On the front line: quantitative virus dynamics in honeybee (Apis mellifera L.) colonies along a new expansion front of the parasite Varroa destructor

Mechanical transfer of honey bee (Hymenoptera: Apidae) virus sequences to wax by worker traffic and aerosolization

Honey bees (Apis mellifera L.) are of undeniable value to agriculture. However, increased mortality of honey bees, mostly due to winter losses associated with parasites and pathogens, have put strain on the apiculture industry. Advancing our knowledge of honey bee viruses and their interactions within the colony environment is vital in mitigating their effect on honey bee health. Our study examined virus sequences detected on beeswax sampled from empty colonies which died during the previous winter. Based on a cage study using virus-containing bees, we confirmed that the introduction of BQCV sequences to wax foundation was possible through workers walking on, and contacting, comb surfaces (worker traffic). Furthermore, we found that BQCV may aerosolize within an incubator to contaminate wax at detectable levels among independent cages. A second cage study explored the potential effects of virus aerosolization on transmission between groups of adult worker bees within cages, having no direct contact. This experiment did not support aerosol transmission between groups of bees in confined spaces. Further work on waxborne virus transmission within colony environments, and potential effects of aerosolization under a wider array of conditions, is crucial to broadening our knowledge of honey bee virus transmission. Our work also highlights potential dangers for beekeepers re-using equipment from dead colonies.

RNA metagenomics revealed insights into the viromes of honey bees (Apis mellifera) and Varroa mites (Varroa destructor) in Taiwan

The honey bee (Apis mellifera) is a vital pollinator for crops. However, they are infested by an ecto-parasite that has spread worldwide, Varroa mite (Varroa destructor). The Varroa mite is a vector of various western honey bee viruses. In this study, the prevalence of seven honey bee viruses (Deformed wing virus, Lake Sinai virus, Acute bee paralysis virus, Sacbrood virus, Kashmir bee virus, Black queen cell virus, Israeli acute paralysis virus), was screened with the honey bees, which were collected from fourteen apiaries from March 2023 to January 2024, and the Varroa mites, which were collected from two apiaries from July to October 2023 by using RT-PCR. Subsequently, metagenomic analyses were conducted on seven honey bee samples and two Varroa mite samples using next-generation sequencing with poly-A capture and rRNA depletion library construction methods. The results showed that 50% to 85.7% of honey bee viruses in each sample were detected by both methods, with up to three additional viruses identified when combining the two approaches. These findings underscore the importance of integrating both methods for comprehensive virome analysis. According to the virome analysis, 28 honey bee viruses were identified in honey bees and 11 in Varroa mites. Among these, 23 viruses were newly recorded in Taiwanese honey bee populations. Notably, three of the newly recorded viruses, Acute bee paralysis virus, Israeli acute paralysis virus, and Apis mellifera filamentous virus, are known to cause symptoms in honey bees, posing potential risks to their health. Six of these viruses were also detected in Varroa mites, highlighting their role in viral transmission. This study represents the first virome analysis of honey bees and Varroa mites in Taiwan, providing critical insights into honey bee health and establishing a foundation for future health assessment indices and mitigation strategies.

Factors influencing the prevalence of acute bee paralysis virus in Apis mellifera and insights into its phylogenetic relationships

Acute bee paralysis virus (ABPV) is a notable pathogen frequently detected in managed honeybee (Apis mellifera) colonies. Although infections are often covert, they can lead to severe outcomes in the presence of Varroa destructor infestations. This study aims to evaluate the prevalence of ABPV and its correlation with a range of biotic and abiotic stressors in managed beehives located in the Central Anatolia and Mediterranean Regions of Türkiye during the spring-summer and autumn seasons of 2021. ABPV was identified in 38.6% of the samples (27/70) using real-time RT-PCR. The high prevalence observed was linked to Varroa destructor infestations, elevated temperatures and dry climatic conditions, migratory beekeeping practices, and disruptions in colony management during the COVID-19 pandemic. Phylogenetic relationships among ABPV strains were elucidated through partial sequencing of the capsid and RNA-dependent RNA polymerase protein coding genes, employing maximum likelihood tree construction with the Tamura 3-parameter model. Turkish ABPV strains clustered into a distinct subclade, sharing 98.4-99% nucleotide identity with European strains, indicative of a monophyletic origin and geographic segregation at the regional or continental level. These findings highlight the necessity for robust surveillance and research programs to monitor ABPV prevalence and mitigate its detrimental effects on colony health and productivity. Additionally, the phylogenetic insights provided by this study enhance our understanding of the geographic distribution and evolutionary dynamics of ABPV strains, offering critical information for future molecular epidemiological research and apicultural management strategies.

Validation and comparison of EvaGreen- and TaqMan-based real-time qRT-PCR for diagnosis of the black queen cell virus in the honey bees

The black queen cell virus (BQCV) is a common agent that causes covert infection in hives and has a global distribution. In this study, TaqMan probe and EvaGreen (EG) dye-based real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays based on the amplification of coding senquences for the BQCV structural protein (SP) and the non-structural protein (NSP) were developed and validated for the detection of BQCV in adult bee and larvae/pupae. Additionally, the performances of commonly used EG and TaqMan chemicals for real-time qRT-PCR analyses were compared. The operating range for BQCV-SP TaqMan and EG real-time qRT-PCRs ranged 2.61-7.61 log10 RNA copies/reaction and 2.61-7.79 log10 RNA copies/reaction, respectively. The operating range for BQCV-NSP TaqMan and EG real-time qRT-PCRs ranged 6.83-11.83 log10 RNA copies/reaction and 6.98-11.98 log10 RNA copies/reaction, respectively. Based on these novel assays, the prevalence of BQCV in adult bees and larvae/pupae was 84% (88/105) and 44% (46/105), respectively. BQCV viral load was also within the operating range determined during assay validation. Comparable results were obtained in analytical and diagnostic performance analyses of the EG dye and TaqMan probe chemicals. Highly sensitive and analytically specific for the detection of BQCV, these real-time qRT-PCR assays will benefit the etiological and epidemiological studies of BQCV.

Genetic Diversity in Candidate Single-Nucleotide Polymorphisms Associated with Resistance in Honeybees in the Czech Republic Using the Novel SNaPshot Genotyping Panel

Background/Objectives: The increasing pressure from pathogens and parasites on Apis mellifera populations is resulting in significant colony losses. It is desirable to identify resistance-associated single-nucleotide polymorphisms (SNPs) and their variability for the purpose of breeding resilient honeybee lines. This study examined the genetic diversity of 13 SNPs previously studied for associations with various resistance-providing traits, including six linked to Varroa-specific hygiene, five linked to suppressed mite reproduction, one linked to immune response, and one linked to chalkbrood resistance. Methods: Genotyping was performed using a novel SNaPshot genotyping panel designed for this study. The sample pool consisted of 308 honeybee samples in total, covering all 77 administrative districts of the Czech Republic. Results: All examined loci were polymorphic. The frequency of positive alleles in our population is medium to low, depending on the specific SNP. An analysis of genotype frequencies revealed that most loci exhibited the Hardy-Weinberg equilibrium. A comparison of the allele and genotype frequencies of the same locus between samples from hives and samples from flowers revealed no significant differences. The genetic diversity, as indicated by the heterozygosity values, ranged from 0.05 to 0.50. The fixation index (F) was, on average, close to zero, indicating minimal influence of inbreeding or non-random mating on the genetic structure of the analyzed samples. Conclusions: The obtained results provide further insights into the genetic variation of SNPs associated with the immune response and resistance to pathogens in honeybee populations in the Czech Republic. This research provides a valuable foundation for future studies of honeybee diversity and breeding.

