Outlining Good Management Practices to Reduce and Mitigate Viral Infection

By Nicole McCormick, Alberta Tech Transfer Program Technician

How can you manage honey bee viruses in your operation?

After learning about the many transmission routes of honey bee viruses, we can now use this knowledge to identify how we can effectively manage them. Unfortunately, there are currently no treatments available to help combat viral infections. Therefore, “natural”, non-chemical management must be the primary method of virus control, applying the principals of Integrated Pest Management (IPM). An IPM plan is a knowledge heavy, producer lead decision-making process, which encourages the natural control of pests to prevent disease outbreak1.

main components of IPM we will be focusing on throughout this article: cultural practices, monitoring, physical control, biological control, and chemical control2. Due to the lack of chemotherapies for honey bee viruses, beekeepers must lean on the other four components of IPM as they are highly relevant to viral management.

One of the main inducers of viral infection is the onset of colony stress. Some examples of these stressors are: varroa mite infestation, co-infection with other pathogens, and lack of proper nutrition3. Therefore, the management and prevention of viral infections tends to revolve around reducing colony stressors in order to keep bees vigorous. Additionally, viral management is also comprised of both minimizing transmission and reducing viral levels4. By using the components of IPM as a guide, beekeepers can implement management practices that reduce colony stressors, limit viral transmission, and in turn lower viral titers within colonies.

The final piece of this virus puzzle will focus on how beekeepers can work to reduce and mitigate viral infections within honey bee colonies. This will be done by highlighting good management practices and potential control methods that fall under each section of IPM.

1. Cultural Practices

Cultural management practices are currently one of the most important aspects of IPM when working to control viral diseases. Management practices to reduce colony stressors, including colony/apiary management, queen management, equipment rotation, and viral-vector management (i.e., varroa mites), are all forms of cultural management.

Viruses can remain present in healthy colonies at low levels, but when the colony is put under stress, these unapparent infections can turn into overt infections (i.e., exhibiting clear signs of infection)3. Due to this, management of colony stressors is a critical factor in mitigating viral disease. All of these cultural management practices work together to promote bee health, which in turn limits viral transmission and infection levels within a colony5

Apiary Management: It is important to select an apiary location that is surrounded by an abundance of rich floral sources during the beekeeping season5. Ensuring that colonies have access to adequate nutritional resources provides the means for fast build-up, as vigorous bees tend to have the lowest levels of pathogen infections5. Specifically in viral defense, it is important that colonies have access to a variety of pollen sources. Ensuring the availability of abundant and diverse protein and lipid sources, can help reduce the level of virus-induced mortality6. Additionally, the distance between apiaries can be very important in limiting viral transmission4. It is suggested that apiaries are a minimum of 1 kilometre apart with the number of colonies in each apiary adjusted based on the surrounding floral density, this is usually between 20-40 colonies per apiary4. This will help reduce the amount of overlap between foragers from different apiaries and competition for floral sources4 Finally, it is important that as beekeepers move between apiaries, there is no exchange of infected comb or hive products5. This can be done by implementing good biosecurity practices between yards, such as the frequent sterilization of beekeeping equipment and limited exchange of bee products (i.e., honey and brood frames) between yards5

Colony Management: One of the most beneficial disease management practices is separating sick colonies from healthy colonies4. Colonies that have high disease levels, whether it be viral, bacterial, fungal, or parasitic, threaten the health of surrounding hives and it is important that these colonies are isolated in order to reduce disease transmission2 This is especially important for Chronic Bee Paralysis Virus (CBPV) infected colonies, as transmission can happen topically when infected bees encounter neighboring bees during activities such as robbing, drifting, and foraging7 Implementing this practice is a form of transmission risk management that can reduce viral spread, as well as reduce the transmission of other pathogens that may synergistically work to increase viral levels3,4. Colony placement within an apiary can also help reduce viral transmission, as having bee pallets place well apart and hive entrances in different orientations can reduce bee drifting4. Finally, supplementing colonies with additional nutritional resources (i.e., pollen patties/protein substitute and sugar syrup) during times of dearth reduces nutritional stress, and therefore is an important practice in ensuring that viral levels do not rise4

Queen Management: Colonies that are experiencing signs of viral disease can be managed by replacing the queen2. Introducing a young healthy queen can stop vertical transmission of viruses and improve colony health8. If queen replacement is not an option, the existing queen can be caged for 10-14 days to create a break in the brood cycle, allowing for the consistent removal of diseased brood8. This method mainly works for brood diseases such as Sacbrood Virus (SBV)8. The use of honey bee stocks selected for virus resistance can be an additional management technique.2 Genetic stocks that have been bred to promote genes associated with hygienic behaviour (i.e., removal of infected brood), help mitigate viral diseases and associated pests9. Due to the close relationship between varroa mites and viral transmission, selecting a genetic stock that has been bred for varroa resistance (e.g., hygienic behaviour, varroa sensitive hygiene) will also reduce viral levels10 Colonies with these genetics have lower varroa levels, reduced viral titers, and increased colony survival10

Equipment Rotation: As discussed in Part 2 of this series, viruses can be harboured in the wax, honey, pollen, and wood structures of honey bee colonies4 As equipment gets older it is more likely to contain higher levels of virus particles which in turn can contribute to the severity of a viral infection4. Therefore, old equipment should be replaced with new equipment to help limit viral titers within a colony8. It is recommended that 10-20% of equipment (i.e., frames and brood boxes) is rotated out of use each year.

