiment in 23 urban gardens in the city of Zurich (Switzerland), distributed along gradients of urban and local management intensity, and measured functional traits related to resource use. At each site, we quantified the feeding niche partitioning (calculated as the average distance in the multidimensional trait space) between the wild bee community and the honeybee population. Using multilevel structural equation models (SEM), we tested direct and indirect effects of resource availability, urban beekeeping, and wild bees on the community feeding niche partitioning. We found an increase in feeding niche partitioning with increasing wild bee species richness. Moreover, feeding niche partitioning tended to increase in experimental sites with lower resource availability at the landscape scale, which had lower abundances of honeybees. However, beekeeping intensity at the local and landscape scales did not directly influence community feeding niche partitioning or wild bee species richness. In addition, wild bee species richness was positively influenced by local resource availability, whereas local honeybee abundance was positively affected by landscape resource availability. Overall, these results suggest that direct competition for resources was not a main driver of the wild bee community. Due to the key role of resource availability in maintaining a diverse bee community, our study encourages cities to monitor floral resources to better manage urban beekeeping and help support urban pollinators.

A large-scale dataset reveals taxonomic and functional specificities of wild bee communities in urban habitats of Western Europe

Wild bees are declining, mainly due to the expansion of urban habitats that have led to land-use changes. Effects of urbanization on wild bee communities are still unclear, as shown by contrasting reports on their species and functional diversities in urban habitats. To address this current controversy, we built a large dataset, merging 16 surveys carried out in 3 countries of Western Europe during the past decades, and tested whether urbanization influences local wild bee taxonomic and functional community composition. These surveys encompassed a range of urbanization levels, that were quantified using two complementary metrics: the proportion of impervious surfaces and the human population density. Urban expansion, when measured as a proportion of impervious surfaces, but not as human population density, was significantly and negatively correlated with wild bee community species richness. Taxonomic dissimilarity of the bee community was independent of both urbanization metrics. However, occurrence rates of functional traits revealed significant differences between lightly and highly urbanized communities, for both urbanization metrics. With higher human population density, probabilities of occurrence of above-ground nesters, generalist and small species increased. With higher soil sealing, probabilities of occurrence of above-ground nesters, generalists and social bees increased as well. Overall, these results, based on a large European dataset, suggest that urbanization can have negative impacts on wild bee diversity. They further identify some traits favored in urban environments, showing that several wild bee species can thrive in cities.

Contribution of Home Gardens to Sustainable Development: Perspectives from A Supported Opinion Essay

Home gardening has a long history that started when humans became sedentary, being traditionally considered an accessible source of food and medicinal plants to treat common illnesses. With trends towards urbanization and industrialization, particularly in the post-World War II period, the importance of home gardens as important spaces for growing food and medicinal plants reduced and they began to be increasingly seen as decorative and leisure spaces. However, the growing awareness of the negative impacts of agricultural intensification and urbanization for human health, food quality, ecosystem resilience, and biodiversity conservation motivated the emergence of new approaches concerning home gardens. Societies began to question the potential of nearby green infrastructures to human wellbeing, food provisioning, and the conservation of traditional varieties, as well as providers of important services, such as ecological corridors for wild species and carbon sinks. In this context. and to foster adaptive and resilient social-ecological systems, our supported viewpoint intends to be more than an exhaustive set of perceptions, but a reflection of ideas about the important contribution of home gardens to sustainable development. We envision these humble spaces strengthening social and ecological components, by providing a set of diversified and intermingled goods and services for an increasingly urban population.