The intensity of the transcriptional response varies across infection with distinct viral strains in an insect host

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.

Genotype B of deformed wing virus and related recombinant viruses become dominant in European honey bee colonies

The Varroa destructor mite's transmission of deformed wing virus (DWV) to honey bees is responsible for most winter mortalities of colonies worldwide. Four DWV genotypes (A, B, C and D) and numerous recombinants have been described. The most recent studies have reported the greater prevalence of DWV-B over DWV-A in several countries, including European ones, while C and D genotypes appear rare or extinct. However, no global evaluation of DWV-A and DWV-B distribution was available at the European level to date. In this study, we quantified both DWV genotypes by real-time PCR from pools or individual honey bees and from V. destructor mites sampled in 15 European countries between 2010 and 2017. These data and the sequencing of the viral RNA provide a first insight into DWV diversity, with a clear dominance of DWV-B and recombinants (A/B) in Europe. Chimeric sequencing reads were used to locate the recombinant junctions along the DWV genome. These were not randomly distributed, but mainly clustered in three genomic areas: the 5'UTR, leader peptide and helicase coding sequences. In our study, the DWV recombinant genomes shared at least the VP1-VP3 coding sequences with the DWV-B. Further studies are needed to explore the apicultural context explaining these differences in DWV genotype dominance.

Deformed wing virus genotypes A and B do not elicit immunologically different responses in naïve honey bee hosts

Iflavirus aladeformis (Picornavirales: Iflaviridae), commonly known as deformed wing virus(DWV), in association with Varroa destructor Anderson and Trueman (Mesostigmata: Varroidae), is a leading factor associated with honey bee (Apis mellifera L. [Hymenoptera: Apidae]) deaths. The virus and mite have a near global distribution, making it difficult to separate the effect of one from the other. The prevalence of two main DWV genotypes (DWV-A and DWV-B) has changed over time, leading to the possibility that the two strains elicit a different immune response by the host. Here, we use a honey bee population naïve to both the mite and the virus to investigate if honey bees show a different immunological response to DWV genotypes. We examined the expression of 19 immune genes by reverse transcription quantitative PCR (RT-qPCR) and analysed small RNA after experimental injection with DWV-A and DWV-B. We found no evidence that DWV-A and DWV-B elicit different immune responses in honey bees. RNA interference genes were up-regulated during DWV infection, and small interfering RNA (siRNA) responses were proportional to viral loads yet did not inhibit DWV accumulation. The siRNA response towards DWV was weaker than the response to another honey bee pathogen, Triatovirus nigereginacellulae (Picornavirales: Dicistroviridae; black queen cell virus), suggesting that DWV is comparatively better at evading host antiviral defences. There was no evidence for the production of virus-derived Piwi-interacting RNAs (piRNAs) in response to DWV. In contrast to previous studies, and in the absence of V. destructor, we found no evidence that DWV has an immunosuppressive effect. Overall, our results advance our understanding of the immunological effect that DWV in isolation elicits in honey bees.

Avoiding the tragedies of parasite tolerance in Darwinian beekeeping

Bee declines have been partly attributed to the impacts of invasive or emerging parasite outbreaks. For western honeybees, Apis mellifera, major losses are associated with the virus-vectoring mite, Varroa destructor. In response, beekeepers have focused breeding efforts aimed at conferring resistance to this key parasite. One method of many is survival-based beekeeping where colonies that survive despite significant Varroa infestations produce subsequent colonies. We argue that this 'hands-off' approach will not always lead to Varroa resistance evolving but rather tolerance. Tolerance minimizes host fitness costs of parasitism without reducing parasite abundance, whereas resistance either prevents parasitism outright or keeps parasitism intensity low. With clear epidemiological distinctions, and as honeybee disease dynamics impact other wild bees owing to shared pathogens, we discuss why tolerance outcomes in honeybee breeding have important implications for wider pollinator health. Crucially, we argue that unintentional selection for tolerance will not only lead to more spillover from honeybees but may also select for pathogens that are more virulent in wild bees leading to 'tragedies of tolerance'. These tragedies can be avoided through successful breeding regimes that specifically select for low Varroa. We emphasize how insights from evolutionary ecology can be applied in ecologically responsible honeybee management.

Regional patterns and climatic predictors of viruses in honey bee (Apis mellifera) colonies over time

Honey bee viruses are serious pathogens that can cause poor colony health and productivity. We analyzed a multi-year longitudinal dataset of abundances of nine honey bee viruses (deformed wing virus A, deformed wing virus B, black queen cell virus, sacbrood virus, Lake Sinai virus, Kashmir bee virus, acute bee paralysis virus, chronic bee paralysis virus, and Israeli acute paralysis virus) in colonies located across Canada to describe broad trends in virus intensity and occurrence among regions and years. We also tested climatic variables (temperature, wind speed, and precipitation) as predictors in an effort to understand possible drivers underlying seasonal patterns in viral prevalence. Temperature was a significant positive predictor of the total number of viruses per sample, which was highest in British Columbia (mean = 5.0). Lake Sinai virus (LSV) was the most prevalent overall (at 89%) and had the highest infection intensity, at an average of 3.9 × 108 copies per bee. Acute bee paralysis virus was the least prevalent virus (at 4.7%) and had the lowest infection intensity (1.9 × 105 copies per bee). Surprisingly, including Varroa abundance as a covariate did not significantly improve model fit for any virus. All viruses, except Kashmir bee virus, varied by region, and one or more climatic variables were significant predictors for six of the nine viruses. Although climatic effects were often inconsistent among individual viruses, we show that climatic variables can be better predictors of virus intensity and occurrence than Varroa mite abundance, at least when infestation rates are low.

Physiological trade-offs in male social insects: Interactions among infection, immunity, fertility, size, and age in honey bee drones

Female social insects represent a dramatic exception of the evolutionarily conserved physiological trade-off between reproduction and life span, where aging is positively correlated with reproduction. However, whether this facet of life history also pertains to male social insects, remains largely unknown. Male honey bees (drones) die in the act of copulation, placing them under opposing selective pressures. At the individual level, there is inter-male competition for a single successful mating attempt, leading to selective pressure that favors an increase in male fitness. Honey bee drones are haploid individuals and lack the allelic variation in their genome compared to diploid females. We hypothesized that this genetic limitation may result in trade-offs between pathological stress and fitness traits in honey bee males. In our study, we observed differences in size and fertility measures in old and young drones along with stressors of several endemic viruses and the transcriptional immune response. We found that infection does not appear to decrease fertility in old drones, despite evidence for a shift in immune expression away from established mechanisms. Contrary to our expectations, drones additionally do not appear to exhibit a physiological trade-off between size and fertility. These findings demonstrate that drones of different size are likely of different mating quality and that higher quality drones likely favor retaining reproductive output over immune function.

