Varroa control in the bee shed

The last colonies to be treated for Varroa this late summer (early autumn?) are those in the bee shed. These have had consistently low levels of mites all season … levels were so low that we uncapped two full frames of drone brood (individually) from one of them in June without finding a single mite.

Nevertheless, because …

  • mite levels can rise dramatically from low levels if not tackled – for example, see the modelled expansion of the Varroa population.
  • reduced queen laying at this time of year means mites have fewer pupae to target resulting in elevated infestation levels in the critical winter bees (and why this is important). In recent sampling of pupae we’ve seen an increase in the number of mites in capped in cells which we assume is due to this.
  • we need to keep these colonies with the lowest practical mite levels.

… they were treated anyway. I’m reasonably confident that sublimated oxalic acid (which is the active ingredient in Api-Bioxal) does little or no harm to the colony, and am sure that the mite reduction is always beneficial. I’d therefore prefer to treat than regret not treating at a later stage in the winter or early next season.

Expose the bees to the vapour … not the beekeeper

There’s nothing fundamentally different about treating colonies in the bee shed than those outside. Using a Sublimox vaporiser is very straightforward. However, two points need a little more care than normal.

The first is the sealing of the colony. To be effective the vapour must be evenly spread throughout the hive. Because of the ‘tunnel-like’ entrances there are more potential gaps from which the vapour can escape. I therefore do my best to push the hive tightly against the entrance tunnel after sealing the latter with a block of foam. The floors on these hives were built by Pete Little and have a commendably leakproof Varroa tray, making them ideal for sealing the open mesh floor. As an aside, don’t try squirting the vapour in from the entrance … direct inspection through the Perspex crownboard suggests that (at least in my setup) the vapour only poorly permeates the hive if administered like this. Been there, done that. The goal is to get the oxalic acid crystals spread evenly and thoroughly throughout the hive, ensuring maximum exposure to the mites, and maximising the duration of activity against,

The second point relates to the ‘leakiness’ of the hive and the fact that it’s in an enclosed space (the shed). There’s therefore no chance of standing upwind and allowing escaping vapour to drift away safely. Operator protection is particularly important as the shed is liable to fill with oxalic acid vapour. Eye protection and a suitable particle mask rated for acid particulates are essential. It’s a case of “lighting the blue touch paper and retiring to a safe distance”. With a Sublimox you can simply invert the machine – into the ‘delivery’ mode – and leave it hanging out of a hole through the sidewall of the floor (see photo above right). There’s a couple of seconds before sublimation starts which you can use to step out into the fresh air, only returning once the vapour has cleared.

Finally, if you run your vaporiser off a generator it should also be left outside the shed. Don’t gas the bees when you’re gassing the bees 😉

Plus a recalcitrant swarm that’s on it’s second round of treatment due to the stubbornly high mite levels. Grrrr.

4 thoughts on “Varroa control in the bee shed

  1. Bridget

    We also have low varroa in our bee shed and especially this year. When we lost a colony in the spring SASA tested a sample for nosema but we had all clear for varroa as well. In June we culled some drone brood and that was clear. Treated with Api Bioxal 2 weeks ago and no drop so far. I remember that last autum there was very little drop though we still did the OA trickle in Jan. I’m wondering whether we will do the trickle this year.

    1. David Post author

      Hi Bridget
      I think low Varroa is at least partially due to the poor mid-season nectar flows here which gave an enforced brood break to some colonies when the Q stopped laying. I also had some queens take ages to mate. Limited amounts of honey, but low mite counts …
      I will treat mid-winter. I always do. I use sublimation exclusively now though and appreciate that there is evidence that trickling OA might be more detrimental to the colony.
      The really good things about the shed are the colony build up early season and being able to inspect whatever the weather … I wish I’d built a larger one.
      Best Wishes

      1. Bridget

        Yes we had an obvious, even to us, 10 day break in August when the weather was poor though the heather nectar has been excellent. However our colonies were not quite strong enough to take full advantage of it. however last year we had a good crop whereas those around us did not so swings and roundabouts. I expect we will trickle in January. We don’t have anyone in the association that uses sublimation, most of us too new to beekeeping with just a few hives, so no one to give us a demonstration of how it works. The talk by the prof from Sussex at the SBA conference was all in favour and had me nearly convinced enough to rush out and buy one for the association!

        1. David Post author

          I think an association purchase of a sublimation makes a lot of sense. It should mean a good one can be purchased and it’s justified by the limited use any one individual makes of it. If you are going to buy one it’s worth considering the range of hive types used – the Varrox-type need sliding into the entrance (usually), whereas the Sublimox-type can simply be inserted through a 7mm hole in the side of the floor. Of course, it might be a bit more tricky to coordinate in an area with a low density of beekeepers.

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