Category Archives: Equipment

Repeated oxalic acid vaporisation

Synopsis : Does repeated oxalic acid vaporisation of colonies rearing brood work sufficiently well? Is it as useful a strategy as many beekeepers claim?

Introduction

Oxalic acid is a simple chemical. A dicarboxylic acid that forms a white crystalline solid which dissolves readily in water to form a colourless solution. It was originally extracted from wood-sorrels, plants of the genus Oxalis, hence the name. In addition to the wood-sorrels it is present in a wide range of other plants including rhubarb leaves (0.5% oxalic acid 1 ), the berries and sap of Virginia creeper and some fruits, such as starfruit. Additionally, fungi excrete oxalic acid to increase the availability of soil nutrients.

Oxalic acid is inexpensive to produce by a variety of processes and was possibly the first synthesised natural product. About 120,000 tonnes are produced annually and it is mainly used for bleaching wood (and often sold as ‘wood bleach’) and cleaning products – including teeth. It chelates iron and so is used for rust removal and is used as a dye fixative (or mordant 2 ).

Spot the difference ...

Oxalic acid and API-Bioxal … the same but different

It is also, when used properly, devastatingly effective against the ectoparasitic mite Varroa destructor.

And, even more importantly, when used properly it is extremely well-tolerated by honey bees.

Great!

Not so fast …

Unfortunately for beekeepers, some of the commercially available i.e. licensed and approved, oxalic acid-containing treatments either contain unnecessary additives and/or have limitations in their approved modes of administration that reduces their efficiency and use in real world beekeeping situations.

Oxalic acid-containing miticides and their use

A quick search of the UK’s 3 Veterinary Medicines Directorate snappily titled Product Information Database for ‘target species = bees’ and ‘active ingredient = oxalic acid’ yields three products :

  • Varromed (BeeVital GmbH) which is a solution containing formic acid and oxalic acid
  • Oxybee (DANY Bienenwohl GmbH) which is an oxalic acid solution PLUS a separate powder containing essential oils and sugar. As far as I can tell, Oxybee looks to be the same product as Dany’s BienenWohl powder and solution, which – although listed and licensed – I cannot find for sale 4 in the UK
  • API-Bioxal (Chemicals Laif S.P.A) which is purchased as a powder composed of 88% oxalic acid dihydrate together with silica and glucose

I’m going to largely ignore Varromed and Oxybee for the rest of this post. I’m sure they’re perfectly good products but I’ve not used either of them so cannot comment from personal experience.

Keeping your powder dry

More relevant to this post, Oxybee and Varromed are both liquids, and this post is about vaporising (aka sublimating) oxalic acid.

And vaporisation involves using the powdered form of oxalic acid.

Which neatly brings me to the methods of application of oxalic acid-containing treatments to kill mites.

I’m sure there are some weird and wonderful ones, but I’ll be limiting any comments to just three which – from my reading of the instructions – are the only ones approved (and then not for all of the products listed above) : 5

  • Spraying a solution onto the surface of the bee-covered frames
  • Dribbling or trickling a solution onto each seam of bees between the frames
  • Vaporisation or sublimation of powdered oxalic acid by heating it in a metal pan to convert it to a gas. This permeates the hive, settling on all the surfaces – woodwork, comb, bees – and remains active against mites for a period after administration

Broodless is best

Oxalic acid, however it is administered, does not penetrate brood cappings. Therefore all of the approved products are recommended for use when the colony is broodless.

Typically – though not exclusively – this happens in the winter, but the beekeeper can engineer it at other times of the season.

If the colony is broodless you can expect any oxalic acid-containing miticide to reduce the mite population by 90% or more. There are numerous studies that support this level of efficacy and it’s what you should be aiming for to give the colony the best start to the season.

I discussed at length how to determine whether a winter colony is broodless a fortnight ago in Broodless?

This post is a more extensive response to several comments (made to that Broodless? article) that recommended repeated vaporisation of oxalic acid at, either 4, 5 or 7 day intervals.

The idea is that this kills the phoretic mites present when the colony is first treated and the mites subsequently released as brood emerges.

How many repeats?

I’ve seen anything from two to seven recommended online.

I’ll discuss this further below, but I’d note that the very fact that there’s such variation in the recommended repeat treatments – perhaps anything from two, fours days apart to seven at weekly intervals (i.e. spanning anything from 8 days to 49 days) – suggests to me that we don’t know the optimal treatment schedule.

Which is a little weird as, a) Varroa is a globally-distributed problem for beekeepers and is more or less invariant (as is the brood cycle of the host honey bee), and b) repeated treatment regimes have been used for over 20 years.

Which brings me back to a crude comparison of vaporisation vs dribbling, or …

Sublimation vs. trickling

A hive can be sublimated with oxalic acid without opening the hive. The vaporiser alone is introduced through the hive entrance or – in the case of certain models – the vapour is squirted through a hole in the floor, brood box or eke. In contrast, trickling oxalic acid requires the removal of the crownboard.

In the video above I’m using a Sublimox vaporiser. The hive entrance is sealed with foam and the open mesh floor is covered with a tightly fitting slide-in tray. As you can see, very little vapour escapes.

Although oxalic acid is well tolerated by bees, and it has no effect upon sealed brood, a solution of oxalic acid is detrimental to open brood. Therefore, trickled oxalic acid weakens the colony – because the acidity kills some or all of the open brood – and repeated trickling of oxalic acid is likely to compound this (see Al Toufailia et al., 2015). In contrast, repeated oxalic acid vaporisations appear not to be detrimental to the colony (caveat … I’m not aware of any long-term studies of this, or for the impact on the queen).

API-Bioxal approved methods of administration

The instructions for API-Bioxal clearly state that only a single treatment by vaporisation is approved per year. The exact wording is:

Maximal dose 2.3g per hive as a single administration. One treatment per year.

In contrast, when used as a solution for trickling the instructions state:

Up to two treatments per year (winter and/or spring-summer season in brood-free colonies).

This seems nonsensical to me considering what we now know about oxalic acid – remember, API-Bioxal was licensed in the same year (2015) that Al Toufailia et al., demonstrated it was detrimental to open brood, and I’m reasonably sure this had been shown previously (but can’t currently find the reference).

But, it gets worse …

API-Bioxal contains oxalic acid with powdered silica and glucose. I presume the silica is to keep it free-running. I’m not aware that powdered silica kills mites and I’m damned certain that glucose has no miticidal activity 😉 .

Neither of these two additives – which I’ve previously called cutting agents – are there to increase the activity of the oxalic acid … and the presence of the glucose is a real problem when vaporising.

Single use ...

Caramel coated Sublimox vaporiser pan

When glucose is heated to 160°-230°C it caramelises (actually, this happens at 150°C 6 ), coating the inside of the vaporising pan. This needs to be cleaned out afterwards 7. The instructions state:

Cool down and clean the vaporizer after use to remove possible residue (max 6%, around 0.140 g).

However, I don’t want to focus on what I consider to be a very effective but decidedly sub-optimal product … instead I want to discuss whether repeat treatment with oxalic acid actually works when there is brood present.

Why is repeat treatment recommended?

Remember, it’s not recommended or approved by the manufacturers of API-Bioxal or the Veterinary Medicines Directorate. I really should have titled this section ’Why is repeat treatment recommended by those who advocate it?’

But that wouldn’t fit on a single line 😉 .

When you sublimate oxalic acid, the gas cools and the oxalic acid crystals settle out on every surface within the hive – the walls, the frames, the comb, the bees etc.. For this reason, I prefer to vaporise oxalic acid when the colony is not tightly clustered. I want everything to be coated with oxalic acid, and I particularly want every bee to be coated because that’s where most of the mites are.

Unless they’re in capped cells 🙁 .

And if they’re in capped cells, the only way the Varroa (released when the brood emerges) will come into contact with oxalic acid is if it remains present and active within the hive. Unfortunately, it’s unclear to me exactly how long the oxalic acid does remain active, or what accounts for a drop in its activity.

But it does drop.

If you treat a colony with brood present and count the mites that appear on the Varroa tray every day it looks something like this:

Mite drop per day before and after treatment

’Something like’ because it depends upon the phoretic mite levels and the amount and rate of brood uncapping. For example, you often see higher mite drops from 24-48 hours than 0-24 hours after treatment.

I know not why.

The drop in the first 48 hours – presumably almost all phoretic mites – can be very much higher than the drop from day three onwards 8.

The duration of activity after vaporisation

Some studies claim oxalic acid remains active for 2-3 weeks after administration. I’m a little sceptical that it’s effective for that long and my own rather crude observations of post-treatment mite drop (of brooding colonies) suggests it returns to background levels within 5-7 days.

I could rabbit on about this for paragraphs as I’ve given it a reasonable amount of thought, but fortunately the late Pete Little did the experiment and showed that:

The recommended dose for colonies with brood is three or four doses seven days apart, however I found out that this is not effective enough, and treated 7, 6, 5 4, 3, 2 days apart to find out the most effective which is 5.

It therefore makes sense that three treatments at five day intervals should be sufficient. This period comfortably covers a complete capped brood cycle (assuming there is no drone brood in the colony) which is 12 days long.

Repeated oxalic acid vaporisation treatment regime.

If there is drone brood present you would theoretically need four treatments at 5 day intervals to be sure of covering the 15 day capped brood cycle of drones.

But it turns out there are some additional complications to consider.

Dosage

In the UK the recommended i.e. approved, maximum dose of API-Bioxal is 2.3 g by vaporisation. Remember my comments about the other rubbish stuff API-Bioxal contains, 2.3 g of API-Bioxal actually contains a fraction over 2 g of oxalic acid dihydrate.

