Synergistic parasite-pathogen interactions mediated by host immunity can drive the collapse of honeybee colonies

Estimates of the vitality and performances of Apis mellifera mellifera and hybrid honey bee colonies in Siberia: a 13-year study

Honeybees display a great range of biological, behavioral, and economic traits, depending on their genetic origin and environmental factors. The high diversity of honeybees is the result of natural selection of specific phenotypes adapted to the local environment. Of particular interest is adaptation of local and non-local bee colonies to environmental conditions. To study the importance of genotype-environment interactions on the viability and productivity of local and non-local bee colonies, we analyzed the long-term dynamics of the main traits in dark forest bees (Apis mellifera mellifera) and hybrid colonies. From 2010 to 2022, a total of 64 colonies living in an apiary in Siberia, Russia, were monitored and tested to assess their biological, behavioral, and economic traits in a temperate continental climate. We detected significant correlations between the studied biological and behavioral indicators of the bee colony such as colony strength, overwintering ability, infection of colonies with diseases, hygienic behavior, and others. No relationships between the biological and economic (honey productivity) traits of bee colonies are shown. The overall result of our study is that local dark forest bee, A.m.mellifera, showed higher values for all analyzed traits than hybrid colonies. Compared to hybrids, dark forest bee colonies showed more gentleness, productivity, and survivorship. The results from our study indicate a specific local adaptation of the A.m.mellifera subspecies in a temperate continental climate. Siberia represents a unique region for the conservation of the dark forest bee. The creation of conservation areas is one way to protect local bee populations, well adapted to local environmental conditions, from uncontrolled importation of bee breeds from different regions.

Molecular investigation and infection patterns of seven viruses of honey bee (Apis mellifera L, 1758) populations from southeastern Morocco

An epidemiological survey of honey bee viruses was conducted on 87 clinically healthy beehives located in southeastern Morocco. The sampled colonies were analyzed by reverse transcriptase (RT)-PCR / Real Time RT-qPCR with the aim of detecting and / or quantifying the following viruses: acute bee paralysis virus (ABPV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV), sacbrood virus (SBV), black queen cell virus (BQCV), Kashmir bee virus (KBV) and Israeli acute paralysis virus (IAPV). With the exception of the last two of these viruses, all the other five were detected with different prevalence rates. DWV showed the highest prevalence rate (89.65 %), followed by BQCV (17.24 %), ABPV (8.04 %), CBPV (4.59 %), and SBV (2.29 %). This study represents the first molecular detection of BQCV in the country. Among all investigated colonies, only eight were virus free (9.2 %). By contrast, single infection was detected in 64.37 % of colonies, 21.8 % showed mixed infection with two viruses, while 4.6 % showed three. Nucleotide sequences of a portion of the DWV polyprotein gene obtained for six honey bee samples showed the greatest nucleotide identity with sequences of DWV from Sweden and Ireland. The negative effect of migratory beekeeping as opposed to stationary beekeeping was highlighted given that stationary beehives showed infection with up to three viruses only, while migratory beehives showed up to five viruses. The results of this study are of crucial importance as they shed light on the current status of honey bee health in southeastern Morocco.

Effects of common co-occurring pesticides (a neonicotinoid and fungicide) on honey bee colony health in a semi-field study

Multiple stressors are linked to declines of insects and important pollinators, such as bees. Recently, interactive effects of multiple agrochemicals on bees have been highlighted, including fungicides, which increase toxicity of neonicotinoid insecticides. Here, we use a semi-field study across two seasons in controlled foraging tunnels to test the effects of a field application of a commercial fungicide product with two active ingredients (pyraclostrobin and metconazole) applied at label rates. We also examine its interactive effects with the neonicotinoid insecticide clothianidin, at a conservative field-realistic dose of 2.23 ppb, on 48 honey bee colonies. We found combined effects of pesticide exposure, including additive 2.93-fold increases in mortality, and an additional effect of increased infestation levels of the ectoparasitic mite, Varroa destructor. Pesticide treatments also reduced colony activity, reduced colony weight, and increased sugar consumption of whole colonies. These findings indicate that typical sublethal exposure levels to common, co-occurring agrochemicals in the field significantly affect the health of whole honey bee colonies, highlighting an unintended consequence of increasing pesticide applications.

Caught in the act: the invasion of a viral vector changes viral prevalence and titre in native honeybees and bumblebees

Novel transmission routes change pathogen landscapes and may facilitate disease emergence. The varroa mite is a virus vector that switched to western honeybees at the beginning of the last century, leading to hive mortality, particularly in combination with RNA viruses. A recent invasion of varroa on the French island of Ushant introduced vector-mediated transmission to one of the last varroa-naive native honeybee populations and caused rapid changes in the honeybee viral community. These changes were characterized by a drastic increase in deformed wing virus type B prevalence and titre in honeybees, as well as knock-on effects in bumblebees, particularly in the year following the invasion. Slow bee paralysis virus also appeared in honeybees and bumblebees, with a 1 year delay, while black queen cell virus declined in honeybees. This study highlights the rapid and far-reaching effects of vector-borne transmission that can extend beyond the directly affected host species, and that the direction of the effect depends on the pathogen's virulence.

Varroa destructor parasitism and Deformed wing virus infection in honey bees are linked to peroxisome-induced pathways

The ectoparasitic mite Varroa destructor transmits and triggers viral infections that have deleterious effects on honey bee colonies worldwide. We performed a manipulative experiment in which worker bees collected at emergence were exposed to Varroa for 72 h, and their proteomes were compared with those of untreated control bees. Label-free quantitative proteomics identified 77 differentially expressed A. mellifera proteins (DEPs). In addition, viral proteins were identified by orthogonal analysis, and most importantly, Deformed wing virus (DWV) was found at high levels/intensity in Varroa-exposed bees. Pathway enrichment analysis suggested that the main pathways affected included peroxisomal metabolism, cyto-/exoskeleton reorganization, and cuticular proteins. Detailed examination of individual DEPs revealed that additional changes in DEPs were associated with peroxisomal function. In addition, the proteome data support the importance of TGF-β signaling in Varroa-DWV interaction and the involvement of the mTORC1 and Hippo pathways. These results suggest that the effect of DWV on bees associated with Varroa feeding results in aberrant autophagy. In particular, autophagy is selectively modulated by peroxisomes, to which the observed proteome changes strongly corresponded. This study complements previous research with different study designs and suggests the importance of the peroxisome, which plays a key role in viral infections.

Synergistic resistance of honeybee (Apis mellifera) and their gut microorganisms to fluvalinate stress

Fluvalinate is widely used in the control of Varroa destructor, but its residues in colonies threaten honeybees. The effect of fluvalinate-induced dysbiosis on honeybee-related gene expression and the gut microenvironment of honeybees has not yet been fully elucidated. In this study, two-day-old larvae to seven-day-old adult worker bees were continuously fed different amounts of fluvalinate-sucrose solutions (0, 0.5, 5, and 50 mg/kg), after which the expression levels of two immune-related genes (Hymenoptaecin and Defensin1) and three detoxication-related genes (GSTS3, CAT, and CYP450) in worker bees (1, 7, and 20 days old) were measured. The effect of fluvalinate on the gut microbes of worker bees at seven days old also was explored using 16S rRNA Illumina deep sequencing. The results showed that exposure of honeybees to the insecticide fluvalinate affected their gene expression and gut microbial composition. As the age of honeybees increased, the effect of fluvalinate on the expression of Hymenoptaecin, CYP450, and CAT decreased, and the abundance of honeybee gut bacteria was affected by increasing the fluvalinate concentration. These findings provide insights into the synergistic defense of honeybee hosts against exogenous stresses in conjunction with honeybee gut microbes.

