Category Archives: Science

A virus that changes bee behaviour

Particle physicists might not agree, but I think that evolution is the most powerful force in the universe. It is responsible for the fabulous diversity of life, for everything from the 6,000,000 kg Pando clonal colony of quaking aspen covering 43 hectares of the Fishlake National Forest in Utah, to the teeniest of tiniest of viruses.

As a microbiologist I’m acutely aware of the role evolution has played in the genetic arms race between hosts and pathogens. This is what is responsible for the multi-faceted immune system higher organisms carry – the antibodies, the lymphocytes, the complement and interferon responses, and everything else.

In turn, the fast replicating bacteria and viruses have evolved countermeasures to subvert these immune mechanisms, to switch them off entirely or to decoy them into targeting the wrong thing. This ‘arms race’ has gone on since well before the evolution of multicellular organisms (~600 million years ago) … and continues unabated.

Evolution is powerful for one simple reason; if a particular genetic combination 1 ‘works’ it will be passed on to the progeny. If a virus evolves a way to resist the immune response of the host, or to spread between hosts more efficiently, then the trait will be inherited.

Molecular mechanisms and behavioural changes

Some of changes work at the molecular level, invisible without exquisitely sensitive in vitro analysis; protein A binds to protein B and, in doing so, stops protein B from doing whatever it should have be doing. These are important but often very subtle.

Rabies: Slaying a mad dog, 1566 illustration from Wellcome Images

Other changes are far more obvious. Take rabies for example (or don’t, it’s not recommended as it has a near-100% case fatality rate) … the primary host of the rabies virus are carnivorous mammals. Infection causes gross behavioural changes that facilitate virus transmission. The animal becomes bolder and much more aggressive, resulting in virus transmission through biting.

Recent studies have elegantly demonstrated that this (also) is an example of protein A binding to protein B at the molecular level, it’s just that the phenotype 2 is very much more marked.

A protein on the surface of the virus resembles a snake venom toxin and has the ability to bind to nicotinic acetylcholine receptors present in the central nervous system of the mammalian host. These receptors ‘do what they say on the tin’ and bind the neurotransmitter acetylcholine. If the virus protein binds the receptor the response to acetylcholine is blunted and this, in turn, leads to hyperactivity, one of the key behavioural responses caused by rabies viruses.

That’s enough about mad dogs.

If virus-induced behavioural changes are so obvious, why haven’t lots of different examples already been identified and characterised?

Sniffles

Part of the problem is the blurring of distinctions between overt behavioural changes and the direct symptoms induced due to the virus replicating.

Human rhinovirus, the aetiological agent of the common cold, causes upper respiratory tract infections. You get a runny nose and you sneeze a lot.

Gesundheit

Your behaviour changes.

However, it’s generally accepted that the sneezing and runny nose are a result of the physiological response to infection, rather than a virus-induced behavioural response to facilitate transmission.

It’s worth noting that all that “stuff” that comes out of your nose contains infectious virus, so it’s perhaps an artificial distinction between the general symptoms of sickness and evolutionarily-selected host behavioural changes caused by the virus.

Which in a roundabout way …

… allows me to finally introduce the topic of bee viruses that cause host behavioural changes involved in their transmission.

Or, rather, one bee virus that does this … though I’m certain that there will be more.

Israeli Acute Paralysis Virus (IAPV) is an RNA virus transmitted horizontally by direct contact between bees, or while feeding on developing pupae, by the parasitic mite Varroa destructor. It was implicated as a causative agent of Colony Collapse Disorder (CCD), though really compelling evidence supporting it as the primary cause never materialised.

It’s a virus UK beekeepers should be aware of, but unworried by, as it is extremely rare in the UK.

A recent paper has shown two behavioural changes in response to IAPV infection in honey bees. One of them – that facilitates horizontal transmission between colonies – is also partially explained at the molecular level.

The paper was published a couple of months ago:

Geffre et al., (2020) Honey bee virus causes context-dependent changes in host social behavior. Proc. Natl. Acad. Sci. USA 117:10406-10413. 3

I’m going to focus on the results, rather than the methods, though the methods are rather cool. They used barcoded bees to allow the automated image analysis of every bee in a colony for some of the studies where they had introduced known IAPV infected individuals.

Responses of nestmates to IAPV infected bees

Imagine watching a few hundred waggle dances and being able to recount the position, distance and response of every bee ‘watching’ 4 the dance, and then being able to summarise the results.

Over five days.

Non-stop.

Including nights (and yes, bees do still waggle dance at night – a subject for the future).

The scientists orally infected groups of 30 bees with a sub-lethal dose of IAPV, marked them and released them into an observation hive. They then recorded their movements around the hive and their interactions with other bees in the colony. In particular, they focussed on trophallaxis interactions where one bee ‘feeds’ another.

Trophallaxis is also considered to be a method of communication in the hive and has been implicated in disease transmission.

The authors love their whisker plots and statistical analysis.

Who doesn’t? 😉

However, they generally make for rather underwhelming images in a bee blog for entertaining reading. Here .. see what I mean …

Number of trophallaxis interactions per hour.

Suffice to say that the results obtained were statistically significant.

They showed that the infected bees in the colony actually moved about the colony more than their nestmates. Conversely, they were engaged in fewer trophallaxis interactions i.e. it appeared as though they were being ‘ignored’ by their nestmates.

Were they really being ignored altogether or did their nestmates approach them, detect something was amiss and move away?

Antennation

Antennation is the mechanism by which bees recognise nestmates. They use the sensitive chemoreceptors on their antenna to detect cuticular hydrocarbons (CHC) which are distinctive between bees from different hives.

Antennation is a precursor to trophallaxis.

After all, bees do not want to feed a foreigner, or exchange chemicals involved in communications, or even potentially risk being exposed to a new pathogen.

Good as the barcoding and camera system is, it’s not good enough to record antennation within the observation hive. To do this they manually 5 recorded antennation events between IAPV-infected bees and nestmates in cages in the laboratory 6.

In these studies IAPV-infected bees were engaged in the same number of antennation events as control bees. This strongly suggests that the nestmate could detect there was something ‘wrong’ with the IAPV-infected individuals. In support of this conclusion, the authors also demonstrated that bees inoculated with a double stranded RNA (dsRNA) stimulator of the honey bee immune response were also also antennated equally, but engaged in less trophallaxis interactions.

Therefore, these studies appear to show that nestmates exhibit a behavioural response to IAPV-infected bees (and bees with elevated immune responses, recapitulating their response to pathogen infection) that is likely to be protective, reducing the transmission of horizontally acquired viruses.

It’s worth noting two things here.

  1. There were no virus transmission studies conducted. It’s assumed that the lack of trophallaxis reduces virus transmission. That still needs to be demonstrated.
  2. This response is not induced by the virus on the host. It’s a response by nestmates of the host to virus infected individuals (or individuals that present as ‘sick’). As such it’s not the same as the rabies example I started this post with.

Virus-induced behavioural responses

But do the IAPV-infected bees behave differently when they come into contact with other bees who are not their nestmates?

After all, IAPV is a pathogenic virus and its continuing presence within a population (not just a single hive) depends upon it being spread from hive to hive.

For a highly pathogenic virus this is very important. If you spread from bee to bee within a hive and kill the lot you also go extinct … this partly explains the mechanism by which highly virulent viruses become less virulent over time.

But back to IAPV. What happens when IAPV-inoculated bees interact with bees from a different hive?

For example, what would happen if they drifted from one hive to another in a densely populated apiary? Drifting is a significant contributor to the spread of bees between adjacent colonies – studies show that 1% of marked bees drift to adjacent hives over a 3 day window. This partially accounts for the genetic mix of workers (up to 40% are unrelated to the queen that heads the colony) in a hive, a fact generally unappreciated by beekeepers.

The authors first showed that IAPV-infected bees could apparently leave and return to the hive with a similar frequency as uninfected foragers. Their flying was not compromised.

They then resorted again to recording interactions in the laboratory between IAPV-infected bees or control dsRNA-inoculated bees and workers from a different hive.

This was where it gets particularly interesting.

Hello stranger

The dsRNA-immunostimulated bees (remember, these induce a generalised immune response characteristic of a ‘sick’ bee) were treated aggressively by unmatched workers from a different hive.

In contrast, the IAPV-infected bees (which were ‘sick’ and would have been undergoing immunestimulation caused by the IAPV infection) experienced significantly less aggression than both uninoculated workers (which induced an intermediate response) and the dsRNA-inoculated.

This strongly suggests that IAPV is somehow able to modulate the appearance or behaviour (and one often determines the other) of the host to make it more acceptable to an unmatched worker.

They extended this study to conduct “field-based assays at the entrances of three normally managed honey bee colonies”, monitoring whether IAPV-infected bees were more likely to be accepted by the guard bees at the entrance of the hive.

They were. The IAPV-infected bees received a less aggressive reception and/or entered the hives much more easily than the controls.

But what about proteins A and B?

Good question.

The behavioural alterations described above must be explainable in terms of the molecular changes that IAPV induces in the bees. By that I mean that the virus must make, or induce the making of, a chemical or protein or other molecule, the presence of which explains their acceptance by the foreign guard bees.

And the obvious candidates are the cuticular hydrocarbons (CHC) that are recognized during antennation, which I introduced earlier.

And here the story leaves us with some tantalising clues, but no definitive answer.

The scientists demonstrate that there were marked differences between the CHC profile of IAPV-infected and control bees. Again, they used their favoured whisker plots to show this, but collated all of the CHC data into an even more difficult to explain scatter plot of linear discriminant analysis.

CHC profiles (relative abundance) shown using linear discriminant analysis.

The key take home message here is that for each of the CHC’s analysed there were differences in both the quality and relative abundance between the control bees, bees immunestimulated with dsRNA and the IAPV-infected bees.

These differences were so marked that you can see distinct clustering of points in the analysis above … these bees ‘look’ 7 different to the guard bees that antennate them.

This is a great story.

It’s as yet incomplete. To complete the understanding we will need to know which of those CHC’s, or which combination, when suppressed (or overrepresented) induce the guard bees to say “Welcome, step this way … “.

We’ll then of course need to find out how IAPV induces the change in CHC profile, which takes us right back to protein A and protein B again.

Ever the pedant

Much as I like this science I’d perhap argue that, again, the virus isn’t directly inducing a behavioural change in the host.

What it’s doing is inducing a behavioural change in the response to the infected host (by the guard bee). So perhaps this again isn’t quite the same as the rabies example we kicked off with.

A behavioural change in the host might include IAPV-infected bees drifting more, or drifting further. Alternatively, perhaps a colony with widespread IAPV infection could more easily indulge in robbing neighbouring colonies as they would experience less aggression from guard bees.

Smaller is better ...

Reduced entrance to prevent robbing …

I can see immediate evolutionary benefits to a virus that induced these types of behavioural changes. It’s not an original idea … the late Ingemar Fries suggested it in a paper two decades ago 8.

I’m also certain that researchers are looking for evidence supporting these types of directly-induced behavioural changes caused by viral pathogens in honey bees.

All religion, my friend, is simply evolved out of fraud, fear, greed, imagination, and poetry

Edgar Allen Poe may or may not have said this.

However, while we’re on the thorny subject of pathogen-induced behavioural changes in the host, it might be worth mentioning a couple of more controversial areas in which it has been proposed.

In the snappily titled paper “Assortative sociality, limited dispersal, infectious disease and the genesis of the global pattern of religion diversity” Fincher and Thornhill argue 9 that the wide diversity of religions in the tropics (compared to temperate regions) is driven by infectious disease selecting for three anti-contagion behaviours; in-group assortative sociality; out-group avoidance; and limited dispersal. It’s an interesting idea and I’m pleased I don’t have to test it experimentally. Their argument is that these three behavioural changes select for fractionation, isolation and diversification of the original culture … and hence the evolution of religions.

Conversely, perhaps microorganisms induce religious behaviours (rather than religion per se) that facilitate their transmission. This is exemplified in the entertainingly titled paper “Midichlorians – the biomeme hypothesis: is there a microbial component to religious rituals?” by Panchin et al., (2014). They argue that microbes – and they are really thinking about the gut microbiota here – might be able to influence their hosts (humans) to gather for religious rituals at which both ideas (memes) and infections are more easily transmitted.

Perhaps something to think about when mindlessly spinning out all that summer honey in the next few weeks?

Party, party

I think it’s fair to say that both the papers in the section above have some way to go until they achieve mainstream acceptance … if they ever do.

Furthermore, the general area in which parasites, bacteria and viruses, induce changes in the behaviour of their hosts’ is really in its infancy. We are aware of a lot of behavioural changes, but few are understood at the molecular level 10. As such, we often don’t know whether the association is correlative or causative.

Evolution is certainly a powerful enough selective force to ensure that even extremely subtle benefits to the pathogen may become a genetically-fixed feature of the complex interaction it has with the host.

Respiratory viruses, such as the common cold, Covid-19 and influenza infect millions of people globally and are readily transmitted by direct or indirect contact.

That’s why most of the readers of this post have a face mask nearby and a bottle of hand sanitizer ‘at the ready’. Or should.

Direct transmission benefits the virus as it does not have to survive on a door handle, milk bottle or petrol filling pump.

But direct transmission requires that people meet and are in close contact.

And a paper 10 years ago demonstrated that infection with influenza virus resulted in increased social interactions in the 48 hours post-exposure, compared with the same period pre-exposure 11.

It’s amazing what viruses can do … or might do … or (just look around you) are doing.


