Sick Bees Varroa problem – Remedial action for Deformed Wing Virus using OAV

We received a few Emails from folks sharing the news that their Wintering Bees were appearing out the front of the Beehive entrance, with Deformed Wings. Cause = virus – generally caused by Varroa Destructor Mite feeding on Larvae in capped cells.

Here is kiwimana’s reply:
I beelieve some remedial action is required right now because…

…..if the girls are new Bees – it might pay to just open a few cappings in the centre of 1x honey frame near brood to see if they feed, new bees find it difficult to open cappings anyway but if they are emerging with DWV – they may not be able to feed at all.


….if there is DWV…. it means the girls are already at high risk – the reasoning ?
because when DWV is already present, its due to Varroa being inside the cells.

Therefore, the brood is already sick inside the cells, this means sick nurse bees are hatching/emerging – plus their first job is Nursing – so they will spread viruses to the new eggs/larvae
Deformities are caused by the Varroa feeding on the larvae after the cell is capped.

The act of feeding off the larvae by Varroa, leads to transference of viruses which in turn – cause the deformities.
While Varroa are in cells they are also mating vigorously so inevitably new Varroa, emerge with hatching Bees.

Important to share that – Deformed wings are not formed in older already walking worker bees, they will be only housing the viruses in their abdomens – deformities only appear with newly emerging bees.

– we would suggest that you need to treat immediately ! OAV – every 3 days – for 6 weeks.

Why 6 weeks ?

Mainly because your hive is sick.

It will take time for them to recover and your Queen needs to recover also.

So best to assume newer eggs will have viruses already, assume also that emerging varroa are now walking around the hive and hitch-hiking on the nurse bees. While the nurse bees feed the larvae, the Varroa are going into cells and the cycle starts again.

Realistically if you have eggs – its going to be 21 days for them to hatch – its best to assume, they will emerge sick also with viruses.

You really want to get the cover of the OAV in there now,

Benefits ?

OAV – will encourage natural bee cleaning and housekeeping behaviour – with lots of cell-cleaning.

Treating every 3 days will benefit the newer laid eggs which are your new-season bees and you want their cells to be free of Varroa.

So between the 14 to 21 days – you will probably see a large amount of mite-fall as the cells are hatching, you will also see Deformed-wing-bees emerging.

After another 3 weeks – You will expect what outcome ?
….the next hatching of 21 days
– require inspection of Cells there should be no Varroa or minimal
– there should be well-formed Bees emerging
– other deformed wing bees should have died or been removed from the hive

Which means it takes 42 days to recover = 6 weeks

You should see healthy Brood frames and Healthy Queen by week 6.

What Next ?

OAV – treat in 14 days again after inspecting which should reveal:

  • New eggs
  • Improved and fuller laying patterns
  • More capped cells
  • No deformed wing Bees
  • Perhaps Drone laying starting

After This ?

Once you are confident, monitor by oiling your inspection board and checking varroa mite drops weekly.

move to treating fortnightly if you see under 6 mites.

if you see more than 6 mites – treat weekly until levels drop again.

Things you can’t control !

The reality is your colonies are at risk all the time as Foraging is where your girls will obviously pick up varroa and rather sadly is that there may be a person around you, who has bees and is not treating at all !
So on-going treatment is generally going to bee more beneficial.

I hope that you find this of help – I think waiting might not be my thought mainly because I have lost hives when I waited to treat, unfortunately the varroa is such a challenging BEAST now compared to even a couple of years ago.



What is OAV ?

OAV means “Oxalic Acid Vaporisation”

How does it work ?

Vaporization is when there is heat-exchange from the vaporizer tool which ‘burns’ off the oxalic acid crystals which creates a smoke vapour in the hive.
The smoke vapour is made of small particles which are spread around the hive by movement of the Honey Bees. It is unknown the exact action of the particles but scientists surmise that the particles may paralyse the Varroa Destructor Mite which then cannot feed and it dies. The other particles around the hive are then ‘cleaned-up’ by the Bees in their normal behaviour of housekeeping which is all about removing ‘foreign’ ‘things’ from the hive.

It has been a treatment method used in Canada since 2001.

This treatment method has not been identified as causing any resistance to the Varroa Destructor Mite after 17 years of use, it is described as organic due to the oxalic acid crystals are produced from plant concentrates in the brassica plant family.

What is used in the OAV treatment method:

  • Kiwi Vaporizer
  • Oxalic Acid Crystals
  • Battery
  • Charger
  • Cloths
  • Timer
  • Protective gear including Mask and Gloves

Kiwimana uses OAV regularly, with integrated pest management equipment eg: kiwimana meshboard, sugar shake Jars, Drone management frames.
Meshboard used to check mite fall – weekly / 24 or 48 hours
Sugar Shake jar to check mites on walking Bees
Drone management Frames – added in August ready for Spring wax building
OAV is actioned on a fortnightly basis

Treating when Honey frames on ?

