Category Archives: Science

Superinfection exclusion

Alpha

Beta

Gamma

Delta 

The majority of readers will identify these as the current circulating variant strains of Covid 1. The World Health Organisation decided upon this naming system as being easier and more practical to discussed (sic) by non-scientific audiences 2.

All viruses vary, and viruses with genomes made from ribonucleic acid (RNA) vary more than those which have deoxyribonucleic acid (DNA) genomes. This is because the enzymes that replicate RNA virus genomes do not have an error correction facility. 

The virus that causes Covid-19 is an RNA virus and so is Deformed wing virus (DWV), probably the most significant virus to bees and beekeepers (other than those who have Covid that is).

Virus variation

Why does virus variation matter? 

Or, asking the same question in a more roundabout way, why don’t RNA viruses evolve error correcting enzymes (after all, the DNA viruses have these … can it be that difficult?).

If the enzyme makes errors then that’s surely a bad thing?

Actually … for the particular ‘lifestyle’ that these viruses practice, errors and variation are a good thing.

They benefit the virus.

But you know all this already, even if you don’t think you do.

Covid cases caused by the delta variant

The SARS-Cov2 delta variant now accounts for at least 99% of cases of Covid-19 in the UK. It accounted for just 0.1% of cases in late February.

The delta variant is much more transmissible. It carries errors, or mutations as they’re more correctly known, that – for whatever reason – means it can be passed from person to person much more efficiently 3.

These mutations benefit the virus and allow it to spread further and faster 4.

If the mutations (‘errors’) that the virus acquires are beneficial – by increasing transmission, by expanding the cell, tissue or host range, by helping evade the immune response in a partially vaccinated population (!) for example – then the virus will successfully replicate and produce more viruses carrying the same mutation.

And a bunch of additional ones as well … acquired during the last round of replication.

Strains and types

At some point a virus acquires sufficient mutations from an earlier incarnation that it’s identified as a distinct strain.

For example, SARS-Cov2 is ~82% identical at the genome level to SARS-Cov1 which caused the SARS pandemic in 2003 5. SARS-Cov2 did not evolve from SARS-Cov1, but they share a common ancestor. They are different strains or types of coronavirus.

There are no hard and fast rules that define when a virus is considered a different strain or type. Often it’s historical, reflecting the geographic origin, or the source from which the virus was isolated. Different strains may exhibit different phenotypes – host range, transmission, disease etc. – but don’t have to.

For example (before we get back to honey bee viruses) there are three ‘types’ of poliovirus that are about 80% identical at the genetic level. They all cause exactly the same disease (poliomyelitis) and they replicate in an identical manner – same cell, tissue and host range for example. However, to the human immune system they ‘look’ different. The immune response to poliovirus type 1 will not protect you from infection with poliovirus type 3. That’s why the poliovirus vaccine contains a mixture of all three types, to protect you from all polioviruses.

You can even get infected with two types of poliovirus simultaneously, and the virus can replicate in the same cells in your gut … or, if you’re unfortunate, your brain.

I’ll return to dual infections shortly as it’s an important topic … and related to the study I’m going to discuss.

Deformed wing virus

There are two types of DWV, designated type A and type B 6.

Originally these had names that reflected their original isolation.

DWV type A was termed Deformed wing virus and was isolated from honey bees displaying the characteristic symptoms of developmental deformities shown in the image below.

DWV type B was termed Varroa destructor virus type 1 and was isolated from the ectoparasitic mite Varroa destructor.

It “does what is says on the tin” … DWV symptoms in a recently emerged worker

These viruses are very similar to each other. They are something like 85% identical at the level of the RNA genome. More importantly than this genetic identity (or perhaps similarity would be a better term to use here) is the fact that they appear to cause very similar diseases in honey bees.

Although early studies suggested there were some differences in their virulence, more recent work from Prof. Rob Paxton in Germany, from my lab, and from Dr. Eugene Ryabov and colleagues in the USA suggests these two types of DWV are actually very similar, at least in pathogenesis.

There do appear to be some differences, with the suggestion that type A does not replicate in Varroa whereas (full disclosure, the following study is from my lab) type B does. Undoubtedly, the other genetic differences between the types will confer some subtle variation in phenotype (effectively what they ‘do’), but – as far as beekeeping is concerned – they should probably be considered the same.

A protective, non-lethal type A DWV? 

All of which made a 2015 colony-level study 7 of DWV infection rather intriguing.

This reported the survival of colonies that were infected with a “non-lethal” type B strain which were protected from infection with the “lethal” type A strain 8. The authors summarised the significance of this study like this:

We propose that this novel stable host-pathogen relationship prevents the accumulation of lethal variants, suggesting that this interaction could be exploited for the development of an effective treatment that minimises colony losses in the future.

At the time there was a flurry of excitement and discussion about this 9

Superinfection exclusion

They proposed that the mechanism that prevented the infection with the type A strain was superinfection exclusion.

Virologists love mechanisms … 🙂 

Which brings me back to virus variation. 

Imagine a population of variant viruses trying to infect a new host … like a bee.

Survival of the fittest – selection for better replicating viruses from a mixed population

In mixed infections, a virus that has an advantage over the others in the population ends up ‘winning’ the competition for the resources of the host. They therefore make more progeny viruses.

One of the advantages could be that the virus simply replicates faster

Another – more subtle, but the same outcome – is that the virus prevents other viruses from infecting the same cell (and, by extension, host).

By excluding competing viruses it effectively ‘wins’ the competition.

Superinfection exclusion – one virus (type) can prevent infection by related but different viruses

And some viruses do exactly this using a variety of cellular mechanisms.

For example, many viruses turn off the expression of the cellular receptor (think of this as the door) they use to enter the cell. If there’s no receptor (no door) then another virus cannot enter.

With no other viruses to compete with in the same cell there can only be one type of virus produced 10.

There are other mechanisms as well, but we’ll stick with the receptor one as it’s easy to comprehend.

Superinfection of a cell containing a virus that has the ability to turn off the cellular receptor it uses will effectively exclude the second virus from replicating … hence superinfection exclusion.

What don’t we know about DWV?

A lot 🙁

We don’t know how it gets into cells. We don’t know a huge amount about its replication and we know precious little about the way it interacts with the cellular machinery (the ‘stuff’ in the cell that the virus hijacks to make more viruses) of the host. 

However, since 2015 we do know that all the types of DWV that have been carefully studied appear to be more or less equally virulent. None appear to be ‘non-lethal’ as claimed for the type A virus in the superinfection exclusion paper.

This prompted us to look in a bit more detail at the consequences of dual or sequential infections with DWV in the laboratory. 

Is there a precedence at work?

In mixed infections, does one virus always ‘win’ and predominate in the new virus population?

In sequential infections, does it matter the order in which the viruses are acquired?

And mixed infections are pretty much the norm for DWV infection. All bees, whether previously exposed to Varroa or in Varroa-free regions, appear to have low levels of DWV already present. If parasitised by the mite, these bees must experience a mixed infection.

In addition, studies we published several years ago 11 showed that recombinant viruses – essentially hybrids between type A and type B DWV – often predominated in heavily Varroa-infested colonies 12.

If mixed infections cannot occur, how do such hybrids form?

Some of the answers to these questions are in our recently paper published in the ISME Journal. Gusachenko, O. et al., (2021) First come, first served: superinfection exclusion in Deformed wing virus is dependent upon sequence identity and not the order of virus acquisition. ISME J (2021). https://doi.org/10.1038/s41396-021-01043-4

Mixed DWV infections

I don’t propose to give a pupa-by-pupa account of the studies we conducted. You can read the paper – it’s open access and (because Olesya ‘Alex’ Gusachenko, the lead author, did most of the writing) relatively easy to comprehend 😉

But here are a few highlights.

Over the last few years we have produced reagents that allow us to produce almost ‘pure’ stocks of type A, type B or hybrid type A/B 13 strains of DWV.

At least 99.99% of these stocks are of one DWV type. Note that there will still be variation within this population as the replication errors probably generate one mutation per virus in the population. We therefore refer to these virus stocks as near clonal.

Injection of honey bee pupae with any of these viruses resulted in very similar levels and kinetics of replication – all the viruses replicate as far and as fast as each other.

In mixed injections, when two viruses were administered simultaneously, both replicated to equivalent levels. 

We therefore found no evidence for the dominance of one strain over another.

Sequential DWV infections

But it got more interesting when we did sequential injections. We did these by injecting with one virus, waiting 24 hours and then injecting with a second virus.

Using type A and type B DWV both viruses had replicated to similar high levels (billions of virus per pupa) within 48 hours, irrespective of the order of addition. 

If superinfection exclusion was operating we would have perhaps expected type A to have prevented or reduced the replication of type B. However, that didn’t appear to be the case.

Competition between sequential infecting DWV isolates. VVV is type B, VDD is type A and VVD is a hybrid between them.

But, when we looked at sequential infections between type A and a type A/B hybrid we did see that replication of the second virus was delayed.

Delayed, but not stopped altogether.

It would take a complete post to describe the figure above 🙁 . We’ve quantified the virus present 5-7 days after sequential injections with type A (VDD), type B (VVV) or a hybrid virus (VVD) 14.

The columns labelled VDD→VVV or VVV→VDD show the viruses and order of addition. The dots represent the amount of virus present at 5 or 7 days post injection. When the viruses were more similar to each other – for example, the VVV→VVD or VVD→VVV pairs on the right – there was a greater impact on the replication of the virus added second.

The same but different

We extended these studies to look at sequential infections with two viruses that only differed by 4 nucleotides (the building blocks) of the 10,140 nucleotides in the RNA genome of DWV i.e. 99.6% identical.

Cunningly, these four differences allowed us to unambiguously identify which virus was replicating.

In this part of the study the virus added second did not replicate to detectable levels. 

So … our data clearly demonstrates that viruses that were more similar to each other were more likely to inhibit replication during sequential infections.

In addition, no individual virus type was dominant over any others. 

This didn’t look much like classic superinfection exclusion to us.

Red or green viruses

Not content with generating graphs and tables we went on to take photographs of virus infected pupae. 

You can’t beat a nice colour image when trying to impress the peer reviewers 😉 .

Remember that DWV is too small to see with even the most powerful light microscope. You could fit several billion on the head of a pin.

We therefore engineered the virus genome to ‘show’ us where it was replicating.

Green bees

We did this by introducing an additional gene that fluoresced green or red when under UV light. I’ve discussed green viruses before … the red version uses similar technology, but using a different fluorescent reporter gene.

DWV replication (showed by green fluorescent signal) in the head, wing and abdomen of honey bee pupae

Using the red or green viruses we showed very similar results to those described above. When we superinfected with a genetically similar virus, its replication was inhibited. When it was genetically more divergent it could replicate (and we could visualise it as red or green foci of infection in a variety of tissues of the developing pupa).

Red and green viruses

We also infected bee with the red and green viruses simultaneously. Most of the fluorescent foci of infection were red or green, but a small number were both red and green. 

Green (EGFP) and red (mCherry) expressing DWV coinfecting a honey bee pupa. Arrow indicates dually infected cells.

The most likely explanation for having both colours overlapping in the photograph was because the virus were replicating in the same cells in the honey bee pupa.

Since this was exactly the sort of situation that was needed to generate recombinants (hybrids or chimeras) between the two different DWV viruses we specifically looked for them 15.

And there were lots and lots of recombinants …

Recombination between DWV viruses. The size and position of ‘bubbles’ indicate the location and number of junctions.

The bubble plot above shows the location and frequency of junctions. One virus is plotted on the horizontal and one on the vertical axis. It’s a sort of two-dimensional map of the virus. Think of a junction as where one virus ends and the other starts. They are located throughout the DWV genome – hundreds of them.

This suggests that pupae infected with both type A and type B DWV will act as ‘factories’ for the production of thousands more different hybrid variants between the two viruses.

Most of these hybrids will grow poorly.

Many will be uncompetitive.

But some – like the delta variant of SARS-Cov2 – might be more transmissible.

And some could be more pathogenic.

Or – the nightmare scenario – both 😯 .

What’s this got to do with practical beekeeping?

Every time a beekeeper moves bees about s/he is also moving viruses about.

This happens when you move bees to out apiary, when selling a nuc or when importing a queen.

Double brood ...

Moving viruses (and bees) to a new apiary …

This will contribute to the constant mixing of DWV variants that occurs when bees drift between hives, when drones mate with queens, when phoretic Varroa jumps onto a bee that is robbing a collapsing colony.

There’s a difference of course.

All those bee-driven mixing events are local and small scale … a few bees and a few miles.

But if you import a nuc from Greece via Northern Ireland both the distance and number of bees (and hence number of viruses) is much greater.

Of course, most of this mixing will just generate more mixtures of viruses.

It will also generate more recombinants.

But there’s always the possibility it might throw up a highly virulent, highly transmissible variant.

Which would not be a ‘good thing’.

And if it does, a ‘non-lethal type A strain’ (should such a thing actually exist) is not going to help prevent infection by the mechanism of superinfection exclusion I’m afraid 🙁 .

Without doubt the best way to prevent infection is to minimise the mite numbers in your colonies. This is a subject I’ll be tackling again in a couple of weeks.

But, before I go, do we understand how the more closely related strains of DWV prevent superinfection? 

Yes … probably, and it’s all to do with the immune response of the bee

I’ll discuss this in the future as it’s a mechanism that could be exploited to produce bees immune to the ravages of DWV.


 

Queen introduction

I’m probably less qualified to write about queen introduction than almost any other aspect of beekeeping. This is not because I’ve not introduced any queens. Quite the opposite, it’s something I do more or less routinely many times a season. 

The reason(s) I’m really not qualified to discuss the topic are:

  • I almost exclusively use the method I first used and I’ve not done any side-by-side comparisons with other methods to determine which work ‘best’. I have a method that works well enough i.e. somewhere between most of the time and almost always. That’s good enough for me.
  • I’m not aware of any recent scientific studies on the subject so cannot use those to make informed decisions – or interpretations – of why some methods work and others don’t 1.

Nevertheless, not being qualified has never stopped me before 2 and it’s a topic that some beekeepers struggle with and many beekeepers worry about.

Successful introduction ...

Successful introduction …

So here goes …

Art or science?

David Cushman/Roger Patterson make the point that: 

” … you can have two colonies in the same condition, in the same apiary, on the same day and if you introduce a queen in the same condition into each, one will succeed and the other will fail.”

This doesn’t mean that 50% of introductions fail (although it reads that way). What he/they mean is that there appears to be no rhyme or reason why one succeeds and the other does not.

On another day, both might succeed … or both might fail 🙁

Is it therefore an art or a science?