Honey bee viruses in the yellow-legged hornet Vespa velutina (Lepelieter 1836): Prevalence, loads, and detection of replicative DWV and LSV forms

Apiaries in Galicia, northwestern Spain, are currently facing the invasive alien species Vespa velutina, which is well established in the region. The pressure on honey bee colonies is high, resulting in both economic and ecological losses. Honey bee colonies also face the challenge of viruses, which are becoming increasingly diverse. In recent years, honey bee viruses have been spreading across taxonomic groups beyond Apoidea, infecting the Vespoidea superfamily. This cross-species spillover has raised concerns in the scientific community due to the potential risk of viruses spreading in ecosystems. Currently, there is a lack of knowledge on this topic, and further research is needed to address this issue. This study employed qPCR and sequencing to investigate the prevalence, loads, and presence of replicative forms of important honey bee viruses in V. velutina individuals collected from 11 apiaries in Galicia. All V. velutina individuals tested positive for DWV, BQCV, AKI complex (ABPV, KBV, and IAPV), or LSV but not for CBPV. DWV showed the highest prevalence (97.0 %) and loads, with both DWV-A (67.4 %) and DWV-B (32.6 %) being detected. The AKI complex (46.3 %) and LSV (43.3 %) were also common, whereas BQCV (11.9 %) was rarer. LSV is detected for the first time in V. velutina. LSV-2 was the dominant strain (82.1 %), and two less frequent (17.9 %) unknown strains were also detected. All 44 screened V. velutina samples carried the replicative form of DWV, and six of these also carried the replicative form of LSV, raising for the first time the possibility of co-infection in the hornet. The detection of honey bee viruses in V. velutina, and the ability of these viruses to spread to other species, may indicate a potential risk of spillover in the apiaries.

Molecular Characterization and Phylogenetic Analysis of Honeybee (Apis mellifera) Mite-Borne Pathogen DWV-A and DWV-B Isolated from Lithuania

Deformed wing virus (DWV) is known as one of the main viruses that affect honeybees' health all around the world. The virus has two widespread genotypes, DWV-A and DWV-B (VDV-1), transmitted mainly by V. destructor mites. In this study, we collected honeycombs with covered broods from 73 apiaries in eight Lithuanian regions and initially investigated the prevalence of V. destructor mites. Mites were collected from May to the end of July in 2021 from 124 hives. The prevalence of V. destructor infestations in beehives reached 30% and 63% in investigated apiaries. The presence of DWV-A and DWV-B pathogens in mites and broods was examined by RT-qPCR targeting the CRPV-capsid region. The molecular characterization of the virus in mite samples was based on sequence analysis of the RNA-dependent RNA polymerase (RdRp) region. In addition, leader polypeptide (LP), structural protein (Vp3), Helicase, and RdRp genes were used for phylogenetic characterization of dual infection. The prevalences of DWV-B in mites and broods were 56.5% and 31.5%, respectively, while DWV-A was detected in 12.9% of mite samples and 24.7% of brood samples. Some of the examined mite samples harboured dual virus infections. Our findings showed that bee colonies from the same apiary were not always infected by the same viruses. Some bee colonies were virus-free, while others were highly infected. Phylogenetic analysis of 21 sequences demonstrated the presence of highly variable DWV-B and DWV-A genotypes in Lithuania and possible recombinant variants of the virus. This study represents the first molecular characterization of mite-borne pathogens hosted by honeybees (Apis mellifera) in Lithuania.

Origins, diversity, and adaptive evolution of DWV in the honey bees of the Azores: the impact of the invasive mite Varroa destructor

Deformed wing virus (DWV) is a honey bee virus, whose emergence from relative obscurity is driven by the recent host-switch, adaptation, and global dispersal of the ectoparasitic mite Varroa destructor (a highly efficient vector of DWV) to reproduction on honey bees (Apis mellifera). Our study examines how varroa affects the continuing evolution of DWV, using the Azores archipelago, where varroa is present on only three out of the eight Islands, as a natural experimental system for comparing different evolutionary conditions and trajectories. We combined qPCR of 494 honey bee colonies sampled across the archipelago with amplicon deep sequencing to reveal how the DWV genetic landscape is altered by varroa. Two of the varroa-free Islands were also free of DWV, while a further two Islands were intriguingly dominated by the rare DWV-C major variant. The other four Islands, including the three varroa-infested Islands, were dominated by the common DWV-A and DWV-B variants. The varroa-infested Islands had, as expected, an elevated DWV prevalence relative to the uninfested Islands, but not elevated DWV loads, due the relatively high prevalence and loads of DWV-C on the varroa-free Islands. This establishes the Azores as a stable refuge for DWV-C and provides the most convincing evidence to date that at least some major strains of DWV may be capable of not just surviving, but actually thriving in honey bees in the absence of varroa-mediated transmission. We did not detect any change in DWV genetic diversity associated with island varroa status but did find a positive association of DWV diversity with virus load, irrespective of island varroa status.

Varroa destructor shapes the unique viral landscapes of the honey bee populations of the Azores archipelago

The worldwide dispersal of the ectoparasitic mite Varroa destructor from its Asian origins has fundamentally transformed the relationship of the honey bee (Apis mellifera) with several of its viruses, via changes in transmission and/or host immunosuppression. The extent to which honey bee-virus relationships change after Varroa invasion is poorly understood for most viruses, in part because there are few places in the world with several geographically close but completely isolated honey bee populations that either have, or have not, been exposed long-term to Varroa, allowing for separate ecological, epidemiological, and adaptive relationships to develop between honey bees and their viruses, in relation to the mite's presence or absence. The Azores is one such place, as it contains islands with and without the mite. Here, we combined qPCR with meta-amplicon deep sequencing to uncover the relationship between Varroa presence, and the prevalence, load, diversity, and phylogeographic structure of eight honey bee viruses screened across the archipelago. Four viruses were not detected on any island (ABPV-Acute bee paralysis virus, KBV-Kashmir bee virus, IAPV-Israeli acute bee paralysis virus, BeeMLV-Bee macula-like virus); one (SBV-Sacbrood virus) was detected only on mite-infested islands; one (CBPV-Chronic bee paralysis virus) occurred on some islands, and two (BQCV-Black queen cell virus, LSV-Lake Sinai virus,) were present on every single island. This multi-virus screening builds upon a parallel survey of Deformed wing virus (DWV) strains that uncovered a remarkably heterogeneous viral landscape featuring Varroa-infested islands dominated by DWV-A and -B, Varroa-free islands naïve to DWV, and a refuge of the rare DWV-C dominating the easternmost Varroa-free islands. While all four detected viruses investigated here were affected by Varroa for one or two parameters (usually prevalence and/or the Richness component of ASV diversity), the strongest effect was observed for the multi-strain LSV. Varroa unambiguously led to elevated prevalence, load, and diversity (Richness and Shannon Index) of LSV, with these results largely shaped by LSV-2, a major LSV strain. Unprecedented insights into the mite-virus relationship were further gained from implementing a phylogeographic approach. In addition to enabling the identification of a novel LSV strain that dominated the unique viral landscape of the easternmost islands, this approach, in combination with the recovered diversity patterns, strongly suggests that Varroa is driving the evolutionary change of LSV in the Azores. This study greatly advances the current understanding of the effect of Varroa on the epidemiology and adaptive evolution of these less-studied viruses, whose relationship with Varroa has thus far been poorly defined.