Oxalic acid smoke vapour particles do not appear to flavour the honey, the vapour tends to dissipate so is not intensely concentrated in the honey supers – the more boxes on your hive, the weaker the vapours are. The levels of oxalic acid are not assumed to be of harm to humans however, it is advised that Honey testing is recommended.

OAV method does not appear to harm the queen, her laying patterns, walking bees, reproduction of queens, drones, eggs, larvae.

Oxalic Acid crystals are used as a legal treatment method in New Zealand.

Disclaimer: kiwimana do not accept liability for the actions taken by person/persons in the use of the OAV treatment method and the tools used in this treatment method, this treatment method is used at the persons own risk – further No liability is accepted directly or indirectly from its application as conditions of use are outside kiwimana’s control. All safety use advice given when using this treatment method is provided at point of sale.
For point of reference : Material Safety Data Sheet link

Media Credits

7 thoughts on “Sick Bees Varroa problem – Remedial action for Deformed Wing Virus using OAV

  1. Avatar photo
    gmhunternz says:

    OAV method you have set out, I read about on your site last year, I used in June 2017 after finding K wing bees ,white mummies and black mummies in front of the hive, It work out fine you could see the hive recovering each day.

    That hive is still going great, they re Queened them selves in march this year and went into the winter a strong hive with very low mite count.

  2. Avatar photo
    David says:

    High levels of DWV are caused by Varroa transferring virus to developing pupae, not by nurse bees feeding larvae with DWV which I think is what is being suggested in your article. Bees emerging with high levels of DWV are doomed … no amount of OAV (or anything else) can save them.

    If you want to ‘rescue’ a hive with high levels of Varroa and DWV-symptomatic bees you need to simultaneously:

    * hammer the Varroa levels down
    * get rid of the bees (AND BROOD) with high levels of DWV

    and you can do this by doing a shook swarm and treating immediately. Shook swarm, treat and feed syrup for a fortnight. You don’t need to treat for 6 weeks in this scenario as all the mites are phoretic.

    Tough love, but better than a prolonged treatment regime that maintains high virus levels for weeks.


  3. Avatar photo
    Martin Spinks says:

    I have been treating My bench hive with OAV through winter, but have now added Bayvarol strips as can’t get mite numbers below 100/day from the 28 frames. I’ll continue with OAV as well. Interesting that with a dry board below the floor grill, I notice a number of live mites crawling around as well as a lot of dead ones. Maybe the dead ones have been killed by the OA or Bayvarol, and the live ones have been groomed off by the bees, falling through to the base.

    • Avatar photo
      Margaret Groot says:

      Hi Martin,
      The key to varroa levels also includes knowing what is in cells. A bit of a two-fold approach so you can rule out
      contributing factors… It’s a good sign that you are getting high varroa mite drops. OAV is all about regular treating to
      make the environment for the varroa prohibitive for breeding and settling in. The drop means that the
      oxalic acid/synthetic treatment is killing walking and varroa arriving into the hive on foraging/flying bees.
      So first job is efficient killing of arriving varroa so this lessens the ability for varroa to build-up in hive.
      Interestingly : The bees may be picking up varroa while foraging because maybe other beekeepers in your area,
      are not managing their varroa levels well.
      The its about identifying if there is infestation in cells, in cells which are capped – varroa mate and breed.
      So removing caps and checking inside cells is next, as thats where significant problems start.
      Often folks panic when they see large amounts of mite-drops, but it actually means that the treatments are working.
      BUT it is important to have a look inside capped-cells for varroa presence to prove if your treatments are working.
      Remember OAV will need re-application due to its organic nature but it doesn’t mean its not working – its designed
      to kill walking varroa on walking bees – killing walking varroa means good mite drops.

      DON’T panic about high mite drops – bee happy as you are preventing varroa from settling-in in a capped cell.
      You generally have more of a problem is there are varroa breeding in cells… but you can’t tell if you have an
      infestation if haven’t checked in cells. So plan an inspection of the brood frames, use a capping scratcher to
      gently remove caps, choose caps that are sunken or discoloured. You want to see white larvae or developing bees.

      So our advice is to inspect and…
      1. look at your new bees and check they are fully-formed with no deformed wings.
      2. Checking brood (inside capped drone and worker brood) close to the bottom of the frames.

      If you have lots of deformed winged bees, with lots of varroa in cells then you have an “infestation”.
      BUT if your cells are mostly clear and your new bees are nice and fluffy and well-formed then
      your treatments are killing new arriving varroa.

      Note that bee-season is also varroa season. I personally would do the cell checks and then
      decide from there whether your hive has infestation and sickness or merely varroa being
      killed on arrival in the hive.

      Happy to discuss, I am available on 0211752137.
      …it’s the kiwimana buzz…
      PS: we have added your question to our next newsletter
      as others may be experiencing the same problem.

Leave a Reply

Your email address will not be published. Required fields are marked *