I don’t know. All you can do is get the basics correct and cross your fingers …

For understandable reasons, beekeepers feel rather precious about their queens. In particular, beekeepers who do not rear their own queens (and so have no spares waiting in the wings) can get a bit paranoid about queen introduction. 

What if it goes wrong?

The colony will potentially be left irretrievably queenless and – if you purchased the queen – you’ll be £40 out-of-pocket 3.

If you do rear your own queens you can perhaps be a bit more blasé about queen introductions. Potentially you can also do the sort of side-by-side comparisons I mentioned above … though there aren’t many studies where this has been done in a rigorous way. 

Most seem to find a method that works for them and then stick with it … which is what I’ve done and what I’m going to describe.

This is what I mean by ‘get the basics correct’.

I’ll also mention an alternate method I irregularly use for what I consider to be really difficult situations and/or really valuable queens.

But before we get into the methodology, it’s worth making some general comments about the state of the recipient colony and the queen being introduced.

Is the colony really queenless?

Trying to introduce a new queen into a colony that is not actually queenless will not end well.

One or both of the queens will probably not survive the experience. Either the workers will reject (and slaughter) the incoming queen, or the queens will fight and may both be damaged and lost.

It is therefore important that the recipient colony is queenless.

By queenless I mean that there is no queen present.

I do not mean no laying queen present. If you try and introduce a new queen into a colony with a failed (non laying) queen or a virgin (unmated) queen you will have problems.

Sod’s Law is explicit in these instances … the valuable new mated laying queen will be lost 🙁

Queen above the QE

A virgin queen (in this instance on the wrong side of the queen excluder)

The very best way to be sure the colony is queenless is to remove the current queen before introducing the new one. That necessitates finding the queen in the first place. 

What if you can’t find the queen but you’re sure that the colony is queenless?

Well, there are only two possibilities if you can’t find the queen, these are:

  1. The colony is queenless … you’re good to go.
  2. The colony is not queenless … but you’ve looked so hard for so long they’re now disturbed and running manically around the frames, getting more and more agitated and angry. Neither the bees or you are any sort of state to allow the queen to be discovered. Close the hive up. Have a cup of tea. Try again tomorrow.

I discussed methods of determining whether the colony is queenright (though not by extrapolation, the opposite i.e. queenless – see below) last season. Towards the end of that post I described the addition of a ‘frame of eggs’ to determine if the colony is queenright or not. I won’t repeat all the details here.

If the colony draw queen cells on the introduced frame then you can be sure that the colony is queenless. See (1) above … you’re good to go 🙂

Not queenless, but not queenright

That same post describes the concepts of queenright and queenless.

A colony that is queenright has a mated queen capable of laying fertilised eggs (though she may temporarily not be laying, for example due to a dearth of nectar).

A queenless colony contains no queen.

But there’s an intermediate stage … or potentially two intermediate stages if you allow me a little leeway.

A colony containing a failed queen that’s either not laying at all (and not going to restart), or only laying drone (unfertilised) eggs is neither queenright not queenless. This colony will not draw queen cells on the introduced frame. You cannot safely introduce a new queen into such a colony before first finding and removing the failed queen.

A colony containing laying workers will also not 4 produce queen cells from the introduced frame of eggs. 

Laying workers ...

Laying workers …

A colony with laying workers behaves as though it’s queenright but is actually queenless. It’s not really an intermediate stage, but the consequences are the same. Again, they are highly unlikely to accept an introduced queen.

Deal with the laying workers first and then requeen … and good luck, laying workers can be a nightmare 🙁

OK … let’s assume the colony really is queenless … what’s the easiest way to introduce a new queen?

Add a sealed queen cell

Almost without exception, a queenless colony can be requeened by adding a sealed queen cell. The virgin queen will emerge, go on one or two mating flights and return and head the colony. This method of queen introduction is almost foolproof in my experience. 

Where do you get the queen cell from? Another colony, your mentor, a friend in your beekeeping association, a local queen rearer … necessity is the mother of invention 5.

Assuming the cell is a natural queen cell … cut the queen cell out of the comb with a generous amount of surrounding comb. Don’t risk damaging the queen cell. Keep it vertical … there are stages during development when the pupa is susceptible to damage. Ideally choose and use a cell 24-48 hours from emergence as they’re a lot more robust late in the development cycle.

Use your thumb to make an indentation towards the top of a frame near the centre of the broodnest, above some capped and emerging brood. Using the generous ‘edge’ of comb surrounding your chosen queen cell push this into the indentation so the cell is secure. Close up the colony and a) check for emergence in 48 hours or so 6 and b) a fortnight later for successful mating.

Adding a grafted queen to a colony

If the cell is from a grafted larvae it is even easier … press the plastic cell cup holder into the comb and push the frames together. I describe this in a recent discussion of grafting.

How successful is this method of ‘queen’ introduction?

I’d estimate at least 85%.

A very small percentage of queen cells fail to emerge (or rather, the queen fails to emerge from the cell … but you knew what I meant 😉 ).

A slightly larger percentage of queens fail to mate (or fail to return from a mating flight). But, even in a bad season, it’s rarely more than 10-15%.

The new queen is accepted by the colony because she emerged there and they all live happily ever after 😉 .

What?

I know, I know … that’s not really queen introduction.

You’re right. But it works. Very well.

These are the two methods I use for queen introduction.

Candy-plugged queen cage

I have a large supply 7 of JzBz queen introduction and shipping cages. 

JzBz queen cages

JzBz queen cages

I really like them because they were free they are reusable, they have a tube-like entrance that can be plugged with candy/fondant and they have a central region to protect the queen from aggressive workers outside the cage. 

Some cages offer no areas of refuge for the queen and workers can damage the queen through the perforations. Avoid cages that are all perforations.

The JzBz cages can be purchased with a removable plastic cap (shown below the cage in the image). These fit over the end of the tube and can seal the cage until you judge the colony is likely to gracefully receive the new queen … as described below 8.

JzBz queen introduction and shipping cage

Using a JzBz cage for queen introduction:

  • Plug the tube of the JzBz cage with queen candy or fondant. Queen candy can be purchased commercially and kept frozen for long periods. I almost always use fondant these days as I have spare boxes of the stuff from autumn feeding.
  • Add a short piece of wire or a cocktail stick through the perforations at one end of the cage to hang the cage – entrance tube pointing downwards – between two frames. Do this before adding the queen to avoid risking skewering the queen at a later stage 9
  • Place the queen in the cage without any attendants (see below for comments on removing them). Close and seal the cage. Seal the candy tube with the plastic cap.
  • Hang the cage in the centre of the broodnest, above some emerging brood. Leave the colony for 24 hours.

The idea here is that the colony gets the chance to accept the new queen without getting the opportunity to slaughter her.

Look for signs of aggression

Colonies that have been queenless for a few hours (say 2-24) before adding the new queen are usually very willing to accept a replacement. Adding a queen immediately after removing the old queen is likely to result in some aggression to the caged queen.

Check the colony after 24 hours. I usually lift the cage out and place it gently on the top bars to observe the interaction of the workers and the queen.

Checking for aggression

If the colony show no aggression to the caged queen – look for bees trying to sting through the cage or biting at the cage – then remove the plastic cap and re-hang the cage between the frames.

If they show aggression leave them another 24 hours and check again 10

Once you remove the cap the queen will be released by the workers after they eat through the candy/fondant. This takes just a few hours. 

Check again a week later to ensure the colony has accepted the queen.

Nicot introduction cage

I use the method described above for almost every queen I introduce. 

The only exception is if I have to requeen a colony that has previously not accepted a queen using the method described above. Usually such a colony will also be broodless (just based on the timings of determining they are queenless and failing once to successfully introduce a queen). 

Under these circumstances I use a Nicot queen introduction cage.

Nicot queen introduction cages

I find a frame from another colony with a hand-sized patch of emerging brood. The comb needs to be level so that the cage can sit on top without gaps for the queen to escape.

Then do the following:

  1. Remove all the bees from the frame and place the Nicot cage over the brood using the short plastic ‘legs’ to hold it into the comb 11.
  2. Secure the cage in place using one or two elastic bands.
  3. Introduce the queen through the removable – and eminently losable 12 – door.

In practice it’s easier to do this in the order 3-1-2 … place the queen on the frame, cover with the cage and then secure it with the elastic band.

Add the frame and cage to the hive, locating it centrally. Push the frames together. 

The emerging workers will immediately accept the queen and feed her. Other workers will feed the queen through the edges of the cage.

One corner of the cage has an entrance tunnel that can be filled with candy/fondant. I don’t think I’ve ever used this. In my experience the colony releases the queen by burrowing under one edge of the cage after a few days. If they don’t, check and remove the cage a week later.

I don’t think I’ve ever failed to successfully introduce a queen using one of these cages, but it’s a relatively small sample size.

Thorne’s sell a metal mesh version of this cage that has integral ‘legs’. I’ve not used it, but the principle is the same. Keep it in a box or the sharp cut metal edges will butcher your fingers – it’s difficult picking up queens with heavily bandaged digits.

You could also ‘fold’ your own from mesh floor material. One with deeper ‘sides’ could be pushed down to the midrib of the comb, so reducing the chances of the bees burrowing under the edge of the cage.

Mated or virgin? 

I use the JzBz cage for introducing either mated or virgin queens. I’m not aware of any significant difference in the acceptance rate between them. 

However, it’s worth noting that acceptance is dependent upon essentially ‘matching’ the expectations of the colony with the state of the queen. 

A virgin queen will be less likely to be accepted by a colony from which a mated laying queen has recently been removed. Leave them 24-48 hours. 

Likewise, I remove nearly mature queen cells from a colony I’m requeening with a mated queen. I don’t want to risk an early-emerged virgin queen from ‘raining on the parade’ of the introduced queen.

I’ve only used the Nicot cage for mated queens. Since the latter is usually used for a broodless colony I want the minimum possible delay before there is new brood in the colony.

Alone or with attendants?

If you purchase a queen and receive her by post there will be a few workers caged with her.

I always remove these although some suggest that they do not adversely influence acceptance rates 13. I remove them because I’m a bit paranoid about viruses … these workers come from an ‘unknown’ hive (quite possibly not the same one that the queen came from) and will carry a potentially novel range of Deformed wing virus variants (and possibly others as well).

I don’t want these in my hive so I remove the workers

It’s also worth noting that Wyatt Mangum has an interesting report in American Bee Journal indicating that the presence of attendants significantly increases the acceptance time 14 for an introduced queen 15. In some cases the presence of attendants resulted in the colony showing aggression for longer than it took for the bees to eat through the candy plug … that’s not going to end well for the queen.

The safest way to remove attendants is to open the caged queen in a dim room with a single closed window. The bees will fly to the window (perhaps with a little encouragement).

A mated queen probably will not fly at all and can be re-caged. A virgin queen can fly well and will also end up at the window. Gently grab her by her wings and re-cage her.

You can do all this in the apiary … it requires confidence and dexterity. I know this because I recently tried it with a virgin queen in my apiary, using lashings of overconfidence and hamfistedness.

She flew away 🙁

Inevitably you can buy a gadget to help you with this – the queen muff

Conclusions

There is always a slight risk that queen introductions will not be successful. The queen pheromones have such a fundamental role in colony maintenance that disrupting them – or suddenly changing them – may lead to rejection. 

However, the methods described above are sufficiently successful that I’ve not found the need to look for better alternatives. They’re also sufficiently fast that I’m not tempted to try some of the ‘quick and dirty’ approaches 16 to save time.

Finally, it’s worth noting that it is usually easier to requeen a nucleus colony than a full hive. If I ever bought one of those €500 breeder queens I’d introduce her to a nuc first and then unite the nuc back with the original colony.

But that’s not going to happen 😉


 

Fainting goats … and queens

Myotonia congenita is a genetic disorder that affects the muscles used for movement. Myotonia refers to the delayed relaxation of these skeletal muscles, resulting in a variety of obvious symptoms including temporary paralysis, stiffness or transient weakness.

In humans these symptoms are often manifest as difficulty in swallowing, gagging and frequent falls. Children are affected more than adults. One of the most dramatic manifestations are the falls (‘fainting’) that can occur as a result of a hasty movement. 

Although physiologically distinct, ‘fainting’ is a reasonably accurate description of the sudden loss of movement and the transient nature of the disorder. Like fainting, loss of movement is usually quickly resolved. However, unlike fainting, myotonia congenita involves muscular rigidity or stiffness, so more closely resembles catalepsy.

Genes

There are two types of myotonia congenita, termed Thomsen disease and Becker disease, both of which are usually associated with mutations in the gene CLCN1 1. This encodes a chloride channel (a ‘hole’ through the cell membrane that allows the transfer of chloride ions) critical for muscle fibre activity. 

Cartoon of a transmembrane chloride channel.

With loss-of-function mutations in CLNC1 the muscle fibre continues to to be activated. When stimulated, for example if the fibre is triggered to suddenly contract for jumping or running (or  to stop a fall), the muscle fibre is hyper-excitable and continues to contract, and shows delayed relaxation

Around 1 in 100,000 people exhibit myotonia congenita, though it is about ten times more common in northern Scandinavia. Treatment involves use of a number of anticonvulsant drugs.

The same loss-of-function CLCN1 mutation in humans is seen in symptomatically similar horses, dogs … and goats.

Goats

In the late 19th century four goats were imported to Marshall County, Tennessee. Their strange behaviour when startled was first described in 1904 and defined as a congenital myotonia by Brown and Harvey in 1939. 

The eponymous Tennessee fainting goat

These pre-war studies formed the basis of of our understanding of both the physiology and genetics of myotonia congenita, though the specific mutation in the CLCN1 gene was only confirmed several years after it had been identified in humans.

Since then myotonic goats have become an internet staple, with any number of slightly distressing (for me at least, if not for the goats) YouTube videos showing their characteristic fainting when surprised or frightened 2.

Don’t bother watching them.

If you want to see a fainting goat in action watch little ‘Ricky’ jump up onto a swinging seat on the National Geographic website.

It’s a perfect example.

He jumps up, gets a mild fright as the swing moves, goes stiff legged and simply rolls over and falls to the ground. A few moments later he’s back on his feet again, looking slightly shaken perhaps, but none the worse for wear.

Queens

All of that preamble was to introduce the topic of fainting queens. 

A fainting queen

This was a subject I’d heard about, but had no experience of until last week.

Periodically it gets discussed on Beesource or the Beekeepingforum – usually the topic is raised by a relatively small-time amateur beekeeper (like me) and it gets a little airtime before someone like Michael Palmer, Michael Bush, Hivemaker or Into the Lion’s Den 3 shuts down the conversation with a polite “Yes, I see it a few times a year. They recover”, or words to that effect.