 

Barcoding bees

Every jar of honey I prepare carries a square 20mm label that identifies the apiary, batch, bucket and the date on which is was jarred. The customer can scan it to find out about local honey … and hopefully order some more.

The label looks a bit like this:

Scan me!

This is a QR code.

You’ll find QR codes on many packaged goods in the supermarket, on bus stop adverts, on … well, just about anything these days.  QR codes were first used in 1994 and are now ubiquitous.

QR is an abbreviation of quick response.

It’s a machine-readable two-dimensional barcode that is used to provide information about the thing it’s attached to.

QR codes contain positional and informational content. In the image above the three corners containing large squares allow the orientation to be unambiguously determined.

Within the mass of other, much smaller, black and white squares are several alignment points, an indication of the encoding 1 and the ‘information payload’. 

Large QR codes can contain more information and more error correction (so they can be read if damaged 2 ). Conversely, small QR codes contain reduced amounts of information and less error correction, but can still be used to uniquely identify individual things in a machine-readable manner.

A barcoded bee and barcode diagram.

And those ‘things’ include bees.

I am not a number 3

I had intended to write a post on how pathogens alter honey bee behaviour. This has been known about in general terms for some time, but only at a rather crude or generic level. 

To understand behavioural changes in more detail you need to do two things:

  • observe bees in a ‘natural setting’ (or at least as natural as can be achieved in the laboratory)
  • record hundreds or thousands of interactions between bees to be able to discriminate between normal and abnormal behaviour. 

And that isn’t easy because they tend to all look rather similar.

Lots of bees

How many of the bees above are engaging in trophallaxis?

Does the number increase or decrease over the next five minutes? What about the next hour?

And is it the same bees now and in an hour?

And what is trophallaxis anyway? 

I’ll address the last point after describing the technology that enables these questions to be answered.

And, since it’s the same technology that has been used to monitor the behavioural changes induced by pathogens, I’ll have to return to that topic in a week or two. 

Gene Robinson and colleagues from the University of Illinois at Urbana–Champaign have developed a system for barcoding bees to enable their unique identification 4.

Not just a few bees … not just a couple of dozen bees … every bee in the colony.

Though, admittedly, the colonies are rather small 😉

Each barcode carries a unique number, readable by computer, that can be tracked in real time.

So, unlike Patrick McGoohan, these bees are a number.

bCode

The scientists designed a derivative of the QR code that could be printed small enough to be superglued to the thorax of a worker bee. They termed these mini-QR-like codes bCodes 5. The information content of a bCode was limited by its size and the reference points it had to carry that allowed the orientation of the bee to be determined.

In total the bCode could carry 27 bits of data. Eleven bits (each essentially on or off, indicated by a black or white square) encoded the identification number, allowing up to 2048 bees to be uniquely numbered. The remaining 16 bits were the error-correction parity bits that had to be present to ensure the number could be accurately decoded.

If you’re thinking ahead you’ll realise that the maximum number of bees they could therefore simultaneously study was 2048. That’s about 1/25th of a very strong colony at the peak of the season, or the number of bees covering both sides of a two-thirds full frame of sealed brood.

It’s enough bees to start a one frame nucleus hive, which will behave like a mini-colony 6 and, in due course, expand to be a much larger colony.

And if you’re thinking a long way ahead you’ll realise the every barcode must be affixed to each bee in the same orientation. How otherwise would you determine whether the bees were head to head or abdomen to abdomen?

Labelling bees

This is the easy bit.

Each bCode was 2.1mm square and weighed 0.6mg i.e. ~0.7% of the weight of a worker bee. Honey bees can ‘carry’ a lot more than that. When they gorge themselves before swarming they ingest ~35mg of honey. 

The bCode therefore should not be an encumbrance to the bee (and they confirmed this in an exhaustive series of control studies).

A single frame of sealed brood was incubated and the bees labelled within a few hours of emergence. Typically, two batches of ~700 bees each were labelled from a single frame for a single experiment.

Each bee was anaesthetised by chilling on ice, the bCode glued in place (remember … in the same orientation on every bee) and the bee allowed to recover.

Labelling a single bee took 1-2 minutes.

Labelling 1400 bees takes several people a long time.

I said it was easy.

I didn’t say it was interesting.

Smile for the camera

I’ve not yet discussed the goal of the study that needed barcoded bees. It’s not really important while I’m focusing on the technology. Suffice to say the scientists wanted to observe bees under near natural conditions.

Which means a free-flying colony, on a frame of comb … in the dark.

Free-flying because caged bees do not behave normally.

On a frame of comb because they were interested in the interactions between bees under conditions in which they would normally interact.

And in the dark because that’s what it’s like inside a beehive (and it’s one of the features that scout bees favour when selecting a site for a swarm).

Camera and hive setup.

The scientists used an observation hive with a difference. It had an entrance to allow the bees to fly and forage freely and it contained a single sided, single frame. In front of the frame was a sheet of glass separated by 8mm from the comb. This prevented the bees from clambering over each other, which would have obscured the bCodes 7. Behind the frame was an 850nm infrared lamp to increase contrast, and the front was illuminated by several additional infrared lamps.

Bees cannot see light in the infrared range, so they were effectively in the dark.

The camera used (an Allied Vision Prosilica GX6600 … not your typical point and shoot) recorded ~29MP images every second. A typical experiment would involve the collection of about a million images occupying 4-6 terabytes of hard drive space 8.

The recorded images were processed to determine the temporal location of every bee with a visible (and readable) bCode. This was a computationally interesting challenge and involved discarding some data – e.g. barcodes that moved faster than a bee can walk or barcodes that fell to the bottom of the hive and remained motionless for days (i.e. dead bees). About 6% of the data was discarded during this post-processing analysis.

Trophallaxis

Which finally gets us to the point where we can discuss trophallaxis. 

Honey bees and other social insects engage it trophallaxis.

It involves two insects touching each other with their antennae while orally transferring liquid food. It occurs more frequently than would be required for just feeding and it has been implicated in communication and disease transmission

bCoded bees and trophallaxis

So, if you are interested in trophallaxis, how do you determine which bees are engaging in it, and which are just facing each other head to head?

In the image above the two bees in the center horizontally of the insert 9 are engaged in trophallaxis. The others are not, even those immediately adjacent to the central pair.

Image processing to detect trophallaxis – head detection.

This required yet more image processing. The image was screened for bees that were close enough together and aligned correctly. An additional set of custom computer-vision algorithms then determined the shape, size, position and orientation of the bees’ heads. To be defined as trophallaxis the heads had to be connected by thin shapes representing the antennae or proboscis.

And when I say the image … I mean all million or so images.

Bursty behaviour

And after all that the authors weren’t really interested in trophallaxis at all.

What they were really interested in was the characteristics of interactions in social networks, and the consequences of those interactions.

This is getting us into network theory which is defined as “Well out of my depth”

Transmission of things in a network depends upon interactions between the individuals in the network.

Think about pheromones, or honey, or email … or Covid-19.

It’s only when two individuals interact that these can be transmitted between the individuals. And the interaction of individuals is often characterised by intermittency and unpredictable timing. 

Those in the know – and I repeat, I’m not one of them – call this burstiness. 

If you model the spread of ‘stuff’ (information, food, disease) through a bursty human communication network it is slower than expected.

Is this an inherent characteristic of bursty networks?

Are there real bursty networks that can be analysed.

By analysing trophallaxis Gene Robinson and colleagues showed that honey bee communication networks were also bursty (i.e. displayed intermittent and unpredictable interactions), closely resembling those seen in humans.

However, since they had identified every trophallaxis interaction over several days they could follow the spread of ‘stuff’ through the interacting network.

By simply overlaying the real records of millions of interactions over several days of an entire functional community with an event transmitted during trophallaxis they could investigate this spread..  

For example, “infect” (in silico) bee 874 in the initial second and follow the spread of the “infection” from bee to bee through the real network of known interactions.

In doing this they showed that in a real bursty network, interactions between honey bees spread ‘stuff’ about 50% faster than in randomised reference networks. 

Why isn’t entirely clear (certainly to me 10, and seemingly to the authors as well). One obvious possibility is that the topology of the network i.e. the contacts within it, are not random. Another is that the temporal features of a bursty network influence real transmission events. 

Scientists involved in network theory will have to work this out, but at least they have a tractable model to test things on …

… and at a time when some remain in lockdown, when others think it’s all a hoax, when social distancing is 2m 11, when some are wearing masks and when prior infection may not provide protective immunity anyway, you’ll appreciate that ‘how stuff spreads’ through a network is actually rather important.

Stay safe


 

If it quacks like a duck …

Quack

… it might be a trapped virgin queen.

I discussed the audio monitoring of colonies and swarm prediction last week. Whilst interesting, I remain unconvinced that it is going to be a useful way to predict swarming. 

And, more importantly, that replacing the manual aspects of hive inspections is desirable. I’m sure it will appeal to hands off beekeepers, though I’m not sure that’s what beekeeping is about.

However there was a second component to what was a long and convoluted publication 1 which I found much more interesting.

Listening in

If you remember, the researchers fitted hives with sensitive accelerometers and recorded the sounds within the hive for two years. Of about 25 colonies monitored, half swarmed during this period, generating 11 prime swarms and 19 casts.

In addition to the background sounds of the hive, with changes in frequency and volume depending upon activity, some colonies produced a series of very un-bee-like toots and quacks.

Have a listen …

The audio starts with tooting, the quacking starts around 8-9s, and there’s overlapping tooting and quacking from near the 21s mark.

Queen communication

I’ve previously introduced the concept of pheromone-based communication within the hive. For example, the mated queen produces the queen mandibular and queen footprint pheromones, the concentrations of which influence the preparation and development of new queen cells.

Tooting and quacking is another form of queen communication, this time by virgin queens in the colony.

It’s not unusual to hear some of these sounds during normal hive inspections, but only during the swarming season and only when the colony is in the process of requeening.

If you rear queens, and in my experience particularly if you use mini-mating nucs, you will regularly hear “queen piping” – another term for the tooting sound – a day or so after placing a mature charged queen cell into the small colony.

But we’re getting ahead of ourselves. 

How does the queen make these sounds?

Queen piping or tooting

Queen tooting has been observed. The queen presses her thorax tight down against the comb and vibrates her strong thoracic wing muscles. Her wings remain closed. The comb acts as a sounding board, amplifying the sound in the hive (and presumably transmitting the vibrations through the comb as well).

This doesn’t happen just anywhere … the virgin queen is usually near the cell she has recently emerged from. 

And this swarm cell is usually on the periphery of a frame.

This is because the laying queen only rarely ventures to the edges of frames, so the concentration of her footprint pheromone is lower in this area, eventually resulting in queen cells being produced there

In their study, accelerometers embedded in the periphery of comb were able to detect much stronger tooting and quacking signals, supporting the conclusions of Grooters (1987) 2 who had first published studies on the location of piping queens.

Queen tooting and quacking

Queen piping is usually recorded at around 400 Hz and consists of one or more 1 second long pulses, followed by a number of much shorter pulses. In previous studies the frequency of tooting had been shown to be age-related. It starts at ~350 Hz and rises in frequency to around 500 Hz as the virgin queen matures over several days.

Compare the image above with the audio file linked further up the post. The tooting is followed by an extended period of quacking, and then both sounds occur at the same time.

Going quackers

The duck-like quacking is presumably also made by queens vibrating their flight muscles while pressed up against the comb.

I say ‘presumably’ as I don’t think it has been observed, as opposed to heard.

The reason for this is straightforward, the queens that are quacking are still within the closed queen cell.

Quacking is a lower frequency sound (is this because of the confines of the queen cell, the way the sound is produced, or the ‘maturity’ of the queen’s musculature?) but has also been shown to increase in frequency – from ~200 Hz to ~350 Hz – the longer the queen remains within the cell.

Afterswarms = casts

Before discussing the timing of tooting and quacking we need to quickly revisit the process of swarming. I’ve covered some of this before when discussing the practicalities of swarm control, so will be brief.

  1. Having “decided” to swarm the colony produces swarm cells. Usually several.
  2. Weather permitting, the prime swarm headed by the original laying queen leaves the hive, on or around the day that the first of the maturing queen cells is capped.
  3. Seven days after the cell was capped the first of the newly developed virgin queens emerges. 
  4. If the colony is strong, this virgin also swarms (a cast swarm). Some texts, including the publication being discussed, call these afterswarms.
  5. Over the following hours or days, successively smaller cast swarms may leave the hive, each headed by a newly emerged virgin queen.

Not all colonies produce multiple cast swarms, but initially strong colonies often do.

From a beekeeping point of view this is bad news™. It can leave the remnants of the original colony too weak to survive and potentially litters the neighbourhood with grapefruit, orange and satsuma-sized cast swarms. 

Irritating 🙁

Whether it’s good for the bees depends upon the likelihood of casts surviving. The very fact that evolution has generated this behaviour suggests it can be beneficial. I might return to this point at the end of the post.

Tooting timing

The Grooters paper referred to earlier is probably the definitive study of queen tooting or piping. The recent Ramsey publication appears to largely confirm the earlier results 3, but has some additional insights on colony disturbance during inspections 4.

Here is the acoustic trace of an undisturbed colony producing a prime swarm and two casts.

Timing of tooting and quaking in a swarming colony

I’ve added some visible labels to the image above indicating the occurrence of tooting and quacking in an undisturbed naturally swarming colony.

  • The prime swarm exited the hive on the afternoon of the 13th. No tooting had been recorded before that date.
  • On the 17th tooting starts and increases in frequency over the next two days.
  • Quacking starts 6 hours after the tooting starts.
  • The first cast swarm (afterswarm) exits the hive on the 19th and is followed by a three hour break in tooting.
  • Tooting and quacking then continue until the second cast swarm on the afternoon of the 21st.