Backyard buzz: human population density modifies the value of vegetation cover for insect pollinators in a subtropical city

Urbanisation drives overall declines in insect pollinators. Although urban green spaces can provide suitable habitat for pollinators much remains to be learned about how urban landscapes either promote or negatively impact pollinators. We investigated how backyard design, local (100 m) and landscape (500 m) scale vegetation cover and human population density were associated with non-eusocial native bee species, eusocial bees (Apis mellifera and Tetragonula spp.), and hoverflies, in residential green spaces of the subtropical city Brisbane, Australia. We found that associations between bee abundance and vegetation cover were moderated by human density, but the direction of this effect differed for non-eusocial and eusocial species. Non-eusocial bee abundance was positively associated with tree cover at local and landscape scales when human densities were low, but negatively so at high human population densities. We suggest this may be because the quality of vegetation for non-eusocial bees deteriorates as human density increases. In contrast, abundance of eusocial bees was negatively associated with increasing local cover of grass and shrubs at low levels of human density, but positively associated at high densities. This affinity to humans could partly be explained by domesticated “kept” hives. We found no effect of urban gradients on bee species richness. Hoverfly abundance was negatively related to human density and positively related to vegetation cover at local and landscape scales. At the backyard scale, both bee species richness and bee and hoverfly abundances were positively associated to flower abundance. Backyards with more vegetation cover had higher densities of non-eusocial bees. Our results thus support the idea that urban greening in densely populated areas at multiple spatial scales can benefit a range of insect pollinators.

The potential consequences of 'bee washing' on wild bee health and conservation

Concern around declining bee populations globally has become an environmental issue of mainstream importance. Policymakers, scientists, environmental non-government organizations, media outlets and the public have displayed great interest in conservation actions to support pollinators. As with many environmental causes, green washing, or in this case ‘bee washing’, has become rampant. Bee washing can lead to multiple negative consequences, including misinformation, misallocation of resources, increasing threats and steering public understanding and environmental policy away from evidence-based decision-making. Here I will discuss the multiple potential consequences of bee washing on efforts to conserve declining wild bees and promote wild bee health.

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Concern around declining bee populations globally has become an environmental issue of mainstream importance.

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Policymakers, scientists, environmental non-government organizations, media outlets and the public have displayed interest in conservation action to support pollinators.

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‘Bee washing’, has become rampant.

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Narratives and actions tend to focus on low-hanging fruit, actions which are easy to address and/or the selling of commercial items where industry benefits but the species of concern do not.

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Negative consequences include misinformation, misallocation of resources, increasing threats and steering environmental policy away from evidence-based decision-making.

Phylogenetic, functional and taxonomic responses of wild bee communities along urbanisation gradients

Increasing urbanisation is one of the primary drivers of land-use change that threaten biodiversity. Wild bee communities have been reported with contrasting responses to urbanisation, with varying effects on abundance and taxonomical diversity. The suite of functional traits exhibited by wild bee species might determine their persistence in urban areas. Urbanisation thus can impose an environmental filter with potential consequences on the functional and phylogenetical diversity of wild bee communities. Here, we sampled 2944 wild bee specimens from 156 species in 29 sites located along an urbanisation gradient using a replicated design in three mid-sized cities in the Loire valley (France). We show that urban landscape cover has a negative effect on overall species richness and taxonomical diversity indices, while total abundance remains constant. Species loss was taxon dependent, mainly driven by Andrenidae and Halictidae. Only a few species, especially of the genus Lasioglossum, were positively affected by the urban landscape cover. Urban and peri-urban areas differed in their composition of bee assemblages. Species turnover was the main component of beta diversity, driving community dissimilarities through the urban gradient. Urbanisation favours bees with small body sizes, social structure and extended flight periods but did not affect the phylogenetic or the functional diversity of communities. Our findings have implications for understanding the factors involved in the environmental filter exerted through the urban gradient on bee communities helping to implement conservation measures and managing urban spaces for bees.

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'.

Early-phase colonisation by introduced sculptured resin bee (Hymenoptera, Megachilidae, Megachile sculpturalis) revealed by local floral resource variability

