Tag Archives: sublimation


There’s a saying that goes something like “Ask three beekeepers an opinion on … and you’ll get five answers”. And if it isn’t a saying, then it should be. Have a look at the online forums and you’ll see numerous threads with multiple – often wildly contradictory – answers. This can be a problem for experienced beekeepers and is a total nightmare for new beekeepers.

Inevitably, beekeeping is an inexact science. There are too many variables to be dogmatic about things – the weather, colony strength, available forage, parasite levels, time, beekeeping ability etc. 

Compatibility, standardisation and efficiency 

However, one thing that most beekeepers should agree on is that compatibility of equipment is important. For efficiency, your equipment needs to be compatible e.g. using a roof that fits any of your hives. Without compatibility you will inevitably experience the frustration of trying to make incompatible equipment ‘fit’ together, or have to make repeated trips to the apiary with the correct kit.

Been there, done that 🙁

Compatibility is best achieved by standardisation i.e. all hives are of the same size and design, built to an agreed specification or standard, ideally by a single manufacturer. I suggest ‘single manufacturer’ as some don’t adhere to the standards as closely as others. Unless you are, and intend to stay, a single hive owner (and there are very good reasons why you shouldn’t) this is an ideal that is rarely achieved.

If you have more than one apiary you’re likely to be moving hives between them. Again, compatibility is important. Finally, if you are being mentored, acting as a mentor to others or intending to sell nucleus colonies, it helps if your hive equipment is compatible with others.

This compatibility starts with the frame size – and therefore defines the brood/super dimensions – and the frame spacing (e.g. Hoffman/Manley), but extends to whether the hives are bottom or top bee space, the types of floors, entrance blocks, clearer boards, split or division boards, feeders etc. 

Which hive?

We’re spoilt for choice in the UK … literally.

Compare the hive types sold by some of the largest suppliers of beekeeping equipment in the UK and USA e.g. Thorne’s and Dadant. Thorne’s list about eight removable-frame hives (National, WBC, Langstroth, Commercial, Dadant, Smith, Rose and Dartington). Dadant list just one (Langstroth, albeit in 8 or 10 frame widths). I know that some hives use the same frame sizes, but have also simplified things by ignoring the range of frame depths offered – 14×12’s, shallows, mediums, deeps etc. In this post I’m only really concerned with box compatibility.

No wonder many starting beekeeping ask “Which hive should I buy?”. They’re probably advised to get whatever is in use locally, often Nationals, but increasingly Langstroths in some places or Smiths in parts of Scotland. The recommendation to start with whatever is used locally is both logical and pragmatic. The beginner is likely to have to source a nucleus colony to start with and (hopefully) this will have been purchased locally, from a more experienced beekeeper (their mentor?) with gentle bees of known provenance, adapted to the local climate and inspected before purchase.

In the overall scheme of things I don’t think the choice of hive type is particularly important. None are inherently better than others, though a few are perhaps worse. The bees, Apis mellifera, are the same and certainly don’t care. Far more important is that the equipment acquired is compatible – with what is already owned, with what might be purchased, built or inherited in the future, and with what others use.

Running out of kit

A universal truth about beekeeping is that, sooner or later, you’ll run out of equipment. For beginners it’s during their first swarm season when they suddenly find they need a complete additional hive to undertake the classic Pagden ‘artificial swarm’ method. Alternatively, or perhaps simultaneously, they capture a swarm and have to house that. It’s not unusual for all this to happen in the same week of the same month of the first year of beekeeping.

It can be a little chaotic 🙂

Gaffer tape apiary

Gaffer tape apiary …

There are two or three obvious ways to reduce the equipment crisis. Firstly, use a version of the vertical split rather than a Pagden artificial swarm, thereby reducing the need for an additional floor and roof for starters. Secondly, bodge a solution … use stacked supers as a makeshift broodbox, build roofs out of Correx (abandoned For Sale signs should always be repurposed) or use an upturned plant tray or piece of polythene-covered plywood. Finally, borrow suitable kit from a friendly local beekeeper … which brings us back to compatibility again.

Don’t for a moment think that a dozen colonies and a decade’s experience stops a beekeeper running out of equipment. A couple of years ago we had a bumper summer and I ran out of supers. Most colonies had 2-3 supers on already and there seemed to be no end in sight to the nectar flow. It was fantastic. A generous friend loaned me a dozen supers to buy me enough time to remove the first fully capped supers, extract the honey and recycle the boxes. Without this act of generosity – only possible as my friend was downsizing – my hives would have become packed with nectar and the colonies might have swarmed.


