Pathways for Novel Epidemiology: Plant-Pollinator-Pathogen Networks and Global Change

The propagation of disturbances in ecological networks

Despite the development of network science, we lack clear heuristics for how far different disturbance types propagate within and across species interaction networks. We discuss the mechanisms of disturbance propagation in ecological networks, and propose that disturbances can be categorized into structural, functional, and transmission types according to their spread and effect on network structure and functioning. We describe the properties of species and their interaction networks and metanetworks that determine the indirect, spatial, and temporal extent of propagation. We argue that the sampling scale of ecological studies may have impeded predictions regarding the rate and extent that a disturbance spreads, and discuss directions to help ecologists to move towards a predictive understanding of the propagation of impacts across interacting communities and ecosystems.

Ecological and social factors influence interspecific pathogens occurrence among bees

The interspecific transmission of pathogens can occur frequently in the environment. Among wild bees, the main spillover cases are caused by pathogens associated with Apis mellifera, whose colonies can act as reservoirs. Due to the limited availability of data in Italy, it is challenging to accurately assess the impact and implications of this phenomenon on the wild bee populations. In this study, a total of 3372 bees were sampled from 11 Italian regions within the BeeNet project, evaluating the prevalence and the abundance of the major honey bee pathogens (DWV, BQCV, ABPV, CBPV, KBV, Nosema ceranae, Ascosphaera apis, Crithidia mellificae, Lotmaria passim, Crithidia bombi). The 68.4% of samples were positive for at least one pathogen. DWV, BQCV, N. ceranae and CBPV showed the highest prevalence and abundance values, confirming them as the most prevalent pathogens spread in the environment. For these pathogens, Andrena, Bombus, Eucera and Seladonia showed the highest mean prevalence and abundance values. Generally, time trends showed a prevalence and abundance decrease from April to July. In order to predict the risk of infection among wild bees, statistical models were developed. A low influence of apiary density on pathogen occurrence was observed, while meteorological conditions and agricultural management showed a greater impact on pathogen persistence in the environment. Social and biological traits of wild bees also contributed to defining a higher risk of infection for bivoltine, communal, mining and oligolectic bees. Out of all the samples tested, 40.5% were co-infected with two or more pathogens. In some cases, individuals were simultaneously infected with up to five different pathogens. It is essential to increase knowledge about the transmission of pathogens among wild bees to understand dynamics, impact and effects on pollinator populations. Implementing concrete plans for the conservation of wild bee species is important to ensure the health of wild and human-managed bees within a One-Health perspective.

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

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

Shift in virus composition in honeybees (Apis mellifera) following worldwide invasion by the parasitic mite and virus vector Varroa destructor

Invasive vectors can induce dramatic changes in disease epidemiology. While viral emergence following geographical range expansion of a vector is well known, the influence a vector can have at the level of the host's pathobiome is less well understood. Taking advantage of the formerly heterogeneous spatial distribution of the ectoparasitic mite Varroa destructor that acts as potent virus vector among honeybees Apis mellifera, we investigated the impact of its recent global spread on the viral community of honeybees in a retrospective study of historical samples. We hypothesized that the vector has had an effect on the epidemiology of several bee viruses, potentially altering their transmissibility and/or virulence, and consequently their prevalence, abundance, or both. To test this, we quantified the prevalence and loads of 14 viruses from honeybee samples collected in mite-free and mite-infested populations in four independent geographical regions. The presence of the mite dramatically increased the prevalence and load of deformed wing virus, a cause of unsustainably high colony losses. In addition, several other viruses became more prevalent or were found at higher load in mite-infested areas, including viruses not known to be actively varroa-transmitted, but which may increase opportunistically in varroa-parasitized bees.

