Category Archives: Problems

Quick thinking & second thoughts

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

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

Nest sites, bait hives and evolution

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

Under offer ...

Under offer …

The most important of these are:

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

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

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

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

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

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

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

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

Or both.

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

Bait hive compromises

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

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

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

Another day, another bait hive, another swarm …

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

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

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

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

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

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

However, I ignore it for the following reasons:

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

Scout bee activity

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

The two stage process of swarming

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

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

Swarm of bees

Swarm of bees

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

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

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

What’s a reasonable length of time?

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

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

Early warning systems

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

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

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

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

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

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

Questions and answers

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

And Tuesday was no exception.

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

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

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

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

A caffeine-fueled Q&A Zoom session

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

Many questions are rather predictable.

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

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

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

Do all swarms bivouac?

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

I think the original wording was something like:

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

And I didn’t know the answer.

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

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

Brutally honest, 100% accurate and unchallengeable 10.

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

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

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

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

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

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

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

Second thoughts

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

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

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

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

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

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

Absence of evidence is not evidence of absence.

So, what were the assumptions I made?

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

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

So, what’s wrong with these assumptions?

A noisy, smelly dance floor

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

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

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

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

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

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

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

But?

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

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

Apple blossom ...

Apple blossom … and signs that a bivouacked swarm perished here

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

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

Clearly this requires a bit more thought and research.

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

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


 

Brexit and beekeeping

The ‘oven ready’ deal the government struck with the EU in the dying hours of 2020 was a bit less à la carte and a bit more table d’hôte.

The worst of the predictions of empty supermarket shelves and the conversion of Essex into a 3500 km2 lorry park have not materialised 1.

But there are other things that haven’t or won’t appear.

And one of those things is bees.

Bee imports

There is a long history of bee imports into the UK, dating back at least a century. In recent years the number of imports has markedly increased, at least partially reflecting the increasing popularity of beekeeping. 

Going up! Imports of queens, nucs and packages to the UK, 2007-2020 (National Bee Unit data)

Queens are imported in cages, usually with a few attendant workers to keep them company. Nucs are small sized colonies, containing a queen, bees and brood on frames. 

Packages are the ‘new kid on the block’ (in the UK) with up to 2500 per year being imported after 2013. Packages are queenless boxes of bees, containing no frames or brood.

Empty boxes after installing packages of bees

They are usually supplied in a mesh-sided box together with a queen. The bees are placed into a hive with frames of foundation and the queen is added in an introduction cage. They are fed with a gallon to two of syrup to encourage them to draw comb.

Installing a package of bees

It’s a very convenient way to purchase bees and avoids at least some of the risk of importing diseases 2. It’s also less expensive. This presumably reflects both the absence of frame/foundation and the need for a box to contain the frames.

But, post-Brexit, importation of packages or nucs from EU countries is no longer allowed. You are also not allowed to import full colonies (small numbers of these were imported each year, but insufficient to justify adding them to the graph above).

Queen imports are still allowed.

Why are were so many bees imported?

The simple answer is ‘demand’.

Bees can be reared inexpensively in warmer climates, such as southern Italy or Greece. The earlier start to the season in these regions means that queens, nucs or packages can be ready in March to meet the early season demand by UK beekeepers.

If you want a nuc with a laying queen in March or April in the UK you have two choices; a) buy imported bees, or b) prepare or purchase an overwintered nuc.

I don’t have data for the month by month breakdown of queen imports. I suspect many of these are also to meet the early season demand, either by adding them to an imported package (see above) or for adding to workers/brood reared and overwintered in a UK hive that’s split early in the season to create nucleus colonies.

Some importers would sell the latter on as ‘locally reared bees’. They are … sort of. Except for the queen who of course determines the properties of all the bees in the subsequent brood 🙁

An example of being “economical with the truth” perhaps?

Imported queens were also available throughout the season to replace those lost for any number of reasons (swarming, poor mating, failed supersedure, DLQ’s, or – my speciality – ham-fisted beekeeping) or to make increase.

And to put these imports into numerical context … there are about 45,000 ‘hobby’ beekeepers in the UK and perhaps 200+ bee farmers. Of the ~250,000 hives in the UK, about 40,000 are managed by bee farmers.

What are the likely consequences of the import ban?

I think there are likely to be at least four consequences from the ban on the importation of nucs and packages to the UK from the EU:

  1. Early season nucs (whatever the source) will be more expensive than in previous years. At the very least there will be a shortfall of ~2000 nucs or packages. Assuming demand remains the same – and there seems no reason that it won’t, and a realistic chance that it will actually increase – then this will push up the price of overwintered nucs, and the price of nucs assembled from an imported queen and some ‘local’ bees. I’ve seen lots of nucs offered in the £250-300 range already this year.
  2. An increase in imports from New Zealand. KBS (and perhaps others) have imported New Zealand queens for several years. If economically viable this trade could increase 3.
  3. Some importers may try and bypass the ban by importing to Northern Ireland, ‘staging’ the bees there and then importing them onwards to the UK. The legality of this appears dubious, though the fact it was being considered reflects that this part of the ‘oven ready’ Brexit deal was not even table d’hôte and more like good old-fashioned fudge.
  4. Potentially, a post-Covid increase in bee smuggling. This has probably always gone on in a limited way. Presumably, with contacts in France or Italy, it would be easy enough to smuggle across a couple of nucs in the boot of the car. However, with increased border checks and potential delays, I (thankfully) don’t see a way that this could be economically viable on a large scale.