It’s at these times that equipment compatibility becomes paramount. I could borrow and use those supers as my friend also ran Nationals. The beginner can of course borrow any type of kit, but if the artificially swarmed colony needs to subsequently be united with the original box then it’s much easier if the equipment is compatible (note the thin shim in use in the picture below, between the incompatible poly boxes on top and standard cedars). As it turned out, the supers I borrowed weren’t 100% compatible as my friend used top bee space whereas mine were bottom bee space … the bees and I coped.

This need to mix’n’match equipment happens every season. You might want to move frames about to boost particular colonies, to mix frames removed from several strong colonies to make up nucs for overwintering, to unite nucleus colonies after using the newly mated queen from one of them, or merge two very uneven strength colonies for overwintering. It even happens when trying to efficiently ‘use up’ two- or three-frame nucs used for queen mating at the end of the season – it’s far easier to simply drop these into full-size hives than do the same thing with brood and bees from mini-nucs.

Uniting with newspaper ...

Uniting with newspaper …

Not only the big box items

Equipment standardisation and compatibility also extends to things other than frames and boxes. There’s a host of other items where it’s beneficial to have one type only, and for that type to be compatible with your other equipment. Floors are a good example; if they’re all made to the same design and dimensions then the removable Correx Varroa trays, the entrance reducers and the travel screens/entrance blocks are perfectly interchangeable. Both crownboards and roofs should also be broadly standardised and compatible. For example, all my colonies have year-round insulation in the crownboard and all the roofs are uninsulated. I previously had some insulated roofs and some uninsulated crownboards. Inevitably, moving or uniting hives resulted in the odd colony lacking insulation altogether. D’oh!

Pragmatic rationalisation

I’ve slowly achieved a reasonable level of standardisation and compatibility across my apiaries. I’m hoping that this will be improved further in 2017. After using a range of hives – purchased, borrowed and homemade, I’m settling on:

  • Standard depth, bottom bee space, Nationals in cedar or poly but – critically – these boxes must be interchangeable. To this end I’m using standard cedar broods and supers, or Swienty poly equivalents. These have the same external dimensions (18″/46cm), so can be stacked as required, and the interface between boxes is completely flat.
  • Just two floor designs. One has a fully sealed Varroa tray – built by Pete Little – and is used exclusively in the bee shed. The entrance reducer is fitted permanently to these floors. The second type are the so-called ‘kewl’ floors with a Dartington-inspired underfloor entrance. All my kewl floors are homemade. Despite this (and my amateur DIY skills), they take the same size Correx Varroa tray, all have holes drilled in the correct places to a) attach luggage scales for winter ‘hefting’, and b) deliver vaporised miticides. In addition, all take the same size and design entrance block for transport or other operations when the entrance needs to be sealed (vaporisation, vertical splits or Bailey comb changes).
  • Roofs are all uninsulated, interchangeable and either standard wood/metal or simple sheets of folded Correx. They serve no other purpose than weatherporoofing. I gave away all my insulated roofs when I moved North.
  • All crownboards are insulated, either with inbuilt Kingspan blocks or by the addition of an 18″ square block on top. None have feeder holes. Almost all are reversible and I’ve got ekes to achieve the same separation when I need space to feed fondant.
  • All nucleus hives are Thorne’s Everynucs. This design has a removable floor, so two bodies can be stacked for uniting.

But … if I were to start again from scratch I’d probably use Langstroths. I use Nationals because I’ve invested in Nationals, not because I think they’re inherently better.

Exceptions to the rule

Or compromises …

  • All of my bait hives are MB/Paradise poly Nationals (or stacked supers from the same manufacturer). All have simple Correx floors and roofs, or those supplied at purchase. Almost none of these items – floors, boxes or roofs – are readily compatible with production hives. This poly hive design has an infuriating lip/overhang that makes them incompatible with standard National equipment (see images above). Bait hives tend to get lugged about a bit more than production hives so their low weight is a bonus. My continued use of these hives is a perfect example of meanness and generosity … I’m too mean to get rid of them and I’m too generous to palm them off on an unsuspecting beginner.
  • My Everynucs are not directly (i.e. box to box) compatible with National hives though of course the frames are. I therefore can’t stack nucs onto standard brood boxes – for uniting, for overwintering or for certain types of queen rearing operations. This is a compromise I have to make due to a) the finances and time I have invested in these poly nucs, and b) their overall benefits and quality, both of which I remain convinced about. I have a few lovely cedar nuc boxes built by Pete Little that can be used for the queenright queen rearing method developed by Steve Rose if needed.
  • I have a few Paynes 8-frame nuc boxes used solely to capture swarms (or for dire emergencies). These are lightweight boxes with flimsy lids and no removable floor … ideal for use in one hand at the top of a ladder.
Paynes nuc box ...