Climate change reshaping plant-fungal interaction

Plant diseases pose a severe threat to modern agriculture, necessitating effective and lasting control solutions. Environmental factors significantly shape plant ecology. Human-induced greenhouse gas emissions have led to global temperature rise, impacting various aspects, including carbon dioxide (CO2) concentration, temperature, ozone (O3), and ultraviolet-B, all of which influence plant diseases. Altered pathogen ranges can accelerate disease transmission. This review explores environmental effects on plant diseases, with climate change affecting fungal biogeography, disease incidence, and severity, as well as agricultural production. Moreover, we have discussed how climate change influences pathogen development, host-fungal interactions, the emergence of new races of fungi, and the dissemination of emerging fungal diseases across the globe. The discussion about environment-mediated impact on pattern-triggered immunity (PTI), effector-triggered immunity (ETI), and RNA interference (RNAi) is also part of this review. In conclusion, the review underscores the critical importance of understanding how climate change is reshaping plant-fungal interactions. It highlights the need for continuous research efforts to elucidate the mechanisms driving these changes and their ecological consequences. As the global climate continues to evolve, it is imperative to develop innovative strategies for mitigating the adverse effects of fungal pathogens on plant health and food security.

Emerging threats and opportunities to managed bee species in European agricultural systems: a horizon scan

Managed bee species provide essential pollination services that contribute to food security worldwide. However, managed bees face a diverse array of threats and anticipating these, and potential opportunities to reduce risks, is essential for the sustainable management of pollination services. We conducted a horizon scanning exercise with 20 experts from across Europe to identify emerging threats and opportunities for managed bees in European agricultural systems. An initial 63 issues were identified, and this was shortlisted to 21 issues through the horizon scanning process. These ranged from local landscape-level management to geopolitical issues on a continental and global scale across seven broad themes-Pesticides & pollutants, Technology, Management practices, Predators & parasites, Environmental stressors, Crop modification, and Political & trade influences. While we conducted this horizon scan within a European context, the opportunities and threats identified will likely be relevant to other regions. A renewed research and policy focus, especially on the highest-ranking issues, is required to maximise the value of these opportunities and mitigate threats to maintain sustainable and healthy managed bee pollinators within agricultural systems.

Identity and diversity of pollens collected by two managed bee species while in blueberry fields for pollination

The nutritional needs and foraging behavior of managed bees often lead to pollen collection from flowers other than the focal crop during crop pollination. To understand the pollen needs and preferences of managed bees during blueberry pollination, we identified pollen collected by Apis mellifera Linnaeus, 1758 (Hymenoptera: Apidae) and Bombus impatiens Cresson, 1863 (Hymenoptera: Apidae) colonies across two years. Bumble bees collected a wider diversity of pollens compared to honey bees, whereas honey bees were more focused on abundant resources. Despite blueberries being the most abundant resource in the landscape, it was not the most collected pollen by either bee species in 2018. However, it was the most collected pollen by bumble bees in 2019 and they collected substantially more blueberry pollen than honey bees in both years. In 2018, buckthorn, Rhamnus L. (Rosales: Rhamnaceae) or Frangula Mill. (Rosales: Rhamnaceae), and willow, Salix L. (Malpighiales: Salicaceae), pollens were abundantly collected by both bee species. In 2019, cherry, Prunus L. (Rosales: Rosaceae), and willow (Salix) pollens were collected at high proportions by both species. Brambles, Rubus L. (Rosales: Rosaceae), and white clover, Trifolium repens L. (Fabales: Fabaceae), were also common pollen sources for honey bees, whereas oak, Quercus L. (Fagales: Fagaceae), was collected by bumble bees. Landscape analyses also revealed that certain land cover types were positively correlated with the collection of preferred pollen types. Herbaceous wetlands were associated with collection of buckthorn (Rhamnus/Frangula), willow (Salix), and cherry (Prunus) pollen, which were primary pollen resources for both bee species. There was no correlation between landscape diversity and pollen diversity, suggesting that colonies forage based on nutritional requirements rather than resource availability.

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.

Bees and thrips carry virus-positive pollen in peach orchards in South Carolina, United States

Prunus necrotic ringspot virus (PNRSV) and prune dwarf virus (PDV) are pollen-borne viruses of important stone fruit crops, including peaches, which can cause substantial yield loss. Although both horizontal and vertical (i.e., seed) transmission of both viruses occurs through pollen, the role of flower-visiting insects in their transmission is not well understood. Bees and thrips reportedly spread PNRSV and PDV in orchards and greenhouse studies; however, the field spread of PNRSV and PDV in peach orchards in the southeastern United States is not explored. We hypothesized that bees and thrips may facilitate virus spread by carrying virus-positive pollen. Our 2-yr survey results show that 75% of captured bees are carrying virus-positive pollen and moving across the orchard while a subsample of thrips were also found virus positive. Based on morphology, Bombus, Apis, Andrena, Eucera, and Habropoda are the predominant bee genera that were captured in peach orchards. Understanding the role of bees and thrips in the spread of PNRSV and PDV will enhance our understanding of pollen-borne virus ecology.

