Organisms respond to infectious agents through diverse immune strategies, and may need to cater a specific response to distinct pathogen challenges, such as various strains of a virus, to maximize fitness. Deformed wing virus (DWV) is one of the most damaging viruses of honey bees (Apis mellifera) across the globe, with variant DWV-B currently expanding at the expense of variant DWV-A. While previous research has characterized general host transcriptomic responses to viral exposure, host responses to different DWV strains have not been fully explored. Here, we performed experimental infections with the two dominant strains of DWV, A and B, as well as a mixed infection, and conducted transcriptomic analyses to compare differences in host molecular response to infection. We confirmed canonical anti-viral response to DWV infection, including upregulation of Toll pathway genes and the antimicrobial peptides abaecin and hymenoptaecin. Furthermore, our results suggest a potential role of aerobic glycolysis during viral infection in honey bees. DWV-A and mixed infections were associated with differential expression of a much larger number of host genes than infection with DWV-B. That DWV-B potentially elicits a reduced host immune response may provide a mechanistic explanation for its higher virulence and global emergence. Overall, this study provides the first evidence for strain-specific immune responses to DWV infection, and integrates these findings into the broader domain of insect immunity and host-pathogen dynamics.

The Natura 2000 network is central to Europe's conservation efforts to address biodiversity decline, with ongoing plans to expand protected areas and restore habitats across the European Union. However, due to the relative scarcity of biodiversity assessments within Natura 2000 sites, our understanding of how effective these areas are at protecting biodiversity and how they can be improved remains limited. At the same time, urban green spaces and associated disturbed, unmanaged vacant areas, also known as urban wastelands, have gained attention as potential conservation targets due to their high insect species richness. Here, we assess and compare the biodiversity of pollinators within Natura 2000 reserves and urban wastelands to evaluate their relative value for biodiversity protection and pollination services. To achieve this, we compared pollinator communities, their flower-visitation patterns and pollination services using potted experimental plants in flower-rich Natura 2000 sites and paired non-protected, unmanaged, yet similarly flower-rich urban wastelands. While the total biomass and overall abundance of insects did not differ between the two habitat types, wild bee abundance and richness were higher in urban wastelands, whereas pollinator communities were more heterogeneous among Natura 2000 sites. Though insect flower-visitation network metrics were similar across both habitats, seed set of experimental plants was higher in urban wastelands compared to Natura 2000 sites, indicating lower pollination services in the nature reserves. Our findings suggest that while Natura 2000 areas contained unique biodiversity compared to urban wastelands, the current status of protected areas in Germany is inadequate to conserve biodiversity hotspots for bees, including endangered species and the pollination services they provide. We highlight the potential for urban areas to support biodiversity conservation as well as the need to develop targeted strategies for bee conservation in Natura 2000 areas.

Bees are crucial for food security and biodiversity. However, managed bees are increasingly considered drivers of wild bee declines, leading to stakeholder conflicts and restrictive policies. We propose avenues to reconcile wild and managed bee proponents and point out knowledge gaps that hinder the development of evidence-based policies.

RNA viruses often comprise multiple variants that co-circulate in a host population, with potentially complex dynamics. Deformed wing virus (DWV), arguably the most impactful virus of honey bees (Apis mellifera), nowadays exists as two major variants, genotypes A (DWV-A) and B (DWV-B), which provide an amenable window into the dynamics of multi-variant pathogens. DWV-B has increased in prevalence over the past two decades in honey bees in Europe, largely replacing DWV-A. DWV-B arrived over a decade ago in the New World, where its prevalence has also increased markedly in temperate North American honey bees. The Yucatan Peninsula of Mexico is home to a high density of both managed and feral Africanized honey bees (AHBs), which are also known to be infected by DWV, though variant dynamics in this tropical location have not been explored. Here, we present two temporally separated datasets on viral prevalence that demonstrate the presence of both DWV genotypes in Yucatecan AHBs in 2010, though with surprisingly little change in the high prevalence of DWV-A and low prevalence of DWV-B through to 2019. Epidemiological modeling suggests that the dynamics of DWV genotypes in AHBs of Yucatan may be due to a form of superinfection exclusion (SIE). We model one potential form of SIE, inter-genotype recombination meltdown. In addition to providing information on the epidemiology of a major honey bee virus in the Neotropics, our results provide broader insight into the evolutionary dynamics of viruses that comprise two or more co-occurring variants.

