Foodborne Transmission of Deformed Wing Virus to Ants (Myrmica rubra)

Neighbors sharing pathogens: the intricate relationship between Apis mellifera and ants (Hymenoptera: Formicidae) nesting in hives

Ants are ubiquitous and eusocial insects that exhibit frequent physical contact among colony members, thereby increasing their susceptibility to diseases. Some species are often found in beehives and in their surroundings, where they exploit the food resources of honey bees. This intricate relationship may facilitate the interspecific transmission of honey bee pathogens to ants, although ants themselves may contribute to spillback phenomena. The objective of this study was to assess the presence and abundance of honey bee pathogens in ants sampled from Italian apiaries. A total of 37 colonies within 24 apiaries across 7 regions were monitored. In total, 6 pathogens were detected in adult ants and 3 in the brood. In particular, the study revealed a high prevalence of honey bee pathogens in ants, with DWV, BQCV, and CBPV being the most commonly encountered. The brood also tested positive for the same viruses. Notably, all analyzed viruses were found to be replicative in both adult ants and ant broods. Furthermore, co-infections were prevalent, suggesting complex pathogen interactions within ant populations. Statistical analysis indicated significant differences in pathogen prevalence and abundance among ant species and sample types. The findings highlight active infection in both the ants and the brood, suggesting a potential role of ants as reservoir hosts and vectors of honey bee pathogens emphasizing the need for further research to understand the implications of interspecific pathogen transmission on ant and bee health.

Co-Occurrence of Wing Deformity and Impaired Mobility of Alates with Deformed Wing Virus in Solenopsis invicta Buren (Hymenoptera: Formicidae)

Deformed wing virus (DWV), a major honey bee pathogen, is a generalist insect virus detected in diverse insect phyla, including numerous ant genera. Its clinical symptoms have only been reported in honey bees, bumble bees, and wasps. DWV is a quasispecies virus with three main variants, which, in association with the ectoparasitic mite, Varroa destructor, causes wing deformity, shortened abdomens, neurological impairments, and colony mortality in honey bees. The red imported fire ant, Solenopsis invicta Buren, is one of the most-invasive and detrimental pests in the world. In this study, we report the co-occurrence of DWV-like symptoms in S. invicta and DWV for the first time and provide molecular evidence of viral replication in S. invicta. Some alates in 17 of 23 (74%) lab colonies and 9 of 14 (64%) field colonies displayed deformed wings (DWs), ranging from a single crumpled wing tip to twisted, shriveled wings. Numerous symptomatic alates also exhibited altered locomotion ranging from an altered gait to the inability to walk. Deformed wings may prevent S. invicta alates from reproducing since mating only occurs during a nuptial flight. The results from conventional RT-PCR and Sanger sequencing confirmed the presence of DWV-A, and viral replication of DWV was confirmed using a modified strand-specific RT-PCR. Our results suggest that S. invicta can potentially be an alternative and reservoir host for DWV. However, further research is needed to determine whether DWV is the infectious agent that causes the DW syndrome in S. invicta.

Antiviral immune response reveals host-specific virus infections in natural ant populations

Hosts can carry many viruses in their bodies, but not all of them cause disease. We studied ants as a social host to determine both their overall viral repertoire and the subset of actively infecting viruses across natural populations of three subfamilies: the Argentine ant (Linepithema humile, Dolichoderinae), the invasive garden ant (Lasius neglectus, Formicinae) and the red ant (Myrmica rubra, Myrmicinae). We used a dual sequencing strategy to reconstruct complete virus genomes by RNA-seq and to simultaneously determine the small interfering RNAs (siRNAs) by small RNA sequencing (sRNA-seq), which constitute the host antiviral RNAi immune response. This approach led to the discovery of 41 novel viruses in ants and revealed a host ant-specific RNAi response (21 vs. 22 nt siRNAs) in the different ant species. The efficiency of the RNAi response (sRNA/RNA read count ratio) depended on the virus and the respective ant species, but not its population. Overall, we found the highest virus abundance and diversity per population in Li. humile, followed by La. neglectus and M. rubra. Argentine ants also shared a high proportion of viruses between populations, whilst overlap was nearly absent in M. rubra. Only one of the 59 viruses was found to infect two of the ant species as hosts, revealing high host-specificity in active infections. In contrast, six viruses actively infected one ant species, but were found as contaminants only in the others. Disentangling spillover of disease-causing infection from non-infecting contamination across species is providing relevant information for disease ecology and ecosystem management.