There is a growing interest to document and better understand patterns and processes involved in non-native bee introductions and subsequent colonisation of new areas worldwide. We studied the spread of the East Asian bee Megachile sculpturalis in Serbia and south-eastern Europe; the bee was earlier established in the USA (since 1994) and western Europe (since 2008). Its establishment in Serbia remained dubious throughout most of 2017–2019, following its first detection. We hereby report on its establishment and spreading, which were corroborated in 2019 under specific circumstances. Owing to an exceptionally poor blooming of Styphnolobium japonicum in 2019, we recorded a high activity density of M. sculpturalis concentrated on a scarce key food resource. We present a novel quantitative approach for an improved early detection of M. sculpturalis, based on the interplay between the bee local occurrence pattern and dynamics of key food-plant(s) availability. This approach seems particularly effective during the early-phase colonisation, at initially low population density of introduced bees. We address the importance of integration of the genuine plant usage patterns with context-specific bee assessment options in establishing effective monitoring. The improved understanding of M. sculpturalis local dynamics triggered the questions about possible origin(s) and modes of its dispersal east of the Alps. To explore the possible scenarios of M. sculpturalis introduction(s), we extended the study to a wider spatio-temporal context – the region of SE Europe (2015–2019). The two complementary study approaches (at local and regional scale) provided more comprehensive evidence of bee dispersal history and the detection patterns in varied recording contexts. Based on this two-scale approach, we suggest that a diffusive mode of M. sculpturalis introduction into Serbia now seems to be a more plausible scenario (than a long-distance jump). We argue that the integration of outcomes from the contrasting approaches (a systematic surveillance, based on plant resources and a broad-scale opportunistic recording) could be of great methodological relevance for the development of future monitoring protocols.

Keeping Up with Insect Pollinators in Paris

There is growing interest in urban pollinator communities, although they may be subject to biotic homogenization in densely artificial landscapes. Paris (France) is one of the densest cities in the world, yet over the years many insect pollinator species have been reported there. We conducted in-depth surveys of Parisian green spaces for two years, in order to improve our knowledge of these assemblages. We explored several types of green spaces, monitoring pollinators throughout their activity season. We listed 118 species of wild bees and 37 species of hoverflies, updating pre-existing lists with 32 additional species. Bee assemblages showed functional diversity with 18.5% parasitic species and 17.7% oligolectic species. We also found several bee and hoverfly species under special conservation status. Over the study period, we observed seasonal succession of species, with diversified phenological niches. The greatest taxonomic and functional diversity was found in green spaces combining several habitats with ecological management. Despite its very dense urbanism, Paris is home to diverse pollinator communities. As a result, nearly half of the wild bee species of the wider Ile-de-France administrative region can be found within the city. This highlights the need to also consider dense urban environments in insect pollinator conservation strategies.

A review of the opportunities to support pollinator populations in South African cities

Globally insects are declining, but some guilds of pollinators are finding refuge in urban landscapes. The body of knowledge on urban pollinators is relatively mature, which means it is now possible to begin to make generalization. Unfortunately, studies do not represent climatic regions evenly and there is a gap in research from the African continent. This study aimed to address some of the gaps on urban pollination knowledge in South Africa and to identify opportunities to improve urban habitats for pollinators. We reviewed the international literature on urban pollinators and the South African literature on pollinators with a landscape ecology focus, drawing on literature with an emphasis on agricultural and ecosystem services. The findings show that some taxa (e.g. large-bodied, cavity nesting bees) will exploit urban environments increasing in abundance with urban intensity. Moderately sensitive taxa (such as small-bodied, ground-nesting bees) take advantage of urban environments only if local habitats are supportive of their needs for resource provision and habitat connectivity. The South African urban poor rely on pollination services for subsistence agriculture and the reproduction of wild-foraged medicines and food. Potential interventions to improve habitat quality include strategic mowing practices, conversion of turf-grass to floral rich habitats, scientific confirmation of lists of highly attractive flowers, and inclusion of small-scale flower patches throughout the urban matrix. Further research is needed to fill the Africa gap for both specialized and generalized pollinators (Diptera, Halictids, Lepidoptera and Hopliini) in urban areas where ornamental and indigenous flowering plants are valued.

Anthropogenic influences on bee foraging

Efficient foraging is vital to bee fitness but is challenging in the Anthropocene.