Parasite and virus dynamics in the honeybee Apis mellifera unicolor on a tropical island recently invaded by Varroa destructor

In La Réunion, the established honeybee subspecies Apis mellifera unicolor, an endemic subspecies of African lineage, is facing considerable challenges. Since the introduction of the Varroa destructor mite in 2017 high colony losses have been recorded. We investigated the dynamics of V. destructor and two viruses, the Deformed Wing Virus (DWV), known to be transmitted by the mite, and the Chronic Bee Paralysis Virus (CBPV), in A. m. unicolor. Colonies from two apiaries located at 300 and 900 m a.s.l were monitored twice for one year without any acaricide treatment. The brood area, V. destructor infestation rates, DWV and CBPV prevalence and load were recorded monthly. A. m. unicolor maintained brood rearing throughout the year. Varroa destructor infestation resulted in high colony mortality (up to 85 %) and high phoretic mite rates (up to 52 mites per hundred bees). The establishment of DWV in colonies occurred after that of V. destructor and the mite infestation rate had a significant effect on the virus prevalence and load. CBPV appeared only transiently throughout the surveys. The data showed that, in tropical colonies with permanent brood rearing, V. destructor and DWV can reach high levels, but are still subject to seasonal variations that appear to be influenced by environmental conditions. This suggests that beekeeping practices could be adapted by favouring sites and periods for transhumance or acaricide treatment.

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.

Integrated Pest Management Strategies to Control Varroa Mites and Their Effect on Viral Loads in Honey Bee Colonies

Honey bee viruses in combination with varroa mite are very damaging for honey bee colonies worldwide. There are no effective methods to control the viral load in honey bee colonies except regular and effective control of mites. Integrated Pest Management strategies are required to effectively control mites with veterinary medicines based on organic compounds. We evaluated the effect of two brood interruption techniques, queen caging (QC) and trapping comb (TC), followed by an oxalic acid treatment, on the mite fall, colony strength, and viral load of Deformed Wing Virus (DWV) and Acute Bee Paralysis Virus (ABPV). In this paper, we report the data obtained in two experimental sites, in Slovenia and Italy, in terms of the varroacide efficacy, colony strength, and viral load. The number of adult bees after the adoption of the two techniques showed similar decreasing trends in both locations. The viral load of Acute Bee Paralysis Virus did not show any significant reduction after 25 days, reported as the number of Real-Time PCR cycles needed to detect the virus. The viral load of DWV also did not show a significant reduction after 25 days. The acaricidal efficacy of the applied protocols was high in both experimental groups and in both apiaries. Both the queen caging and trapping comb techniques, followed by an oxalic acid treatment, can be considered effective varroa treatment strategies, but further studies should be carried out to evaluate the long-term effects on viral loads to plan the Integrated Pest Management strategy with the right timing before wintering.

Evaluation of the Potential Effect of Postbiotics Obtained from Honey Bees against Varroa destructor and Their Combination with Other Organic Products

The Varroa destructor mite infests Apis mellifera colonies and causes significant harm. Traditional treatments have become less effective because of mite resistance development and can also generate residues inside beehives. This study aimed to gauge the efficacy of a beehive-derived postbiotic in reducing V. destructor viability and to explore its synergies with organic compounds. Four lactic acid bacteria (LAB) species, Leuconostoc mesenteroides, Lactobacillus helsingborgensis, Bacillus velezensis, and Apilactobacillus kunkeei, were isolated and tested in a postbiotic form (preparations of inanimate microorganisms and/or their components) via bioassays. L. mesenteroides, L. helsingborgensis, and B. velezensis notably reduced the mite viability compared to the control, and they were further tested together as a single postbiotic product (POS). Further bioassays were performed to assess the impact of the POS and its combinations with oxalic acid and oregano essential oil. The simple products and combinations (POS/Oregano, POS/Oxalic, Oregano/Oxalic, and POS/Oregano/Oxalic) decreased the mite viability. The most effective were the oxalic acid combinations (POS/Oregano/Oxalic, Oxalic/Oregano, POS/Oxalic), showing significant improvements compared to the individual products. These findings highlight the potential of combining organic products as a vital strategy for controlling V. destructor infection. This study suggests that these combinations could serve as essential tools for combating the impact of mites on bee colonies.

The Varroa paradox: infestation levels and hygienic behavior in feral scutellata-hybrid and managed Apis mellifera ligustica honey bees

The Varroa destructor mite is a parasitic threat to managed and feral honey bee colonies around the world. Beekeepers use miticides to eliminate Varroa in commercial hives, but these chemicals can diminish bee health and increase miticide resistance. In contrast, feral honey bees have developed multiple ways to counteract mites without chemical treatment. We compared mite levels, grooming habits, and mite-biting behavior between feral Africanized honey bees (genomically verified Apis mellifera scutellata hybrids) and managed Italian honey bees (A. mellifera ligustica). Surprisingly, there was no difference in mite infestation levels between scutellata-hybrids and managed bees over one year despite the regular use of miticides in managed colonies. We also found no differences in the social immunity responses of the two groups, as measured by their hygienic habits (through worker brood pin-kill assays), self-grooming, and mite-biting behavior. However, we provide the first report that both scutellata-hybrids and managed honey bees bite off mite chemosensory forelegs, which the mites use to locate brood cells for reproduction, to a significantly greater degree than other legs (a twofold greater reduction in foreleg length relative to the most anterior legs). Such biting may impair mite reproduction.

Susceptible and infectious states for both vector and host in a dynamic pathogen-vector-host system

Deformed wing virus (DWV) is a resurgent insect pathogen of honeybees that is efficiently transmitted by vectors and through host social contact. Continual transmission of DWV between hosts and vectors is required to maintain the pathogen within the population, and this vector-host-pathogen system offers unique disease transmission dynamics for pathogen maintenance between vectors and a social host. In a series of experiments, we measured vector-vector, host-host and host-vector transmission routes and show how these maintain DWV in honeybee populations. We found co-infestations on shared hosts allowed for movement of DWV from mite to mite. Additionally, two social behaviours of the honeybee, trophallaxis and cannibalization of pupae, provide routes for horizontal transmission from bee to bee. Circulation of the virus solely among hosts through communicable modes provides a reservoir of DWV for naïve Varroa to acquire and subsequently vector the pathogen. Our findings illustrate the importance of community transmission between hosts and vector transmission. We use these results to highlight the key avenues used by DWV during maintenance and infection and point to similarities with a handful of other infectious diseases of zoonotic and medical importance.