Since these commercial guys handle hundreds or perhaps thousands of queens a year I think we can safely assume it’s a relatively rare phenomenon. 

Since I don’t handle hundreds or thousands of queens a year – and you probably don’t either – I thought the incident was worth recounting, so you know what to expect should it ever happen.

And to do that I have to first explain the fun I had with the first of the two queens in the hive I was inspecting.

A two queen colony

It was late afternoon and I was inspecting the last of our research colonies in the bee shed.

The hive had two brood boxes and a couple of supers. Nothing particularly surprising in that setup at this time of the season; the colony was quite strong, the spring honey had been extracted and a couple of supers had been returned to the hive for cleaning.

However, it wasn’t quite that straightforward. 

The lower brood box had been requeened ~3 weeks earlier with a mature queen cell from one of my queen rearing attempts. I’d seen that the virgin had emerged and restricted her to the lower box at my last visit. 

I’d added a queen excluder (QE) over the lower box with the intention of removing all the old frames above the QE once the brood had emerged.

However, at that last visit I’d ended up with a good looking 4 ‘spare’ virgin queen. Although I had no need for her at the time, and no time to make up a nuc 5, I decided to put her in a fondant-plugged introduction cage in this upper box.

This ‘upper’ queen couldn’t fly and mate in the week I was away, but I reasoned that I could merge the colony with the bottom box if the ‘lower’ queen failed to mate 6.

So, after adding the virgin queen to the top box I added a second QE and the two supers.

She can fly …

Having removed the supers and the upper QE I carefully inspected the upper box looking for the virgin queen who had been released from the cage

No sign of her 🙁

I went through the box again.

Time to try some of the ‘queen finding tricks’.

I moved three frames out of the way having examined them very carefully. The remaining 8 frames were then spaced out as four, well separated, pairs. I let the colony settle for a few minutes and then looked at the inner face of each pair of frames.

No sign of her 🙁

I looked again … nada, rien, niets, nunda, dim byd and sod it 7.

The obvious conclusion was that the colony had killed the queen after releasing her from cage. 

How uncharitable.

I reassembled the upper brood box and lifted it off the lower QE, in preparation to leave it outside the shed door while I went through the lower box. 

As I carried the brood box to the door I briefly looked up and saw a 8 virgin queen climbing up the inner pane of one of the shed windows, flapping frantically and fast approaching the opening that would allow her escape.

For obvious reasons I have no photographs of the next few minutes.

Bee shed window ...

Bee shed window …

For those unfamiliar with the bee shed windows, these have overlapping outer and inner panes, so are always open. They provide a very effective ‘no moving parts’ solution to clearing the shed of bees very quickly.

Which was the very last thing I wanted at that moment 😉

… rather well

I had a brood box and hive tool in my hands, the shed door was wide open, there was all sorts of stuff littering the floor and the virgin queen was inches away from making a clean getaway.

It’s worth noting that when virgin queens are disturbed and fly they almost always return to the hive. However, the hives in the shed have a single entrance and all the hives were already occupied with queens. I couldn’t let her fly and hope for the best … it probably wouldn’t end well.

By balancing half the brood box on an unoccupied corner of an adjacent hive roof I made a largely ineffective swipe for the queen, but disturbed her enough she flew away from the window in spirals around my head.

I    s  t  r  e  t  c  h  e  d    to reach the shed door and pulled it close, so reducing the possible exits from eight to seven. A small victory.

I put the brood box safely on the floor, leaning at an angle against the hive stand 9, and abandoned the hive tool.

The next 5 minutes were spent ineptly trying to catch the queen. When she wasn’t flying around the shed (where the lighting isn’t the best) she usually made for the same window.

The one behind the hive with four supers stacked on top 🙁

After a few more laps of the shed, dancing around the precariously balanced brood box and reaching around the hive tower for the window, I finally caught her.

And caged her 10.

I’m looking for publisher for my latest book, ‘Slapstick beekeeping’. If any readers know of a publisher please ask them to contact me.

After all that I should have had a little rest. I’d had enough excitement for the afternoon 11.

But there was still the queen in the bottom box to find and mark.

Feeling faint

The queen in the bottom box was mated and laying well. 

I made a near-textbook example of finding her 12.

After moving aside a few frames I should have announced (to the non-existent audience), She’s on the other side of the next frame … ” (the big reveal) ” … ah ha! There you are my beauty!”.

Holding the frame in one hand I checked my pockets for my marking cage 13.

All present and correct.

I then calmly picked her up by her wings. She was walking towards me, bending slightly as she crossed over another bee, so her wings were pushed up and away from her abdomen.

A perfect ‘handle’.

I didn’t touch her abdomen, thorax or head.

A swooning queen

And, as soon as I lifted her from the frame, she fell into a swoon and ‘dropped dead’.

This is an ex-parrot

Her wings were extended to the sides, her abdomen was curled round in a foetal position and she appeared completely motionless.

It is pining for the fjords

I dropped her into the marking cage and took the photo further up the page.

It was 6:49 pm.

For several minutes there was no obvious movement at all. Her legs and antennae were immobile. She showed no sign of breathing.

I gently shook her out onto a small piece of Correx on a nuc roof to watch and photograph her. I picked her up by the wing and held her in my palm … perhaps she needed some warmth to ‘come round’.

Was that a twitch?

Or was that me shaking slightly because I’d inadvertently killed her? 

Several more minutes of complete catatonia 14 passed … and then a gentle abdominal pulsing started.

This was now 10-11 minutes after I’d first picked her up.

Which got a bit stronger and was accompanied by a feeble waggle of the antennae.

And was followed a minute or so later by a bit of uncoordinated leg flexing.

And after 15 minutes she took her first steps.

It looked like she’d been on an ‘all nighter’ and was still rather the worse for wear.

I slipped her into a JzBz queen cage, sealed it with a plastic cap, and left it hanging between a couple of brood frames.

From picking her up to placing the caged queen into the brood box had taken 24 minutes.

Caged queen after fainting (and recovering … more or less)

I reasoned that if …

  • she fully recovered they’d feed her through the cage and I could release her the following morning
  • I’d released her immediately and she’d acted abnormally the colony might have killed her off
  • she did not recover I would at least be able to find the corpse easily ( 🙁  ) and so could confidently requeen the colony (with the virgin I’d tucked away safely in my pocket)

The following morning the cage was covered in bees and she looked just fine, so I released her. 

Somewhere under that lot is the recovered queen – still caged

She walked straight down between the frames as though nothing untoward had happened.

I didn’t have the heart to mark and clip her … I didn’t want to risk her ‘fainting’ again and, if she had, didn’t have the time to hang around while she recovered 15.

So was this ‘fainting’ myotonia congenita?

I suspect not.

Another name for the Tennessee fainting goat is the ‘stiff-legged’ goat. This reflects the characteristic rigidity in the limbs when the muscles fail to relax. The queen’s legs were curled under her, rather than being splayed out rigidly.

However, this interpretation may simply reflect my near complete ignorance of the musculature of honey bees 😉

However, I do know that the basics of muscle contraction and relaxation are essentially the same in invertebrate and vertebrate skeletal muscle. There are differences in the innervation of muscle fibres, but the fundamental role of chloride channels in allowing muscle relaxation is similar.

Therefore, for this fainting queen to be affected by myotonia congenita she should have a mutation in the CLCN1 gene encoding the chloride channel.

Although the honey bee genome has been sequenced a direct homolog for CLCN1 appears not to have been identified, though there are plenty of other chloride channels present 16

The majority of the 60 or so mapped mutations associated with myotonia congenita (in humans) are recessive. Two copies of the mutated gene (in diploids, like humans or female honey bees) are needed for the phenotype to occur.

Of course, drones are haploid so it should be easier to detect the phenotype.

I’ve never heard of drones ‘fainting’ when beekeepers practise their queen marking skills on them. Have you?

Repeated fainting

I’ll try to mark and clip this queen again.

It will be interesting to see if she behaves in the same way 17.

A quick scour of the literature (or what passes for the ‘literature’ on weird beekeeping phenomena i.e. the discussion fora) failed to turn up examples of the same queen repeatedly fainting.

Or any mention of daughter queens showing the same behaviour.

All of which circumstantially argues against this being myotonia congenita.

However, there are many other causes of sudden fainting (from the NHS website):

  • standing up too quickly – (low blood pressure)
  • not eating or drinking enough
  • being too hot
  • being very upset, angry, or in severe pain
  • heart problems
  • taking drugs or drinking too much alcohol

… though I can exclude the last one as my bees are teetotal 😉

So, there you have it, a brief account of a cataleptic queen … and her recovery.


Notes

A fortnight after the events described above I clipped and marked the queen. I did everything the same – picked her up by the wings in the shed (so again not exposed to bright sunlight – which may be relevant, see the comment by Ann Chilcott).

She (the queen) didn’t faint. She behaved just like the remaining 4 queens I marked on the same afternoon.

So no repeat of the ‘amateur dramatics’ 🙂

More from the fun guy

Great fleas have little fleas upon their backs to bite ’em,
And little fleas have lesser fleas, and so ad infinitum.

Augustus de Morgan’s quote from A Budget of Paradoxes (1872) 1 really means that everything is preyed upon by something, which in turn has something preying on it.

The Flea, engraving from Robert Hooke’s Micrographia (1665)

As a virologist I’m well aware of this.

There are viruses that parasitise every living thing.

Whales have viruses and so do unicellular diatoms. All the ~30,000 named bacteria have viruses. It’s likely that the remaining 95% of bacteria that are unnamed also have viruses.

There are even viruses that parasitise viruses. The huge Mimivirus that infects amoebae 2 is itself parasitised by a small virophage (a fancy name for a virus that infects viruses) termed Sputnik.

Whether these interactions are detrimental depends upon your perspective.

The host may suffer deleterious effects while the parasite flourishes.

It’s good for the latter, but not the former.

Whether these interactions are detrimental for humans 3 also depends upon your perspective.

The deliberate introduction of rabbit haemorrhagic disease virus to Australia benefitted sheep farmers who were plagued with rabbits … but it was bad news for rabbit farmers 4.

Biocontrol

Beneficial parasitism, particularly when humans use a pathogen to control an unwanted pest, is often termed biocontrol, a convenient abbreviation for biological pest control.

There are numerous examples; one of the first and best known is control of greenhouse whitefly infestations with the parasitoid wasp Encarsia formosa.

Tomato leaf with whitefly nymphs (white) parasitized by E. formosa (black).

One of the benefits of biocontrol is its self-limiting nature. The wasp will stop replicating once it runs out of whitefly to parasitise.

A second benefit is the specificity of the interaction between the host and whatever is administered to control it; by careful selection of the biocontrol agent you can target what you want to eradicate without lots of collateral damage.

Finally, unlike toxic chemicals such as DDT, the parasitoid wasp – and, more generally, other biocontrol agents – do not accumulate in the environment and cause problems for the future.

And, with all those benefits, it’s unsurprising to discover that scientists have investigated biocontrol strategies to reduce Varroa mite infestation of honey bee colonies.

It’s too early for an aside, but I’ll make one anyway … I’ve discussed the potential antiviral activity of certain fungi a couple of years ago. That wasn’t really biocontrol. It was a fungal extract that appeared to show some activity against the virus. Although that story has gone a bit quiet, one of the authors – Paul Stamets – is also a co-author of the Varroa control paper discussed below.

Biocontrol of Varroa using entomopathogenic fungi

Entomopathogenic means insect killing 5. There are several studies on the use of insect killing fungi to control Varroa 6, with the most promising results obtained with a variety of species belonging to the genus Metarhizium

Metarhizium produces asexual spores termed mitospores. The miticidal activity is due to the adhesion of these mitospores to Varroa, germination of the spore and penetration by fungal hyphae 7 through the exoskeleton of the mite and proliferation within the internal tissues.

A gruesome end no doubt.

And thoroughly deserved 🙂

Although Metarhizium is entomopathogenic it has a much greater impact on Varroa than it does on honey bees. This is the specificity issue discussed earlier.

It is for this reason that scientists have continued to explore ways in which Metarhizium could be used for biocontrol of Varroa.

But there’s a problem …

Although dozens of strains of Metarhizium have been screened, the viability – and therefore activity – of the mitospores is significantly reduced by the relatively high temperatures within the colony.

The spores would be administered, they’d show some activity and some Varroa would be slaughtered. However, over time treatment efficacy would reduce as spores – either administered at the start of the study, or resulting from subsequent replication and sporulation of Metarhizium on Varroa – were inactivated.

As beekeepers you’ll be familiar with the limitation this would impose on effective control of mites.

Varroa spend well over half of their life cycle capped in a cell while it feeds on developing pupae. Anything added to kill mites must be present for extended periods to ensure emerging mites are also exposed and killed.

This is why Apiguard involves two sequential treatments of a fortnight each, or why Apivar strips must be left in a hive for more than 6 weeks.

In an attempt to overcome these limitations, scientists are using directed evolution and repetitive selection to derive strains of Metarhizium that are better able to survive within the hive, and so better able to control Varroa than the strains they were derived from.

Good news and bad news

Like many scientific papers on honey bees 8 those with even a whiff of ‘saving the bees’ get a lot of positive press coverage.

This often implies that the Varroa ‘problem’ is now almost solved, that whatever tiny, incremental advance is described in the paper represents a new paradigm in bee health.

This is both understandable and disappointing in equal measure.

It’s understandable because people (not just beekeepers) like bees. News publishers want ‘good news’ stories to intersperse with the usual never-ending menu of woe they serve up.

It’s disappointing because it’s a variant of “crying wolf”. We want the good news story to describe how the impact of Varroa can now be easily mitigated.

It gets our hopes up.

Unfortunately, reality suggests most of these ‘magic bullets’ are a decade away from any sort of commercial product.

They will probably get mired in licensing problems.

And they may not be any better than what we currently use.

You finally end up as cynical as I am. This might even force you to read the original manuscript, rather than the Gung ho press release or the same thing regurgitated on a news website.

And, if you do that, you’ll better understand some of the clever approaches that scientists are applying to the development of effective biocontrol for Varroa.

We’re not there yet, but progress is being made.

V e r y   s l o w l y.

The paper I’m going to discuss below is Han, J.O., et al. (2021) Directed evolution of Metarhizium fungus improves its biocontrol efficacy against Varroa mites in honey bee colonies. Sci Rep 11, 10582.