Integrative population genetics and metagenomics reveals urbanization increases pathogen loads and decreases connectivity in a wild bee

As urbanization continues to increase, it is expected that two-thirds of the human population will reside in cities by 2050. Urbanization fragments and degrades natural landscapes, threatening wildlife including economically important species such as bees. In this study, we employ whole genome sequencing to characterize the population genetics, metagenome and microbiome, and environmental stressors of a common wild bee, Ceratina calcarata. Population genomic analyses revealed the presence of low genetic diversity and elevated levels of inbreeding. Through analyses of isolation by distance, resistance, and environment across urban landscapes, we found that green spaces including shrubs and scrub were the most optimal pathways for bee dispersal, and conservation efforts should focus on preserving these land traits to maintain high connectivity across sites for wild bees. Metagenomic analyses revealed landscape sites exhibiting urban heat island effects, such as high temperatures and development but low precipitation and green space, had the highest taxa alpha diversity across all domains even when isolating for potential pathogens. Notably, the integration of population and metagenomic data showed that reduced connectivity in urban areas is not only correlated with lower relatedness among individuals but is also associated with increased pathogen diversity, exposing vulnerable urban bees to more pathogens. Overall, our combined population and metagenomic approach found significant environmental variation in bee microbiomes and nutritional resources even in the absence of genetic differentiation, as well as enabled the potential early detection of stressors to bee health.

Area Wide Monitoring of Plant and Honey Bee (Apis mellifera) Viruses in Blueberry (Vaccinium corymbosum) Agroecosystems Facilitated by Honey Bee Pollination

Healthy agroecosystems are dependent on a complex web of factors and inter-species interactions. Flowers are hubs for pathogen transmission, including the horizontal or vertical transmission of plant-viruses and the horizontal transmission of bee-viruses. Pollination by the European honey bee (Apis mellifera) is critical for industrial fruit production, but bees can also vector viruses and other pathogens between individuals. Here, we utilized commercial honey bee pollination services in blueberry (Vaccinium corymbosum) farms for a metagenomics-based bee and plant virus monitoring system. Following RNA sequencing, viruses were identified by mapping reads to a reference sequence database through the bioinformatics portal Virtool. In total, 29 unique plant viral species were found at two blueberry farms in British Columbia (BC). Nine viruses were identified at one site in Ontario (ON), five of which were not identified in BC. Ilarviruses blueberry shock virus (BlShV) and prune dwarf virus (PDV) were the most frequently detected viruses in BC but absent in ON, while nepoviruses tomato ringspot virus and tobacco ringspot virus were common in ON but absent in BC. BlShV coat protein (CP) nucleotide sequences were nearly identical in all samples, while PDV CP sequences were more diverse, suggesting multiple strains of PDV circulating at this site. Ten bee-infecting viruses were identified, with black queen cell virus frequently detected in ON and BC. Area-wide bee-mediated pathogen monitoring can provide new insights into the diversity of viruses present in, and the health of, bee-pollination ecosystems. This approach can be limited by a short sampling season, biased towards pollen-transmitted viruses, and the plant material collected by bees can be very diverse. This can obscure the origin of some viruses, but bee-mediated virus monitoring can be an effective preliminary monitoring approach.

Contrasting seed traits of co-existing seeds lead to a complex neighbor effect in a seed-rodent interaction

Scatter-hoarding rodents play important roles in seed dispersal and predation in many forest ecosystems. Existing studies have shown that the seed foraging preference of rodents is directly affected by seed traits and indirectly affected by the traits of other co-existing seeds nearby (i.e., neighbor effect). Plant seeds exhibit a combination of diverse seed traits, including seed size, chemical defense, and nutrient content. Therefore, it is difficult to evaluate the influence of each single seed trait on such neighbor effects. Here, by using artificial seeds, we investigated the impacts of contrasts in seed size, tannin content, and nutrient content on neighbor effects. We tracked 9000 tagged artificial seeds from 30 seed-seed paired treatments in a subtropical forest in southwest China. The contrast in seed size between paired seeds created obvious neighbor effects measured through three seed dispersal related indicators: the proportion of seeds being removed, the proportion of seeds cached, and the distance transported by rodents. However, the magnitudes and the signs of the neighbor effects differed among pairs, including both apparent mutualism and apparent competition, depending on the contrast in seed size between paired seeds. The contrasts of tannin and nutrient content between paired seeds showed relatively few neighbor effects. Our results suggest that the contrast in seed traits between the target seed and its neighboring seeds should be considered when studying rodent-seed interactions. Furthermore, we expect that similar complex neighbor effects may also exist in other plant-animal interactions, such as pollination and herbivory.

