The most fun you can have in a beesuit

Synopsis : Queen rearing is enjoyable and educational. Don’t let the experts put you off. You don’t need to graft day-old larvae to rear queens.

Introduction

A long time ago 1 I bought, read and re-read Ted Hooper’s excellent book Guide to Bees and Honey. Every time I read it I’d find something I’d missed the last time and, even now, there are nuanced comments I think I am only now beginning to understand.

I’m exaggerating slightly when I say ’read and re-read’ as there was one chapter I pretty-much skipped over each time.

That was the chapter on queen rearing.

What put me off?

It was probably his description of opening queen cells with the tip of a penknife to check how far development had progressed, re-sealing the cell and returning the frame to the hive.

She’s gone …

I knew enough about bees to know that the future success of the hive depended upon it successfully requeening after swarming.

But I didn’t know enough to stop them swarming 😉 .

I’d also already had to ‘borrow’ a frame of cells from a friend to rescue a terminally queenless colony of mine. ’Enthusiastically clumsy’ defined my beekeeping skillset, and was probably the comment the 2 examiner made in his notes during my BBKA Basic assessment.

The prospect of meddling with developing queens, with something so precious, seemed like total madness.

Surely it’s better to let them get on with it?

For the first couple of years of beekeeping, I thought of queens as an exquisitely fragile – and by implication valuable – resource. The prospect of rearing them, handling them, putting them in little boxes or – surely not? – prising a cell open to see if they’d developed sufficiently, was an anathema to me.

Consequently, I repeatedly skipped the chapter on queen rearing.

Too difficult … not for me … nope, not interested.

The BBKA Annual Convention

Before they moved the event to Harper Adams, the BBKA used to hold its spring convention at the Royal Agricultural showground just outside Warwick. My (then) local association provided stewards for the event and I was asked – or volunteered – to help the late Terry Clare run the queen rearing course one year.

I’d never done any queen rearing … and still hadn’t completely read that chapter in Hooper’s book.

I’d like to take this opportunity to apologise to those who paid to attend the course … at least those who received any ‘help’ from me, though everything else about the course was very good.

Checking grafted larvae

Checking grafted larvae

After an introductory lecture from Terry, we spent a warm afternoon in a poorly lit room practising grafting larvae. A thin cloud of disorientated bees circled our heads before being ushered out through the windows. Most of the larvae on the frames were visible from across the room 3 but at least they didn’t turn to mush with our neophyte fumblings as we transferred them from comb to plastic queen cups.

Terry moved from table to table, checking progress. He explained things well. Very well. The preparation and procedures seemed a whole lot more accessible than they had in Hooper’s book.

I’m a reasonably quick learner and that afternoon convinced me I should, and could, at least try it on my own.

The session ended with a wrap-up lecture in which Terry encouraged us all to ‘have a go’, and not be put off by an initial lack of success.

He assured us it would be worthwhile and enjoyable.

We dispersed into the late afternoon sun, talking of bees and queens and our plans for the season ahead.

Balmy April weather

There was an early spring that year, colonies had overwintered well and were strong. The Convention was held in early April if I remember and the good weather continued for at least another 2-3 weeks.

Well before the end of the month I had my first successfully grafted larvae being reared as queens.

Success!

It wasn’t an overwhelming success.

I probably grafted a dozen, got half accepted, lost more during development 4 and ended with just two virgins. I don’t have notes from those days, but I’m pretty sure only one got successfully mated.

So, success in a very limited way, but still success 🙂 .

It still makes me smile.

Terry’s presentation had clarified the mechanics of the process. It no longer seemed like witchcraft. It was all very logical. He’d made it clear that the little specialised equipment needed was either ’as cheap as chips’ 5 or could easily be built at home by someone as cack-handed as I was am 6.

The practical session had given me confidence I could see and manipulate huge fat larvae that were far too old to be reared as queens larvae. Even with my ’hands like feet’ moving a delicate larva from comb to plastic queen cup seemed possible, if not entirely natural.

JzBz plastic queen cups

I scrounged some JzBz cups from someone/somewhere, built a cell bar frame and some fat dummies 7 the week after the Convention and used one of my colonies as a cell raiser and the other as the source of larvae.

And, at a first approximation, everything sort of worked.

I could rear queens from larvae I had selected 🙂 .

Try, try and try again

I repeated it again the following month. I was more successful. The nucs I produced were either overwintered or built up strongly enough to be moved into full hives.

I think one went to my mentee. My association encouraged relative newcomers to mentor, probably one of the best ways to improve your beekeeping (other than queen rearing).

Within a year I had 6-8 colonies or nucs and twice than number the year after that.

Almost all were headed by queens I had reared … ‘almost’ as my swarm control skills were still developing 😉 .

Now, over a decade later, my swarm control skills have improved considerably … as has my queen rearing.

I remain resolutely cack-handed but I’m now a lot more confident in my hamfistedness.

I still mainly use the same technique Terry Clare taught on that course in Stoneleigh, though I’ve now also used a number of other approaches and successfully reared queens using most of them. Even the cell bar frame I built is still in use, though I’ve built some fancier fat dummies.

Fat dummy with integral feeder

Fat dummy … with integral feeder and insulation

Queen rearing has taught me more about keeping bees than any other aspect of the hobby … more about judging the state of the colony, the quality of the bees, the suitability of the environment, the weather, the forage etc.