It’s freely available should you want to read the bits I get wrong 😉

Solving the temperature-sensitivity problem of mitospores

The strain of Metarhizium chosen for these studies was M. brunneum F52. This had previously been demonstrated to have some efficacy against Varroa. Almost as important, it can be genetically manipulated and there was some preliminary evidence that its pathogenicity for Varroa – and hence control potential – could be improved.

Genetic manipulation covers a multitude of sins. It could mean anything from selection of pre-existing variants from a population to engineered introduction of a toxin gene for destruction of the parasitised host.

In this study the authors used directed evolution of a population of Metarhizium to select for strains with more heat tolerant spores.

Directed evolution of Metarhizium to select mitospores with increased thermotolerance

This is not genetic engineering. They grew spores under stressful conditions and increasing temperatures. Hydrogen peroxide (H2O2) , a mild mutagen, was added in some cases. Nutritional stress also increases population variation. Spores selected using nutritional stress are better able to withstand UV and heat stress.

The optimal growth temperature for the strain of Metarhizium they started with was 27°C. By repeated selection cycles at increasing temperatures they derived spores that grew at 35°C, the temperature within a colony.

Ladders and snakes

A well known phenomena of repeated selection in vitro (i.e. in a test tube in the laboratory, though you actually grow Metarhizium on agar plates) is that a pathogen becomes less pathogenic.

It was therefore unsurprising that – when they eventually tested the thermotolerant spores – only about 3% of the Varroa that died did so due to Metarhizium infection.

Field selection after directed evolution of Metarhizium in the laboratory

They therefore modified the repetitive selection, but this time did it on Varroa-infested colonies in the apiary. Mites that died from Metarhizium mycoses 9 were used as a source to cultivate more Metarhizium.

They were therefore selecting for both thermotolerant (because the experiments were being conducted in hives at 35°C) and pathogenic fungi, because they only cultivated mitospores from Varroa that had died from mycoses.

And it worked …

Amplification of Varroa mycoses by Metarhizium. Black arrows indicate the treatment dates.

After four rounds of selection over 60% of the mites that died did so because they were infected with Metarhizium.

All very encouraging … but note I was very careful with my choice of words in that last sentence. I’ll return to this point shortly.

Before that, here’s the ‘proof’ that the strain selected by directed evolution (which they termed JH1078) possessed more thermostable spores.

Thermostable spores

They measured this by recording the percentage that germinated. At 35°C ~70% of JH11078 spores germinated compared to only ~45% of the M. brunneum F52 strain they started with.

But it’s not all good news

My carefully chosen “60% of the mites that died” neatly obscures the fact that you could get a significant increase in mites dying of Metarhizium, but still have almost all the mites in the hive surviving unscathed.

The authors continued repeated Metarhizium monthly treatments for a full season after the selection experiments described above. The apiary contained 48 colonies, 24 received Metarhizium JH1078 and the remainder received no treatment.

Did Metarhizium treatment stop the well documented increase in Varroa levels observed in colonies not treated with miticides?

Varroa levels in Metarhizium treated and untreated (control) colonies.

Er … no.

They describe this data (above) as showing a ‘delay’ in the exponential increase in Varroa … but acknowledge that it ‘did not totally prevent it’.

Hmmm … looking at the error bars in the last few timepoints I’d be hard pressed to make the case that there was any significant difference in Varroa increase caused by treatment.

And while we’re here look at the mite infestation rate … 10-25 mites per 100 bees.

These are catastrophically high numbers and, unsurprisingly, 42 (~88%) of the 48 colonies – whether treated or untreated – died by the end of 2018, succumbing to “Varroa, pathogen pressure and intense yellow jacket predation”

There was some evidence that colonies receiving Metarhizium treatment survived a bit longer than the untreated controls, but the end results were the same.

Almost every colony perished.

Metarhizium vs. oxalic acid

Typically a paper on a potential improved biocontrol method for Varroa would do a side-by-side comparison with a widely used, currently licensed treatment.

There’s only one comparative experiment between Metarhizium and dribbled oxalic acid treatment. It’s buried at the end of the Supplementary Data 10. In it they show ‘no significant difference’ between the two treatments.

Frankly this was a pretty meaningless experiment … it was conducted in June 2020 when colonies would have been bulging with brood. Consequently 90% of the mites would have been hidden under the cappings. They assayed mite levels only 18 days after a single application of Metarhizium or oxalic acid.

Although it showed ‘no significant difference’ – like the “60% of the mites that died” quote – it obscures the fact that most mites were almost certainly completely untouched by either treatment.

What does this study show?

This study involved a large amount of work.

The directed evolution in the laboratory is a very nice example of how the combination of phenotypic selection and natural variation can rapidly yield new strains with desirable characteristics.

Combination of this with in vivo selection for enhanced pathogenesis successfully produced a novel strain of Metarhizium with some of the features desirable for biocontrol of Varroa.

However, in the apiary-based studies the majority of the colonies, whether treated or not, died.

This shows that, although scientists might have made a promising start, they are still a very long way from having an effective biocontrol solution for Varroa.

Unmanaged Varroa replicates to unmanageable levels

One of the Supplementary Data figures illustrated the Varroa drop per month from colonies in the research apiary.

Cumulative mite drop per colony for the month of July 2018

This is relatively late in the study, July 2018. These hives were established from commercial packages of bees in April 2017. They were either treated with the experimental Metarhizium spores or were untreated controls for the 15 months between April 2017 and July 2018 11.

Look at those Varroa numbers!

This is the mite drop just after the peak of the season. Brood levels would be close to maximum in their short, warm summer 12. The majority of the mite population would have been safely tucked away feasting on developing brood.

This is not the mite drop after miticide treatment … it’s just the drop due to bee grooming, natural mite mortality and the general ‘friction’ in the hive.

The average is 2866 mites dropped per month per hive 😥

Maybe nothing could have saved hives as heavily infested as these? 13

Don’t wait for Metarhizium … be vigilant now

These numbers – of mites and dead colonies – are a stark warning of the replication potential of Varroa and the damage is causes our bees.

Left untreated, Varroa will replicate to very high levels.

Colony mortality – either directly due to the mite and viruses, or indirectly due to the weakened colonies succumbing to robbing – is a near-inevitable consequence.

I’ve discussed the importance of Varroa management repeatedly over the years. It’s a topic I’ll be returning to again – probably in August when it starts to become a necessity.

In the meantime, keep an eye on the mite levels in your own colonies as they get stronger during the season.

While you’re doing that think of the scientists who are looking for practical, effective and environmentally-friendly strategies to control Varroa. Understand that these studies are time-consuming, progress is glacial incremental … and they might not work anyway.

Of course, if we finally manage to develop a suitable Metarhizium-based mite control strategy then bees and beekeepers will not be the only beneficiaries.

Metarhizium has its own parasites. Some of the best characterised of these are small RNA viruses.

If beekeepers are sprinkling billions of Metarhizium spores over their colonies every year then these viruses will be having a great time 😉


 

Radar love

The average beefarmer in the UK is probably somewhere in their mid-60’s 1. This means that in 1973, when the Dutch rock band Golden Earring had their only notable chart success Radar love, they were about 18.

Bear with me …

As 18 year olds they probably wore denim flares and loud shirts with spearpoint collars. They would go to the local disco to meet similarly-attired members of the opposite sex (whose shorter hair may have been their only distinguishing feature).

They knew when and where to meet … the weekly Saturday night (obviously 2 ) disco.

There was no point in turning up at 10 in the morning … the disco was closed 🙁

Similarly, despite their ‘cool threads’, wearing them to the launderette would have resulted in almost certain disappointment … the dance partners they were seeking weren’t likely to be found doing the laundry 🙁

No, the disco was the place to go. 

Radar love would have been on the playlist. It reached the top 10 in the charts in many countries.

Hold that thought … we’ll return to Radar love in a few minutes … 3

The birds and the bees

Of course, these young beefarmers didn’t just go to the disco to dance

Oh no.

They had an ulterior motive 😉

They knew that they had a good chance of meeting a like-minded (and similarly attired) member of the opposite sex who was also ‘looking for love’.

These meetings were effectively ritualised … a particular time and place.

Let’s forget the bell bottoms and hippie shirts now … I only added that detail so that any readers who know an ageing beefarmers can have a little giggle imagining them dressed for the disco 😉 

OK, back to the disco … metaphorically.

The disco is not fundamentally dissimilar to the lek used by male grouse 4

Greater sage-grouse at a lek, with multiple males displaying for the less conspicuous females

A lek is defined as a location where males congregate to compete and mate with females. Importantly, there are no direct benefits – such as food or territory – that the females gain from attending the lek 5.

How do the males know where to congregate?

Grouse tend to live for several years 6. Older grouse know where the lek is because they attended last season. Juveniles probably tag along and learn from their elders despite the fact they are too immature to mate, or lack the social dominance (or plumage 7 ) to compete.

As a consequence of this male hierarchy the location of the lek is invariant.

The birds congregate at the same place each year.

One of the features of leks is that males show high levels of fidelity to a single lekking site.

So now we know something about the birds … what about the bees?

Drones congregate in particular – rather ill defined – landscape features called drone congregation areas (DCA’s).

These, like a black grouse lek, are stable from day to day and year to year.

The drones compete (for the queen, though not directly with each other by displaying) and offer the queen no territorial or food benefits … meaning that DCA’s are effectively insect leks 8

Drone congregation areas

There are studies going back well over 50 years on DCA’s. There are no hard and fast rules that define their location (at least to humans … thankfully virgin queens have no problems finding them). However, you can sometimes hear them; they sound like a small swarm, the noise caused by thousands of drones circling 5-40 metres above the ground in a swirling, traffic cone-shaped, perhaps a 100 metres or more in diameter.

How do drones know where to congregate? There is no male hierarchy 9. An individual drone lives for just a few weeks and perishes before winter. 

The location must be somehow ‘hard-coded’ in the environment. Effectively a set of features that – once located – attract the drones back repeatedly until they either mate with a queen, or die trying 10.

Many studies have attempted to identify DCA’s – geographic features on the ground, sheltered from strong winds, a dip in the horizon etc. These have tended to produce rather mixed results.

I don’t think we’re anywhere close to being able to point to an intersection of two hedges and say “Over there … that’s where drones will congregate”.

An alternative approach is to go fishing for DCA’s.

Literally. 

Having identified a number of potential DCA’s from landscape analysis, you can dangle a virgin queen from a helium balloon and sample the drone density in each of the areas.

It sounds a lot simpler than it is … there’s a nice account by Aude Sorel in Bee Culture if you’re interested.

By definition, the drone congregation areas are the ones you trap the most drones in.

Right?

Well, possibly not.

Perhaps the very method used to sample the drones attracted them there in the first place? 

It’s been known since the 1960’s that high concentrations of queen mandibular pheromone can attract drones to almost any location – in one notable example, even 800 metres out to sea 11.

If you use bait, how can you be certain that the areas you define are ‘real’. 

A better way to define a DCA would be to observe individual drones accumulating in a particular area … to watch them leaving the hive, fly the tens or hundreds of metres to the same place they flew to yesterday, and record them ‘strutting their funky stuff’.

Have you ever tried to follow a drone in flight?

They’re strong and fast. They need to be to outcompete other drones when chasing the queen.

It’s almost impossible to track them across the apiary, let alone over the hedge, across two fields and into the lee of a copse.

But scientists can now do exactly that … using a technique called harmonic radar tracking.

The title of this post should now make a bit more sense … it’s the use of radar to find where drones go ‘looking for love’ 😉

Harmonic radar tracking

A harmonic radar system emits a stimulus signal. This signal is picked up by a harmonic tag (the transponder) which uses the low frequency stimulus energy to generate a second harmonic which is then re-radiated back out to a receiving system.

The harmonic signal emitter/receiver is portable … if you’ve got a lorry.

Harmonic radar emitter and detector – with Rothamsted Manor in the background.

Fortunately, the transponder is tiny … small and light enough to be glued to the back of a bee.

Drone with harmonic radar transponder attached.

Harmonic radar has been used to study orientation flights in honey bees 12, to track Asian hornets, and to follow butterfly flight paths 13 (amongst other things).

And now it’s been used to map drone congregation areas by tracking the flights of individual drones from the hive.

Harmonic radar is a relatively short range system. You can’t track transponder-tagged insects flying miles away. The effective range is just a few hundred metres for most systems.

However, for drone congregation areas this shouldn’t be a major limitation. Drones generally fly shorter distances to mate than queens (an evolutionary mechanism to avoid inbreeding) and DCA’s have often been found near to apiaries 14.

Tracking drones by harmonic radar

The study, by Woodgate et al., was published a couple of weeks ago in iScience. The full reference is:

Woodgate et al., Harmonic radar tracking reveals that honeybee drones navigate between multiple aerial leks, iScience (2021), https://doi.org/10.1016/j.isci.2021.102499

It’s available under open access (i.e. free, for anyone) and I recommend you read it if you’re interested.

I’m just going to pick out a few highlights.

During two sequential seasons the authors tracked over 600 flights by at least 78 drones. These included 19 first flights (orientation flights) and – for four drones – 6-8 consecutive flights, including their first ever orientation flight.

Orientation flights were typically observed as multiple loops in different directions, centred on the hive from which the drone originated.

Drone orientation flights

The average duration of these orientation flights was ~13 minutes and the drones observed only took one or two before changing their flight pattern (see below) and seeking drone congregation areas.

Worker bees typically take more (~6) orientation flights than drones. Presumably foragers need to ‘map’ the hive location better because they may end up returning to it (and they’ve failed if they don’t) from any location.

As we’ll see in a minute, drones tend to use particular ‘flyways’ which are probably determined by landscape features. Drones also may return to a different hive to the one they set out from.

Identifying drone congregation areas by harmonic radar tracking

Scientists love ‘heat maps’.

These are a graphical way of depicting levels of activity of one kind or another.

If you overlay the flights by every transponder-tagged drone in each of the two years of this study you generate a map (like C and E shown below). In this study they used a ‘white to red’ scale where the paler the colouration, the more drones were detected in that particular point on the map.

You can easily see the hive location (points 1, 2 and 3) as all flights originated there.

Heat map of the landscape used by drones.

Actually, C and E are a bit confusing because they include the orientation flights which are centred on the hives. If you exclude these you end up with the heat maps D and F on the right.

From these the authors could detect particular areas where the drones tended to concentrate … these are proposed to be the drone congregation areas. There were four within range of the harmonic radar system – A-D above (confusingly labelled on images D and F).

There are a few obvious features of these proposed DCAs:

  1. They are in approximately (but not exactly) the same position in the two study years.
  2. The frequency with which they were visited changes. A is visited less frequently in the second year (panel F) than in the first (panel D).
  3. The most distant DCA (at least that could be mapped in this study) was ~600 metres from the hive. 
  4. Each DCA had a roughly symmetrical ‘core’ of 30-50 metres, significantly smaller than many drone trapping studies suggest..