Is that all?

There may be other consequences, but those are the ones that first came to mind.

Of the four, I expect #1 is a nailed-on certainty, #2 is a possibility, #3 is an outside possibility but is already banned under the terms of the Northern Ireland Protocol which specifically prohibits using Northern Ireland as a backdoor from Europe, and #4 happens and will continue, but is small-scale.

Of course, some, all or none of this ban may be revised as the EU and UK continue to wrangle over the details of the post-Withdrawal Agreement. Even as I write this the UK has extended the grace period for Irish sea border checks (or ‘broken international law’ according to the EU). 

This website is supposed to be a politics-free zone 4 … so let’s get back to safer territory.

Why is early season demand so high?

It seems likely that there are three reasons for this early season demand:

  1. Commercial beekeepers needing to increase colony numbers to provide pollination services or for honey production. Despite commercials comprising only ~0.4% of UK beekeepers, they manage ~16% of UK hives. On average a commercial operation runs 200 hives in comparison to less than 5 for hobby beekeepers. For some, their business model may have relied upon the (relatively) inexpensive supply of early-season bees.
  2. Replacing winter losses by either commercial or amateur beekeepers. The three hives you had in the autumn have been slashed to one, through poor Varroa management, lousy queen mating or a flood of biblical proportions. With just one remaining hive you need lots of things to go right to repopulate your apiary. Or you could just buy them in.
  3. New beekeepers, desperate to start beekeeping after attending training courses through the long, dark, cold, wet winter. And who can blame them? 

For the rest of the post I’m going to focus on amateur or hobby beekeeping. I don’t know enough about how commercial operations work. Whilst I have considerable sympathy if this change in the law prevents bee farmers fulfilling pollination or honey production contracts, I also question how sensible it is to depend upon imports as the UK extricates itself from the European Union.

Whatever arrangement we finally reached it was always going to be somewhere in between the Armageddon predicted by ‘Project Fear’ and the ‘Unicorns and sunlit uplands’ promised by the Brexiteers.

Where are those sunlit uplands?

And that had been obvious for years.

I have less sympathy for those who sell on imported bees to meet demand from existing or new beekeepers. This is because I think beekeeping (at least at the hobbyist level) can, and should, be sustainable.

Sustainable beekeeping

I would define sustainable beekeeping as the self-sufficiency that is achieved by:

  • Managing your stocks in a way to minimise winter losses
  • Rearing queens during the season to requeen your own colonies when needed (because colonies with young queens produce brood later into the autumn, so maximising winter bee production) and to …
  • Overwinter nucleus colonies to make up for any winter losses, or for sale in the following spring

All of these things make sound economic sense. 

More importantly, I think achieving this level of self-sufficiency involves learning a few basic skills as a beekeeper that not only improve your beekeeping but are also interesting and enjoyable.

I’ve previously discussed the Goldilocks Principle and beekeeping, the optimum number of colonies to keep considering your interest and enthusiasm for bees and the time you have available for your beekeeping.

It’s somewhere between 2 and a very large number. 

For me, it’s a dozen or so, though for years I’ve run up to double that number for our research, and for spares, and because I’ve reached the point where it’s easy to generate more colonies (and because I’m a lousy judge of the limited time I have available 🙁 ).

Two is better than one, because one colony can dwindle, can misbehave or can go awry, and without a colony to compare it with you might be none the wiser that nothing is wrong. Two colonies also means you can always use larvae from one to rescue the other if it goes queenless.

And with just two colonies you can easily practise sustainable beekeeping. You are no longer dependent on an importer having a £30 mass-produced queen spare.

What’s wrong with imported bees?

The usual reason given by beekeepers opposed to imports is the risk of also importing pathogens.

Varroa is cited as an example of what has happened. 

Tropilaelaps or small hive beetle are given as reasons for what might happen.

And then there are usually some vague statements about ‘viruses’. 

There’s good scientific evidence that the current global distribution of DWV is a result of beekeepers moving colonies about.

More recently, we have collaborated on a study that has demonstrated an association between honey bee queen imports and outbreaks of chronic bee paralysis virus (CBPV). An important point to emphasise here is that the direction of CBPV transmission is not yet clear from our studies. The imported queens might be bringing CBPV in with them. Alternatively, the ‘clean’ imported queens (and their progeny) may be very susceptible to CBPV circulating in ‘dirty’ UK bees. Time will tell.

However, whilst the international trade in plants and animals has regularly, albeit inadvertently, introduced devastating diseases e.g. Hymenoscyphus fraxineus (ash dieback), I think there are two even more compelling reasons why importation of bees is detrimental.

  1. Local bees are better adapted to the environment in which they were reared and consequently have increased overwintering success rates.
  2. I believe that inexpensive imported bees are detrimental to the quality of UK beekeeping.

I’ve discussed both these topics previously. However, I intend to return to them again this year. This is partly because in this brave new post-Brexit world we now inhabit the landscape has changed.

At least some imports are no longer allowed. The price of nucs will increase. Some/many of these available early in the season will be thrown together from overwintered UK colonies and an imported queen.

These are not local bees and they will not provide the benefits that local bees should bring.

Bad beekeeping and bee imports

If imported queens cost £500 each 5 there would be hundreds of reasons to learn how to rear your own queens. 

