Evidence of presence and replication of honey bee viruses among wild bee pollinators in subtropical environments

Strategies to Mitigate the Adverse Impacts of Viral Infections on Honey Bee (Apis mellifera L.) Colonies

Honey bees (Apis mellifera) play a crucial role in global food production through the pollination of various crops. These vital insects are susceptible to a range of viral pathogens that can disrupt their normal behavior and physiology, ultimately affecting colony dynamics and survival. There are diverse viruses that infect honey bees at different life stages, with a year-round prevalence. There are multiple pathways through which viruses can be transmitted among colonies. Notably, there is also a lack of commercial treatments against viral infections in bees, but some promising strategies exist to mitigate their negative effects, including vector control, and the implementation of good beekeeping practices and biosecurity measures. While methods for treating infected colonies have garnered attention, they receive less focus compared to aspects like transmission methods and seasonal prevalence of viruses. This article aims to review the aforementioned strategies in light of the available literature. It presents succinct and practical approaches categorized based on their potential direct or indirect effects on viruses, providing beekeepers and researchers with an overview of both fully established and still-developing methods. Controlling the ectoparasitic Varroa destructor mite population, which significantly impacts viral prevalence and virulence in bees, is crucial for reducing infections. Practical approaches such as selectively breeding honey bee populations resistant to viruses and ensuring proper nutrition are important strategies. Moreover, genetic methods have also been proposed and tested. The article not only emphasizes these methods but also discusses knowledge gaps and suggests future solutions to improve the health and productivity of honey bee colonies.

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.

The Role of Pathogens in Bumblebee Decline: A Review

Bumblebees, the most important wild pollinators in both agricultural and natural ecosystems, are declining worldwide. The global decline of bumblebees may threaten biodiversity, pollination services, and, ultimately, agricultural productivity. Several factors, including pesticide usage, climate change, habitat loss, and species invasion, have been documented in the decline of bumblebee species, but recent studies have revealed the dominating role of pathogens and parasites over any of these causes. Unfortunately, there is a lack of a full understanding of the role of pathogens and parasites in the decline of bumblebee species. The current study provides a comprehensive review of how pathogens and parasites contribute to the decline of bumblebee species. The study also explores the prevalence of each pathogen and parasite within bumblebee populations. Furthermore, we address the synergistic effects of pathogens and other stressors, such as pesticides, climatic effects, and habitat loss, on bumblebee populations. To summarize, we propose possible conservation and management strategies to preserve the critical role of bumblebees in pollination services and thus to support ecosystem and agricultural health.

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.

Molecular Detection and Phylogenetic Analysis of Deformed Wing Virus and Sacbrood Virus Isolated from Pollen

Among many pathogens and pests, honey bee viruses are known as one of the most common cause of diseases in honey bee colonies. In this study, we demonstrate that pollen grains and bee bread are potential sources of viral DNA. We extracted DNA from 3 types of pollen samples: directly provided by beekeepers (n = 12), purchased from trade markets (n = 5), and obtained from honeycombs (bee bread, n = 10). The extracted DNA was used for molecular detection (RT-PCR analysis) of six of the most widely distributed honey bee viruses: deformed wing virus, sacbrood virus, acute bee paralysis virus, black queen cell virus, Kashmir bee virus, Israeli acute paralysis virus, and chronic bee paralysis virus. We successfully managed to establish only the deformed wing virus (DWV) and the sacbrood virus (SBV), with different distribution frequencies depending on the territory of the country. The phylogenetic analyses of Bulgarian isolates were performed with the most similar sequences available in molecular databases from other countries. Phylogenies of Bulgarian viral strains demonstrated genetically heterogeneous populations of DWV and relatively homogenous populations of SBV. In conclusion, the results obtained from the current study have shown that pollen is a valuable source for molecular detection of honey bee pathogens. This allows epidemiological monitoring of honey bee diseases at a regional and a national level.

An invasive ant increases deformed wing virus loads in honey bees

The majority of invasive species are best known for their effects as predators. However, many introduced predators may also be substantial reservoirs for pathogens. Honey bee-associated viruses are found in various arthropod species including invasive ants. We examined how the globally invasive Argentine ant (Linepithema humile), which can reach high densities and infest beehives, is associated with pathogen dynamics in honey bees. Viral loads of deformed wing virus (DWV), which has been linked to millions of beehive deaths around the globe, and black queen cell virus significantly increased in bees when invasive ants were present. Microsporidian and trypanosomatid infections, which are more bee-specific, were not affected by ant invasion. The bee virome in autumn revealed that DWV was the predominant virus with the highest infection levels and that no ant-associated viruses were infecting bees. Viral spillback from ants could increase infections in bees. In addition, ant attacks could pose a significant stressor to bee colonies that may affect virus susceptibility. These viral dynamics are a hidden effect of ant pests, which could have a significant impact on disease emergence in this economically important pollinator. Our study highlights a perhaps overlooked effect of species invasions: changes in pathogen dynamics.