So, in summary, tooting starts after the prime swarm leaves and stops temporarily when the first cast leaves the hive. Quacking starts after the tooting starts and then continues until the last swarm leaves the hive.

Why all the tooting and quacking?

The timing of queen tooting is consistent with it being made by a virgin queen that has emerged from the cell. The cessation of tooting upon swarming (the first afterswarm) suggests that the virgin left with the swarm. The restarting of tooting a few hours later suggests a new virgin queen has been released from another cell and is announcing her presence to the colony.

In previous studies, Grooters had shown that replaying the tooting sound to mature virgin queens actively chewing their way out of a queen cell delayed their emergence by several hours. This delay allowed the attendant workers to reseal the cell and obstruct her emergence for several days.

These timings and the behaviour(s) they are associated with suggest they are a colony-level communication strategy to reduce competition between queens. 

The newly emerged virgin queen toots (pipes) to inform the workers that there is ‘free’ queen in the colony. The workers respond by holding back emergence of other mature queens. 

If all (or several) of the virgin queens emerged and ran around the hive simultaneously they would effectively be ‘competing’ for the hive resources needed for successful swarming i.e. the workers. 

By controlling and coordinating a succession of queen emergence, a strong colony has the opportunity to generate one, two or more cast swarms whilst sufficient workers remain in the hive. It presumably helps ensure the casts are of a sufficient size to give them the best chance of survival.

At what point does this succession stop or break down? One possibility is that this happens when there are insufficient workers to prevent additional virgin queens from emerging.

Unanswered questions

Why do mature virgin queens within the cell quack? It is clearly a response to tooting, rather than being standard behaviour of a soon-to-emerge queen. 

Hear! Hear the pipes are calling, Loudly and proudly calling (from Scotland the Brave)

Is the quacking to attract workers to help reseal the cell?

I suspect not. At least, I suspect there is a more pressing need to attract the workers. After all, wouldn’t it be easier for the queen to simply stop chewing her way out for a few hours? 

Isn’t there a risk that a quacking cell-bound queen might attract the virgin queen running around ‘up top’ who might attempt to slaughter her captive half-sister? 

Possibly, so perhaps the workers that are attracted to the quacking cell also protect the cell, preventing the loose virgin queen from damaging the yet-to-emerge queens.

This would make sense … if the virgin leaves with a cast, the workers that will remain must be sure that there will be a queen available to head the colony

And finally, back to the tooting. I also wonder if this has additional roles in colony communication. For example, what other responses does it induce in the workers? 

Does the increasing frequency of tooting inform the workers that the virgin is maturing and that they should ready themselves for swarming? Perhaps tooting above a certain frequency induces workers to gorge themselves with honey to ensure the swarm has sufficient stores?

In support of this last suggestion, studies conducted almost half a century ago by Simpson and Greenwood 5 concluded that a 650 Hz artificial piping sound induced swarming in colonies containing a single mobile (i.e. free) virgin queen.

Casts

The apparently self-destructive swarming where a colony generates a series of smaller and smaller casts seems to be a daft choice from an evolutionary point of view.

Several studies, in particular from Thomas Seeley, have shown that swarming is a risky business for a colony … and that the majority of the risk is borne by the swarm, not the parental colony. 

87% of swarmed colonies will rear a new queen and successfully overwinter, but only 25% of swarms survive. And the latter figure must only get smaller as the size of the swarms decrease. 

One possibility is that under entirely natural conditions a colony will not undergo this type of self-destructive swarming. Perhaps it is a consequence of the strength of colonies beekeepers favour for good nectar collection or pollination?

Alternatively, perhaps it reflects the way we manage our colonies. Ramsey and colleagues also record tooting and quacking from colonies disturbed during hive inspections. In at least one of these their interpretation was that there were multiple queens ‘free’ in the hive simultaneously, presumably because workers had failed to restrict the emergence of at least one virgin queen.

So, perhaps hive inspections that (inadvertently) result in the release of multiple virgin queens are the colonies that subsequently slice’n’dice themselves to oblivion by producing lots of casts.

I can only remember one colony of mine doing this … and it started days after the previous inspection, but that doesn’t mean the disturbance I created during the inspection wasn’t the cause.

I’d be interested to know of your experience or thoughts.


Colophon

The title of this post is derived from the Duck Test:

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

This probably dates back to the end of the 19th Century. It’s a form of abductive 6 reasoning or logical inference. It starts with an observation or set of observations and then seeks to find the simplest and most likely conclusion from those observations. In comparison to deductive reasoning, logical inference does not lead to a logically certain conclusion. 

Inevitably, Monty Python stretched the logical inference a little too far in the Witch Logic scene from Monty Python and the Holy Grail:

What do you do with witches? Burn them! And what do you burn apart from witches? Wood! So, why do witches burn? ‘cos they’re made of wood? So; how do we tell if she is made of wood? Build a bridge out of ‘er! Ah, but can you not also make bridges out of stone? Oh yeah. Does wood sink in water? No, it floats! It floats! Throw her into the pond! What also floats in water? Bread! Apples! Very small rocks? Cider! Gra-Gravy! Cherries! Mud! Churches? Churches! Lead, Lead. A Duck! Exactly. So, logically… If she weighs the same as a duck, she’s made of wood… and therefore… a witch!

Does DWV replicate in mites?

Buckle up.

After a gentle tale of bad beekeeping last week 1 I think it’s time for a bit of science.

Does deformed wing virus replicate in Varroa mites?

Varroa destructor – focus stacked image

Actually, do any pathogenic virus of honey bees replicate in mites?

Does it matter?

Not really … in comparison to the 2.1 billion people who don’t have access to safe drinking water 2, it’s unimportant.

But if you’re interested in how viruses are transmitted between bees, or how the virus population evolves, then knowing whether the virus replicates in Varroa is important.

For example, perhaps replication in Varroa amplifies a particular sub-population of virus that are more virulent, or more transmissable?

Or causes bees to drift more, so spreading the virus more widely in the environment?

Behaviour-altering viruses are interesting. There has been recent a report that IAPV 3 changes the social behaviour of honey bees to potentially increase transmission 4.

So, if it does matter …

Why now?

Three things prompted me to write this post now:

  1. A recent paper on Black Queen Cell Virus replicating in Varroa was briefly discussed on the Bee-L mailing list. This paper repeated many of the errors of assumption in the historical literature  on virus replication in Varroa 5.
  2. The experiments done to address this question over the last couple of decades have been either contradictory or uninformative. Or both. Or just not very good 🙁
  3. We have just published a study 6 that specifically addresses whether deformed wing virus can replicate in mites. Inevitably 7 I think it’s the most complete answer to date but, as will become clearer, it raises more questions than it answers and I know we don’t yet understand the full story.

To understand the problem you need to have a little background on both viruses and Varroa. Our paper is on deformed wing virus (DWV) and I’ll almost exclusively be using this as an example. If I use the word ‘virus’ I mean DWV.

However, the generalities of the shortcomings in some of the historical studies and the way we tackled the problem is relevant to any virus of honey bees. In that regard, when I use the word ‘virus’ it could probably mean any virus of honey bees.

Background to viruses

Viruses are obligate intracellular parasites. They can only replicate inside a living cell. The majority of pathogenic viruses of honey bees have a genome composed of single stranded positive sense RNA.

I did remind you to buckle up? … here we go.

All single strand positive sense RNA viruses share a broadly similar replication strategy.

Virus replication – select for full size and legend.

The virus enters the cell and the genome is translated to make proteins. There are essentially two types of proteins made:

  • the structural proteins – these form the new progeny virus particles. They are what package the new virus genomes into particles (thereby protecting it from damage) to infect the next cell, or host.
  • the non-structural proteins – these proteins are the ‘motor’ that makes new virus genomes 8. They do not form part of the virus particle.

After translation the non-structural proteins replicate the virus genome. To do this they first make a single stranded negative-sense template from which they eventually copy hundreds or thousands of more positive-strands.

The positive strands (only) associate with the structural proteins to form new virus particles. These leave the cell and go on to infect another cell, or another bee.

It’s as simple as that 🙂

A few important things to remember:

  • negative strands are never present in the virus particle. Since they would be non-infectious the virus has evolved all sorts of elegant ways of excluding them from the particle.
  • there are lots of positive strands produced from each negative strand. A ratio of 1000:1 or higher is not unusual 9.
  • without the initial production of the non-structural proteins the virus cannot replicate.

Background to Varroa

I’ve discussed Varroa extensively in previous posts. A full description of the life cycle was presented in the post Know your enemy. For lots of juicy background detail please refer back to that post.

As far as this post is concerned the important facts are as follows:

  • Varroa feeds on developing honey bee pupae and, during the (misnamed) phoretic stage of the life cycle, on adult bees.
  • the mite ingests a rich ‘soup’ of cells and proteins from the bee. For a long time it was thought that the mite fed on haemolymph (effectively bee blood), but some currently favour the evidence that Varroa feeds on the fat body of bees. As far as this post goes, it’s irrelevant whether the mite feeds on haemolymph or the fat body 10.
  • when the mite feeds on a virus-infected bee is also ingests the virus.
  • when the mite subsequently feeds on a different bee (for example, to initiate another round of incestuous replication) it transmits some of the virus in its saliva to the new bee.

There, that wasn’t so bad was it?

Evidence for virus replication in Varroa

I’m not going to provide an exhaustive review the extensive literature here. It goes back to the mid-90’s and is pretty dull and rather hard going in places.

There are also lots of papers on DWV replication in bumble bees … does it?

Essentially the evidence for replication of viruses in mites is the presence of virus negative strands in the mite. Time and again this has been presented as “definitive proof” that the virus replicates in Varroa.

Does that seem reasonable?

You already know enough Varroa and virus biology to see the flaw in this conclusion.

Q. What did that mite last feed on?

A. A virus-infected pupa.

Q. And what was therefore present in abundance in that pupa?

A. Negative strands of the virus genome.

Just because viral negative strands are detectable in the mite does not mean that they were produced in the mite when (if?) the virus replicated.

Perhaps they were simply ingested with the soup of proteins and cells that the mite eats?

This is an error based upon a positive result. There is an assumption that the positive result tells you something … but it doesn’t, or at least it might not.

Evidence against virus replication in Varroa

This one is more subtle and – in contrast to the above –  is an error based on a negative result.

It’s always dangerous drawing scientific conclusions from negative results. Perhaps the experiment just didn’t work? Perhaps it wasn’t sensitive enough? This is why lots of controls are needed.

Scientists looked in detail at all of the proteins present in Varroa mites. They used a method called mass spectroscopy that detects tiny fragmented proteins which they identified by comparison with a database of known proteins.

Orbitrap ID-X Tribrid Mass Spectrometer

If one of the tiny fragments matches, there’s a reasonable chance that the entire protein was present. If lots of different tiny fragments match one protein there’s compelling evidence that the entire protein was present in the sample 11.

Using mass spectroscopy scientists detected the structural proteins of deformed wing virus. However, using the same methods, they could not detect the non-structural proteins.

Since the non-structural proteins were ‘absent’ the virus could not have been replicating in the mite as they are a prerequisite for replication.

Seems logical, but is again potentially wrong.

Perhaps the tiny protein fragments of the non-structural proteins of DWV are ‘sticky’ and remain associated with cellular fats and membranes 12 during the purification process?

What about controls? Did the authors demonstrate they could detect the non-structural proteins of a virus that does replicate in Varroa? Was the sensitivity of their assay sufficient to detect the levels of non-structural proteins expected to be present? Did they provide evidence they could detect other similarly low abundance proteins?

No.

Should honey bee viruses replicate in Varroa?

Viruses are obligate intracellular parasites. They depend upon proteins and processes in the cell for their replication. This often means that viruses are restricted to a very narrow range of hosts. Sometimes viruses will only replicate in certain tissues or cell types of a single host species.

Varroa and honey bees are both Arthropods, but belong to different classes (Arachnida and Insecta respectively) within this phylum. They are therefore rather distantly related.

This does not mean that a virus of honey bees cannot replicate in the mite. There are several human viruses that also replicate in the mosquito (Dengue, Yellow Fever, Zika for example) during transmission. However, it’s an interesting philosophical cul-de-sac which is distracting us from the main event.

Genetically engineered deformed wing virus

Keeping up?

Good.

Now we’re getting to the more exciting stuff 13.

For some time now my lab have been able to genetically engineer deformed wing virus. This means we can make changes to the virus that help us do interesting or informative experiments.

For example, Olesya ‘Alex’ Gusachenko in my team built a virus that expresses a protein that turns bees green.

Green bees

This is allowing us to look in detail at the specific tissues the virus replicates in, or at transmission of the virus between bees. I’ll discuss green bees again in the future.

To investigate whether deformed wing virus replicates in Varroa we used a virus that had been engineered to contain a tiny genetic tag. It was equivalent to altering 0.05% of the virus genetic material. This genetic modification had three really important features:

  • it was unique and was not present in any other strains of deformed wing virus
  • although present in the virus genome it did not change any of the characteristics of the virus 14.
  • it was easy to detect. Alex developed an assay that could detect really tiny amounts (probably less than 100 copies) of genomes that contained this modification.

An artificial diet for Varroa

The final thing I need to introduce is how to keep Varroa mites in the laboratory 15. The experts can maintain Varroa in incubators, feeding them on little drops of honey bee haemolymph in what are called feed packets.

We’re not experts. But we know people who are.