Paynes nuc box …

Outstanding improvements to compatibility

Outstanding as in ‘not yet achieved’ that is. Sorry if you were expecting some brilliant insights here 😉 Regular readers are unlikely to have been mislead.

The entrance holes through the bee shed wall are of two sizes and the larger ones will be replaced (reduced) at some point. When I first built them I overestimated the size needed. The oversized entrances are too big for a weak colony to defend and the different sizes means I need two types of foam entrance blocks when vaporising.

Secondly, I have to decide on a standard way to block/reduce the entrance of the poly Everynucs. I’ve previously used a hotchpotch collection of wire mesh, foam or wooden blocks. The entrance on these nucs is ridiculously large and I’ve been dabbling with a few simple designs over the winter. I need a simple and inexpensive ‘fix’ as I have a lot of these boxes … as usual, Correx is my friend!

Reduced entrance ...

Reduced entrance …

Finally, I’ve recently purchased a stack of Abelo poly hives for work and will be interested to see how these perform this season. These boxes are ‘Nationals’, but ever so slightly different from the Swienty and cedar boxes. However, the dimensions and interfaces of broods and supers are definitely compatible, so they should mix’n’match OK. This purchase was a perfect example of how beekeepers end up with a wide range of different gear … they are supplied ready-painted, so save time, and they were cheap as chips in the Abelo sale 😉

Of course, the widely divergent views expressed on some of the discussions forums simply reflects a bad case of midwinter cabin fever and the contrariness of some contributors.

And irritatingly, some take the same frame sizes, but with either short or long lugs. Grrr.

And if you are a beginner reading this I would encourage you to read a couple of previous posts on mentoring and the benefits of buying local bees.

Get dribbling

There has been a prolonged spell of cold weather in Eastern Scotland. Temperatures have rarely risen above 5°C, with hard frosts overnight. However, a warm front moved in on Tuesday night and the last few days have been significantly warmer. The lack of activity at the hive entrances and a quick peek under the insulation through the perspex crownboards (where fitted) indicated the bees were all tightly clustered during the cold spell. Furthermore, the absence of debris on the removable Varroa monitoring trays fitted to many of the open mesh floors, suggested that little or no brood was being reared.

Ridiculous to the sublime

Ridiculous to the sublime

Varroa counts

Varroa trays ...

Varroa trays …

There was another clue that the colonies are likely broodless. I had been recording the natural Varroa drop of a few colonies over the last month. I did this by simply counting Varroa at each visit, calculated on a mites/day basis. Although generally low (and very low in a few colonies), it had been steadily increasing. This is a good indication there were more phoretic mites in the colony … again, presumably due to the absence of suitable brood for them to parasitise.

It’s worth noting that the natural mite drop is a notoriously unreliable method of accurately determining mite levels in a colony. For example, it’s dependent upon the amount of sealed brood in the colony. With no sealed brood all mites must be phoretic. In contrast, with limitless sealed brood 80-90% of the mites are within cells. However, although estimates from mite drop are not hugely accurate, they are a lot better than doing nothing. The National Bee Unit has published a Varroa calculator. This allows you to use a combination of the mite drop per day, the time of year, length of season and level of drone brood to predict the total numbers of mites in the colony. For some inexplicable reason this asks for the level of drone brood in December … with 0% not being an available option  🙁

Time to treat

With little or no brood in the colonies, now is a perfect time to treat with an oxalic acid-containing preparation to hammer down the remaining mite population. I’ve previously discussed the importance of this midwinter treatment (see Two treatments … a double whammy). In many ways it’s preparation for the season ahead, rather than for the protection of the bees already present in the colony. The lower the mite levels are at the beginning of the season, the longer it will take for the mite population to reach dangerously high levels.



