Sublime sublimation

Sublimox vaporiser

Sublimox vaporiser …

Sublimation is the conversion of a substance in the solid phase into the gas phase without going via the intermediate liquid phase. With suitable heating oxalic acid (OA) powder can be converted into a vapour which, when spread through the hive, provides a quick and effective way to reduce the mite levels … hence it’s often referred to as oxalic acid vaporisation (or vaporization … if you search the web on this topic you’ll find at least four variant spellings). With too much heating OA decomposes to formic acid and carbon monoxide, so the temperature of the vaporiser is critical to generate the optimal cloud of OA vapour (or vapor!). I’ve been using a Sublimox vaporiser this season with good results and provide a description of the machine and its use here.

Vaporisation vs dribbling

Most beekeepers are familiar with midwinter treatment with 3.2% OA solution (in syrup), applied by ‘dribbling‘ 5ml per seam across the clustered colony. Under these conditions the colony needs to be broodless as a) it’s not effective against mites in capped cells and b) the OA dissolved in syrup is toxic to brood. It’s also reported that the ingested OA may be suppress subsequent brood rearing, at precisely the time the colony should be getting started for the upcoming season. Vaporisation or sublimation avoids this toxicity … the OA is introduced to the hive as a gas which permeates the entire colony, recrystallising as tiny crystals on all surfaces – bees, comb, internal walls etc. Studies of OA vaporisation has shown it is ~95% effective in reducing phoretic mite numbers. I recommend you read the extensive coverage by Randy Oliver @ Scientific Beekeeping who covers efficacy, mode of action and toxicity (though I’ll return to this last bit later).

Sublimox vaporiser

This is an active vaporiser which blows a jet of vaporised OA through a small (8mm) nozzle. The machine consists of a handle, a box of electrickery (which I’ve not opened) and a heating pan surrounded with a safety guard. The machine is rated at 230V AC and 300W so you need either a car battery and inverter or a suitable generator (which is what I use). The vaporiser is simplicity itself to use. One gram of OA powder is placed into a small plastic ‘cup’, the preheated vaporiser is inverted and the ‘cup’ engaged with the heating pan. The nozzle is pushed through a hole in the hive body and the vaporiser is inverted again (so it’s now the correct way up – see the top photo on this page). The OA drops into the heating cup, immediately vaporises and is blown through the nozzle into the hive. It takes 40-50 seconds to use all the OA, at which point you can move on to the next hive.

This video shows the effect of dropping a few millilitres of water into the heating pan … it’s almost exactly the same when using OA, but less likely to cover my camera with a fine dusting of OA crystals 😉

Preparing the hive

Entrance block

Entrance block …

To fill the hive with vaporised OA it’s important that as little as possible leaks out during the short period of treatment. I use a Correx Varroa tray underneath the open mesh floor. In addition, the kewl floors I use are easy to block using a simple L-shaped piece of softwood (I use these when transporting hives; when screwed onto the front of the floor there’s no danger of bees escaping). Part of the beauty of OA vaporisation is that the hive does not even need to be opened. I’ve drilled 9mm holes just above the open mesh floor level, through either the side or back of my floors. This is a better location to insert the nozzle of the Sublimox as there’s space under the frames to allow the gas to spread evenly and quickly throughout the hive. This is easier than the alternatives of using an eke with a suitable hole in it, or drilling through the side wall of the brood box (this is too close to the frames and you get poor spread of the gas – I’ve tried this on hives with a perspex crown board and it’s very obvious).

With a standard floor you could use a simple entrance block with a suitable hole in it. The nozzle gets hot … keep it away from poly hives or nucs! I treat my Everynuc poly nucs directly through the (cavernous) front entrance which I block using a thick piece of wood with a 9mm hole through the middle.

Preparing the beekeeper

OA vapour is pretty unpleasant and causes significant irritation to the eyes and lungs if exposed. Take care. You will need suitable eye protection and a mask of some sort. I use standard (and very inexpensive) safety goggles and a 3M dust/mist mask. You should also wear gloves when handling OA. It’s also wise to stand upwind of colonies being treated and to take care not to breath in any OA vapour that leaks out of gaps in the hive.

In use

I’ve treated four swarms this year using OA vaporisation. Three had very low mite levels, but the small churchyard swarm dropped several hundred mites in the 2-3 days following treatment. I don’t routinely count the mite drop on each day post treatment (I have a life) but have noticed it can increase over the first 2-3 days and then tails off over the following week or so. In large scale studies in Europe 95% efficacy was reported with mite drop continuing for up to a fortnight. There are a number of useful references on the Scientific Beekeeping site if you want to follow this up further.