An organism’s body size is a fundamental trait linked to its metabolism, life-history and dispersal. In holometabolous insects, whose size is fixed at adult eclosion, body size can be influenced by environmental factors during development (e.g. nutrition and temperature), or by ecological filtering during adulthood. In bees, larger body size has been linked to advantages in foraging efficiency, thermoregulation, and survival, while excessive variation in body size within populations may indicate developmental instability. Shifts in adult body size have been associated with temperature changes, food resource availability and habitat fragmentation, all of which can be modulated by urbanisation. However, the relationship between urban landscapes and wild bee body size remains poorly understood. In this study we investigated how local floral (food) resources, landscape structure and temperature influence the body size of the great banded furrow bee, Halictus scabiosae. Our findings highlight that food resources, semi-natural cover and edge density are the most significant environmental factors influencing body size shifts. Specifically, H. scabiosae body size increased with the species richness of flowering host plants at the local patch level. Within sampling sites, body size variation was positively associated with semi-natural cover, suggesting that habitat structure or competition may contribute to size heterogeneity, potentially disrupting size uniformity. Conversely, it was negatively associated with edge density, indicating that a higher amount of ecotones may promote greater size uniformity within populations. Our findings reinforce the idea that enhancing floral resources and improving habitat connectivity through green corridors can support wild bee populations in urban areas.

Wild fauna and flora are facing variable and challenging environmental disturbances. One of the animal groups that is most impacted by this, concerns pollinators. Pollinators face multiple threats, but the spread of anthropogenic chemicals (i.e. pesticides) form a major potential driver of these threats. WildPosh is a multi-actor, transdisciplinary project whose overarching mission and ambition are to significantly improve the evaluation of risk to pesticide exposure of wild pollinators, and enhance the sustainable health of pollinators and pollination services in Europe. As chemical exposure varies geographically, across cropping systems, inside the crop system and among pollinators, we will characterise exposure by doing fieldwork in 4 countries representing the four main climatic European regions, Mediterranean, Atlantic, Continental and Boreal climate in Germany, England, Estonia and Spain. We will also develop experiments in controlled conditions on different species of bees, syrphid flies, moths and butterflies, and collect in silico data on their traits and on toxicity of pesticides. With WildPosh, we aim to achieve the following objectives:1. Determining the real-world agrochemical exposure profile of wild pollinators at landscape level, within and among sites;2. Using integrated and controlled laboratory and semi-field experiments to characterise causal relationships between pesticides and pollinator health;3. Building an open database on pollinator traits/distribution and chemicals to define exposure and toxicity scenarios by developing databases on ecological traits and the spatial distribution of pollinators in relation to their potential exposure to pesticide;4. Proposing integrated systems-based risk assessment tools for risk assessment for wild pollinators; and5. Driving policy and practice through interactive innovation, meeting the need for monitoring tools, novel and innovative screening protocols for practice and policymaker use.

Though many wild bee species nest in the ground, little is known of their potential exposure to pesticide residues in soil, or the effects of such exposure. Here, we introduce Anthophora plumipes as a potential model ground-nesting solitary bee species for controlled exposure to pesticides through soil. Bees from a naturally occurring population were allowed to nest in loam blocks containing varying concentrations of the neonicotinoid imidacloprid. Measured residues of imidacloprid in brood provisions and in bee bodies remained at < 0.01