A longitudinal study of queen health in honey bees reveals tissue specific response to seasonal changes and pathogen pressure

The health of honey bee queens is crucial for colony success, particularly during stressful periods like overwintering. To accompany a previous longitudinal study of colony and worker health, we explored niche-specific gut microbiota, host gene expression, and pathogen prevalence in honey bee queens overwintering in a warm southern climate. We found differential gene expression and bacterial abundance with respect to various pathogens throughout the season. Biologically older queens had larger microbiotas, particularly enriched in Bombella and Bifidobacterium. Both Deformed Wing Virus A and B subtypes were highest in the fat body tissue in January, correlating with colony Varroa levels, and Deformed Wing Virus titers in workers. High viral titers in queens were associated with decreased vitellogenin expression, suggesting a potential trade-off between immune function and reproductive capacity. Additionally, we found a complex and dynamic relationship between these viral loads and immune gene expression, indicating a possible breakdown in the coordinated immune response as the season progressed. Our study also revealed a potential link between Nosema and Melissococcus plutonius infections in queens, demonstrating that seasonal opportunism is not confined to just workers. Overall, our findings highlight the intricate interplay between pathogens, metabolic state, and immune response in honey bee queens. Combined with worker and colony-level metrics from the same colonies, our findings illustrate the social aspect of queen health and resilience over the winter dearth.

Life-history stage determines the diet of ectoparasitic mites on their honey bee hosts

Ectoparasitic mites of the genera Varroa and Tropilaelaps have evolved to exclusively exploit honey bees as food sources during alternating dispersal and reproductive life history stages. Here we show that the primary food source utilized by Varroa destructor depends on the host life history stage. While feeding on adult bees, dispersing V. destructor feed on the abdominal membranes to access to the fat body as reported previously. However, when V. destructor feed on honey bee pupae during their reproductive stage, they primarily consume hemolymph, indicated by wound analysis, preferential transfer of biostains, and a proteomic comparison between parasite and host tissues. Biostaining and proteomic results were paralleled by corresponding findings in Tropilaelaps mercedesae, a mite that only feeds on brood and has a strongly reduced dispersal stage. Metabolomic profiling of V. destructor corroborates differences between the diet of the dispersing adults and reproductive foundresses. The proteome and metabolome differences between reproductive and dispersing V. destructor suggest that the hemolymph diet coincides with amino acid metabolism and protein synthesis in the foundresses while the metabolism of non-reproductive adults is tuned to lipid metabolism. Thus, we demonstrate within-host dietary specialization of ectoparasitic mites that coincides with life history of hosts and parasites.

Assessment of Efficacy of Algerian Propolis against the Parasitic Mite Varroa destructor and Safety for Honey Bees by Spray Treatment

Varroa destructor is an ectoparasitic mite and is considered one of the most important causes of honey bee population loss. In the last years, substances of botanical origin have emerged as natural alternatives to diminish the mite population levels. Propolis is a natural product and is used by honey bees for multiple tasks, including protection from pathogens and parasites, and varroacidal activity of propolis extracts has been shown. In this study, we investigated the potential of propolis, collected by native Algerian honey bee subspecies (Apis mellifera intermissa and A. m. sahariensis) in different locations in Algeria and extracted by ultrasound, to control mites of V. destructor and tested the safety for the honey bees. The most important results were that the best propolis extracts at 10% killed 100% of the Varroa mites within 3-4 h in a Petri dish assay. In addition, when we sprayed A. m. intermissa bees infested with Varroa mites with a 10% concentration in a mini-hive setup, we scored a high mite mortality of 85-87% with the best propolis extracts, and importantly, there was no mortality in the bees. Our data demonstrated that propolis extracts in Algeria could be used in honey bee colonies by spraying against Varroa mite infestations, which may develop as an easy method for local beekeepers to control Varroa in their hives. Further research should investigate the mechanism of action.

Alcohol extract of the gypsy mushroom (Cortinarius caperatus) inhibits the development of Deformed wing virus infection in western honey bee (Apis mellifera)

Deformed wing virus (DWV) transmitted by the parasitic mite Varroa destructor is one of the most significant factors contributing to massive losses of managed colonies of western honey bee (Apis mellifera) subspecies of European origin reported worldwide in recent decades. Despite this fact, no antiviral treatment against honey bee viruses is currently available for practical applications and the level of viral infection can only be controlled indirectly by reducing the number of Varroa mites in honey bee colonies. In this study, we investigated the antiviral potential of the gypsy mushroom (Cortinarius caperatus) to reduce DWV infection in honey bees. Our results indicate that the alcohol extract of C. caperatus prevented the development of DWV infection in cage experiments as well as after direct application to honey bee colonies in a field experiment. The applied doses did not shorten the lifespan of honey bees. The reduced levels of DWV in C. caperatus-treated honey bees in cage experiments were accompanied by significant changes in the gene expression of Tep7, Bap1, and Vago. The C. caperatus treatment was not effective against the trypanosomatid Lotmaria passim. No residues of C.caperatus were found in honey harvested in the spring from colonies supplemented with the mushroom extract for their winter feeding. These findings suggest that C. caperatus alcohol extract could be a potential natural remedy to treat DWV infection in honey bees.

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.

Quantitative trait loci mapping for survival of virus infection and virus levels in honey bees

Israeli acute paralysis virus (IAPV) is a highly virulent, Varroa-vectored virus that is of global concern for honey bee health. Little is known about the genetic basis of honey bees to withstand infection with IAPV or other viruses. We set up and analyzed a backcross between preselected honey bee colonies of low and high IAPV susceptibility to identify quantitative trait loci (QTL) associated with IAPV susceptibility. Experimentally inoculated adult worker bees were surveyed for survival and selectively sampled for QTL analysis based on SNPs identified by whole-genome resequencing and composite interval mapping. Additionally, natural titers of other viruses were quantified in the abdomen of these workers via qPCR and also used for QTL mapping. In addition to the full dataset, we analyzed distinct subpopulations of susceptible and non-susceptible workers separately. These subpopulations are distinguished by a single, suggestive QTL on chromosome 6, but we identified numerous other QTL for different abdominal virus titers, particularly in the subpopulation that was not susceptible to IAPV. The pronounced QTL differences between the susceptible and non-susceptible subpopulations indicate either an interaction between IAPV infection and the bees' interaction with other viruses or heterogeneity among workers of a single cohort that manifests itself as IAPV susceptibility and results in distinct subgroups that differ in their interaction with other viruses. Furthermore, our results indicate that low susceptibility of honey bees to viruses can be caused by both, virus tolerance and virus resistance. QTL were partially overlapping among different viruses, indicating a mixture of shared and specific processes that control viruses. Some functional candidate genes are located in the QTL intervals, but their genomic co-localization with numerous genes of unknown function delegates any definite characterization of the underlying molecular mechanisms to future studies.

