The post last week on the preparation of oxalic acid (OA; the active ingredient in the commercially available and VMD approved product Api-Bioxal) generated a slew questions. Inevitably, some of these drifted off topic … at least as far as the specific content of the post was concerned.
This partly reflects the deficiency of a weekly blog as a means of communicating.
It may also reflect the inadequacy of the indexing system 1.
Comprehensive coverage of subject, and peripherally related topics, would require a post so long that most readers 2 would give up halfway through.
And it would take so long to write that the weekly post format would have to be abandoned.
The resulting magnum opus would be a masterpiece of bad punctuation, littered with poor puns and would leave me nothing to write the following week …
This week I’ve attempted to address a series of oxalic acid-related points that should have been mentioned before, that I’ve received questions about, or I think justify a question (and answer).
Should I trickle treat or vaporise?
One of the key features of approved miticides is that, used according to the instructions and at the appropriate time, they are very effective.
Conversely, use them incorrectly or at the wrong time and they will be, at best, pretty hopeless.
In the case of OA, both trickle treating (dribbling) or vaporisation (sublimation) can achieve 90% or more reduction in the levels of phoretic mites.
Therefore, the choice between them is not on the grounds of efficacy but should be on their ease of us, convenience, safety or other factors.
Trickle treating is fast, requires a minimum amount of specialised equipment and only limited PPE (personal protection equipment).
I’d strongly recommend using a Trickle 2 bottle from Thorne’s to administer the solution. It is infinitely better than a syringe, which requires the use of at least two hands.
If you hold the crownboard up at an angle with one hand you can administer the OA solution using the other. Wear gloves and your bee suit. It takes as long to read as it does to do.
With a Trickle 2 bottle and some pre-warmed OA-containing solution it should be possible to open, treat and close a colony in well under two minutes. Like this …
On a cold day very few bees will be disturbed. The OA will dribble down through the clustered colony and the mites will get what they deserve 🙂
Temperature and treatment choice
It’s usually the temperature that determines whether I trickle or vaporise. I prefer to trickle when the colony is clustered, but would usually treat by sublimation on a warmer day.
At what temperature does cold become warm? About 8-9°C … i.e. about the temperature at which the bees start to cluster.
Partly this is to reduce the number of bees that might be disturbed – I can vaporise a colony without opening the box.
However, my crashingly unscientific opinion – based entirely on gut feeling and guesswork 3 – is that the OA vapour perfuses through loose clusters better, whereas the solution is more likely to come into contact with the mites when dribbling down through the cluster.
I have no data to support this – don’t say you weren’t warned!
Through choice I’d not treat (unless I had to) if the temperature was much below 3-4°C. The bees get rapidly chilled should something goes wrong – you drop the bottle, get a bee in your veil or whatever.
Of course, if you haven’t got a vaporiser your choice is limited to trickle treating. Likewise, if you don’t enjoy scouring caramelised glucose from the pan of your vaporiser you should probably stick to trickling Api-Bioxal solution.
The only additional thing to consider is whether there’s brood present in the hive – I discuss this in more detail below.
How can I use a vaporiser and an Abelo poly floor?
I use a lot of Abelo poly hives. Mine are all the ‘old design‘ with the floor that features a long landing board and an ill-fitting Varroa tray. The new ones don’t look fundamentally different from the website 4.
My storage shed has a shoulder-high stack of unused Abelo floors as I prefer my own homemade ‘kewl’ floors.
However, inevitably some Abelo floors get pressed into use during the season and – through idleness, disorganisation and a global virus pandemic – remain in use during the winter 🙁
I’ve now worked out how to vaporise colonies using these floors. Please remember, my vaporiser is a Sublimox which has a brass (?) nozzle through which the vapour is expelled. The nozzle gets very hot and melts polystyrene.
Don’t ask me how I know 🙁
The underside of the open mesh floor can be sealed by inverting the Varroa tray and wedging a block of foam underneath at the back. I didn’t think this would work until I tried it, and was pleasantly impressed.
This is important as it significantly reduces the loss of OA vapour. Any vapour that escapes is OA that will not be killing mites.
The Sublimox can be simultaneously inserted and inverted through the front entrance. This takes some deft ‘wrist action’ but results in minimal loss of OA vapour.
To protect the poly I use a piece of cardboard. You simply rest the nozzle on this.
As soon as the vaporiser is removed the bees will start to come out, so use the cardboard to block the entrance for a few minutes, by which time they will have settled.