Herbivory on the pedunculate oak along an urbanization gradient in Europe: Effects of impervious surface, local tree cover, and insect feeding guild

Urbanization is an important driver of the diversity and abundance of tree-associated insect herbivores, but its consequences for insect herbivory are poorly understood. A likely source of variability among studies is the insufficient consideration of intra-urban variability in forest cover. With the help of citizen scientists, we investigated the independent and interactive effects of local canopy cover and percentage of impervious surface on insect herbivory in the pedunculate oak (Quercus robur L.) throughout most of its geographic range in Europe. We found that the damage caused by chewing insect herbivores as well as the incidence of leaf-mining and gall-inducing herbivores consistently decreased with increasing impervious surface around focal oaks. Herbivory by chewing herbivores increased with increasing forest cover, regardless of impervious surface. In contrast, an increase in local canopy cover buffered the negative effect of impervious surface on leaf miners and strengthened its effect on gall inducers. These results show that-just like in non-urban areas-plant-herbivore interactions in cities are structured by a complex set of interacting factors. This highlights that local habitat characteristics within cities have the potential to attenuate or modify the effect of impervious surfaces on biotic interactions.

Butterfly declines in protected areas of Illinois: Assessing the influence of two decades of climate and landscape change

Despite increasing concern regarding broad-scale declines in insects, there are few published long-term, systematic butterfly surveys in North America, and fewer still that have incorporated the influence of changing climate and landscape variables. In this study, we analyzed 20 years of citizen science data at seven consistently monitored protected areas in Illinois, U.S.A. We used mixed models and PERMANOVA to evaluate trends in butterfly abundance, richness, and composition while also evaluating the effects of temperature and land use. Overall butterfly richness, but not abundance, increased in warmer years. Surprisingly, richness also was positively related to percent impervious surface (at the 2 km radius scale), highlighting the conservation value of protected areas in urban landscapes (or alternately, the potential negative aspects of agriculture). Precipitation had a significant and variable influence through time on overall butterfly abundance and abundance of resident species, larval host plant specialists, and univoltine species. Importantly, models incorporating the influence of changing temperature, precipitation, and impervious surface indicated a significant overall decline in both butterfly abundance and species richness, with an estimated abundance decrease of 3.8%/year and richness decrease of 1.6%/year (52.5% and 27.1% cumulatively from 1999 to 2018). Abundance and richness declines were also noted across all investigated functional groups except non-resident (migratory) species. Butterfly community composition changed through time, but we did not find evidence of systematic biotic homogenization, perhaps because declines were occurring in nearly all functional groups. Finally, at the site-level, declines in either richness or abundance occurred at five of seven locations, with only the two largest locations (>300 Ha) not exhibiting declines. Our results mirror those of other long-term butterfly studies predominantly in Europe and North America that have found associations of butterflies with climate variables and general declines in butterfly richness and abundance.

Pathogens Spillover from Honey Bees to Other Arthropods

Honey bees, and pollinators in general, play a major role in the health of ecosystems. There is a consensus about the steady decrease in pollinator populations, which raises global ecological concern. Several drivers are implicated in this threat. Among them, honey bee pathogens are transmitted to other arthropods populations, including wild and managed pollinators. The western honey bee, Apis mellifera, is quasi-globally spread. This successful species acted as and, in some cases, became a maintenance host for pathogens. This systematic review collects and summarizes spillover cases having in common Apis mellifera as the mainteinance host and some of its pathogens. The reports are grouped by final host species and condition, year, and geographic area of detection and the co-occurrence in the same host. A total of eighty-one articles in the time frame 1960-2021 were included. The reported spillover cases cover a wide range of hymenopteran host species, generally living in close contact with or sharing the same environmental resources as the honey bees. They also involve non-hymenopteran arthropods, like spiders and roaches, which are either likely or unlikely to live in close proximity to honey bees. Specific studies should consider host-dependent pathogen modifications and effects on involved host species. Both the plasticity of bee pathogens and the ecological consequences of spillover suggest a holistic approach to bee health and the implementation of a One Health approach.