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.

Virus replication in the honey bee parasite, Varroa destructor

IMPORTANCE

The parasitic mite Varroa destructor is a significant driver of worldwide colony losses of our most important commercial pollinator, the Western honey bee Apis mellifera. Declines in honey bee health are frequently attributed to the viruses that mites vector to honey bees, yet whether mites passively transmit viruses as a mechanical vector or actively participate in viral amplification and facilitate replication of honey bee viruses is debated. Our work investigating the antiviral RNA interference response in V. destructor demonstrates that key viruses associated with honey bee declines actively replicate in mites, indicating that they are biological vectors, and the host range of bee-associated viruses extends to their parasites, which could impact virus evolution, pathogenicity, and spread.

Effects of Deformed Wing Virus-Targeting dsRNA on Viral Loads in Bees Parasitised and Non-Parasitised by Varroa destructor

The Varroa destructor mite is a devastating parasite of honey bees; however the negative effects of varroa parasitism are exacerbated by its role as an efficient vector of the honey bee pathogen, Deformed wing virus (DWV). While no direct treatment for DWV infection is available for beekeepers to use on their hives, RNA interference (RNAi) has been widely explored as a possible biopesticide approach for a range of pests and pathogens. This study tested the effectiveness of three DWV-specific dsRNA sequences to lower DWV loads and symptoms in honey bees reared from larvae in laboratory mini-hives containing bees and varroa. The effects of DWV-dsRNA treatment on bees parasitised and non-parasitised by varroa mites during development were investigated. Additionally, the impact of DWV-dsRNA on viral loads and gene expression in brood-parasitising mites was assessed using RNA-sequencing. Bees parasitised during development had significantly higher DWV levels compared to non-parasitised bees. However, DWV-dsRNA did not significantly reduce DWV loads or symptoms in mini-hive reared bees, possibly due to sequence divergence between the DWV variants present in bees and varroa and the specific DWV-dsRNA sequences used. Varroa mites from DWV-dsRNA treated mini-hives did not show evidence of an elevated RNAi response or significant difference in DWV levels. Overall, our findings show that RNAi is not always successful, and multiple factors including pathogen diversity and transmission route may impact its efficiency.

A preliminary survey reveals that common viruses are found at low titers in a wild population of honey bees (Apis mellifera)

A major threat to honey bee (Apis mellifera Linnaeus, Hymenoptera: Apidae) health continues to be parasitism by the mite Varroa destructor, which has been linked to high colony losses worldwide. Besides feeding on developing and adult bees, Varroa is also a prolific vector of honey bee-associated viruses. Because they live in unmanaged conditions, wild honey bee colonies are not treated against Varroa, which has enabled the natural selection of more mite-tolerant bees. To date, few studies have explored the prevalence of viruses in unmanaged colonies. The Welder Wildlife Refuge (WWR) in Texas is a unique site to study the viral landscape of unmanaged honey bees in the United States. The goals of this study were to identify and quantify viruses in wild colonies at the WWR, to examine changes in the prevalence of viruses in these colonies over time, and to compare the presence and titers of viruses between wild colonies at the WWR and those from the nearest managed apiary. We collected bees from colonies at the WWR in 2013, 2016, and 2021, and analyzed selected viruses for their presence and titers via quantitative polymerase chain reaction. In 2021, we also sampled bees from the nearest managed apiary for comparison. We found low average virus titers in all wild colonies sampled, and no difference in virus titers between colonies at the WWR and those from the managed apiary. Our study indicates that virus titers in wild colonies at the WWR are similar to those found in nearby colonies, and that these titers fluctuate over time.

Epidemiology, factors influencing prevalence and level of varroosis infestation (Varroa destructor) in honeybee (Apis mellifera) colonies in different agroecologies of Southwest Ethiopia

Little information is available on the epidemiology of varroosis caused by Varroa mite, Varroa destructor infestation in Ethiopia, although it is a devastating honeybee disease that results in significant economic losses in beekeeping. Therefore, between October 2021 and October 2022, a cross-sectional study was carried out in different agroecology zones in Southwest Ethiopia to determine the prevalence and associated risk factors for varroosis, as well as the effects of this disease on honeybee colonies and honey production. A multivariate logistic regression analysis was performed to identify possible risk factors for the prevalence of V. destructor. A total of 384 adult honeybee and worker or drone brood samples were collected from honeybee colonies and examined using standard diagnostic techniques in the laboratory. The result shows that the prevalence of V. destructor was found to be 39.3% (95% CI 34.44-44.21) and 43.2% (38.27-48.18) in adult honeybees and brood, respectively. The major risk factors for the prevalence of V. destructor in the study areas included agroecology (OR = 5.2, 95% CI 1.75-14.85), type of hive (OR = 2.9, 95% CI 1.17-17.03), management system (OR = 4.3, 95% CI 1.23-14.70), and colony management (OR = 3.5, 95% CI 1.31-9.14). The lower level of colony infestation in adult bees and brood was measured as 1.97 ± 0.14 and 3.19 ± 0.25, respectively. Season, colony status, colony management, and agroecology were among the determinant factors of the level of varroa mite infestation in adult bees and brood. The results of the study demonstrated that honey production losses are largely attributable to V. destructor infestation. Therefore, it is critical to inform the community about the effects of V. destructor on honey production and develop and implement effective management strategies for this disease. In addition, further research should be done to identify and isolate additional factors that contribute to varroosis in honeybees in different regions.

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.

Biotechnical Control of Varroa in Honey Bee Colonies: A Trade-Off between Sustainable Beekeeping and Profitability?

Beekeeping faces several challenges, such as the Varroa mite. Few studies have measured the economic performance of farms in relation to the practices used for Varroa control. Our study analyzed various biotechniques (total brood removal, TBR; queen caging, QC; royal cell insertion, CI) and other methods (chemical treatments, CT; thymol use, THY) adopted by Italian beekeepers to show whether the adoption of biotechniques leads to farm profitability or a necessary trade-off between sustainability and profitability. Beekeepers were interviewed about the methods and operations conducted on their farms. The net incomes (NIs) of the farms were calculated and inter- and intrafarm comparisons were performed. A detailed schema of each practice was designed. The net income derived from TBR was the highest in eight out of the nine case studies, followed by CI and then QC. The NI calculated for farms using CT was lower than that for farms using other methods in two of the case studies. We also analyzed different biotechniques applied by the same farm and found that the NI resulting from TBR was higher than that achieved from the use of QC and CI. Our study suggests that use of biotechniques represents a long-term sustainable solution for reducing the level of Varroa infestation, which affects farm net income.