I’ve also used OA vaporisation on almost all my colonies this autumn, instead of Apiguard treatment. If the colony has sealed brood the usual estimate is that at least 80% of the mites are occupying capped cells. These mites are unaffected by OA vaporisation (until they emerge) and it is therefore necessary to perform repeat treatments. Taking account of the life cycle of the mite and empirical measurements made by Hivemaker reported on the Beekeeping Forum, three treatments at five day intervals are required to have the maximum effect. Ideally this should be on a day or at a time when most of the colony is ‘at home’ … though the crystallised OA continues to be effective for several days after initial treatment. Fortunately, OA vaporisation has little or no effect on the queen, unlike many other mite treatments. The colony gets mildly agitated during treatment but calms down again within minutes and resumes foraging. In the colonies I’ve looked at after treatment there appears to be no gap in egg laying (I’ve also treated casts with virgin queens that have gone on to mate successfully). This is ideal for the autumn treatment when you want the colony to raise as many bees for overwintering as possible. In contrast, Apiguard regularly stops the queen from laying.

And finally …

There are other OA vaporisers made, and instructions on the web for a variety of DIY items – some looking more dangerous (to the operator, not the mite) than others. The majority of these are passive vaporisers, in which the OA is placed in a cool heating pan which is then placed on the floor of the colony and heated up. I’ve not used this type. They have the advantage of being less expensive and only require a 12V supply. However, they are slower to use as the pan takes longer to heat up and then needs to be cooled in a bucket of water between applications. They are also incompatible with the kewl floors I use and I presume – depending on how hot they get – with poly hives and nucs. I think the efficacy of the two types is supposed to be broadly similar.

I listened to Bob Smith talk at the MSWCC conference last week on shook swarms. I sat there thinking that a shook swarm followed shortly afterwards by a single shot of OA vapour would give a colony a really good opportunity to build up well, free of pathogens that have accumulated in the comb and free of the majority of phoretic mites and their viral payload.


The Sublimox vaporiser is not inexpensive. It costs about €380 from Icko Apiculture. This is a lot, but is about the same as three 3kg tubs of Apiguard (C. Wynn Jones list this at £87 a tub at the time of writing) which is enough to treat 90 colonies with two treatments per colony. In contrast, OA dihydrate powder in bulk (not from Thorne’s) is about £20 for 5kg … enough for 1250 colonies (assuming 4 treatments per colony – 3 doses in the autumn and one midwinter). For beekeeping associations, particularly those with large shared apiaries when treatments could and should – see a later post – be coordinated, it might be a very good investment.


17 thoughts on “Sublime sublimation

  1. David

    Thanks David, I’d been looking at vaporisation, for a while and never come to a conclusion. The passive vaporisers are quite a bit cheaper but this looks much easier and also more practical. I like the fact you can access via a small hole. Any idea how long they should last in normal usage?

    300W, just wondering if I could do with a battery and an inverter – although the generator looks good (and multi-purpose).

    Thanks again, I see Icko have sold out, maybe you’ve caused a run on them!

    1. David Post author

      In fairness … I’ve not used one of the passive vaporisers so can’t make proper comparisons. However, most need to cool the ‘pan’ before adding the OA, so are likely to take significantly longer per hive. The main reason I’ve not bothered with them is the floors/entrances that I routinely use which aren’t really compatible, though I’m aware some have bodged workable solutions.

      I’ve no idea how long the Sublimox will last. It’s provided in a neat little carry box and gets washed out properly after use. It’s well made. It’s also used by some of the commercials I know, where value for money must be important. Considering the price I’m hoping it’ll last a very long time 😉

      A battery/inverter combo should work fine. I chose the genny on the advice of someone who had used one. I also had an apiary unreachable by car and a battery/inverter weighs quite a bit more than the generator.

      I’d also noted that Icko had sold out … they delivered mine very quickly. Good service.


      1. David

        Thanks, that’s helpful to know that the commercial guys use, probably means it would last forever with my smaller number!

        I’m lucky with access to my hives, they are all car accessible or I can run an extension lead from the house. I did see that generator was light though, the (slightly cheaper) Toolstation version was about twice the weight.

        It is very tempting ….

        1. David

          That’s it – I bit the bullet and bought one from Italy. I should have done it when the pound was worth a lot more.

          It’s just arrived, so now to work out the best way to avoid the toffee effects of Apibioxal.

          A question if I can, did you have to bend the tube that comes out of the front? Mine runs down much more than yours rather than straight out of the front. It may need a little easing …

          1. David Post author

            No tube bending needed on mine … worked ‘out of the box’. The €/£ hurts at the moment. As does the $/£. Blame Brexit. Nevertheless … it’s well made and should last, so you’ll soon forget the cost. Have fun 😉

          2. David

            Thanks David, had time to give it a little persuasion this morning and now going in the right direction. Initial tests with water and it works well. It looks like a well made piece of kit.