Do pesticide and pathogen interactions drive wild bee declines?

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

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

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

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

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

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‘Bee washing’, has become rampant.

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

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

Two Pathogenic Fungi Isolated From Chalkbrood Samples and Honey Bee Viruses They Carried

Ascosphaera apis and some Aspergillus species are the main pathogenic fungi of honey bee, and A. apis is the pathogen of chalkbrood disease. However, the infection mechanism of them is incompletely known and it is still unclear whether other factors impact their pathogenesis. In this study, Aspergillus tubingensis were obtained from the chalkbrood bee samples for the first time. Our results showed that A. tubingensis could promote the accumulation of the spores of A. apis. Pathogenicity test found that inoculation of the spores of the two fungi alone or their combination could induce disease characterization of chalkbrood and stonebrood but the extent was less than those in field. To further identify other pathogens impacted the pathogenesis, we found several honey bee viruses presented in the pathogenic fungi A. apis and A. tubingensis, which were different from previous reported. Our results indicated that acute bee paralysis virus (ABPV) and chronic bee paralysis virus (CBPV) could replicate in these two fungi and increased in titer with the going of cultivation time. In addition, CBPV could not only transmit vertically to the next generation by spores, but also spread horizontally to different fungi through hyphal anastomosis. These results suggested that the honey bee chalkbrood contained the other pathogenic fungi besides A. apis, the interactions between different pathogens of chalkbrood microbial communities may influence the prevalence of chalkbrood. Moreover, the discovery of honey bee viruses and their transmission mode in these two fungi enhanced the potential of exploring fungi virus as valuable factors that cause fungal disease outbreak.

Honey bee viruses are highly prevalent but at low intensities in wild pollinators of cucurbit agroecosystems

Managed and wild bee populations are in decline around the globe due to several biotic and abiotic stressors. Pathogenic viruses associated with the Western honey bee (Apis mellifera) have been identified as key contributors to losses of managed honey bee colonies, and are known to be transmitted to wild bee populations through shared floral resources. However, little is known about the prevalence and intensity of these viruses in wild bee populations, or how bee visitation to flowers impacts viral transmission in agroecosystems. This study surveyed honey bee, bumble bee (Bombus impatiens) and wild squash bee (Eucera (Peponapis) pruinosa) populations in Cucurbita agroecosystems across Pennsylvania (USA) for the prevalence and intensity of five honey bee viruses: acute bee paralysis virus (ABPV), deformed wing virus (DWV), Israeli acute paralysis virus (IAPV), Kashmir bee virus (KBV), and slow bee paralysis virus (SBPV). We investigated the potential role of bee visitation rate to flowers on DWV intensity among species in the pollinator community, with the expectation that increased bee visitation to flowers would increase the opportunity for transmission events between host species. We found that honey bee viruses are highly prevalent but in lower titers in wild E. pruinosa and B. impatiens than in A. mellifera populations throughout Pennsylvania (USA). DWV was detected in 88% of B. impatiens, 48% of E. pruinosa, and 95% of A. mellifera. IAPV was detected in 5% of B. impatiens and 4% of E. pruinosa, compared to 9% in A. mellifera. KBV was detected in 1% of B. impatiens and 5% of E. pruinosa, compared to 32% in A. mellifera. Our results indicate that DWV titers are not correlated with bee visitation in Cucurbita fields. The potential fitness impacts of these low viral titers detected in E. pruinosa remain to be investigated.

Pathogens Spillover from Honey Bees to Other Arthropods

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

Eristalis flower flies can be mechanical vectors of the common trypanosome bee parasite, Crithidia bombi

Flowers can be transmission platforms for parasites that impact bee health, yet bees share floral resources with other pollinator taxa, such as flies, that may be hosts or non-host vectors (i.e., mechanical vectors) of parasites. Here, we assessed whether the fecal-orally transmitted gut parasite of bees, Crithidia bombi, can infect Eristalis tenax flower flies. We also investigated the potential for two confirmed solitary bee hosts of C. bombi, Osmia lignaria and Megachile rotundata, as well as two flower fly species, Eristalis arbustorum and E. tenax, to transmit the parasite at flowers. We found that C. bombi did not replicate (i.e., cause an active infection) in E. tenax flies. However, 93% of inoculated flies defecated live C. bombi in their first fecal event, and all contaminated fecal events contained C. bombi at concentrations sufficient to infect bumble bees. Flies and bees defecated inside the corolla (flower) more frequently than other plant locations, and flies defecated at volumes comparable to or greater than bees. Our results demonstrate that Eristalis flower flies are not hosts of C. bombi, but they may be mechanical vectors of this parasite at flowers. Thus, flower flies may amplify or dilute C. bombi in bee communities, though current theoretical work suggests that unless present in large populations, the effects of mechanical vectors will be smaller than hosts.