One thing that was noticeable by comparison of the orientation flights and the proposed DCAs was that they did not overlap.

So how do the drones ‘find’ the DCA if they don’t discover them on an orientation flight?

Flyways, straight and convoluted flights

Heat maps are cumulative data.

It was also possible to look at the individual flight paths of drones on their way to and from a DCA (in exactly the same way as they mapped orientation flights).

Analysis of these showed that drones adopted two distinct types of flight – an approximately straight, direct flight interspersed with periods of convoluted, looping flight. There are lots of pictures of these in the paper but, rather than showing another published image, here’s my “no expense made spared” diagram of these two patterns of flight.

Drone flight paths showing distinct direct and convoluted elements.

The convoluted flight defines the drone congregation areas. In these the drones showed very distinctive behaviour – the further they were from the centre of the DCA the more strongly they accelerated back towards the centre. 

Drone flight paths (inevitably) overlapped in DCAs.

However, they also overlapped in the straight line flight. Drones tended to use particular flyways from the hives to, and between, the DCAs.

Scientists have previously identified (or at least suggested the existence of) these flyways that drones use to travel to and from the hive and the DCAs 15

However, what they had previously not identified was that drones often visit more than one DCA in a single (potential) mating flight.

In 20% of the flights analysed drones visited more than one DCA. 

Finally, drones tended to only spend about 2 minutes flying around very fast (at ~5 m/s rather than the sedate ~3 m/s they fly around the hive at 16 ) within the proposed DCA.

This suggests that drones might routinely patrol several DCAs in a single flight, moving on unless a queen is present.

Harmonic radar mapping the flights of virgin queens

I’ve often preceded the term ‘drone congregation area’ in the text above with the word ‘proposed’. A DCA has a very specific meaning that describes the places where drones congregate to attempt to mate with a virgin queen.

None of the studies above showed queen mating, or even the presence of a queen.

But, of course, the authors tried that as well.

They transponder-tagged queens (94 in total) and tracked their orientation flights and mating flights (26 in total). The orientation flights were remarkably similar to those of the drones; the average number of these flights was 3 and no queen went on more than 6 orientation flights.

Unfortunately the tracking of queen mating flights was less successful 17.

Queens flew out of range (I’ll return to this shortly), the transponder fell off, or parts of the flight were not picked up by radar. Some of the queens ‘followed’ (or for which tracking was attempted) did get mated, but not apparently in the DCAs identified during the flight tracking of drones.

This type of study clearly needs further work …

Conclusions

Drone congregation areas could be detected using harmonic radar tracking of transponder-tagged drones. Unlike other well-studied lekking areas, males (drones) did not display lek fidelity, but instead visited several in rotation 18.

The DCAs are a consequence of drones exhibiting a convoluted flight pattern in particular locations. The conservation of the flyways – the routes taken by the drones – between DCAs suggest they might contribute to the location of the DCAs.

Understanding what defines these flyways might allow better prediction of DCA locations.

Previous studies have shown that queens tend to fly further to DCAs than drones, presumably to avoid inbreeding. One possibility is that tagged queens in this study might have been more likely to visit the four DCAs identified if they were placed in mating nucs situated further away from this study site.

But, of course, they could have then flown off in a different direction altogether 🙁

Finally, it’s worth noting that a different pattern of queen mating activity had been described for dark, native (Apis mellifera mellifera) and near-native bees. This is apiary vicinity mating (AVM), and is nicely described by Jon Getty on his website

I now have some native black bees. I’m also experiencing the worst spring of my entire beekeeping career for queen mating. I am increasingly interested in AVM as a mechanism for saving the queen from drowning or freezing to death while attempting to reach a DCA 🙁


 

It’s a drone’s life

What has a mother but no father, but has both a grandmother and grandfather?

If you’ve not seen this question before you’ve not attended a ‘mead and mince pies’ Christmas quiz at a beekeeping association. 

Drone

Drone … what big eyes you have …

The answer of course is a drone. The male honey bee. Drones are produced from unfertilised eggs laid by the queen, so formally they have no father. Drones are usually haploid (one set of chromosomes), whereas queens and workers are diploid 1

Anyway, enough quiz questions. With the relaxation in Covid restrictions we may all be able to attend in person this Christmas 2, so I don’t want to spoil it by giving all the answers away in advance.

The long cold spring has been pretty tough for new beekeepers, it’s been a struggle for smaller colonies and it’s been really hard for drones.

Spring struggles

New beekeepers have had to develop the patience of Job to either acquire bees in the first place or start their inspections. Inevitably new beekeepers are bursting with enthusiasm 3 and the cold northerlies, unseasonal snow (!) and low temperatures have prevented inspections and delayed colony development (and hence the availability and sale of nucs).

Small colonies 4 are struggling to rear brood and to collect sufficient nectar and pollen.

This is an interesting topic in its own right and deserves a post of its own 5. In a nutshell, below a certain threshold of bees, colonies are unable to keep the brood warm enough and have sufficient foragers to collect nectar and pollen.

As a consequence, smaller colonies are low on stores and at risk of starvation. 

It’s a Catch-22 situation … to rear sufficient brood to collect an excess of nectar (or pollen) the colony needs more adult workers. 

I don’t know what the cutoff is in terms of adult bees, but most of my colonies with <7 frames of brood have needed feeding this spring.

One feature of these smaller colonies is that, unless they have entire frames of drone comb 6, there is little if any drone brood in the hive.

There might be drones present in the colony, but I don’t know whether they were reared there or drifted there from another hive.

And, for those of us attempting to rear queens, drones are an essential indicator that queen mating will be timely and successful.

On a brighter note …

But it’s not all gloom and doom.

Strong colonies are doing very well.

Several of mine have a box packed full of brood and I’m relying on a combination of …

  • lots of space by giving them more supers than they need
  • low ambient temperatures
  • crossed fingers

… as my swarm prevention strategy 😉

Beginners take note … one of these is likely to help (space), one is frankly pretty risky (chilly) and the last is not a proven method despite being widely used by many beekeepers 😉

I’m pretty confident that colonies will not swarm at 13-14°C.

I am inspecting colonies every 7 days and have only seen two with charged queen cells. One was making early swarm preparations; I used the nucleus method of swarm control and then split the colony into nucs a fortnight ago 7.

The other colony contained my first attempt at grafting this year, which seems to have gone reasonably well 8.

Lots of brood, nectar and drones

A typical brood frame from one of these strong colonies contains a good slab of sealed or open brood, some pollen around the sides and an interrupted arc of fresh nectar above the brood. 

In the photo above you can see pollen on the right hand side of the frame and glistening fresh nectar in the top left and right hand corners.

Typically these strong colonies also have partially filled supers, though it’s pretty clear that the oil seed rape is likely to go over before the weather warms enough (or the colonies get strong enough) to fully exploit it.

Spring honey is going to be in short supply and my fantastic new honey creamer is going to sit idle 🙁

Drones

What you probably can’t really see in the picture above is that these strong colonies also contain good numbers of drones.

Strong colonies … ample drones

I can count about a dozen in the closeup above. 

I like seeing drones in a strong, healthy colony early(ish) in the season 9.

Firstly, the presence of drones indicates that the colony (and presumably others in the neighbourhood which are experiencing a similar environment and climate) will soon be making swarm preparations. This means I need to redouble my efforts to check for queen cells to avoid losing swarms 🙁  … think of it as a long-range early warning system.

But it also means I can start thinking about queen rearing 🙂

Secondly, although these drones are unlikely to mate with my queens, you can be sure they’re going to have a damned good go at mating with queens from other local apiaries.

In addition to being strong and healthy, this colony is well-tempered, steady on the comb and pleasant to work with. The production of a few hundred thousand frisky drones prepared to lay down their lives 10 to improve the local gene pool is my small act of generosity to local beekeepers 11.

How many drones?

Honey bee colonies that nest in trees or other natural cavities produce lots of drone comb. Studies of feral colonies on natural comb show that about 17% of the comb is dedicated to rearing drones (but also used for storing nectar at other times of the season).

Foundationless triptych ...

Foundationless triptych …

Similarly, beekeepers who predominantly use foundationless frames regularly see significantly greater amounts of drone comb (and drone brood and drones) in their colonies. With the three-panel bamboo-supported frames I use it’s not unusual for one third of some frames to be entirely drone comb.

In contrast, beekeepers who only use standard worker foundation will be used to seeing drone comb occupying much less of the brood nest. Under these circumstances it’s usually restricted to the edges or corners of frames.

However, given the opportunity e.g. a damaged patch of worker comb or if you add a super frame into the brood box, the workers will often rework the comb (or build new brace comb) containing just drone cells.

The bees only build drone comb when they need it.

A newly hived swarm will build sheet after sheet of new comb, but it will all be for rearing worker brood. If you give them foundationless frames they only build worker comb and if you provide worker foundation they don’t rework it to squeeze in a few drone cells.

The colony will also not build new drone comb late in the season. Drone comb is drawn early in the season because the drones are needed before queens are produced.

The timing of drone production

Studies in the late 1970’s 12 demonstrated that drone brood production peaks about one month before the the main period of swarming. Similar studies in other areas have produced similar results.

Why produce all those drones when there are no queens about?

The timing is due to the differences in the development time (from egg to eclosion) of drones and queens, together with the differences in the time it takes before they are sexually mature.

Drones take 50% longer to develop than queens – 24 days vs. 16 days. After emergence the queen take a few days (usually quoted as 5-6) to reach sexual maturity before she embarks on her mating flight(s).

In contrast, drones take from 6-16 days to reach sexual maturity.

Swarming tends to occur when charged queen cells in the hive are capped. These cells will produce new virgin queens about a week later and – weather permitting – these should go on mating flights after a further six days. 

Therefore a colony that swarms in very early June will need sexually mature drones available 12-14 days later (say, mid-June) to mate with the newly emerged queen that will subsequently return to head the swarmed colony. These drones will have to have hatched from eggs laid in the first fortnight of May to ensure that they are sexually mature at the right time.

Decisions, decisions

How does the colony know to produce drones at the right time? Is it the workers or the queen who makes this decision?

I’ve recently answered a question on this topic for the Q&A pages in the BBKA Newsletter. In doing some follow-up reading I’ve discovered that (inevitably) it’s slightly more complicated than I thought … which was already pretty complicated 🙁

The workers build the comb and therefore determine the amount of drone vs. worker comb the brood nest contains.

I don’t think it’s known how the workers measure the amount of brood comb in the nest, but they clearly can. We do know that bees can count 13 and that they have some basic mathematical skills like addition and subtraction.

Perhaps these maths skills 14 include some sort of averaging, allowing them to sample empty cells, measure them and so work out the proportion that are drone or worker.

Whatever form this ‘counting’ takes, it requires direct contact of the bees with the comb. You cannot put a few frames of drone comb in the hive behind a mesh screen and stop the bees from building more drone comb. It’s not a volatile signal that permeates the hive.

However they achieve this, they are also influenced by the amount of capped drone brood already present in the colony. If there’s lots already then the building of additional drone comb is inhibited 15.

Colonies therefore regulate drone production through a negative feedback process.

So … does the queen simply lay every cell she comes across, trusting the worker population has provided the correct proportions of drone and worker comb?

Not quite

Studies by Katie Wharton and colleagues 16 showed that the queen could also regulate drone production.

Wharton confined queens on 100% drone or worker comb in a frame-sized queen ‘cage’ for a few days.

Frame sized queen ‘cage’ …

She then replaced the comb in the cage with 50:50 mix of drone and worker comb and recorded the number of eggs laid in drone or worker cells over a 24 hour period (and then allowed the eggs to develop).

Queens that had only been able to lay worker brood for the first four days of confinement laid significantly more drone brood when given the opportunity.

The scientists showed reasonably convincingly that this was a ‘decision’ made by the queen, rather than influenced by the workers e.g. by preparing biased number of drone or worker cells for eggs to be laid in, by preferentially ‘blocking’ certain cell types with honey or by selectively cannibalising drone or worker eggs.

Interestingly, queens initially confined on worker comb laid significantly (~25%) more eggs on the 50:50 comb than those confined on drone comb. I’m not sure why this is 17.

Wharton and colleagues conclude “these results suggest that the regulation of drone brood production at the colony level may emerge at least in part by a negative feedback process of drone egg production by the queen”.  

So it seems likely that drone production in a colony reflects active decisions made by both workers and the queen.

Why has this spring been really hard for drones?

To be ready for swarming, colonies therefore need to start drone production quite early in the season – at least 4-5 weeks before any swarms are likely.

Late May ’21 forecast. Swarmy weather? I don’t think so …

But with consistently poor weather, these drones are unlikely to be needed. Colonies will not have built up enough to be strong enough to swarm.

Producing drones is a high energy process – they are big bees and require a lot of carbohydrate and protein during development.

Under natural conditions 18 a colony puts as many resources into drone production over the season as it does into swarms.

Thomas Seeley has a nice explanation of this in The Lives of Bees – if you take the dry weight of primary swarms and casts produced by a colony it’s about the same as the dry weight of drones produced throughout the season. 

Rather than waste energy in drone production the workers remove unwanted drone eggs and larvae. The queen lays them, but the workers prevent them being reared.

How do the workers decide the drones aren’t going to be needed?

Do workers have excellent long-range weather forecasting abilities?

Probably not 19

If the weather is poor the colony will be unable to build up properly because forage will be limited. As a consequence, the colony (and others in the area) would be unlikely to swarm and so drones would not be needed for queen mating.

Free and Williams (1975) demonstrated that forage availability was the factor that determined whether drones were reared and maintained in the colony. 

Under conditions where forage was limited, drone eggs and larvae were rejected (cannibalised) and adult drones were ejected from the hive.

Unwanted drone ejected from a colony in early May

Beekeepers are familiar with drones being ejected from colonies in the autumn (again, a time when forage becomes limiting), but it also happens in Spring.

And at other times when nectar is in short supply …

Those of you currently enjoying a good nectar flow from the OSR should also look at colonies during the ‘June gap’. With a precipitous drop in nectar available in the environment once the OSR stops yielding, colonies can be forced to eject drones.

It’s tough being a drone … which may explain why one of my PhD students has the name @doomeddrone on Twitter 😉


 

A no competition, competition

Unless you’re in an unseasonably warm part of the country, mid-April is usually early enough to put out your bait hives. This year, because of the unusually cold snap in the last week or so, it might still be a bit early. However, colonies are developing well and as soon as the weather properly warms up they will start thinking about swarming.

