Honeybees (Apis mellifera) have been managed for honey and wax production for at least 4500 years. Hive products (honey, wax, Royal Jelly, propolis etc.) remain globally valuable. However, of far greater value is the contribution made by honeybees to agricultural crop pollination. Industrial-scale migratory beekeeping is critical for many high-value crops such as top fruit, almonds and blueberries. As the only large-scale managed pollinator, honeybees account for a significant proportion of the estimated €150bn value provided by insect pollination to global agriculture (of which at least €20bn is in the EU).
Both honey and pollination depend upon strong, healthy colonies, a situation that has been threatened over the last century by the global spread of the ectoparasitic mite Varroa destructor. The mite originated in the Far East, probably as a parasite of the Eastern honeybee Apis cerana, transferred to A. mellifera and has subsequently spread to all continents except Australia, reaching the USA in ‘87 and the UK in ‘92. All colonies in the UK, with the exception of those in the far North and West, some Scottish islands (e.g. Colonsay) and the Isle of Man have the mite. Varroa acts as a vector for a range of RNA viruses of honeybees which are transferred when the mite feeds on haemolymph from the developing pupa. Following the introduction of Varroa to the UK, overwintering colony losses doubled to ~20% and are significantly higher in long winters (>34% in ‘12/’13).
The virus disease most regularly reported in Varroa-infested colonies is due to Deformed Wing Virus (DWV), a member of the Iflaviridae which, as a picorna-like virus, is distantly related to poliovirus (an enterovirus). Although DWV is found in the majority (95%+) of colonies, irrespective of the Varroa status, it replicates to high levels and causes developmental deformities (malformed, atrophied wings and abdominal stunting; see right) in mite-infested colonies. Significantly, high levels of DWV also reduce worker lifespan; this is thought to be the major contribution to overwintering losses where worker numbers are critical.
We study the biology, pathogenesis and transmission of DWV in honeybees, using a combination of molecular, reverse genetic and systems-based methods. In recent studies (Moore et al., 2011) we have demonstrated that a recombinant form (RF) of DWV predominates after Varroa transmission. We have investigated the virus population in the bee before and after transmission, the response of the bee to virus infection (e.g. by microarray analysis of changes in host gene expression) and the sequence of the virus population replicating in the Varroa mite. The results of these studies will have implications for the diagnosis and potential therapeutic treatment of DWV-mediated infections in managed honeybee colonies.
Why is this important?
Our research shows that the transmission of DWV by the Varroa mite selects for virulent strains of the virus. If we can understand why these virus strains cause disease, and why not all bees exposed to Varroa during development develop disease, we will be in a better position to control the virus and reduce overwintering colony losses. Our research involves both high-tech molecular biology studies of virus control and low-tech (and inexpensive) changes in beekeeping practices to reduce the incidence of the virulent strain of DWV.
David Evans is an experienced beekeeper and regularly talks about this research and beekeeping to local and national beekeeping associations. If you are interested in this research and represent a BKA please contact us for further details.
Relevant recent publications
Ryabov, EV, Wood, GR, Fannon, JM, Moore, JD, Bull, JC, Chandler, D, Mead, A, Burroughs, N & Evans, DJ 2014, ‘ A virulent strain of Deformed Wing Virus (DWV) of Honeybees (Apis mellifera) prevails after Varroa destructor -mediated, or in vitro , transmission ‘ PLoS Pathogens , vol 10, no. 6, e1004230.
Wood, GR, Ryabov, EV, Fannon, JM, Moore, JD , Evans, DJ & Burroughs, N 2014, ‘ MosaicSolver: a tool for determining recombinants of viral genomes from pileup data ‘ Nucleic Acids Research , vol 42, no. 16, e123.
- A MatLab implementation of the MosaicSolver sequential algorithm is available from the University of Warwick Systems Biology Software Downloads page
Vanbergen, A. & IPI members. 2013. Threats to ecosystem service: pressures on pollinators. Frontiers in Ecology and the Environment 11, 251-259.
Ryabov, E. and Evans, D.J 2011 ‘The plight of the honeybee’ Microbiology Today 38, 218 – 221
Moore, J., Jironkin, A., Chandler, D., Burroughs, N., Evans, D. J. & Ryabov, E. V. 2011. Recombinants between Deformed wing virus and Varroa destructor virus-1 may prevail in Varroa destructor-infested honeybee colonies. Journal of General Virology 92, 156-161.