Virus transmission via honey bee prey and potential impact on cocoon-building in labyrinth spiders (Agelena labyrinthica)

Interspecies transmission of RNA viruses is a major concern for human and animal health. However, host-range, transmission routes and especially the possible impact of these viruses on alternative hosts are often poorly understood. Here, we investigated the role of the labyrinth spider, Agelena labyrinthica, as a potential alternative host of viruses commonly known from western honey bees, Apis mellifera. Field-collected spiders were screened for Acute bee paralysis virus (ABPV), Black queen cell virus, Chronic bee paralysis virus, Deformed wing virus type A and B (DWV-B), Israeli acute paralysis virus, Lake Sinai virus and Sacbrood virus. In a laboratory experiment, labyrinth spiders were fed with ABPV and DWV-B infected honey bees or virus free control food. Our results show that natural infections of A. labyrinthica with these viruses are common in the field, as 62.5% of the samples were positive for at least one virus, supporting their wide host range. For DWV-B, the laboratory data indicate that foodborne transmission occurs and that high virus titres may reduce cocoon building, which would be the first report of clinical symptoms of DWV in Araneae. Since cocoons are tokens of fitness, virus transmission from honey bees might affect spider populations, which would constitute a concern for nature conservation.

Can immune gene silencing via dsRNA feeding promote pathogenic viruses to control the globally invasive Argentine ant?

Pest control methods that can target pest species with limited environmental impacts are a conservation and economic priority. Species-specific pest control using RNA interference is a challenging but promising avenue in developing the next generation of pest management. We investigate the feasibility of manipulating a biological invader's immune system using double-stranded RNA (dsRNA) in order to increase susceptibility to naturally occurring pathogens. We used the invasive Argentine ant as a model, targeting the immunity-associated genes Spaetzle and Dicer-1 with dsRNA. We show that feeding with Spaetzle dsRNA can result in partial target gene silencing for up to 28 days in the laboratory and 5 days in the field. Dicer-1 dsRNA only resulted in partial gene knockdown after 2 days in the laboratory. Double-stranded RNA treatments were associated with significant gene expression disruptions across immune pathways in the laboratory and to a lower extent in the field. In total, 12 viruses and four bacteria were found in these ant populations. Some changes in viral loads in dsRNA-treated groups were observed. For example, Linepithema humile Polycipivirus 2 (LhuPCV2) loads increased after 2 days of treatment with Spaetzle and Dicer-1 dsRNA treatments in the laboratory. After treatment with the dsRNA in the field, after 5 days the virus Linepithema humile toti-like virus 1 (LhuTLV1) was significantly more abundant. However, immune pathway disruption did not result in a consistent increase in microbial infections, nor did it alter ant abundance in the field. Some viruses even declined in abundance after dsRNA treatment. Our study explored the feasibility of lowering a pest's immunity as a control tool. We demonstrate that it is possible to alter immune gene expression of pest species and pathogen loads, although in our specific system the affected pathogens did not appear to influence pest abundance. We provide suggestions on future directions for dsRNA-mediated immune disruption in pest species, including potential avenues to improve dsRNA delivery as well as the importance of pest and pathogen biology. Double-stranded RNA targeting immune function might be especially useful for pest control in systems in which viruses or other microorganisms are prevalent and have the potential to be pathogenic.

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.

Larger, more connected societies of ants have a higher prevalence of viruses

The benefits of cooperative living for foraging, nesting, defence and buffering environmental challenges lead animals with the most highly social lifestyles to dominate many ecosystems. However, living in larger, more highly connected groups should also increase the risks of pathogen exposure and transmission. While over long timescales selective responses could buffer the impacts of potential higher pathogen prevalence, similar processes are unlikely over short timescales. The red fire ant Solenopsis invicta is ideal for measuring the effects of group size on pathogen prevalence because two types of society coexist in this species: smaller single-nest single-queen colonies that are highly aggressive to their neighbours and larger multiple-queen colonies that exchange resources with neighbouring nests. We compare the presence of viruses between these two colony types using metagenomic sequence classification of RNA-sequencing reads. We find that queens from multiple-queen colonies have 8.3-times higher viral load and 1.5-times higher viral diversity than queens from single-queen colonies. This finding characterizes a rarely considered cost of transitions to more highly social living. Furthermore, our results show that highly social invertebrates can harbour many viruses.