Varroa destructor exacerbates the negative effect of cold contributing to honey bee mortality

Several concurrent stress factors can impact honey bee health and colony stability. Although a satisfactory knowledge of the effect of almost every single factor is now available, a mechanistic understanding of the many possible interactions between stressors is still largely lacking. Here we studied, both at the individual and colony level, how honey bees are affected by concurrent exposure to cold and parasitic infection. We found that the parasitic mite Varroa destructor, further than increasing the natural mortality of bees, can induce an anorexia that reduces their capacity to thermoregulate and thus react to sub-optimal temperatures. This, in turn, could affect the collective response of the bee colony to cold temperatures aggravating the effect already observed at the individual level. These results highlight the important role that biotic factors can have by shaping the response to abiotic factors and the strategic need to consider the potential interactions between stressors at all levels of the biological organization to better understand their impact.

Risk assessment of honeybee larvae exposure to pyrethroid insecticides in beebread and honey

Honeybee is an essential pollinator to crops, evaluation to the risk assessment of honeybee larvae exposure to pesticides residue in the bee bread and honey is an important strategy to protect the bee colony due to the mixture of these two matrices is main food for 3-day-old honeybee larvae. In this study, a continuous survey to the residue of five pyrethroid insecticides in bee bread and honey between 2018 and 2020 from 17 major cultivation provinces which can be determined as Northeast, Northwest, Eastern, Central, Southwest, and Southern of China, there was at least one type II pyrethroid insecticide was detected in 54.7 % of the bee bread samples and 43.4 % of the honey. Then, we assayed the acute toxicity of type II pyrethroid insecticides based on the detection results, the LD50 value was 0.2201 μg/larva (beta-cyhalothrin), 0.4507 μg/larva (bifenthrin), 2.0840 μg/larva (fenvalerate), 0.0530 μg/larva (deltamethrin), and 0.1640 μg/larva (beta-cypermethrin), respectively. Finally, the hazard quotient was calculated as larval oral ranged from 0.046 × 10-3 to 2.128 × 10-3. Together, these empirical findings provide further insight into the accurate contamination of honey bee colonies caused by chemical pesticides, which can be used as a valuable guidance for the beekeeping industry and pesticide regulation.

Signatures of adaptive decreased virulence of deformed wing virus in an isolated population of wild honeybees (Apis mellifera)

Understanding the ecological and evolutionary processes that drive host-pathogen interactions is critical for combating epidemics and conserving species. The Varroa destructor mite and deformed wing virus (DWV) are two synergistic threats to Western honeybee (Apis mellifera) populations across the globe. Distinct honeybee populations have been found to self-sustain despite Varroa infestations, including colonies within the Arnot Forest outside Ithaca, NY, USA. We hypothesized that in these bee populations, DWV has been selected to produce an avirulent infection phenotype, allowing for the persistence of both host and disease-causing agents. To investigate this, we assessed the titre of viruses in bees from the Arnot Forest and managed apiaries, and assessed genomic variation and virulence differences between DWV isolates. Across groups, we found viral abundance was similar, but DWV genotypes were distinct. We also found that infections with isolates from the Arnot Forest resulted in higher survival and lower rates of symptomatic deformed wings, compared to analogous isolates from managed colonies, providing preliminary evidence to support the hypothesis of adaptive decreased viral virulence. Overall, this multi-level investigation of virus genotype and phenotype indicates that host ecological context can be a significant driver of viral evolution and host-pathogen interactions in honeybees.

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.

Plants and Their Derivatives as Promising Therapeutics for Sustainable Control of Honeybee (Apis mellifera) Pathogens

The most important pollinator for agricultural crops is the Western honeybee (Apis mellifera). During the winter and summer seasons, diseases and stresses of various kinds endanger honeybee numbers and production, resulting in expenses for beekeepers and detrimental effects on agriculture and ecosystems. Researchers are continually in search of therapies for honeybees using the resources of microbiology, molecular biology, and chemistry to combat diseases and improve the overall health of these important pollinating insects. Among the most investigated and most promising solutions are medicinal plants and their derivatives. The health of animals and their ability to fight disease can be supported by natural products (NPs) derived from living organisms such as plants and microbes. NPs contain substances that can reduce the effects of diseases by promoting immunity or directly suppressing pathogens, and parasites. This literature review summarises the advances that the scientific community has achieved over the years regarding veterinary treatments in beekeeping through the use of NPs. Their impact on the prevention and control of honeybee diseases is investigated both in trials that have been conducted in the laboratory and field studies.

Establishment and Application of CRISPR-Cas12a-Based Recombinase Polymerase Amplification and a Lateral Flow Dipstick and Fluorescence for the Detection and Distinction of Deformed Wing Virus Types A and B

Deformed wing virus (DWV) is one of the important pathogens of the honey bee (Apis mellifera), which consists of three master variants: types A, B, and C. Among them, DWV types A (DWV-A) and B (DWV-B) are the most prevalent variants in honey bee colonies and have been linked to colony decline. DWV-A and DWV-B have different virulence, but it is difficult to distinguish them via traditional methods. In this study, we established a visual detection assay for DWV-A and DWV-B using recombinase polymerase amplification (RPA) and a lateral flow dipstick (LFD) coupled with the clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein (Cas) 12a fluorescence system (RPA-CRISPR-Cas12a-LFD). The limit of detection of this system was ~6.5 × 100 and 6.2 × 101 copies/μL for DWV-A and DWV-B, respectively. The assays were specific and non-cross-reactive against other bee viruses, and the results could be visualized within 1 h. The assays were validated by extracting cDNA from 36 clinical samples of bees that were suspected to be infected with DWV. The findings were consistent with those of traditional reverse transcription-quantitative polymerase chain reaction, and the RPA-CRISPR-Cas12a assay showed the specific, sensitive, simple, and appropriate detection of DWV-A and DWV-B. This method can facilitate the visual and qualitative detection of DWV-A and DWV-B as well as the monitoring of different subtypes, thereby providing potentially better control and preventing current and future DWV outbreaks.

Individual and social defenses in Apis mellifera: a playground to fight against synergistic stressor interactions

The honeybee is an important species for the agri-food and pharmaceutical industries through bee products and crop pollination services. However, honeybee health is a major concern, because beekeepers in many countries are experiencing significant colony losses. This phenomenon has been linked to the exposure of bees to multiple stresses in their environment. Indeed, several biotic and abiotic stressors interact with bees in a synergistic or antagonistic way. Synergistic stressors often act through a disruption of their defense systems (immune response or detoxification). Antagonistic interactions are most often caused by interactions between biotic stressors or disruptive activation of bee defenses. Honeybees have developed behavioral defense strategies and produce antimicrobial compounds to prevent exposure to various pathogens and chemicals. Expanding our knowledge about these processes could be used to develop strategies to shield bees from exposure. This review aims to describe current knowledge about the exposure of honeybees to multiple stresses and the defense mechanisms they have developed to protect themselves. The effect of multi-stress exposure is mainly due to a disruption of the immune response, detoxification, or an excessive defense response by the bee itself. In addition, bees have developed defenses against stressors, some behavioral, others involving the production of antimicrobials, or exploiting beneficial external factors.