But most beekeepers don’t …

Although many beekeepers practise ‘passive’ queen rearing e.g. during swarm control, it offers little flexibility or opportunity to rear queens outside the normal swarming season, or to improve your stocks.

In contrast, ‘active’ queen rearing i.e. selection of the best colonies to rear several queens from, is probably practised by less than 20% of beekeepers.

This does not need to involve grafting, instrumental insemination or rows of brightly coloured mini-nucs. It does not need any large financial outlay, or huge numbers of colonies to start with.

But it does need attention to detail, an understanding of – or a willingness to learn – the development cycle of queens, and an ability to judge the qualities of your bees.

Essentially what it involves is slightly better beekeeping.

But, the availability of Italian, Greek or Maltese queens for £20 each acts as a disincentive.

Why learn all that difficult ‘stuff’ if you can simply enter your credit card details and wait for the postie?

Overwintering 5 frame poly nuc

Overwintering 5 frame poly nuc

And similar arguments apply to overwintering nucleus colonies. This requires careful judgement of colony strength through late summer, and the weight of the nuc over the winter.

It’s not rocket science or brain surgery or Fermat’s Last Theorem … but it does require a little application and attention.

But, why bother if you can simply wield your “flexible friend” 6 in March and replace any lost colonies with imported packages for £125 each?

Rant over

Actually, it wasn’t really a rant. 

My own beekeeping has been sustainable for a decade. I’ve bought in queens or nucs of dark native or near-native bees from specialist UK breeders a few times. I have used these to improve my stocks and sold or gifted spare/excess nucs to beginners.

I’ve caught a lot of swarms in bait hives and used the best to improve my bees, and the remainder to strengthen other colonies.

The photographs of packages (above) are of colonies we have used for relatively short-term scientific research. 

I’m going to be doing a lot of queen rearing this season. Assuming that goes well, I then expect to overwinter more nucs than usual next winter. 

I then hope that the bee import ban remains in place for long enough until I can sell all these nucs for an obscene profit which I will use to purchase a queen rearing operation in Malta. 😉

And I’m going to write about it here.


Notes

BBKA statement made a day or two after this post appeared. The BBKA and other national associations are concerned about the potential import of Small Hive Beetle (SHB) into the UK via Northern Ireland. Whilst I still think this breaches the Northern Ireland Protocol, it doesn’t mean it won’t be attempted (and there’s at least one importer offering bees via this route). It’s not clear that the NI authorities have the manpower to inspect thousands of packages.

It’s worth noting that SHB was introduced to southern Italy in 2014 and remains established there. The most recent epidemiological report shows that it was detected as late as October 2020 in sentinel apiaries and is also established in natural colonies.

With a single exception – see below – every country into which SHB has been imported has failed to eradicate it. As I wrote in November 2014:

“Once here it is unlikely that we will be able to eradicate SHB. The USA failed, Hawaii failed, Australia failed, Canada failed and it looks almost certain that Italy has failed.”

And Italy has failed.

The one exception was a single import to a single apiary in the UK. Notably, the illegal import was of queens, not nucs or packages. Eradication involved the destruction of the colonies, the ploughing up of the apiary and the entire area being drenched in insecticide.

Going the distance

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

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

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

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

How do bees measure distance?

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

Does that seem logical?

Foragers forage randomly, but usually return directly

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

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

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

Going up!

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

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

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

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

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

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

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

Ouch!

Splash landing

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

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

Bees flying over calm water underestimate distances

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

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

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

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

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

Such as their height above the surface?

Or perhaps the distance travelled?

Going with the flow

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

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

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

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

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

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

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

Esch & Burns experiment to support the optic flow hypothesis

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

Tunnel vision

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

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

The tunnel experiment.

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

‘Tunneling’ bees misreport distances

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

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

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

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

Interpreting the waggle run

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

Determining distances from waggle dance observation

How could the bees get it so wrong?

Increased optic flow

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

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

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

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

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

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

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

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

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

It’s all relative

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

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

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

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

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

How do we know this? 17

Changing the environment

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

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

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

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

Where do they search for the feeder?

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

Context dependent dance calibration

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

Odometer calibration depends upon the environment

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

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

In the diagram above, you shouldn’t use dance calibration for bees trained to direction A to determine the distance bees going in direction B would forage.

Phew!

Optic flow, waggle dancing and implications for practical beekeeping

None 😉

At least, none that I can think of.

A Caterham 7 isn’t an ideal car for a beekeeper but would be a lot of fun to help you understand optic flow 😉

Most of us keep our bees in mixed environments. Your apiary isn’t situated with a cliff edge on one side and an unbroken prairie on the other. Since the environment is mixed, the waggle dance calibration is not going to be wildly different, whichever way the bees fly off in. You can therefore use an approximate figure of 1 second per kilometre to estimate the the distance at which your bees are foraging, irrespective of the direction they go.


Notes

Most of the referenced studies are at least two decades old. Honey bees have remained a fertile research tool for neurobiologists. Our understanding of honey bee vision continues to improve. However, I cannot discuss any of these more recent studies with reference to optic flow. Anyway, just because they’re old doesn’t make the experiments any less elegant or interesting 🙂

 

The waggle dance

Ask a non-beekeeper what they know about bees and you’ll probably get answers that involve honey or stings.

Press them a little bit more about what they know about other than honey and stings and some will mention the ‘waggle dance’. 