The pollen virome: A review of pollen-associated viruses and consequences for plants and their interactions with pollinators

The movement of pollen grains from anthers to stigmas, often by insect pollinator vectors, is essential for plant reproduction. However, pollen is also a unique vehicle for viral spread. Pollen-associated plant viruses reside on the outside or inside of pollen grains, infect susceptible individuals through vertical or horizontal infection pathways, and can decrease plant fitness. These viruses are transferred with pollen between plants by pollinator vectors as they forage for floral resources; thus, pollen-associated viral spread is mediated by floral and pollen grain phenotypes and pollinator traits, much like pollination. Most of what is currently known about pollen-associated viruses was discovered through infection and transmission experiments in controlled settings, usually involving one virus and one plant species of agricultural or horticultural interest. In this review, we first provide an updated, comprehensive list of the recognized pollen-associated viruses. Then, we summarize virus, plant, pollinator vector, and landscape traits that can affect pollen-associated virus transmission, infection, and distribution. Next, we highlight the consequences of plant-pollinator-virus interactions that emerge in complex communities of co-flowering plants and pollinator vectors, such as pollen-associated virus spread between plant species and viral jumps from plant to pollinator hosts. We conclude by emphasizing the need for collaborative research that bridges pollen biology, virology, and pollination biology.

Population Genomics for Insect Conservation

Insects constitute vital components of ecosystems. There is alarming evidence for global declines in insect species diversity, abundance, and biomass caused by anthropogenic drivers such as habitat degradation or loss, agricultural practices, climate change, and environmental pollution. This raises important concerns about human food security and ecosystem functionality and calls for more research to assess insect population trends and identify threatened species and the causes of declines to inform conservation strategies. Analysis of genetic diversity is a powerful tool to address these goals, but so far animal conservation genetics research has focused strongly on endangered vertebrates, devoting less attention to invertebrates, such as insects, that constitute most biodiversity. Insects' shorter generation times and larger population sizes likely necessitate different analytical methods and management strategies. The availability of high-quality reference genome assemblies enables population genomics to address several key issues. These include precise inference of past demographic fluctuations and recent declines, measurement of genetic load levels, delineation of evolutionarily significant units and cryptic species, and analysis of genetic adaptation to stressors. This enables identification of populations that are particularly vulnerable to future threats, considering their potential to adapt and evolve. We review the application of population genomics to insect conservation and the outlook for averting insect declines.

Honeybees affect floral microbiome composition in a central food source for wild pollinators in boreal ecosystems

Basic knowledge on dispersal of microbes in pollinator networks is essential for plant, insect, and microbial ecology. Thorough understanding of the ecological consequences of honeybee farming on these complex plant-pollinator-microbe interactions is a prerequisite for sustainable honeybee keeping. Most research on plant-pollinator-microbe interactions have focused on temperate agricultural systems. Therefore, information on a wild plant that is a seasonal bottleneck for pollinators in cold climate such as Salix phylicifolia is of specific importance. We investigated how floral visitation by insects influences the community structure of bacteria and fungi in Salix phylicifolia inflorescences under natural conditions. Insect visitors were experimentally excluded with net bags. We analyzed the microbiome and measured pollen removal in open and bagged inflorescences in sites where honeybees were foraging and in sites without honeybees. Site and plant individual explained most of the variation in floral microbial communities. Insect visitation and honeybees had a smaller but significant effect on the community composition of microbes. Honeybees had a specific effect on the inflorescence microbiome and, e.g., increased the relative abundance of operational taxonomic units (OTUs) from the bacterial order Lactobacillales. Site had a significant effect on the amount of pollen removed from inflorescences but this was not due to honeybees. Insect visitors increased bacterial and especially fungal OTU richness in the inflorescences. Pollinator visits explained 38% variation in fungal richness, but only 10% in bacterial richness. Our work shows that honeybee farming affects the floral microbiome in a wild plant in rural boreal ecosystems.