Queen rearing has improved the quality of my bees, year upon year, so that they suit my environment and colony management.

But – more importantly and perhaps a little selfishly – queen rearing has given me more enjoyment than any other aspect of beekeeping.

I’d prefer to rear queens than get a bumper honey crop … but because I rear queens that suit me and the environment, I do pretty well for honey as well.

10%

I give 20-30 talks a season to beekeeping associations. When I’m talking about queen rearing I usually ask the organisers about the number in their association that actively rear queens.

By actively I mean that do more than simply allow colonies to requeen themselves during swarm control. Don’t get me wrong, I’m not denigrating this essential aspect of beekeeping. We all (have to) do it.

To me ‘active’ queen rearing doesn’t necessarily mean grafting larvae, incubators, mini-nucs and all that palaver. But it does mean:

  • preparing a colony to be in a suitable state to rear new queens 8.
  • rearing queens from larvae selected (though not necessarily individually selected) from a colony with desirable characteristics e.g. good temper, productivity, frugality.
  • rearing more than one queen at a time, with the excess used for making increase, for sale, for ’just in case’ situations etc.

There’s perhaps a slightly grey area where you split a hive (with desirable characteristics) that’s making swarm preparations into multiple nucs, each of which gets an immature queen cell.

But, let’s not get bogged down in definitions … that’s not the point of this post (which, although it might not be obvious yet, is to encourage you to ’have a go’).

And, when I ask 9, I’m regularly told that only a small number, perhaps ~10%, of association members actively rear queens.

Why so few?

Enjoyable, educational, useful … choose any three

Of course, there’s no requirement that a beekeeper gets involved in queen rearing. You can keep bees for years without rearing queens, other than during swarm control and by making up splits. I know a few beekeepers who have been keeping bees like this for decades … by many criteria they are skilled and successful beekeepers.

But sometimes, which might mean ‘often’, being able to rear queens and having some of those ‘spare’ queens available is extremely useful.

Spare queens, heading nucs in the apiary, can be overwintered to make up losses. These can be sold or donated in Spring to meet the enormous 10 demand for bees early in the season. The availability of a queen can ‘fix’ an aggressive colony, can rescue an otherwise doomed colony, or can effectively ‘gain’ a month of brood rearing and nectar collection should the old queen fail.

And that extra month of brood might make the difference between successful overwintering or not.

In my view, once you can rear your own queens you are pretty-much self-sufficient … there are very few situations that cannot be rescued.

And all of those benefits are before you even consider the two other things I mentioned above:

  • that successful queen rearing will inevitably improve your more general skills as a beekeeper, and
  • you will get a lot of satisfaction and enjoyment from doing it … literally ’the most fun you can have in a beesuit’ 11.

Why so few?

Beekeeping, like many other hobbies, can appear an esoteric pastime. Weird terminology, hierarchical organisation 12, specialised equipment, unusual costumes and a tendency to still use arcane practises.

And queen rearing – probably like candle making or the production of excellent mead 13 – is a specialised niche within what is already a rather niche activity.

It has its own terminology, equipment and methods.

To the uninitiated – even to another beekeeper, like me reading Ted Hooper’s book – it can appear fiendishly difficult.

And, unfortunately, some practitioners make it sound esoteric, specialised and difficult.

It’s a sort of one-upmanship.

They promote methods that may not suit the beginner, that require lots of resources, or that involve techniques that sound exceptionally skilful, even when they’re not. Not deliberately perhaps, but that’s what happens.

All of which means that:

  • people are dissuaded from trying it in the first place
  • those that do try (with trepidation because, you know, ”it’s difficult”) and that achieve only limited success, have their initial impression reinforced and are unlikely to try again

It’s very easy to talk yourself out of trying something you think will be difficult and/or you are unlikely to succeed at.

Actually, it’s not only easy, it’s also entirely understandable.

Why go to all that trouble if it’s unlikely to work?

After all, you can usually buy queens ‘next day delivery’ for £50 … surely that would be easier?

Perhaps … if they’re available when you want them. Really early in the season? Think again. During the peak swarming season when everyone else wants to requeen their colonies they accidentally destroyed all the queen cells in. Nope.

But, as Terry Clare so ably instructed … it is not that difficult to rear your own.

There’s more than one way to do it

I’ve written an entire post on this topic and it applies as much to queen rearing as it does to other aspects of our hobby.

If not more.

There are many different ways of successfully achieving the three key components of the process:

  1. preparing the colony to receive larvae
  2. presenting the larvae
  3. getting the resulting virgin queens mated

Today’s post isn’t an introduction to queen rearing … it’s meant instead as an encouragment to try queen rearing.

If you’ve got a year or two of beekeeping experience and one, or preferably two, colonies you have the essentials you need to start. It’s what I started with … and look how that ended 😉 .

Over the next three months I’ll write two or three more posts on the basics, in good time for you to ’have a go’ in 2023.

Preliminary setup for Ben Harden queen rearing

If you’re impatient to read more, I’ve already written about two methods I have used extensively – the Ben Harden system and queen rearing with a Cloake board.

However, throughout these descriptions I’ve emphasised the use of individual grafted larvae.