This is the active ingredient.

When comparing different experiments where some have used ‘plain’ oxalic acid dihydrate and others have used – or will use – API-Bioxal, it’s important to consider the amount of the active ingredient only 9 .

In the US, oxalic acid was registered as an approved treatment for Varroa in 2015. By vaporisation, the approved dosage is 1 g of oxalic acid dihydrate per brood box i.e. half that approved in the UK.

Remember also that a deep Langstroth is 5% larger (by volume) than a National brood box.

And Jennifer Berry and colleagues in the University of Georgia have recently determined whether repeated administration of vaporised oxalic acid to a colony rearing brood is an effective way of controlling and reducing Varroa infestations (Berry et al., 2021).

And the answer is … decidedly underwhelming

Here are the experimental details.

The paper doesn’t state 10 when the experiment was done but they measured honey production in the treated colonies and were definitely brood rearing, so I’m assuming late summer.

Colonies were treated with 1 g / box (double Langstroth deeps) vaporised oxalic acid every five days for a total of 35 days i.e. 7 applications. Mite infestation levels (percent of workers carrying phoretic mites) were measured before and after treatment. Almost 100 colonies were used in the experiment, in three apiaries, randomly split into treated and control groups.

Let’s get the easy bit out of the way first … there was no difference in brood levels, adult bees or food stores at the end of the study. The treated hives were not disadvantaged by being treated … but they didn’t gain an advantage either 🙁 .

Mite levels after treatment normalised to pre-treatment levels (dotted line = no change)

During the experiment the percent mite infestation (PMI) levels in the untreated control colonies increased (as expected) by ~4.4. This is an average and there was quite a bit of variation, but it means that an initial mite infestation level of 4 (average) increased to 8.4 i.e. over 8 mites on every 100 adult workers in the hive.

3% is often considered the cutoff above which treatment is necessary.

Overall, the PMI of treated colonies reduced over the duration of the experiment … but only by 0.7.

From a colony health perspective this is a meaningless reduction.

Seven treatments with the recommended (in the US) dose of oxalic acid stopped the mite levels increasing, but did not reduce them.

Repeated administration of the US-approved oxalic acid dose by vaporisation does not reduce mite levels in a way that seems likely to significantly benefit the colony.

🙁

Dosage, again

I’m not sure the primary data used to justify the US approved 1 g / box dosage. Early studies by Thomas Radetzki (PDF) showed a 95% reduction in mite levels using a dose of 1.4 g. This was a large study involving ~1500 colonies and a dose of 2.8 g was not significantly more effective. I’m quoting the figures for broodless colonies 11.

The Berry results were similar to two smaller previous studies by Jamie Ellis and colleagues (Jack et al., 2020, 2021) who demonstrated that 1 g oxalic acid vaporised three times at weekly intervals was ineffective in controlling mite levels.

However Jack et al., (2021) also applied a similar treatment schedule using different doses of oxalic acid.

Data from Jack et al., 2021 using different repeat doses of oxalic acid

Ignore the intermediate values in panel A, just look at the pretreatment and ‘3 weeks’ mite infestation values.

Mite levels increased in untreated controls and decreased in all treated colonies. However, there was a clear dose response where the more oxalic acid used the greater the impact on the mite levels.

Four grams of oxalic acid reduced the mite infestation rate significantly … from ~5% to ~2% (I’ll return to this). However, the intermediate levels of oxalic acid, whilst reducing mite levels, did not do so significantly from the next closest amount of oxalic acid. For example, 1 g wasn’t significantly more effective than no treatment (as already stated), 2 g was not significantly more effective than 1 g and 4 g was not significantly more effective than 2 g.

But wait … there’s more

I’m familiar with two other studies that look at dose and/or repetition and efficacy (there are more, but this isn’t meant to be an exhaustive review, more a ”Do we know enough?” overview).

Gregoric et al., (2016) published a 12 study that appeared to use combinations of treatments in multiple apiaries. The abstract claims 97% reduction using three 1 g vaporisations, though these are spread over a 57 day period (!) stretching from mid-August to late-November. Mite drop in November following treatment was ~75% (presumably broodless) , but only 10-20% in August. Interestingly I can’t find the figure 97% anywhere in the results …

Finally, Al Toufailia et al., (2015) investigated the dose response to vaporised oxalic acid, showing an 80% reduction in infestation at 0.56 g and 93-98% who using 1.125, 2.25 and 4 g of oxalic acid. All of these studies were determined using broodless colonies.

The Al Toufailia and Jack studies – as well as the Berry study – also reported on adverse effects on the colony. With certain exceptions vaporisation was well tolerated. Some colonies went queenless. Where the queen was caged in late summer to render it broodless (Jack et al.,) some colonies subsequently failed to overwinter successfully (though, look on the bright side, mite levels were reduced 😉 ).

Don’t do that at home … I presume they impacted the production of winter bees.

confused.com

I’m not sure there’s a compelling, peer-reviewed study that definitively shows that repeat treatments of vaporised oxalic acid administered to a brood rearing colony reduces mite levels sufficiently.

Yes, the Jack et al., (2020) showed a significant reduction in the infestation rate (using 4 g three times at seven day intervals), but it was still around 2%.

In late summer, with 20-30,000 bees in the box and 6 frames of brood, that’s still ~600 mites (and potentially more in the capped brood).

In midwinter with about 10,000 workers and much smaller amounts of brood in the hive a 2% infestation rate is still 200 mites.

That’s still a lot of mites for a nearly broodless colony … I treat my colonies when broodless (and assume I’m killing ~90% of the mites present) and am disappointed if there are 45 mites on the Varroa tray. 50 mites on 10,000 workers is an infestation rate of 0.5%.

I’ve waffled on for too long.

All those advocating – or using – repeated oxalic acid vaporisation on brood rearing colonies in late autumn/winter need to think about:

  • dosage … 1 g is clearly too little (at a 5-7 day interval, but what if it was at a 4 day interval?), 2 g is better and 4 g is well-tolerated and certainly more effective
  • frequency … which I suspect is related to dosage. The goal must be to repeat sufficiently frequently that there is never a period when oxalic acid levels fall below a certain amount (and I don’t know what that amount is). 1 g on a daily basis might work well … who knows?
  • duration … you must cover a full capped brood cycle with the repeats
  • adverse effects … inevitable, but can be minimised with a rational treatment schedule

Broodless is best

It really is.

But, if your colonies are never broodless 13 then I wouldn’t be confident that repeat treatment was controlling Varroa levels sufficiently.

I have treated repeatedly with oxalic acid. In the good old days before API-Bioxal appeared. It certainly reduced Varroa levels, but not as well as my chosen Apivar does these days.

Repeated oxalic acid vaporisation is regularly proposed as the solution to Varroa but I’m certainly not confident that the data is there to support this claim.

Take care out there 😉


Notes

In a future post I’ll revisit this … I’ve got a pretty clear idea of how I’d go about demonstrating whether repeated oxalic acid treatments are effective in meaningfully reducing mite levels i.e. sufficient to protect the colony overwinter and through to the following late summer.

References

Al Toufailia, H., Scandian, L. and Ratnieks, F.L.W. (2015) ‘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’, Journal of Apicultural Research, 54(2), pp. 108–120. Available at: https://doi.org/10.1080/00218839.2015.1106777.
Berry, J.A. et al. (2022) ‘Assessing Repeated Oxalic Acid Vaporization in Honey Bee (Hymenoptera: Apidae) Colonies for Control of the Ectoparasitic Mite Varroa destructor’, Journal of Insect Science, 22(1), p. 15. Available at: https://doi.org/10.1093/jisesa/ieab089.
Gregorc, A. et al. (2016) ‘Integrated varroa control in honey bee (Apis mellifera carnica) colonies with or without brood’, Journal of Apicultural Research, 55(3), pp. 253–258. Available at: https://doi.org/10.1080/00218839.2016.1222700.
Jack, C.J., van Santen, E. and Ellis, J.D. (2020) ‘Evaluating the Efficacy of Oxalic Acid Vaporization and Brood Interruption in Controlling the Honey Bee Pest Varroa destructor (Acari: Varroidae)’, Journal of Economic Entomology, 113(2), pp. 582–588. Available at: https://doi.org/10.1093/jee/toz358.
Jack, C.J., van Santen, E. and Ellis, J.D. (2021) ‘Determining the dose of oxalic acid applied via vaporization needed for the control of the honey bee (Apis mellifera) pest Varroa destructor’, Journal of Apicultural Research, 60(3), pp. 414–420. Available at: https://doi.org/10.1080/00218839.2021.1877447.

Broodless?

Synopsis : The colony needs to be broodless for effective oxalic acid treatment in winter. You might be surprised at how early in the winter this broodless period can be (if there is one). How can you easily determine whether the colony is broodless?

Introduction

In late spring or early summer a broodless colony is a cause for concern. Has the colony swarmed? Have you killed the queen? Since worker brood takes 21 days from egg to emergence, a broodless colony has gone 3 weeks without any eggs being laid.

You’re right to be concerned about the queen.

Of course, since you’ve been inspecting the hive on a 7-10 day rotation, you noticed the absence of eggs a fortnight ago, so you’re well on your way to knowing what the problem is, and therefore being able to solve it 😉 .

But in late autumn or early winter a broodless colony is not a cause for concern.

It’s an opportunity.

Are they rearing brood? Probably by now … it’s mid-January

In my view it’s a highly desirable state for the colony to be in.