Karl von Frisch

That the waggle dance is such a well-known feature of honey bee biology is probably explained by two (related) things; it involves a relatively complex form of communication in a non-human animal, and because Karl von Frisch – the scientist who decoded the waggle dance – received the Nobel Prize 1 for his studies in 1973.

Von Frisch did not discover the waggle dance. Nicholas Unhoch described the dance at least a century before Von Frisch decoded the movement, and Ernst Spitzner – 35 years earlier still – observed dancing bees and suggested they were communicating odours of food resources available in the environment.

Inevitably, Aristotle also made a contribution. He described flower constancy 2 and suggested that foragers could communicate this to other bees.

Language and communication are important. The development of language in early humans almost certainly contributed to the evolution of our culture, society and technology. Communication in non-human animals, from the chirping of grasshoppers to the singing of whales, is of interest to scientists and non-scientists alike.

It is therefore unsurprising that the ‘dance language’ of honey bees is also of great interest. Although not a ‘language’ in the true sense of the word, Von Frisch described the symbolic language of bees as “the most astounding example of non-primate communication that we know” over 50 years ago. This still applies.

The waggle dance

The waggle dance usually takes place in the dark on the vertical face of a comb in the brood nest, usually close to the nest entrance. The dance is performed by a successful forager i.e. one that has located a good source of pollen, nectar or water, and provides information on the presence, the quality, identity, direction and distance of the source, so enabling nest-mates to find and exploit it.

The dance consists of two phases:

  1. The figure of eight-shaped ‘return phase’ in which the bee circles back, alternately clockwise and anticlockwise, to the start of …
  2. The ‘waggle phase’, which is a short linear run in which the dancer vigorously waggles her abdomen from side to side.

The direction of the food source is indicated by the angle of the waggle phase from gravity i.e. a vertical line down the face of the comb. This angle (α in the figure below) indicates the bearing from the direction of the sun that needs to be followed to reach the food source. 

For example, if the dancer performs a waggle phase vertically down the face of the comb, the food source must be opposite the current position of the sun.

The waggle dance

The distance information is conveyed by the duration of the waggle phase. The longer this run is, the more distant the source. A run of 1 second duration indicates the food source is about 1 kilometre away.

The quality of the food source is indicated by the vigour of the waggling during the waggle phase and the speed with which the return phase is conducted. 

Surely it can’t be that simple?

Yes, it can.

What I’ve described above allows you to interpret the waggle dance sufficiently well to know where your bees are foraging.

Next time you lift a frame from a hive and see a dancing bee, circling around in a little cleared ‘dance floor’ surrounded by a group of attentive workers, try and decode the dance.

Remember that the dance is performed with relation to gravity in the darkened hive. You’re looking to identify the angle from a vertical line up the face of the brood comb to determine the direction from the sun.

Time a few waggle phases (one elephant, two elephants etc.) and you’ll know how far away the food source is.

Really, it’s that simple?

Of course not 😉

The waggle dance was decoded more than half a century ago and remains an active subject for researchers interested in animal communication.

What you’ll miss in your observations is an indication of the type of nectar or pollen resource that the dancing bee is communicating. The dancing worker carries the odour of the food source and may also regurgitate nectar, presumably helping those ‘watching’ (remember, it’s dark … nothing to see here!) determine the type of resource to look for when they leave the hive.

You will also be unable to detect the pulsed thoracic vibrations that the dancing bee produces. These are also indicators of the quality of the food source; better (e.g. higher sucrose content) resources elicit increased pulse duration, velocity amplitude and duty cycle, though the number of pulses is related to the duration of the waggle phase, and so is another potential indicator of distance.

Inevitably, there are also pheromones involved.

There always are 😉

The dancing bee produces two alkanes, tricosane and pentacosane, and two alkenes, Z-(9)-tricosene and Z-(9)-pentacosene. These appear to stimulate foraging activity 3.

But it’s cloudy … or rain stops play … or nighttime

What happens to dancing bees if foraging is interrupted, for example by poor weather or night? 

The dancing bee continues to change the angle of the waggle phase as the sun moves across the sky. This means that a dancing bee will correctly signal the direction to the food source, even if they have not left the hive for several hours.

During their initial orientation flights they learn the sun’s azimuth as a function of the time of day, and use this to compensate for the sun’s time-dependent movement.

Some bees even dance during the night, in which case the watching workers must presumably make their own compensations for the time that has elapsed since the dance 4.

And what happens if the sun is obscured … by clouds, or buildings or dense woodland? How can those directions be followed?

Under these circumstances the foraging bee detects the position of the sun by the pattern of polarised light in the sky. 

Scout bees

The waggle dance is also performed by scout bees on the surface of a bivouacked swarm. In this instance it is used to communicate the quality, direction and distance of a new potential nest site. 

Swarm of bees

Swarm of bees

The intended audience in this instance are other scout bees, rather than the general forager population 5. These scouts use a quorum decision making process to determine the ‘best’ nest site in the area to which the bivouacked swarm eventually relocates.

The shape of the bivouac often lacks a true vertical surface. However, since it’s in the open the dancing bees can orientate the waggle run directly with relation to the sun’s direction, rather than to gravity.

Under experimental conditions the dancing bee can communicate the presence and quality of a food source on a horizontal comb, but – with no reference to gravity – all directional information is lost 6.

The round dance

The duration of the waggle phase is related to the distance from the nest to the food source. Therefore the recognisable waggle dance tends to get difficult to interpret for sources very close to the nest.

