https://www.scu.edu.au/research/bee-research-and-extension-lab/

Authored by Dr Cooper Schouten and Dr Emily Remnant, Peer reviewed by Dr Rob Manning and Jon Lockwood, December 2024

 

Introduction

Since the incursion of Varroa destructor in June 2022, 1000s of bees and 1000s of mites have been tested for honey bee viruses. Industry organisations during webinars have reported that no major viruses of concern have been detected, including Deformed Wing Virus (DWV). While deformed wings in honey bees (Apis mellifera) have been observed by beekeepers in areas with Varroa mite infestations and this a key symptom of DWV, these deformities can also result from other factors. These include physical trauma during pupal development (e.g. being bitten by mites during feeding), hot and cold weather, nutritional deficiencies, exposure to pesticides, and genetic mutations (McMahon et al., 2016; Kevill et al., 2017; Grozinger and Flenniken, 2019). This is not to say DWV is not in Australia, but it hasn’t been detected yet. Two new viruses that have been detected that are new to Australia are two different species of Rhabdovirus, Apis Rhabdovirus-1 (ARV-1) and Apis Rhabdovirus-2 (ARV-2).

 

 

Apis Rhabdovirus-1 (ARV-1) [1] and Apis rhabdovirus-2 (ARV-2)

Distribution and Hosts 

ARV-1 has been identified in Apis mellifera in Africa, Europe, Tonga (Remnant et al., 2017), United States and Israel (Levin et al., 2017), New Zealand (Lester et al., 2024), Turkey (Altay et al., 2024), Slovenia (Šimenc Kramar and Toplak., 2024) and Southern Brazil (Da Silva et al., 2023). ARV-1 is highly prevalent in Varroa destructor mites (Remnant et al., 2017; Norton et al., 2021) and has been detected in Bumble bees (Bombus impatiens) in the United States (Levin et al., 2017). ARV-2 is less studied globally but it is also highly prevalent in Apis mellifera and Varroa destructor and it is often found alongside ARV-1 as co-infections in bees (Kadlečková et al., 2023) and mites (Eliash et al., 2022), which suggests a potential interaction between the two rhabdovirus species. ARV-1 and ARV-2 have recently been detected in Australian honey bees in apiaries that are positive for Varroa destructor mites, which suggests the virus has arrived with the V. destructor incursion. 

Replication and viral load in Varroa and Honey Bees

A specific immune response to ARV-1 and ARV-2 rhabdoviruses has been detected in both A. mellifera and V. destructor, which indicates the viruses actively infect and  replicate in both the bees and the mites (Remnant et al., 2017). ARV-1 can reach high viral loads in individual honey bees and mites, with around 10^8 viral genome copies per individual (Levin et al., 2017). High titers (levels) of Rhabdovirus have been detected in honey bees in NSW. It is currently unclear whether high viral loads of Rhabdoviruses result in any noticeable symptoms in honey bees, but for other honey bee viruses, usually high viral loads are associated with more severe symptoms.

Significance 

While Rhabdoviruses are not as well-studied as some other viruses of honey bees, their presence in Varroa mites is noteworthy because they have a different genetic makeup to most honey bee viruses. Most viruses transmitted by Varroa are positive-sense single-stranded RNA viruses – their RNA genome occurs in a positive direction meaning the information carried in the genome can directly be translated into proteins. ARV-1 and ARV-2 are unusual as they are both negative-sense RNA viruses, where the viral genome is a negative RNA strand which first needs to be converted to a positive RNA (by RNA polymerase) before it can create protein and become a viral particle. The detection of ARV-1 RNA in B. impatiens (the bumble bee, which are not parasitized by Varroa) suggests that it may not require the mite for transmission, and ARV-1 may be shared among co-foraging bee species, however further work needs to be done to confirm this. 

Practical implications for beekeepers

We don’t know a lot about Rhabdovirus impacts on honey bees, but as with other viruses, we could assume that proactively keeping mite populations low will help reduce the spread, incidence and impacts of Rhabdovirus also.

[1] n.b. Levin et al propose it be named BRV-1 to avoid confusion with ‘Adelaide River virus’ also referred to as ARV.

 

 

References and further reading

Altay, K., Isidan, H., Erol, U., Turan, T., Sahin, O. F., Kalin, R., … & Mogulkoc, M. N. (2024). Molecular survey and phylogenetic analysis of bee pathogens; with a note first detection of Apis mellifera Filamentous Virus, Varroa destructor virus-1, Apis rhabdovirus-1, and Apis rhabdovirus-2 in Türkiye. Journal of Apicultural Research, 1-13.

Da Silva, L. A., De Camargo, B. R., Rodrigues, B. M. P., Berlitz, D. L., Fiuza, L. M., Ardisson-Araújo, D. M. P., & Ribeiro, B. M. (2023). Exploring viral infections in honey bee colonies: insights from a metagenomic study in southern Brazil. Brazilian Journal of Microbiology, 54(3), 1447-1458.

Eliash, N., M. Suenaga, and A.S. Mikheyev, Vector-virus interaction affects viral loads and co-occurrence. BMC Biology, 2022. 20(1): p. 284.

Grozinger, C. M., & Flenniken, M. L. (2019). Bee viruses: Ecology, pathogenicity, and impacts. Annual Review of Entomology, 64, 205-226.

Kadlečková, D., et al., The Virome of Healthy Honey Bee Colonies: Ubiquitous Occurrence of Known and New Viruses in Bee Populations. 2022. 7(3): p. e00072-22.

Kevill, J. L., Highfield, A., Mordecai, G. J., Martin, S. J., & Schroeder, D. C. (2017). ABC assay: Method development and application to quantify the role of three DWV master variants in overwinter colony losses of European honey bees. Viruses, 9(11), 314.

Lester, P.J., et al., Viral communities in the parasite Varroa destructor and in colonies of their honey bee host (Apis mellifera) in New Zealand. Scientific Reports, 2022. 12(1): p. 8809.

Levin, S., Galbraith, D., Sela, N., Erez, T., Grozinger, C. M., & Chejanovsky, N. (2017). Presence of Apis rhabdovirus-1 in populations of pollinators and their parasites from two continents. Frontiers in microbiology, 8, 2482.

Norton, A.M., et al., Adaptation to vector‐based transmission in a honeybee virus. Journal of Animal Ecology, 2021. 90(10): p. 2254-2267.

McMahon, D. P., Natsopoulou, M. E., Doublet, V., Fürst, M., Weging, S., Brown, M. J., … & Paxton, R. J. (2016). Elevated virulence of an emerging viral genotype as a driver of honeybee loss. Proceedings of the Royal Society B: Biological Sciences, 283(1833), 20160811.

Remnant, E. J., Shi, M., Buchmann, G., Blacquière, T., Holmes, E. C., Beekman, M., & Ashe, A. (2017). A diverse range of novel RNA viruses in geographically distinct honey bee populations. Journal of virology, 91(16), 10-1128.

Šimenc Kramar, L., & Toplak, I. (2024). Identification of Twenty-Two New Complete Genome Sequences of Honeybee Viruses Detected in Apis mellifera carnica Worker Bees from Slovenia. Insects, 15(11), 832.

 

 

Article published with permission from Dr Cooper Schouten, Southern Cross University