If the colony is broodless then the ectoparasitic Varroa mites cannot be hiding away under the cappings, gorging themselves on developing pupae and indulging in their – frankly repellent – incestuous reproduction.

Urgh!

Instead the mites will all be riding around the colony on relatively young workers (and in winter, physiologically all the workers in the hive are ‘young’, irrespective of their age) in what is incorrectly termed the phoretic stage of their life cycle.

This is incorrect as phoresy means “carried on the body of another organism without being parasitic” … and these mites are not just being carried around, they’re also feeding on the worker bees.

You can read all about phoretic mites, their diet and their repulsive reproductive habits in previous posts.

What is the opportunity?

A broodless colony in the winter is an opportunity because phoretic mites (whether misnamed or not) are very easy to kill because they’re not protected by the wax capping covering the sealed brood.

Total mite numbers surviving OA treatment depends upon the proportion in capped cells

And today’s post is all about identifying when the colony is broodless.

Discard your calendar

I’ve said it before 1 … the activities of the colony (swarming, nectar gathering, broodlessness 2 ) are not determined by the calendar.

Instead they’re determined by the environment. This covers everything from the available forage to the climate and recent weather 3.

And the environment changes. It changes from year to year in a single location – an early spring, a late summer – and it differs between locations on the same calendar date.

All of which means that, although you can develop a pretty good idea of when you need to intervene or manage things – like adding supers, or conducting swarm control – these are reactive responses to the state of the colony, rather than proactive actions applied because it’s the 9th of May 4.

And exactly the same thing applies to determining when the colony is broodless in the winter. Over the last 6 years I’ve had colonies that are broodless sometime between between mid October and mid/late December. They’re not broodless for this entire period, but they are for some weeks starting from about mid-October and ending sometime around Christmas.

Actually, to be a little more precise, I generally know when they start to be broodless, but I rarely monitor when they stop being broodless, not least because it’s a more difficult thing to determine (as will become clear).

Don’t wait until Christmas

A broodless colony is an opportunity because the phoretic mites can easily be killed by a single application of oxalic acid.

Many beekeepers treat their colonies with oxalic acid between Christmas and New Year.

It was how they were taught when they started beekeeping, it’s convenient because it’s a holiday period, it’s a great excuse to escape to the apiary and avoid another bellyful of cold cuts followed by mince pies (or the inlaws 5 ) and because it’s ‘midwinter’.

But, my experience suggests this is generally too late in the year.  The colony is often already rearing brood by the time you’ve eaten your first dozen mince pies.

If you’re going to go to the trouble of treating your colonies with oxalic acid, it’s worth making the effort to apply it to achieve maximum efficacy 6.

I’m probably treating my colonies with oxalic acid in 8-9 days time. The queens have stopped laying and there was very little sealed brood present in the colonies I briefly checked on Monday this week. The sealed brood will have all emerged by the end of next week.

It’s worth making plans now to determine when your colonies are broodless. Don’t just assume sometime between Christmas and New Year ’will be OK’.

But it’s too early now for them to be broodless … or to treat with oxalic acid

If your colonies are going to go through a broodless period this winter 7 it’s more likely to be earlier rather than later.

Why?

Because if the colonies had a long broodless period stretching into mid-January or later it’s unlikely they’ll build up strongly enough to swarm … and since swarming is honey bee reproduction, it’s a powerful evolutionary and selective pressure.

Colonies that start rearing brood early, perhaps as early as the winter solstice, are more likely to build up strongly, and therefore are more likely to swarm, so propagating the genes for early brood rearing.

But surely it would be better to treat with oxalic acid towards the end of the winter?

Mites do not reproduce during the misnamed phoretic stage of the life cycle. Therefore, aside from those mites lost (hopefully through the open mesh floor) due to allogrooming, or that just die 8, there will be no more mites later in the broodless period than at the beginning.

Since the mites are going to be feeding on adult workers (which is probably detrimental to those workers), and because it’s easier to detect the onset of broodlessness (see below), it makes sense to treat earlier rather than later.

Your bees will thank you for it 😉 .

How to detect the absence of brood

Tricky … how do you detect if something is not present?

I think the only way you can be certain is to conduct a full hive inspection, checking each side of every frame for the presence of sealed brood.

Perhaps not the ideal conditions for a full hive inspection

But I’m not suggesting you do that.

It’s a highly intrusive thing to do to a colony in the winter. It involves cracking open the propolis seal to the crownboard, prising apart the frames and splitting up the winter cluster.

On a warm winter day that’s a disruptive process and the bees will show their appreciation 🙁 . On a cold winter day, particularly if you’re a bit slow checking the frames (remember, the bees will appear semi-torpid and will be tightly packed around any sealed brood present, making it difficult to see), it could threaten the survival of the colony.

And don’t even think about doing it if it’s snowing 🙁 .

Even after reassembling the hive the colony is likely to suffer … the broken propolis seals will let in draughts, the colony will have to use valuable energy to reposition themselves.

A quick peek

I have looked in colonies for brood in the winter. However, I don’t routinely do this.

Now, in mid/late autumn the temperature is a bit warmer and it’s less disruptive. I checked half a dozen on Sunday/Monday. It was about 11°C with rain threatening. I had to open the boxes to retrieve the Apivar strips anyway after the 9-10 week treatment period.

Recovered Apivar strips

I had repositioned the Apivar strips about a month ago, moving them in from the outside frames to the edges of the shrinking brood nest. By then – early October – most of the strips were separated by just 3 or 4 frames.

The flanking frames were all jam packed with stores. The fondant blocks were long-gone and the bees had probably also supplemented the stores with some nectar from the ivy.

Over the last month the brood nest continued to shrink, but it won’t have moved somewhere else in the hive … it will still be somewhere between the Apivar strips, and about half way is as good a place as any to start.

Apivar strip (red bars) placement and the shrinking brood nest

So, having removed the crownboard and the dummy board, I just prise apart the frames to release the Apivar strips and then quickly look at the central frame between them. If there’s no sealed brood there, and you can usually also have a look at the inner faces of the flanking frames down the ‘gap’ you’ve opened, then the colony is probably broodless.

It takes 45-60 seconds at most.

It’s worth noting that my diagram shows the broodnest located centrally in the hive. It usually isn’t. It’s often closer to the hive entrance and/or (in poly boxes) near the well insulated sidewall of the hive.

Hive debris

But you don’t need to go rummaging through the brood box to determine whether the colony is broodless (though – as noted earlier – it is the probably the only was you can be certain there’s no brood present).

The cappings on sealed brood are usually described as being ‘biscuit-coloured’.

Not this colour of biscuit

‘Biscuit-coloured’ is used because all beekeepers are very familiar with digestive biscuits (usually consumed in draughty church halls). If ‘biscuit-coloured’ made you instead think of Fox’s Party Rings then either your beekeeping association has too much money, or you have young children.

Sorry to disappoint you … think ‘digestives’ 😉 .

That’s more like it …

The cappings are that colour because the bees mix wax and pollen to make them air-permeable. If they weren’t the developing pupa wouldn’t be able to breathe.

And when the developed worker emerges from the cell the wax capping is nibbled away and the ‘crumbs’ (more biscuity references) drop down through the cluster to eventually land on the hive floor.

Where they’re totally invisible to the beekeeper 🙁 .

Unless it’s an open mesh floor … in which case the crumbs drop through the mesh to land on the ground where they’ll soon get lost in the grass, carried off by ants or blown away 🙁 .

It should therefore be obvious that if you want detect the presence of brood emerging you need to have a clean tray underneath the open mesh floor (OMF).

Open mesh floors and Correx boards

Most open mesh floors have a provision to insert a Correx (or similar) board underneath the mesh. There are good and bad implementations of this.

Poor designs have a large gap between the mesh and the Correx board, with no sealing around the edges 9. Consequently, it’s draughty and stuff that lands on the board gets blown about (or even blown away).

Good designs – like the outstanding cedar floors Pete Little used to make – have a close-fitting wooden tray on which the Correx board is placed. The tray slides underneath the open mesh floor and seals the area from draughts 10.

Open mesh floor and close-fitting Varroa tray by Pete Little

Not only does this mean that the biscuity-coloured crumbs stay where they fall, it also means that this type of floor is perfect when treating the colony with vaporised oxalic acid. Almost none escapes, meaning less chance of being exposed to the unpleasant vapours if you’re the beekeeper, and more chance of being exposed to the unpleasant vapours if you’re a mite 😉 .

Since the primary purpose of these Correx trays is to determine the numbers of mites that drop from the colony, either naturally or during treatment, it makes sense if they are pale coloured. It’s also helpful if they are gridded as this makes counting mites easier.

Easy counting ...

Easy counting …

And, with a tray in situ for a 2-3 days you can quickly get an idea whether there is brood being uncapped.

Reading the runes

The diagram below shows a schematic of the colony (top row) and the general appearance of debris on the Varroa tray (bottom row).

It’s all rather stylised.

The brood nest – the grey central circle is unlikely to be circular, or central 11.

The shrinking broodnest (top) and the resulting pattern on the Varroa tray (bottom)

Imagine that the lower row of images represent the pattern of the cappings that have fallen onto the tray over at least 2-3 days.

Biscuit-coloured cappings on Varroa tray

As the brood nest shrinks, the area covered by the biscuit-coloured cappings is reduced. At some point it is probably little more than one rather short stripe, indicating small amounts of brood emerging on two facing frames.

With just one observation highlighted should you plan to treat next week?

Let’s assume you place the tray under the open mesh floor and see that single, short bar of biscuity crumbs (highlighted above). There’s almost nothing there.

Do you assume that it will be OK to treat them with oxalic acid the following week?

Not so fast!