The presence of identical deformed wing virus sequence variants in co-occurring Apis species in Northern Thailand may represent a potential epidemiological threat to native honey bees of Southeast Asia

Widespread native honey bee species in South and East Asia (Apis cerana, Apis dorsata and Apis florea) and the imported western honey bee (Apis mellifera) share habitats and potentially also share pathogens. Chief among the threats facing A. mellifera in Europe and North America is deformed wing virus (DWV), including its two principal genotypes: A and B (DWV-A and DWV-B respectively). Though DWV-A has been recorded in Asia's native Apis species, it is not known if DWV-B, or both DWV-A and DWV-B, are currently widespread in Asia and, if so, whether viral transmission is primarily intraspecific or interspecific. This study aims to fill these knowledge gaps by (i) determining the DWV genotype in four co-occurring Apis host species using qPCR and (ii) inferring viral transmission between them using nucleotide sequences of DWV from Apis host species collected at three independent localities in Northern Thailand. We found DWV-A and -B in all four Apis species, the exotic A. mellifera and the native A. cerana, A. dorsata and A. florea. That DWV-A sequences were identical across Apis species at the same locality, with a similar pattern for DWV-B sequences, suggests that DWV's epidemiology is largely driven by ongoing interspecific transmission (spillover) of DWV across co-occurring native and exotic Apis species. Both genotypes of DWV represent a serious threat to Asia's exotic and native honey bee species.

Age-related response to mite parasitization and viral infection in the honey bee suggests a trade-off between growth and immunity

Host age at parasites' exposure is often neglected in studies on host-parasite interactions despite the important implications for epidemiology. Here we compared the impact of the parasitic mite Varroa destructor, and the associated pathogenic virus DWV on different life stages of their host, the western honey bee Apis mellifera. The pre-imaginal stages of the honey bee proved to be more susceptible to mite parasitization and viral infection than adults. The higher viral load in mite-infested bees and DWV genotype do not appear to be the drivers of the observed difference which, instead, seems to be related to the immune-competence of the host. These results support the existence of a trade-off between immunity and growth, making the pupa, which is involved in the highly energy-demanding process of metamorphosis, more susceptible to parasites and pathogens. This may have important implications for the evolution of the parasite's virulence and in turn for honey bee health. Our results highlight the important role of host's age and life stage at exposure in epidemiological modelling. Furthermore, our study could unravel new aspects of the complex honey bee-Varroa relationship to be addressed for a sustainable management of this parasite.

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.

Transcriptomic Responses Underlying the High Virulence of Black Queen Cell Virus and Sacbrood Virus following a Change in Their Mode of Transmission in Honey Bees (Apis mellifera)

BACKGROUND

Over the last two decades, honey bees (Apis mellifera) have suffered high rates of colony losses that have been attributed to a variety of factors, chief among which are viral pathogens, such as deformed wing virus (DWV), whose virulence has increased because of vector-based transmission by the invasive, ectoparasitic varroa mite (Varroa destructor). A shift in the experimental mode of transmission of the black queen cell virus (BQCV) and sacbrood virus (SBV) from fecal/food-oral (direct horizontal) to vector-mediated (indirect horizontal) transmission also results in high virulence and viral titers in pupal and adult honey bees. Agricultural pesticides represent another factor that acts independently or in interaction with pathogens, and they are also thought to cause colony loss. Understanding the molecular mechanisms underlying the higher virulence following a vector-based mode of transmission provides deeper insight into honey bee colony losses, as does determining whether or not host-pathogen interactions are modulated by exposure to pesticides.

METHODS

Through an experimental design with controlled laboratory, we investigated the effects of the modes of transmission of BQCV and SBV (feeding vs. vector-mediated via injection) alone or in combination with chronic exposure to sublethal and field-realistic concentrations of flupyradifurone (FPF), a novel agricultural insecticide, on honey bee survival and transcription responses by using high-throughput RNA sequencing (RNA-seq) analysis.

RESULTS

Co-exposure to viruses via feeding (VF) or injection (VI) and FPF insecticide had no statistically significant interactive effect on their survival compared to, respectively, VF or VI treatments alone. Transcriptomic analysis revealed a distinct difference in the gene expression profiles of bees inoculated with viruses via injection (VI) and exposed to FPF insecticide (VI+FPF). The number of differentially expressed genes (DEGs) at log2 (fold-change) > 2.0 in VI bees (136 genes) or/and VI+FPF insecticide (282 genes) was very high compared to that of VF bees (8 genes) or the VF+FPF insecticide treatment (15 genes). Of these DEGs, the expression in VI and VI+FPF bees of some immune-related genes, such as those for antimicrobial peptides, Ago2, and Dicer, was induced. In short, several genes encoding odorant binding proteins, chemosensory proteins, odor receptors, honey bee venom peptides, and vitellogenin were downregulated in VI and VI+FPF bees.

CONCLUSIONS

Given the importance of these suppressed genes in honey bees' innate immunity, eicosanoid biosynthesis, and olfactory associative function, their inhibition because of the change in the mode of infection with BQCV and SBV to vector-mediated transmission (injection into haemocoel) could explain the high virulence observed in these viruses when they were experimentally injected into hosts. These changes may help explain why other viruses, such as DWV, represent such a threat to colony survival when transmitted by varroa mites.

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.

Effect of feed supplementation with probiotics and postbiotics on strength and health status of honey bee (Apis mellifera) hives during late spring

Currently, beekeeping faces many risks, such as deteriorating health of honeybees in hives, which results in high mortality rates, mainly during winter. An important consequence is the emergence/re-emergence of communicable diseases such as varroosis or nosemosis. These diseases jeopardize the continuity of the sector because of the absence of effective treatments and harmful residues that they can be retained on wax or honey. This study aimed to evaluate how feed supplementation with probiotic and postbiotic products derived from lactic acid bacteria affected the strength, dynamic population, and sanitary parameters of honey bees. Three groups of 30 hives were established and fed with feed supplemented with control, probiotic, or postbiotic products, with a total of nine applications over two months in late spring. Two monitoring tests were conducted to evaluate the strength and health status of hives. Hives that consumed postbiotic products enhanced their strength, increased bee population and egg laying of the queen, and maintained their reserves of pollen, whereas these parameters decreased in hives belonging to other groups. Furthermore, although the results suggested a favorable effect of postbiotic products on the trend of N. ceranae infection levels, probiotics showed intermediate results. While awaiting long-term results regarding V. destructor infestation, which showed similar trends in all groups, feed supplementation with postbiotics could be an important tool for beekeepers to enhance the strength and health status of their hives.

The final frontier: ecological and evolutionary dynamics of a global parasite invasion

Studying rapid biological changes accompanying the introduction of alien organisms into native ecosystems can provide insights into fundamental ecological and evolutionary theory. While powerful, this quasi-experimental approach is difficult to implement because the timing of invasions and their consequences are hard to predict, meaning that baseline pre-invasion data are often missing. Exceptionally, the eventual arrival of Varroa destructor (hereafter Varroa) in Australia has been predicted for decades. Varroa is a major driver of honeybee declines worldwide, particularly as vectors of diverse RNA viruses. The detection of Varroa in 2022 at over a hundred sites poses a risk of further spread across the continent. At the same time, careful study of Varroa's spread, if it does become established, can provide a wealth of information that can fill knowledge gaps about its effects worldwide. This includes how Varroa affects honeybee populations and pollination. Even more generally, Varroa invasion can serve as a model for evolution, virology and ecological interactions between the parasite, the host and other organisms.