How protection of honey bees can help and hinder bee conservation

Pollinators are globally recognised for their role in ecosystem function and reports of pollinator declines are a source of public and academic concern. However, pollinator decline is often erroneously interpreted as if crop pollination services are under threat, which can lead to misguided efforts to protect introduced and/or widespread crop pollinating species that are not in decline, without addressing the needs of other imperilled species. The honey bee (Apis mellifera L.) in particular has widespread recognition for its role as an integral agricultural pollinator and is the focus of many pollinator campaigns. However, we argue outside of their native range that honey bees are inappropriate as umbrella or flagship species for the conservation of pollinators.

Supporting Bees in Cities: How Bees Are Influenced by Local and Landscape Features

Simple Summary

Cities are complex ecosystems that, while generally contributing to an overall reduction in biodiversity, can support surprisingly unique communities of organisms including bees. Bees are both ecologically and economically essential, therefore preserving and conserving these insects represents a significant challenge as cities continue to expand and diminish surrounding landscapes. Some attempts to support bees in cities have included establishing and improving urban green spaces. Exactly how bees and, to a lesser extent, other pollinators respond to these green spaces in addition to other urban landscape and local features, however, remains incompletely understood. Therefore, this review summarizes the current literature and generalizable trends in pollinator response to urban landscape and local features. While some functional traits or characteristics of bees such as dietary breadth and nesting strategy are more conclusively understood and supported, other characteristics such as sociality remain less generalizable. Lack of knowledge on bee responses to city features is in part due to the individual variation exhibited across different groups and species. To promote greater biodiversity in urban spaces, research should focus on specific responses to urban local and landscape features and how green spaces can be optimized for sustainable bee conservation.

Abstract

Urbanization is a major anthropogenic driver of decline for ecologically and economically important taxa including bees. Despite their generally negative impact on pollinators, cities can display a surprising degree of biodiversity compared to other landscapes. The pollinating communities found within these environments, however, tend to be filtered by interacting local and landscape features that comprise the urban matrix. Landscape and local features exert variable influence on pollinators within and across taxa, which ultimately affects community composition in such a way that contributes to functional trait homogenization and reduced phylogenetic diversity. Although previous results are not easily generalizable, bees and pollinators displaying functional trait characteristics such as polylectic diet, cavity-nesting behavior, and later emergence appear most abundant across different examined cities. To preserve particularly vulnerable species, most notably specialists that have become underrepresented within city communities, green spaces like parks and urban gardens have been examined as potential refuges. Such spaces are scattered across the urban matrix and vary in pollinator resource availability. Therefore, ensuring such spaces are optimized for pollinators is imperative. This review examines how urban features affect pollinators in addition to ways these green spaces can be manipulated to promote greater pollinator abundance and diversity.

Possible Spillover of Pathogens between Bee Communities Foraging on the Same Floral Resource

Simple Summary

Floral resource availability is one of the keys to preserving the health of bee communities. However, flowers also present a risk of pathogen transmission, as infected pollinators could deposit pathogens while foraging, exposing other pollinators to infection via the consumption of contaminated nectar or pollen. Here, we studied, over time, the prevalence of seven viruses in bee communities that share the same small surface of floral resource in order to assess the risk of virus spillover. In total, 2057 bee specimens from 30 species were caught, identified and checked for the presence of viruses. Specimens from the Halictidae family were the dominant wild bees. The prevalence of viruses was quite high: at least one virus was detected in 78% of the samples, and co-infections were frequent. The genetic diversity of the viruses was also investigated to look for the possible association of geographic origin or host with shared ancestry.

Abstract

Viruses are known to contribute to bee population decline. Possible spillover is suspected from the co-occurrence of viruses in wild bees and honey bees. In order to study the risk of virus transmission between wild and managed bee species sharing the same floral resource, we tried to maximize the possible cross-infections using Phacelia tanacetifolia, which is highly attractive to honey bees and a broad range of wild bee species. Virus prevalence was compared over two years in Southern France. A total of 1137 wild bees from 29 wild bee species (based on COI barcoding) and 920 honey bees (Apis mellifera) were checked for the seven most common honey bee RNA viruses. Halictid bees were the most abundant. Co-infections were frequent, and Sacbrood virus (SBV), Black queen cell virus (BQCV), Acute bee paralysis virus (ABPV) and Israeli acute paralysis virus (IAPV) were widespread in the hymenopteran pollinator community. Conversely, Deformed wing virus (DWV) was detected at low levels in wild bees, whereas it was highly prevalent in honey bees (78.3% of the samples). Both wild bee and honey bee virus isolates were sequenced to look for possible host-specificity or geographical structuring. ABPV phylogeny suggested a specific cluster for Eucera bees, while isolates of DWV from bumble bees (Bombus spp.) clustered together with honey bee isolates, suggesting a possible spillover.