Varying impact of neonicotinoid insecticide and acute bee paralysis virus across castes and colonies of black garden ants, Lasius niger (Hymenoptera: Formicidae)

Pesticides and pathogens are known drivers of declines in global entomofauna. However, interactions between pesticides and viruses, which could range from antagonistic, over additive to synergistic, are poorly understood in ants. Here, we show that in ants the impact of single and combined pesticide and virus stressors can vary across castes and at the colony level. A fully-crossed laboratory assay was used to evaluate interactions between a sublethal dose of the neonicotinoid thiamethoxam and Acute bee paralysis virus (ABPV) in black garden ants, Lasius niger. After monitoring colonies over 64 weeks, body mass, neonicotinoid residues and virus titres of workers and queens, as well as worker behavioural activity were measured. ABPV, but not thiamethoxam, reduced activity of workers. Neonicotinoid exposure resulted in reduced body mass of workers, but not of queens. Further, thiamethoxam facilitated ABPV infections in queens, but not in workers. Overall, virus exposure did not compromise detoxification and body mass, but one colony showed high virus titres and worker mortality. Although the data suggest additive effects at the level of individuals and castes, co-exposure with both stressors elicited antagonistic effects on colony size. Our results create demand for long-term holistic risk assessment of individual stressors and their interactions to protect biodiversity.

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.

Possible Spillover of Pathogens between Bee Communities Foraging on the Same Floral Resource

Simple Summary

Floral resource availability is one of the keys to preserving the health of bee communities. However, flowers also present a risk of pathogen transmission, as infected pollinators could deposit pathogens while foraging, exposing other pollinators to infection via the consumption of contaminated nectar or pollen. Here, we studied, over time, the prevalence of seven viruses in bee communities that share the same small surface of floral resource in order to assess the risk of virus spillover. In total, 2057 bee specimens from 30 species were caught, identified and checked for the presence of viruses. Specimens from the Halictidae family were the dominant wild bees. The prevalence of viruses was quite high: at least one virus was detected in 78% of the samples, and co-infections were frequent. The genetic diversity of the viruses was also investigated to look for the possible association of geographic origin or host with shared ancestry.

Abstract

Viruses are known to contribute to bee population decline. Possible spillover is suspected from the co-occurrence of viruses in wild bees and honey bees. In order to study the risk of virus transmission between wild and managed bee species sharing the same floral resource, we tried to maximize the possible cross-infections using Phacelia tanacetifolia, which is highly attractive to honey bees and a broad range of wild bee species. Virus prevalence was compared over two years in Southern France. A total of 1137 wild bees from 29 wild bee species (based on COI barcoding) and 920 honey bees (Apis mellifera) were checked for the seven most common honey bee RNA viruses. Halictid bees were the most abundant. Co-infections were frequent, and Sacbrood virus (SBV), Black queen cell virus (BQCV), Acute bee paralysis virus (ABPV) and Israeli acute paralysis virus (IAPV) were widespread in the hymenopteran pollinator community. Conversely, Deformed wing virus (DWV) was detected at low levels in wild bees, whereas it was highly prevalent in honey bees (78.3% of the samples). Both wild bee and honey bee virus isolates were sequenced to look for possible host-specificity or geographical structuring. ABPV phylogeny suggested a specific cluster for Eucera bees, while isolates of DWV from bumble bees (Bombus spp.) clustered together with honey bee isolates, suggesting a possible spillover.