With just a single observation there’s a danger that you could be seeing the first brood emerging when there’s lots more still capped on adjacent frames.

It’s unlikely – particularly in winter – but it is a possibility.

Far better is to make a series of observations and record the trajectory of cappings production. Is it decreasing or is it increasing?

Multiple observations allows the expanding or contracting brood nest to be monitored

With a couple of observations 10-12 days apart you’ll have a much better idea of whether the brood area is decreasing over time, or increasing. Repeated observations every 10-12 days will give you a much better idea of what’s going on.

Developing brood is sealed for ~12 days. Therefore, if brood rearing is starting, the first cappings that appear on the Varroa tray are only a small proportion of the total sealed brood in the colony.

Very little cappings but certainly not broodless

Of course, in winter, the laying rate of the queen is much reduced. Let’s assume she’s steadily laying just 50 eggs per day i.e. about 12.5 cm2. By the time the first cappings appear on the Varroa tray (as the first 50 workers emerge) there will be another 600 developing workers occupying capped cells … and the worry is that they’re occupying those cells with a Varroa mite.

The cessation of brood rearing

In contrast, if there’s brood in the colony but the queen is slowing down and eventually stops egg laying, with repeated observations 12 the amount and coverage of the biscuit-coloured cappings will reduce and eventually disappear.

At that point you can be reasonably confident that there is no more sealed brood in the colony and, therefore, that it’s an appropriate time to treat with oxalic acid.

In this instance – and unusually – absence of evidence is evidence of absence 🙂 .

But my bees are never broodless in the winter

All of the above still applies, with the caveat that rather than looking for the absence of any yummy-looking biscuity crumbs on the tray, you are instead looking for the time that they cover the minimal area.

If the colony is never broodless in winter it still makes sense to treat with oxalic acid when the brood is at the lowest level (refer back to the first graph in this post).

At that time the smallest number of mites are likely to be occupying capped cells.

However, this assumption is incorrect if the small number of cells are very heavily parasitised, with multiple mites occupying a single sealed cell. This can happen – at least in summer – in heavily mite infested hives. I’ve seen 12-16 mites in some cells and Vincent Poulin reported seeing 26 in one cell in a recent comment.

Urgh! (again)

I’m not aware of any data on infestation levels of cells in winter when brood levels are low, though I suspect this type of multiple occupancy is unlikely to occur (assuming viable mite numbers are correspondingly low). I’d be delighted if any readers have measured mites per cell in the winter, or know of a publication in which it’s reported 13.

This isn’t an exact science

What I’ve described above sounds all rather clinical and precise.

It isn’t.

Draughts blow the cappings about on the tray. The queen’s egg laying varies from day to day, and can stop and start in response to low temperatures or goodness-knows-what-else. The pattern of cappings is sometimes rather difficult to discern. Some uncapped stores can have confoundingly dark cappings etc.

But it is worth trying to work out what’s going on in the box to maximise the chances that the winter oxalic acid treatment is applied at the time when it will have the greatest effect on the mite population.

By minimising your mite levels in winter you’re giving your bees the very best start to the season ahead.

Unrestricted mite replication – the more you start with the more you end up with (click image for more details)

The fewer mites you have at the start of the season, the longer it takes for dangerously high mite levels (i.e. over 1000 according to the National Bee Unit) to develop. Therefore, by reducing your mite levels in the next few weeks you are increasing your chances that the colony will be able to rear large numbers of healthy winter bees for next winter.

That sounds to me like a good return on the effort of making a few trips to the apiary in November and early December …


 

Winter covers and colony survival

Synopsis : A recent study shows increased overwinter colony survival of ‘covered’ hives wrapped in Correx and with insulation under the roof. What provides the most benefit, and are the results as clear cut as they seem?

Introduction

A recent talk by Andrew Abrahams to the Scottish Native Honey Bee Society coincided with me catching up my 1 backlog of scientific papers on honey bees. I’d been reading a paper on the benefits of wrapping hives in the winter and Andrew commented that he did exactly that to fend off the worst of the wet weather. Andrew lives on the island of Colonsay about 75 km south of me and we both ‘benefit’ from the damp Atlantic climate.

The paper extolled the virtues of ‘covered’ hives and the data the researchers present looks, at first glance, compelling.

For example, <5% of covered hives perished overwinter in contrast to >27% of the uncovered control hives.

Wow!

Why doesn’t everyone wrap their hives?

However, a closer look at the paper raises a number of questions about what is actually benefitting (or killing) the colonies.

Nevertheless, the results are interesting. I think the paper poses rather more questions than it answers, but I do think the results show the benefits of hive insulation and these are worth discussing.

Bees don’t hibernate

Hibernation is a physiological state in which the metabolic processes of the body are significantly reduced. The animal becomes torpid, exhibiting a reduced heart rate, low body temperature and reduced breathing. Food reserves e.g. stored fat, are conserved and the animal waits out the winter until environmental conditions improve.

However, bees don’t hibernate.

Winter cluster 3/1/21 3°C (insulation block removed from the crownboard)

If you lift the lift the roof from a hive on a cold midwinter day you’ll find the bees clustered tightly together. But, look closely and you’ll see that the bees are moving. Remove the crownboard and some bees will probably fly.

The cluster conserves warmth and there is a temperature gradient from the outside – termed the mantle – to the middle (the core).

If chilled below ~5.5°C a bee becomes semi-comatose 2 and unable to warm herself up again. The mantle temperature of the cluster never drops below ~8°C, but the core is maintained at 18-20°C when broodless or ~35°C if they are rearing brood. I’ve discussed the winter cluster in lots more detail a couple of years ago.

The metabolic activity of the clustered winter bees is ‘powered’ by their consumption of the stores they laid down in the autumn. It seems logical to assume that it will take more energy (i.e. stores) to maintain a particular cluster temperature if the ambient temperature is lower.

Therefore, logic would also suggest that the greater the insulation properties of the hive – for a particular difference in ambient to cluster temperature – the less stores would be consumed.

Since winter starvation is bad for bees (!) it makes sense to be thinking about this now, before the temperatures plummet in the winter.

Cedar and poly hives

I’m not aware of many comparative studies of the insulation properties of hives made from the two most frequently used materials – wood and polystyrene. However, Alburaki and Corona (2021) have investigated this and shown a small (but statistically significant) difference in the inner temperature of poly Langstroth hives when compared to wooden ones.

Poly hives were ~0.5°C warmer and, perhaps more importantly, exhibited much less variation in temperature over a 24 hour period.

Temperature and humidity in poly and wood hives

In addition to the slight temperature difference, the humidity within the wooden hives was significantly higher than that of poly.

The hives used in this study were occupied by bees and the temperature and humidity were recorded from sensors placed in a modified frame in the ‘centre of the brood box’. The external ambient temperature averaged 0°C, but fluctuated over a wide range (-10°C to 20°C) during the four month study 3.

Temperature anomalies

Whilst I’m not surprised that the poly hives were marginally warmer, I was surprised how low the internal hive temperatures were. The authors don’t comment on whether the ‘central’ frame was covered with bees, or whether the bees were rearing brood.

The longitudinal temperature traces (not reproduced here – check the paper) don’t help much either as they drop in mid-February when I would expect brood rearing to be really gearing up … Illogical, Captain.

The authors avoid any discussion on why the average internal temperature was at least 5-8°C cooler than the expected temperature of the core of a clustered broodless colony, and ~25°C cooler than a clustered colony that was rearing brood.

My guess is that the frame with the sensors was outside the cluster. For example, perhaps it was in the lower brood box 4 with the bees clustered in the upper box?

We’ll never know, but let’s just accept that poly hives – big surprise 😉 – are better insulated. Therefore the bees should need to use less stores to maintain a particular internal temperature.

And, although Alburaki and Corona (2021) didn’t measure this, it did form part of a recent study by Ashley St. Clair and colleagues from the University of Illinois (St. Clair et al., 2022).

Hive covers reduce food consumption and colony mortality

This section heading repeats the two key points in the title of this second paper.

I’ll first outline what was done and describe these headline claims in more detail. After that I’ll discuss the experiments in a bit more detail and some caveats I have of the methodology and the claims.

I’ll also make clear what the authors mean by a ‘hive cover’.

The study was conducted in central Illinois and involved 43 hives in 8 apiaries. Hives were randomly assigned to ‘covered’ or ‘uncovered’ i.e. control – groups (both were present in every apiary) and the study lasted from mid-November to the end of the following March.

Ambient (blue), covered (black) and control (dashed) hive temperatures

There were no significant differences in internal hive temperature between the two groups and – notably – the temperatures were much higher (15°-34°C) than those recorded by Alburaki and Corona (2021).

All colonies, whether covered or uncovered, got lighter through the winter, but the uncovered colonies lost significantly more weight once brood rearing started February. The authors supplemented all colonies with sugar cakes in February and the control colonies used ~15% more of these additional stores before the study concluded.

I don’t think any of these results are particularly surprising – colonies with additional insulation get lighter more slowly and need less supplemental feeding.

The surprising result was colony survival.

Less than 5% (1/22) of the covered hives perished during the winter but over 27% (6/21) of the control hives didn’t make it through to the following spring.

(Un)acceptable losses

To put these last figures into context the authors quote a BeeI Informed Partnership survey where respondents gave a figure of 23.3% as being ’acceptable’ for winter colony losses.

That seems a depressingly high figure to me.

However, look – and weep – at the percentage losses across the USA in the ’20/’21 winter from that same survey 5.

Bee Informed Partnership 2021 winter colony losses (preliminary data)

This was a sizeable survey involving over 3,300 beekeepers managing 192,000 colonies (~7% of the total hives in the USA).