Viral Co-Infections and Antiviral Immunity in Honey Bees

Over the past few decades, honey bees have been facing an increasing number of stressors. Beyond individual stress factors, the synergies between them have been identified as a key factor in the observed increase in colony mortality. However, these interactions are numerous and complex and call for further research. Here, in line with our need for a systemic understanding of the threats that they pose to bee health, we review the interactions between honey bee viruses. As viruses are obligate parasites, the interactions between them not only depend on the viruses themselves but also on the immune responses of honey bees. Thus, we first summarise our current knowledge of the antiviral immunity of honey bees. We then review the interactions between specific pathogenic viruses and their interactions with their host. Finally, we draw hypotheses from the current literature and suggest directions for future research.

A longitudinal experiment demonstrates that honey bee colonies managed organically are as healthy and productive as those managed conventionally

Honey bee colony management is critical to mitigating the negative effects of biotic and abiotic stressors. However, there is significant variation in the practices implemented by beekeepers, which results in varying management systems. This longitudinal study incorporated a systems approach to experimentally test the role of three representative beekeeping management systems (conventional, organic, and chemical-free) on the health and productivity of stationary honey-producing colonies over 3 years. We found that the survival rates for colonies in the conventional and organic management systems were equivalent, but around 2.8 times greater than the survival under chemical-free management. Honey production was also similar, with 102% and 119% more honey produced in conventional and organic management systems, respectively, than in the chemical-free management system. We also report significant differences in biomarkers of health including pathogen levels (DWV, IAPV, Vairimorpha apis, Vairimorpha ceranae) and gene expression (def-1, hym, nkd, vg). Our results experimentally demonstrate that beekeeping management practices are key drivers of survival and productivity of managed honey bee colonies. More importantly, we found that the organic management system-which uses organic-approved chemicals for mite control-supports healthy and productive colonies, and can be incorporated as a sustainable approach for stationary honey-producing beekeeping operations.

Unraveling the Role of Antimicrobial Peptides in Insects

Antimicrobial peptides (AMPs) are short, mainly positively charged, amphipathic molecules. AMPs are important effectors of the immune response in insects with a broad spectrum of antibacterial, antifungal, and antiparasitic activity. In addition to these well-known roles, AMPs exhibit many other, often unobvious, functions in the host. They support insects in the elimination of viral infections. AMPs participate in the regulation of brain-controlled processes, e.g., sleep and non-associative learning. By influencing neuronal health, communication, and activity, they can affect the functioning of the insect nervous system. Expansion of the AMP repertoire and loss of their specificity is connected with the aging process and lifespan of insects. Moreover, AMPs take part in maintaining gut homeostasis, regulating the number of endosymbionts as well as reducing the number of foreign microbiota. In turn, the presence of AMPs in insect venom prevents the spread of infection in social insects, where the prey may be a source of pathogens.

Sunflower-Associated Reductions in Varroa Mite Infestation of Honey Bee Colonies

Landscapes can affect parasite epidemiology in wild and agricultural animals. Honey bees are threatened by loss of floral resources and by parasites, principally the mite Varroa destructor and the viruses it vectors. Existing mite control relies heavily on chemical treatments that can adversely affect bees. Alternative, pesticide-free control methods are needed to mitigate infestation with these ectoparasites. Many flowering plants provide nectar and pollen that confer resistance to parasites. Enrichment of landscapes with antiparasitic floral resources could therefore provide a sustainable means of parasite control in pollinators. Floral rewards of Asteraceae plants can reduce parasitic infection in diverse bee species, including honey and bumble bees. Here, we tested the effects of sunflower (Helianthus annuus) cropland and pollen supplementation on honey bee resistance to macro- and microparasites. Although sunflower had nonsignificant effects on microparasites, We found that increased sunflower pollen availability correlated with reduced Varroa mite infestation in landscapes and pollen-supplemented colonies. At the landscape level, each doubling of sunflower crop area was associated with a 28% reduction in mite infestation. In field trials, late-summer supplementation of colonies with sunflower pollen reduced mite infestation by 2.75-fold relative to artificial pollen. United States sunflower crop acreage has declined by 2% per year since 1980, however, suggesting reduced availability of this floral resource. Although further research is needed to determine whether the observed effects represent direct inhibition of mite fecundity or mite-limiting reductions in honey bee brood-rearing, our findings suggest the potential for sunflower plantings or pollen supplements to counteract a major driver of honey bee losses worldwide.

Nationwide Screening for Bee Viruses in Apis mellifera Colonies in Egypt

Honey bees are essential for crop and wild plant pollination. However, many countries have reported high annual colony losses caused by multiple possible stressors. Diseases, particularly those caused by viruses, are a major cause of colony losses. However, little is known about the prevalence of honey bee pathogens, particularly virus prevalence, in Egyptian honey bees. To address this shortfall, we determined the prevalence of widespread bee viruses in honey bee colonies in Egypt-whether it is affected by geography, the season, or infestation with Varroa destructor (varroa) mites. Honey bee worker samples were collected from 18 geographical regions across Egypt during two seasons: winter and summer of 2021. Three apiaries were chosen in each region, and a pooled sample of 150 worker bees was collected from five colonies in each apiary then screened by qPCR for 10 viral targets: acute bee paralysis virus (ABPV), black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV) genotypes A (DWV-A), B (DWV-B) and D (Egyptian bee virus), Israeli acute paralysis virus (IAPV), Kashmir bee virus (KBV), sacbrood virus (SBV), and slow bee paralysis virus (SBPV). Our results revealed that DWV-A was the most prevalent virus, followed by BQCV and ABPV; the DWV genotype now spreading across the world, DWV-B, was not detected. There was no difference in varroa infestation rates as well as virus prevalence between winter and summer. However, colonies infected with BQCV had a significantly higher varroa count (adjusted p < 0.05) in the winter season, indicating that there is a seasonal association between the intensity of infestation by varroa and the presence of this virus. We provide data on the current virus prevalence in Egypt, which could assist in the protection of Egypt's beekeeping industry. Moreover, our study aids in the systematic assessment of the global honey bee virome by filling a knowledge gap about the prevalence of honey bee viruses in Egypt.

Negative but antagonistic effects of neonicotinoid insecticides and ectoparasitic mites Varroa destructor on Apis mellifera honey bee food glands

Collaborative brood care by workers is essential for the functionality of eusocial Apis mellifera honey bee colonies. The hypopharyngeal food glands of workers play a crucial role in this context. Even though there is consensus that ubiquitous ectoparasitic mites Varroa destructor and widespread insecticides, such as neonicotinoids, are major stressors for honey bee health, their impact alone and in combination on the feeding glands of workers is poorly understood. Here, we show that combined exposure to V. destructor and neonicotinoids antagonistically interacted on hypopharyngeal gland size, yet they did not interact on emergence body mass or survival. While the observed effects of the antagonistic interaction were less negative than expected based on the sum of the individual effects, hypopharyngeal gland size was still significantly reduced. Alone, V. destructor parasitism negatively affected emergence body mass, survival, and hypopharyngeal gland size, whereas neonicotinoid exposure reduced hypopharyngeal gland size only. Since size is associated with hypopharyngeal gland functionality, a reduction could result in inadequate brood care. As cooperative brood care is a cornerstone of eusociality, smaller glands could have adverse down-stream effects on inclusive fitness of honey bee colonies. Therefore, our findings highlight the need to further study how ubiquitous stressors like V. destructor and neonicotinoids interact to affect honey bees.