Transgenerational genomic analyses reveal allelic oscillation and purifying selection in a gut parasite Nosema ceranae

Standing genetic variation is the predominant source acted on by selection. Organisms with high genetic diversity generally show faster responses toward environmental change. Nosema ceranae is a microsporidian parasite of honey bees, infecting midgut epithelial cells. High genetic diversity has been found in this parasite, but the mechanism for the parasite to maintain this diversity remains unclear. This study involved continuous inoculation of N. ceranae to honey bees. We found that the parasites slowly increased genetic diversity over three continuous inoculations. The number of lost single nucleotide variants (SNVs) was balanced with novel SNVs, which were mainly embedded in coding regions. Classic allele frequency oscillation was found at the regional level along the genome, and the associated genes were enriched in apoptosis regulation and ATP binding. The ratio of synonymous and non-synonymous substitution suggests a purifying selection, and our results provide novel insights into the evolutionary dynamics in microsporidian parasites.

Seasonal variations impact on SARS-CoV-2 incidence and mortality in southern and northern hemispheres: Two years pandemic period based study

Objectives

The Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2) infection is a highly challenging problem in the world. The impact of weather conditions on the spread of SARS-CoV-2 has been hypothesized, but the level of understanding remains lacking. This study investigates the impact of seasonal variations on SARS-CoV-2 incidence and mortality in the Southern and Northern hemispheres.

Methods

We enlisted all the countries from both hemispheres and then randomly selected 20 countries, 10 countries from each hemisphere. After that, we recorded the SARS-CoV-2 daily cases and deaths in these selected countries from the Worldometer for the period of two years from December 31, 2019, to December 31, 2021.

Results

During the study period, in 10 selected countries of the Northern hemisphere, the number of SARS-CoV-2 cases was 18381.6 ± 419.7 and deaths 300.4 ± 6.4. However, the number of cases in the southern hemisphere is 6282.9 ± 205.8, and mortality was 210.0 ± 7.7. In the Northern hemisphere, the number of SARS-CoV-2 cases (p = 0.001) and deaths (p = 0.001) significantly increased compared to the southern hemisphere. The maximum number of cases and deaths occurred during the winter (18806.4 ± 785.3) and autumn (17034.1 ± 538.4) periods in both the hemisphere compared to spring and summer. Similarly, the number of deaths increased in winter (391.0 ± 13.4, p = 0.001) and autumn (308.6 ± 11.6) compared to spring and summer in both hemispheres.

Conclusions

The highest occurrence of SARS-CoV-2 cases and deaths was found during the winter and autumn seasons, while the lowest was found in the spring and summer during the study period of two years. The health officials inform the public about the seasonal occurrence of the SARS-CoV-2 outbreak and take priority preventive measures to minimize the disease burden.

Increasing flower species richness in agricultural landscapes alters insect pollinator networks: Implications for bee health and competition

Ecological restoration programs are established to reverse land degradation, mitigate biodiversity loss, and reinstate ecosystem services. Following recent agricultural intensification that led to a decrease in flower diversity and density in rural areas and subsequently to the decline of many insects, conservation measures targeted at pollinators have been established, including sown wildflower strips (WFS) along field margins. Historically successful in establishing a high density of generalist bees and increasing pollinator diversity, the impact of enhanced flower provision on wider ecological interactions and the structure of pollinator networks has been rarely investigated. Here, we tested the effects of increasing flower species richness and flower density in agricultural landscapes on bee‐plant interaction networks. We measured plant species richness and flower density and surveyed honeybee and bumblebee visits on flowers across a range of field margins on 10 UK farms that applied different pollinator conservation measures. We found that both flower species richness and flower density significantly increased bee abundance, in early and late summer, respectively. At the network level, we found that higher flower species richness did not significantly alter bee species' generality indices, but significantly reduced network connectance and marginally reduced niche overlap across honeybees and bumblebee species, a proxy for insect competition. While higher connectance and niche overlap is believed to strengthen network robustness and often is the aim for the restoration of pollinator networks, we argue that carefully designed WFS may benefit bees by partitioning their foraging niche, limiting competition for resources and the potential for disease transmission via shared floral use. We also discuss the need to extend WFS and their positive effects into spring when wild bee populations are established.