We collaborated with our friends Alan Bowman, Ewan Campbell and Craig Christie in Aberdeen University who helped us with the Varroa feed packet part of the experiment.

A mite-infested apiary in Aberdeen with Luke, from my lab, and Craig discussing craft beers.

Critically, Alan’s lab have developed a feed packet system that contains no honey bee material. They can maintain Varroa in the lab without feeding them on mushed up bees. This means we had total control over what our Varroa could eat.

The feed packet contents are a closely guarded secret 16 but will be published soon.

Enough! Enough! Does DWV replicate in mites?

This is how we did the experiment. We grew large amounts of our genetically-tagged virus in honey bee pupae.

We purified the virus and treated it with an enzyme called RNAse.

As described above, the genome of DWV is made from the chemical RNA. RNAse degrades and destroys RNA.

However, viruses are resistant to RNAse because the RNA genome is protected inside the structural protein coat that forms outer layer of the virus particle.

We treated the purified virus preparation with RNAse to remove all RNA that was not inside the virus particles. This contaminating RNA could otherwise compromise the experiment.

Importantly, RNAse degrades both positive and negative strand RNA molecules. Therefore, we could be certain that our virus input into the experiment contained no contaminating negative strand RNA (and confirmed this in several controls).

We then added our virus to the feed packets being used to maintain groups of ten Varroa. After 4 days we harvested the Varroa and extracted all the RNA from them. We also had control mites which were not fed our tagged virus, but were otherwise treated in an identical manner.

All the mites contained very large amount of DWV-specific positive strand RNA. This was unsurprising. Even if our tagged DWV did not replicate in mites they had been feeding on honey bee pupae packed with DWV only four days ago.

We then looked for the presence of negative strand RNA. Again, there were reasonable amounts present, entirely consistent with their previous diet of DWV-infected honey bees. The control mites contained good levels of negative strand RNA.

DWV replicates in Varroa

However, only the mites fed the tagged virus contained a variably weak but consistent signal for the unique genetic tag we had introduced.

We interpret that as very good evidence that DWV does replicate in Varroa.

Is this level of replication significant?

Significant in terms of what?

It’s significant in that this experiment demonstrates for the first time the de novo production of replication intermediates (the negative strand RNA) in mites.

I’m not unbiased ( 🙂 ) but I think this is some of the best evidence supporting DWV replication in Varroa. It also demonstrates the types of experiments that are probably needed to determine whether other honey bee viruses replicate in the mite. The presence of negative strands is not enough. As the figure above shows, at least in the case of DWV, the majority come from the bee pupa the mite last fed on and we have no way to determine whether they are newly replicated or not.

But is the replication significant in terms of the amplification of the virus?

The presence of this signal confirms that there is some replication of DWV in Varroa. The fact that the signal is weak suggests that virus replication is not very extensive or very fast.

For comparison, if we inject the equivalent of 10 DWV virus particles into a honey bee pupa 17 they will be replicate to produce 1,000,000,000 (one billion) viruses within 48 hours. Assuming a conservative ratio of positive to negative strands, these individual pupae would each contain a million copies of negative strand RNA two days after infection.

We have yet to fully quantify specific negative strand levels replicated in Varroa, but it looks a whole lot less than that to me.

These are technically very demanding experiments and will take some time to complete. In the meantime we can and should ask a more relevant question.

Is this replication significant in terms of the biology of the virus?

By ‘biology of the virus’ I mean things like differential amplification of specific variants of the virus in the mite, so changing the virus population. For example, does virus adaptation occur, selecting for DWV variants that are more transmissable by Varroa?

We don’t know yet, but at least we have a system which will allow us to test this.

Although we have additional genetically-tagged variants of DWV we can test in the future, in mixed infections one will only be consistently selected over the others if it has a growth advantage.

We don’t yet know such a growth advantage even exists and there might be better ways to determine if it does. These are not straightforward experiments to undertake.

Based upon the limited replication we see in mites I do not think that the replication is significant in terms of increasing the amount of infectious virus in the mite. In contrast, the very high level of replication in honey bees may well allow the evolution of particular strains with particular characteristics.

Where is the replicating virus in Varroa?

We treated the mite like a simple bag of RNA.

We didn’t determine whether the virus was present in muscle, or brain or the ovaries.

The location of the virus is really important.

If the virus is replicating in a tissue that facilitates transmission to the next bee 18, particularly if certain types of virus are being selected because they grow better there, then it might be significant.

Some tissues allow viruses to be transmitted, others do not.

For example, poliovirus is a very distant cousin of DWV. Poliovirus is transmitted faecal-orally 19 in contaminated water supplies. After ingestion it replicates really well in the small intestine. It then has a short distance to travel (!) until it is excreted again. So, the primary site of poliovirus replication (the gut), is ideal as it ensures an obvious route for transmission.

Actually, poliovirus replicates so well in the gut that in about 0.5% of infected people it escapes from the gut and enters the peripheral nervous system. It then travels to the spinal cord and finally reaches the brain.

Poliovirus replicates pretty well in the brain as well … so well that it destroys some of the grey matter causing paralytic poliomyelitis 20.

But, as far as the virus is concerned, the brain is a dead-end. There’s no way out. Virus that replicates in the brain can never infect another person. How could it get from the brain to a water supply?

What about DWV? Is DWV replicating in tissues that enables transmission to another host?

Replication in the gut, in salivary glands or possibly the ovaries would all be consistent with transmission (with the ovaries as a source for vertical transmission to progeny mites – though they have already fed at the same spot on the pupa so determining this might be difficult). However, if DWV is replicating in mite muscle or brain it may well be irrelevant in terms of honey bee virus biology as there’s no obvious way out of those tissues.

Questions and answers

We attempted to answer a seemingly simple question “Can DWV replicate in mites?

We think the answer is yes.

But, as you can see from the few paragraphs above, that short question and even shorter answer has generated lots more questions.

And some of them are much more difficult to answer than the one we tackled 🙁

Identifying the site(s) of virus replication in Varroa would normally require microdissection of a variety of different tissues. Is the virus present? Is it replicating?

But a virus that expresses a fluorescent green protein during replication should make things a lot more straightforward … but more on that some other time.


Notes

The paper containing this study is available – open access (i.e. free) – the full title and journal details are: Gusachenko et al., (2020) Green Bees: Reverse Genetic Analysis of Deformed Wing Virus Transmission, Replication, and Tropism. Viruses 12: 532.

The memory of swarms

I’m writing this waiting for the drizzle to clear so I can go to the apiary and make up some nucs for swarm control. Without implementing some form of swarm control it’s inevitable that my large colonies will swarm 1.

Swarming is an inherently risky process for a colony. Over 75% of natural swarms perish, often because they do not build up strongly enough to overwinter successfully.

As a mechanism for reproduction swarming is somewhat unusual in that the intact colony is split into two not fully functional ‘halves’ 2.

By not fully functional I mean that neither the swarmed colony, nor the swarm are guaranteed to survive.

The swarmed colony lacks a queen, but has ample stores.

The swarm has a queen but has only the stores carried in the bellies of the workers.

The swarmed colony needs to rear a new queen. The swarm needs to find a new nest site, move there, build comb, rear brood, forage etc.

That seems like the very opposite of intelligent design, but it’s the way evolution has made things work. This being the case it involves a whole range of compromises and quick fixes that make it work.

One of these involves the memory of worker bees, which is what this post is about.

Two-stage swarming

A range of events within the hive – which for reasons that will become obvious I will term the original nest site – trigger the urge to swarm. I discussed some of these when covering swarm prevention. Swarming is then essentially a two-stage process. 

The two stage process of swarming

The first stage is the swarm leaving the original nest site and establishing a bivouac nearby. This is the classic cluster of bees hanging from a branch.

The bivouac sends out scout bees to search the nearby area for potential new nest sites. After ‘discussion’ (comprehensively covered by Thomas Seeley in Honeybee Democracy) between the scouts they reach a consensus of the best site.

The second stage is the relocation of the bivouacked colony to the new nest site. For example, this could be the church tower, a hollow tree or a bait hive. This site is likely to be within a few hundred metres of the original nest site, but can be further away.

All of which should raise some questions in the minds of beekeepers who are familiar with the “less than 3 feet or more than 3 miles” rule.

Have these bees not read the rules?

If you want to move a hived colony of bees you’ll often be told, or have read, that you need to move them either less than three feet or more than 3 miles.

Worker bees have a foraging range of about 3 miles. Within this range they have an uncanny ability to return to the hive location using features of the landscape to orientate themselves. The ‘final approach’ uses scent from the hive entrance.

Therefore, if you move a colony 3 feet they’ll still find the general location using landscape features, and then orientate to the hive entrance using scent.

If you move a colony 10 miles away everything is new to them and they’ll embark on some orientation flights to learn the new landscape features.

But if you move the colony a mile they’ll use the landscape features to return to the site of the original hive … to find it gone 🙁 3

Swarms break all these rules.

The bivouac is (in my experience) always more than 3 feet from the hive entrance. If the scout bees make the choice (e.g. selecting a bait hive to occupy), the swarm always relocates to a new nest site less than three miles from the site it left 4.

And a beekeeper who drops a bivouacked colony into a skep can move it wherever she wants, even back to the same hive stand it recently vacated.

If the swarm followed the rules, the majority of the workers would return from the bivouacked swarm to the original nest site.

At least they would if they had orientated to the original nest site in the first instance.

Are the bees naive?

About half of a workers life is spent as a forager collecting water, pollen or nectar. But before they venture out of the hive, the first half of a worker bees life is spent building comb, nursing larvae or cleaning cells.

Therefore, one possibility is that the bees present in a swarm have no knowledge of the hive location because they’ve never before left the hive.

We know that the proportion of workers that leave the colony when it swarms is about 75%. This has been determined in a number of independent studies and is remarkably consistent, irrespective of the size of the colony that swarms.

If 75% of the workers leave the colony when it swarms it is mathematically impossible for the swarm not to include older foragers (assuming the laying rate of the queen is steady).

In fact, we don’t need to resort to any underhand mathematics as the age classes of bees in a swarm have been measured. I’ve discussed this before when comparing natural and artificial swarms.

Age distribution of bees in swarms

Age distribution of bees in swarms

The median age of adult bees in the hive is 19 days. The median age of bees in a swarm is 10 days. Therefore swarms do contain younger bees, but not exclusively so.

One of the reasons for this bias towards younger bees must be to do with the relatively short lifespan of foragers. Many of the older bees in the swarm will have perished long before the new brood laid by the queen emerges.

Permanent amnesia?

The bivouacked swarm doesn’t dwindle in size as the older foragers drift back to the original nest site. Other than a few hundred scout bees, the majority of the bivouacked swarm huddle together to protect the queen, buried somewhere in the centre, from the elements.

They don’t fly or forage … they’re waiting for the signal from the scout bees that a new nest site has been located.

And, once they relocate to the church tower, the hollow tree or a bait hive, the older foragers stay in the new nest location. It’s as though the bees in a swarm that previously knew where the original nest site was have amnesia.

And this makes sense. If they did return to the original nest site the swarm (whether bivouacked or relocated) would shrink in size and it’s chances of surviving would be severely diminished. Other than a full belly of honey a swarm can rely on nothing. They need as many bees as possible to take on all the roles needed to establish a new colony – comb builders, nurses, foragers etc.

But have they really forgotten the original nest site?

Temporary amnesia?

It turns out that swarms do retain a memory of their original nest site.

In 1993 Gene Robinson and colleagues demonstrated that a swarm shaken out from its new nest site preferentially returns to the original nest site, rather than to an equidistant alternate 5.

This ability must rely on the memory of the foragers in the swarm. Therefore it is likely to be lost in a relatively short time (days, not weeks) 6.

Firstly, the foragers will be busy reorienting to the new nest site, effectively overwriting the memory of the original nest location. In good weather this takes just a couple of days.

Secondly, these ageing bees don’t have long to live, so there will be ever-decreasing numbers of them to lead a shaken out swarm back to the original location.

Rain stops play

Sometimes the bivouacked colony never relocates to a new nest site. Either the scouts never achieve a consensus or – more likely – bad weather forces the swarm to hunker down.

When you hive a bivouacked swarm you will often find a small crescent or two of new wax on the branch they were clinging to. If the bees get trapped by bad weather I think the comb building continues. It’s not unusual to find comb in hedgerows near apiaries where bees that have got trapped have ended up trying to make a new nest.

Natural comb

Natural comb …

What does the memory – or lack of it – of swarms mean for practical beekeeping?

The (temporary) amnesia of swarms means you can collect a bivouacked swarm and move it wherever you want. A swarm that relocates to your bait hive can also be moved, but don’t wait too long. Within just a few days of a swarm arriving the bees will have reoriented to their new location. I always try and move bait hives to their final location within three days of a swarm appearing.


Notes

The drizzle stopped and I spent the entire day finding queens and making up nucs.

Note to self … a super-strong colony with no queen cells, wall-to-wall brood and no very young larvae or eggs probably has a faulty queen excluder 🙁

Second note to self … Sod’s law dictates that the colony with the faulty queen excluder probably has supers filled with drone comb 🙁

Aristotle’s hairless black thieves

Aristotle not in his beesuit

Almost every article or review on chronic bee paralysis virus 1 starts with a reference to Aristotle describing the small, black, hairless ‘thieves‘, which he observed in the hives of beekeepers on Lesbos over 2300 years ago 2.

Although Aristotle was a great observer of nature, he didn’t get everything right.

And when it came to bees, he got quite a bit wrong.

He appreciated the concept of a ‘ruling’ bee in the hive, but thought that the queen was actually a king 3. He also recognised different castes, though he thought that drones (which he said “is the largest of them all, has no sting and is stupid”) were a different species.