The gaffer tape in the photo above is sealing the ventilation holes in the entrance block, again keeping valuable OA vapour inside the hive.
And on a related point …
My favoured nuc is the Everynuc. This is a Langstroth-sized box with a removable floor and an integral feeder that more-or-less converts the box to take National frames. It’s well-insulated, robust, easy to paint and – in my view – a more flexible design that the all-in-one single moulded boxes (like the offering from Maisemores).
However, the entrance of the Everynuc is too big.
The disadvantage of this is that a DIY entrance reducer is needed if the nuc is weak and at risk from robbing.
Conversely, the large entrance and short (~2cm) “landing board” is preferable during OA vaporisation. I carry a nuc-width strip of wood, 2 cm thick, with a central 7 mm hole.
With this balanced on the landing board, the vaporiser can be inserted and inverted without loss of vapour or risk of melting the poly. It’s a quick and dirty fix that I discovered several years ago and have never got round to improving.
How do I know if the colony is broodless?
Oxalic acid is a single-use treatment, remaining active in the hive for significantly less time than a brood cycle (see mite counts below). Therefore, the ‘appropriate time’ to use it is when the colony is broodless.
An additional consideration is that open brood is very sensitive and responds unfavourably to a warm acid bath in OA i.e. it dies 5.
In contrast, sealed brood is impervious to OA vapour or solution.
So, how can you tell if the colony is broodless or not?
The easiest way to determine whether the colony has sealed brood is – on a slightly better day – to open the box and have a look.
Done quickly and calmly I suspect this is more distressing for the beekeeper than it is for the colony. You think the bees will be aggressive or distressed. In reality they’re usually pretty lethargic and often very few fly at all.
You only need to look at the frame in the centre of the cluster. If there’s brood present it will be where the bees are most concentrated. You will probably well see the queen nearby.
Gently, gently, quicky peeky
Remove the roof and insulation and lift one corner of the crownboard. Give them a gentle puff of smoke under the crownboard 6. Wait 30 seconds or so and gently remove the crownboard.
There will be bees on the underside of the crownboard. Stand it carefully to the side out of the breeze. The bees will probably crawl to the upper edge, remember to shake them off into the hive rather than crush them when you place it back on the hive.
The colony is likely to be clustered if the weather is 8°C or cooler. Remove the outer frame furthest from the cluster. If it’s late autumn or early winter this should still be heavy with stores. Here’s one I pulled out last week.
Now you have space to work. Viewed from above the cluster will often be spread over several frames and shaped approximately like a rugby ball.
In the hive shown above they occupied the front five seams 7 with a few stragglers between frames 6 and 7.
I used my hive tool between frames 3 and 4 to split the colony, just levering them a centimetre or so apart, so I could then separate frame 3 from 2 and lift it out.
The queen was on the far side of frame 3.
It looks like magic to inexperienced beekeepers, but it really isn’t …
The top of the frame was filled with sealed stores, the lower part of the frame was almost full of uncapped stores.
There was no sealed brood and no eggs or larvae that I could see 8. An adjacent hive looked very similar. Again, the queen was on the reverse side of the first frame I checked. The bees were barely disturbed. Almost none flew and the boxes were carefully sealed up again.
No brood, so ready to treat 🙂
Can I determine if there’s brood present without opening the hive?
You should be able to tell if brood is emerging by the appearance of the characteristic biscuit-coloured wax crumbs on the Varroa tray.
Think digestive rather than Fox’s Party Rings
To see this evidence you need to start with a clean Varroa tray. In addition, the underside of the open mesh floor must be sufficiently draught-free that the cappings aren’t blown around, or accessible to slugs.
Remember that there might be only a very small amount of brood emerging. They may also be uncapping stores (which will have much paler cappings).
Leave the tray in place for a few days and check for darker stripes of crumbs/cappings under the centre of the cluster.
Note that the photograph above was taken in mid-February. A late autumn colony would almost certainly have significantly less brood cappings present on the tray. The brood cappings are the two and a bit distinct horizontal stripes concentrated just above centre. The stores cappings are the white crumbs forming the just discernible stripes the full width of the tray.
You cannot use this method to infer anything about whether there’s unsealed brood present. At least, not with any certainty. If, in successive weeks, the amount of brood cappings increases there’s almost certainly unsealed brood present. Conversely, if brood cappings are reducing there may not be unsealed brood if the queen is just shutting down.
While you’re staring at the tray …
Look for Varroa.
It’s useful to have an idea of the mite drop in the few days before OA treatment.