If hive covers reduce losses to just 5% why does Illinois report winter losses of 47%? 6

Are the losses in this manuscript suspiciously low?

Or, does nobody use hive covers?

I don’t know the answers to these questions, but I also wasn’t sure when I started reading the paper what the authors meant by a hive ‘cover’ … which is what I’ll discuss next.

Hive covers

The hives used in this study were wooden Langstroths and the hive covers were 4 mm black corrugated polypropylene sleeves.

This is what I call Correx … one of my favourite materials for beekeeping DIY.

These hive covers are available commercially in the USA (and may be here, I’ve not looked). At $33 each (Yikes) they’re not cheap, but how much is a colony worth?

Significantly more than $33.

I’ve not bothered to make the conversion of Langstroth Deep dimensions (always quoted in inches 🙁 ) to metric and then compared the area of Correx to the current sheet price of ~£13 … but I suspect there are savings to be made by the interested DIYer 7.

However, knowing (and loving) Correx, what strikes me is that it seems unlikely to provide much insulation. At only 4 mm thick and enclosing an even thinner air gap, it’s not the first thing I’d think of to reduce heat loss 8.

4 mm Correx sheet

Thermal resistance is the (or a) measure of the insulating properties of materials. It’s measured in the instantly forgettable units of square metre kelvin per watt m2.K/W.

I couldn’t find a figure for 4 mm Correx, but I did manage to find some numbers for air.

A 5 mm air gap – greater than separates the inner and outer walls of a 4 mm Correx hive cover – has a thermal resistance of 0.11 m2.K/W.

Kingspan

It’s not possible to directly compare this with anything meaningful, but there is data available for larger ‘thicknesses’ of air, and other forms of insulation.

An air gap of 100 mm has a thermal resistance of about 0.17 m2.K/W. For comparison, the same thickness of Kingspan (blown phenolic foam wall insulation, available from almost any building site skip) has a thermal resistance of 5, almost 30 times greater.

And, it turns out, St. Clair and colleagues also added a foam insulation board on top of the hive crownboard (or ‘inner cover’ as they call it in the USA). This board was 3.8 cm thick and has somewhat lower thermal resistance than the Kingspan I discussed above.

It might provide less insulation than Kingspan, but it’s a whole lot better than Correx.

This additional insulation is only briefly mentioned in the Materials and Methods and barely gets another mention in the paper.

A pity, as I suspect it’s very important.

Perspex crownboard with integrated 50 mm Kingspan insulation

I’m very familiar with Kingspan insulation for hives. All my colonies have a 5 cm thick block present all year – either placed over the crownboard, built into the crownboard or integrated into the hive roof.

Two variables … and woodpeckers

Unfortunately, St. Clair and colleagues didn’t compare the weight loss and survival of hives ‘covered’ by either wrapping them in Correx or having an insulated roof.

It’s therefore not possible to determine which of these two forms of protection is most beneficial for the hive.

For reasons described above I think the Correx sleeve is unlikely to provide much direct thermal insulation.

However, that doesn’t mean it’s not beneficial.

At the start of this post I explained that Andrew Abrahams wraps his hives for the winter. He appears to use something like black DPM (damp proof membrane).

Hive wrapped in black DPM (to prevent woodpecker damage)

Andrew uses it to keep the rain off the hives … I’ve used exactly the same stuff to prevent woodpecker damage to hives during the winter.

It’s only green woodpeckers (Picus viridis) that damage hives. It’s a learned activity; not all green woodpeckers appear to know that beehives are full of protein-rich goodies in the depths of winter. If they can’t grip on the side of the hive they can’t chisel their way in.

When I lived in the Midlands the hives always needed winter woodpecker protection, but the Fife Yaffles 9 don’t appear to attack hives.

Here on the west coast, and on Colonsay, there are no green woodpeckers … and I know nothing about the hive-eating woodpeckers of Illinois.

So, let’s forget the woodpeckers and return to other benefits that might arise from wrapping the hive in some form of black sheeting during the winter.

Solar gain and tar paper

Solar gain is the increase in thermal energy (or temperature as people other than physicists with freakishly large foreheads call it) of something – like a bee hive – as it absorbs solar radiation.

On sunny days a black DPM-wrapped hive (or one sleeved in a $33 Correx/Coroplast hive ‘cover’) will benefit from solar gain. The black surface will warm up and some of that heat should transfer to the hive.

And – in the USA at least – there’s a long history of wrapping hives for the winter. If you do an internet search for ‘winterizing hives’ or something similar 10 you’ll find loads of descriptions (and videos) on what this involves.

Rather than use DPM, many of these descriptions use ‘tar paper’ … which, here in the UK, we’d call roofing felt 11.

Roofing felt – at least the stuff I have left over from re-roofing sheds – is pretty beastly stuff to work with. However, perhaps importantly, it has a rough matt finish, so is likely to provide significantly more solar gain than a covering of shiny black DPM.

I haven’t wrapped hives in winter since I moved back to Scotland in 2015. However, the comments by Andrew – who shares the similarly warm and damp Atlantic coastal environment – this recent paper and some reading on solar gain are making me wonder whether I should.

Fortunately, I never throw anything away, so should still have the DPM 😉

Winter losses

Illinois has a temperate climate and the ambient temperature during the study was at or below 0°C for about 11 weeks. However, these sorts of temperatures are readily tolerated by overwintering colonies. It seems unlikely that colonies that perished were killed by the cold.

So what did kill them?

Unfortunately there’s no information on this in the paper by St. Clair and colleagues.

Perhaps the authors are saving this for later … ’slicing and dicing’ the results into MPU’s (minimal publishable units) to eke out the maximum number of papers from their funding 12, but I doubt it.

I suspect they either didn’t check, checked but couldn’t determine the cause, or – most likely – determined the cause(s) but that there was no consistent pattern so making it an inconclusive story.

But … it was probably Varroa and mite-transmitted Deformed wing virus (DWV).

It usually is.

Varroa

There were some oddities in their preparation of the colonies and late-season Varroa treatment.

Prior to ‘winterizing’ colonies they treated them with Apivar (early August) and then equalised the strength of the colonies. This involves shuffling brood frames to ensure all the colonies in the study were of broadly the same strength (remember, strong colonies overwinter better).

A follow-up Varroa check in mid-October showed that mite levels were still at 3.5% (i.e. 10.5 phoretic mites/300 bees) and so all colonies were treated with vaporised oxalic acid (OA).

Sublimox vaporiser

Sublimox vaporiser … phoretic mites don’t stand a chance

In early November, mite levels were down to a more acceptable 0.7%. Colonies received a second OA treatment in early January.

For whatever reason, the Apivar treatment appears to have been ineffective.

When colonies are treated for 6-10 weeks with Apivar (e.g. early August to mid-October) mite levels should be reduced by >90%.

Mite infestation levels of 3.5% suggest to me that the Apivar treatment did not work very well. That being the case, the winter bees being reared through August, September and early October would have been exposed to high mite levels, and so acquired high levels of DWV.

OA treatment in mid-October would kill these remaining mites … but the damage had already been done to thediutinus’ winter bees.

That’s my guess anyway.

An informed guess, but a guess nevertheless, based upon the data in the paper and my understanding of winter bee production, DWV and rational Varroa management.

In support of this conclusion it’s notable that colonies died from about week 8, suggesting they were running out of winter bees due to their reduced longevity.

If I’m right …

It raises the interesting question of why the losses were predominantly (6 vs 1) of the control colonies?

Unfortunately the authors only provide average mite numbers per apiary, and each apiary contained a mix of covered and control hives. However, based upon the error bars on the graph (Supporting Information Fig S1 [PDF] if you’re following this) I’m assuming there wasn’t a marked difference between covered and control hives.

I’ve run out of informed guesses … I don’t know the answer to the question. There’s insufficient data in the paper.

Let’s briefly revisit hive temperatures

Unusually, I’m going to present the same hive temperature graph shown above to save you scrolling back up the page 13.

Ambient (blue), covered (black) and control (dashed) hive temperatures

There was no overall significant difference in hive temperature between the control and covered colonies. However, after the coldest weeks of the winter (7 and 8 i.e. the end of February), hive temperatures started to rise and the covered colonies were consistently marginally warmer. By this time in the season the colonies should be rearing increasing amounts of brood.

I’ve not presented the hive weight changes. These diverged most significantly from week 8. The control colonies used more stores to maintain a similar (actually – as stated above – marginally lower) temperature. As the authors state:

… covered colonies appeared to be able to maintain normal thermoregulatory temperatures, while consuming significantly less stored food, suggesting that hive covers may reduce the energetic cost of nest thermoregulation.

I should add that there was no difference in colony strength (of those that survived) between covered and control colonies; it’s not as though those marginally warmer temperatures from week 9 resulted in greater brood rearing.

Are lower hive temperatures ever beneficial in winter?

Yes.

Varroa management is much easier if colonies experience a broodless period in the winter.

A single oxalic acid treatment during this broodless period should kill 95% of mites – as all are phoretic – leaving the colony in a very good state for the coming season.

If you treat your colonies early enough to protect the winter bees there will inevitably be some residual mite replication in the late season brood, thereby necessitating the midwinter treatment as well.

I’m therefore a big fan of cold winters. The colony is more likely to be broodless at some point.

I was therefore reassured by the similarity in the temperatures of covered and control colonies from weeks 48 until the cold snap at the end of February. Covered hives should still experience a broodless period.

I’m off for a rummage in the back of the shed to find some rolls of DPM for the winter.