Regular readers, look away now

I’ve written a lot about bait hives in previous years. Anyone who assiduously follows this site and – unlike me 😉 – remembers what’s been written before can skip ahead to the next section.

But for those who need an aide memoire

The purpose of a bait hive is to attract a swarm that you (surely not?) or someone else has temporarily misplaced i.e. lost 1. When a colony swarms it settles in a temporary bivouac from which the scout bees fly to survey the area for a suitable new nest site.

The two stage process of swarming

The scout bees have very particular requirements.

They’re looking for cavities of about 40 litres volume with a small, clearly visible, south facing, entrance near the base.

Evolution and fussy house hunters

Bees have evolved to nest in trees – not quaint cartoon churches as shown above – and cavities in trees come in all shapes and sizes.

This is why they don’t care what shape the cavity is. However, cavities with small entrances are easier to defend, which is why they prefer them 2.

In addition, bees favour cavities situated more than 5 metres above ground level. Again, this makes evolutionary sense. It’s not just Winnie the Pooh that likes honey. The higher up a tree they nest, the less likely they would be detected by a bear 3 on the ground. And if the nest remains undetected (or unreachable by a climbing bear) there’s a chance the colony will thrive and reproduce (swarm) to pass on the ‘high altitude’ nest site preference gene.

And if you’ve evolved to nest in a tree cavity in a wood filled with other trees, it again makes evolutionary sense for the entrance to be clearly visible. If it wasn’t, bees on their orientation flights would inevitably get confused (and therefore lost).

Finally, bees have a strong preference for cavities that smell … of bees.

A cavity that’s already heavily propolised, or contains used drawn comb, offers distinct advantages to the incoming swarm. They will have less work to do and so more chance of building up before winter arrives.

The ideal bait hive

And you can reproduce these requirements by offering a used single brood box National hive with a solid floor and an entrance reducing block in place … facing south and situated well off the ground.

I discussed the evolutionary selection pressures that have shaped the preference for a 40 litre box rather than that convenient spare nuc box I’m repeatedly asked about a smaller box a few weeks ago.

In that post I also discussed why I ignore the preference for bait hives located 5 metres above the ground:

  • I want to be able to watch scout bee activity. This is tricky if they’re a long way off the ground 4.
  • It’s a lot safer retrieving a bait hive from a hive stand at knee level than it is when climbing a ladder. I usually move occupied bait hives late in the evening (when the bees are all in residence) and prefer not to do this balanced precariously on top of a ladder.
  • And – though not listed last time – my knee level bait hives are sufficiently successful I don’t need to increase their attractiveness. I don’t doubt they’d be more efficient located at altitude 5 but they work well enough that I don’t  feel the need to risk altitude sickness or a broken leg …

But, what I’ve not really discussed before is the location where bait hives should be sited and the importance of appreciating the ‘competitive‘ aspects of bait hives.

Natural competition

When you place a bait hive in the environment, whether it’s in your garden or the corner of a field or 5 metres up an oak tree 6, you are providing a potential nest site that will be judged in competition with other natural sites in the area.

And ‘the area’ is probably about 25 square kilometres.

If you struggle to visualize that then it’s the area covered by this circle centred on the roof of Fortnum & Mason’s, where there are some hives. London Zoo to Battersea Power Station and the Round Pond to Southwark Bridge … a large area 7.

Fortnum & Mason, 181 Piccadilly, London … scout bee range (in theory at least)

Scout bees survey over 3 km from their nest site, though swarms rarely relocate that far 8.

Why don’t they move ‘that far’?

Again, evolution may have selected bees that choose not to move away from the environment in which the swarming colony has flourished and built up strongly enough to be able to swarm.

Scout bees find nests, they don’t survey the available forage around those nests. So it makes sense to stay in the general area where forage is proven to be good enough (to allow swarming).

However, I suspect a compelling reason that swarms don’t move far from their original nest site is that there are plenty of alternative nest sites available.

Church towers 9, roof spaces, chimneys, tree cavities 10, compost bins, abandoned sheds etc.

Choices, choices

Think about the environment near your hives. Whether urban or rural, there are bound to be thousands of potential cavities within 3 km.

Some will be too small, some will be poorly defendable 11 and some will be unsuitable for other reasons.

But there are very likely to be some that are ideal, or pretty close to it.

Mature woodland and older man made environments are likely to have ample choices.

Occupied bait hive

Occupied bait hive …

And then there’s your lonely bait hive.

Chance in a million?

How can it possibly compete with all those natural cavities in the environment?

Bait hive ...

Bait hive …

The first thing to do is to ensure it adheres as close as is practically possible (and safely achievable) to the idealised requirements determined by Martin Lindauer, Thomas Seeley and others.

  • a 40 litre cavity = National brood box 
  • a small entrance of 10-15cm2 = entrance block, solid floor
  • south facing
  • shaded but in full view
  • over 5m above ground level 12
  • smelling of bees = one old, dark comb against the sidewall (no stores!)

Secondly, locate it within ~500 metres of your own apiary (to hopefully re-capture your own ‘lost’ swarms 13 ) or, more speculatively, anywhere in an environment in which there are other managed or feral colonies.

Which does not mean over the fence from another beekeeper’s apiary!

Be courteous … don’t poach 🙂

The density of bees throughout much of the UK is very high. Look at Beebase to see the numbers of apiaries within 10 km of your own. When I lived in Warwickshire it was ~180-220, in Fife it was ~35-40 14.

In the talks I’ve given on bait hives this winter – where I customise the presentation to the audience location – few areas with active BKAs have under 100 apiaries within 10 km of their teaching apiary.

In both Fife or Warwickshire I never failed to attract swarms to bait hives in my garden every single year … and in several years up to three swarms to a single bait hive location.

And, with one or two exceptions, these weren’t swarms I had lost 15.

The density of managed colonies in the UK means that a suitable bait hive just about anywhere stands a chance of being occupied.

So, that’s how to win the competition with the natural nest sites that are available.

No competition

But do not put out multiple bait hives in one area.

I have recently re-read an old paper by Thomas Seeley and Kirk Visscher on quorum sensing by scout bees. Quorum sensing is a term for a decision making process where enough bees agree on the same choice, rather than the majority.

Seeley and Visscher (2004) Quorum sensing experiment

Like many good experiments it has an elegant simplicity.

They reasoned that if you provided a bivouacked swarm with a choice of suitable nest sites it would reduce the numbers of scouts that favoured each nest site, and in doing so, would increase the time to reach a decision as to which was best.

And it does.

More potential nest sites leads to an increase in time taken to reach a decision

Unsurprisingly, with more nest box sites to choose between, the scout bees per box were reduced in number (top panel), dancing to advertise preferred nest sites was delayed (second panel), and piping – the ‘prepare for take-off’ signal (third panel) for the bivouacked swarm – was also delayed.

I’ll discuss how this favours a quorum sensing mechanism (and some other aspects of the study) if and when I get time in the future.

For the moment the key take home message is ‘more choice = slower decision making’ by the swarm.

And, if you delay the decision making, there’s a chance it’ll start raining, or the swarm will be collected by another beekeeper … or they’ll opt to move into the old tower of that quaint cartoon church.

One area?

I started the last subsection with the sentence ‘But don’t put out multiple bait hives in one area’.

What is one area?

I was being deliberately vague because I don’t know the answer.

Since I don’t know where the bees might come from 16, I don’t know what’s within range of the bivouacked swarm.

Widely separated bait hives (black) are likely to be within reach of more swarms than clustered bait hives (white)

In practical terms this means I space my bait hives at least 500 metres apart. Widely separated bait hives are likely to be within reach of more swarms than clustered bait hives.

More importantly, clustered bait hives are likely to lead to competition between scout bees from the same swarm, resulting in reduced scout bee attention..

Until recently I’ve not kept bees in my garden. I would always place a bait hive in the garden and one near my out apiaries. With permission, I’d locate them in other places as well.

Having moved, I now have much more space and have bees in the ‘garden’. When my bait hives go out 17 they will be placed in likely spots on opposite sides of our bit of scrubby wooded hillside 18 .

But what’s a likely spot?

Ley lines

And if you thought that last bit was slightly vague … brace yourself.

Over the years I’ve noticed that some bait hive locations are much more successful than others.

Under offer ...

Under offer …

My tiny courtyard garden in Fife was a magnet for swarms. I placed a bait hive in a warm corner of the garden on the day we moved in, and within 10 days a swarm had arrived.

Planting tray roof …

Every year, without fail, multiple swarms would occupy bait hives 19 in that corner of the garden. I even had two swarms competing for one bait hive in 2019.

A sheltered south-east facing hedgerow in Warwickshire was equally effective.

Bait hive

Smelling faintly of propolis and unmet promises

As was a south-west facing spot sheltered next to my greenhouse in a previous garden.

Des Res?

Des Res?

But other locations have been far less successful.

Of course, this is a positive reinforcement exercise. I’m more likely to site a bait hive in a location I’ve previously been successful in.

But what else might account for this differential success rate? And can it be exploited in the rational location of bait hives?

Is it, as some suggest, that bait hives work best when they are located at the intersection of ley lines? This, and the possibility of creating Varroa-resistant bees by exploiting geopathic stress lines, surely deserves a post of its own 20.

Call me sceptical

However, as a scientist – and knowing others have been more than a little sceptical about the existence of ley lines – I think there’s a more prosaic explanation.

Without exception, my most successful sites for bait hives have been well sheltered to the north, and – in most cases – to the north-east and north-west directions as well.

For example, the bait hive is situated on the south face of a wall running east-west (Under offer, above), or in a corner sheltered to the north and east (Planting tray roof, above), or facing south-east in a very dense hedgerow running north-east to south-west (Smelling faintly etc., above), or sheltered by surrounding walls or outhouses but with a clear entrance facing south-west (Des res?, above).

And … since I’ve been aware of this for at least five years, and probably subconsciously aware of it for much longer, that’s exactly the type of location I choose to site my bait hives.

Which is, of course, another example of positive reinforcement 🙂

However, it works for me. I choose sites that are well sheltered to the sides and back of the bait hive, and I try and orientate the bait hive to face south (ish).

At knee level 😉

Give it a try.


 

Quick thinking & second thoughts

I gave my last talk of the winter season on Tuesday to a lovely group at Chalfont Beekeepers Society. The talk 1 was all about nest site selection and how we can exploit it when setting out bait hives to capture swarms.

It’s an enjoyable talk 2 as it includes a mix of science, DIY and practical beekeeping.

Nest sites, bait hives and evolution

The science would be familiar to anyone who has read Honeybee Democracy by Thomas Seeley. This describes his studies of the features considered important by the scout bees in their search for a new nest site 3.

Under offer ...

Under offer …

The most important of these are:

  • a 40 litre cavity (shape unimportant)
  • a small entrance of 10-15cm2
  • south facing
  • shaded but in full view
  • over 5m above ground level
  • smelling of bees

All of which can easily be replicated using a National brood box with a solid floor. Or two stacked supers.

And – before you ask – a spare nuc box is too small to be optimal.

That doesn’t mean it won’t work as a bait hive, just that it won’t work as well as one with a volume of 40 litres 4.

Evolution has shaped the nest site selection process of honey bees. They have evolved to preferentially occupy cavities of about 40 litres.

Presumably, colonies choosing to occupy a smaller space (or those that didn’t choose a larger space 5 ) were restricted in the amount of brood they could raise, the consequent strength of the colony and the weight of stores they could lay down for the winter.

Get these things wrong and it doesn’t end well 🙁

A swarm occupying a nuc box-sized cavity would either outgrow it before the end of the season, potentially triggering another round of swarming, or fail to store sufficient honey.

Or both.

Over thousands of colonies and thousands of years, swarms from colonies with genetics that chose smaller cavities would tend to do less well. In good years they might do OK, but in bad winters they would inevitably perish.

Bait hive compromises

If you set out a nuc box as a bait hive, you’re probably not intending to leave the swarm in that box.

But the bees don’t know that. Their choices have been crafted over millenia to give them the best chance of survival.

All other things being equal they are less likely to occupy a nuc box than a National brood box.

Another day, another bait hive, another swarm …

For this reason I don’t use nuc boxes as bait hives.

However, I don’t recapitulate all the features the scout bees look for in a ‘des res’.

I studiously ignore the fact that bees prefer to occupy nest sites that are more than 5 metres above ground level.

This is a pragmatic compromise I’m prepared to make for reasons of convenience, safety and enjoyment.

Bees have probably evolved to favour nest sites more than 5 metres above ground level to avoid attention from bears. The fact that there are no bears in Britain, and haven’t been since the Middle Ages 6, is irrelevant.

The preference for high altitude nest sites was ‘baked into’ the genetics of honey bees over the millenia before we hunted bears 7 to extinction.

However, I ignore it for the following reasons:

  • convenience – I usually move occupied bait hives within 48 hours of a swarm arriving. It’s easier to do this from a knee height hive stand than from a roof ladder.
  • safety – I often move the bait hive late in the evening. Rather than risk disturbing a virgin queen on her mating or orientation flights (assuming it’s a cast that has occupied the bait hive) I move them late in the day. In the ‘bad old days’ when I often didn’t return from the office until late, this was sometimes in the semi-dark. Easy and safe to do at knee height … appreciably less so at the top of a ladder.
  • enjoyment – I can see the scout bees going about their business at a hive near ground level without having to get the binoculars out. Their behaviour is fascinating. If you’ve not watched them I thoroughly recommend it.

Scout bee activity

The swarming of honey bees is a biphasic process. In the first phase the colony swarms and forms a temporary bivouac nearby to the original nest site.

The two stage process of swarming

The scout bees search an area ~25 km2 around the bivouacked swarm for suitable nest sites. They communicate the quality and location of new nest sites by performing a waggle dance on the surface of the bivouac.

Once sufficient scouts have been convinced of the suitability of one of the identified nest sites the second phase of swarming – the relocation of the swarm – takes place.

Swarm of bees

Swarm of bees

However, logic dictates that the scout bees are likely to have already identified several potential new nest sites, even before the colony swarms and clusters in a bivouac.

There are only a few hundred scout bees in the swarmed colony, perhaps 2-3% of the swarm.

Could just a few hundred scouts both survey the area and reach a quorum decision on the best location within a reasonable length of time?

What’s a reasonable length of time?

The bivouacked swarm contains a significant amount of honey stores (40% by weight) but does not forage. It’s also exposed to the elements. If finding sites and reaching a decision on the best nest site isn’t completed within a few days the swarm may perish.

Which is why I think that scout bees are active well before the colony actually swarms.