Grafting is the transfer of larvae from the comb where the egg hatched to a wax or plastic queen queen cup. For best results the larvae should no more than ~18 hours old.

A suitable larva may well be no bigger than the egg it hatched from.

Already I can feel beginners switching off … “Too difficult … not for me … nope, not interested.”

Although grafting is an easily learned and reasonably straightforward technique it can appear very daunting to the beginner.

Perhaps I’m therefore also guilty of making queen rearing sound ‘esoteric, specialised and difficult’.

Am I guilty as well?

Indubitably, m’lud.

But … in my defence please consider the two recent posts on Picking winners.

The purpose of those posts was to highlight – for people (like me) that already routinely use grafting as part of their queen rearing – that the bees may choose different larvae to rear as queens than the beekeeper might choose.

The beekeeper is essentially non-selective, whereas the bees are very selective.

I think this is interesting and it’s got me wondering about the qualities the bees select and whether they’d be beneficial for my beekeeping.

But there’s another equally important ‘take home message’ from these two posts. This is relevant to beekeepers who do not already rear queens (but who would like to) but that are put off by the thought of grafting.

And that is that you can easily produce excellent quality queen cells without grafting or ‘handling’ larvae at all.

If you refer back to that three point list above, point 2 ( ‘presenting the larvae’) can be as straightforward as simply adding a frame of eggs and larvae to a suitably prepared hive.

That’s it.

What could be easier?

No magnifying glasses, no headtorch, no treble ‘0’ sable paintbrush, no JzBz plastic cups, no cell bar frame, no ’do I or don’t I prime the cups with royal jelly?’, no desperate searching around the frame for larvae of the right size, no worries about larvae getting chilled, or drying out …

Pick a frame, any frame

As long as it has eggs and young larvae … and comes from a donor colony that has the characteristics you like in your bees.

Eggs and young larvae

Eggs and young larvae

There’s little point in rearing queens from poor quality bees.

For starters I’d suggest you select a frame from a colony of calm, well behaved bees.

If none of your colonies are dependably calm and well behaved you definitely need to learn to rear queens, but you should ask a friend or mentor 14 for a frame of eggs and larvae from a good colony.

Bees are very good at picking larvae suitable for rearing into queens. Let them do the ‘heavy lifting’. Once the queen cells are ready you cut them out of the frame and use them in the same way as you would use cells from grafted larvae.

So, having hopefully convinced you that you don’t need to graft larvae to produce queen cells, that seems like a logical place to end this post.

In future posts I’ll discuss points 1 and 3 in that numbered list above.

You already know almost everything you now need to know about point 2 😉 .


 

Picking winners, part 2

Synopsis : Some larvae are nutritionally deprived and may produce sub-optimal queens. Grafting may miss the ‘best’ larvae the colony would select for rearing as emergency queens.

Introduction

A fortnight ago I discussed the preference colonies show for heavy eggs – or more accurately for larvae reared from heavy eggs – when producing queens under the emergency response.

Why might this be interesting?

The longevity of the queen and the absolute dependence the colony has on her quality means that the choice of larvae they rear new queens from is of fundamental importance.

These are the larvae that develop to produce queens with the traits that benefit the colony – in fecundity, disease resistance and a range of other characteristics.

It cannot be random.

If they make the right choice the colony will flourish, swarm and their genes will be perpetuated.

That is a significant evolutionary selective pressure. Its application over the 90 million years or so since the evolution of eusociality has resulted in the honey bees we have today.

Now, these traits favoured by the bees might not all benefit our beekeeping, but some of them should. Longevity, fecundity and disease resistance are likely to be evolutionarily favourable traits, and will also be useful for beekeepers.

Defensiveness and swarminess … er, not so much 😉 .

But the bees have little time to select the best larvae. They have 6 days from the day the egg is laid until a larva is too old 1 to reliably develop into a queen.

In practice they select very young larvae (or even 3 day old eggs) so ensuring the resulting queen is fed for the maximum time with royal jelly, thereby producing a larger queen with more ovarioles.

So what do the bees choose?

Given the choice, which larvae are selected by the bees to rear new queens?

Artificial experiments and nepotism

The ‘heavy eggs’ experiment I discussed a fortnight ago was primarily designed to study kin selection and nepotism in honey bees. The study was conducted over a decade ago 2, but wasn’t published until 2021, though the results were known before then 3.

If you remember, nepotism in honey bees is a nice idea; particular patrilines of workers (fathered by the same drone) should favour larvae of the same patriline. However, there have been no convincing studies that actually support this, and there are compelling theoretical arguments why nepotism could actually be detrimental to the colony.

Parts of the study I’m going to discuss this week were also designed to test for nepotism. I’m going to ignore these 4 and instead focus on some more interesting results that I think have practical relevance for beekeeping.

In addition, the study this week uses methods that are more typical of those used by beekeepers and that avoid the artificiality of rearing larvae in vitro before reintroducing them to a queenless colony.

In this regard I’d argue that they more closely resemble what’s happening in a colony rearing emergency queens. Furthermore, they should be easier for beekeepers to understand, and to repeat … not for experimental purposes, but when rearing queens.

Sagili et al., (2018)

The majority of the studies I’m going to discuss are from Sagili et al., (2018). The title ’Honey bees consider larval nutritional status rather than genetic relatedness when selecting larvae for emergency queen rearing’ neatly summaries their conclusions, but some of the detail is worth discussing in a bit more detail.