“Migratory beekeeping and its influence on the prevalence and dispersal of pathogens to managed and wild bees”

Demand for food is growing along with the human population, leading to an increase in plant production. Many crops are pollinated by insects, so the global demand for managed pollinators is also increasing. The honey bee has traditionally been considered the main provider of crop pollination services. For providing it beekeepers seasonally transport hives to different locations after the flowering of different crops. These movements could be detrimental to pollinators by: i) stressing honey bees, making them more susceptible to pathogens and parasites; ii) spreading bee parasites and pathogens across locations; iii) increasing the transmission of parasites and pathogens between managed and wild pollinators and vice versa (spillover and spillback, respectively). To understand the impact of migratory beekeeping on bee health, we conducted a systematic review to identify the main trends and provide a complete picture of existing knowledge on the subject. We found 52 studies analysing pathogen-related impacts of migratory beekeeping on honey bees. However, only 16 investigations tested the effect of migratory practices on the prevalence and spread of pathogens and parasites. We found no studies that assessed the impact of migratory beekeeping on the occurrence and spread of pests and diseases in wild bees. In general, migratory beekeeping tends to increase the prevalence of pathogens and parasites in honey bee colonies. However, the results were very heterogeneous, probably due to several uncontrolled underlying factors such as management, biological and geographical factors, and the interactions between them. In conclusion, there is an urgent need for studies to assess the impact of migratory beekeeping on bee health, given the current global bee decline and the expected increase in migratory beekeeping due to climate change and crop pollination demand.

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Migratory beekeeping may affect the health of both managed and wild bees.

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Only 16 studies compare the prevalence of pathogens between migratory and stationary hives.

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Results are heterogeneous due to the complex interaction of the underlying factors.

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Overall, the prevalence of pathogens and parasites increased in migratory honey bees.

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The impact of migratory beekeeping on the health of wild bees is unknown.

The effects of urbanisation on ecological interactions

Cities are expanding worldwide and urbanisation is considered a global threat to biodiversity. Urban ecology has provided important insights on how urban environmental changes might affect individuals, populations, and species; however, we know little about how the ecological impacts of urbanisation alter species interactions. Species interactions are the backbone of ecological communities and play a crucial role in population and community dynamics and in the generation, maintenance and structure of biodiversity. Here, I review urban ecological studies to identify key mechanistic pathways through which urban environmental processes could alter antagonistic and mutualistic interactions among species. More specifically, I focus on insect predation, parasitoidism and herbivory, competition, insect host-pathogen interactions, and pollination. I furthermore identify important knowledge gaps that require additional research attention and I suggest future research directions that may help to shed light on the mechanisms that affect species interactions and structure insect communities and will thus aid conservation management in cities.

Do pesticide and pathogen interactions drive wild bee declines?

There is clear evidence for wild insect declines globally. Habitat loss, climate change, pests, pathogens and environmental pollution have all been shown to cause detrimental effects on insects. However, interactive effects between these stressors may be the key to understanding reported declines. Here, we review the literature on pesticide and pathogen interactions for wild bees, identify knowledge gaps, and suggest avenues for future research fostering mitigation of the observed declines. The limited studies available suggest that effects of pesticides most likely override effects of pathogens. Bees feeding on flowers and building sheltered nests, are likely less adapted to toxins compared to other insects, which potential susceptibility is enhanced by the reduced number of genes encoding detoxifying enzymes compared with other insect species. However, to date all 10 studies using a fully-crossed design have been conducted in the laboratory on social bees using Crithidia spp. or Nosema spp., identifying an urgent need to test solitary bees and other pathogens. Similarly, since laboratory studies do not necessarily reflect field conditions, semi-field and field studies are essential if we are to understand these interactions and their potential effects in the real-world. In conclusion, there is a clear need for empirical (semi-)field studies on a range of pesticides, pathogens, and insect species to better understand the pathways and mechanisms underlying their potential interactions, in particular their relevance for insect fitness and population dynamics. Such data are indispensable to drive forward robust modelling of interactive effects in different environmental settings and foster predictive science. This will enable pesticide and pathogen interactions to be put into the context of other stressors more broadly, evaluating their relative importance in driving the observed declines of wild bees and other insects. Ultimately, this will enable the development of more effective mitigation measures to protect bees and the ecosystem services they supply.