Coinfection patterns of two marine apicomplexans are not associated with genetic diversity of their polychaete host

Coinfections of two or more parasites within one host are more of a rule than an exception in nature. Interactions between coinfecting parasites can greatly affect their abundance and prevalence. Characteristics of the host, such as genetic diversity, can also affect the infection dynamics of coinfecting parasites. Here, we investigate for the first time the association of coinfection patterns of two marine apicomplexans, Rhytidocystis sp. and Selenidium pygospionis, with the genetic diversity of their host, the polychaete Pygospio elegans, from natural populations. Host genetic diversity was determined with seven microsatellite loci and summarized as allelic richness, inbreeding coefficient, and individual heterozygosity. We detected nonsignificant correlations between infection loads and both individual host heterozygosity and population genetic diversity. Prevalence and infection load of Rhytidocystis sp. were higher than those of S. pygospionis, and both varied spatially. Coinfections were common, and almost all hosts infected by S. pygospionis were also infected by Rhytidocystis sp. Rhytidocystis sp. infection load was significantly higher in dual infections. Our results suggest that factors other than host genetic diversity might be more important in marine apicomplexan infection patterns and experimental approaches would be needed to further determine how interactions between the apicomplexans and their host influence infection.

Dietary Supplement of Grape Wastes Enhances Honeybee Immune System and Reduces Deformed Wing Virus (DWV) Load

Ingredients rich in phenolic compounds and antioxidants of winemaking wastes, which play an important role in the prevention of various diseases and the control of viruses, are being explored. Currently, there is a concern about honeybee population loss, with deformed wing virus (DWV) being the most common virus infecting apiaries and one of the main causes of honeybee decline. Hence, the effect of grape pomace powder (GPP) as a dietary supplement to enhance the immune system of honeybees affected by DWV was evaluated. The characteristics of the ingredient GPP, obtained by spray-drying, revealed a high anthocyanin content (1102.45 mg 100 g^-1), and it was applied at doses of 0.5, 1, 2.5 and 5% as a dietary supplement for bees infected by DWV. The results showed that the GPP treatments strengthened the immune response of honeybees against DWV. Moreover, the expression of the Relish gene was significantly higher in bees fed with GPP compared to the infected control. This study, which is framed in the search of food waste valorization for environmental sustainability, proves the feasibility of using grape wastes as dietary supplements for pollinators, and provides knowledge of the influence of polyphenols on the expression profiles of immune-related genes in honeybees.

Current Knowledge on Bee Innate Immunity Based on Genomics and Transcriptomics

As important pollinators, bees play a critical role in maintaining the balance of the ecosystem and improving the yield and quality of crops. However, in recent years, the bee population has significantly declined due to various pathogens and environmental stressors including viruses, bacteria, parasites, and increased pesticide application. The above threats trigger or suppress the innate immunity of bees, their only immune defense system, which is essential to maintaining individual health and that of the colony. In addition, bees can be divided into solitary and eusocial bees based on their life traits, and eusocial bees possess special social immunities, such as grooming behavior, which cooperate with innate immunity to maintain the health of the colony. The omics approach gives us an opportunity to recognize the distinctive innate immunity of bees. In this regard, we summarize innate bee immunity from a genomic and transcriptomic perspective. The genetic characteristics of innate immunity were revealed by the multiple genomes of bees with different kinds of sociality, including honeybees, bumblebees, wasps, leaf-cutter bees, and so on. Further substantial transcriptomic data of different tissues from diverse bees directly present the activation or suppression of immune genes under the infestation of pathogens or toxicity of pesticides.

A deeper understanding of system interactions can explain contradictory field results on pesticide impact on honey bees

While there is widespread concern regarding the impact of pesticides on honey bees, well-replicated field experiments, to date, have failed to provide clear insights on pesticide effects. Here, we adopt a systems biology approach to gain insights into the web of interactions amongst the factors influencing honey bee health. We put the focus on the properties of the system that depend upon its architecture and not on the strength, often unknown, of each single interaction. Then we test in vivo, on caged honey bees, the predictions derived from this modelling analysis. We show that the impact of toxic compounds on honey bee health can be shaped by the concurrent stressors affecting bees. We demonstrate that the immune-suppressive capacity of the widespread pathogen of bees, deformed wing virus, can introduce a critical positive feed-back loop in the system causing bistability, i.e., two stable equilibria. Therefore, honey bees under similar initial conditions can experience different consequences when exposed to the same stressor, including prolonged survival or premature death. The latter can generate an increased vulnerability of the hive to dwindling and collapse. Our conclusions reconcile contrasting field-testing outcomes and have important implications for the application of field studies to complex systems.

Epidemiology of the Microsporidium Nosema ceranae in Four Mediterranean Countries

Nosema ceranae is a highly prevalent intracellular parasite of honey bees' midgut worldwide. This Microsporidium was monitored during a long-term study to evaluate the infection at apiary and intra-colony levels in six apiaries in four Mediterranean countries (France, Israel, Portugal, and Spain). Parameters on colony strength, honey production, beekeeping management, and climate were also recorded. Except for São Miguel (Azores, Portugal), all apiaries were positive for N. ceranae, with the lowest prevalence in mainland France and the highest intra-colony infection in Israel. A negative correlation between intra-colony infection and colony strength was observed in Spain and mainland Portugal. In these two apiaries, the queen replacement also influenced the infection levels. The highest colony losses occurred in mainland France and Spain, although they did not correlate with the Nosema infection levels, as parasitism was low in France and high in Spain. These results suggest that both the effects and the level of N. ceranae infection depends on location and beekeeping conditions. Further studies on host-parasite coevolution, and perhaps the interactions with other pathogens and the role of honey bee genetics, could assist in understanding the difference between nosemosis disease and infection, to develop appropriate strategies for its control.

Contact varroacidal efficacy of lithium citrate and its influence on viral loads, immune parameters and oxidative stress of honey bees in a field experiment

With an almost global distribution, Varroa destuctor is the leading cause of weakening and loss of honey bee colonies. New substances are constantly being tested in order to find those that will exhibit high anti-Varroa efficacy at low doses/concentrations, without unwanted effects on bees. Lithium (Li) salts stood out as candidates based on previous research. The aims of this study were to evaluate Li citrate hydrate (Li-cit) for its contact efficacy against Varroa, but also the effect of Li-cit on honey bees by estimating loads of honey bee viruses, expression levels of immune-related genes and genes for antioxidative enzymes and oxidative stress parameters on two sampling occasions, before the treatment and after the treatment. Our experiment was performed on four groups, each consisting of seven colonies. Two groups were treated with the test compound, one receiving 5 mM and the other 10 mM of Li-cit; the third received oxalic acid treatment (OA group) and served as positive control, and the fourth was negative control (C group), treated with 50% w/v pure sucrose-water syrup. Single trickling treatment was applied in all groups. Both tested concentrations of Li-cit, 5 and 10 mM, expressed high varroacidal efficacy, 96.85% and 96.80%, respectively. Load of Chronic Bee Paralysis Virus significantly decreased (p &lt; 0.01) after the treatment in group treated with 5 mM of Li-cit. In OA group, loads of Acute Bee Paralysis Virus and Deformed Wing Virus significantly (p &lt; 0.05) increased, and in C group, loads of all viruses significantly (p &lt; 0.01 or p &lt; 0.001) increased. Transcript levels of genes for abaecin, apidaecin, defensin and vitellogenin were significantly higher (p &lt; 0.05—p &lt; 0.001), while all oxidative stress parameters were significantly lower (p &lt; 0.05—p &lt; 0.001) after the treatment in both groups treated with Li-cit. All presented results along with easy application indicate benefits of topical Li-cit treatment and complete the mosaic of evidence on the advantages of this salt in the control of Varroa.