It’s always interesting to know what goes on in the hive.

During inspections we see frames of brood – capped and open cells. Other than the larvae getting bigger as they get older they all look much of a muchness … but they’re not.

All larvae are equal, but some are more equal than others 😉 .

Hungry mouths

The queen lays an egg in an empty cell. Other than the egg, the cell remains empty for 3 days when the egg hatches to release the larva. Without prompt and regular feeding the larva will starve or suffer setbacks in development.

Unrealised potential … a frame with eggs and young larvae

For this reason the nurse bees make frequent visits to the occupied cells to determine their content and needs.

Is it an egg or a larva?

Is it hungry?

And these visits continue during the 5 days of larval development.

How many visits do they make, how often is a larva fed, and are all larvae treated equally?

Sagili and colleagues used observation hives and video cameras to record nurse bees visiting cells containing larvae of precise ages 5. They recorded visits over 4 hours to 2 day old larvae, and one hour observations of 5 day old larvae.

In four separate hives, 4-8% of the young (2 day old) larvae did not receive a visit from a nurse bee during the 4 hour period they were filmed.

Of the 5 day old larvae, again ~10% didn’t receive a visit during the observation period and, of those fed, the longest interval between feeds was ~36 minutes. However, over one hour, the older larvae that were being fed were visited very regularly; the median interval between feeds was a little under 4 minutes and they were fed for a total of ~7 minutes over one hour.

Clearly some larvae, for whatever reason, get little or no attention for extended periods, whereas those that are visited, are fed very frequently.

Nutritionally deprived and non-deprived larvae

Larvae that are infrequently visited are likely to be nutritionally deprived … or, using the technical jargon beloved of beekeepers and scientists alike, hungry 6.

Do nurse bees respond differently to nutritionally deprived and non-deprived larvae?

Which are visited first and fed first?

The scientists caged the queen on a frame and allowed her to lay eggs for 24 hours. They then removed the queen (caging her elsewhere in the hive) and waited for the eggs to hatch. 24 hours later the larvae were caged under either 13 mm mesh or 3 mm mesh. Workers can access the larvae through the 13 mm mesh, but cannot get through 3 mm mesh. Cages were left in place for four hours to create two populations of larvae on the same frame; nutritionally deprived and non-deprived.

Small and large mesh cages over day-old larvae

They then again used video recording of randomly selected larvae to record and quantify the attention and feed visits they received.

The purpose of this part of the study was to determine whether the nurse bees could discriminate between larvae that were nutritionally deprived and those that were not.

And they could …

Inspections and feeding visits to nutritionally deprived and non-deprived larvae

Deprived larvae were visited (inspected) sooner, the black bars in the graph above, and fed earlier. You can just about determine this from the graph; the stats are more convincing (but less comprehensible 😉 ).

In addition, deprived larvae received more frequent inspections, more frequent feeds and were fed for longer.

Acceptance of larvae for queen rearing

A colony rendered suddenly queenless will attempt to rear a replacement under what is called the emergency response. Suitable young larvae are selected, fed a diet rich in royal jelly and the cell is reshaped to be orientated vertically.

This vertical orientation is a major inducement for the workers to continue to feed the developing larva with royal jelly (She et al., 2011). This is exploited in queen rearing techniques that involve the grafting of young larvae into wax or plastic cups which are then placed, open end down, in a queenless colony.

Sagili et al., investigated whether nutritionally deprived and non-deprived larvae were favoured when queens were reared under the emergency response.

Interestingly, they did so using larvae in natural comb and following grafting into plastic queen cups.

Which were favoured for queen rearing? Grafted or natural, nutritionally deprived or non-deprived?

In both instances the larvae were presented to a queenless and broodless colony, using 6 recipient colonies in each case.

Larval acceptance for queen rearing using two different methods – grafted and in natural comb

In the case of grafting, 12 of each type of larvae were presented on a cell bar frame. When transferring comb (prepared as described before using caged larvae) the entire frame was introduced.

The recipient colony did not discriminate between the nutritionally deprived and non-deprived larvae when they were grafted, but they showed a marked preference for the non-deprived larvae in natural comb.

In addition, they reared significantly more queens from grafted larvae than they did from larvae in comb.

All larvae are equal, but some are more equal than others …

Since I’m enthusiastic about queen rearing, this last set of experiments was by far the most interesting part of the study.

There are two results that are particularly striking.

Firstly, more queens were reared from grafted larvae than were reared following the transfer of a frame of larvae. The difference was significant, with almost twice as many queens being produced following grafting. It’s also worth noting that the bees only had 24 grafted larvae to choose from, compared to a much larger number of larvae on the transferred natural comb.

More is better … right?

Secondly, the workers showed no preference between nutritionally deprived and non-deprived grafted larvae, but showed a strong preference for the well-fed larvae in natural comb.

So, what do these results mean?