He also reported that bees stored noises in earthenware jars (!) and carried stones on windy days to avoid getting blown away 4.

However, over subsequent millenia, a disease involving black, hairless honey bees has been recognised by beekeepers around the world, so in this instance Aristotle was probably correct.

Little blacks, maladie noire, schwarzsucht

The names given to the symptomatic bees or the disease include little blacks or black robbers in the UK, mal nero in Italy, maladie noire in France or schwarzsucht (black addiction) in Germany. Sensibly, the Americans termed the disease hairless black syndrome. All describe the characteristic appearance of individual diseased bees.

Evidence that the disease had a viral aetiology came from Burnside in the 1940’s who demonstrated the symptoms could be recapitulated in caged bees by injection, feeding or spraying them with bacterial-free extracts of paralysed bees. Twenty years later, Leslie Bailey isolated and characterised the first two viruses from honey bees. One of these, chronic bee paralysis virus (CBPV), caused the characteristic symptoms described first by Aristotle 5.

CBPV causes chronic bee paralysis (CBP), the disease first described by Aristotle.

CBPV infection is reported to present with two different types of symptoms, or syndromes. The first is the hairless, black, often shiny or greasy-looking bees described above 6. The second is more typically abnormal shivering or trembling of the wings, often associated with abdominal bloating 7. These bees are often found on the top bars of the frames during an inspection. Both symptoms can occur in the same hive 8.

CBP onset appears rapid and the first thing many beekeepers know about it is a large pile (literally handfuls) of dead bees beneath the hive entrance.

It’s a distressing sight.

Despite thousands of bees often succumbing to disease, the colony often survives though it may not build up enough again to overwinter successfully.

BeeBase has photographs and videos of the typical symptoms of CBPV infection.

Until recently, CBP was a disease most beekeepers rarely actually encountered.

Emerging and re-emerging disease

I’ve got a few hundred hive year’s worth 9 of beekeeping experience but have only twice seen CBP in a normally-managed colony. One was mine, another was in my association apiary a few years later.

A beekeeper managing 2 to 3 colonies might well never see the disease.

A bee farmer running 2 to 3 hundred (or thousand) colonies is much more likely to have seen the disease.

As will become clear, it is increasingly likely for bee farmers to see CBP in their colonies.

Virologists define viral diseases as emerging if they are new in a population. Covid-19, or more correctly SARS-CoV-2 (the virus), is an emerging virus. They use the term re-emerging if they are known but increasing in incidence.

Ebola is a re-emerging disease. It was first discovered in humans in 1976 and caused a few dozen sporadic outbreaks 10 until the 2013-16 epidemic in West Africa which killed over 11,000 people.

Often the terms are used interchangeably.

Sporadic and rare … but increasing?

Notwithstanding the apparently sporadic and relatively rare incidence of CBP in the UK (and elsewhere; the virus has a global distribution) anecdotal evidence suggested that cases of disease were increasing.

In particular, bee farmers were reporting increasing numbers of hives afflicted with the disease, and academic contacts overseas involved in monitoring bee health also reported increased prevalence.

Something can be rare but definitely increasing if you’re certain about the numbers you are dealing with. If you only have anecdotal evidence to go on you cannot be certain about anything very much.

If the numbers are small but not increasing there are probably other things more important to worry about.

However, if the numbers are small but definitely increasing you might have time to develop strategies to prevent further spread.

Far better you identify and define an increasing threat before it increases too much.

With research grant support from the UKRI/BBSRC (the Biotechnology and Biological Sciences Research Council) to the Universities of Newcastle (Principle Investigator, Prof. Giles Budge) and St Andrews, and additional backing from the BFA (Bee Farmers’ Association), we set out to determine whether CBPV really was increasing and, if so, what the increase correlated with (if anything).

This component of the study, entitled Chronic bee paralysis as a serious emerging threat to honey bees, was published in Nature Communications last Friday (Budge et al., [2020] Nat. Comms. 11:2164 https://doi.org/10.1038/s41467-020-15919-0).

The paper is Open Access and can be downloaded by anyone without charge.

There are additional components of the study involving the biology of CBPV, changes in virus virulence, other factors (e.g.environmental) that contribute to disease and ways to mitigate and potentially treat disease. These are all ongoing and will be published when complete.

Is chronic bee paralysis disease increasing?

Yes.

We ‘mined’ the National Bee Units’ BeeBase database for references to CBPV, or the symptoms associated with CBP disease. The data in BeeBase reflects the thousands of apiary visits, either by call-out or at random, by dedicated (and usually overworked) bee inspectors. In total we reviewed almost 80,000 apiary visits in the period from 2006 to 2017.

There were no cases of CBPV in 2006. In the 11 years from 2007 to 2017 the CBP cases (recorded symptomatically) in BeeBase increased exponentially, with almost twice as much disease reported in commercial apiaries. The majority of this increase in commercial apiaries occured in the last 3 years of data surveyed.

Apiaries recorded with chronic bee paralysis between 2006 and 2017.

BeeBase covers England and Wales only. By 2017 CBPV was being reported in 80% of English and Welsh counties.

During the same period several other countries (the USA, several in Europe and China) have also reported increases in CBPV incidence. This looks like a global trend of increased disease.

But is this disease caused by CBPV?

It should be emphasised that BeeBase records symptoms of disease – black, hairless bees; shaking/shivering bees, piles of bees at the hive entrance etc.

How can we be sure that the reports filed by the many different bee inspectors 11 are actually caused by chronic bee paralysis virus?

Or indeed, any virus?

To do this we asked bee inspectors to collect samples of bees with CBPV-like symptoms during their 2017 apiary visits. We then screened these samples with an exquisitely sensitive and specific qPCR (quantitative polymerase chain reaction) assay.

Almost 90% of colonies that were symptomatically positive for CBP were also found to have very high levels of CBPV present. We are therefore confident that the records of symptoms in the historic BeeBase database really do reflect an exponential increase of chronic bee paralysis disease in England and Wales since 2007.

Interestingly, about 25% of the asymptomatic colonies also tested positive for CBPV. The assay used was very sensitive and specific and allowed the quantity of CBPV to be determined. The amount of virus present in symptomatic bees was 235,000 times higher than those without symptoms.

Further work will be needed to determine whether CBPV is routinely present in similar proportions of ‘healthy’ bees, and whether these go on and develop or transmit disease.

Disease clustering

Using the geospatial and temporal (where and when) data associated with the BeeBase records we investigated whether CBPV symptomatic apiaries were clustered.

For example, in any year were cases more likely to be near other cases?

They were.

Across all years of data analysed together, or for individual years, there was good evidence for spatial clustering of cases.

We also looked at whether cases in one year clustered in the same geographic region in subsequent years.

They did not.

Clustering of CBPV – spatial and temporal analysis.

This was particularly interesting. It appears as though there were increasing numbers of individual clustered outbreaks each year, but that the clusters were not necessarily in the same geographic region as those in previous or subsequent years.

The disease appears somewhere, increases locally and then disappears again.

Apiary-level disease risk factors

The metadata associated with Beebase records is relatively sparse. Details of specific colony management methods are not recorded. Local environmental factors – OSR, borage, June gap etc. – are also missing. Inevitably, some of the factors that may be associated with increased risk are not recorded.

A relatively rare disease that is spatially but not temporally clustered is a tricky problem for which to define risk factors. Steve Rushton, the senior author on the paper, did a sterling job of analysing the data that was available.

The two strongest apiary-level factors that contributed to disease risk were:

  1. Commercial beekeeping – apiaries run by bee farmers had a 1.5 times greater risk of recording CBP disease.
  2. Importing bees – apiaries which had imported bees in the two preceding years had a 1.8 times greater risk of recording CBP disease.

Bee farming is often very different from amateur beekeeping. The colony management strategies are altered for the scale of the operation and for the particular nectar sources being exploited. For example, colonies may already be booming to exploit the early season OSR. This may provide ideal conditions for CBPV transmission which is associated with very strong hives and/or confinement.

Bee imports does not mean disease imports

There are good records of honey bees imported through official channels. This includes queens, packages and nucleus colonies. Between 2007 and 2017 there were over 130,000 imports, 90% of which were queens.

An increased risk of CBP disease in apiaries with imported bees does not mean that the imported bees were the source of the disease.

With the data available it is not possible to distinguish between the following two hypotheses:

  1. imported honey bees are carriers of CBPV or the source of a new more virulent strain(s) of the virus, or
  2. imported honey bees are susceptible to CBPV strain(s) endemic in the UK which they were not exposed to in their native country.

There are ways to tease these two possibilities apart … which is obviously something we are keen to complete.

All publicity is good publicity …

… but not necessarily accurate publicity 🙁

We prepared a press release to coincide with the publication of the paper. Typically this is used verbatim by some reporters whereas others ask for an interview and then include additional quotes.

Some more accurately than others 🙁

The Times, perhaps reflecting the current zeitgeist, seemed to suggest a directionality to the disease that we certainly cannot be sure of:

The Times

Its sister publication, The Sun, “bigged it up” to indicate – again – that bees are being wiped out.

The Sun

And the comments included these references to the current Covid-19 pandemic:

  • “Guess its beevid – 19. I no shocking”
  • “It’s the radiation from 5g..google it”
  • Local honey is supposed to carry antibodies of local virus and colds – it helps humans to eat the stuff or so they say. So it could be that the bees are actually infected by covid. No joke.

All of which I found deeply worrying, on a number of levels.

The Telegraph also used the ‘wiped out’ reference (not a quote, though it looks like one). They combined it with a picture of – why am I not surprised? – a bumble bee. D’oh!

The Telegraph

The Daily Mail (online) had a well-illustrated and pretty extensive article but still slipped in “The lethal condition, which is likely spread from imports of queen bees from overseas …”. The unmoderated comments – 150 and counting – repeatedly refer to the dangers of 5G and EMFs (electric and magnetic fields).

I wonder how many of the comments were posted from a mobile phone on a cellular data or WiFi network?

😉

Conclusions

CBPV is causing increasing incidence of CBP disease in honey bees, both in the UK and abroad. In the UK the risk factors associated with CBP disease are commercial bee farming and bee imports. We do not know whether similar risk factors apply outside the UK.

Knowing that CBP disease is increasing significantly is important. It means that resources – essentially time and money – can be dedicated knowing it is a real issue. It’s felt real to some bee farmers for several years, but we now have a much better idea of the scale of the problem.

We also know that commercial bee farming and bee imports are both somehow involved. How they are involved is the subject of ongoing research.

Practical solutions to mitigate the development of CBP disease can be developed once we understand the disease better.


Full disclosure:

I am an author on the paper discussed here and am the Principle Investigator on one of the two research grants that funds the study. Discussion is restricted to the published study, without too much speculation on broader aspects of the work. I am not going to discuss unpublished or ongoing aspects of the work (including in any answers to comments or questions that are posted). To do so will compromise our ability to publish future studies and, consequently, jeopardise the prospects of the early career researchers in the Universities of St Andrews and Newcastle who are doing all the hard work.

Acknowledgements

This work was funded jointly by BBSRC grants BB/R00482X/1 (Newcastle University) and BB/R00305X/1 (University of St Andrews) in partnership with The Bee Farmers’ Association and the National Bee Unit of the Animal and Plant Health Agency.

The scent of death

It’s late May. Outside it’s dark, so you’re trapped inside until sunrise. Inside it’s warm, dark and humid. You and your sisters are crowded together with barely enough space to turn around.

And your mother keeps laying more eggs … perhaps 2000 a day. If it wasn’t for the fact that about 2000 of your sisters perish each day you’d have no space at all.

Most of them die out in the fields. Missing in action.

I counted them all out and I didn’t count them all back, as the late Brian Hanrahan did not say in 1982 😉

But some die inside. And in the winter, or during prolonged periods of poor weather, your sisters all die inside.

Which means there’s some housekeeping to do.

Bring out your dead

Dead bees accumulating in the hive are a potential source of disease, particularly if they decompose. Unless these are removed from the colony there’s a chance the overall health of the colony will be threatened.

Not all bees die of old age. Many succumb to disease. The older bees in the colony may have a higher pathogen load, reinforcing the importance of removing their corpses before disease can spread and before the corpses decompose.

Corpses

Honey bees, like many other social insects, exhibit temporal polyethism i.e. they perform different tasks at different ages.

One of the tasks they perform is removing the corpses from the colony.

The bees that perform this task are appropriately termed the undertaker bees.

Gene Robinson in Cornell conducted observational studies on marked cohorts of bees. In these he identified the roles and activities of the undertaker bees. At any one time only 1-2% of the bees in the colony are undertakers 1.

These are ‘middle aged’ bees i.e. 2-3 weeks after eclosion, similar to guard bees. Although called undertakers, they do not exclusively remove corpses. Rather they are generalists that are more likely to remove the corpses, usually depositing them 50-100m from the hive and then returning.

They preferentially occupy the lower regions of the hive – presumably because gravity means the corpses accumulate there – where they also perform general hive cleansing roles e.g. removing debris.

Bees, like all of us, are getting older all the time. Some bees may spend only one day as undertakers before moving on to foraging duties. Presumably – I don’t think we know this yet – the time a bee remains as an undertaker is influenced by the colony’s need for this activity, the laying rate of the queen and, possibly, the numbers of other bees performing this role 2.

No no he’s not dead, he’s, he’s restin’!

Dead parrot

In Monty Python’s Dead Parrot sketch Mr. Praline (John Cleese) argues with the shop owner (Michael Palin) that the Norwegian Blue parrot he’d purchased was, in fact, dead.