I don’t expect it will increase my winter survival rates (which are pretty good) and I’m not going to conduct a controlled experiment to see if it does.

If I can find the DPM I’ll wrap a few hives to protect them from the winter weather. With luck I should be able to rescue an additional frame or two of unused stores in the spring (I often can anyway). I stack this away safely and then use it when I’m making up nucs for queen mating.

I suspect that the insulation over the crownboard provides more benefit than the hive ‘wrap’. As stated before, all my colonies are insulated like this year round as I’m convinced it benefits the colony, reducing condensation over the cluster and keeping valuable warmth from escaping. However, wrapping the hive for solar gain and/or weather protection is also worth considering.


References

Alburaki, M. and Corona, M. (2022) ‘Polyurethane honey bee hives provide better winter insulation than wooden hives’, Journal of Apicultural Research, 61(2), pp. 190–196. Available at: https://doi.org/10.1080/00218839.2021.1999578.

St. Clair, A.L., Beach, N.J. and Dolezal, A.G. (2022) ‘Honey bee hive covers reduce food consumption and colony mortality during overwintering’, PLOS ONE, 17(4), p. e0266219. Available at: https://doi.org/10.1371/journal.pone.0266219.

Winter projects

Synopsis : Now is the time to make plans for the long winter ahead; frame building, winter projects, some light reading or an escape to somewhere warmer and with better wine?

Introduction

The good late summer September weather 1 has been replaced with the first of the equinoctial gales. Actually, more of a 30-40 mph stiff breeze with an inch or two of rain than a real gale. Nevertheless, wet and windy enough to preclude any outdoor jobs, and instead make my thoughts turn to winter projects.

The more northerly (or southerly) the latitude, the longer the winter is. Here in north west Scotland there’s virtually no practical beekeeping to be done between the start of October and early/mid April i.e. over 6 months of the year.

Some beekeepers fill these empty months by taking a busman’s holiday … disappearing to Chile or New Zealand or somewhere equally warm and pleasant, where they can talk beekeeping – or even do some beekeeping – and, coincidentally 2 enjoy some excellent wines.

Santiago bee graffiti

Santiago, Chile, bee graffiti …

Others ignore bees and beekeeping for the entire winter and think (and do) something completely different. They build model railways, or practise their ju-jitsu or – if really desperate – catch up on all the household chores that were abandoned during the bee season.

They then start the following season relatively unprepared. Almost certainly, next season will be similar to last season. They’ll make similar mistakes, run out of frames mid-season and lose more swarms than they’d like.

Rinse and repeat.

Alternatively, with a little thought, some reading, a bit of effort and some pleasant afternoons in the shed/garage/lounge, they can both plan for the season ahead and prepare some of the kit that they might need.

As Benjamin Franklin said ”By failing to prepare, you are preparing to fail.”

Looking back to look forward

I’ve discussed beekeeping records previously (and should probably revisit the topic). My records in the early years were terse, patchy, illegible and of little real use, perhaps other than in the few days that separated colony inspections.

Better than nothing

Better than nothing … just.

My records now are equally terse, but up-to-date and reasonably informative. I’ve got a numbering system for my colonies and queens that means they can be tracked through the season. The records are dated (rather than ’last Friday’) so I can calculate when important events – like queen emergence or mating – are due.

They’re also legible, which makes a huge difference. I could just about read my old scrawled pencil notes a few days after an inspection, but would have had no chance 5 months later.

By which time I’d have lost the little notebook anyway.

So, at some point over the next few months – sooner rather than later – I’ll look through my records, update the ‘queen pedigree’ table 3 and summarise things for the season ahead.

In the spring I’ll update a new sheet of records with a short note on overwintering strength/success and then we’ll be ready to go.

But, in reviewing the records I’ll remind myself about the things I ran out of, the timing of swarm control (when there’s the maximum pressure on available kit) and ideas I might have noted down on how things could have been done better 4.

Reading and listening

The winter is a great time to catch up on a bit of theory. Some beekeepers do exam after exam, pouring over Yates’s Study Notes until they can recite chapters verbatim.

I’ve done enough exams in my lifetime for … a lifetime, and have no intention of doing any more.

However, I’m always happy to do a bit of reading. I’ve currently got The Native Irish Honey Bee and Joe Conti’s The Hopkins Method … (which I’ll return to shortly) by my desk. I’m also partially successfully at keeping up with some of the relevant scientific literature 5.

A larger and more enthusiastic audience than usually seen at a beekeeping talk

There are also numerous winter talks available. Some are through local associations, others are available more widely. I ‘virtually’ attended one this evening where there were questions from as far apart as Orkney and Tasmania.

Of particular relevance to Scottish beekeepers, it’s worth noting that our association membership fees are usually significantly less than south of the border (probably because your SBA membership is separate), so you can inexpensively belong to a couple of associations and benefit from their talks programmes and – if you’re lucky – Co-Op purchasing schemes 😉

My attendance at these talks is less good than it should be, largely because I give a lot of talks each winter, but I instead benefit from the Q&A sessions which can be both entertaining and informative.

OK … enough theory

Theory is all well and good, but beekeeping is a practical pastime and just because it’s dark, cold, wet and windy, doesn’t mean there isn’t practical stuff you could be doing.

Competitive beekeepers will use the time to prepare the perfect wax block or bottle of mead for their – local or national – annual honey show.

I’m not competitive, and my wax is pretty shonky but I’ve had fun making (and more fun testing) mead 😉

But there are lots of other things to do …

The known knowns

By reading your comprehensive notes you will know that you ended the season with 5 colonies, that swarming started in mid-May but was over by early July, and that you’ve got one really stellar queen you’d like to raise 2-3 nucs from.

All of which means you are going to need a minimum of 60 new frames next season. These need to be ready before swarming starts.

Bamboo foundationless frames

Bamboo foundationless frames

How did I get to 60?

About a third of brood frames should be rotated out and replaced each season (~20). The nucleus method of swarm control uses the fewest frames, but you’re likely to have to use swarm control for all your colonies (~25). Then there’s a further 15 frames for the 3 additional nucs you want to prepare. Of course, if you’ve got lots of stored drawn comb 6 or you use double brood boxes, or Pagden’s artificial swarm method these numbers will be different.

The point is, you will need extra frames next season.

I’m ending this season with about 20 colonies and so expect to need over 200 frames next year, possibly more if queen rearing goes well. Some frames will be recycled foundationless frames but others will contain normal wired foundation.

And what about supers? 2022 was a good year for honey. If you had enough supers and super frames you’ll probably be OK in an average year.

Whether it’s average or not, it’s always easier to build the frames – well-fortified with tea and cake – in the winter, rather than in a rush as you prepare to go to the apiary.

Exactly the same type of arguments apply to any other routine piece of kit – broods, supers, crownboards, roofs, clearers. Buy or assemble and prepare them in the winter.

After Tim Toady try something new

A few weeks ago I introduced the Tim Toady concept. For just about any beekeeping activity, there are numerous ways that it can be completed. There must be dozens of different methods for swarm control or queen rearing, perhaps more.

Of course, however many methods there are, all – at least all the effective ones – are based upon the basic timings of brood development and of the viable fractions of the colony. These things don’t change.

The biology of the honey bee is effectively unvarying.

Queens take 16 days to develop, drones take 32 days (from the egg) to reach sexual maturity. A queen and the flying bees are a viable fraction, as are the nurse bees and young brood etc.

Despite being based around these invariant 7 biological facts, not all swarm control or queen rearing methods are equal. Certainly, the end results might be similar, but some methods are easier, use less equipment, need less apiary visits or whatever i.e. some methods probably suit your beekeeping better than others.

My advice about this plethora of different methods to achieve the same ends remains exactly what it was a month ago … learn one method really, really well. Understand it. Become so familiar with it that you don’t need to worry about its success 8.

And then, after a bit of winter theory, plan to try something different.

And the winter is the ideal time to build any new things you might need to try this alternative method next season.

Here are a couple of my past and current winter projects.

Morris boards

Probably 90% of my queens are produced using the Ben Harden approach. It was the method I first learnt, and remains the method I’m most confident with. I’ve found it a reliable small scale method for rearing queens.

But, as they say, ’familiarity breeds attempt’ (at something new) and I’ve always liked the elegance of the Cloake board. This is a split board with an integral queen excluder and a horizontal slide. You place it between the boxes in a strong double-brood colony. By inserting the slide, opening upper front and lower rear entrances and simultaneously closing the front lower hive entrance you render the top box temporarily queenless and enable it to get stuffed with all the returning foragers 9. The queenless upper box is now in an ideal state for starting new queen cells from added grafts.

Morris board

But most of my west coast bees don’t end up as booming double brooders … the standard Cloake board needs too many bees for my location.

Parallel Cloake boards 

Which is where the Morris board comes in. It’s effectively two parallel Cloake boards. Paired with a ‘twinstock-type’ divided upper brood box (or two cedar nuc boxes) it works in the same way as the Cloake board, but only needs sufficient bees to pack a 5-frame nuc so is better suited to my native bees.

Here’s one I started earlier … a Morris board under construction

You can buy Morris boards … or you can easily build them. This was one of my winter projects in ’20/’21. I’ve used them for the last two years successfully and have been pleased with the results.

I don’t think I understand their use as well as the Ben Harden system … but I will. In particular, I have yet to crack the sequential use of one side, then the other to rear a succession of queens.

Portable queen cell incubator

This was my one big project last winter. Unfortunately, we had a shocker 10 of a summer on the west coast and it was rarely used. I did put a few queen cells through it successfully, but queen rearing generally was hit and miss (mainly miss) so it’s yet to prove its full worth.