Effects of Urbanization on Plant-Pollinator Interactions in the Tropics: An Experimental Approach Using Exotic Plants

Simple Summary

Island environments of the Southwest Pacific, like New Caledonia, generally present poorly diversified bee fauna. Thus, they are particularly prone to the establishment of introduced bee species. These exotic species may compete with native bees for plant resources, disrupt pollination of native plants, and enhance the reproduction of exotic ones. To conserve local plant–pollinator interactions, it is essential to assess the factors favoring the presence and the activity of exotic bees. Here, we focused on the effects of urbanization on plant–pollinator interactions. We set up experimental plant communities composed of four exotic species in two contrasted habitats—a natural environment vs. an urban environment—and observed plant–pollinator interactions. We showed that the urban environment was largely dominated by exotic bees. We also showed that some exotic bee species can interact preferentially with a single exotic ornamental plant species. Overall, our results indicate that Nouméa is an entry point for exotic bees, which should encourage local authorities to maintain biosecurity measures to effectively limit the arrival of exogenous bees. Lastly, the use of exotic horticultural plants in green public spaces should be questioned regarding their potential attractiveness to exotic bees.

Abstract

Land-use changes through urbanization and biological invasions both threaten plant-pollinator networks. Urban areas host modified bee communities and are characterized by high proportions of exotic plants. Exotic species, either animals or plants, may compete with native species and disrupt plant–pollinator interactions. These threats are heightened in insular systems of the Southwest Pacific, where the bee fauna is generally poor and ecological networks are simplified. However, the impacts of these factors have seldom been studied in tropical contexts. To explore those questions, we installed experimental exotic plant communities in urban and natural contexts in New Caledonia, a plant diversity hotspot. For four weeks, we observed plant–pollinator interactions between local pollinators and our experimental exotic plant communities. We found a significantly higher foraging activity of exotic wild bees within the city, together with a strong plant–pollinator association between two exotic species. However, contrary to our expectations, the landscape context (urban vs. natural) had no effect on the activity of native bees. These results raise issues concerning how species introduced in plant–pollinator networks will impact the reproductive success of both native and exotic plants. Furthermore, the urban system could act as a springboard for alien species to disperse in natural systems and even invade them, leading to conservation concerns.

Confronting the Modern Gordian Knot of Urban Beekeeping

With insect population declines, cities are important habitats for wild pollinators. Urban beekeeping is an increasingly popular activity, yet honeybees present important risks to wild insect pollinators in cities. We argue for new, scientifically evidenced urban pollinator strategies to simultaneously enhance the benefits of urban beekeeping while protecting wild pollinators.

Human dimensions of insect pollinator conservation

Insect pollinators are becoming visible to societies. Many peer-reviewed papers evidence biophysical and ecological aspects of managed and non-managed insect pollinators. Evidence on stressors of declines yield peer-reviewed calls for action. Yet, insect pollinator declines are inherently a human issue, driven by a history of land-use trends, changes in technologies, and socio-cultural perceptions that unwittingly cause and perpetuate declines. Conservation requires integrating social and ecological understandings to reconfigure human behaviors across societies' sectors. We review recent literature on the social and cultural dimensions of insect pollinators. People now like bees. We discuss the social challenges and opportunities that accompany this newfound public enthusiasm. These include the generalization of honey bees as representative of bee diversity and pollinator conservation issues, the changing perceptions of pollinators, the paucity of policy research, and how any call to 'save the bees' must be a call to stabilize agriculture. We call for greater coordination among biological and socio-cultural researchers to advance insect pollinator conservation practices and policies fit for the Anthropocene.