The shop owner tries to persuade Mr. Praline that the parrot is resting.

Or stunned.

Or pining for the fjords.

The inference here is that it’s actually rather difficult to determine whether something is dead or not 3.

So if you struggle with an unresponsive parrot how do you determine if a bee is dead?

More specifically, how do undertaker bees in a dark, warm, humid hive determine that the body they’ve just tripped over is a corpse?

As opposed to a resting bee 4.

The scent of death

Almost forty years ago Kirk Visscher at Cornell studied necrophoresis (removal of the dead) in honey bees 5.

He noted that it had two distinct characteristics; it happened rapidly (up to 70 times faster than debris removal) and dead bees that were solvent-washed or coated in paraffin-wax were removed very much more slowly.

Kirk Visscher concluded that the undertaker bees “probably use chemical cues appearing very rapidly after the death of a bee” to identify the corpses.

Visscher studied honey bees, Apis mellifera. I’m not aware of any recent studies in A. mellifera that have better defined these ‘chemical cues’. However, a very recent preprint has been posted on bioRχiv describing how the closely related Eastern honey bee, Apis cerana, undertakers identify the dead.

As an aside, bioRχiv (pronounced bioarkive) is a preprint server for biology. Manuscripts published there have not been peer reviewed and will potentially be revised and/or withdrawn. They might even be wrong. Many scientists increasingly use bioRχiv to post completed manuscripts that have been submitted for publication elsewhere. The peer review and publication process is increasingly tortuous and long-winded. By posting preprints on bioRχiv other scientists can read and benefit from the study well before full publication elsewhere.

It’s also used as a ‘marker’ … we did this first 😉

The preprint on bioRχiv is Death recognition by undertaker bees by Wen Ping, submitted on the 5th of March 2020.

Odours and pongs

Death recognition in honey bees is rapid. Visscher demonstrated that a dead worker bee was usually removed within 30 minutes, well before it would have started producing the pong associated with the processes of decay.

Corpse recognition occurs in the dark and in the presence of lots of other bees. Logically, an odour of some sort might be used for identification. Both visual and tactile signals would be unlikely candidates.

In searching for the odour or chemical clues (the term used by Visscher), Ping made some assumptions based on prior studies in social insects. In Argentine ants a reduction in dolichodial and iridomyrmecin is associated with corpse recognition, and addition of these compounds (respectively a dialdehyde and a monoterpene) prevented necrophoresis.

Conversely, some social insects produce signals associated with death or disease. Dead termites give off a mix of 3-octanone, 3-octanol and the combination of β-ocimene and oleic acid production is a marker of diseased brood in honey bees.

What else could be assumed about the chemicals involved? Corpse removal is an individual effort. There’s only one pallbearer. Therefore the chemical, whatever it is, doesn’t need to be a recruitment signal (unlike the alarm pheromone for example).

Finally, the signal needs to operate over a very short range. There’s no point in flooding the hive with a persistent long-range chemical as that would make the detection of the corpse impossible.

Cuticular hydrocarbons

Cuticular hydrocarbons (CHC) are widely used in insect communication. They are long chain hydrocarbons (chemicals composed solely of carbon and hydrogen) that have many of the characteristics expected of a ‘death chemical’.

Nonacosane – a long chain CHC with 29 carbons and 60 hydrogen atoms

They are generally short-range, low volatility compounds. Honey bees use CHC’s for communication during the waggle dance and to distinguish colony mates by guard bees. They also have structural roles, being a major component of wax comb and, in the cuticle, they help maintain water balance in bees.

As would be expected from chemicals with a wide variety of roles, there’s a huge range of CHC’s. Taking all the above together, Wen Ping searched for CHC’s that functioned during necrophoresis.

Cool corpses and cuticular hydrocarbons

Wen studied undertakers removing segments of dead bees and determined that the chemical signal was most probably a component of the cuticle.

Living bees in his studies had a body temperature of ~44°C. In contrast, dead bees rapidly cooled to ambient temperatures. Wen demonstrated that corpse removal was significantly delayed if the corpses were warmed to ~44°C, but then occurred rapidly once they were allowed to cool. Finally, dead bees washed with hexane (which removes CHC’s) were removed even if the corpse was warm.

Taken together, these results suggest that a cuticular hydrocarbon that was produced and released from warm bees, but reduced or absent in cold bees, was a likely candidate for the necrophoresis signal.

But which one?

Gas chromatography

A gas chromatograph analyses volatile gases. Essentially gas vapour is passed through a thin coated tube and gaseous compounds of different molecular weights bind and elute at different times. It’s a very precise technique and allows all the components of a mixture to be identified by comparison with known standards.

Gas chromatography of volatiles from live (red) and dead (blue) bees.

Ping studied the volatile CHC’s in the airspace immediately surrounding dead bees or live bees using gas chromatography. There were some significant differences, shown by the absence of peaks in the blue trace of gases from the cold, dead bees. All of the peaks were identified and nine of the twelve peaks were CHC’s.

CHC’s with chain lengths of 27 or 29 carbons exhibited the greatest difference between live warm bees and cool dead bees and synthetic versions of these and the other CHC’s were tested to see which – upon addition – delayed the removal of dead bees.

Three had a significant impact in the dead bee removal assay – with chain lengths of 21, 27 and 29 carbons. These include the compounds heptacosane (C27H56)and nonacosane (C29H60).

Summary

The results section rather fizzles out in the manuscript posted to bioRχiv and I wouldn’t be surprised to see modifications to this part of the paper in a peer reviewed submission.

The overall story can be summarised like this. Live bees are warm and produce a range of CHC’s. Dead bees cool rapidly and some of the volatile CHC levels decrease in the immediate vicinity of the corpse. The undertaker bees specifically monitor the levels of (at least) heptacosane and nonacosane 6 as a means of discriminating between live and dead bees. Within 30 minutes of death local heptacosane and nonacosane levels have dropped below a level associated with life and the undertaker bee removes the corpse.

One final point worth making again. This study was conducted on Apis cerana. Our honey bees, A. mellifera, may use the same necrophoresis signals. Alternatively, they might use different chemicals in the same way.

Or they might do something else entirely.

Personally, I bet it’s a similar mechanism, potentially using different chemical.

There are mixed species colonies of A. mellifera and A. cerana. Do the undertakers only remove same-species corpses?

Global warming and hive cooling

The discussion of the bioRχiv paper raises two interesting points, both of which are perhaps a little contrived but still worth mentioning.

We’re living in a warming world.

Temperatures are rising

Dead bees cooling to ambient temperature lead to reduced CHC production. If global temperatures rise, so will the ambient temperature. Potentially this could decrease the reduction in the levels of CHC’s i.e. the dead bees might not look (er, smell!) quite so dead. This could potentially reduce corpse removal, with the concomitant potential for pathogen exposure.

I suspect that we’ll have much bigger problems to worry about than undertaker bees if the global temperatures rise that high …

But Wen also points out that the rise in global temperatures is also associated with more extreme weather, including very cold weather. Perhaps cold anaesthetised or weak bees will be prematurely removed from the hive under these conditions because their CHC levels have dropped below a critical threshold?

Finally, do dead bees lying on open mesh floors (OMFs) cool more rapidly and so trigger more efficient undertaking? Perhaps OMFs contribute more to hive hygiene than just allowing unwanted Varroa to drop through?


 

Do bees feel pain?

Even the most careful hive manipulations sometimes result in bees getting rolled between frames, or worse, crushed when reassembling the hive. Some beekeepers clip one wing of the queen to reduce the chance of losing a swarm, or uncap drone brood in the search for Varroa.

All of these activities can cause temporary or permanent damage, or may even kill, bees. A careful beekeeper should try and minimise this damage, but have you ever considered whether these damaged bees suffer pain?

Before considering the scientific evidence it’s important to understand the distinction between the detection of, for example, tissue damage and the awareness that the damage causes is painful and causes suffering.

Detection is a physiological response that is present in most animal species, the pain associated with it may not be.

What is pain?

Tissue damage, through chemical, mechanical or thermal stimuli, triggers a signal in the sensory nervous system that travels along nerve fibres to the brain. Or to whatever the animal has that serves as the equivalent of the brain 1.

This response is termed nociception (from the Latin nocēre, meaning ‘to harm’) and has been recorded in mammals, other vertebrates and in all sorts of invertebrates including leeches, worms and fruit flies. It has presumably evolved to detect damaging stimuli and to help the animal avoid it or escape.

But nociception is not pain.

Pain is a subjective experience that may result from the nociceptive response and can be defined as ‘an aversive sensation or feeling associated with actual or potential tissue damage’.

Most humans, being sentient, experience pain following the triggering of a nociceptive response and, understandably, conflate the two.

But they are separate and distinct. How do we know? Perhaps the first hint is that different people experience different levels of pain following the same harmful experience; an excruciatingly painful experience for one might be “just a scratch’ to another.

‘Tis but a scratch

With people it’s easy to demonstrate the distinction between nociception and pain – you simply ask them.

Can you feel that?

Does that hurt?

For the same stimuli you may receive a range of answers to the second question, depending upon their subjective experience of pain.

Painkillers

But you cannot ask a leech, or a worm or a fruit fly or – for the purpose of this post – a bee, whether a particular stimulus hurts.

Well, OK, you can ask but you won’t get an answer 😉

You can determine whether they ‘feel’ the stimulus. Since this is a simply physiological response you can measure all sorts of features of the electrical signal that passes from the nociceptors (the receptors in the tissue that detect damaging events) through the nerve fibres to the brain. This involves electrophysiology, a well established experimental science.

But how can we determine whether animals feel pain?

What do you do when you have a bad headache?

You take a painkiller – an aspirin or paracetamol. You self-medicate to relieve the pain.

Actually, even before you reach for the paracetamol, your body is already self-medicating by the release of endogenous opioids which help suppress the pain.

In cases of extreme pain injection of the opiate morphine may be necessary. Morphine is a very strong painkiller, or analgesic. Opioids bind to opioid receptors and this binding is blocked by a chemical called naloxone, an opiate antagonist. I’ll come back to naloxone in a minute.

But first, back to the unhelpfully unresponsive bee that may or may not feel pain …

It is self-medication with analgesics that forms the basis of the standard experiment to determine whether an animal feels pain.

The principle is straightforward. Two identical foods are prepared, one containing a suitable analgesic (e.g. morphine) and the other a placebo. If an animal is in pain it will preferentially eat the food containing the morphine.

Conversely, if they do not feel pain they will – on average – eat both types of food equally 2.

But this experiment will only work if morphine ‘works’ in bees.

Does morphine ‘work’ in bees?

An unpleasant or harmful stimulus induces a nociceptive response which might include taking defensive action like retreating or flying away. Studies have shown that the magnitude of this defensive action in honey bees is reduced or blocked altogether by prior injection with morphine.

This is a dose-response effect. The more morphine injected the smaller the nociceptive response by the bee. Importantly we know it’s the morphine that is having the effect because it can be counteracted by injection with naloxone.

So, morphine does work in bees 3.

We can therefore test whether bees choose to self-medicate with morphine to determine whether they feel pain.

And this is precisely what Julie Groening and colleagues from the University of Queensland did, and published three years ago in Scientific Reports. The full reference is Groening, J., Venini, D. & Srinivasan, M. In search of evidence for the experience of pain in honeybees: A self-administration study. Sci Rep 7, 45825 (2017); https://doi.org/10.1038/srep45825

Ouch … or not?

The experiment was very simple. Bees were subjected to one of two different injuries; a continuous pinch to the hind leg, or the amputation of part of the middle leg. They were then offered sugar syrup alone and sugar syrup containing morphine.

The hypothesis proposed was that if bees felt pain they would be expected to consume more of the sugar syrup containing morphine.

To ensure statistically relevant results they used lots of bees. Half were injured and half were uninjured and used as controls. If syrup laced with morphine tasted unpleasant you would expect the control group to demonstrate this by eating less.

Throughout the experiments the authors were therefore looking for a difference in syrup alone or syrup with morphine consumption between the injured bee and the uninjured controls.

All of the experiments produced broadly similar results so I’ll just show one data figure.

Relative consumption of morphine (M) and pure sucrose solution (S) by injured (i; amputated) or control (c) bees.

Both groups of bees preferred the pure syrup (the two box plots on the right labelled S_c or S_i) over the morphine-laced syrup (M). However, the bees with the amputation did not consume any more of the morphine-containing syrup (M_i) than the controls (M_c).

Therefore they did not self-medicate.

Very similar results were obtained with the bees carrying the hind leg clip (recapitulating an attack by a competing forager or predator, which often target the rear legs). The injured bees consumed statistically similar amounts of plain or morphine-laced syrup as the control group.

The one significant difference observed was that bees with amputations consumed about 20% more syrup overall than those with the rear leg ‘pinch’ injury. The authors justified this as indicating that the amputation likely induced the innate immune system, necessitating the production of additional proteins (like the antimicrobial peptides that fight infection), so leading to elevated energy needs. Speculation, but it seems reasonable to me.

Feeling no pain

This study, using a pretty standard and well-accepted experimental strategy, strongly suggests that bees do not feel pain.

It does not prove that bees feel pain. It strongly supports the theory that they do not. You cannot prove things with science, you can just disprove them. Evidence either supports or refutes a hypothesis; in this case the evidence (no self-medication) supports the hypothesis that bees do not feel pain because, as has been demonstrated with several other animals, they would self-medicate if they did feel pain.