Let’s have a quick recap:

  • developing larvae receive different amounts of ‘attention’ from nurse bees
  • about 10% of developing larvae received no (or only a limited number of) visits during an extended observation period. The presumption is that these larvae are likely to be nutritionally deprived (though this was not demonstrated)
  • nurse bees can readily distinguish between nutritionally deprived and non-deprived larvae; the former receive earlier inspections, are fed sooner and more frequently
  • when rearing emergency queens, workers preferentially select larvae in natural comb that are not nutritionally deprived. In contrast, they make no distinction between nutritionally deprived and non-deprived grafted larvae

We know from numerous studies that high quality queens must be well fed during larval development. The best queens are produced from very young larvae (or even 3 day old eggs) that are then fed for an extended period with copious amounts of royal jelly in a strong hive full of nurse bees.

Queens produced under these conditions are larger and have more ovarioles, so should lay more eggs for longer.

It makes sense that nurse bees can distinguish between ‘hungry’ and replete larvae … the former need feeding or they won’t develop properly. The former may already have been held back developmentally … not an ideal start for a new queen.

Since nurse bees can determine the nutritional status of very young larvae, logic would dictate that they would select those that are not nutritionally deprived to rear new queens from.

After all, the future of the colony, and any resulting swarms will depend on it.

So, why don’t they make a similar distinction when presented with grafted larvae?

Selection vs. maintenance of larvae for queen rearing

The key difference between the grafted larvae and those in natural comb was the orientation of the ‘cells’ in which the larvae were presented to the queenless and broodless colony.

Grafted larvae were presented in a vertically orientated plastic queen cup, whereas the cells in natural comb are horizontal 7.

Cell bar frame with vertically orientated plastic Nicot queen cups

The interpretation is that larvae in vertically orientated cells are not selected by the nurse bees, but are instead just maintained as developing queens.

In contrast, larvae in horizontal(ish) natural comb are selected as the starting material for new queens, and the resulting reshaping of the comb to form the queen cell leads to their maintenance as developing queens.

Significance for beekeeping and queen rearing

The increased number of queens reared from grafted larvae probably reflects this ‘maintenance’ response being triggered in the nurse bees. ’Any’ larva presented in a suitably orientated cell must have been preselected as suitable … so the bees feed them up with royal jelly.

The nurse bees don’t know that these grafted larvae were selected by the beekeeper, not on the basis of them being nutritionally replete, but more likely because they were visible, about the right size, and in an accessible part of the comb.

But … think back to the first experiment. This suggested that ~10% of all larvae are nutritionally deprived because they have received, at best, infrequent visits over the last few hours. If the beekeeper hadn’t picked them during grafting, it’s unlikely the bees would have selected them as being suitable for producing queens.

Are 10% of grafted queens sub-optimal? Remember, the differences may be subtle.

The other point I found interesting is that the bees reared fewer queens in natural comb than from grafted larvae.

Why?

Charged queen cell

One possibility is that the reshaping of the comb is a physical limitation and restricts queen production. Perhaps this is why so many are at the edge of combs? 8 

Another is that the bees only rear ’enough’ queens for their needs, but that they can only determine what ‘enough’ is using larvae in natural comb.

Whilst these are certainly possible I think there’s an intriguing alternative … only a small proportion, even of well fed larvae, are considered suitable by the colony for queen rearing and so selected by the nurse bees.

Yes, the bees favour larvae that are not nutritionally deprived, but perhaps there are additional characteristics that are also desirable (and that vary between larvae).

Quantity and quality

Grafting larvae is a well established method of producing large numbers of queens. If the donor colony is good quality there’s every reason to expect that the resulting queens will be good.

Most, if not all, commercially reared queens come from grafted larvae (where quantity is paramount and quality might be a secondary concern) … probably hundreds of thousands of queens a year are produced like this. It’s the method I’ve used for many years.

Queen cells from grafted larvae …

But this paper raises two or three interesting ideas:

  • about 10% of larvae selected at random for grafting are likely to be nutritionally deprived and so would not have been chosen by the nurse bees. The presumption is that these will produce sub-standard queens.
  • nurse bees might be a lot more selective in the larvae they choose for emergency queens, only favouring a subset of even those not nutritionally deprived.
  • queen rearing methods that present larvae in natural comb might produce fewer queens but those queens may have the desirable characteristics selected by the bees (potentially resulting in better quality but a smaller quantity).

If this last point is correct, it’s worth noting that queen rearing methods – like the Hopkins method – that use larvae in frames placed horizontally over the colony 9, may trigger the queen maintenance response rather than allowing the selection of larvae by the nurse bees.

It would be very interesting to determine whether the bees would discriminate between nutritionally deprived and non-deprived larvae presented on a horizontal frame.

Two final thoughts;

  1. Grafting works well, but that doesn’t mean it’s the best way to produce top-quality queens.
  2. The desirable characteristics nurse bees favour (for colony survival and reproduction) may not be beneficial for beekeeping.

But I’d be surprised if they weren’t 🙂


Note

I’ve not had a chance to discuss it, but Free et al., (1989) previously demonstrated that nutritionally deprived larvae received more attention from nurse bees. I’ll deal with how the workers detect the nutritional status of larvae in the future.