Viral species differentially influence macronutrient preferences based on honey bee genotype

Food quantity and macronutrients contribute to honey bee health and colony survival by mediating immune responses. We determined if this held true for bees injected with chronic bee paralysis virus (CBPV) and deformed wing virus (DWV), two common honey bee ssRNA viruses. Pollen-substitute diet and syrup consumption rates and macronutrient preferences of two Varroa-resistant stocks (Pol-Line and Russian bees) were compared to Varroa-susceptible Italian bees. Bee stocks varied in consumption, where Italian bees consumed more than Pol-Line and Russian bees. However, the protein: lipid (P:L) ratios of diet consumed by the Italian and Russian bees was greater than that of the Pol-Line bees. Treatment had different effects on consumption based on the virus injected. CBPV was positively correlated with syrup consumption, while DWV was not correlated with consumption. P:L ratios of consumed diet were significantly impacted by the interaction of bee stock and treatment, with the trends differing between CBPV and DWV. Variation in macronutrient preferences based on viral species may indicate differences in energetic costs associated with immune responses to infections impacting different systems. Further, virus species interacted with bee genotype, indicating different mechanisms of viral resistance or tolerance among honey bee genotypes.

Epidemiology of a major honey bee pathogen, deformed wing virus: potential worldwide replacement of genotype A by genotype B

The western honey bee (Apis mellifera) is of major economic and ecological importance, with elevated rates of colony losses in temperate regions over the last two decades thought to be largely caused by the exotic ectoparasitic mite Varroa destructor and deformed wing virus (DWV), which the mite transmits. DWV currently exists as two main genotypes: the formerly widespread DWV-A and the more recently described and rapidly expanding DWV-B. It is an excellent system to understand viral evolution and the replacement of one viral variant by another. Here we synthesise published results on the distribution and prevalence of DWV-A and -B over the period 2008-2021 and present novel data for Germany, Italy and the UK to suggest that (i) DWV-B has rapidly expanded worldwide since its first description in 2004 and (ii) that it is potentially replacing DWV-A. Both genotypes are also found in wild bee species. Based on a simple mathematical model, we suggest that interference between viral genotypes when co-infecting the same host is key to understanding their epidemiology. We finally discuss the consequences of genotype replacement for beekeeping and for wild pollinator species.

Larval exposure to parasitic Varroa destructor mites triggers specific immune responses in different honey bee castes and species

Innate immune systems are key defenses of animals and particularly important in species that lack the sophisticated adaptive immune systems as found in vertebrates. Here, we were interested to quantify variation in innate immune responses of insects in hosts that differ in their parasite susceptibility. To do this, we studied immune responses in honey bees, which can host a remarkable number of different parasites, which are major contributors of declining bee health and colony losses. The most significant parasite of honey bees is the mite Varroa destructor, which has infested the majority of global honey bee populations, and its control remains a major challenge for beekeepers. However, a number of nonmanaged honey bees seem able to control Varroa infections, for example, the Eastern honey bee Apis ceranacerana or the African honey bee Apis mellifera scutellata. These bees therefore make interesting study subjects to identify underlaying resistance traits, for example, by comparing them to more susceptible bee genotypes such as Western honey bees (A. melliferaligustica). We conducted a series of interlinked experiments and started with behavioral assays to compare the attractiveness of bee larvae to mites using different honey bee genotypes and castes. We found that 6-day-old larvae are always most attractive to mites, independently of genotype or castes. In a next step, we compared volatile profiles of the most attractive larvae to test whether they could be used by mites for host selection. We found that the abundance of volatile compounds differed between larval ages, but we also found significant differences between genotypes and castes. To further study the expected underlaying physiological differences between potentially resistant and susceptible host larvae, we compared the larval hemolymph proteomes of the three honey bee genotypes and two castes in response to mite exposure. We identified consistent upregulation of immune and stress-related genes in Varroa-exposed larvae, which differed between genotypes and castes. Tolerant honey bee castes and genotypes were characterized by stronger or more distinct immune esponses. In summary, we provide first insights into the complex involvement of the innate immune system of tolerant honey bees against mite infestations, which could be used for future breeding purposes.

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Honey bee larvae are most susceptible to mite infestations shortly before brood cell capping.

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Larval attractiveness to mites is independent of bee caste or genotype.

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Volatile compound abundance differed between genotypes, castes, and larval ages.

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Mite exposure induces specific immune and stress responses in different genotypes and castes.

Silent threat in honey bee colonies: infection dynamics and molecular epidemiological assessment of black queen cell virus in Turkey

Viruses can have devastating effects and cause epidemics in honey bee (Apis mellifera) colonies. Black queen cell virus (BQCV), which is one of the most common honey bee viruses, affects queen bee larvae and their pupae. This study provides information on the dynamics of BQCV infection in honey bees, using molecular diagnostics to investigate the effects of other pathogens and seasonal patterns that are considered relevant to the epidemiology of BQCV. The results showed a relatively high prevalence of the viruses studied. The prevalence of BQCV, acute bee paralysis virus, and deformed wing virus in worker bees was found to be 90%, 62%, and 84%, respectively. The prevalence of BQCV was 58% in larvae and pupae. Furthermore, the prevalence of Nosema ceranae was 46% in worker bees. Statistical analysis showed possible combined effects of BQCV and other examined viruses in terms of infection dynamics, while BQCV did not show seasonal variation. The BQCV isolates detected in this study were placed in a phylogenetic framework using sequence data from comprehensive sampling in previous studies. The analysis suggested that the Turkish strains of BQCV clustered together with Australian and European strains and consisted of homogeneous populations that had evolved from a common ancestor. This is the first report of BQCV infection dynamics in honey bees in Turkey.

The antiviral role of NF-κB-mediated immune responses and their antagonism by viruses in insects

The antiviral role of innate immune responses mediated by the NF-κB family of transcription factors is well established in vertebrates but was for a long time less clear in insects. Insects encode two canonical NF-κB pathways, the Toll and Imd ('immunodeficiency') pathways, which are best characterised for their role in antibacterial and antifungal defence. An increasing body of evidence has also implicated NF-κB-mediated innate immunity in antiviral responses against some, but not all, viruses. Specific pattern recognition receptors (PRRs) and molecular events leading to NF-κB activation by viral pathogen-associated molecular patterns (PAMPs) have been elucidated for a number of viruses and insect species. Particularly interesting are recent findings indicating that the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway detects viral RNA to activate NF-κB-regulated gene expression. We summarise the literature on virus-NF-κB pathway interactions across the class Insecta, with a focus on the dipterans Drosophila melanogaster and Aedes aegypti. We discuss potential reasons for differences observed between different virus-host combinations, and highlight similarities and differences between cGAS-STING signalling in insects versus vertebrates. Finally, we summarise the increasing number of known molecular mechanisms by which viruses antagonise NF-κB responses, which suggest that NF-κB-mediated immunity exerts strong evolutionary pressures on viruses. These developments in our understanding of insect antiviral immunity have relevance to the large number of insect species that impact on humans through their transmission of human, livestock and plant diseases, exploitation as biotechnology platforms, and role as parasites, pollinators, livestock and pests.