You can model these events using BEEHAVE. This is an interesting in silico model of a beehive. With mite numbers of ~10 at the beginning of the year, maximum levels reached are low to mid-hundreds by late summer, reducing to a couple of hundred the following winter. This assumes no intervening treatment and runs the model using all the default settings. In contrast, using the same parameters but starting the year with ~100 mites, levels peak at between 3000 and 4000 mites, returning to about 1800 in December.

Remember that the National Bee Unit recommends mite levels should not exceed 1000 or there is a risk of “significant adverse effects on the colony”. Therefore, the midwinter treatment is an important preparation for the year ahead, delaying the point at which these dangerously high mite levels are achieved.

Have your hives got less than 100 mites in them now?

Remember also that, with no sealed brood, midwinter is also the ideal time to expose as many mites as possible to the treatment. With the exception of prolonged treatment with hard chemicals like Apistan or Apivar, it’s probably the only time you’ll achieve greater than 95% reduction in mite numbers. With little or no brood present there’s nowhere for the mites to hide.

Dribbling or vaporisation?

An oxalic acid-containing treatment is recommended in midwinter. This can be delivered by dribbling or sublimation (vaporisation). Under optimal conditions, efficacy of the two methods is broadly similar (90%+) though there is some evidence that dribbled oxalic acid is slightly detrimental to colonies (when compared with sublimation, but not when compared to doing nothing).

Sublimox in use

Sublimox in use …

Api-Bioxal is the VMD-approved oxalic acid-containing treatment. If used for dribbling be aware that the suggested concentration on the side of the packet is higher than conventionally used in the UK. It’s also worth noting that it’s not available pre-mixed so has to be made up from powder. In this regard it’s a less useful product than the pre-mixed oxalic acid solution that Thorne’s (and possibly other suppliers) sold each winter. The one- or two-hive beekeeper needs to weigh out very small amounts accurately, or get together with others to make a large batch. Hardly what I’d call progress. Furthermore, the inclusion of glucose and powdered silica (as an anti-caking agent) in Api-Bioxal means it leaves a caramelised mess if used for vaporisation. Although a scouring pad and elbow grease will get rid of this mess, it’s another example of how the “approved” commercial product is actually less good – and no more effective – than the oxalic acid dihydrate that beekeepers have been using for 20 years or more.

Notwithstanding these negative comments, Api-Bioxal works well and is less expensive (per treatment) than most of the other VMD-approved Varroa treatments.

Don’t delay, get out and get dribbling …

The forecast for the next 7-10 days is for significantly warmer temperatures. This means that the queen – if she was having a break from egg-laying – will start laying again. There will be open brood by this weekend and sealed brood in your colonies by about the 15th of December. Dribbled oxalic acid is detrimental to – and may kill – open brood so if this is your preferred method of treatment then don’t delay. If you sublimate you’ve got a few days leeway, but don’t delay any longer than that.

Here are a couple of old videos showing trickling (dribbling) oxalic acid onto a large and small colony in the middle of winter. The Trickle bottle from Thorne’s makes administering the treatment very quick and easy.

Of course, sublimation using an active vaporiser like a Sublimox is even faster and doesn’t involve opening the colony. Here’s an example showing treatment of a recently hived swarm in midsummer … I could have removed the Sublimox after about 30 seconds.

The Daily Mail may be predicting the coldest winter since the last ice age (so perhaps there will be another broodless period§) but I wouldn’t rely on them to influence something as important as the midwinter treatment for reducing Varroa levels.

Here’s a perfect example of the problems encountered by the ‘topical blogger’. I wanted to write about midwinter Varroa treatment in the middle of winter, at a time when others – particular new beekeepers – should be treating their own colonies. Typically these treatments are made in late December or early January. However, the long-range (10 day) forecast in late November suggested the second week of December might be suitable. Some of this was therefore written in very late November, the Varroa drop comments added once I’d completed counting around the 4th to the 6th, and the post finished off the following day once I’d treated my own colonies.

This assumes that the queen started laying on the 7th, the first full day with elevated temperatures.

§ I didn’t open any colonies to confirm they were broodless. I was happy enough to take the clues from the increased mite drop on the Varroa trays and the absence of debris indicating uncapping of brood cells. However, I was told by friends that other colonies they opened on the 7th were broodless.