Portable queen cell incubator version 2

This is version 2 of the incubator. I’m gradually compiling a list of opponents for version 3 11 that should correct a few things that could be improved – capacity, level of insulation, heat distribution – though the current incarnation is probably more than adequate.

Building – and testing, which actually took a lot more time – the queen cell incubator was a lot of fun. I discovered (and created 🙁 ) a series of problems that needed to be solved and, relatively inexpensively 12, enjoyed sorting them all out. I could work in my warm, well-lit workroom, drink gallons of tea, and dabble with 12V electrickery without endangering my life.

I’ve used it this season powered by a 12V transformer indoors, from an adapter in the car or from a battery with solar backup in the apiary.

However, to use it properly I need to rear more queens … which brings me to … 

Queen rearing without grafting

Both the Ben Harden and Cloake/Morris board methods of rearing queens use a suitably-prepared colony in which young larvae are presented. Typically 13 these larvae are grafted from a suitable donor colony.

Grafting is perceived by some as a ‘dark art’ – though perhaps not exactly malicious – involving a combination of sorcery, spells, fabulous eyesight and rock-steady hands 14.

It isn’t, but this perception certainly dissuades many from attempting queen rearing.

Capped queen cells

Capped queen cells produced using the Ben Harden queenright queen rearing system

I find grafting relatively easy and routinely expect 80-90% ‘take’ of the grafted larvae. My sorcery and spells are clearly OK. However, in the future, my eyesight and manual steadiness/dexterity are likely to decline as I get older 15.

I’ve also been reading some papers on how the colony selects larvae to develop into queens. Their strategy isn’t based upon what they can see and pick up with a 000 sable paintbrush … funny that.

I’m therefore going to try one of the graft-free methods of rearing queen cells, and the approach I intend to use is the Hopkins method. Hence the part-read copy of Joe Conti’s book mentioned earlier.

The Hopkins method of queen rearing

This method involves the presentation of a frame of suitably-aged eggs and larvae horizontally over a brood box packed with young bees. Importantly I mentioned both eggs and larvae as, under the emergency response colonies preferentially rear new queens from 3 day old eggs.

The resulting queen cells are cut from the frame and used to prime nucs or mini-nucs.

Even with my presbyopia and ’hands like feet’ I should be able to manage that 😉

The intention is to couple the Hopkins method with a 12-frame double-brood queenless nuc box which is subsequently split into several nucs for mating the new queens. And, if that wasn’t enough, I’m hoping I can integrate this with some swarm prevention for the donor colonies … time will tell.

All of that means I need some new kit 🙂

Before butchery photo … an eke being adapted for the Hopkins method of queen rearing

I purchased some Maisie’s poly nuc boxes, floors, feeders and ekes in the summer sales. In the winter I’ll spend some time butchering them with my (t)rusty Dremel ‘multi-tool’ to accommodate the horizontal brood or super frames (and a cell bar with grafts for good measure) before painting them a snazzy British racing green or Oxford blue 16.

More poly hive butchering

I’ve already done a little poly hive butchering this winter.

I’ve got about 20 Everynucs from Thorne’s. These are a thick-walled, well made nuc with a couple of glaring design flaws. However, I’m prepared to overlook these as, a) they’re relatively easy to fix, and b) they cost me a chunk of money and I’m loathe to spend at least the same amount again to replace them.

In addition, bees overwinter fantastically well in them.

Here's one I prepared earlier

Here’s one I prepared earlier … an overcrowded overwintered nuc in April

I’ve also got a few compatible feeders which are really designed for feeding syrup. You can add fondant, but the bees then need to follow a rather convoluted path to access it.

Everynuc feeder ...

Everynuc feeder …

I decided to modify the feeders to allow both by fitting a syrup-proof dam about half way along the feeder and drilling some 3-4 cm holes through the resulting ‘dry’ side of the feeder 17 .

Wooden syrup-proof dam and holes in an Everynuc feeder

Fondant, ideally in a transparent/translucent plastic food container 18 is inverted over the holes and the bees have direct access to it, even in the very coldest weather.

Munchity crunchity … direct access to the fondant

The Ashforth-type syrup feeder still works if needed and I no longer need 8 gallons just to top up each nuc 19. Typically my nucs won’t need feeding in midwinter, but if they do I should be able to position the fondant directly over the cluster allowing them the best chance of reaching it.

Winter weight

This is a practical project carried over from last year. I’m interested in the changing weight of the hive as the colony segues from ‘maintenance’ mode to early season brood rearing. I’ve drawn some cartoon graphs where there’s a clearly visible inflection point, with the hive weight dropping much faster once brood rearing starts.

Hive scales

I’m keen to have some real data rather than just my crummy cartoons. I already have the tools for the job, my no expense spared made hive scales. Tests last year showed that these were pretty accurate; I was about 8% shy of the actual weight (which doesn’t matter a jot, it’s the percentage change in weight that’s critical) and, more importantly, produced readings that were reproducible within a percent or two.

However, last year I was thwarted by bad weather, a lack of Gore-tex and an unexpected delay in evolving gills. I’ve now bought a sou’wester and, in the name of science, am preparing to brave the elements every week or so to weigh half a dozen hives.

And in between all that lot I’ll be building frames 🙂 20


Note

The other winter project already part-completed is moving this site to a new server. Frankly this has been a bit of a palaver, but I think it’s now sorted.

If you had problems connecting over the last few evenings, apologies. If things still seem odd, slow, broken or unresponsive drop me a note in the comments or by email. Of course, if you can’t connect at all you’ll never read this postscript 🙁 .

The changes I’ve made will enable some new things to be incorporated over the next few months, once I’ve got a bit of spare time and have built all of those frames 😉

Mini-nucs: the basics

Synopsis : Mini-nucs are a good way to get queens mated. They are inexpensive, use few resources and are relatively straightforward to use. This post describes the basic features and use of mini-nucs for mating in miniature.

Introduction

Mini-nucs are the small hives some beekeepers use for queen mating.

Pedantically, queen rearing could be considered the generation of queen cells with – in due course – the production of virgin queens. However, it’s a rather pointless exercise if it’s not also followed – in pretty short order – by queen mating.

A queen needs the support (and probably encouragement!) of a colony of some sort while she becomes sexually mature, goes on her orientation and mating flights, packs her spermathecae and then starts laying eggs.

The hive can be anything from a full-sized double-brood colony, possibly containing over 40,000 bees, to a container no larger than two egg boxes primed with 300 ml (perhaps no more than 1000) of bees.

Kieler mini-nuc

Clearly, dedicating a full colony for queen mating (unless she is destined to stay in the same box of course) is resource-intensive and impractical. For this reason most beekeepers who rear more than a very few queens will use smaller hives for queen mating.

Even using 4-6 frame nucleus colonies for queen mating is very demanding of resources; each needs to be started with a frame or two of emerging brood and the adhering bees and a frame of stores, possibly with some additional bees shaken in on top. Getting half a dozen queens mated in these ‘full-sized’ nucs might requires ‘gutting’ two complete colonies 1.

But you don’t need to use a full-sized nuc … with care you can scale things down … a lot.

How mini is a mini-nuc?

When I started beekeeping the hive choice for queen mating was either a ‘full-size’ 5 frame nuc or the mini-nucs manufactured by Apidea or Kieler (the latter are sometimes sold as Warnholz mating hives).

Apidea mini-nuc

I’ve used Kieler’s for years. They are the only type I own … largely because they were appreciably cheaper than Apidea’s. Were and are … a Kieler costs about £22 and the Apidea is £36 2.

Since I started (which wasn’t that long ago) the choices have proliferated. There are now a plethora of plastic or polystyrene equivalents to Apidea’s or Kieler’s. Some may be better, some may be worse. Many are less expensive (at least than an Apidea).

I’m sure all can be made to work and the general principles I discuss below probably apply to the majority of these true mini-nucs (and any number of homemade equivalents). Note that both Kieler’s and Apidea’s can be extended by the addition of a second story which are really needed for overwintering queens in these small boxes. If you aspire to try that, make sure whatever make you choose is extendable.

Kieler with ‘upper storey’ added … not so mini now

In addition to these mini-nucs there are now hives that take frames about 15 cm square, or homemade versions using half-size super frames in a super divided four ways. None of these are really mini-nucs. I’ve no real experience of them and so can’t talk about their pros and cons. Friends who have them tend to rave about how good they are, but I’ve too much incompatible equipment already and can’t justify their additional cost (they can be three times the price of a Kieler).

A love-hate relationship

I have a love-hate relationship with my mini-nucs.

I love …

  • the limited resources needed to set them up. A cup full of bees, a lump of fondant and a mature queen cell gets you started.
  • their value for money. A Kieler costs less than a pretty cheap commercial queen and you can produce 2-3 mated queens in a single Kieler in one season. If you buy (or sell) queens they pay for themselves within a season.
  • the speed with which queens get mated and start laying. In my experience this is significantly less time than a 5 frame nuc, and less still than a full hive.

However, it’s not all good news. There’s a lot to dislike about mini-nucs as well, this includes …

  • the work involved in setting them up properly. I’ll discuss this further below.
  • their size and my fat fingers. The clue is in the name. Mini-nuc. Finding the queen is easy, but manipulating the frames can be a little awkward.
  • the maintenance they need. Mini-nucs are high maintenance. If you’re not careful, during a dearth of nectar they will starve, during a glut they will pack the box completely, during a cold spell they will freeze and during a heatwave they will abscond. And, if none of these things happen, they’ll get robbed out by wasps 3.