The Beneficial Effect of Pollen on Varroa Infested Bees Depends on Its Influence on Behavioral Maturation Genes

Honey bees collect nectar and pollen to fulfill their nutritional demands. In particular, pollen can influence longevity, the development of hypopharyngeal glands, and immune-competence of bees. Pollen can also mitigate the deleterious effects caused by the parasitic mite Varroa destructor and related deformed wing virus (DWV) infections. It has been shown that V. destructor accelerates the physiological and behavioral maturation of honey bees by influencing the interaction between two core physiological factors, Vitellogenin and juvenile hormone. In this study, we test the hypothesis that the beneficial effects of pollen on Varroa-infested bees are related to the hormonal control underpinning behavioral maturation. By analyzing the expression of genes associated to behavioral maturation in pollen-fed mite-infested bees, we show that treatment with pollen increases the lifespan of mite-infested bees by reversing the faster maturation induced by the parasite at the gene expression level. As expected, from the different immune-competence of nurse and forager bees, the lifespan extension triggered by pollen is also correlated with a positive influence of antimicrobial peptide gene expression and DWV load, further reinforcing the beneficial effect of pollen. This study lay the groundwork for future analyses of the underlying evolutionary processes and applications to improve bee health.

Bee Stressors from an Immunological Perspective and Strategies to Improve Bee Health

Honeybees are the most prevalent insect pollinator species; they pollinate a wide range of crops. Colony collapse disorder (CCD), which is caused by a variety of biotic and abiotic factors, incurs high economic/ecological loss. Despite extensive research to identify and study the various ecological stressors such as microbial infections, exposure to pesticides, loss of habitat, and improper beekeeping practices that are claimed to cause these declines, the deep understanding of the observed losses of these important insects is still missing. Honeybees have an innate immune system, which includes physical barriers and cellular and humeral responses to defend against pathogens and parasites. Exposure to various stressors may affect this system and the health of individual bees and colonies. This review summarizes and discusses the composition of the honeybee immune system and the consequences of exposure to stressors, individually or in combinations, on honeybee immune competence. In addition, we discuss the relationship between bee nutrition and immunity. Nutrition and phytochemicals were highlighted as the factors with a high impact on honeybee immunity.

The Role of Nosema ceranae (Microsporidia: Nosematidae) in Honey Bee Colony Losses and Current Insights on Treatment

Honeybee populations have locally and temporally declined in the last few years because of both biotic and abiotic factors. Among the latter, one of the most important reasons is infection by the microsporidia Nosema ceranae, which is the etiological agent of type C nosemosis. This species was first described in Asian honeybees (Apis cerana). Nowadays, domestic honeybees (Apis mellifera) worldwide are also becoming infected due to globalization. Type C nosemosis can be asymptomatic or can cause important damage to bees, such as changes in temporal polyethism, energy and oxidative stress, immunity loss, and decreased average life expectancy. It causes drastic reductions in workers, numbers of broods, and honey production, finally leading to colony loss. Common treatment is based on fumagillin, an antibiotic with side effects and relatively poor efficiency, which is banned in the European Union. Natural products, probiotics, food supplements, nutraceuticals, and other veterinary drugs are currently under study and might represent alternative treatments. Prophylaxis and management of affected colonies are essential to control the disease. While N. ceranae is one potential cause of bee losses in a colony, other factors must also be considered, especially synergies between microsporidia and the use of insecticides.

Critical View on the Importance of Host Defense Strategies on Virus Distribution of Bee Viruses: What Can We Learn from SARS-CoV-2 Variants?

Bees, both wild and domesticated ones, are hosts to a plethora of viruses, with most of them infecting a wide range of bee species and genera. Although viral discovery and research on bee viruses date back over 50 years, the last decade is marked by a surge of new studies, new virus discoveries, and reports on viral transmission in and between bee species. This steep increase in research on bee viruses was mainly initiated by the global reports on honeybee colony losses and the worldwide wild bee decline, where viruses are regarded as one of the main drivers. While the knowledge gained on bee viruses has significantly progressed in a short amount of time, we believe that integration of host defense strategies and their effect on viral dynamics in the multi-host viral landscape are important aspects that are currently still missing. With the large epidemiological dataset generated over the last two years on the SARS-CoV-2 pandemic, the role of these defense mechanisms in shaping viral dynamics has become eminent. Integration of these dynamics in a multi-host system would not only greatly aid the understanding of viral dynamics as a driver of wild bee decline, but we believe bee pollinators and their viruses provide an ideal system to study the multi-host viruses and their epidemiology.

Presence of Known and Emerging Honey Bee Pathogens in Apiaries of Veneto Region (Northeast of Italy) during Spring 2020 and 2021

A progressive honey bee population decline has been reported worldwide during the last decades, and it could be attributed to several causes, in particular to the presence of pathogens and parasites that can act individually or in synergy. The health status of nine apiaries located in different areas of the Veneto region (northeast of Italy) was assessed for two consecutive years (2020 and 2021) in spring, during the resumption of honey bee activity, for determining the presence of known (Nosema spp., Varroa mite and viruses) and less known or emerging pathogens (Lotmaria passim and Crithidia mellificae) in honey bees. After honey bees sampling from each of the nine apiaries, Nosema apis, Nosema ceranae, L. passim, C. mellificae, ABPV, CBPV, IAPV, KBV, BQCV, SBV, DWV-A, DWV-B and V. destructor were investigated either by microscopic observation or PCR protocols. The viruses BQCV, SBV, CBPV followed by N. ceranae and L. passim were the most prevalent pathogens, and many of the investigated hives, despite asymptomatic, had different degrees of co-infection. This study aimed to highlight, during the resumption of honey bee activity in spring, the prevalence and spreading in the regional territory of different honey bee pathogens, which could alone or synergistically alter the homeostasis of bees colonies. The information gathered would increase our knowledge about the presence of these microorganisms and parasites in the territory and could contribute to improve beekeepers practice.

Research progress on VARROA DESTRUCTOR

Varroa destructor is the most serious threat for western honeybees worldwide. It parasitizes mostly on honeybee's pupae and larvae, resulting in impaired development, decreased immunity, residual wings, loss of flight ability, and even direct death. At the same time, it can cause a series of diseases, greatly infesting bee colonies. This paper introduces the classification, distribution and biological characteristics of Varroa destructor, and discusses its transmission mode, harm form and common control measures.

Social Apoptosis in Varroa Mite Resistant Western Honey Bees (Apis mellifera)

Honey bees are eusocial animals that exhibit both individual and social immune responses, which influence colony health. This is especially well-studied regarding the mite Varroa destructor Anderson and Trueman (Parasitiformes: Varroidae), a parasite of honey bee brood and disease vector. Varroa was introduced relatively recently to Apis mellifera L. (Hymenoptera: Apidae) and is a major driver of the catastrophic die-off of honey bee colonies in the last decade. In contrast, the original host species, Apis cerana Fabricius (Hymenoptera: Apidae) is able to survive mite infestations with little effect on colony health and survival. This resilience is due in part to a newly identified social immune response expressed by developing worker brood. Varroa infested female A. cerana brood experience delayed development and eventually die in a process called 'social apoptosis'. Here, an individual's susceptibility to Varroa results in colony level resistance. We tested for the presence of the social apoptosis trait in two Varroa resistant stocks of A. mellifera (Pol-line and Russian) with different selection histories and compared them to a known Varroa-susceptible stock (Italian). We assessed the survival and development of worker brood reared in either highly or lightly infested host colonies, then receiving one of three treatments: uninfested, experimentally inoculated with a Varroa mite, or wounded to simulate Varroa damage. We found that response to treatment was only differentiated in brood reared in lightly infested host colonies, where experimentally infested Russian honey bees had decreased survival relative to the mite-susceptible Italian stock. This is the first evidence that social apoptosis can exist in Western honey bee populations.