Flower sharing and pollinator health: a behavioural perspective

Disease is an integral part of any organisms' life, and bees have evolved immune responses and a suite of hygienic behaviours to keep them at bay in the nest. It is now evident that flowers are another transmission hub for pathogens and parasites, raising questions about adaptations that help pollinating insects stay healthy while visiting hundreds of plants over their lifetime. Drawing on recent advances in our understanding of how bees of varying size, dietary specialization and sociality differ in their foraging ranges, navigational strategies and floral resource preferences, we explore the behavioural mechanisms and strategies that may enable foraging bees to reduce disease exposure and transmission risks at flowers by partitioning overlapping resources in space and in time. By taking a novel behavioural perspective, we highlight the missing links between disease biology and the ecology of plant-pollinator relationships, critical for improving the understanding of disease transmission risks and the better design and management of habitat for pollinator conservation. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Experimental cross species transmission of a major viral pathogen in bees is predominantly from honeybees to bumblebees

Cross-species transmission of a pathogen from a reservoir to a recipient host species, spillover, can have major impacts on biodiversity, domestic species and human health. Deformed wing virus (DWV) is a panzootic RNA virus in honeybees that is causal in their elevated colony losses, and several correlative field studies have suggested spillover of DWV from managed honeybees to wild bee species such as bumblebees. Yet unequivocal demonstration of DWV spillover is lacking, while spillback, the transmission of DWV from a recipient back to the reservoir host, is rarely considered. Here, we show in fully crossed laboratory experiments that the transmission of DWV (genotype A) from honeybees to bumblebees occurs readily, yet we neither detected viral transmission from bumblebees to honeybees nor onward transmission from experimentally infected to uninoculated bumblebees. Our results support the potential for viral spillover from honeybees to other bee species in the field when robbing resources from heterospecific nests or when visiting the same flowers. They also underscore the importance of studies on the virulence of DWV in wild bee species so as to evaluate viral impact on individual and population fitness as well as viral adaption to new host species.

Side effects of a fungus-based biopesticide on stingless bee guarding behaviour

Pathogenic fungi have been used worldwide to control crop pests and are assumed to pose negligible threats to the survival of pollinators. Although eusocial stingless bees provide essential pollination services and might be exposed to these biopesticides in tropical agroecosystems, there is a substantial knowledge gap regarding the side effects of fungal pathogens on behavioural traits that are crucial for colony functioning, such as guarding behaviour. Here, we evaluated the effect of Beauveria bassiana on the sophisticated kin recognition system of Tetragonisca angustula, a bee with morphologically specialized entrance guards. By combining behavioural assays and chemical analyses, we show that guards detect pathogen-exposed nestmates, preventing them from accessing nests. Furthermore, cuticular profiles of pathogen-exposed foragers contained significantly lower amounts of linear alkanes than the unexposed ones. Such chemical cues associated with fungal conidia may potentially trigger aggression towards pathogen-exposed bees, preventing pathogen spread into and among colonies. This is the first demonstration that this highly abundant native bee seems to respond in a much more adaptive way to a potentially infectious threat, outweighing the costs of losing foraging workforce when reducing the chances of fungal pathogen outbreaks within their colonies, than honeybees do.

Vulnerability of island insect pollinator communities to pathogens

Island ecosystems, which often contain undescribed insects and small populations of single island endemics, are at risk from diverse threats. The spread of pathogens is a major factor affecting not just pollinator species themselves, but also posing significant knock-on effects to often fragile island ecosystems through disruption of pollination networks. Insects are vulnerable to diverse pathogens and these can be introduced to islands in a number of ways, e.g. via the introduction of infected managed pollinator hosts (e.g. honey bees and their viruses, in particular Deformed wing virus), long-range migrants (e.g. monarch butterflies and their protozoan parasite, Ophryocystit elektroscirrha) and invasive species (e.g. social wasps are common invaders and are frequently infected with multi-host viruses such as Kashmir bee virus and Moku virus). Furthermore, these introductions can negatively affect island ecosystems through outcompeting native taxa for resources. As such, the greatest threat to island pollinator communities is not one particular pathogen, but the combination of pathogens and introduced and invasive insects that will likely carry them.