If it’s high then treatment is clearly needed.
If it’s low (1-2 per day) you have a useful baseline to compare the number that fall after treatment.
You may well be surprised (or perhaps disappointed) at the number that appear from a colony that has already had an autumn treatment.
It’s worth remembering that 9 there will be more mites present in the winter if you treated early enough in the autumn to protect the winter bees (blue line).
Conversely, if you get little or no mite drop with an OA treatment in the winter it indicates the bees have not been rearing brood in the intervening period. That means the diutinus winter bees were reared before or during the last treatment, meaning they will have been exposed to high mite levels (red line).
This is not a good thing™.
In my experience the daily mite drop is highest 24-48 hours after treatment. I usually try and monitor it over 5-7 days by which time the drop has reached a basal level, presumably because the OA has disappeared or stopped being effective.
Finally, the ambient temperature has an influence on the Varroa drop. I’ll write about this sometime in the future, but it’s worth looking out for.
- Which actually isn’t too bad … use the search facility at the top of the right hand sidebar. It finds stuff in titles, in tags and in post texts.
Alternatively, the menu bar has lots of relevant stuff under various semi-logical subheadings.
- Or this writer.
- No evidence, no side-by-side comparisons, no placebo-controlled randomised double blind trials, nothing, nada!
- Do any readers know whether they are compatible?
- It appears not to be harmed by vaporised OA, in studies from the University of Sussex.
- Not through the entrance … you want to push the bees down rather than up.
- Six, if you also count the one against the front wall of the hive. In poly hives the bees often rear brood in these outer frames which is something that rarely happens in cedar boxes, other than at the peak of the season.
- Mid-afternoon, mid-November, murky light and my eyes!
- Assuming your autumn treatment actually worked.
Really enjoyed your talk for Warwickshire on Zoom last week!
Also thought you might like to know that the homemade nuc DJE1 you bequeathed me via WLBKA is still going strong and is in regular use as my bait hive! Thanks again!
Delighted you enjoyed the talk on Bee Sheds … it’s been a busy winter of talks. I’d also offered Warwickshire County a talk on bait hives which covers both the science of swarm relocation and the desirable features of a bait hive. If they’d chosen that you’d be aware that my homemade nucs are probably too small to attract the largest prime swarms. Considering my laughably amateur DIY skills I’m astounded – and pleased – that the box is still sufficiently intact to be usable.
With Best Wishes
I had a chap deliver some logs to my houese today. He noticed my beehives and asked how are they doing? I said fine and that I treated with oxalic acid. His reply was that he kept hives in Pendine South Wales and a friend of his ( he described as a Quantum Physicist) had devised a varroa control consisting of a device which generates a frequency. You put one in each hive apparently. I won’t relate the whole story, save to say the chap uses this device to control varroa in his own hives apparently successfully and does not use any other method.
I thought I’d check with you if you’d come across such devices and if they’ve been tested in controlled trials?
Or is it pie in the sky?
Hello Paul … maybe I’m being harsh … I’ve never seen any controlled trials (or uncontrolled trials) of these sorts of devices. I have seen them advertised.
I understand how miticides work, so the drop in mite numbers following their use makes sense to me. I understand how brood breaks, drone uncapping or other non-chemical interventions work, so again these make sense to me. I don’t understand the underlying principles that are supposed to make these frequency oscillators (or whatever they are) work, and have seen no evidence that they do work, so remain highly sceptical.
They’re advertised from £20-30, need no electrical input and have “Stop Varroa now and forever”. Why doesn’t every commercial beekeeper worldwide use them?
Finally, although they’re cheap, my bees are valuable (at least to me). I don’t want to risk losing them to Varroa and viruses to prove something I find hard to believe total bunkum.
I note that in most publications that a concentration of 3.2% is quoted for the trickle method of Oxalic Acid at 5ml per seam.
Api-bioxal 35g pack gives a concentration for 10 hives of 4.2% for the trickle method.
Which one is correct / recommended?
I have bought a 35g pack and intend following every other publication that I have read in achieving a 3.2% trickle concentration. Is it a simple case of diluting the chemical in this pack to achieve a 3.2% solution or do I need to leave it at the recommended 4.2% as stated on the packet to be fully effective.
Answers to these Q’s (and more) can be found in the post last week on Oxalic acid (Api Bioxal) preparation.