It used to be thought that there was a distinct directionless dance (the ’round dance’) for these nearby i.e. 10-40 metres, food sources. However, more recent study 7 suggests that dancers were able to convey both distance and direction information irrespective of the separation of nest and food source. This indicates that bees have just one type of dance for forager recruitment, the waggle dance.

Do all bees communicate using a waggle dance?

There are a very large number of bee species. In the UK alone there are 270 species, 250 of which are solitary.

There’s a clue.

Solitary bees are like me at a disco … they have no one to dance with 🙁

I’ll cut to the chase to help you erase that vision.

The only bees that use the waggle dance are honey bees. These all belong to the genus Apis.

They include our honey bee, the western honey bee (Apis mellifera), together with a further seven species:

  1. Black dwarf honey bee (Apis andreniformis)
  2. Red dwarf honey bee (Apis florea)
  3. Giant honey bee (Apis dorsata)
  4. Himalayan giant honey bee (Apis laboriosa
  5. Eastern honey bee (Apis cerana)
  6. Koschevnikov’s honey bee (Apis koschevnikovi)
  7. Philippine honey bee (Apis nigrocincta)

Dancing and evolution

Dwarf honey bees nest in the open on a branch and dance on the horizontal surface of the nest. The waggle run is orientated ‘towards’ the food source. Apis dorsata is also an open-nesting bee, but forms large vertically-hanging combs. It dances relative to gravity, and indicates the direction by the angle of the waggle run in the same way that A. mellifera does.

The cavity nesting bees, A. cerana, A. mellifera, A. koschevnikovi, and A. nigrocinta produce the most developed form of the dance.

The dances of A. mellifera and A. cerana are sufficiently similar that they can follow and decode the dance of the other.

The complexity of the nest site and the waggle dance reflects the evolution of these bee species. The earliest to evolve (i.e. the most primitive), A. andreniformis and florea, have the simplest nests and the most basic waggle dance. In contrast, the cavity nesting species evolved most recently, form the most complex brood nests and have the most derived waggle dance.

When and why did the waggle dance evolve?

Assuming that the waggle dance did not independently evolve (there’s no evidence it did, and ample evidence due to its similarity between species that it evolved only once) it must have first appeared at least 20 million years ago, when extant honey bee species diverged during the early Miocene.

The ‘why’ it evolved is a bit more difficult to address.

Behavioural changes often arise in response to the environment in which a species evolves.

Bipedalism in non-human primates (like the australopithecines) is hypothesised to have evolved in part due to a reduction in forest cover and the increase in savannah. Apes had to walk further between clumps of trees and bipedalism offered greater travel efficiency.

Perhaps the waggle dance evolved to exploit a particular type or distribution of food reserves?

In this regard it is interesting that the ‘benefit’ of waggle dance communication varies through the season.

If you turn a hive on its side the combs are horizontal 8. Under these conditions the dancing bees can communicate the presence and quality of a food source. However, they cannot communicate its location (either direction or distance).

No directional or distance information is now available

In landmark studies Sherman and Visscher 9 showed that, at certain periods during the season, the absence of this positional information did not affect the weight gain by the hive i.e. the foraging efficiency of the colony.

They concluded that during these periods forage must be sufficiently abundant that simply stimulating foraging was sufficient. Remember those alkanes and alkenes produced by dancing bees that do exactly that?

Tropical habitats

This observation, and some elegant experimental and modelling studies, suggest that dancing is beneficial when food resources are: 

  • sparsely distributed – therefore difficult (and energetically unfavourable) to find by individual scouting
  • clustered or short-lived resources – when it’s gone, it’s gone
  • distributed with high species richness – if there’s a huge range of flowers, which are the most energetically rewarding (sugar-rich) to collect nectar from?

One of the experimental studies that contributed to these conclusions (though there’s still controversy in this area) was the demonstration that waggle dancing was beneficial in a tropical habitat, but not in two temperate habitats. This makes sense, as food resources have different spatiotemporal distribution in these habitats. Tropical habitats are characterised by clustered and short-lived resources.

Therefore the suggestion is that the waggle dance of Apis species evolved, presumable early in the speciation of the genus, in a tropical region where food resources were patchily distributed, available for only limited period and present alongside a wide variety of other (less good) choices.

For example, like individual trees flowering in a forest …

Finally, it’s worth noting that there is evidence that bees that dance are able to successfully exploit food resources further away than would otherwise be expected from their body size.

This also makes sense.

It’s much less risky flying off over the horizon if you know there’s something to collect once you get there 10.


Notes

If you arrived here from my Twitter feed (@The_Apiarist) you’ll have seen the tweet started with the words “Dance like nobody’s watching”, words that are often attributed to Mark Twain. 

The full quote is something like “Dance like nobody’s watching; love like you’ve never been hurt. Sing like nobody’s listening; live like it’s heaven on earth”.

Pretty sound advice.

But it’s not by Mark Twain. It’s actually from a country music song by Susanna Clark and Richard Leigh. This was first released on the Don Williams album Traces in 1987. So only about 90 years out 😉 

OA Q&A

The post last week on the preparation of oxalic acid (OA; the active ingredient in the commercially available and VMD approved product Api-Bioxal) generated a slew questions. Inevitably, some of these drifted off topic … at least as far as the specific content of the post was concerned.

This partly reflects the deficiency of a weekly blog as a means of communicating.

