As worried as we may be of varroa, deformed wing virus (DWV) and other varroa associated viruses are the true killer. Australia doesn’t have DWV virus at present, and we hope it stays that way.
Suppressed in ovo virus infection
Researchers internationally have been focusing on how to reduce the chances of queens transmitting varroa associated viruses to her offspring. DWV is present at high levels in the reproductive organs of queens, but some queens suppress some virus infections and lay virus-free eggs.
This trait is called ‘suppressed in ovo virus infection’ (SOV). The queen passes this trait on to her offspring, and it is something that can be selected for in breeding programs.
SOV is measured by collecting 10 eggs from a colony and pooling them into a single sample before testing for viruses. Queens that lay virus free eggs are selected to breed the next generation.
SOV keeps virus titres low, and colonies headed by SOV queens have fewer and less severe DWV infections.
Virus resistance means that bees are less likely to contract viruses, and selecting and breeding with queens that have the ‘suppressed in ovo virus infection’ trait, they are less likely to pass on viruses to their offspring. Bees that contract viruses but do not suffer from ill-effects are said to be virus tolerant
Virus tolerance
Viruses can also be present without colonies suffering ill-effects. This is known as virus tolerance (VT).
VT was investigated internationally in workers produced by 12 queens from each of four European populations that were naturally resistant to varroa. The workers were compared to workers produced by 12 queens from a varroa susceptible population, spread across four apiaries.
Adults and larvae infected with acute bee paralysis virus (ABPV) and DWV were found to have similar virus levels, but the naturally varroa resistant stocks survived virus infections for longer, suggesting improved tolerance to high viral loads. It is possible these populations have co-evolved — viruses, varroa, and the bees — and reached an equilibrium that enables all to survive.
Acknowledgements:
- Holmes, Gerdts, Grassl, Mikeheyev, Roberts, Remnant, Chapman (2024) Resilient beekeeping in the face of Varroa. AgriFutures Australia.
- Plan Bee (National Honey Bee Genetic Improvement Program) is supported by funding from the Australian Government Department of Agriculture, Fisheries and Forestry as part of its Rural Research and Development for Profit program. The project is further supported by AgriFutures Australia, the Department of Regional NSW, University of Sydney, University of New England Animal Genetics and Breeding Unit, Better Bees WA Inc, Wheen Bee Foundation, Costa Group, Olam, Beechworth Honey, Monson’s Honey and Pollination, South Pacific Seeds, Australian Queen Bee Breeders Association, Australian Honey Bee Industry Council, and commercial beekeepers.
- Amiri et al (2018) Quantitative patterns of vertical transmission of Deformed wing virus in honey bees. PLoS One 13: e0195283
- Bouuaert et al (2021) Breeding for virus resistance and its effects on Deformed wing virus infection patterns in honey bee queens. Viruses 13: 1074
- De Graaf et al (2020) Heritability estimates of the novel trait ‘suppressed in ovo virus infection’ in honey bees (Apis mellifera). Scientific Reports 10: 14310
- Locke et al (2021) Adapted tolerance to virus infections in four geographically distinct Varroa destructor-resistant honeybee populations. Scientific Reports 11: 12359
- Ravoet et al (2015) Vertical transmission of honey bee viruses in a Belgian queen breeding program. BMC Veterinary Research 11: 61
- This article was peer-reviewed by Emily Remnant and John Roberts.