A four-decade profile of apicultural demographics and production in New Zealand, 1980-2020

The demand for honey and pollination services has continued to grow in many countries worldwide, including New Zealand. This has influenced changes in the demographics of the managed population of honey bees (Apis mellifera). We examined historical data to describe how the apicultural demographics in New Zealand have changed temporally and geographically in the four decades to 2020. We also describe trends in honey production and the economic value of pure honey exported from New Zealand between 2000 and 2020. Our findings suggest that commercial apiculture has been key to the intensification of beekeeping in New Zealand during the study period. This is supported by evidence showing pronounced expansion of beekeeping operations among those with more than 1,000 colonies. The intensification has resulted in the density of apiaries increasing threefold across New Zealand during the four decades. While higher numbers of colonies per area produced higher volumes of honey, there was no corresponding improvement in production efficiency. Honey yields per apiary or colony, as indicators of production efficiency, appear to decline from the mid-2000s. The volume of pure honey export increased over 40-fold, a magnitude approximately ten times higher than that of production increase. This reflects a substantial increase in returns from honey exports, mostly driven by the price of mānuka honey. Our findings add to a pool of information to support evidence-based decision making to enhance honey bee health and develop the apicultural industry in New Zealand.

Conservation measures or hotspots of disease transmission? Agri-environment schemes can reduce disease prevalence in pollinator communities

Insects are under pressure from agricultural intensification. To protect pollinators, conservation measures such as the EU agri-environment schemes (AES) promote planting wildflowers along fields. However, this can potentially alter disease ecology by serving as transmission hubs or by diluting infections. We tested this by measuring plant-pollinator interactions and virus infections (DWV-A, DWV-B and ABPV) across pollinator communities in agricultural landscapes over a year. AES had a direct effect on DWV-B, reducing prevalence and load in honeybees, with a tentative general dilution effect on load in early summer. DWV-A prevalence was reduced both under AES and with increasing niche overlap between competent hosts, likely via a dilution effect. By contrast, AES had no impact on ABPV, its prevalence driven by the proportion of bumblebees in the community. Epidemiological differences were also reflected in the virus phylogenies, with DWV-B showing recent rapid expansion, while DWV-A and ABPV showed slower growth rates and geographical population structure. Phylogenies indicate that all three viruses freely circulate across their host populations. Our study illustrates how complex interactions between environmental, ecological and evolutionary factors may influence wildlife disease dynamics. Supporting pollinator nutrition can mitigate the transmission of important bee diseases, providing an unexpected boost to pollinator conservation. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

Black queen cell virus detected in Canadian mosquitoes

Black queen cell virus (BQCV) is a ubiquitous honeybee virus and a significant pathogen to queen bee (Apis mellifera) larvae. However, many aspects of the virus remain poorly understood, including the transmission dynamics. In this study, we used next-generation sequencing to identify BQCV in Aedes vexans (n = 4,000) collected in 2019 and 2020 from Manitoba, Canada. We assembled de novo the nearly complete (>96%) genome sequence of the virus, which is the first available from North America and the first report of BQCV being harbored by mosquitoes. Phylogenetic tree reconstructions indicated that the genome had 95.5% sequence similarity to a BQCV isolate from Sweden. Sequences of a potential vector (Varroa destructor) and a microsporidian associated with BQCV (Nosema apis) were not identified in the mosquito samples, however, we did detect sequences of plant origin. We, therefore, hypothesize that the virus was indirectly acquired by mosquitoes foraging at the same nectar sources as honeybees.

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.

Varroa destructor resistance to tau-fluvalinate: relationship between in vitro phenotypic test and VGSC L925V mutation

BACKGROUND

Varroa destructor is a parasitic mite of the honey bee, Apis mellifera. Its presence in colonies can lead to a collapse within a few years. The use of acaricides has become essential to manage the hive infestation. However, the repeated and possibly incorrect use of acaricide treatments, as tau-fluvalinate, has led to the development of resistance. The in vitro phenotypic test allows the proportion of susceptible or resistant individuals to be known following an exposure to an active substance. In Varroa mites, resistance to tau-fluvalinate is associated with the presence of mutations at the position 925 of the voltage-gated sodium channel (VGSC).

RESULTS

Here, we compared the results obtained with an in vitro phenotypic test against tau-fluvalinate and those obtained with an allelic discrimination assay on 13 treated and untreated Varroa populations in France. The correlation between the phenotype and the genetic profile rate is found to be 0.89 Varroa mites having resistant phenotypic profile have a probability of 63% to present the L925V mutation (resistance detection reliability). However, 97% of the Varroa mites having the susceptible phenotype do not present the L925V mutation (susceptible detection reliability).

CONCLUSION

The L925V mutation explains most of the resistance to tau-fluvalinate in V. destructor in the populations tested. However, other mutations or types of resistance may also be involved to explain the survival of Varroa mites in the phenotypic test. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Acute and chronic viruses mediated by an ectoparasite targeting different developmental stages of honeybee (Apis mellifera and Apis cerana) brood

The health of the western honeybee, Apis mellifera, the most crucial pollinator, has been challenged globally over the past decades. An ectoparasitic mite, Varroa destructor, together with the viruses it vectored, is generally regarded as the vital pathogenic agent. Although the poor health status of A. mellifera compared to its eastern counterpart, Apis cerana, has been broadly identified, the underlying mechanism remains poorly understood and comparison between susceptible and resistant hosts will potentially ameliorate this predicament. Here, we investigated the impacts of two widespread viruses-deformed wing virus type A (DWV-A) and Israeli acute paralysis virus (IAPV), mediated by V. destructor mite, on the capped developing honeybee brood, in the absence of adult workers, of A. mellifera and A. cerana, with positive and negative controls. Our results demonstrated that the endogenous viruses imposed limited damage on the hosts even if the brood was wounded. In contrast, the exogenous viruses introduced by ectoparasites triggered variable mortality of the infested brood between host species. Intriguingly, death causes of both honeybee species presented a similar trend: the acute IAPV generally causes morbidity and mortality of late larvae, while the chronic DWV-A typically leads to brood mortality during and after pupation. Notably, the susceptible immature A. cerana individuals, supported by higher observed mortality and a lower virus tolerance, serve the interests of the colony and foster the overall survival of a resistant honeybee superorganism. These results improve our understanding of the interactions between viruses carried by ectoparasites and their developing hosts, and the novel insight of weak individuals fostering strong colonies may promote breeding efforts to mitigate the indefensible colony losses globally.

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.