References

Free, J.B., Ferguson, A.W., and Simpkins, J.R. (1989) The Effect of Different Periods of Brood Isolation on Subsequent Brood-Cell Visits by Worker Honeybees (Apis Mellifera L.). Journal of Apicultural Research 28: 22–25 https://doi.org/10.1080/00218839.1989.11100815. Accessed November 22, 2022.
Sagili, R.R., Metz, B.N., Lucas, H.M., Chakrabarti, P., and Breece, C.R. (2018) Honey bees consider larval nutritional status rather than genetic relatedness when selecting larvae for emergency queen rearing. Sci Rep 8: 7679 https://www.nature.com/articles/s41598-018-25976-7. Accessed November 21, 2022.
Shi, Y.Y., Huang, Z.Y., Zeng, Z.J., Wang, Z.L., Wu, X.B., and Yan, W.Y. (2011) Diet and Cell Size Both Affect Queen-Worker Differentiation through DNA Methylation in Honey Bees (Apis mellifera, Apidae). PLOS ONE 6: e18808 https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0018808. Accessed November 22, 2022.

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.

Picking winners, part 1

Synopsis : Queenless colonies prefer to rear new queens from heavy eggs. How was this determined and what are the implications for our queen rearing?

Introduction

Arguably the most important decision a colony will ever make is the selection of the eggs or larvae from which a new queen is raised. Other decisions are obviously important, such as the nest site a swarm occupies, but if the choice of ’starting material’ for the new queen is poor then the resulting colony is unlikely to thrive.

Actually, I suspect this isn’t arguable at all; whether it’s a replacement queen to take over after the colony swarms, or a supersedure queen to replace the ageing matriarch as she runs out of sperm or energy, a poorly chosen larva will – sooner or later – result in the demise of the colony.

Let’s hope they’ve chosen a good ‘un (they will have!)

Conversely, a good larva, fed well by nurse bees, that mates with enough drones and evades marauding swallows on the return to the hive – and the clumsily wielded hive tool of the beekeeper – will end up heading a strong colony. This strong colony will collect a surfeit of pollen and nectar, so ensuring good overwintering survival. It will be better able to defend itself against wasps or other robbing bees, and will be less susceptible to disease 1.

Reproduction

A strong, healthy colony will build up well in the spring and produce one or more swarms 2. If these survive – undoubtedly also helped by having good genetics – the colony will have reproduced and can be considered successful.

A small swarm ...

Honey bee reproduction in action

This type of ’success’ is what evolution selects for, so you can be absolutely certain that the choice of eggs/larvae from which new queens are reared is not random.

Cooperation vs. nepotism

Rearing new queens involves cooperation. In fact, as eusocial insects, almost everything that happens in the colony is cooperative. Multiple nurse bees feed the developing queens, hundreds of scout bees survey the environment for new nest sites and thousands of related workers provision the hive with pollen and nectar.

It’s often stated that these workers are ‘half sisters’ … they share the same mother (the queen) but different fathers (drones).

And there are quite a lot of fathers … .

The queen mates with at least a dozen drones during the mating flights she takes. Some calculations suggest it’s significantly more than a dozen drones. Whatever the number, workers fathered by the same drone will be more related to each other than they will be to workers fathered by a different drone.

On average workers within a single patriline (i.e. fathered by the same drone) are supersisters and share 75% of their genes. In contrast, workers in different patrilines (i.e. different drones) only share 25% of their genes.

And this is potentially a problem for cooperation.

It might be expected that nurse bees would select their supersister larvae when rearing new queens. Doing so would help ensure the propagation of their genes in subsequent generations, rather than those of their half sisters.

This would be an example of nepotism; ’showing special favour or unfair preference to a relative’ 3.

Lots of studies have attempted – largely unsuccessfully – to demonstrate nepotism in social insects, but that doesn’t mean it’s not worth looking again.

Do worker honey bees exhibit nepotism when selecting larvae to rear new queens?

Nepotism vs. colony diversity

It’s easy to talk yourself out of an experiment.

You have a good idea, do a bit of reading, discuss it with your friends and collaborators and then – belatedly – consider the underlying theory.

At which point it all sort of falls apart and you find numerous reasons not to do the experiment in the first place.

It was a daft idea because of x, y and z.

Think of all the time and money you’ve saved … back to the drawing board.

And there are good theoretical reasons why nepotism is unlikely to be seen in social insects like honey bees.

The most compelling of these is that genetic diversity within the colony is beneficial.

And nepotism, by definition, reduces diversity.

A quick recap on the diversity story … colonies with limited genetic diversity e.g. those headed by poorly mated queens, are less ‘fit’ than colonies with extensive genetic diversity. Fitter colonies are bigger, stronger, healthier and more likely to reproduce. The seminal study on this was by Mattila and Seeley (2007) which I discussed briefly in Polyandry and colony fitness.

So, theoretically, nepotism is a ‘bad thing’ … don’t bother doing the experiment.

But hold on a second, we also know that different patrilines of workers ‘smell’ very different to each other because they produce distinct cuticular hydrocarbons (CHC).

If nepotism is such a ‘bad thing’ why retain the (evolutionarily ‘expensive’) genetic machinery to generate all these different CHC’s? Why not just make all workers from one queen distinct from those derived from a different queen?

Individual colonies need to have distinct CHC’s to prevent robbing, but why are different patrilines distinct in their CHC profile?

Maybe nepotism occurs after all?

Better do the experiment.

Nepotism and larval selection

The study I’m going to briefly discuss was recently published by AL-Kahtani and Bienefeld (2021). It’s interesting and reasonably definitive in my view. However, whilst it addresses the ”Do bees exhibit nepotism during larval selection?” question 4 I think there are features of the study that are somewhat artificial which might restrict the generality of the conclusions they reach.