Early warning systems

If scout bees are active before a colony swarms they could be expected to find and scrutinize my bait hive(s).

If I see them doing this I’m forewarned that a colony within ~3 km (the radius over which scout bees operate) is potentially making swarm preparations.

Since I’ll always have a bait hive or two within 3 km of my own apiaries I’ll check these hives at the earliest opportunity, looking for recently started queen cells.

Whether they’re my colonies or not, it’s always worth knowing that swarming activity has started. Within a particular geographic area, with similar weather and forage, there’s usually a distinct swarming period.

If it’s not one of my colonies then it soon might be 😉

So, in addition to just having the enjoyment of watching the scout bees at work, a clearly visible – ground level – bait hive provides a useful early warning system that swarming activity has, or soon will, start.

Questions and answers

Although talking about swarms and bait hives is enjoyable, as I’ve written before, the part of the talk I enjoy the most is the question and answer session.

And Tuesday was no exception.

I explained previously that the Q&A sessions are enjoyable and helpful:

Enjoyable, because I’m directly answering a question that was presumably asked because someone wanted or needed to know the answer 8.

Helpful, because over time these will drive the evolution of the talk so that it better explains things for more of the audience.

Actually, there’s another reason in addition to these … it’s a challenge.

A caffeine-fueled Q&A Zoom session

It’s fun to be ‘put on the spot’ and have to come up with a reasonable answer.

Many questions are rather predictable.

That’s not a criticism. It simply reflects the normal range of topics that the audience either feels comfortable asking about, or are interested in. Sometimes even a seemingly ‘left field’ question, when re-phrased, is one for which there is a standard answer. The skill in this instance is deciphering the question and doing the re-phrasing.

But sometimes there are questions that make you think afresh about a topic, or they force you to think about something you’ve never considered before.

And there was one of those on Tuesday which involved biphasic swarming and scout bee activity.

Do all swarms bivouac?

That wasn’t the question, but it’s an abbreviated form of the question.

I think the original wording was something like:

Do all swarms cluster in a bivouac or do some go directly from the original hive/location to the new nest site?

And I didn’t know the answer.

I could have made a trite joke 9 about not observing this because my own colonies swarm so infrequently 🙄

I could have simply answered “I don’t know”.

Brutally honest, 100% accurate and unchallengeable 10.

But it’s an interesting question and it deserved better than that.

So, thinking about it, I gave the following answer.

I didn’t know, but thought it would be unlikely. For a swarm to relocate directly from the original nest site the scout bees would need to have already reached a quorum decision on the best location. To do this they would need to have found the new nest site (which wouldn’t be a problem) and then communicate it to other scout bees, so that they could – in turn – find the site. Since this communication involves the waggle dance it would, by definition, occur within the original hive. Lots of foragers will also be waggle dancing about good patches of pollen and nectar so I thought there would be confusion … perhaps they always need to form a bivouac on which the scout bees can dance? Which explains why I think it’s unlikely.

In a Zoom talk you can’t ponder too long before giving an answer or the audience will assume the internet has crashed and they’ll drift off to make tea 11.

An attentive beekeeping audience … I’d better think fast or look stupid

You therefore tend to mentally throw together a few relevant facts and assemble a reasonable answer quite quickly.

And then you spend the rest of the week thinking about it in more detail …

Second thoughts

I still don’t know the answer to the question Do all swarms bivouac?”, but I now realise my answer made some assumptions which might be wrong.

I’ll come to these in a minute, but first let me address the question again with the help of the people who actually did the work.

I’ve briefly looked back through the relevant literature by Seeley and Lindauer and cannot find any mention of swarms relocating without going via a bivouac. I may well have missed something, it wouldn’t be the first time 12.

However, their studies are a little self-selecting and may have overlooked swarms that behaved like this.

Both were primarily interested in the waggle dance and the decision making process, they therefore needed to be able to observe it … most easily this is on the surface of the bivouac.

Martin Lindauer mainly studied colonies that had naturally swarmed, naming them after the location of the bivouac, and then studied the waggle dancing on the surface of the clustered swarm. In contrast, Tom Seeley created swarms by caging the queen and adding thousands of very well fed bees.

Absence of evidence is not evidence of absence.

So, what were the assumptions I made?

There were two and they both relate to confusion between waggle dancing foragers and scout bees.

  1. Swarming usually occurs during a strong nectar flow. Therefore there are likely to be lots of waggle dancing foragers in the hive at the same time the scouts are trying to persuade each other – using their own fundamentally similar – waggle dances.
  2. Bees ‘watching’ are unable to distinguish between scouts bees and foragers.

So, what’s wrong with these assumptions?

A noisy, smelly dance floor

Foragers perform the waggle dance on the ‘dance floor’. This is an area of vertical comb near the hive entrance. It’s position is not fixed and can move – further into the hive if the weather is cold, or even out onto a landing board (outside the hive) in very hot weather 13.

So, although the dance floor occupied by foragers isn’t immovable, it is defined. There’s lots of other regions of the comb that scouts could use for their communication i.e. there could be spatial separation between the forager and scout bee waggle dances.

Secondly, foragers provide both directional and olfactory clues about the identity and location of good sources of pollen and nectar. In addition to two alkanes and two alkenes produced by dancing foragers 14 they also carry back scents “acquired from the environment at or en route to the floral food source” which are presumed to aid foragers recruited by the waggle dancer to pinpoint the food source.

Importantly, non-dancing returning foragers do not produce these alkanes and alkenes. Perhaps the dancing scouts don’t either?

A dancing scout would also lack specific scents from a food source.

Therefore, at least theoretically, there’s probably a good chance that scout bees could communicate within the hive. Using spatially distant dances and a unique combination of olfactory clues (or their absence) scouts may well be able to recruit other scouts to check likely new nest sites.

All of which would support my view that bait hives provide a useful early warning system for colonies that are in the very earliest stages of swarm preparations … rather than just an indicator that there’s a bivouacked swarm in the vicinity.

But?

All this of course then begs the question … if the scout bees can communicate within the hive, why does the swarm need to bivouac at all?

The bivouac must be a risky stage in the already precarious process of swarming. 80% of wild swarms perish. At the very least it’s subject to the vagaries of the weather. Surely it would be advantageous to stay within the warm, dry hive until a new nest site is identified?

Apple blossom ...

Apple blossom … and signs that a bivouacked swarm perished here

This suggests to me that the bivouac serves additional purposes within the swarming process. A couple of possibilities come to mind:

  • the gravity-independent, sun-orientated waggle dancing 15 on the surface of the bivouac may be a key part of the decision making process, not possible (for reasons that are unclear to me) within the confines of the hive.
  • the bivouac acts to temporally coordinate the swarm. A swarm takes quite a long time to settle at the bivouac. Many bees leave the hive during the excitement of swarming but not all settle in the bivouac. Perhaps it acts as a sorting mechanism to bring together all the bees that are going to relocate, separate from those remaining in the swarmed colony?

Clearly this requires a bit more thought and research.

If your association invites me to discuss swarms and bait hives next winter I might even have an answer.

But, as with so many things to do with bees, knowing that answer will only spawn additional questions 😉


 

Frequently asked questions

The 2020/21 winter has been very busy with online talks to beekeeping associations. I’m averaging about five a month, with only the fortnight over Christmas and New Year being a bit quieter. 

When chatting to the organisers of these talks it’s clear that they are getting increasingly successful 1. Audience numbers are encouragingly high as people become more familiar with online presentations.

Beekeepers know they can lounge around in their pyjamas drinking wine, chat with their friends before and after the talk 2, and listen to a beekeeping presentation … a sort of lockdown multitasking.

Some of you that spend hours each day on Zoom will know exactly what I’m talking about 😉

I still lament the absence of homemade cakes, but I suspect the online format is here to stay. At least for some associations, or at least some of the winter programme each year. 

Talking to myself

There’s little point in doing science unless you tell others about it and, as as a scientist, I have presented at invited seminars and conferences for my entire career. 

Some readers will be familiar with public speaking in one form or another. They’ll be familiar with the frisson of excitement that precedes stepping up to the podium in a large auditorium. 

Assuming there’s a large audience filling the large auditorium of course 😉

Those with little experience of speaking might wish the audience was a bit smaller, or a lot smaller … or not there at all.

But the reality is that the audience is a really important part of a presentation. At least, they are once the speaker has sufficient confidence to calm down, to stop worrying they’ll say something stupid, and to ‘read’ the audience. 

An attentive beekeeping audience

By observing the audience the speaker can determine whether they’re still interested and attentive. Not just in the topic (after all, they’re sitting there rather than disappearing to the coffee shop), but in particular parts of the presentation. 

Are you going too fast?

Have you lost their attention?

Was that fancy animated slide you spent 20 minutes on a dismal failure?

Did that last witty aside work … or did it crash and burn? 3

Almost none of which can be determined when delivering a Zoom-type online presentation 🙁

You can ‘see’ the audience.

Or parts of it.

Postage stamp-sized headshots, with poor lighting, distracting backgrounds 4 and enough pixelation to make nuanced judgements about boredom or even species sometimes tricky.

Is that a Labradoodle in the audience … or just another lockdown haircut?

Has the internet frozen … or has everyone simply fallen asleep?

It’s not ideal, but it’s the best we’ve got for now.

Which makes the question and answer sessions even more important than usual.

Mixed abilities

My talks usually include a 5 minute intermission. Talking for an hour uninterrupted is actually quite tiring 5 and it’s good to make a cup of tea and gather my thoughts for ’round two’.

It also allows the audience to raise questions about subjects mentioned in the first half that left them confused.

Fortunately these ‘half time’ questions tend to be reassuringly limited in number 6.

Have a break, have a Kit Kat

However, at the end of the talk there is usually a much more extensive Q&A session. This often covers both the topic of the talk and other beekeeping issues. 

A typical audience contains beekeepers with a wide range of beekeeping experience. Enthusiastic beginners 7 jostle for screen space with ‘been there, done that, bought the T-shirt’ types who have forgotten more than I’ll ever know.

Inevitably this means the talk might miss critical explanations for beginners and omit some of the nuanced details appreciated by the more experienced. As the poet John Lydgate said:

You can please some of the people all of the time, you can please all of the people some of the time, but you can’t please all of the people all of the time 8.

Think about this simple statement:

Varroa feed on the haemolymph of developing pupae.”

The beginner might not know what haemolymph is … or, possibly, even what Varroa is.

The intermediate beekeeper might be left wondering whether the mite also feeds on nurse bees when ‘crowdsurfing’ around the colony during the phoretic stage of the life cycle.

And the experienced beekeeper is questioning whether I know anything about the subject at all as I’ve not mentioned fat bodies and their apparently critical role in mite nourishment.

So I encourage questions … to help please a few more of the people 😉

You’re on mute!

In my experience these are best submitted via the ‘chat’ function. The host – an officer of the BKA or a technically-savvy member press ganged into hosting the talk – can then read them out to me.

Or I can … if I can find my glasses.

One or two beekeeping associations have a Zoom ‘add in’ that allows the audience to ‘upvote’ written questions, so that the most popular appear at the top of the list 9. This works really well and helps ‘please more of the people more of the time’.

The alternative, of asking the audience member to unmute their mic and ask the question is somewhat less satisfactory. It’s not unusual to watch someone wordlessly ‘mouthing’ the question while the host (or I) try and explain how to turn the microphone on.

Finally, it’s worth emphasising that the Q&A session is – as far as I’m concerned – one of the most helpful and enjoyable parts of the evening.

Enjoyable, because I’m directly answering a question that was presumably asked because someone wanted or needed to know the answer 10

Helpful, because over time these will drive the evolution of the talk so that it better explains things for more of the audience.

Anyway – that was a longer introduction than I intended – what sort of questions have been asked frequently this winter (and the talks they usually appeared in).

What do you define as a strong colony? (Preparing for winter)

Strong colonies overwinter better than weak colonies. They contain more bees. This means that the natural attrition rate of bees during the winter shouldn’t reduce the colony size so much that it struggles to thermoregulate the cluster

Midwinter cluster

A strong colony in midwinter

I also think large winter clusters retain better ‘contact’ with their stores, so reducing the chances of overwinter isolation starvation.

Strong colonies are also likely to be healthy colonies. Since the major cause of overwintering colony losses is Varroa and the viruses it transmits, a strong healthy colony should overwinter better than a weak unhealthy colony. 

Colony age structure from August to December.

However, you cannot necessarily judge the strength of a colony in June/July as an indicator of colony strength in the late autumn and winter.

This is because the entire population of bees has turned over during that period. 

A hive bulging with bees in summer might look severely depleted by November if the mite levels have not been controlled in the intervening period.

The phrase ‘a strong colony’ is also relative … and influenced by the strain of bees. Native black bees rarely need more than a single brood box. Compare them to a prolific carniolan strain and they’re likely to look ‘weak’, but if they’re filling the single brood box then they’re doing just fine.

When should I do X? (Rational Varroa control and others)

When usually means ‘what date?’

X can be anything … adding Apivar strips, uniting colonies, adding supers, dribbling oxalic acid.

This is one of the least satisfactory questions to answer but the most important beekeeping lesson to learn.

A calendar is essentially irrelevant in beekeeping.

Due to geographic/climatic differences and variation in the weather from year to year, there’s almost nothing that can be planned using a calendar.

Only three things matter, the:

  1. state of the colony
  2. local environment – an early spring, a strong nectar flow, late season forage etc.
  3. development cycle of queens, workers and drones

By judging the first of these, with knowledge of the second and a good appreciation of the third, you can usually work out whether treatments are needed, colonies united or supers added etc.

This isn’t easy, but it’s well worth investing time and effort in.

Honey bee development

Honey bee development

The last of these three things is particularly important during swarm control and when trying to judge whether (or when) a colony will be broodless or not. The development cycle of bees is effectively invariant 11, so understanding this allows you to make all sorts of judgements about when to do things. 

For example, knowing the numbers of days a developing worker is an egg, larva and pupa allows you to determine whether the colony is building up (more eggs being laid than pupae emerging) or winding down for autumn (or due to lack of forage or a failing queen).

Likewise, understanding queen cell development means you know the day she will emerge, from which you can predict (with a little bit of weather-awareness) when she will mate and start laying.

How frequently should you monitor Varroa? (Rational Varroa control)

This question regularly occurs after discussion of problematically high Varroa loads, particularly when considering whether midseason mite treatment is needed. 

Do you need to formally count the mite dropped between every visit to the apiary?

Absolutely not.

If you are the sort that does then be aware it’s taking valuable time away from your trainspotting 😉 12

The phoretic mite drop is no more than a guide to the Varroa load in the hive. 