Out, damned mites

Sublimox vaporiser

Sublimox vaporiser …

Today was very mild, slightly damp and breezy after a prolonged cold spell (at least here in Scotland). The long, cold spell means that colonies are broodless. Now is an ideal time to apply your midwinter Varroa treatment. Don’t wait until the Christmas holidays, don’t wait until the weekend after next … colonies will probably have sealed brood again by then. For maximum effect treat while the colony is broodless and decimate the phoretic mite population.

I treated all my colonies late this afternoon and evening. I finished the last using a headtorch for illumination and tidied up under bright moonlight. The bees looked good and it was great to be doing some beekeeping again, if only briefly.

 A longer post justifying why the colonies were considered broodless and why it is so important to treat when they are broodless will appear this Friday.

The rather weak title is a variant of Shakespeare’s “Out, damned spot” from the play Macbeth. The words are spoken by the sleepwalking Lady Macbeth who is going insane with guilt after her husband killed Duncan (the King of Scotland). The spot refers to Duncan’s blood. Mites on the Varroa tray look like tiny spots of blood …


Those pesky mites

DWV symptoms

DWV symptoms

If you haven’t yet treated your colonies to reduce Varroa levels before the winter arrives it may well be too late. High Varroa levels are known to result in the transmission of virulent strains of deformed wing virus (DWV). These replicate to very high levels and reduce the lifespan of bees. If this happens to the ‘winter bees’ raised in late summer/early autumn there’s a significant chance that the colony will die during the winter.

Mite levels in most of my colonies have been very low this year. Partly due to thorough Varroa management in the 2015/16 winter (the only thing I can take credit for), partly due to the relative sparsity of beekeepers in Fife, partly due to the late Spring and consequent slow build-up of colonies and partly due to an extended mid-season brood break when requeening. Most colonies yielded only a small number of mites (<50) during and after a 3 x 5 day treatment regime (to be discussed in detail in a later post) by sublimation.

Infested arrivals

The low mite drop definitely wasn’t due to operator error or vaporiser malfunction. At the same time I treated a swarm that had moved into a bait hive in early June …

Out, damn'd mite ...

Out, damn’d mite …

This is ~20% of the Varroa tray. Have a guess at the number of mites in this view only. Click on the image to read the full legend which includes the mite count.

The image above was taken on the 18th of September, a day or two after starting the second round of 3 x 5 day treatments. The colony really was riddled. When a colony swarms 35% of the mites in the colony leave with the swarm (or, in this case, arrives with it). For this reason the swarm was treated for mites shortly after it arrived in June. It did have a reasonably high mite load but subsequently built up very quickly and didn’t experience the mid-season brood break my other colonies benefitted from.

The colony now has an acceptable mite drop (<1 per day). Similar colonies are still rearing brood – I’ve not checked this one, but they are bringing in some pollen from somewhere – so there’s a possibility the majority of the remaining mites are tucked away in sealed cells. I’ll keep a close eye on this colony through the next few weeks and will be treating again midwinter to further reduce the parasite burden.

Treat ’em right

If you are treating this late in the season make sure you use a miticide that is appropriate for the conditions. Apiguard (a thymol-containing treatment) is almost certainly unsuitable unless you’re living in southern France as it needs a temperature of 15°C to be effective. MAQS has a recommended temperature minimum of 10°C which may be achievable.

Hard chemicals such as Apivar and Apistan can be used at lower temperatures but there’s little point in treating with Apistan unless you’re certain all your mites are sensitive. They almost certainly are not as Apistan/Bayvarol resistance is very widespread in the UK mite population. Just because you get an increased mite drop in the presence of Apistan does not mean treatment has been effective. Perhaps all you’ve done is killed the sensitive mites in the population, leaving the remainder untroubled. This is what’s known as a bad idea … both for your bees next season and for your neighbours.

 I’m posting this now due to the large number of searches for, and visits to, pages on use of Apiguard or other Varroa treatments. These are currently running second to ‘fondant‘ in one form or another.

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.

Vaporising Api-Bioxal

Vaporising Api-Bioxal leaves a burnt caramelised residue in the vaporiser. This is difficult to clean. Does this damage the vaporiser or make it work less efficiently?

Forget it ...