Vector Management: Due to the close linkage between varroa mite infestation and viral infection, there is a strong emphasis on the use of effective mite management techniques to reduce vector-based transmission of varroa-related viruses11 In a study done by Woodford et al. in 2022, it was found that following an intensive varroa control treatment, where colonies were shaken onto new equipment and treated with a miticide, there was 99% reduction in virus levels within the first month. While this method of varroa control is not feasible for large operations, these results emphasize the importance of varroa control when managing viral levels. However, even after successful varroa treatments, the threat of virus infection isn’t completely diminished as viral levels do not drop to zero7. Viral infection has the potential to become cyclical as varroa infestation repeatedly occurs7. Therefore, constant, and effective control of varroa mites is important to reduce vector mediated transmission of viruses 7 .

2. Monitoring

Frequently monitoring colony health is a very important aspect of any disease management plan. However, monitoring for viruses can prove to be difficult as they can persist within a colony as an unapparent or asymptomatic infection, and lab diagnostics can be very costly12. Overt virus infections tend to go hand-in-hand with other pathogens such as, varroa mites and Nosema4. Therefore, monitoring for bee pathogens is extremely important for viral management, as colonies suffering from other diseases are likely to be suffering from viral diseases as well3. Visual inspections for viral diseases are difficult and not always accurate. An alternative is to take samples of suspected diseased colonies and send to a diagnostic laboratory for confirmation12. Having exact data regarding viral presence and levels creates a record of colony health. Producers can then look at viral levels throughout their operation and use critical thresholds as a tool for making management decisions7. In a study done by Woodford et al., in 2022 a threshold of 5,000,000 genome copies (GC)/bee of Deformed Wing Virus (DWV) was associated with symptomatic infection. Therefore, a critical threshold of 5,000,000 GC/bee can be used for guidance and to determine the success of certain cultural and physical controls, in combination with other IPM practices, such as separating sick colonies from healthy colonies.

3. Physical Control

Reusing old comb for food storage and brood rearing is a common practice for producers, as frequently introducing new frames is not always feasible9 Introducing foundation requires mass amounts of bee energy to draw out new comb, therefore stunting productivity9. Gamma irradiation of old frames is a potential option to eliminate pathogens harboured in honey, pollen, and wax without destroying the comb13. It was found that irradiation rendered DWV inactive and reduced the infectivity of Black Queen Cell Virus (BQCV), indicating that there are some beneficial effects13. However, some research has shown that not all viruses are inactivated and only subtle improvements on bee health have been observed9,13. For example, it was found that this process had little to no effect on Chronic Bee Paralysis Virus (CBPV) infectivity13. This method is not as useful as cultural management practices as it has a broad range of effectivity and can be expensive to implement on a large scale, nonetheless it has proved to reduce viral titers for select viruses13

4. Biological and Chemical Control

As previously mentioned, there are no chemotherapies for viral diseases in honeybees. However, new advancements in RNA interference (RNAi) technology appear to be promising in the field of honey bee viral management. RNAi is a natural immune defense in which double stranded RNA (dsRNA) bind and destroy alike RNAs so that specific genes can be silenced, or replication can be reduced14. This process has been used in honey bee populations to combat viral diseases by either feeding or injecting dsRNA to inhibit the replication of RNA viruses, such as DWV15. Unfortunately, this tends to be a difficult process that has many variable outcomes as dsRNA is expensive to produce and does not remain viable outside of the lab for long periods of time16. However, a new study has shown that genetically engineered bacterial organisms that are naturally present within the bee gut can be used as a transport vessel to easily administer and spread the dsRNA to the bee16 This has proven to be successful in protecting honey bees from DWV and potentially other RNA viruses (i.e., Varroa Destructor Virus, CBPV, BQCV, and SBV)16. Additionally, this has also been found to be a potential control method for varroa mites as the bacteria can be engineered to carry a dsRNA that targets essential genes within the mite after they feed on host bees, causing them to die more quickly16. This is not yet a management practice that can be used commercially; however, it shows promise for the future of viral management in honey bees.

Thank you for following along with this three-part series on honeybee viruses! I hope that this series was able to help deepen your understanding of common honey bee viruses and can be useful to you in the future as you manage your bees. Keep an eye out in the next few months as the Alberta Tech Transfer Program will be releasing a compact field guide on virus identification, transmission, and management!