It may also reflect the inadequacy of the indexing system 1.

Comprehensive coverage of subject, and peripherally related topics, would require a post so long that most readers 2 would give up halfway through.

And it would take so long to write that the weekly post format would have to be abandoned.

The resulting magnum opus would be a masterpiece of bad punctuation, littered with poor puns and would leave me nothing to write the following week …

This week I’ve attempted to address a series of oxalic acid-related points that should have been mentioned before, that I’ve received questions about, or I think justify a question (and answer).

Should I trickle treat or vaporise?

One of the key features of approved miticides is that, used according to the instructions and at the appropriate time, they are very effective.

Conversely, use them incorrectly or at the wrong time and they will be, at best, pretty hopeless.

In the case of OA, both trickle treating (dribbling) or vaporisation (sublimation) can achieve 90% or more reduction in the levels of phoretic mites.

Therefore, the choice between them is not on the grounds of efficacy but should be on their ease of us, convenience, safety or other factors.

Trickle treating is fast, requires a minimum amount of specialised equipment and only limited PPE (personal protection equipment).

I’d strongly recommend using a Trickle 2 bottle from Thorne’s to administer the solution. It is infinitely better than a syringe, which requires the use of at least two hands.

If you hold the crownboard up at an angle with one hand you can administer the OA solution using the other. Wear gloves and your bee suit. It takes as long to read as it does to do.

With a Trickle 2 bottle and some pre-warmed OA-containing solution it should be possible to open, treat and close a colony in well under two minutes. Like this …

On a cold day very few bees will be disturbed. The OA will dribble down through the clustered colony and the mites will get what they deserve 🙂

Temperature and treatment choice

It’s usually the temperature that determines whether I trickle or vaporise. I prefer to trickle when the colony is clustered, but would usually treat by sublimation on a warmer day.

At what temperature does cold become warm? About 8-9°C … i.e. about the temperature at which the bees start to cluster.

Partly this is to reduce the number of bees that might be disturbed – I can vaporise a colony without opening the box.

However, my crashingly unscientific opinion – based entirely on gut feeling and guesswork 3 – is that the OA vapour perfuses through loose clusters  better, whereas the solution is more likely to come into contact with the mites when dribbling down through the cluster.

I have no data to support this – don’t say you weren’t warned!

Through choice I’d not treat (unless I had to) if the temperature was much below 3-4°C. The bees get rapidly chilled should something goes wrong – you drop the bottle, get a bee in your veil or whatever.

Single use ...

Caramel coated Sublimox vaporiser pan

Of course, if you haven’t got a vaporiser your choice is limited to trickle treating. Likewise, if you don’t enjoy scouring caramelised glucose from the pan of your vaporiser you should probably stick to trickling Api-Bioxal solution.

The only additional thing to consider is whether there’s brood present in the hive – I discuss this in more detail below.

How can I use a vaporiser and an Abelo poly floor?

I use a lot of Abelo poly hives. Mine are all the ‘old design‘ with the floor that features a long landing board and an ill-fitting Varroa tray. The new ones don’t look fundamentally different from the website 4.

Abelo poly National hives ...

Abelo poly National hives …

My storage shed has a shoulder-high stack of unused Abelo floors as I prefer my own homemade ‘kewl’ floors.

However, inevitably some Abelo floors get pressed into use during the season and – through idleness, disorganisation and a global virus pandemic – remain in use during the winter 🙁

I’ve now worked out how to vaporise colonies using these floors. Please remember, my vaporiser is a Sublimox which has a brass (?) nozzle through which the vapour is expelled. The nozzle gets very hot and melts polystyrene.

Don’t ask me how I know 🙁

The underside of the open mesh floor can be sealed by inverting the Varroa tray and wedging a block of foam underneath at the back. I didn’t think this would work until I tried it, and was pleasantly impressed.

Abelo poly floor set up for OA vaporisation

This is important as it significantly reduces the loss of OA vapour. Any vapour that escapes is OA that will not be killing mites.

The Sublimox can be simultaneously inserted and inverted through the front entrance. This takes some deft ‘wrist action’ but results in minimal loss of OA vapour.

To protect the poly I use a piece of cardboard. You simply rest the nozzle on this.

As soon as the vaporiser is removed the bees will start to come out, so use the cardboard to block the entrance for a few minutes, by which time they will have settled.

No expense spared cardboard ‘protector’ for poly floor

The gaffer tape in the photo above is sealing the ventilation holes in the entrance block, again keeping valuable OA vapour inside the hive.

And on a related point …

My favoured nuc is the Everynuc. This is a Langstroth-sized box with a removable floor and an integral feeder that more-or-less converts the box to take National frames. It’s well-insulated, robust, easy to paint and – in my view – a more flexible design that the all-in-one single moulded boxes (like the offering from Maisemores).

However, the entrance of the Everynuc is too big.

Everynuc entrance

Open wide …

The disadvantage of this is that a DIY entrance reducer is needed if the nuc is weak and at risk from robbing.

Conversely, the large entrance and short (~2cm) “landing board” is preferable during OA vaporisation. I carry a nuc-width strip of wood, 2 cm thick, with a central 7 mm hole.

With this balanced on the landing board, the vaporiser can be inserted and inverted without loss of vapour or risk of melting the poly. It’s a quick and dirty fix that I discovered several years ago and have never got round to improving.

How do I know if the colony is broodless?