Haplodiploid inheritance, in which females are diploid and males are haploid, is found in all species of Hymenoptera. Sex in haplodiploids is commonly determined by the alleles present at a complementary sex determination (CSD) locus, with heterozygosity triggering the female developmental pathway. The identity of this locus differs among taxa and is only known in a few species. Here, we map a single CSD locus to a 2 kbp region in the genome of the red mason bee Osmia bicornis . It overlaps the long noncoding RNA ANTSR , which has been identified as the sex-determining gene in the invasive ant Linepithema humile . This locus is homozygous in diploid males and exhibits extremely high levels of haplotype diversity, consistent with the action of frequency-dependent selection. The elevated levels of heterozygosity in the CSD locus enable us to fine-map potentially functional genetic variation within it. We also identify elevated levels of genetic diversity in the ortholog of the CSD locus in other bee genera, suggesting that it may govern sex determination widely in bees. Our data are consistent with the hypothesis that ANTSR evolved a role in sex determination at least 150 million years ago and is the ancestral sex-determination locus of bees and ants. ### Competing Interest Statement The authors have declared no competing interest. Erik Philip-Sörensens Stiftelse Swedish Research Council, 2022-06725

Pollinators face significant global decline due to agricultural intensification. Local conservation measures (CMs), such as an annual flower field, an organic crop field, or a perennial semi‐natural habitat (SNH), are implemented to counteract this negative trend, with variable success, as local CMs may not support ecological processes at spatially larger landscape scales. This can be achieved by planning CMs at the landscape level (landscape CMs), for example multiple fields with a specific CM or combinations of different types of CMs. However, interactive effects between combined landscape CMs may limit their efficacy. It remains unclear whether multiple combined landscape CMs can be more efficient than single landscape CMs (synergistic effect), reduce each other's effectiveness (antagonistic effect) or sum together (additive effect) to promote biodiversity. We assessed the interactive effects of three landscape CMs: organic crops, annual flower fields and perennial SNH, on wild bee species richness and densities at the landscape scale. We surveyed wild bees within multiple transects in 32 landscapes and upscaled bee densities to the landscape scale. We observed a synergistic effect between landscape‐scale organic crops and perennial SNH. Specifically, non‐ Bombus wild bee densities increased with higher area shares of organic crops in landscapes with high area shares of perennial SNH. This is likely due to their provision of complementary resources. For bumblebees, we found an additive effect of organic crops and perennial SNH, suggesting that bumblebees benefit from both landscape CMs regardless of their respective availability. However, antagonistic effects were more common, for example between landscape‐scale annual flower fields and organic farming, both providing similar floral resources and disturbance regimes. Only in landscapes with a low area of annual flower fields did bee densities and species richness increase with area shares of organic crops. Synthesis and applications . Interactive effects of combined landscape CMs determine landscape‐scale bee densities and species richness. In particular, functionally different and complementary resources of landscape CMs can create synergistic effects while antagonistic effects occur when similar resources are provided in different landscape CMs. Hence, we recommend that future bee conservation schemes should use smart mixing of landscape CMs, based on judicious evaluation to maximize complementary benefits and reduce redundancy with respect to landscape‐scale floral resources and provision of nesting habitat, while considering the habitat requirements of different bee taxonomic groups.

Floral nectar sugar composition is assumed to reflect the nutritional demands and foraging behaviour of pollinators, but the relative contributions of evolutionary and abiotic factors to nectar sugar composition remain largely unknown across the angiosperms. We compiled a comprehensive dataset on nectar sugar composition for 414 insect-pollinated plant species across central Europe, along with phylogeny, paleoclimate, flower morphology, and pollinator dietary demands, to disentangle their relative effects. We found that phylogeny was strongly related with nectar sucrose content, which increased with the phylogenetic age of plant families, but even more strongly with historic global surface temperature. Nectar sugar composition was also defined by floral morphology, though it was not related to our functional measure of pollinator dietary demands. However, specialist pollinators of current plant-pollinator networks predominantly visited plant species with sucrose-rich nectar. Our results suggest that both physiological mechanisms related to plant water balance and evolutionary effects related to paleoclimatic changes have shaped floral nectar sugar composition during the radiation and specialisation of plants and pollinators. As a consequence, the high velocity of current climate change may affect plant-pollinator interaction networks due to a conflicting combination of immediate physiological responses and phylogenetic conservatism.