Hi David, I just wanted to start off by saying how much I enjoy reading your posts – you’re a brilliant scientist and an excellent writer. David I have a request, I was wondering if you can write up another post encouraging all beekeepers to monitor and treat for varroa. Since I’ve been a beekeeper a lot of newbies have come on the scene with nothing but good intentions to try and save or help the bees. I have no issue with this approach but do however have issue with the live and let die or treatment free beekeeping approach which so many choose to be embracing due to a complete lack of understanding. I was just thinking that a well written article stressing the importance of good colony management would be a great idea. Thanks DavidPaul
I’m not sure I’d agree with your assessment of either my science or writing 😉 but thank-you anyway.
I have written extensively on the importance of mite management. I’ve even got a post entitled Leave and Let Die, a rather poor pun on the James Bond film title and the phrase you used in your comment. It discusses the near-inevitable consequences of not treating. Whether it’s well written is questionable. I also give numerous talks on the subject … probably a dozen already this autumn/winter.
The problem with encouraging chemical intervention to manage mite numbers is that many of the ‘treatment free’ group are convinced that what they’re doing is better for their bees, on the basis that the chemicals harm the bees, or weaken them or whatever.
Earlier this year I wrote a post (Measles, mites and anti-vaxxers) on the similarities between some treatment-free advocates and anti-vaxxers. I think the comparison remains valid. It generated some heated responses and, by email, some abuse.
I’ll return to these topics every now and again. However, until someone does a proper scientifically valid comparison of colony losses by beekeepers who treat, much as I advocate, and beginners who do not treat having drunk the ‘treatment-free’ Kool-Aid, the hard data showing the differences in losses simply doesn’t exist (at least as far as I’m aware).
But maybe we don’t even need that sort of data? With proper intervention in late summer and winter you can easily keep winter losses below 10%. Compare this figure to the average UK or US winter loss surveys which are regularly in the 20-30% range. Many of these beekeepers treat their bees, they just do it with the wrong stuff, at the wrong time … but it shows the level of losses that can be routinely expected without proper mite management.
Finally, I’m not saying it’s not possible to keep bees without treatment. It clearly is. A beekeeper who does this year on year with losses at or below 10% is probably an exceptionally skilled beekeeper (far more skilled than I am that’s for certain), and may also benefit from either an isolated location in which the host/parasite (bee/mite) combination has evolved to have reduced pathogenesis, or bees with some genetic resistance to mites or viruses.
By all means suggest some of the newbees read some of the articles on the perils of not treating. If they have ambitions to be treatment-free then it might be worth learning to first keep bees healthy with chemical intervention then – once they’re competent beekeepers – they can try going treatment-free. At least that way they’ll also have a comparison of what’s possible as well.
I think your point about isolated location is a key one. Where I live, I know lots of beekeepers near me and I bet there are plenty I don’t within a few miles. You can’t maintain treatment-free and varroa-free under these conditions, or I don’t believe so. All the while there is movement of bees/queens/hives round the UK then the pest is spread. Plus if you don’t treat then your bees are spreading varroa round to other beekeepers.
We’ve got some research demonstrating the impact of moving bees around as a very effective means of transmitting Varroa … and more importantly viruses. It’s a landscape-scale study and once it’s published I’ll write something about it here. Again, it’s something many beekeepers do without thinking, but it’s a sure-fire way of introducing or spreading disease.
The beekeeper density also influences the number of swarms and the success rates with bait hives, though even here in Fife where there are relatively few beekeepers my bait hives are still pretty effective.
Why do you think oxalic acid is a single-use treatment please? I’m an English expat in upstate New York where in winter we regularly deal with -15C (sorry we use F over here, so around zero F and well below that to say – 25 C on bad days) and we use oav on our hives 5 times or so from mid- August at a 4 to 5 day interval to try to match the mite breeding cycle and then again once at the winter solstice when the bees are broodless. This may sound a bit cumbersome but with a good vapouriser it is easy to do a hive in 20 seconds and it really knocks back the mites such that winter losses are 5% or less. Obvious caveats about feeding properly etc.
(This may not be relevant but we have a constant almost dearthless period of pollen (and nectar to a lesser extent) from late March to early November. Maple (sycamore) to aster and goldenrod. And then frozen hell!)
I should have justified my use of the phrase ‘single-use’. Thanks for picking me up on it.
In the UK, repeat usage of OA is not approved. That doesn’t mean that people don’t do it of course. Repeat vaporisations at a 5 day interval is an effective way of treating colonies with brood present … as you’re clearly aware.