            Thanks for the articles, they gave me the confidence to order it.

            So, now to get my gas mask thing put together and I’m away!


          3. David Post author

            Well done … perhaps I should ask Icko for a percentage of future sales? The only issue I’ve had with the Sublimox is the two little grub screws holding the cage onto the bottom of the pan can work loose. Give them an occasional tighten (or perhaps a dab of that Loctite stuff that holds screws firmly) and all should be well.

            Varroa be gone!

  2. Steve

    Hi David,
    Like the blog, a bit late to this topic, can you tell be if the Sublimox vaporiser ejects the gas through expansion or is driven out using a fan, I have a temp controlled hot plate vaporiser but a change of entrance and some poly hives make it tricky to use, hence my interest in blowing vapor into the hive.

    1. David Post author

      Hi Steve
      The Sublimox expels the gas by expansion. The plastic ‘cups’ have a neat rubber O ring around the edge, forming a reasonable seal with the heated chamber. Upon inversion the OA is dropped directly into the hot chamber and immediately sublimes, the expanding gas being forced out of the nozzle. It’s remarkably effective, probably taking less than 30 seconds per hive. The gas is forced out pretty forcefully so readily gets to every corner of the hive. I’ve yet to find a hive that I can’t bodge some sort of simple way of squirting the gas in – on all my standard hives I’ve drilled a suitable hole through the edge lip of the floor, on poly nucs I simply hold a piece of wood across the entrance with the Sublimox nozzle poked through a hole. The only think to be aware of is that the nozzle gets hot so needs to be kept away from direct contact with either poly hives, or foam stuffed into the hive entrance (I learned the latter the hard way 😉 ).
      I’ve seen one or two neat solutions to using the passive vaporisers (like the Varrox) through the OMF … including most recently this post:

  3. Andy

    This may be of value to some people who are trying to make a vaporizer similar to the Sublimox. While researching temperatures on average you will find that 185 C is the advised maximum working temperature for oxalic. If you look at Davids video there is no way the device will work like that at 185 C.In order for it to work like that it needs to be over 230 C.I finally got a friend to check the temperature of his Sublimox. Its resting temperature is between 260 and 275 C.It would appear that all the oxalic is burnt off in about 30 seconds so the fear of the formic at higher temperatures isn’t an issue.

    1. David Post author

      Thanks Andy
      Very useful for those attempting DIY I would think.
      I should add that I can’t provide any advice on build your own for one of these bits of kit. Firstly, I’ve invested in a Sublimox and secondly, they are way beyond my capabilities.

    1. David Post author

      OxaVap sell a model called the ProVap 110 which looks like a pretty similar product. It has a graphical display of temperature which the Sublimox lacks (but can’t imagine needing). From reading the instructions – which is as close as I’ve got to the machine (i.e. don’t take this as an endorsement, I’ve no idea how well the ProVap 110 works, but I’m certain how good the Sublimox is) – it appears to need cleaning in between hive treatments which is different from the Sublimox. ‘snl’ who is associated with OxaVap is a regular poster on the Beesource forums.

  4. James Orme

    I’m assembling all the kit needed to treat my colonies next month.
    Do you have an earth spike for the generator?

    1. David Post author

      Nope … I wear wellies.
      Seriously, I do use an RCD and I do feel nervous using the genny in the rain, but I’ve currently (pun intended) had no problems.

  5. Phil

    Hi David,
    With your experience using the Sublimox Vaporiser would you still recommend purchasing one as I’m travelling to France shortly and hoping to pick one up ?

    1. David Post author

      In a heartbeat … or a little longer after I’d managed to save up for one 😉

      Seriously, I think it depends upon the number of colonies you’re wanting to treat. They aren’t worth it for one or two. However, I routinely have a dozen and sometimes double that. The Sublimox is also compatible with the hives I use – my Kewl floors are adapted with a suitable-sized hole and I treat my poly hives using a similarly adapted eke. I don’t have to worry about melting the poly or even opening most of the colonies. Finally, although I’ve not used a Varrox-type passive pan vaporiser, I think the Sublimox offers a little more control over when and where the vapour is delivered (and a lot more than the vmVaporiser). You only invert the machine (which starts the process) once the nozzle is inserted into the sealed hive and, because the heating is near instantaneous, after waiting a predetermined 30+ seconds almost no additional vapour escapes. It’s still necessary to use PPE of course, but I feel completely confident about restricting the risk of exposure to the absolute minimum.

      The only issue I’ve had with the machine is needing replacement rubber seals which I sourced from someone on the BKF.


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