Wild bees are crucial pollinators of flowering plants and concerns are rising about their decline associated with pesticide use. Interspecific variation in wild bee response to pesticide exposure is expected to be related to variation in their morphology, physiology, and ecology, though there are still important knowledge gaps in its understanding. Pesticide risk assessments have largely focussed on the Western honey bee sensitivity considering it protective enough for wild bees. Recently, guidelines for Bombus terrestris and Osmia bicornis testing have been developed but are not yet implemented at a global scale in pesticide risk assessments. Here, we developed and tested a new simplified method of pesticide exposure on wild bee species collected from the field in Belgium. Enough specimens of nine species survived in a laboratory setting and were exposed to oral and topical acute doses of a sulfoximine insecticide. Our results confirm significant variability among wild bee species. We show that Osmia cornuta is more sensitive to sulfoxaflor than B. terrestris, whereas Bombus hypnorum is less sensitive. We propose hypotheses on the mechanisms explaining interspecific variations in sensitivity to pesticides. Future pesticide risk assessments of wild bees will require further refinement of protocols for their controlled housing and exposure.

The transmission of pathogens from reservoir to recipient host species, termed pathogen spillover, can profoundly impact plant, animal, and public health. However, why some pathogens lead to disease emergence in a novel species while others fail to establish or do not elicit disease is often poorly understood. There is strong evidence that deformed wing virus (DWV), an (+)ssRNA virus, spills over from its reservoir host, the honeybee Apis mellifera, into the bumblebee Bombus terrestris. However, the low impact of DWV on B. terrestris in laboratory experiments suggests host barriers to virus spread in this recipient host. To investigate potential host barriers, we followed the spread of DWV genotype B (DWV-B) through a host’s body using RT-PCR after experimental transmission to bumblebees in comparison to honeybees. Inoculation was per os, mimicking food-borne transmission, or by injection into the bee’s haemocoel, mimicking vector-based transmission. In honeybees, DWV-B was present in both honeybee faeces and haemolymph within 3 days of inoculation per os or by injection. In contrast, DWV-B was not detected in B. terrestris haemolymph after inoculation per os, suggesting a gut barrier that hinders DWV-B’s spread through the body of a B. terrestris. DWV-B was, however, detected in B. terrestris faeces after injection and feeding, albeit at a lower abundance than that observed for A. mellifera, suggesting that B. terrestris sheds less DWV-B than A. mellifera in faeces when infected. Barriers to viral spread in B. terrestris following oral infection may limit DWV’s impact on this spillover host and reduce its contribution to the community epidemiology of DWV.

Natural enemies impose a selective pressure on solitary insects that may favour the evolution of sociality. In the socially polymorphic orchid bee Euglossa viridissima, females found nests solitarily and provision a first batch of brood. After brood maturity, a nest can remain solitary (all offspring disperse) or become social, when one or more subordinate daughters forage for nesting material and brood provisions for the dominant mother. Solitary females leave their nest unguarded when foraging whilst a female in a social nest can guard the nest while nestmates are foraging. By observing solitary and social nests, we found that subordinate foragers in social nests undertook longer provisioning trips than solitary females. The presence of a guarding female in a social nest protected the nest against intrusion, possibly favouring longer provisioning trips. Moreover, the frequency of successful attempts by intruders to enter nests was significantly lower in social nests. Our results provide strong support for the parasite defence hypothesis for the evolution of social behaviour.

Implementation of marker-assisted selection (MAS) in modern beekeeping would improve sustainability, especially in breeding programs aiming for resilience against the parasitic mite Varroa destructor. Selecting honey bee colonies for natural resistance traits, such as brood-intrinsic suppression of varroa mite reproduction, reduces the use of chemical acaricides while respecting local adaptation. In 2019, eight genomic variants associated with varroa non-reproduction in drone brood were discovered in a single colony from the Amsterdam Water Dune population in the Netherlands. Recently, a new study tested the applicability of these eight genetic variants for the same phenotype on a population-wide scale in Flanders, Belgium. As the properties of some variants varied between the two studies, one hypothesized that the difference in genetic ancestry of the sampled colonies may underly these contribution shifts. In order to frame this, we determined the allele frequencies of the eight genetic variants in more than 360 Apis mellifera colonies across the European continent and found that variant type allele frequencies of these variants are primarily related to the A. mellifera subspecies or phylogenetic honey bee lineage. Our results confirm that population-specific genetic markers should always be evaluated in a new population prior to using them in MAS programs.