More interestingly, and of relevance to practical beekeeping, they show that bees are highly selective in their choice of eggs/larvae.

Can beekeepers exploit this to produce better quality queens?

The experiment was very simple.

Simplified diagram of the experimental method (see text for details)

Unmated queens from diverse areas of Germany were instrumentally inseminated with sperm from 10 drones, each selected from different unrelated geographic areas.

Six colonies were established (only three shown above) which were subsequently split into a queenright egg-producing colony (EPC; presumably a nuc, though it’s not stated) and a queenless larvae-rearing colony (LRC).

Eggs laid within a 6 hour window were incubated for 48 hours in an incubator, weighed and then allowed to hatch. For the first 48 hours after hatching the larvae were artificially reared by feeding them a sugar/protein diet 5.

This artificial rearing was done to avoid any bias from non-genetic colony odours e.g. due to pollen/nectar.

After 48 hours, 30 larvae, 10 from the matched EPC and 10 from each of the unrelated EPC’s were grafted into plastic queen cups and presented to the LRC for rearing as queens.

The larvae selected were obvious as these were fed and wax was deposited to create the surrounding queen cell.

Did LRC’s preferentially select larvae from the matched EPC?

No.

This larval transfer was done several times to get statistically meaningful results, using six colonies, repeated either twice or three times in successive years. In total 450 grafted larvae were presented to the LRC’s.

Larval acceptance rates were ~48-60%, a figure often exceeded when grafting for queen rearing.

Capped queen cells

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

I suspect this rather mediocre acceptance rate reflects the in vitro rearing of the larvae for the first 2 days, potentially compounded by the age of the larvae which – at 48 hours – are at least 30 hours older than optimal.

But the acceptance rate doesn’t really matter as it was similar whether the larvae were derived from the matched or unmatched EPC. This therefore ’contradicts the hypothesis that kinship plays a central role in the selection of larvae for queen breeding’ (to quote the authors verbatim).

Larval selection is not nepotistic.

But certain larvae were preferentially selected

Despite the fact that the bees didn’t appear to care whether the eggs were from a related colony or not, they did preferentially select larvae produced by certain queens.

And I’ve already given you a clue of the characteristic favoured by the workers … though the characteristic per se wasn’t directly selected by the workers bees.

The six different queens used in this study produced eggs that differed slightly in weight. On average, the heaviest and lightest eggs varied in weight by ~5%.

There was a significant and direct correlation between the average weight of eggs produced by a queen and the likelihood that the resulting larvae would be selected by the larval rearing workers.

Heavier eggs produced larvae that were favoured by the cell raising colony.

Relationship between average egg weight and whether they were accepted for queen rearing

Of course, the cell raising colony never saw the eggs … these were hatched in an incubator and fed for two days before grafting and introduction.

Nevertheless, there was something about heavy eggs that the larval rearing colony favoured.

A total of 248 virgin queens were produced from the 450 larvae grafted (55%). These virgins were weighed and subsequently naturally mated, resulting in 190 egg-laying queens (42% of grafts, or 77% of virgins). Of these, 147 came to a grisly end as they were dissected two months after they started laying to count the number of ovarioles (the sub compartments of the ovaries in which the developing oocytes are produced).

Queen weight and ovariole number have previously been considered as markers of queen quality. Perhaps disappointingly, there were no significant differences in terms of virgin queen weight, ovariole number or the delay in onset of egg laying between queens produced from heavy or light eggs.

Crude criteria of what’s best

I’m not unduly concerned that the crude criteria we use to judge the quality of these queens (weight and ovariole number) failed to demonstrate significant differences. These criteria may not be the same as the ones selected by the bees 6. The fact that we cannot measure differences in the resulting queens does not mean that there were not qualitative differences in queens reared from heavy eggs that would benefit the colony.

Or would have been if they hadn’t been dissected 🙁 .

Where have all my young girls gone?

Bigger AND better … or just bigger?

It just means we were probably not measuring the right things.

However, extending this experiment from the relatively straightforward ‘heavy eggs are favoured’ observation is not trivial. If the scientists cannot see a difference in the queens then they might have to look at colony performance over time, or in adverse years, or when swarming, or in hard winters etc. Each of these may directly or indirectly act as a selective pressure on the queen quality, and hence the choice the bees make in the initial eggs or larvae that are selected for queen rearing.

Caveats

The relationship between egg weight and larval acceptance shown above is based upon the average egg weight produced by each of the 6 queens used in the study.

These average weights varied by about 5% (154.9 to 162.7 micrograms). That’s not a lot, and is narrower than the range of egg weights produced by an individual queen. Unfortunately, this data isn’t presented, but it can be inferred from the standard deviation of the mean egg weight.

For example, the average weight of the heaviest eggs was 162.7 micrograms with a standard deviation of 22.2 micrograms. With some basic assumptions of the distribution of weights, that means that 68% of the eggs were between 140.5 and 184.9 micrograms, but the remaining 32% were heavier or lighter.

Clearly, queens produce eggs that vary considerably in weight … and this has also been shown in previous studies (e.g. AL-Kahtani et al., 2013).