Oxalic acid is a single-use treatment, remaining active in the hive for significantly less time than a brood cycle (see mite counts below). Therefore, the ‘appropriate time’ to use it is when the colony is broodless.

An additional consideration is that open brood is very sensitive and responds unfavourably to a warm acid bath in OA i.e. it dies 5.

In contrast, sealed brood is impervious to OA vapour or solution.

So, how can you tell if the colony is broodless or not?

The easiest way to determine whether the colony has sealed brood is – on a slightly better day – to open the box and have a look.

Done quickly and calmly I suspect this is more distressing for the beekeeper than it is for the colony. You think the bees will be aggressive or distressed. In reality they’re usually pretty lethargic and often very few fly at all.

You only need to look at the frame in the centre of the cluster. If there’s brood present it will be where the bees are most concentrated. You will probably well see the queen nearby.

Gently, gently, quicky peeky

Remove the roof and insulation and lift one corner of the crownboard. Give them a gentle puff of smoke under the crownboard 6. Wait 30 seconds or so and gently remove the crownboard.

There will be bees on the underside of the crownboard. Stand it carefully to the side out of the breeze. The bees will probably crawl to the upper edge, remember to shake them off into the hive rather than crush them when you place it back on the hive.

The colony is likely to be clustered if the weather is 8°C or cooler. Remove the outer frame furthest from the cluster. If it’s late autumn or early winter this should still be heavy with stores. Here’s one I pulled out last week.

Outer frame from a colony in early winter

Now you have space to work. Viewed from above the cluster will often be spread over several frames and shaped approximately like a rugby ball.

In the hive shown above they occupied the front five seams 7 with a few stragglers between frames 6 and 7.

Early winter cluster

I used my hive tool between frames 3 and 4 to split the colony, just levering them a centimetre or so apart, so I could then separate frame 3 from 2 and lift it out.

The queen was on the far side of frame 3.

It looks like magic to inexperienced beekeepers, but it really isn’t …

The top of the frame was filled with sealed stores, the lower part of the frame was almost full of uncapped stores.

There was no sealed brood and no eggs or larvae that I could see 8. An adjacent hive looked very similar. Again, the queen was on the reverse side of the first frame I checked. The bees were barely disturbed. Almost none flew and the boxes were carefully sealed up again.

No brood, so ready to treat 🙂

Can I determine if there’s brood present without opening the hive?

Possibly.

You should be able to tell if brood is emerging by the appearance of the characteristic biscuit-coloured wax crumbs on the Varroa tray.

Think digestive rather than Fox’s Party Rings

Not this colour of biscuit

To see this evidence you need to start with a clean Varroa tray. In addition, the underside of the open mesh floor must be sufficiently draught-free that the cappings aren’t blown around, or accessible to slugs.

Cleaned Varroa tray

Remember that there might be only a very small amount of brood emerging. They may also be uncapping stores (which will have much paler cappings).

Leave the tray in place for a few days and check for darker stripes of crumbs/cappings under the centre of the cluster.

Biscuit-coloured cappings on Varroa tray

Note that the photograph above was taken in mid-February. A late autumn colony would almost certainly have significantly less brood cappings present on the tray. The brood cappings are the two and a bit distinct horizontal stripes concentrated just above centre. The stores cappings are the white crumbs forming the just discernible stripes the full width of the tray.

You cannot use this method to infer anything about whether there’s unsealed brood present. At least, not with any certainty. If, in successive weeks, the amount of brood cappings increases there’s almost certainly unsealed brood present. Conversely, if brood cappings are reducing there may not be unsealed brood if the queen is just shutting down.

While you’re staring at the tray …

Look for Varroa.

It’s useful to have an idea of the mite drop in the few days before OA treatment.

If it’s high then treatment is clearly needed.

If it’s low (1-2 per day) you have a useful baseline to compare the number that fall after treatment.

You may well be surprised (or perhaps disappointed) at the number that appear from a colony that has already had an autumn treatment.

It’s worth remembering that 9 there will be more mites present in the winter if you treated early enough in the autumn to protect the winter bees (blue line).

Mite numbers after early and late autumn treatment

Conversely, if you get little or no mite drop with an OA treatment in the winter it indicates the  bees have not been rearing brood in the intervening period. That means the diutinus winter bees were reared before or during the last treatment, meaning they will have been exposed to high mite levels (red line).

This is not a good thing™.

In my experience the daily mite drop is highest 24-48 hours after treatment. I usually try and monitor it over 5-7 days by which time the drop has reached a basal level, presumably because the OA has disappeared or stopped being effective.

Finally, the ambient temperature has an influence on the Varroa drop. I’ll write about this sometime in the future, but it’s worth looking out for.


 

Oxalic acid (Api Bioxal) preparation

This post updates and replaces one published three years ago (which has now been archived). The registered readership of this site has increased >200% since then and so it will be new to the majority of visitors.

It’s also particularly timely.

I will be treating my own colonies with oxalic acid in the next week or so.

Mites and viruses

Varroa levels in the hive must be controlled for successful overwintering of colonies. If you do not control the mites – and by ‘control’ I mean slaughter 😉 – the viruses they transmit to the overwintering bees will limit the chances of the colony surviving.

The most important virus transmitted by Varroa is deformed wing virus (DWV). At high levels, DWV reduces the lifespan of worker bees.