Despite the major role that insect pollinators play in crop production, agricultural intensification drives them into decline. Various conservation measures have been developed to mitigate the negative effects of agriculture on insect pollinators. In a novel comparison of the efficacy of three conservation measures on honeybee colony growth, we monitored experimental honeybee colonies in 16 landscapes that comprised orthogonal gradients of organic agriculture, annual flower strips and perennial semi-natural habitats. Using structural equation modelling, we assessed the effects of conservation measures on the prevalence of 11 parasites, Varroa destructor loads and their collective impact on colony growth. Increasing area coverage of perennial semi-natural habitat related to higher V. destructor load and indirectly to lower colony growth. Increasing area of annual flower strips was associated with lower V. destructor load and indirectly with higher colony growth. Increasing area of organic farming related to lower parasite richness and also directly to improved colony growth. Synthesis and applications: Landscape features can affect pollinators directly through the provision of food resources and indirectly through modulation of parasite prevalence. To promote honeybee colony health in agro-ecosystems, our results suggest that organic agriculture and annual flower strips should be prioritized conservation measures. Landscape management should consider the merits and demerits of different measures to sustain healthy populations of pollinators in agro-ecosystems.

Land use change is a major pressure on pollinator abundance, diversity and plant-pollinator interactions. Far less is known about how land-use alters the structure of plant-pollinator networks and their robustness to plant-pollinator coextinctions.We analysed the structure of plant-pollinator networks sampled in 12 landscapes along an urbanisation and agricultural intensity gradient, from early spring to late summer 2021, and used a stochastic coextinction model to correlate plant-pollinator coextinction risk with network structure (species and network-level metrics) and landscape context.Networks in intensively managed (i.e., agricultural and urban) landscapes had a lower risk of initiating a coextinction cascade, while networks in less intensively managed landscapes may be less robust. Network structure modulated the frequency and severity of coextinctions and species loss, while the strength of species interactions increased robustness.Urban networks were more species rich and symmetrical due to the high diversity of ornamental plants, while intensively managed agricultural landscapes had smaller, more tightly connected and nested networks.Network structure modulated the frequency of extinctions, which was decreased by greater linkage density, interaction asymmetry and interaction dependence in the networks, while once an extinction occurred, nestedness and linkage density propagated the degree of the coextinction cascade and species loss. At the species level, species strength was inversely correlated with extinction risk, implying that generalist species with a high number of interactions with specialists had the lowest extinction risk.An interplay between land-use and network structure affects community robustness to coextinctions with implications for pollination services and plant reproduction. Land-use change or other global change pressures by reorganising species interactions can alter communities and their potential functioning.Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog.image

Emerging infectious diseases pose a threat to pollinators. Virus transmission among pollinators via flowers may be reinforced by anthropogenic land-use change and concomitant alteration of plant-pollinator interactions. Here, we examine how species' traits and roles in flower-visitation networks and landscape-scale factors drive key honeybee viruses-black queen cell virus (BQCV) and deformed wing virus-in 19 wild bee and hoverfly species, across 12 landscapes varying in pollinator-friendly (flower-rich) habitat. Viral loads were on average more than ten times higher in managed honeybees than in wild pollinators. Viral loads in wild pollinators were higher when floral resource use overlapped with honeybees, suggesting these as reservoir hosts, and increased with pollinator abundance and viral loads in honeybees. Viral prevalence decreased with the amount of pollinator-friendly habitat in a landscape, which was partly driven by reduced floral resource overlap with honeybees. Black queen cell virus loads decreased with a wild pollinator's centrality in the network and the proportion of visited dish-shaped flowers. Our findings highlight the complex interplay of resource overlap with honeybees, species traits and roles in flower-visitation networks and flower-rich pollinator habitat shaping virus transmission. Human-driven landscape change may alter disease transmission among insect pollinators. Here, the authors show that species traits, flower-rich habitat and floral resource overlap with honeybees explain load and prevalence of viruses in wild bees and hoverflies co-occurring with honeybees.