References

1. Dhawan, A. K., Arora, R., & Kumar, V. (2013) Insect pest management: Origin, evolution, and implementation. In A. K., Dhawan, B., Singh, M. B., Bhullar, & R. Arora (Eds.), Integrated pest management (pp. 1-43). Scientific publishers (India).

2. Pernal, S. F. & Clay, H. (Eds.). (2013). Honey Bee Diseases and Pests, 3rd edition. Canadian Association of Professional Apiculturists, Beaverlodge, AB, Canada.

3. Chen, Y., Evans, J., & Feldlaufer, M. (2006). Horizontal and vertical transmission of viruses in the honey bee, Apis mellifera. Journal of Invertebrate Pathology, 92(3), 152-159. https://doi.org/10.1016/j.jip.2006.03.010

4. de Miranda, J. R., Gauthier, L., Ribière, M., & Chen, Y. P. (2011). Honey bee viruses and their effect on bee and colony health. In D. Sammataro & J. A. Yoder (Eds.), Honey Bee Colony Health (pp. 71-102). CRC press. https://doi.org/10.1201/b11318

5. Nagaraja, N., & Rajagopal, D. (2019). Honey Bees: diseases, parasites, pests, predators, and their management. MJP publishers.

6. Dolezal, A. G., Carrillo-Tripp, J., Judd, T. M., Allen Miller, W., Bonning, B. C., & Toth, A. L. (2019). Interacting stressors matter: diet quality and virus infection in honeybee health. Royal Society Open Science, 6(2), 181803. https://doi.org/10.1098/rsos.181803

7. Amiri, E., Meixner, M., Nielsen, S. L., & Kryger, P. (2015). Four categories of viral infection describe the health status of honey bee colonies. PLoS One, 10(10), e0140272. https://doi.org/10.1371/journal.pone.0140272

8. Wei, R., Cao, L., Feng, Y., Chen, Y., Chen, G., & Zheng, H. (2022). Sacbrood Virus: A Growing Threat to Honeybees and Wild Pollinators. Viruses, 14(9), 1871. https://doi.org/10.3390/v14091871 https://doi.org/10.3390/insects10010015

9. de Guzman, L. I., Simone-Finstrom, M., Frake, A. M., & Tokarz, P. (2019). Comb irradiation has limited, interactive effects on colony performance or pathogens in bees, Varroa destructor and wax based on two honey bee stocks. Insects, 10(1), 15.

10. O’Shea-Wheller, T. A., Rinkevich, F. D., Danka, R. G., Simone-Finstrom, M., Tokarz, P. G., & Healy, K. B. (2022). A derived honey bee stock confers resistance to Varroa destructor and associated viral transmission. Scientific Reports, 12(1), 1-19. https://doi.org/10.1038/s41598-022-08643-w

11. Woodford, L., Christie, C. R., Campbell, E. M., Budge, G. E., Bowman, A. S., & Evans, D. J. (2022). Quantitative and qualitative changes in the deformed wing virus population in honey bees associated with the introduction or removal of Varroa destructor. Viruses, 14(8), 1597. https://doi.org/10.3390/v14081597

12. Tantillo G, Bottaro M, Di Pinto A, Martella V, Di Pinto P, Terio V. (2015) Virus infections of honeybees apis mellifera. Italian Journal of Food Safety, 4(3). doi:10.4081/ijfs.2015.5364

13. Simone-Finstrom, M., Aronstein, K., Goblirsch, M., Rinkevich, F., & de Guzman, L. (2018). Gamma irradiation inactivates honey bee fungal, microsporidian, and viral pathogens and parasites. Journal of Invertebrate Pathology, 153, 57-64. https://doi.org/10.1016/j.jip.2018.02.011

14. Brutscher, L. M., & Flenniken, M. L. (2015). RNAi and antiviral defense in the honey bee. Journal of Immunology Research, 2015, 941897. https://doi.org/10.1155/2015/941897

15. Desai, S. D., Eu, Y. J., Whyard, S., & Currie, R. W. (2012). Reduction in deformed wing virus infection in larval and adult honey bees (Apis mellifera L.) by double‐stranded RNA ingestion. Insect Molecular Biology, 21(4), 446-455. https://doi.org/10.1111/j.1365-2583.2012.01150.x

16. Leonard, S. P., Powell, J. E., Perutka, J., Geng, P., Heckmann, L. C., Horak, R. D., Moran, N. A., Perutka, J., Geng, P., Davies, B. W., Ellington, A. D., & Moran, N. A. (2020). Engineered symbionts activate honey bee immunity and limit pathogens. Science, 367(6477), 573-576. DOI: 10.1126/science.aax9039

The Tech Transfer Program is funded by the Government of Canada and the Government of Alberta through the Canadian Agricultural Partnership.