Detection of deformed wing virus (DWV) in the Vietnamese walking stick Medauroidea extradentata (Phasmatodea)

Deformed wing virus (DWV) is a single-stranded positive sense RNA virus that mainly infects honey bees (Apis mellifera) and can have devastating impacts on the colony. Recent studies have shown the presence of this virus in several species of Apis spp. and some other Hymenoptera, but our knowledge of their host range is very limited. We screened previously sequenced RNAseq libraries from different tissues of Vietnamese Walking Stick, Medauroidea extradentata (Phasmatodea) for DWV. We only found this virus in six libraries from anterior and posterior midgut tissue. From the midgut libraries we were able to construct a complete DWV genome sequence, which consisted of 10,140 nucleotides and included one open reading frame. Pairwise genome comparison confirmed strong similarity (98.89 %) of these assembled sequences with only 113 SNPs to the original DWV genome. We hypothesize the M. extradentata acquired this virus via a foodborne transmission by consuming DWV-infected material such as pollen or leaves contaminated with virus infected bee faeces.

Deformed wing virus: using reverse genetics to tackle unanswered questions about the most important viral pathogen of honey bees

Deformed wing virus (DWV) is the most important viral pathogen of honey bees. It usually causes asymptomatic infections but, when vectored by the ectoparasitic mite Varroa destructor, it is responsible for the majority of overwintering colony losses globally. Although DWV was discovered four decades ago, research has been hampered by the absence of an in vitro cell culture system or the ability to culture pure stocks of the virus. The recent developments of reverse genetic systems for DWV go some way to addressing these limitations. They will allow the investigation of specific questions about strain variation, host tropism and pathogenesis to be answered, and are already being exploited to study tissue tropism and replication in Varroa and non-Apis pollinators. Three areas neatly illustrate the advances possible with reverse genetic approaches: (i) strain variation and recombination, in which reverse genetics has highlighted similarities rather than differences between virus strains; (ii) analysis of replication kinetics in both honey bees and Varroa, in studies that likely explain the near clonality of virus populations often reported; and (iii) pathogen spillover to non-Apis pollinators, using genetically tagged viruses to accurately monitor replication and infection.

Deformed Wing Virus in Two Widespread Invasive Ants: Geographical Distribution, Prevalence, and Phylogeny

Spillover of honey bee viruses have posed a significant threat to pollination services, triggering substantial effort in determining the host range of the viruses as an attempt to understand the transmission dynamics. Previous studies have reported infection of honey bee viruses in ants, raising the concern of ants serving as a reservoir host. Most of these studies, however, are restricted to a single, local ant population. We assessed the status (geographical distribution/prevalence/viral replication) and phylogenetic relationships of honey bee viruses in ants across the Asia–Pacific region, using deformed wing virus (DWV) and two widespread invasive ants, Paratrechina longicornis and Anoplolepis gracilipes, as the study system. DWV was detected in both ant species, with differential geographical distribution patterns and prevenance levels between them. These metrics, however, are consistent across the geographical range of the same ant species. Active replication was only evident in P. longicornis. We also showed that ant-associated DWV is genetically similar to that isolated from Asian populations of honey bees, suggesting that local acquisition of DWV by the invasive ants may have been common at least in some of our sampled regions. Transmission efficiency of DWV to local arthropods mediated by ant, however, may vary across ant species.

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.

Bee Viruses: Routes of Infection in Hymenoptera

Numerous studies have recently reported on the discovery of bee viruses in different arthropod species and their possible transmission routes, vastly increasing our understanding of these viruses and their distribution. Here, we review the current literature on the recent advances in understanding the transmission of viruses, both on the presence of bee viruses in Apis and non-Apis bee species and on the discovery of previously unknown bee viruses. The natural transmission of bee viruses will be discussed among different bee species and other insects. Finally, the research potential of in vivo (host organisms) and in vitro (cell lines) serial passages of bee viruses is discussed, from the perspective of the host-virus landscape changes and potential transmission routes for emerging bee virus infections.

Diversity and Global Distribution of Viruses of the Western Honey Bee, Apis mellifera

In the past centuries, viruses have benefited from globalization to spread across the globe, infecting new host species and populations. A growing number of viruses have been documented in the western honey bee, Apis mellifera. Several of these contribute significantly to honey bee colony losses. This review synthetizes the knowledge of the diversity and distribution of honey-bee-infecting viruses, including recent data from high-throughput sequencing (HTS). After presenting the diversity of viruses and their corresponding symptoms, we surveyed the scientific literature for the prevalence of these pathogens across the globe. The geographical distribution shows that the most prevalent viruses (deformed wing virus, sacbrood virus, black queen cell virus and acute paralysis complex) are also the most widely distributed. We discuss the ecological drivers that influence the distribution of these pathogens in worldwide honey bee populations. Besides the natural transmission routes and the resulting temporal dynamics, global trade contributes to their dissemination. As recent evidence shows that these viruses are often multihost pathogens, their spread is a risk for both the beekeeping industry and the pollination services provided by managed and wild pollinators.