In the discussion of the paper the authors suggest that further work is necessary. Scientists often make that kind of sweeping statement to:

  • encourage funders to provide money in the future 😉
  • allow them to incorporate additional, perhaps contradictory, evidence that could be interpreted in a different way to their own results.

Skinning a cat

That is painful … but the proverb There’s more than one way to skin a cat 4 means that there is more than one way to do something.

And there are other ways of interpreting behavioural responses as an indication that animals feel pain.

For example, rather than measuring self-medication with an analgesic, you could look at avoidance learning or protective motor reactions as indicators of pain.

Protective motor reactions include things like preferential and prolonged grooming of regions of the body which have been injured 5. There is no evidence that bees do this.

Avoidance learning

However, there is evidence that bees exhibit avoidance learning. This is a behavioural trait in which they learn to avoid a harmful stimulus that might cause injury.

If a forager is attacked by a predator at a food source (and survives) it stops other bees dancing to advertise that food source when it returns to the hive 6.

Whilst avoidance learning does not indicate that bees feel pain, it does imply central processing rather than a simple nociceptive response. It shows that bees are able to weigh up the risk vs. reward of something good (a rich source of nectar) with something bad (the chance of being eaten when collecting the nectar). This type of decision making demonstrates a cognitive capacity that might make pain experience more likely.

We’re now getting into abstruse areas of neuropsychology … dangerous territory.

Let’s assume, as I do based upon the science presented here and in earlier work, that bees do not feel pain. What, if anything, does this mean for practical beekeeping.

Practical beekeeping

It certainly does not mean we should not attempt to conduct hive manipulations in a slow, gentle and controlled manner. Just because rolled bees are not hurting, or crushed bees are not feeling pain, doesn’t give us carte blanche to be heavy handed.

One of the nociceptive responses is the production of alarm pheromones (sting and mandibular) which are part of the defensive response. Alarm pheromones agitate the hive and make the colony aggressive, much more likely to sting and much more difficult to inspect carefully.

So we should conduct inspections carefully, not because we are hurting the bees, but because they might hurt us.

But there are other reasons that care is needed as well. Crushed bees are a potential source of disease in the hive. One reason undertaker bees remove the corpses is to remove the likelihood of disease spreading in the hive. If bees are crushed the heady mix of viruses, bacteria and Nosema they contain are smeared around all over the place, putting other hive members at risk.

And, as we’re all learning at the moment, good hygiene can be a life-saver.


Colophon

This is the first post written under ‘lockdown’. It’s a little bit later than usual as it has had to travel a   v  e  r  y    l  o  n  g   way along the fibre to ‘the internet’. It’s going to be a very different beekeeping season to anything that has gone before.

At least spring is on the way …

Primroses, 27-3-20, Ardnamurchan

 

Measles, mites and anti-vaxxers

About 11,000 years ago nomadic hunter-gatherers living near the river Tigris discovered they could collect the seeds from wild grasses and, by scattering them around on the bare soil, reduce the distance they had to travel to collect more grain the following year.

This was the start of the agricultural revolution.

They couldn’t do much more than clear the ground of competing ‘weeds’ and throw out handfuls of collected seed. The plough wasn’t invented for a further 6,000 years and wouldn’t have been much use anyway as they had no means of dragging it through the baked-hard soil.

But they could grow enough grains and cereals to settle down, doing less hunting and more gathering. Some grains grew better than others, with ‘ears’ that remained intact when they were picked, making harvesting easier. The neophyte farmers preferentially selected these and, about 10,000 years ago, the first domesticated wheat was produced.

Einkorn wheat (Triticum monococcum), one of the first domesticated cereals

Since they were less nomadic and more dependent upon the annual grain harvest they took increasing care to protect it. They were helped with this by the hunting dogs domesticated from wolves several thousands years earlier. The dogs protected the crops and kept the wild animals, primarily big, cloven-hooved ungulates and the native wild sheep and goats, at a distance.

But those that got too close were trapped and were remarkably good to eat.

And since it was easier to keep animals penned up to avoid the need to actively hunt them it was inevitable that sheep and goats were eventually domesticated (~9,000 years ago) … and the nomadic hunter-gatherers became settled farmers practising recognisably mixed agriculture.

Domestication of cattle

The sheep and goats were a bit weak and scrawny. The large ungulates, the aurochs, gaur, banteng, yak and buffalo 1 had a lot more meat on them.

Inevitably, first aurochs (which are now extinct) and then other wild ungulates, were independently domesticated to produce the cattle still farmed today. This process started about 8,000 years ago.

Auroch bull (left) and modern domesticated bull (right). Auroch were big, strong (tasty) animals.

Cattle were great. Not only did they taste good, but they could be managed to produce milk and were strong enough to act as beasts of burden.

The plough was invented and crop yields improved dramatically because the grain germinated better in the cleared, tilled soil. Loosely knit families and groups started to build settled communities in the most fertile regions.

Bigger farms supported more people. Scattered dwellings coalesced and became villages.

Not everyone needed to farm the land. The higher yields (of grain and meat) allowed a division of labour. Some people could help defend the crops from marauders from neighbouring villages, some focused on weaving wool (from the sheep) into textiles while others taught the children the skills they would need as adults.

Communities got larger and villages expanded to form towns.

Zoonotic diseases

Hunter-gatherers had previously had relatively limited contact with animals 2. In contrast, the domestication of dogs, sheep, goats and cattle put humans in daily contact with animals.

Many of these animals carried diseases that were unknown in the human population. The so-called zoonotic diseases jumped species and infected humans.

There’s a direct relationship between the length of time a species has been domesticated and the number of diseases we share with it.

Domestication and shared zoonotic diseases (years, X-axis)

The emergence of new diseases requires that the pathogen has both the opportunity to jump from one species to another and that the recipient species (humans in this case) transmits the disease effectively from individual to individual.

The nomadic hunter-gatherers had been exposed to many of these diseases as well but, even if they had jumped species, their communities were too small and dispersed to support extensive human-to-human transmission.

Rinderpest and measles

Until relatively recently rinderpest was the scourge of wild and domesticated cattle across much of the globe. Rinderpest is a virus that causes a wide range of severe symptoms in cattle (and wild animals such as warthog, giraffe and antelope) including fever, nasal and eye discharges, diarrhoea and, eventually, death. In naÏve populations the case fatality rate approaches 100%.

Rinderpest outbreak in South Africa, 1896

Animals that survive infection are protected for life by the resulting immune response.

Rinderpest is closely related to canine distemper virus and measles virus. Virologically they are essentially the same virus that has evolved to be specific for humans (measles), dogs (canine distemper) or cattle (rinderpest).

Measles evolved from rinderpest, probably 1,500 to 2,000 years ago, and became a human disease.

Rinderpest was almost certainly transmitted repeatedly from cattle to humans in the 6,000 years since auroch or banteng were domesticated. However, the virus failed to establish an endemic infection in the human population as the communities were too small.

However, by about 1,500 – 2,000 years ago the largest towns had populations of ~250,000 people. Subsequent studies have demonstrated that you need a population of this size to produce enough naÏve hosts (i.e. babies) a year to maintain the disease within the population.

This is because, like rinderpest, measles induces lifelong immunity in individuals that survive infection.

Measles is a devastating disease in an unprotected community. Case fatality rates of 10-30% or higher are not unusual. It is also highly infectious, spreading very widely in the community 3. Survivors may suffer brain damage or a range of other serious sequelae.

Measles subsequently changed the course of history, being partially responsible (along with smallpox) for Cortés’ defeat of the Aztec empire in the 16th Century.

John Enders, Maurice Hilleman and Andrew Wakefield

In the late 1950’s John Enders developed an attenuated live measles vaccine. When administered it provided long-lasting protection. It was an excellent vaccine. Maurice Hilleman, in the early 1970’s combined an improved strain of the measles vaccine with vaccines for mumps and rubella to create the MMR vaccine.

Widespread use of the measles and MMR vaccines dramatically reduced the incidence of measles – in the UK from >500,000 cases a year to a few thousand.

Incidence of measles in England and Wales

If vaccine coverage of 92% of the population is achieved then the disease is eradicated from the community. This is due to so-called ‘herd immunity’ 4 in which there are insufficient naÏve individuals for the disease to be maintained in the population.

Measles cases (and deaths) continued to fall everywhere the vaccine was used.

There was a realistic possibility that the vaccines would – like rinderpest 5 – allow the global eradication of measles.

And then in 1986 Andrew Wakefield published a paper in the Lancet suggesting a causative link between the MMR vaccine and autism in children.

Subsequent studies showed that this was a deeply flawed and biased study. And totally wrong.

There is not and never was a link between autism and measles vaccination 6. But that didn’t stop a largely uncritical press and subsequently even less critical social media picking up the story and disseminating it widely.

Measles and the anti-vaccine movement

Measles vaccination rates dropped because a subset of parents refused to have their kids vaccinated with the ‘dangerous’ measles vaccine.

Several successive birth cohorts had significantly lower than optimal vaccination rates. Measles vaccine coverage dropped to 84% by 2002 in the UK, with regional levels (e.g. parts of London) being as low as 61%. By 2006, twenty years after the thoroughly discredited (and now retracted) Lancet paper vaccine rates were still hovering around the mid-80% level.

As immunisation rates dropped below the critical threshold, measles started to circulate again in the population. 56 cases in 1998 to ~450 in the first 6 months of 2006. In that year there was also the first death from measles for many years – an entirely avoidable tragedy.

In 2008 measles was again declared endemic (i.e. circulating in the population) in the UK.

Similar increases in measles, mumps and rubella were occurring across the globe in countries where these diseases were unknown for a generation due to previous widespread vaccination.

The distrust of the MMR vaccine was triggered by the Wakefield paper but is part of a much wider ‘anti-vaccination movement‘.

“Vaccines are dangerous, vaccines themselves cause disease, there are too many vaccines and the immune system is overloaded, vaccines contain preservatives (thiomersal) that are toxic, vaccines cause sterility etc.”

None of these claims stand up to even rudimentary scientific scrutiny.

All have been totally debunked by very extensive scientific analysis.

The World Health Organisation consider the anti-vaccine movement (anti-vaxxers) one of the top ten threats to global health. Vaccination levels are lower than they need to be to protect the population. Diseases – not just measles – that should be almost eradicated now kill children every year.

Where are the bees in this beekeeping blog?

Bear with me … before getting to the bees I want to move from fact (all of the above) to fantasy. The following few paragraphs (fortunately) has not happened (and to emphasise the point it is all italicised). However, it is no more illogical than the claims already being made by the anti-vaccine movement.

Childhood measles

The inexorable rise of internet misinformation and social media strengthened the anti-vaxxers beliefs further. Their claims that vaccines damage the vaccinees were so widespread and, for the uncritical, naturally suspicious or easily influenced who simply wanting to protect their kids, so persuasive that vaccine rates dropped further. They refused to consider the scientific arguments for the benefits of vaccines, and refused to acknowledge the detrimental effects diseases were having on the community.

The obvious causative link to the inevitable increase in disease rates was not missed – by both the anti-vaxxers and those promoting vaccination. However, the solutions each side chose were very different. Measles remained of particular concern as kids were now regularly dying from this once near-forgotten disease. The symptoms were very obvious and outbreaks spread like wildfire in the absence of herd-immunity 7.

The anti-vaxxers were aware that population size was a key determinant of the ability of measles to be maintained in the population. Small populations, such as those on islands or in very isolated regions, had too few new births annually to maintain measles as an endemic disease.

With the increase in remote working – enabled by the same thing (the internet) responsible for lots of the vaccine misinformation – groups of anti-vaxxers started to establish remote closed communities. Contact with the outside world was restricted, as was the size of the community itself.

A quarter of a million was the cutoff … any more than that and there was a chance that measles could get established in the unprotected population.

Small communities 8 work very well for some things, but very badly for others. Efficiencies of scale, in education, industry, farming and trade became a problem, leading to increased friction. When disease did occur in these unprotected communities it wreaked havoc. Countless numbers of people suffered devastating disease because of the lack of vaccination.

In due course this led to further fragmentation of the groups. They lived apart, leading isolated lives, flourishing in good years but struggling (or failing completely) when times were hard, or when disease was introduced. Some communities died out altogether. 

They chose not to travel because, being unvaccinated, they were susceptible to diseases that were widespread in the environment. Movement and contact between villages, hamlets and then individual farm settlements was restricted further over time.

The benefits of large communities, the division of labour, the economies and efficiencies of scale, were all lost.

They didn’t even enjoy particularly good health.

They had ‘evolved’ into subsistence farmers … again.

OK, that’s enough! Where are the bees?

Anyone who has bothered to read this far and who read Darwinian beekeeping last week will realise that this is meant to be allegorical.

The introduction of Varroa to the honey bee population resulted from the globalisation of beekeeping as an activity, and the consequent juxtaposing of Apis mellifera with Apis cerana colonies.

Without beekeepers it is unlikely that the species jump would have occurred.

Apis cerana worker

Undoubtedly once the jump had occurred transmission of mites between colonies was facilitated by beekeepers keeping colonies close together. We do this for convenience and for the delivery of effective pollination services.

The global spread of mites has been devastating for the honey bee population, for wild bees and for beekeeping.

But (like the introduction to measles in humans) it is an irreversible event.

However, it’s an irreversible event that, by use of effective miticides, can at least be partially mitigated.

Miticides do not do long-term harm to honey bees in the same way that vaccines don’t overload the immune response or introduce toxins or cause autism.

There can be short term side effects – Apiguard stinks and often stops the queen laying. Dribbled oxalic acid damages open brood.

But the colony benefits overall.

