Tag Archives: vaporising

All together now

This is the last of a short series of related posts on rational Varroa control. It brings together the key points made on the choice of how and when to treat, coupled with a treatment strategy that minimises the influence of bees drifting between colonies. The latter is best summarised in three words … coordinated Varroa treatment.

Coordinated Varroa treatment makes sense

Abandoned hives

Abandoned hives …

Most beekeepers treat their own colonies together … it’s logical, easier and cost effective. But what about the other beekeepers in the shared association apiary? What about the colonies two gardens away? What about the large row of colonies in the bottom of the adjacent field? What about that abandoned hive in the hedgerow over the road? What about the feral colony in the church tower? All of these are a potential source of reinfestation. After a week or two of miticide treatment your own colonies are likely to be largely free of phoretic mites … but all those nearby untreated (or yet to be treated, or ineffectively treated … or just plain forgotten) colonies can act as a source of mites and viruses from drifting workers and drones. These will infest and infect your colonies. Robbing bees – not the maelstrom of foragers ripping a colony apart that most beekeepers would recognise, but the silent robbing that can occur largely unseen and unsuspected in many apiaries – will bring a smorgasbord of virus-loaded mites and workers to your recently-treated hives. Remember also, your colonies may well be robbing other untreated, mite-infested colonies nearby. If all colonies ‘within range’ (see below) were treated at the same time these bee behaviours (drifting, robbing) that cannot be altered would have far less impact in transferring mites and viruses.

Coordinated Varroa treatment – over a wide geographic area – hasn’t been widely investigated in the UK. In Europe there have been a number of coordinated treatment trials, for example in isolated mountain valleys, where the geography provides a barrier to bee movement. Due to the unregulated and often undocumented nature of beekeeping in the UK it may well be more difficult to organise effectively. However, this isn’t a reason coordinated Varroa treatment shouldn’t be attempted. There are precedents in the salmon farming industry where all cages within a single water catchment area must be coordinately treated – both in terms of time and (I believe) the compound(s) used for controlling sea lice. This isn’t voluntary because it’s been shown to be effective.

What’s ‘within range‘?

One mile radius ...

One mile radius …

Drifting of foragers and robbing etc. are distance-dependent activities. The more widely separated colonies are, the less likely they are to be an issue. This was amply demonstrated in the recent comments by Tom Seeley that feral colonies hived and co-located in apiaries succumbed to mite-transmitted virus infections, whereas those sited – individually – at least 30 metres apart had lower mite counts and survived better (Sharashkin, L [2016], ABJ 156:157). So perhaps all colonies within 30 metres should be treated together?

Clearly this is too low a limit. Firstly, we know bees can travel much further and the studies described by Seeley didn’t test whether colonies survived even better if spaced even further apart. Secondly, the feral colonies Seeley studies are naturally located approximately half a mile apart from each other. Whilst this is undoubtedly influenced by the availability of hollow trees it suggests that the range could usefully be extended to at least half a mile. I’ve certainly seen robbing occurring between colonies located at least 500 metres apart.

Since the effective limit over which re-infestation might occur isn’t known it perhaps make sense to throw the net a little more widely … a mile for example? This is a convenient distance … covering most beekeepers within a small village in a rural area, those sharing adjacent fields in farmland or perhaps a number of urban apiaries. It’s also a manageably small area, where personal contact and friendly agreement should be sufficient to coordinate treatment. Do you know the location of all of the colonies within a mile of your own? Google maps can help. So can local association membership, or simply accosting people you see wearing a beesuit. I knew of ~20 hives belonging to 4-5 beekeepers within a mile of my previous home apiary. Of course, with any sort of migratory beekeeping – bringing colonies back from the heather, taking them to orchards – or simply moving nucs from a split colony to a new apiary, there’s a possibility of colonies with low mite levels getting exposed to colonies with a high level of infestation. For proper coordinated treatment these movements would have to be taken account of.

In our bee virus research we’re investigating the benefits of large scale coordinated Varroa treatment by working with all the beekeepers on a large island, where the sea provides a natural barrier to mites entering the test area. Over the next three years we will see how mites, and more importantly the viruses they transmit, are controlled by coordinating Varroa treatment within this defined area.

Coordinated Varroa treatment helps mitigate the effects of drifting and robbing between colonies, activities that are usually underestimated and that are known to transmit mites and (inevitably) viruses and other pathogens. This isn’t rocket science. It’s a logical response to the biology of bees and the pathogens that they carry.

How to treat

Spot the difference ...

Spot the difference …

Use a miticide that is appropriate for the conditions, use it according the manufacturers instructions and keep records of the treatment. There are no hard and fast rules, but it’s worth taking account of the following:

  • Avoid using pyrethroid-based miticides if there’s any evidence of resistance. Just because you get a high mite drop with Apistan doesn’t mean there isn’t an even larger resistant population left infesting your colony¹ … there are ways of checking this, perhaps you should?
  • Avoid using Apiguard unless the temperature really is high enough for it to work effectively, which means an average of 15°C for a month. If used at a sub-optimal temperature you’ll be leaving mites behind …
  • Avoid trickling oxalic acid/Api-Bioxal if there’s brood (sealed or unsealed) in the colony. It’s toxic to unsealed brood and the mites in sealed brood will escape unscathed …
  • Avoid vaporising Api-Bioxal unless you enjoy cleaning the gunky mess™ from the vaporiser. If vaporising oxalic acid ensure that the colony is broodless, or be prepared to repeat treatment three times at five day intervals to catch both phoretic and emerging mites …
  • Be aware that some miticides stop the queen from laying. Perhaps try and avoid these when you’re dependent on the colony raising the all-important winter bees that are going to get it through to the following Spring. I don’t actually know how much of an issue this is for colony health and survival, but it always concerned me when the queen went on a go-slow at the very time I wanted her to keep laying strongly through late August/early September.
  • Don’t reduce treatment doses or times … partial treatments are partially effective. This is also a great way to select for miticide-resistant Varroa (though whether they arise depends upon the mechanism of action – resistance to oxalic acid, formic acid and thymol has not been observed).

When to treat

Bee working ivy ...

Bee working ivy …

Earlier than you perhaps think to protect the winter bees from viruses. When I lived in the Midlands I would treat immediately after taking the summer honey crop – perhaps mid/late August. There’s later forage available – himalayan balsam and ivy – both of which some beekeepers either like or have a market for, but collecting it risks exposing the developing winter bees to high levels of Varroa and pathogenic viruses. Now I live in Scotland I’m going to have to develop alternative treatment schedules for colonies going to the heather – brood breaks and/or creative use of a vaporiser in June/July.

Treatment is only part of the solution though …

These articles on Varroa control have focused almost exclusively on miticide treatment. There are also a range of beekeeping practices that can contribute significantly to effective Varroa control, reducing the necessity to treat with chemicals. These include enforced brood breaks, shook swarms, drone brood uncapping, queen trapping and others. A proper integrated pest management strategy involves both chemical and beekeeping interventions to prevent the build up of dangerously high mite levels in the colony. Some of these will be covered in more detail during the coming season.


¹I think there’d be a case to ban the sale and use of Apistan for three years out of every four … pyrethroid resistance in mites appears to be detrimental in the absence of selection i.e. resistance is lost if the miticide is not used for a few years. That way, when used it would be devastatingly effective. This compares to the current situation where Apistan resistance is very widespread, and constantly selected for by continuing use of pyrethroids. Of course, there’s no way to enforce this – despite the fact it would probably be a great benefit for bee health – but now we’re back to the unregulated and undocumented nature of UK beekeeping.

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.