Using NGS data from an RNA-seq library, we reveal a novel variant of slow bee paralysis virus (SBPV) in a pooled sample of adult honey bees (Apis mellifera) collected in southwest Germany. We provide its sequence (NCBI Accession No. PP100271) and demonstrate that it is infective for adult honey bees by feeding.

Heatwave events increase in frequency and duration, yet there is a strong gap in assessing their nonlethal effects on tropical insects, including beneficial social species. The stingless bees are a highly diverse group of pantropical pollinators that provide key ecosystem services. Here, we simultaneously analyzed for the first time the effect of sublethal heat stress (HS) during immature (pupal) development on adult morphology (size, shape, symmetry) and immune response of the three castes/sexes in stingless bee colonies: workers, unmated queens (gynes) and males, as well as its impact on the onset of foraging and lifespan in workers. Individuals experimentally heat stressed during development had smaller body size and reduced symmetry as adults compared with control, non-heat stressed (NHS) individuals, though the strength of the effects of HS also varied between castes and sexes. Notably, males were more prone to the effects of HS compared with workers, and less so gynes; HS reduced the immune response of males, though not that of workers or queens. Workers had significantly earlier onset of foraging and a shorter lifespan when exposed as immatures to HS. Under a worst-case scenario, knock-on negative impacts on individual survival caused by HS could compromise colony fitness. In the long-term, heatwaves may also have repercussions for the persistence of stingless bee species, the sustainability of key ancestral activities like meliponiculture and ecosystem services. Measures to ameliorate the effect of climatic warming are urgently needed to protect these pollinators, which represent an iconic world heritage.

BACKGROUND: Renin-expressing cells are myoendocrine cells crucial for the maintenance of homeostasis. Renin is regulated by cAMP, p300 (histone acetyltransferase p300)/CBP (CREB-binding protein), and Brd4 (bromodomain-containing protein 4) proteins and associated pathways. However, the specific regulatory changes that occur following inhibition of these pathways are not clear. METHODS: We treated As4.1 cells (tumoral cells derived from mouse juxtaglomerular cells that constitutively express renin) with 3 inhibitors that target different factors required for renin transcription: H-89-dihydrochloride, PKA (protein kinase A) inhibitor; JQ1, Brd4 bromodomain inhibitor; and A-485, p300/CBP inhibitor. We performed assay for transposase-accessible chromatin with sequencing (ATAC-seq), single-cell RNA sequencing, cleavage under targets and tagmentation (CUT&Tag), and chromatin immunoprecipitation sequencing for H3K27ac (acetylation of lysine 27 of the histone H3 protein) and p300 binding on biological replicates of treated and control As4.1 cells. RESULTS: In response to each inhibitor, Ren1 expression was significantly reduced and reversible upon washout. Chromatin accessibility at the Ren1 locus did not markedly change but was globally reduced at distal elements. Inhibition of PKA led to significant reductions in H3K27ac and p300 binding specifically within the Ren1 super-enhancer region. Further, we identified enriched TF (transcription factor) motifs shared across each inhibitory treatment. Finally, we identified a set of 9 genes with putative roles across each of the 3 renin regulatory pathways and observed that each displayed differentially accessible chromatin, gene expression, H3K27ac, and p300 binding at their respective loci. CONCLUSIONS: Inhibition of renin expression in cells that constitutively synthesize and release renin is regulated by an epigenetic switch from an active to poised state associated with decreased cell-cell communication and an epithelial-mesenchymal transition. This work highlights and helps define the factors necessary for renin cells to alternate between myoendocrine and contractile phenotypes.