Forget it …

I remortgaged the house, took my kids out of university and cancelled both trips to Mauritius later this year, all so I could afford some Api-Bioxal (a snip at £10.99 for 35g from Thorne’s). Api-Bioxal is the VMD-approved oxalic acid-containing miticide. Only ‘containing’ as – according to the manufacturers instructions – only 88.9% of the dodgy-looking white crystalline powder is actually oxalic acid (OA). The remaining ~11% is a mixture of glucose and powdered silica (VMD documentation [MS Word]) . As cutting agents go, these are relatively harmless. Nevertheless, some have expressed concern that the presence of glucose might leave a horrible gunky mess (a widely accepted technical term) in the bottom of the vaporiser. Let’s see …

Since I’d promised to help a friend with vaporising a few hives that were disappointingly Varroa-riddled when treated earlier in the winter, this seemed a good opportunity to do a side-by-side comparison of Api-Bioxal and OA vaporisation – in terms of residues, not efficacy¹. My vaporiser is an ‘active’ model (made by Sublimox) in which the vaporised oxalic acid is forced out through a small nozzle in about 20-30 seconds (see video). In use, the OA crystals are dropped into a preheated pan – by inverting the Sublimox – so the temperature change from ambient to 157ºC happens more or less instantaneously. Any comments below therefore might not apply to the passive vaporisers like the “Varrox”, or the plethora of home-grown ones² on the forums or variants listed on eBay. In the majority of these types the powder is added to a pan which is then heated to the sublimation temperature³.

At the start of the trial the pan of the Sublimox was clean, contained no residues and was only slightly tarnished (from historical use). This machine has been used dozens of times previously and in each case has been washed out with clean water after use as instructed by the manufacturers.

After a single colony was treated with 1.6g of Api-Bioxal the pan of the Sublimox contained an obvious charred residue.

Single use ...

Single use …

We treated one further hive with Api-Bioxal and took another photograph of the vaporiser ‘pan’ which now contained an even more obvious charred caramelised deposit, bubbled and lumpy in places. This wasn’t a loose flaky deposit, it was burnt onto the base and lower sidewalls of the vaporiser ‘pan’.

Two treatments ...

Two treatments …

In use the ‘collar’ around the plastic (delrin?) cups used to deliver the OA/Api-Bioxal usually have slight traces of the powder left around them. These were particularly obvious when using Api-Bioxal though I’m not sure any greater amount of powder was left here … it just looked a lot worse. It was also more difficult to clean off than ‘pure’ OA.

Plastic cup ...

Plastic cup …

The caramelised charred residues remaining in the vaporiser after two Api-Bioxal treatments needed a combination of scraping with a knife and repeated rinsing with boiling water to remove it. This took several minutes and would clearly be impractical (and irritating) to do between treatments, meaning that the residues would build up quickly over time. Compare the first and second image in the series above to see how much residue builds up at each use (and see the note below regarding the amount vaporised).

Cleaned vaporiser ...

Cleaned vaporiser …

I then added 1.6g of standard oxalic acid dihydrate (Thorne’s) and vaporised it before immediately photographing the unwashed pan and cup. The photo below should therefore be compared directly with the first in this series. You can see the traces of OA powder at the end of the nozzle of the vaporiser, but the pan is completely clean and contains no additional charred and caramelised residues. This vaporisation was done ‘in the open’ (i.e. not into a hive) and it was interesting to see how long it took the extensive cloud of crystals – perhaps 5 x 2 x 2m in extent – to dissipate as it gently drifted away downwind.

Single OA use ...

Single OA use …

But it gets worse …

I actually used much less Api-Bioxal per hive than the manufacturers recommended 2.3g per colony (this is partly because there is published evidence that ~1.4g is sufficient and double that amount provides no increase in mite killing). I didn’t weigh the Api-Bioxal but used one measuring scoop that – from previous tests – is known to contain ~1.6g of OA when full. Had I used the full recommended dose of Api-Bioxal I would have therefore expected the residue build up to be about 50% worse than shown above. On a vaguely brighter note, the powdered Api-Bioxal pours easily and smoothly, presumably because of the anti-caking agents it contains.

What are the implications of this?

I am very disappointed with the amount of residues left in the vaporiser after using even a single (less than recommended) dose of Api-Bioxal. I’m also disappointed with how difficult these are to clean out of the vaporiser. Might these residues damage the vaporiser, for example by blocking the nozzle, or reduce the effectiveness of vaporisation, for example by not allowing the pan to heat as evenly or quickly? I think both of these are a distinct possibility. An advantage of vaporisation is the ease and speed with which OA can be administered. If the vaporiser needs to be cleaned between every (or even every few) hives it would significantly reduce the attractiveness of this type of Varroa treatment. Remember, if you take your PPE seriously – which you should when vaporising oxalic acid – you’ll be wearing gloves, a respirator/mask and goggles throughout this entire procedure, including cleaning out the residues from the hot vaporiser.