I would have liked to see a graph of the weight of individual eggs and an indication of whether or not the resulting larva was accepted as starting material for a new queen.

Secondly, there are methodological problems – acknowledged by the authors – in the relationship between queen quality and egg weight. So few queens were reared from lightweight eggs that it was difficult to determine if these produced poor quality flyweight queens with low numbers of ovarioles.

You can only work with what’s available.

Emergency response and egg/larval selection

The other two caveats I have are to do with the experimental design. The study involved rearing queens under the emergency response; larvae were presented to queenless and broodless colonies. For survival, they had to rear queens from the material presented (but still exhibited a preference).

However, I’d suggest that the vast majority of queens reared by honey bees – over the millions of years that have shaped the evolutionary choices we are now testing – are produced under either the swarming or supersedure responses.

Is egg/larval choice under the emergency response the same?

We don’t know 7.

The non-random construction of queen cells.

Finally, it has been shown that colonies prefer to rear queens from 3 day old eggs rather than 48 hour old larvae. I understand why the authors reared the eggs in vitro, but it does rather ignore the known preferences of the colony (see The bees know best for more on this topic).

Yes … they had no option other than to choose between the offered 48 hour old larvae … but would they have made the same choice if they had been given the eggs in the first place?

Why are heavier eggs preferred … ?

This is where we get to speculation and I’m going to save the discussion for after a follow-up post 8 in the next fortnight or so.

The bottom line is we don’t really know, but we have some pretty good ideas (though some are extrapolated from other social insects).

However, there’s a related question; ”How are the heavier eggs/larvae selected?” … and I think it’s fair to say this remains unclear 9.

… and is this relevant to our queen rearing?

When I rear queens I select larvae from a colony that shows some or all of the traits that I favour in my bees.

I’m a simple beekeeper and I have very simple needs … I want my bees to be calm, well-tempered, steady on the comb and frugal in winter. The best colonies that exhibit these traits are used as a source for grafting larvae when queen rearing.

Nice bees and a nice queen

In contrast, colonies that exhibit lots of chalkbrood, have poor temper, run about the comb or – worst of all – ‘follow’ are never used for queen rearing. Nor are they allowed to replace their queen during swarm control. Instead, these are requeened (as early as practical) from better stock.

I’ve described before my ‘rule of thirds’. When comparing the sum total of the various traits I care about, the best third are used for queen rearing. These queens are used to requeen the worst third and – if there are spares – the intermediate quality third as well.

However, if I run out of queens I’m reasonably happy to let the middle third requeen themselves (for example, during swarm control).

You’d be surprised how quickly the average quality of your bees improves using a strategy like this.

Grafting larvae vs. letting the bees choose

But the ‘best third’ are defined solely by my criteria.

I ignore any preferences the bees might have by choosing the larvae when grafting.

Assuming the queens that head these top third ‘good’ colonies produce a range of egg sizes (which they will), the bees would preferentially select the larvae from the largest eggs.

I just pick the larvae of the right age that I can see 10 and transfer them to a Nicot plastic queen cup.

Eggs and young larvae

Eggs and young larvae

Not the same thing at all.

Perhaps it doesn’t matter? After all, thousands of apparently satisfactory queens are reared by grafting every season.

Perhaps the characteristics the bees select for – whatever they are – are irrelevant for beekeeping? We don’t know, but I’d bet that some of the criteria that benefit the bees – and are evolutionarily selected – might well benefit beekeeping.

Poor ‘take’

Sometimes I get 100% ‘take’ i.e. all the grafted larvae accepted and reared as queens 11.

Sometimes it’s less, a few times it’s almost none 🙁 .

Cell bar frame with three day old queen cells, The Apiarist.

3 day old queen cells …

In the latter instance I usually assume that the cell raising colony is not sufficiently ‘receptive’ but perhaps I’ve chosen undersized larvae (for their age), or perhaps the donor queen only produces undersized larvae (again, for their age)?

In the best tradition of “If at first you don’t succeed, try, try and try again” I usually just have another go. Almost always, I have another go in exactly the same way.

Perhaps if I used larvae from a different (but still good) colony the take would be improved?

Or perhaps if I presented the larvae in a manner that allowed the bees to select those to be developed into queens I might get improved acceptance? 12

I could end up with more queens and – potentially – better queens.

It’s blowing a hoolie tonight

And, as another autumn storm winds itself up to come barreling in from the Atlantic, dreaming about balmy May afternoons in the apiary and improved ways to produce better queens is about as close as I can get to beekeeping 😉 .


References

AL-Kahtani, S.N. and Bienefeld, K. (2021) ‘Strength surpasses relatedness–queen larva selection in honeybees’, PLOS ONE, 16(8), p. e0255151. Available at: https://doi.org/10.1371/journal.pone.0255151.
Al-Kahtani, S.N., Wegener, J. and Bienefeld, K. (2013) ‘Variability of Prenatal Maternal Investment in the Honey Bee (Apis mellifera)’, Journal of Entomology, 10(1), pp. 35–42. Available at: https://doi.org/10.3923/je.2013.35.42.
Mattila, H.R. and Seeley, T.D. (2007) ‘Genetic Diversity in Honey Bee Colonies Enhances Productivity and Fitness’, Science, 317(5836), pp. 362–364. Available at: https://doi.org/10.1126/science.1143046.

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 …