When I lecture or teach queen rearing for beginners I recommend using 5 frame nucs until you can produce good queen cells reproducibly and as needed. Then try some mini-nucs …

General principles

Whatever the make, all mini-nucs are used in broadly the same way.

The empty box contains 3-4 frames, often just consisting of a topbar and a starter strip, and a compartment for food. You can fill the latter with syrup or fondant (or damp granulated sugar). It’s worth noting that some manipulations of these little boxes may require them to be inverted at the start, so you either need to add syrup later or use fondant.

Kieler mini-nucs: four topbar frames and an integral feeder

A cup full (perhaps 250 ml to 300 ml) of bees is added to the mini-nuc and left for a few hours (at least) so that the bees realise they are terminally queenless. You then add a near-to-emergence queen cell, or run a virgin queen in through the entrance.

The mini-nuc needs to be placed in the mating apiary, not too close to queenright hives (or you can lose some of the bees added to the box). These hives are very poor at thermoregulating – there aren’t enough bees present – and they readily overheat. Therefore, place the mini-nuc in dappled shade or somewhere it doesn’t get the full strength of the sun.

Gimme shelter … an Apidea mini-nuc ‘catching a few rays’ … a recipe for absconding

The entrance is opened and 7-10 days after the queen emerges she should be mated and laying. You remove the mated queen and add another near-to-emergence queen cell … ad infinitum, or at least until the end of the season.

After removing the last mated queen of the year you shake the bees out and store the mini-nuc in the shed for the winter months.

What could be easier?

Of course, it’s not quite that straightforward …

Stocking mini-nucs

Ideally you stock a mini-nuc with young worker bees. Older workers are more likely to disappear back to the hive they came from (unless you move the mini-nuc a few miles away) and will be less good at drawing comb. Young bees are also likely to survive for long enough to rear the new brood once the queen is mated and laying.

Note that I also stated worker bees … you should avoid including drones, firstly because they contribute nothing to the functioning of the little colony, and secondly because you probably want the queen to mate with drones from outside the apiary 4.

There are lots of ways of achieving this, some more complicated than others. The best description I’ve read is by ModernBeekeeping in the instructions 5 they provided with Kieler hives.

In brief, this involves:

  • finding the queen in a strong hive and placing her somewhere safe (on a frame in a two-frame nuc, or in a cage in your pocket … she’ll be fine in either for a few hours).
  • moving the brood box to one side and placing an empty brood box on the hive floor.
  • shaking all the bees from the brood frames into the empty brood box. Work fast. The bees will try and clamber out. Give them a few sprays of water from a plant mister to help contain them 6.
  • placing a queen excluder over the bee-filled-but-otherwise-empty brood box, then putting the brood box and brood-filled frames on top of this.
  • retiring for a well-earned cup of tea.

About three hours later …

While you were drinking tea the young bees moved up through the queen excluder to tend the brood. The drones will remain below the queen excluder and a lot of the foragers should be out foraging. You’ve effectively isolated the young bees and so can now harvest them.

Each fully-covered frame has 2500-3000 bees on it … you’ll need about 1000 for each mini-nuc.

Getting them from the frames in the brood box to the mini-nuc involves the following:

  • shaking the bees off the frame into a deep, smooth sided container with curved internal corners/joints. A washing up bowl is suitable, a picnic cooler is better.
  • periodically misting the bees in the container with water. Don’t drown them. Just spray them enough to stop them crawling up the sides too much. It helps to give the container a sharp bash onto the ground every now and then to shake the bees down to the bottom again. But remember … you need live bees in your mini-nuc so treat them as gently as possible.
  • scooping up 300 ml of bees into a flexible, clear measuring container. I use a cut-down 2 litre drink bottle; prepare it in advance by adding 300 ml of water and marking where the meniscus is. That’s the volume of bees you need.

Mister and bee-measuring-scoop

  • quickly pouring the damp bees into the mini-nuc. If you’re using Kielers you do this by adding them through the removable floor with the hive inverted on the ground or table. It’s easier doing it like that than trying to add the roof – one handed, after adding the topbar frames, with bees clambering out everywhere (which can be carnage). Take my advice, fill the feeder with fondant and add the bees to an inverted Kieler.

Kieler’s ready for stocking with bees

Tidying up

The more bees you harvest from the donor hive, the less able it will be to look after the brood it contains 7. Therefore, if you’re filling several mini-nucs you will probably need to harvest the bees from multiple hives. All can be added to the same washing up bowl/picnic cooler before distributing them to the mini-nucs.

Once you have harvested sufficient young bees and populated the mini-nucs:

  • reassemble the donor hives and add back the queen. If you’ve harvested nurse bees from more than one donor, make sure you add the correct queen back to each hive! 8
  • place the mini-nucs somewhere cool and dark. I put them in the garage. Leave them closed up for 24-72 hours and mist them with water twice a day through the mesh floor panel.

Mini-nucs … populated, terminally queenless and panicking in Garrison Kieler (sorry)

Adding the queen cell and relocating to the apiary

  • add the queen cell 1-2 days before the queen is due to emerge. Apidea’s have a neat ‘port’ in the plastic crownboard through which the cell can be added. I do the same thing with a sheet of polythene on Kielers. If you’re doing this indoors (where escaping bees might be an issue for non-beekeeping members of the family) then do it at night with a red head torch. Bee can’t see red light and so won’t fly 9.
  • the following day, place the mini-nuc out in the apiary, open the entrance and let the bees fly. I tend to do this late in the afternoon.

Mini-nucs – note entrances facing in opposing directions

  • check the queen has emerged by recovering the opened queen cell a day or two later. There’s no need to look for the queen.
  • cross your fingers and wait 😉
And they're off

And they’re off …

It’s as easy as that?

Yes, in theory.

In reality though …

As with so many things to do with queen rearing, timing is very important. Typically you need to use the queen cells 10-11 days after grafting. Therefore the mini-nucs should be made up 2-3 days before that. When I lived in the Midlands, for the first round of queen rearing, this might have been in the third week of April.

Remember the proverb ‘March winds and April showers bring forth May flowers’?

In particular the ’April showers’ bit … 😉

In my experience, populating mini-nucs in the rain is probably the worst task in beekeeping.

All the bees are in the box.

They’re not happy being disturbed.

They are particularly unhappy about being unceremoniously shaken into a new box.

And, if it continues raining, they’ll be extremely resentful about being disturbed again when you return from drinking tea (and topping up your anti-histamines) to shake through the box again.

But, the queen cells will not wait.

Queen cells ready to ‘rock and roll’

If you’re going to do this for the first time, choose a really good flying day, ideally when there’s a nice flow on. The bees still won’t like being messed about with, but it will be a whole lot easier for you.

All sorts of other things can go wrong, and sometimes do. I’ve had misters block (having previously been used for syrup), I’ve tipped the picnic cooler over, I’ve put two queens back into one hive … I could go on.

It gets easier with experience and the effort is worthwhile. You’re setting up tiny little hives from which your precious queens will fly and get mated. And once established, they can be used several times without all the palaver involved in stocking them in the first place 🙂

Queen mating

It is my impression that queens tend to get mated faster from mini-nucs than they do from 5-framers, or full hives. Of course, I’ve never done a side-by-side comparison of the two 10, but I have talked to a number of experienced beekeepers who have expressed the same opinion.

Why should this be?

The consensus was that the small boxes give the queen fewer opportunities to hide, meaning that the workers can more easily chivvy her out on orientation and mating flights.

However, while re-reading Gilles Fert’s Raising Honeybee Queens (Fert, 2020) I found a comment that contradicts my experience:

American breeders have noted that queens in very small mini-nucs mate later than those from larger colonies, and with a success rate of just 60% to 70%. They found that tripling the volume of these mini-nucs boosted the success rate to 92%!

I’ll try and track the original source down … and determine whether the ’no space to hide’ and ’chivvied out by the workers’ have any basis in fact or are just the sort of daft ideas beekeepers share when stuck indoors on a wet day.

I’ve certainly not noticed a lower queen mating success using mini-nucs but, statistically, I’ve not used them enough to observe the difference between 70% and 92%.

A queen about to go on an orientation flight

Once you know the queen has emerged just leave the bees to get on with things, other than checking stores and space periodically. On good flying days, or potential queen mating days (which can be worse than you might imagine – it was 14.5°C when the photo above was taken), it’s important not to disturb the colony in case you interrupt an orientation or mating flight.

And, once you have your mated queen, you can use her for whatever you want … requeening production colonies, making up nucs for overwintering, selling or donating.

That’s all folks …

Of course, that’s nothing like all.

When I decided to write about mini-nucs I jotted down a list of interesting things to cover. Almost none of them are in the preceding 2,700 words 🙁

Typical.

That’s because I can’t cover some of the more interesting aspects of mini-nucs without covering the basics first. I’ll therefore return shortly – perhaps even next week – to this topic and waffle on about:

  • DIY modifications/improvements to Kieler’s
  • How to judge the quality of the queen
  • Repeat queen mating and ‘caretaker’ scrub queens
  • Overwintering mini-nucs
  • Emptying mini-nucs at the end of the season
  • And anything else I can think of in the intervening period.

Note

Mating in miniature is the title of a book by Bernard Möbus on queen mating in mini-nucs. It looks a little dated now (it was first published in 1983) but is an interesting read and, although the equipment has changed in the last 40 years, the principles remain much the same. I think it was published by BIBBA, but they no longer list it (and nor do Northern Bee Books). Try eBay?

References 11 

Fert, G. (2020) Raising Honeybee Queens: An illustrated guide. Deep Snow Press. ISBN 978-0-9842873-8-3