Varroa mite and deformed wing virus infestations interactively make honey bees (Apis mellifera) more susceptible to insecticides

Varroa mite is one of the major adverse factors causing honey bee population decline. In this study, Varroa destructor-infested and uninfested honey bee colonies were established by selective applying miticide (Apivar® amitraz). Mite population was monitored monthly (April-October 2016), and deformed wing virus (DWV) loading was detected seasonally (April, July, and October). Four immunity- and two physiology-related gene expressions, natural mortality, and susceptibility to five insecticides were comparatively and seasonally examined in field-collected honey bee workers. Results showed that Apivar-treated bee colonies had minor or undetectable mite and DWV (using RT-qPCR) infestations in whole bee season, while untreated colonies had substantially higher mite and DWV infestations. In untreated colonies, Varroa mite population irregularly fluctuated over the bee season with higher mite counts in Jun (318 ± 89 mites dropped in 48 h) or August (302) than that (25 ± 4 or 34) in October, and mite population density was not dynamically or closely correlated with the seasonal shift of honey bee natural mortality (regression slope = -0.5212). Unlike mite, DWV titer in untreated colonies progressively increased over the bee season, and it was highly correlated (R² = 1) with the seasonal increase of honey bee natural mortality. Significantly lower gene expressions of dor, PPO, mfe, potentially PPOa and eat as well, in untreated colonies also indicated an association of increased DWV infestation with decreased physiological and immunity-related functions in late-season honey bees. Furthermore, bees with lower mite/DWV infestations exhibited generally consistently lower susceptibilities (contact and oral toxicities) to five representative insecticides than the bees without Apivar treatment. All of these data from this study consistently indicated an interaction of Varroa/viral infestations with insecticide susceptibilities in honey bees, potentially through impairing bee's physiology and immunity, emphasizing the importance of mite control in order to minimize honey bee decline.

Honeybees use propolis as a natural pesticide against their major ectoparasite

Honeybees use propolis collected from plants for coating the inner walls of their nest. This substance is also used as a natural antibiotic against microbial pathogens, similarly to many other animals exploiting natural products for self-medication. We carried out chemical analyses and laboratory bioassays to test if honeybees use propolis for social medication against their major ectoparasite: Varroa destructor. We found that propolis is applied to brood cells where it can affect the reproducing parasites, with a positive effect on honeybees and a potential impact on Varroa population. We conclude that propolis can be regarded as a natural pesticide used by the honeybee to limit a dangerous parasite. These findings significantly enlarge our understanding of behavioural immunity in animals and may have important implications for the management of the most important threat to honeybees worldwide.

Simulated vector transmission differentially influences dynamics of two viral variants of deformed wing virus in honey bees (Apis mellifera)

Understanding how vectors alter the interactions between viruses and their hosts is a fundamental question in virology and disease ecology. In honey bees, transmission of deformed wing virus (DWV) by parasitic Varroa mites has been associated with elevated disease and host mortality, and Varroa transmission has been hypothesized to lead to increased viral titres or select for more virulent variants. Here, we mimicked Varroa transmission by serially passaging a mixed population of two DWV variants, A and B, by injection through in vitro reared honey bee pupae and tracking these viral populations through five passages. The DWV-A and DWV-B variant proportions shifted dynamically through passaging, with DWV-B outcompeting DWV-A after one passage, but levels of both variants becoming equivalent by Passage 5. Sequencing analysis revealed a dominant, recombinant DWV-B strain (DWV-A derived 5′ IRES region with the rest of the genome DWV-B), with low nucleotide diversity that decreased through passaging. DWV-A populations had higher nucleotide diversity compared to DWV-B, but this also decreased through passaging. Selection signatures were found across functional regions of the DWV-A and DWV-B genomes, including amino acid mutations in the putative capsid protein region. Simulated vector transmission differentially impacted two closely related viral variants which could influence viral interactions with the host, demonstrating surprising plasticity in vector-host-viral dynamics.

Chemical Stimulants and Stressors Impact the Outcome of Virus Infection and Immune Gene Expression in Honey Bees (Apis mellifera)

Western honey bees (Apis mellifera) are ecologically, agriculturally, and economically important plant pollinators. High average annual losses of honey bee colonies in the US have been partially attributed to agrochemical exposure and virus infections. To examine the potential negative synergistic impacts of agrochemical exposure and virus infection, as well as the potential promise of phytochemicals to ameliorate the impact of pathogenic infections on honey bees, we infected bees with a panel of viruses (i.e., Flock House virus, deformed wing virus, or Sindbis virus) and exposed to one of three chemical compounds. Specifically, honey bees were fed sucrose syrup containing: (1) thyme oil, a phytochemical and putative immune stimulant, (2) fumagillin, a beekeeper applied fungicide, or (3) clothianidin, a grower-applied insecticide. We determined that virus abundance was lower in honey bees fed 0.16 ppb thyme oil augmented sucrose syrup, compared to bees fed sucrose syrup alone. Parallel analysis of honey bee gene expression revealed that honey bees fed thyme oil augmented sucrose syrup had higher expression of key RNAi genes (argonaute-2 and dicer-like), antimicrobial peptide expressing genes (abaecin and hymenoptaecin), and vitellogenin, a putative honey bee health and age indicator, compared to bees fed only sucrose syrup. Virus abundance was higher in bees fed fumagillin (25 ppm or 75 ppm) or 1 ppb clothianidin containing sucrose syrup relative to levels in bees fed only sucrose syrup. Whereas, honey bees fed 10 ppb clothianidin had lower virus levels, likely because consuming a near lethal dose of insecticide made them poor hosts for virus infection. The negative impact of fumagillin and clothianidin on honey bee health was indicated by the lower expression of argonaute-2, dicer-like, abaecin, and hymenoptaecin, and vitellogenin. Together, these results indicate that chemical stimulants and stressors impact the outcome of virus infection and immune gene expression in honey bees.

Identifying the climatic drivers of honey bee disease in England and Wales

Honey bee colony health has received considerable attention in recent years, with many studies highlighting multifactorial issues contributing to colony losses. Disease and weather are consistently highlighted as primary drivers of colony loss, yet little is understood about how they interact. Here, we combined disease records from government honey bee health inspections with meteorological data from the CEDA to identify how weather impacts EFB, AFB, CBP, varroosis, chalkbrood and sacbrood. Using R-INLA, we determined how different meteorological variables influenced disease prevalence and disease risk. Temperature caused an increase in the risk of both varroosis and sacbrood, but overall, the weather had a varying effect on the six honey bee diseases. The risk of disease was also spatially varied and was impacted by the meteorological variables. These results are an important step in identifying the impacts of climate change on honey bees and honey bee diseases.