Sacbrood Virus: A Growing Threat to Honeybees and Wild Pollinators

Sacbrood virus (SBV) is one of the many viruses that infect both the Western honeybee (Apis mellifera) and the Eastern honeybee (Apis cerana). Recently, the interspecies transmission of SBV has been discovered, especially among wild pollinators. This newly discovered evolutionary occurrence regarding SBV indicates a much wider host range than previously believed, causing further concern about the future sustainability of agriculture and the resilience of ecosystems. Over the past few decades, vast numbers of studies have been undertaken concerning SBV infection in honeybees, and remarkable progress has been made in our understanding of the epidemiology, pathogenesis, transmission, and manifestations of SBV infection in honeybees and other pollinators. Meanwhile, some methods, including Chinese medicine, have been established to control and prevent sacbrood disease in A. cerana in Asian countries. In this review, we summarize the existing knowledge of SBV and address the gaps in the knowledge within the existing literature in the hope of providing future directions for the research and development of management strategies for controlling the spread of this deadly disease.

Impact of demographic variability on the disease dynamics for honeybee model

For the last few years, annual honeybee colony losses have been center of key interest for many researchers throughout the world. The spread of the parasitic mite and its interaction with specific honeybee viruses carried by Varroa mites has been linked to the decline of honeybee colonies. In this investigation, we consider honeybee-virus and honeybee-infected mite-virus models. We perform sensitivity analysis locally and globally to see the effect of the parameters on the basic reproduction number for both models and to understand the disease dynamics in detail. We use the continuous-time Markov chain model to develop and analyze stochastic epidemic models corresponding to both deterministic models. By using the disease extinction process, we compare both deterministic and stochastic models. We have observed that the numerically approximated probability of disease extinction based on 30 000 sample paths agrees well with the calculated probability using multitype branching process approximation. In particular, it is observed that the disease extinction probability is higher when infected honeybees spread the disease instead of infected mites. We conduct a sensitivity analysis for the stochastic model also to examine how the system parameters affect the probability of disease extinction. We have also derived the equation for the expected time required to reach disease-free equilibrium for stochastic models. Finally, the effect of the parameters on the expected time is represented graphically.

Recovery and genetic characterization of black queen cell virus

Black queen cell virus (BQCV) is a severe threat to the honeybee (Apis mellifera) worldwide. Although several BQCV strains have been reported in China, the molecular basis for BQCV pathogenicity has not been well understood. Thus, a reverse genetic system of BQCV is required for studying viral replication and its pathogenic mechanism. Here, the complete genome sequence of BQCV was obtained from honeybees using reverse transcription PCR (RT-PCR), namely a BQCV China-GS1 strain (KY741959). Then, a phylogenetic tree was built to analyse the genetic relationships among BQCV strains from different regions. Our results showed that the BQCV China-GS1 contained two ORFs, consistent with the known reference strains, except for the BQCV China-JL1 strain (KP119603). Furthermore, the infectious clone of BQCV was constructed based on BQCV China-GS1 using a low copy vector pACYC177 and gene recombination. Due to the lack of culture cells for bee viruses, we infected the healthy bees with infectious clone of BQCV, and the rescued BQCV resulted in the recovery of recombinant virus, which induced higher mortality than those of the control group. Immune response after inoculated with BQCV further confirmed that the infectious clone of BQCV caused the cellular and humoral immune response of honeybee (A. mellifera). In conclusion, the full nucleotide sequence of BQCV China-GS1 strain was determined, and the infectious clone of BQCV was constructed in this study. These data will improve the understanding of pathogenesis and the host immune responses to viral infection.

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.

Genotype, but Not Climate, Affects the Resistance of Honey Bees (Apis mellifera) to Viral Infections and to the Mite Varroa destructor

This study was conducted to analyze the effect of genotype and climate on the resistance of honey bee (Apis mellifera) colonies to parasitic and viral diseases. The prevalence and intensity of parasitism by Varroa destructor, or infection by Nosema spp., and four honey bee viruses were determined in 365 colonies of predominantly European or African ancestry (descendants of A. m. scutellata) in subtropical and temperate regions of Mexico. Varroa destructor was the most prevalent parasite (95%), whilst N. ceranae was the least prevalent parasite (15%). Deformed wing virus (DWV) and black queen cell virus (BQCV) were the only viruses detected, at frequencies of 38% and 66%, respectively. Varroa destructor was significantly more prevalent in colonies of European ancestry (p < 0.05), and the intensity of parasitism by V. destructor or infection by DWV and BQCV was also significantly higher in colonies of European descent than in African descent colonies (p < 0.01), although no genotype−parasite associations were found for N. ceranae. Additionally, significant and positive correlations were found between V. destructor and DWV levels, and the abundance of these pathogens was negatively correlated with the African ancestry of colonies (p < 0.01). However, there were no significant effects of environment on parasitism or infection intensity for the colonies of both genotypes. Therefore, it is concluded that the genotype of honey bee colonies, but not climate, influences their resistance to DWV, BQCV, and V. destructor.

Viral communities in the parasite Varroa destructor and in colonies of their honey bee host (Apis mellifera) in New Zealand

The parasitic mite Varroa destructor is a leading cause of mortality for Western honey bee (Apis mellifera) colonies around the globe. We sought to confirm the presence and likely introduction of only one V. destructor haplotype in New Zealand, and describe the viral community within both V. destructor mites and the bees that they parasitise. A 1232 bp fragment from mitochondrial gene regions suggests the likely introduction of only one V. destructor haplotype to New Zealand. Seventeen viruses were found in bees. The most prevalent and abundant was the Deformed wing virus A (DWV-A) strain, which explained 95.0% of the variation in the viral community of bees. Black queen cell virus, Sacbrood virus, and Varroa destructor virus 2 (VDV-2) played secondary roles. DWV-B and the Israeli acute paralysis virus appeared absent from New Zealand. Ten viruses were observed in V. destructor, with > 99.9% of viral reads from DWV-A and VDV-2. Substantially more variation in viral loads was observed in bees compared to mites. Where high levels of VDV-2 occurred in mites, reduced DWV-A occurred in both the mites and the bees co-occurring within the same hive. Where there were high loads of DWV-A in mites, there were typically high viral loads in bees.

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.

A derived honey bee stock confers resistance to Varroa destructor and associated viral transmission

The ectoparasite Varroa destructor is the greatest threat to managed honey bee (Apis mellifera) colonies globally. Despite significant efforts, novel treatments to control the mite and its vectored pathogens have shown limited efficacy, as the host remains naïve. A prospective solution lies in the development of Varroa-resistant honey bee stocks, but a paucity of rigorous selection data restricts widespread adoption. Here, we characterise the parasite and viral dynamics of a Varroa-resistant honey bee stock, designated ‘Pol-line’, using a large-scale longitudinal study. Results demonstrate markedly reduced Varroa levels in this stock, diminished titres of three major viruses (DWV-A, DWV-B, and CBPV), and a two-fold increase in survival. Levels of a fourth virus that is not associated with Varroa—BQCV—do not differ between stocks, supporting a disruption of the transmission pathway. Further, we show that when decoupled from the influence of Varroa levels, viral titres do not constitute strong independent predictors of colony mortality risk. These findings highlight the need for a reassessment of Varroa etiology, and suggest that derived stocks represent a tractable solution to the Varroa pandemic.