I’ve got a good vaporiser (no cooling cycle between treatments etc.) and once did a timed comparison of trickling vs. gassing the colonies. Treatment of any individual hive was marginally faster with the vaporiser, at least in terms of OA delivery. However, if I took the preparation time, colony sealing, unsealing, pre-warming of the machine and putting away the generator afterwards, as well as donning PPE, it was appreciably faster to trickle treat.
Unbroken nectar and pollen followed by a cold winter sounds like a great location to keep bees. I find it easier to manage mite levels in Scotland than I did when living in central England. Partly this is because the winters are longer and colder, but also because there is a lower density of beekeepers, so there’s less problems with drifting and robbing.
I have a problem regarding determining a broodless period and thus an optimum time to trickle or vape with OA. It seems to require the judgement of Solomon.
I am looking to write some advice in our Association newsletter for new or recent beekeepers on this topic – this season we shall not be able to have our usual Varroa treatment day at the Association – so we’re trying to provide advice from afar – so to speak.
Recent mild winters here in Manchester have seen some Queens continue to lay, albeit in a reduced fashion, throughout the winter. Waiting on the chance of a cold snap which might lead to a suspension of laying could be risky – if it stays warm the mite levels continue to rise. If I treat just after Xmas I might kill some open brood with the OA but it will still give the mites a headache.
Also I rather suspect that novices might not manage the quick peek you suggest to see if there’s brood, or the monitoring for biscuit cappings on a Varroa floor .What if they find brood? they will want to come back next week and look again, and again? And if the brood break never comes?
Would you agree that its better to do a speculative OA treatment in late December or early January than none at all? I have already previously advised our members about using Apivar post harvest so hopefully they will have got mite numbers down already.
Great to see that your site traffic is building so well – I value reading your posts and will continue to refer our members to your blog.
If you’re sure your queens continue to lay through the winter you have little choice but to treat when the brood is at a minimal level. I think it would be better to treat when there’s brood present, rather than to not treat at all. However, as I’ve indicated in earlier posts and in comments to this post, I increasingly think that late December/early January is too late, and that most queens are laying at least a fortnight or so before then. Even if they never stop laying, the ‘minimal brood period’ is probably earlier than the end of December.
It’s worth comparing locations … here is the Accuweather data for Fife (actual and averages for November):
… and here are the temperatures for Manchester from Accuweather:
Comparison isn’t straightforward because Accuweather has butchered the Y axis scale a bit. Nevertheless, it’s clear you’ve had several days already with lower temperatures than we’ve had.
Are you sure your colonies are still brooding? I know some of mine have been broodless for 3 weeks.
Novices should be able to monitor biscuit-coloured cappings. It’s not difficult. If someone has a clear crownboard try putting a clean tray in that and, every few days, inspect the tray and relate the ‘pattern’ to the position of the winter cluster. You’ll only get brood uncapping from within the cluster. It’s worth the effort involved as you can be certain that treating when brood is present is always going to leave some mites in the colony that could have been killed.
Thanks for promoting the site to your association members.
Good post as usual David.
I have all Abelo hives and my handy other half has mounted my vaporiser on a wooden block on one of the polystyrene trays/floors (which I never use). I just block the entrance then slide the tray in underneath from the back. Seal up gaps with foam and bingo! No escape of gas.
Some of my group have been discussing when to do the vaporisation, (assuming we were not going to open up the hive to check for brood) We’ve mostly gone for the traditional ‘around the shortest day’ as day length is supposed to be the trigger for the queen to start up again. However with all this mild weather I’m not sure she’s actually going to stop!!! Wonder whether it’s worth waiting for a colder spell. How much is temp a factor in brood production? As with most things beekeeping, so many variables!!
Increasingly I think that most beekeepers treat too late in the year and that a broodless period is often encountered earlier rather than later. Try inserting the Varroa tray for a week and look for the cappings.
This season I’ve ignored the temperature altogether – yes, it’s been much warmer – but have made my decision based upon observations of the hive, either direct (open them and have a peek) or indirect (cappings). My OA treatments are done and the majority of my colonies were broodless.
Good to hear that others have solved the “Abelo floor dilemma”. If the mesh is cold do you get a lot of the OA vapour sticking to the mesh rather than getting into the hive? Have you looked underneath to check?
I hadn’t thought to look underneath! Maybe I will next month.
However, my treatments seem to be successful so I assume the vapour is reaching the desired location in the hive. Nothing seems to drop out. I’ll let you know.
Can I ask whether you think supers left on the hive can be used to store honey for extraction?
