We all know the damaging effects that the appropriately named parasitic mite Varroa destructor can have on our honey bee colonies. The mites attach themselves to the bees and their larvae and feed on their host’s haemolymph. In their phoretic stage, they are transported on adult bees, and can thus spread between bees within the hive and between colonies through the processes of drifting, robbing and swarming of the bees.

As well as generally weakening the bees through their parasitism, the mites act as vectors for a number of harmful bee viruses. At low levels in bee populations these viruses may not cause significant harm, but high levels of varroa infestation may result in rapid spread of viruses in the colony, disruption of the normal activities of the bees, and potential colony collapse.

In a survey of 4,500 apiaries in England and Wales in 2010 and 2011, the NBU screened for eight known honey bee viruses and found only low levels (BBKA News, 226, pp 47-48, February 2019), but the most commonly detected virus was deformed wing virus (DWV). This virus used not to be particularly aggressive or damaging and was passed by vertical transmission from the queen to her offspring. However, the varroa mite transmits the virus horizontally from bee to bee, and this has not only increased the rate of transmission, but has changed the way the virus behaves, making it more damaging to bees. As there is no treatment for the virus itself, or indeed for the other viruses that affect honey bees, the only way to limit the damage is by managing the varroa levels to keep them below the level where harm is likely. This is not easy, as the mite has developed strains with resistance to authorised varroacides, and there is always the risk of contaminating the hive products.

An interesting recent development has been described in a paper published in Scientific Reports 8 in October 2018 by Paul Stamets and colleagues at Washington State University (Extracts of Polypore Mushroom Mycelia Reduce Viruses in Honey Bees). This paper describes research into possible antiviral activity in exudates from bracket fungi that grow on trees. The work was also described in an article for the New York Times Opinion | Will Mushrooms Be Magic for Threatened Bees?. As far as we know, the work has not attracted notice here in the UK.

Honey bees had been observed feeding directly on exudates from fungal mycelia, and it was speculated that they might be gaining nutritional or medicinal benefits. The researchers evaluated extracts from the mycelia of several polypore mushroom species for activity against two major honey bee viruses, DWV and LSV (Lake Sinai virus) both in the laboratory and in field studies. LSV was first identified in 2010 in the US and is now widespread in US honey bee colonies. In laboratory experiments, bees were fed the extracts in sucrose syrup at two different concentrations. As a control, extracts were taken from the fungal growth medium, birch wood. After feeding on the extracts, samples of bees were frozen and homogenised for extraction and analysis of nucleic acids using a technique called qPCR for quantification of viral RNA. Primers specific for the two viruses were used.

The results were rather spectacular, with a significant reduction of DWV in caged bees by over 879-fold in one trial for a 1% extract of the fungus Fomes fomentarius compared with the sugar syrup control, and in LSV by 499-fold from an extract of Ganoderma resinaceum.

In field trials, using 5-frame colonies, with bees divided from a common population, bees were sampled for virus levels at the start of treatment and 12 days later after feeding the bees with fungal extracts mixed into sucrose solution using in-hive feeders. Colonies fed extracts from G. resinaceum fungus exhibited a 79-fold greater reduction in DWV and a 45,000-fold greater reduction in LSV compared to controls fed only with sugar syrup.

The fungi tested in the US do grow in Britain, but in any case they can be cultured in the laboratory. The researchers at Washington State are considering setting up a non-profit organisation to supply mycelial extracts, together with bee feeders, for people to put out in their gardens to help protect both honey bees and wild bees from viral infections.

This work does not seem to have been picked up by Kirsty Stainton in her recent article in BBKA News referenced above, but I feel that it could be of sufficient importance to stimulate critical discussion and further research.

Scientific Reports is an open-access online journal published by Nature, with a very wide reach. Articles are peer-reviewed with a 56% acceptance rate and stringent standards. This paper has passed those tests, but perhaps some debate and experimentation by beekeepers would help confirm the usefulness and importance of the findings.

Timothy Riggs, RBKA
February, 2019


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  • New Appointments within the National Bee Unit
    14 January 2022
    We are pleased to announce the temporary appointment of Dhonn Atkinson as the National Bee Inspector (NBI) whilst the current NBI Cristina Ruiz is on maternity leave. Dhonn has held a variety of roles across the National Bee Unit and Animal and Plant Health Agency where he held the role of Regional Bee Inspector for the North East of England.

    Following the retirement of Keith Morgan, Colin Pavey, and shortly Frank Gellatly and the temporary promotion of Sandra Gray, we are pleased to confirm the following movements and appointments:-

    Regional Bee Inspector for Western England – Jonathan Axe has been promoted from the role of Seasonal Bee Inspector.

    Regional Bee Inspector for Eastern England - Pete Davies, an experienced manager has moved from the Central England Region.

    Regional Bee Inspector for Central England - John Geden. John joins the National Bee Unit as an experienced bee farmer.

    Regional Bee Inspector for South East – Daniel Etheridge a seasonal bee inspector has been offered a temporary promotion to manage this area.

    Regional Bee Inspector for Wales – Maggie Gill has been promoted from the role of Seasonal Bee Inspector.

    Regional Bee Inspector for North East England – David Bough a seasonal bee inspector has been offered a temporary promotion to manage this area.

    For full up to date details please visit the contacts page
  • Seasonal Bee Inspector (SBI) vacancies
    21 December 2021
    The National Bee Unit currently has a Seasonal Bee Inspector (SBI) vacancy advertised in:

    East England: Norfolk.

    North East England: East Yorkshire

    Mid-South Wales: Swansea, Neath Port Talbot, Rhondda Cynon Taf, Merthyr Tydfil, South Pembrokeshire, West Carmarthenshire

    West England: South East Shropshire, South Staffordshire, North West Worcestershire

    If you are interested in applying for these jobs, full details can be found on Civil Service Jobs

    If you have any questions regarding the position, please contact the Regional Bee Inspector for the area.

    Closing date for application: 16th January 2022
  • Bee Health Advisory Forum - Science Advisor
    08 November 2021
    The Bee Health Advisory Forum brings Defra & Welsh Government policy and stakeholders together to discuss honey bee health issues and is inviting expressions of interest from applicants interested in being Bee Health Advisory Forum Science Advisors. The closing date for applications is Friday 17th December at 17:00.

    Full details about the role can be downloaded here and can be found on the Bee Health Advisory page. Please circulate to prospective advisors or feel free to apply.