Beehive has Varroa Destructor mite – why can’t I kill them ?

Bee harmed by the paracitic varroa destructor mite

Honey bees harmed with sickness disease caused by paracitic varroa destructor mite in their beehive.


” 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.”

Varroa Question from Martin NZ

Hi Martin,

When you are getting high mite drops on inspection boards – it is a great tool to check varroa presence but – also knowing what is in cells is even more important.

Treating : Oxalic acid vaporisation uses oxalic acid crystals which is made from brassica plants so is an organic treatment which will need regular re-application due to its organic nature and it dissipates. The bees also remove the vapour particles from the hive. Personally I would never recommend using two different treatments at the same time – by doing this you may over-dose your colony.

Note: if using synthetic treatments – you may need to apply a full cycle with recommendation to separate/remove honey frames from the hive as instructed. Any frames where bees store nectar should only be left for the bees not to be extracted for human consumption.

But I think a two-part approach is required so you can rule out any contributing factors… to start it’s a really good sign that you are getting varroa mite drops while treating – but make sure you are oiling your inspection board.

…. if you oil an inspection board and place under the mesh in your base board you will catch falling mites, the oil will stop them from escaping, counting these will give you an indication of varroa mite presence – anything over 6 on the whole inspection board, is concerning in our view. Inspection board is one part of the monitoring.

The fact that the varroa are still moving around may mean possibly you haven’t oiled your inspection board ? with the falling varroa more likely removed off the bees by grooming bees, so the varroa may be in the process of dying. But when you say its on-going heavy mite drops, it may be from varroa emerging with hatching bees.

  • OAV is all about regular treating to make the environment for the varroa prohibitive for breeding and settling in.

The drop means, in actual fact, or shows that the oxalic acid/synthetic treatment is killing varroa on flying/walking bees who arrive back to the hive with varroa after foraging.

We find often folks panic when they see large amounts of mite-drops, but it actually means that the treatments are working.

Oiled Inspection Board – note a pseudoscorpian

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.

Generally you have more of a problem if there are varroa breeding in cells… but you can’t tell if you have an “infestation” – if you haven’t checked inside cells. So the other part of checking for varroa is cell-checks.

  • So plan an inspection of the brood frames

Cell Check

Handy Hint: use a capping scratcher to remove caps on drone cells or to pull out larvae as shown below.

Varroa are usually found right in the bottom of the cell – beekeeper friend says, ” I feed them to my chooks


So you have done your mite-drop checks now the next step is about identifying if there is infestation in cells. Reason is that, it is in the cells which are capped – that is the ideal sealed space where varroa mate and breed.

….. if you find varroa in cells, it means that they have been able to settle in, probably over 5 weeks. Inside the cells, they mate and lay, grow, develop by feeding off the larvae. They feed on the “fat” cells under the abdomen (not feeding on the pharyngeal/blood of a bee). The paracitic nature of varroa means that through that feeding process they transfer disease – so this means that they have been there for over the whole of the drone developmental growth cycle which is over 23 days which is why they are not developing properly. Once emerging with the hatching drone, they (the varroa) toddle off to another cell which has another larvae and so it goes on…..

  • So removing caps / cells and looking inside cells is next, as varroa in cells is where significant problems start.

By removing cappings, you can see if varroa are present. This photo shows varroa in drones cells that were produced from a specifically designed “drone frame” which is placed in the hive in Spring to catch new-season comb building and drone laying in one frame.

The method is to place it in the hive as Spring brood laying starts, it has no foundation so the bees draw the comb into large cells, which the queen will dutifully lay drones in.

The beekeeper then cuts out the drone brood and inspects inside cells.

Using capping-scratcher to remove drone comb on bottom corner of frame

Other factors ?

Interestingly : The bees may be picking up varroa while foraging because maybe other beekeepers in your area,
who are not managing their varroa levels well ? (or not at all)


Varroa presence starts from when a varroa jumps, yes jumps ! …on to a foraging bee. The varroa has probably travelled in on a bee which departed from an infested hive then ended up on a flower your bee was foraging on.

So our advice while inspecting …
1. Observe : Look at your new bees and check they are fully-formed with no deformed wings.
2. Cell Checks : 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 clear of varroa and/or your new bees are nice and fluffy and well-formed then
your treatments are killing new arriving varroa.

Note: If you are using synthetic treatment – you should not have to use another until Autumn.

Varroa Infestation in cells would require immediate treatment – if using Oxalic Acid Vapourisation (OAV) – treat with a full head of oxalic acid crystals, once every three days over four weeks at least – then inspect newer capped cells – if varroa still present in cells continue for another four weeks.

Important note: the more hive-boxes on your beehive the more oxalic crystals you will need – along WITH more regular applications. APPROXIMATELY A 1/4 TEASPOON FOR EACH HIVE BOX per treatment application. ( 5 BOXES = ONE AND A HALF TEASPOON.)

  • By then you should – after 8 weeks – start to see healthy well-formed bees hatching/walking. Plus do some more cell checks as well – if you find some more varroa inside cells – you could vaporise once a week for four more weeks.

Going forward

If you continue to use organic OAV you must monitor. Hopefully start a regular routine, of treating once a fortnight to keep knocking back arriving varroa.

We have used oxalic acid / OAV year-round, we have found no harm to our queen, eggs, larvae or walking bees – we have found that the honey does not appear to be affected by vapours but if you are concerned and want to check you could go to a laboratory to get it tested. Interestingly oxalic acid is found in Honey naturally.

Happy to discuss, I am available on 0211 752 137.

Regards,
Margaret
…it’s the kiwimana buzz…

love this bee, loving the dandelion


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