I always just keep them for the bees, but someone told me recently that with vaporisation it’s OK for humans
I’d ask the “someone” what their evidence is …
Honey already contains detectable oxalic acid, and it can be at quite high levels. However, the instructions on Api-Bioxal specifically states “Administer the treatment without supers”. I presume this is to stop people treating then immediately harvesting honey. Oxalic acid is not wax soluble, so some time after treatment it should be back down to background levels. I don’t know how long and I’ll bet it’s not been determined – OA test kits are expensive. Maybe your ‘someone’ knows?
There is a study looking at residual OA levels in honey in the spring after an autumn/winter treatment (though the precise time was not indicated if I remember correctly). This showed that levels were no higher in OA treated colonies after a few months. That being the case I’d be reasonably confident that a super exposed now would be OK to use for honey extraction next summer.
You have to remember that the instructions are written in a way that is supposed to be unambiguous … but often singularly fails to achieve this. In Scotland I’m on a working group looking at simplifying the advice for Varroa control. I hope that these are the sorts of things that can be addressed.
Short and to the point Jon … was there more you wanted to say?
Oxalic acid does appear to be an endless topic and just when you thought and hoped it was finished I’ve one more question….how long is it ok to store oxalic acid crystals in cool, dark and moisture proof conditions?
With winter looming ever large surely it’s time for a return of the Dr Bodge It franchise?
And to complete question hat trick can you give a heads up on any upcoming talks…? (In the webinar world we could drop in on most like wandering drones)
Thanks so much for all your posts, love them all (except sometimes the super deep science ones cos I get lost)
Oxalic acid is stable and should be kept in a sealed container. When you buy ‘wood bleach’ (which is oxalic acid) it doesn’t have a use by date, but remains functional for years.
Api-Bioxal usually carries a use by date a couple of years after the purchase date. It contains an anti-caking agent which probably helps it stay in a powdered form, but I always carefully exclude the air from the packet and seal it with one of those clip-seal things you can use in the kitchen.
Dr Bodgit has got a couple of large projects on the go, but it’s unlikely either will be finished in the near future. He’s been writing a lot of code recently … 🙂
I’ve got talks scheduled for Braintree beekeepers, Melksham BKA and Ludlow BKA before Christmas, with another dozen or so in the New Year. Some may be restricted to their association members …
Would the methods/results of the studies at the Univ of Sussex (footnote 5) happen to be published?
And thanks again for all your efforts describing the the enormous multi-dimensional aspects of “keeping” bees.
It’s Al Toufailia et al., (2016) Towards integrated control of varroa: 2) comparing application methods and doses of oxalic acid on the mortality of phoretic Varroa destructor mites and their honey bee hosts. J. Apicult. Res. 54:108-120.
I should have added it to the footnote, but was running out of time and caffeine 😉
Hi David. Thanks for another fantastic blog, really enjoyed it. Could I ask what type of bees you have? If I’m not mistaken you’re in the Fife area. What I’m wondering is if your experience with broodless colonies holds true for those of us more effected by the gulf stream and with Amm. There are reports of pollen going into the hives here a couple of days ago. Mahonia it’s thought…
You’re right, I’m in Fife (usually). My bees are local mongrels, but have at least some Amm in the mix as I reared queens from pure Amm stock several seasons ago. I also have some pure Amm on the west coast and they were certainly foraging and bringing in bits and pieces much later than my Fife bees were. However, I can’t comment on whether they were broodless as I’ve no need to check as they’re Varroa-free, so I have no need to treat them 😉
I might stick a cleaned tray underneath the OMF this week and see if there are any cappings on it. If so, I’ll update this comment with an ‘status report’.
If you couldn’t do OA treatments at all, for some reason, what treatment regime would you follow?
Now that Api-Bioxal is licensed I don’t see a time when I couldn’t use it … however, without a midwinter treatment the expectation is that mite levels would grow faster earlier in the following season. I’ve discussed this previously. That being the case, there’s the probability that mite levels will get dangerously high after a season or two of no winter treatments (even assuming late summer treatments are applied).
If that happens it’s likely that intervention would be required earlier in the season … perhaps during the June gap? And perhaps using formic acid (MAQS). It’s potentially a broodless period (or at least reduced brood rearing if there’s a nectar dearth) and it’s probably not too hot to provoke an adverse reaction from the formic acid.
That’s all speculation … other than sometimes treating splits and swarms when needed, my routine of late summer and “whenever the colony is broodless late in the year, but probably not midwinter” treatment seems to work well, negating the requirement for further intervention.