Think about the things that could influence it:

  • A colony trapped in the hive by bad weather has probably got more time to groom, so resulting in an increased mite drop.
  • An expanding colony has excess late stage larvae so reducing the time mites spend living phoretically.
  • A shrinking colony will have fewer young bees, so forcing mites to parasitise older workers. Some of these will lost ‘in the field’ and more may be lost through grooming.
  • Strong colonies could have a much lower percentage infestation, but a higher mite drop than an infested weak colony. You need to act on the latter but perhaps not the former.
  • And a multitude of other things that really deserve a more complete post …

So don’t bother counting Varroa every week … or even every month.

Does what it says on the tin.

I think checking a couple of times a season – towards the end of spring and in mid/late summer – should be sufficient. You can do this by inserting a Varroa tray for a week, by uncapping drone brood and looking for mites, or by doing an alcohol wash on a cupful of workers (but these methods aren’t comparable with each other as they measure different things with different efficiencies). 

But you must also look for the damaging effects of Varroa and viruses at every inspection.

If there are significant numbers of bees with deformed wings – characteristic of high levels of deformed wing virus (DWV) – then intervention will probably be needed. 

DWV symptoms

DWV symptoms

And if there are increasing numbers of afflicted bees since your last regular inspection it’s almost certain that intervention will be needed sooner rather than later.

I should add that I also count mite drop during treatment. This helps me understand the overall mite load in the colony. By reference to the late summer count I can be sure that the treatment worked. 

What do you mean by a quarantine apiary? (Bait hives for profit and pleasure)

This question has popped up a few times when I discuss moving an occupied bait hive and checking the health of the colony. 

A swarm that moves into a bait hive brings lots of things with it …

Up to 40% by weight is honey which is very welcome as they will use it to draw new comb. If there’s good forage available as well it’s unlikely the swarm will need additional feeding.

However, the swarm also brings with it ~35% of the mites that were present in the colony that swarmed. These are less welcome.

I always treat swarms with oxalic acid to give them the best possible start in their new home.

Varroa treatment of a new swarm in a bait hive…

More worrisome is the potential presence of either American or European foul broods. Both can be spread with swarms. The last things you want is to introduce these brood diseases into your main apiary.

For this reason it is important to isolate swarms of unknown provenance. The logical way to do this is to re-site the occupied bait hive to a quarantine apiary some distance away from other bees. Leave it there for 1-2 brood cycles and observe the health and quality of the bees.

What is ‘some distance?’

Ideally further than bees routinely forage, drift or rob. Realistically this is unlikely to be achievable in many parts of the country. However, even a few hundred yards away is better than sharing the same hive stand. 

If you keep bees in areas where foul broods are prevalent then I would argue that this type of precautionary measure is essential … or that the risk of collecting swarms is too great.

And how do you know if foul broods are prevalent in your area?

Register with the National Bee Unit’s Beebase. If there is an outbreak near your apiary a bee inspector will contact you.

Remember also that the presence of foul broods in an area may mean that the movement of colonies is prohibited.

‘Asking for a friend’ type questions

These are great.

These are the sort of questions that all beekeepers are likely to need to ask at sometime in their beekeeping ‘career’.

Typically they take the form of two parts:

  1. a description of a gross beekeeping error
  2. an attempt to make it clear that the error was by someone (anyone) other than the person asking the question 😉

Here are a couple of more or less typical ones 13.

  • My friend (who isn’t here tonight) forgot to remove the queen excluder and three full supers from their colony in August. Should I, oops, she remove them now?
  • Here’s an an entirely hypothetical scenario … what would you recommend treating a colony with in March if the autumn and midwinter mite treatments were overlooked?
  • Should my friend remove the Apiguard trays he a) added in November, or b) placed in his colonies before taking them to the heather?
  • I’d been advised by an expert beekeeper to squish every queen cell a few days after discovering my colony had swarmed in June. It’s now late September … how much longer should I wait for the colony to be queenright?

These are very good questions because they illustrate the sorts of mistakes that many beginners, and some more experienced beekeepers, make. 

There’s absolutely nothing wrong with making mistakes. The problem comes if you don’t learn from them.

I’ve made some cataclysmically stupid beekeeping errors. 

I still do … though fewer now than a decade ago, largely because I’ve managed to learn from some of them.

Partly I learned from thinking things through and partly from asking someone else … “A friend has asked me why his colony died. Was it the piezoelectric vibrations from the mite ‘zapper’ bought from eBay or was the hive he bought not suitable?


 

Going the distance

I’m going to continue with a topic related to the waggle dance this week.

This is partly so I can write about the science of how bees measure distance to a food source.

But it’s also to encourage those who didn’t read the waggle dance post to visit it. Weirdly it was only read by about 50% of the usual Friday/weekend readership and I suspect (from a couple of emails I received) that the weekly post to subscribers ended up in spam folders 1.

If you remember, the duration of the waggle phase of the dance – the straight-line abdomen-wiggling sashay across the ‘dance floor’ – indicates the distance from the nest to the desirable food source 2. The vigour of the wiggle indicates the quality of the source.

How do bees measure distance?

Karl von Frisch, the first to decode the waggle dance, favoured the so-called ‘energy hypothesis’. In this, the distance to a food source was determined by the amount of energy used on the outbound flight.

Does that seem logical?

Foragers forage randomly, but usually return directly

If correct, foragers would only be able to determine the energy used after their second trip to a food source. This presumes their first trip was longer as they searched the environment for something worth dancing about 3.

This would be an easy thing to test, though I’m not sure it was ever investigated 4.

As it happens, far better brains determined that the energy hypothesis was probably incorrect. Many of these studies explored how gravity influences the distances reported by dancing foragers.

Going up!

Bees use more energy when flying up. For example, when flying from ground level to the top of a tall building, when compared to level flight. Similarly, they use more energy flying if they have small weights attached to them 5.

A series of experiments, nicely reviewed by Harald Esch and John Burns 6, failed to provide good support for the energy hypothesis. There were lots of these studies, involving steep mountains, tall buildings or balloons, between the 1950’s and mid-80’s.

Interesting science, and no doubt it was a lot of fun doing the experiments.

For example, bees flying to a sugar feeder situated on top of a tall building dance to ‘report’ the same distance as bees from the same hive flying to a feeder at ground level adjacent to the same building.

Similarly, foragers loaded with weights do not overestimate the distance to a food source, as would be expected if the energy expended to reach it was being measured 7.

Interesting and entertaining science certainly, but none of it providing compelling support for the energy hypothesis

It’s notable that there is a rather telling sentence from the Esch & Burns review that states “While reading the original papers, one gains the impression that evidence supporting the energy hypothesis was favored over arguments against it”.

Ouch!

Splash landing

Although Von Frisch was a supporter of the energy hypothesis 8 he also published a study that provided evidence for our current understanding of how bees measure distance.

Bees generally don’t like flying long distances over water. Von Frisch provided two equidistant nectar sources, one of which was situated on the other side of a lake.

Bees flying over calm water underestimate distances

On very calm days the bees that flew across the lake under-reported the distance to the feeder. This underestimate was by 20-25% when compared to bees flying to an equidistant feeder overland.

Von Frisch commented “the bee’s estimation of distance is not determined through optical examination of the surface beneath her”.

He assumed that the mirror-like water surface provided no optical input as it contained no visual ‘clues’. After all, one calm patch of water looks much like any other. Von Frisch used this as an argument for the energy hypothesis.

He also noted that the bees generally flew very low over the water surface, often so low that they drowned 🙁

Perhaps these bees were flying dangerously low to try and find optical clues.

Such as their height above the surface?

Or perhaps the distance travelled?

Going with the flow

Having debunked the energy hypothesis, Esch & Burns proposed instead the optic flow hypothesis. This states that “foragers use the retinal image flow of ground motion to gauge feeder distance”.

Imagine optic flow as tripping a little odometer in the bee brain that records distance as her eyes observe the environment flashing past during flight. The clever thing about that is that the environment is variable. It’s not like counting off regularly spaced telegraph poles from a train window.

When flying, environmental objects that are nearby will move across her vision much faster than distant objects. Bees don’t have stereo vision, but instead use this speed of image motion to infer range.

Optic flow – the arrow size indicates the speed with which the object apparently moves, and hence its range

Esch & Burns returned again to tall buildings to provide supporting evidence for their optic flow hypothesis. They trained bees to fly between two tall buildings with 228 metres separating the hive and the feeder 9.

Returning foragers reported that the food source was only 125 metres away.

However, the bees didn’t make a direct flight. Instead they flew at altitude for 30-50 metres, descended to fly much lower, then ascended again to approach the feeder again at altitude.

Esch & Burns experiment to support the optic flow hypothesis

The interpretation here was that the high altitude flight provided insufficient optic flow to measure distance. The bees descend to get the visual input needed to judge distance, but it’s only for part of the flight … hence leading to under-reporting the distance separating the hive and feeder.

Tunnel vision

Jurgen Tautz 10 and colleagues trained bees to forage in a short, narrow tunnel 11. This elegant experiment provided compelling support for the optic flow hypothesis.

The tunnel was ~6 m long and with a cross sectional area of ~200 cm2 – big enough for a bee to fly along, but sufficiently narrow so that the bee would be closer to the ‘walls’ than in normal free flight. The walls and floor of the tunnel had a random visual texture. Only the end of the tunnel facing the hive was open.

The tunnel experiment.

These studies were conducted when the terms round and waggle were used to distinguish the dance induced by food sources <50 m and >50 m respectively from the hive 12. Rather than emphasise the shape of the dance I’ll just describe it as a >50 m or <50 m waggle dance.

‘Tunneling’ bees misreport distances

In the first tunnel experiment (1) the feeder was 35 m from the hive. 85% of dances indicated the feeder was <50 m away. However, when the feeder was moved to the opposite end of the tunnel (2) – still only 41 m from the hive – 90% of the dances indicated the feeder was >50 m away.

To test how the random pattern influenced the perceived distance the scientists used a third tunnel (3) lined with lengthwise stripes. In this instance – despite the feeder position being unchanged from experiment 2 – 90% of the dances indicated the feeder was <50 m away.

The stripes were predicted to ‘work’ in the same way as the smooth lake surface, providing no visual clues.

In the fourth experiment (4) the feeder was 6 m along a randomly patterned tunnel, which was placed just 6 m from the hive. Over 87% of dances indicated that the feeder was >50 m away.

Interpreting the waggle run

In open flight 13 there is usually an excellent correlation between the duration of the waggle run and the distance to a feeder (see the graph below 14 ). By extrapolation, the bees in experiments 2 and 4 ‘thought’ they had flown 230 m and 184 m respectively. In reality they had flown only 41 m and 12 m in these experiments.

Determining distances from waggle dance observation

How could the bees get it so wrong?

Increased optic flow

Tunnel-traversing bees fly just a few centimeters away from the visible ‘environment’.

As a consequence, at the same flight speed, they experience greater optic flow.

If, instead of driving around in your lumbering old van, you pack your hive tool in a Caterham 7 for the trip to the apiary you’d be well aware of what I mean.

Caterham 7 … check out that optic flow … then make another trip to collect the smoker

30 mph in a Toyota Hilux feels very much slower than 30 mph in a Caterham 7. This is largely because visual reference points, like the broken white lines between lanes in the road, appear in and disappear from your field of view much faster … because you’re much closer to them.

Because the tunnel dimensions were known it was possible to calculate the calibration of the bee’s odometer. Classically this would be defined in terms of metres of distance flown generating a particular waggle run length or duration.

These tunnel studies demonstrate that distance flown is not what calibrates the odometer. Instead it’s quantified indirectly in terms of the image motion experienced by the eye. Since environments vary the way to express this is the amount of angular image motion that generates a given duration of waggle.

And, using some mathematical trickery we don’t need to bother with 15, it turns out that this angular motion is only dependent upon distance flown, not the speed of flight.

This is important. Headwinds or tailwinds could change the speed of flight, but not the distance flown 16.

It’s all relative

It’s worth emphasising that the dance followers in experiments 2 (above) should still find the feeder.

The waggle dance would ‘instruct’ them to fly 230 m at the bearing indicated and they’d experience the same visual clues en route.

This means that they should still enter the narrow tunnel and experience increased optic flow because of the encroaching walls. But they’d be experiencing the same optic flow the initial dancing bee had experienced, so would not attempt to fly further down the tunnel.

This means that the optic flow experienced is context dependent. It is related to the environment the bees are foraging in.

This makes sense as the dancing bees and dance followers all occupy the same environment.

How do we know this? 17

Changing the environment

If we change the environment the dance followers search at the wrong distance.

I qualified the statement above when I said that the dance followers should still enter the tunnel and find the feeder.

Actually, most recruits will miss the tunnel entrance – remember it’s smaller that a sheet of A5 paper. At 35 m distance a bee would have to get the bearing correct to about 0.16° to enter the tunnel 18.

So the bees that do not enter the tunnel experience a different environment.

Where do they search for the feeder?

They search at the distance indicated by the waggle duration … so bees that missed the tunnel entrance in experiment 2 (above) would have searched for the feeder 230 m from the hive. Similarly, the dance followers in experiment 4 would have searched 184 m away 19

Context dependent dance calibration

And, finally, the calibration of the odometer depends upon the environment.

Odometer calibration depends upon the environment

If the environment experienced by the dancing bee en route to the feeder in experiments 2 and 4 is different, then it generates a different relationship between waggle run duration and distance.

For example, if one feeder was across a closely mown lawn and the other was across dense shrubby woodland, they would each generate a unique optic flow, so changing the image motion experienced, and hence the waggle run generated.

In the diagram above, you shouldn’t use dance calibration for bees trained to direction A to determine the distance bees going in direction B would forage.

Phew!

Optic flow, waggle dancing and implications for practical beekeeping

None 😉

At least, none that I can think of.

A Caterham 7 isn’t an ideal car for a beekeeper but would be a lot of fun to help you understand optic flow 😉

Most of us keep our bees in mixed environments. Your apiary isn’t situated with a cliff edge on one side and an unbroken prairie on the other. Since the environment is mixed, the waggle dance calibration is not going to be wildly different, whichever way the bees fly off in. You can therefore use an approximate figure of 1 second per kilometre to estimate the the distance at which your bees are foraging, irrespective of the direction they go.


Notes

Most of the referenced studies are at least two decades old. Honey bees have remained a fertile research tool for neurobiologists. Our understanding of honey bee vision continues to improve. However, I cannot discuss any of these more recent studies with reference to optic flow. Anyway, just because they’re old doesn’t make the experiments any less elegant or interesting 🙂