Genetic Strain Diversity of Multi-Host RNA Viruses that Infect a Wide Range of Pollinators and Associates is Shaped by Geographic Origins

Emerging viruses have caused concerns about pollinator population declines, as multi-host RNA viruses may pose a health threat to pollinators and associated arthropods. In order to understand the ecology and impact these viruses have, we studied their host range and determined to what extent host and spatial variation affect strain diversity. Firstly, we used RT-PCR to screen pollinators and associates, including honey bees (Apis mellifera) and invasive Argentine ants (Linepithema humile), for virus presence and replication. We tested for the black queen cell virus (BQCV), deformed wing virus (DWV), and Kashmir bee virus (KBV) that were initially detected in bees, and the two recently discovered Linepithema humile bunya-like virus 1 (LhuBLV1) and Moku virus (MKV). DWV, KBV, and MKV were detected and replicated in a wide range of hosts and commonly co-infected hymenopterans. Secondly, we placed KBV and DWV in a global phylogeny with sequences from various countries and hosts to determine the association of geographic origin and host with shared ancestry. Both phylogenies showed strong geographic rather than host-specific clustering, suggesting frequent inter-species virus transmission. Transmission routes between hosts are largely unknown. Nonetheless, avoiding the introduction of non-native species and diseased pollinators appears important to limit spill overs and disease emergence.

Foodborne Transmission and Clinical Symptoms of Honey Bee Viruses in Ants Lasius spp

Emerging infectious diseases are often the products of host shifts, where a pathogen jumps from its original host to a novel species. Viruses in particular cross species barriers frequently. Acute bee paralysis virus (ABPV) and deformed wing virus (DWV) are viruses described in honey bees (Apis mellifera) with broad host ranges. Ants scavenging on dead honey bees may get infected with these viruses via foodborne transmission. However, the role of black garden ants, Lasius niger and Lasius platythorax, as alternative hosts of ABPV and DWV is not known and potential impacts of these viruses have not been addressed yet. In a laboratory feeding experiment, we show that L. niger can carry DWV and ABPV. However, negative-sense strand RNA, a token of virus replication, was only detected for ABPV. Therefore, additional L. niger colonies were tested for clinical symptoms of ABPV infections. Symptoms were detected at colony (fewer emerging workers) and individual level (impaired locomotion and movement speed). In a field survey, all L. platythorax samples carried ABPV, DWV-A and -B, as well as the negative-sense strand RNA of ABPV. These results show that L. niger and L. platythorax are alternative hosts of ABPV, possibly acting as a biological vector of ABPV and as a mechanical one for DWV. This is the first study showing the impact of honey bee viruses on ants. The common virus infections of ants in the field support possible negative consequences for ecosystem functioning due to host shifts.

The detection of honey bee (Apis mellifera)-associated viruses in ants

Interspecies virus transmission involving economically important pollinators, including honey bees (Apis mellifera), has recently sparked research interests regarding pollinator health. Given that ants are common pests within apiaries in the southern U.S., the goals of this study were to (1) survey ants found within or near managed honey bee colonies, (2) document what interactions are occurring between ant pests and managed honey bees, and 3) determine if any of six commonly occurring honey bee-associated viruses were present in ants collected from within or far from apiaries. Ants belonging to 14 genera were observed interacting with managed honey bee colonies in multiple ways, most commonly by robbing sugar resources from within hives. We detected at least one virus in 89% of the ant samples collected from apiary sites (n = 57) and in 15% of ant samples collected at non-apiary sites (n = 20). We found that none of these ant samples tested positive for the replication of Deformed wing virus, Black queen cell virus, or Israeli acute paralysis virus, however. Future studies looking at possible virus transmission between ants and bees could determine whether ants can be considered mechanical vectors of honey bee-associated viruses, making them a potential threat to pollinator health.