Many of the miticides now available are organic acids, acceptable in organic farming and entirely natural (even being part of our regular diet). Some of the hard chemicals used (e.g. the lipid-soluble pyrethroids in Apistan) may accumulate in comb, but I’d argue that there are more effective miticides that should be used instead (e.g. Apivar).

I’m not aware that there is any evidence that miticides ‘weaken’ colonies or individual bees. There’s no suggestion that miticide treatment makes a colony more susceptible to other diseases like the foulbroods or Nosema.

Of course, miticides are not vaccines (though vaccines are being developed) – they are used transiently and provide short to medium term protection from the ravages of the mite and the viruses it transmits.

By the time they are needed again the only bee likely to have been previously exposed is the queen. They benefit the colony and they indirectly benefit the environment. The colony remains strong and healthy, with a populous worker community available for nectar-gathering and pollination.

The much reduced mite load in the colony protects the environment. Mites cannot be spread far and wide when bees drift or through robbing. Other honey bee colonies sharing the environment therefore also benefit.

The genie is out of the bottle and will not go back

Beekeepers (inadvertently) created the Varroa problem and they will not solve it by stopping treatment. Varroa will remain in the environment, in feral colonies and in the stocks of beekeepers who choose to continue treating their colonies.

And in the many colonies of Apis mellifera still kept in the area that overlaps the natural (and currently expanding) range of Apis cerana.

Treatment-free beekeepers may be able to select colonies with partial resistance or tolerance to Varroa, but the mite will remain.

So perhaps the answer is to ban treatment altogether?

What would happen if no colonies anywhere were treated with miticides? What if all beekeepers followed the principles of Darwinian (bee-centric, bee friendly, ‘natural’) beekeeping – well-spaced colonies, allowed to swarm freely, killed off if mite levels become dangerously high – were followed?

Surely you’d end up with resistant stocks?

Yes … possibly … but at what cost?

Commercial beekeeping would stop. Honey would become even scarcer than it already is 9. Pollination contracts would be abandoned. The entire $5bn/yr Californian almond crop would fail, as would numerous other commercial agricultural crops that rely upon pollination by honey bees. There would be major shortages in the food supply chain. Less fruits, more cereals.

Pollination and honey production require strong, healthy populous colonies … and the published evidence indicates that naturally mite resistant/tolerant colonies are small, swarmy and only exist at low density in the environment.

Like the anti-vaxxers opting to live as isolated subsistence farmers again, we would lose an awful lot for the highly questionable ‘benefits’ brought by abandoning treatment.

And like the claims made by the anti-vaxxers, in my view the detrimental consequences of treating colonies with miticides are nebulous and unlikely to stand up to scientific scrutiny.

Does anyone seriously suggest we should abandon vaccination and select a resistant strain of humans that are better able to tolerate measles?


Notes

It is an inauspicious day … Friday the 13th (unlucky for some) with a global pandemic of a new zoonotic viral disease threatening millions. As I write this the UK government is gradually imposing restrictions on movement and meetings. Governments across Europe have already established draconian regional or even national movement bans. Other countries, most notably the USA and Africa, have tested so few people that the extent of Covid-19 is completely unknown, though the statistics of cases/deaths looks extremely serious.

What’s written above is allegorical … and crudely so in places. It seemed an appropriate piece for the current situation. The development of our globalised society has exposed us – and our livestock – to a range of new diseases. We cannot ‘turn the clock back’ without dissasembling what created these new opportunities for pathogens in the first place. And there are knock-on consequences if we did that many do not properly consider.

Keep washing your hands, self-isolate when (not if) necessary, practise social distancing (no handshakes) and remember that your bees are not at risk. There are no coronaviruses of honey bees.

Darwinian beekeeping

A fortnight ago I reviewed the first ten chapters of Thomas Seeley’s recent book The Lives of Bees. This is an excellent account of how honey bees survive in ‘the wild’ i.e. without help or intervention from beekeepers.

Seeley demonstrates an all-too-rare rare combination of good experimental science with exemplary communication skills.

It’s a book non-beekeepers could appreciate and in which beekeepers will find a wealth of entertaining and informative observations about their bees.

The final chapter, ‘Darwinian beekeeping’, includes an outline of practical beekeeping advice based around what Seeley (and others) understand about how colonies survive in the wild.

Differences

The chapter starts with a very brief review of about twenty differences between wild-living and managed colonies. These differences have already been introduced in the preceding chapters and so are just reiterated here to set the scene for what follows.

The differences defined by Seeley as distinguishing ‘wild’ and ‘beekeepers’ colonies cover everything from placement in the wider landscape (forage, insecticides), the immediate environment of the nest (volume, insulation), the management of the colony (none, invasive) and the parasites and pathogens to which the bees are exposed.

Some of the differences identified are somewhat contrived. For example, ‘wild’ colonies are defined fixed in a single location, whereas managed colonies may be moved to exploit alternative forage.

In reality I suspect the majority of beekeepers do not move their colonies. Whether this is right or not, Seeley presents moving colonies as a negative. He qualifies this with studies which showed reduced nectar gathering by colonies that are moved, presumably due to the bees having to learn about their new location.

However, the main reason beekeepers move colonies is to exploit abundant sources of nectar. Likewise, a static ‘wild’ colony may have to find alternative forage when a particularly good local source dries up.

If moving colonies to exploit a rich nectar source did not usually lead to increased nectar gathering it would be a pretty futile exercise.

Real differences

Of course, some of the differences are very real.

Beekeepers site colonies close together to facilitate their management. In contrast, wild colonies are naturally hundreds of metres apart 1. I’ve previously discussed the influence of colony separation and pathogen transmission 2; it’s clear that widely spaced colonies are less susceptible to drifting and robbing from adjacent hives, both processes being associated with mite and virus acquisition 3.

Abelo poly hives

50 metres? … I thought you said 50 centimetres. Can we use the next field as well?

The other very obvious difference is that wild colonies are not treated with miticides but managed colonies (generally) are. As a consequence – Seeley contends – beekeepers have interfered with the ‘arms race’ between the host and its parasites and pathogens. Effectively beekeepers have ‘weaken[ed] the natural selection for disease resistance’.

Whilst I don’t necessarily disagree with this general statement, I am not convinced that simply letting natural selection run its (usually rather brutal) course is a rational strategy.

But I’m getting ahead of myself … what is Darwinian beekeeping?

Darwinian beekeeping

Evolution is probably the most powerful force in nature. It has created all of the fantastic wealth of life forms on earth – from the tiniest viroid to to the largest living thing, Armillaria ostoyae 4. The general principles of Darwinian evolution are exquisitely simple – individuals of a species are not identical; traits are passed from generation to generation; more offspring are born than can survive; and only the survivors of the competition for resources will reproduce.

I emphasised ‘survivors of the competition’ as it’s particularly relevant to what is to follow. In terms of hosts and pathogens, you could extend this competition to include whether the host survives the pathogen (and so reproduces) or whether the pathogen replicates and spreads, but in doing so kills the host.

Remember that evolution is unpredictable and essentially directionless … we don’t know what it is likely to produce next.

Seeley doesn’t provide a precise definition of Darwinian beekeeping (which he also terms natural, apicentric or beefriendly beekeeping). However, it’s basically the management of colonies in a manner that more closely resembles how colonies live in the wild.

This is presumably unnnatural beekeeping

In doing so, he claims that colonies will have ‘less stressful and therefore more healthful’ lives.

I’ll come back to this point at the end. It’s an important one. But first, what does Darwinian mean in terms of practical beekeeping?

Practical Darwinian beekeeping

Having highlighted the differences between wild and managed colonies you won’t be surprised to learn that Darwinian beekeeping means some 5 or all of the following: 6

  • Keep locally adapted bees – eminently sensible and for which there is increasing evidence of the benefits.
  • Space colonies widely (30-50+ metres) – which presumably causes urban beekeepers significant problems.
  • Site colonies in an area with good natural forage that is not chemically treated – see above.
  • Use small hives with just one brood box and one super – although not explained, this will encourage swarming.
  • Consider locating hives high off the ground – in fairness Seeley doesn’t push this one strongly, but I could imagine beekeepers being considered for a Darwin Award if sufficient care wasn’t taken.
  • Allow lots of drone brood – this occurs naturally when using foundationless frames.
  • Use splits and the emergency queen response for queen rearing i.e. allow the colony to choose larvae for the preparation of new queens – I’ve discussed splits several times and have recently posted on the interesting observation that colonies choose very rare patrilines for queens.
  • Refrain from treating with miticides – this is the biggy. Do not treat colonies. Instead kill any colonies with very high mite levels to prevent them infesting other nearby colonies as they collapse and are robbed out.

Good and not so good advice

A lot of what Seeley recommends is very sound advice. Again, I’m not going to paraphrase his hard work – you should buy the book and make your own mind up.

Sourcing local bees, using splits to make increase, housing bees in well insulated hives etc. all works very well.

High altitude bait hive …

Some of the advice is probably impractical, like the siting of hives 50 metres apart. A full round of inspections in my research apiary already takes a long time without having to walk a kilometre to the furthest hive.

The prospect of inspecting hives situated at altitude is also not appealing. Negotiating stairs with heavy supers is bad enough. In my travels I’ve met beekeepers keeping hives on shed roofs, accessed by a wobbly step ladder. An accident waiting to happen?

And finally, I think the advice to use small hives and to cull mite-infested colonies is poor. I understand the logic behind both suggestions but, for different reasons, think they are likely to be to the significant detriment of bees, bee health and beekeeping.

Let’s deal with them individually.

Small hives – one brood and one super

When colonies run out of space for the queen to lay they are likely to swarm. The Darwinian beekeeping proposed by Seeley appears to exclude any form of swarm prevention strategy. Hive manipulation is minimal and queens are not clipped.

They’ll run out of space and swarm.

Even my darkest, least prolific colonies need more space than the ~60 litres offered by a brood and super.

Seeley doesn’t actually say ‘allow them to swarm’, but it’s an inevitability of the management and space available. Of course, the reason he encourages it is (partly – there are other reasons) to shed the 35% of mites and to give an enforced brood break to the original colony as it requeens.

These are untreated colonies. At least when starting the selection strategy implicit in Darwinian beekeeping these are likely to have a very significant level of mite infestation.

These mites, when the colony swarms, disappear over the fence with the swarm. If the swarm survives long enough to establish a new nest it will potentially act as a source of mites far and wide (through drifting and robbing, and possibly – though it’s unlikely as it will probably die – when it subsequently swarms).

A small swarm

A small swarm … possibly riddled with mites

Thanks a lot!

Lost swarms – and the assumption is that many are ‘lost’ – choose all sorts of awkward locations to establish a new nest site. Sure, some may end up in hollow trees, but many cause a nuisance to non-beekeepers and additional work for the beekeepers asked to recover them.

In my view allowing uncontrolled swarming of untreated colonies is irresponsible. It is to the detriment of the health of bees locally and to beekeepers and beekeeping.

Kill heavily mite infested colonies

How many beekeepers reading this have deliberately killed an entire colony? Probably not many. It’s a distressing thing to have to do for anyone who cares about bees.

The logic behind the suggestion goes like this. The colony is heavily mite infested because it has not developed resistance (or tolerance). If it is allowed to collapse it will be robbed out by neighbouring colonies, spreading the mites far and wide. Therefore, tough love is needed. Time for the petrol, soapy water, insecticide or whatever your choice of colony culling treatment.

In fairness to Seeley he also suggests that you could requeen with known mite-resistant/tolerant stock.

But most beekeepers tempted by Darwinian ‘treatment free’ natural beekeeping will not have a queen bank stuffed with known mite-resistant mated queens ‘ready to go’.

But they also won’t have the ‘courage’ to kill the colony.

They’ll procrastinate, they’ll prevaricate.

Eventually they’ll either decide that shaking the colony out is OK and a ‘kinder thing to do’ … or the colony will get robbed out before they act and carpet bomb every strong colony for a mile around.

Killing the colony, shaking it out or letting it get robbed out have the same overall impact on the mite-infested colony, but only slaying them prevents the mites from being spread far and wide.

And, believe me, killing a colony is a distressing thing to do if you care about bees.

In my view beefriendly beekeeping should not involve slaughtering the colony.

Less stress and better health

This is the goal of Darwinian beekeeping. It is a direct quote from final chapter of the book (pp286).

The suggestion is that unnatural beekeeping – swarm prevention and control, mite management, harvesting honey (or beekeeping as some people call it 😉 ) – stresses the bees.

And that this stress is detrimental for the health of the bees.

I’m not sure there’s any evidence that this is the case.

How do we measure stress in bees? Actually, there are suggested ways to measure stress in bees, but I’m not sure anyone has systematically developed these experimentally and compared the stress levels of wild-living and managed colonies.

I’ll explore this topic a bit more in the future.

I do know how to measure bee health … at least in terms of the parasites and pathogens they carry. I also know that there have been comparative studies of managed and feral colonies.

Unsurprisingly for an unapologetic unnatural beekeeper like me ( 😉 ), the feral colonies had higher levels of parasites and pathogens (Catherine Thompson’s PhD thesis [PDF] and Thompson et al., 2014 Parasite Pressures on Feral Honey Bees). By any measurable definition these feral colonies were less healthy.

Less stress and better health sounds good, but I’m not actually sure it’s particularly meaningful.

I’ll wrap up with two closing thoughts.

One of the characteristics of a healthy and unstressed population is that it is numerous, productive and reproduces well. These are all characteristics of strong and well-managed colonies.

Finally, persistently elevated levels of pathogens are detrimental to the individual and the population. It’s one of the reasons we vaccinate … which will be a big part of the post next week.