VARROA – Treatment Free Beekeepers – Swindon Honeybee Conservation Group – UK
This article was original published – February 2016, by – http://treatmentfreebeekeepers.co.uk/
Ron Hoskins – Swindon Honeybee Conservation Group
Ron Hoskins is 85 years old and has been keeping bees since he was a school boy, the depth of experience he has is incredible.
For the past 20 years Ron has been managing his hives without treatments and has been actively selecting and breeding bees for varroa tolerance. In 2010 he hit the news for producing indestructible bees, but his recent work is even more exciting as his bees are now also immune to Deformed Wing Virus (DWV).
Ron’s breeding programme has resulted in three main mechanisms for varroa tolerance being expressed:
Varroa Sensitive Hygiene (VSH)
VSH bees can detect, most likely by smell, when capped brood have become unhealthy due to the varroa mites. The nurse bees will actively uncap the brood and remove it from the hive, disrupting the mites from reproducing successfully. They do this approximately 48 hours before the bees would emerge as adults at what is known as the “purple eye” stage.
Strong VSH – lots of brood uncapped at the purple eye stage
Evidence for this is found on the varroa insert beneath the screened bottom board.
When the bees remove the partially developed larvae they usually grab and pull on the antennae which are nearest the top of the cell. These are translucent in colour because they are only partially developed, and often break off and drop to the floor. They show up most easily on a dark coloured background.
VSH appears to be a fairly common trait, although most bees do not express it to a high degree, and it should be possible to select for in most circumstances. VSH suppresses mite reproduction and helps keep mite levels low.
Ron’s bees also have grooming behaviours where they will help each other to groom and bite mites. Around 20% of the adult mites in the hive at any one time will be phoretic (meaning they are wandering around outside of brood cells). These mites like to hitch a ride on an adult bee and will also wedge themselves into the gap between thorax and abdomen to bite and feed from the bee. The bees cannot groom these mites themselves.
Ron, however, has a snippet of really amazing video footage. A bee with a mite attached does a peculiar waggle dance. It catches the attention of another bee, then bends its body to open up and expose the mite. The attendant bee darts in and bites the mite. It isn’t seen in the video, but presumably the mite is injured and falls from the bee.
Mites that have been bitten show obvious damage when viewed under magnification – legs will be missing or damaged, and the back and body will often show dents and puncture wounds. Particularly interesting is when injured, but still living, mites fall to the floor. These injuries can only have occurred while the mite was alive, and is not post-mortem damage from scavengers.
Observing this type of damage – and particularly finding the ratio of damaged to undamaged adult mites on the drop board – gives an indication of the strength of this behaviour in a given hive. You need a good hand lens (x7 magnification) with a light to see this easily, or a dissecting microscope back in the bee house.
Biting behaviour reduces mite numbers in the hives directly, reducing the direct damage on bees.
Message from Ron:
* The lens I use is a x7 Visibledust Sensor Loupe. It has a 38mm dia lens.
* The microscope is a x10 to x40 Stereo/Zoom/Dissecting ‘scope. (no need to be more powerful) Mine is fitted with Digital camera and program to link with PC.
TypeB Deformed Wing Virus (DWV) – Viral resistance
Viruses in bees are rather complex, and they operate and interact differently from viruses in us humans. Bees have a very minimal immune system so can’t fight off a virus as we do. Instead, all bees have a certain amount of viruses in their system at all times. Most of these are totally benign and don’t harm the bees.
This is because the viruses have co-evolved to live along side the bees without killing them. If a virus gets to be sufficiently virulent that it weakens or kills the bees or the whole colony then they die along with their host. In this way virus usually evolve to become less virulent.
In the case of DWV the varroa mites disrupted the natural equilibrium between the bees and their viruses and a new virulent strain of DWV (known as TypeA) was rapidly spread. DWV is often the final straw that wipes out hives, as the bees are so weakened that they simply cannot support themselves any more. Overtime we expect less virulent strains to take over, and this is what Ron has seen in his bees.
He has had his bees tested and they are carrying a strain of DWV known as TypeB. TypeB has no symptoms and bees can live quite happily with high levels of the virus in their systems. In addition, TypeB appears to prevent reinfection with the virulent TypeA, conferring immunity to the more dangerous form. These results have been confirmed and published in Nature.
This result in particular is very exciting, as it is a previously unrecognised mechanism for disease resistance in bees and offers the potential for “immunising” apiaries by importing the TypeB strain. There is a lot of work still to be done before this type of approach is confirmed to work, but it has the potential to be of huge benefit to all beekeepers if it can be successfully disseminated.
Ron’s methods are laborious and time consuming. He takes mite drop counts from his hives on 48 hour intervals, and classifies them under magnification for bite damage and evidence of dropped antennae. He has tried to recruit beekeepers in his local area to his project but has had very limited uptake – probably in part due to his requirements for frequent microscopy work which is beyond the time availability of most beekeepers.
I think it likely that without his intensive monitoring his line of highly resistant bees would be diluted over a short time through mating with non-tolerant drones, and through less rigorous selection of parent hives. That said the subsequent generations would still be a lot more tolerant than most of the bees TF beekeepers end up using to start their operations.
The next stage seems to me to require dissemination of his bees amongst other treatment free beekeepers to see how they perform away from his carefully controlled conditions. For example his bees could be used to introduce the various traits and the TypeB virus to other beekeeper’s breeding programmes.
Further reading link to Scientific study