Metatranscriptome Analysis of Sympatric Bee Species Identifies Bee Virus Variants and a New Virus, Andrena-Associated Bee Virus-1

Bees are important plant pollinators in agricultural and natural ecosystems. High average annual losses of honey bee (Apis mellifera) colonies in some parts of the world, and regional population declines of some mining bee species (Andrena spp.), are attributed to multiple factors including habitat loss, lack of quality forage, insecticide exposure, and pathogens, including viruses. While research has primarily focused on viruses in honey bees, many of these viruses have a broad host range. It is therefore important to apply a community level approach in studying the epidemiology of bee viruses. We utilized high-throughput sequencing to evaluate viral diversity and viral sharing in sympatric, co-foraging bees in the context of habitat type. Variants of four common viruses (i.e., black queen cell virus, deformed wing virus, Lake Sinai virus 2, and Lake Sinai virus NE) were identified in honey bee and mining bee samples, and the high degree of nucleotide identity in the virus consensus sequences obtained from both taxa indicates virus sharing. We discovered a unique bipartite + ssRNA Tombo-like virus, Andrena-associated bee virus-1 (AnBV-1). AnBV-1 infects mining bees, honey bees, and primary honey bee pupal cells maintained in culture. AnBV-1 prevalence and abundance was greater in mining bees than in honey bees. Statistical modeling that examined the roles of ecological factors, including floral diversity and abundance, indicated that AnBV-1 infection prevalence in honey bees was greater in habitats with low floral diversity and abundance, and that interspecific virus transmission is strongly modulated by the floral community in the habitat. These results suggest that land management strategies that aim to enhance floral diversity and abundance may reduce AnBV-1 spread between co-foraging bees.

RNAseq of Deformed Wing Virus and Other Honey Bee-Associated Viruses in Eight Insect Taxa with or without Varroa Infestation

The global spread of a parasitic mite (Varroa destructor) has resulted in Deformed wing virus (DWV), a previously rare pathogen, now dominating the viromes in honey bees and contributing to large-scale honey bee colony losses. DWV can be found in diverse insect taxa and has been implicated in spilling over from honey bees into associated ("apiary") and other ("non-apiary") insects. Here we generated next generation sequence data from 127 insect samples belonging to diverse taxa collected from Hawaiian islands with and without Varroa to identify whether the mite has indirectly affected the viral landscapes of key insect taxa across bees, wasps, flies and ants. Our data showed that, while Varroa was associated with a dramatic increase in abundance of (predominantly recombinant) DWV in honey bees (and no other honey bee-associated RNA virus), this change was not seen in any other taxa sampled. Honey bees share their environment with other insect populations and exist as a homogenous group, frequently sharing common viruses, albeit at low levels. Our data suggest that the threat of Varroa to increase viral load in an apiary does not automatically translate to an increase in virus load in other insects living in the wider community.

Nosema ceranae causes cellular immunosuppression and interacts with thiamethoxam to increase mortality in the stingless bee Melipona colimana

The microsporidian parasite Nosema ceranae and neonicotinoid insecticides affect the health of honey bees (Apis mellifera). However, there is limited information about the effect of these stressors on other pollinators such as stingless bees (Hymenoptera: Meliponini). We examined the separate and combined effects of N. ceranae and the neonicotinoid thiamethoxam at field-exposure levels on the survivorship and cellular immunity (hemocyte concentration) of the stingless bee Melipona colimana. Newly-emerged bees were subjected to four treatments provided in sucrose syrup: N. ceranae spores, thiamethoxam, thiamethoxam and N. ceranae, and control (bees receiving only syrup). N. ceranae developed infections of > 467,000 spores/bee in the group treated with spores only. However, in the bees subjected to both stressors, infections were < 143,000 spores/bee, likely due to an inhibitory effect of thiamethoxam on the microsporidium. N. ceranae infections did not affect bee survivorship, but thiamethoxam plus N. ceranae significantly increased mortality. Hemocyte counts were significantly lower in N. ceranae infected-bees than in the other treatments. These results suggest that N. ceranae may infect, proliferate and cause cellular immunosuppression in stingless bees, that exposure to sublethal thiamethoxam concentrations is toxic to M. colimana when infected with N. ceranae, and that thiamethoxam restrains N. ceranae proliferation. These findings have implications on pollinators' conservation.