Wrapping up our blog series focused on varroa mite biology, and the host-parasite interactions of mites and honey bees, this week’s blog will focus on the damage caused by varroa mites at the colony level. The impacts of varroa mite parasitism are often cumulative on the overall decline in health and population of a honey bee colony. Read this week’s blog to learn about varroa mite damage at the colony level, and to better understand the management steps beekeepers can utilize to help keep their colonies strong and healthy.

The Host-Parasite Interactions of Varroa Mites and Honey Bees: Colony Level Impacts

The last couple of blogs have explored how varroa mites not only cause direct damage to honey bees through feeding but they also vector viruses which infect honey bees and cause multiple honey bee health issues. Beekeepers often recognize varroa mite damage at the colony level, which occurs when mite levels have reached a critical level, and both the health and population of the colony has been weakened.

Varroa mite damage at the colony level results from a cascade of impacts caused by mites. It starts with the physical damage caused by mites when feeding from honey bee fat bodies. These feeding wounds impair the honey bee’s immune defenses and make them more susceptible to viral transmission. Viruses transmitted by the mites cause a wide array of deformities and health impacts on honey bees, which overall shorten their lifespan. Shortened honey bee lifespan decreases the colony population which also impacts the colony’s ability to effectively manage the hive. For example, a decreased population means less bees are available to forage for resources, which means less resources are available in the hive, and brood production will slow down - further declining the population size. Other cascade impacts from high varroa mite levels include the colony being more susceptible to robbing and pest problems, which further weakens the colony; also, there are less nurse bees in colony which can lead to increased susceptibility to other honey bee diseases.

Furthermore, worker bees that are infested with varroa often exhibit impaired navigation, which reduces the success of them finding their home colony, and increases drifting of bees to neighboring colonies³. Drifting inadvertently transfers mites and viruses between colonies, apiaries, and operations. This phenomenon, known as the “mite bomb effect” demonstrates how an unmanaged colony causes widespread colony infestation and loss throughout a region⁴.

Overall, colonies with high varroa mite levels are at high risk of dying before or during the winter months. Having a high over winter loss has other impacts on a beekeeping operation, such as: not being able to meet pollination contracts, decreased honey production, and decreased production of bees, all of which decreases beekeeping revenues.

Impacts of Varroa destructor (ATTTA 2025) (Created in https://BioRender.com)

Although varroa presents a significant threat to the global beekeeping industry, beekeepers are able to successfully manage this pest using an integrated pest management (IPM) approach. This includes monitoring mite levels throughout the beekeeping season, alternating chemical treatments, providing treatments following the manufacturer’s instructions, and implementing cultural and/or physical control methods (ex. brood interruption). To learn more about IPM read past ATTTA blogs: “An IPM Series: The Importance of Monitoring for Pests and Diseases” (September 28, 2023), “An IPM Series: How Reduced Efficacy Occurs” (October 12, 2023), and “The Advantage of Splitting for Varroa Mite Management: an IPM Approach” (January 16, 2025).

References

1. Doublet, V., Oddie, M.A., Mondet, F., Forsgren, E., Dahle, B., Furuseth-Hansen, E., Williams, G.R., De Smet, L., Natsopoulou, M.E., Murray, T.E. and Semberg, E., 2024. Shift in virus composition in honeybees (Apis mellifera) following worldwide invasion by the parasitic mite and virus vector Varroa destructor. Royal Society Open Science, 11(1), p.231529.
2. Ramsey, S.D., Ochoa, R., Bauchan, G., Gulbronson, C., Mowery, J.D., Cohen, A., Lim, D., Joklik, J., Cicero, J.M., Ellis, J.D. and Hawthorne, D., 2019. Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph. Proceedings of the National Academy of Sciences, 116(5), pp.1792-1801.
3. Geffre, A.C., Gernat, T., Harwood, G.P., Jones, B.M., Morselli Gysi, D., Hamilton, A.R., Bonning, B.C., Toth, A.L., Robinson, G.E. and Dolezal, A.G., 2020. Honey bee virus causes context-dependent changes in host social behavior. Proceedings of the National Academy of Sciences, 117(19), pp.10406-10413.
4. Dynes, T.L., De Roode, J.C., Lyons, J.I., Berry, J.A., Delaplane, K.S. and Brosi, B.J., 2017. Fine scale population genetic structure of Varroa destructor, an ectoparasitic mite of the honey bee (Apis mellifera). Apidologie, 48(1), pp.93-101.