No thanks.


Update … 22/2/16

Chris Strudwick kindly sent me before and after photographs of a Bioenoxal vaporiser that had been used once with Api-Bioxal. The ‘before’ image (left) shows the machine after vaporising 1.6g of Api-Bioxal. The ‘after’ shows the “result of 5 minutes with a nylon pan scourer and water after an initial scraping with a hive tool” … so the gunk can be cleaned off, but it takes time.

Many thanks Chris

¹This would have entailed treating hives with a known Varroa-load with either Api-Bioxal or OA. This was not done.

²Some of the DIY vaporisers are either spectacularly dangerous or have been designed without an appreciation of the temperature control required to vaporise oxalic acid.

³If you have a “Varrox”-type vaporiser I’d be interested to hear your experience with using Api-Bioxal.

Oxalic acid and LSD

Api-Bioxal has recently been approved by the UK Veterinary Medicines Directorate and is available from the usual suspects. At a price.

Oxalic acid ...

Oxalic acid …

OA crystals on bee ...

OA crystals on bee …

Many beekeepers use oxalic acid (OA) to control Varroa numbers, by trickling a low percentage (w/v) solution over colonies in winter, or by vaporisation/sublimation. Oxalic acid dihydrate (a white crystalline powder) has been sold by most of the large beekeeping suppliers for years, and the BBKA have provided instructions on its use as a ‘cleanser’. Until recently OA has not been licensed by the UK’s Veterinary Medicines Directorate (VMD) for use as a Varroa control (hence use of the term ‘cleanser’ by the BBKA) but was available under the EU Cascade Scheme as the product Api-Bioxal from Italy, where it was licensed. Api-Bioxal was licensed by the UK VMD in September 2015.


Librae, solidi, denarii … pounds, shillings and pence

Sublimox vaporiser

Sublimox vaporiser

Assuming the largest quantity available is the most economic way to purchase OA (which may or may not be correct) then Api-Bioxal currently costs about £0.21/g from E.M. Thorne. The same supplier are selling generic OA crystals for £0.016/g. The recommended dose for Api-Bioxal vaporisation is 2.3g/colony (stated on the product label), though the size of the colony isn’t indicated. Aside from the problem of weighing out 2.3g in the apiary, this makes single treatments with Api-Bioxal cost about 50p a shot. My Sublimox vaporiser was provided with a small scoop which dollops out 1.5g at a time of OA (confirmed on a laboratory balance), which is about all that can be conveniently loaded into the white plastic thingy (my poor translation from the original Italian … see the photo right) from which it drops into the heating pan. That’s the amount I use for one treatment of a single brood National hive. Thomas Radetzki has looked at the efficacy of 1.4g and 2.8g doses – most conveniently found in this graph from Randy Oliver’s Scientific Beekeeping website – which are effectively indistinguishable, so I choose to use the lesser amount. Therefore, using generic OA supplied by E.M. Thorne makes treatments cost less than 2.5p each. Quite a difference.

OA is available from other suppliers as well, and is also widely available as a boat deck cleanser … and if you’ve got a large enough yacht you can probably justify buying 25 kg of the stuff for less than £70. Or a lot of hives … at that price it works out at less than 0.5p/treatment 🙂

Time to stock up?

This is why we treat ...

This is why we treat …

The licensing of Api-Bioxal as the first approved OA miticide in the UK is to be welcomed if it encourages beekeepers to reduce mite levels in their colonies. It is, after all, the viral payload the mite transfers between bees, that causes significant levels of overwintering colony losses for beekeepers. I’ve no doubt that the licensing (and the associated testing needed for getting this approval), the packaging and the marketing have added significantly to the costs of the oxalic acid dihydrate. However, at about 20 times the price of the generic powder from the same beekeeping suppliers, there are some who will consider this profiteering.

Over the next few months and years it will be interesting to see whether generic OA disappears from beekeeping suppliers because their customers have all switched to using Api-Bioxal, which they meticulously record in their hive notes under ‘medicines’ … or whether Api-Bioxal fails to succeed because beekeepers continue using the same stuff, admittedly unapproved and unlicensed, they been using for many years without any problems.

* and you thought MAQS was expensive?

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.