This is irrelevant in late May – there are huge numbers of workers and they’re only going to live for about 6 weeks anyway.

In contrast, reduced longevity is very significant in the winter where more limited numbers of overwintering bees must survive for months to maintain the colony through to the Spring. If these bees die early (e.g. in weeks, not months), the colony will dwindle to a pathetic little cluster and likely freeze to death on a cold winter night.

Game over. You are now an ex-beekeeper 🙁

To protect the overwintering bees you must reduce mite levels in late summer by applying an appropriate miticide. I’ve discussed this at length previously in When to treat? – the most-read post on this site.

I’d argue that the timing of this late summer treatment is the most important decision about Varroa control that a beekeeper has to make.

However, although the time for that decision is now long-gone, there are still important opportunities for mite control in the coming weeks.

In the bleak midwinter

Miticides are not 100% effective. A proportion of the mites will survive this late summer treatment 1. It’s a percentages game, and the maximum percentage you can hope to kill is 90-95%.

If left unchecked, the surviving mites will replicate in the reducing brood reared between October and the beginning of the following year. That means that your colony will potentially contain more mites in January than it did at the end of the late summer treatment.

Mid September

Late summer mite treatment and no midwinter treatment.

Over several years this is a recipe for disaster. The graph above shows modelled data that indicates the consequences of only treating in late summer. Look at the mite levels (in red, right hand vertical axis) that increase year upon year.

The National Bee Unit states that if mite levels exceed 1000 then immediate treatment is needed to protect the colony. In the modelled data above that’s in the second year 2.

In contrast, here is what happens when you also treat in “midwinter” (I’ll discuss what “midwinter” means shortly).

Two optimal treatments

Two optimal treatments

Mite numbers remain below 1000. This is what you are aiming for.

For the moment ignore the specific timing of the treatment – midwinter, late December etc.

Instead concentrate on the principle that determines when the second treatment should be applied.

During the winter the colony is likely to go through a broodless period 3.

When broodless all the mites in the colony must, by definition, be phoretic.

There’s no brood, so any mites in the colony must be riding around on the backs of workers.

A phoretic mite is an easy mite to kill 4.

A “midwinter” double whammy

A single oxalic acid based treatment applied during the winter broodless period is an ideal way to minimise the mite levels before the start of the following season.

Oxalic acid is easy to administer, relatively inexpensive and well-tolerated by the bees.

The combination – a double whammy – of a late summer treatment with an appropriate miticide and a “midwinter” treatment with oxalic acid should be all that is needed to control mites for the entire season.

However, “midwinter” does not mean midwinter, or shouldn’t.

Historically, winter mite treatments were applied between Christmas and New Year. It’s a convenient time of the year, most beekeepers are on holiday and it’s a good excuse to avoid spending the afternoon scoffing mince pies in front of the TV.

Or with the outlaws inlaws 😉

But by that time of year many colonies will have started brooding again.

With sealed brood, mites have somewhere to hide, so the treatment will be less effective than it might otherwise have been 5.

Why go to all the trouble of treating if it’s going to be less effective than it could be?

The key point is not the timing … it’s the broodlessness of the colony.

If the colony is broodless then it’s an appropriate time to treat. My Fife colonies were broodless this year by mid-October. This is earlier than previous seasons where I usually have waited until the first protracted cold period in the winter – typically the last week in November until the first week in December.

If they remain broodless this week I’ll be treating them. There’s nothing to be gained by waiting.

Oxalic acid (OA) treatment options

In the UK there are several approved oxalic acid-containing treatments. The only one I have experience of is Api-Bioxal, so that’s the only one I’ll discuss.

I also give an overview of the historical method of preparing oxalic acid as it has a bearing on the amount of Api-Bioxal used and will help you (and me) understand the maths.

OA can be delivered by vaporisation (sublimation), or by tricking (dribbling) or spraying a solution of the chemical.

I’ve discussed vaporisation before so won’t rehash things again here.

Trickling has a lot to commend it. It is easy to do, very quick 6 and requires almost no specialised equipment, either for delivery or personal protection (safety).

Trickling is what I always recommend for beginners. It’s what I did for years and is a method I still regularly use.

The process for trickling is very straightforward. You simply trickle a specific strength oxalic acid solution in thin syrup over the bees in the hive.

Beekeepers have used oxalic acid for years as a ‘hive cleaner’, as recommended by the BBKA and a range of other official and semi-official organisations. All that changed when Api-Bioxal was licensed for use by the Veterinary Medicines Directorate (VMD).

Oxalic acid and Api-Bioxal, the same but different

Api-Bioxal is the VMD-approved powdered oxalic acid-containing miticide. It is widely available, relatively inexpensive (when compared to other VMD-approved miticides) and very easy to use.

Spot the difference ...

Spot the difference …

It’s very expensive when compared to oxalic acid purchased in bulk.

Both work equally well as both contain exactly the same active ingredient.

Oxalic acid.

Api-Bioxal has other stuff in it (meaning the oxalic acid content is a fraction below 90% by weight) and these additives make it much less suitable for sublimation. I’ll return to these additives in a minute or two. These additives make the maths a bit more tricky when preparing small volumes at the correct concentration – this is the purpose of this post.

How much and how strong?

To trickle or dribble oxalic acid-containing solutions you’ll need to prepare it at home, store it appropriately and administer it correctly.

I’ve dealt with how to administer OA by trickling previously. This is all about preparation and storage.

The how much is easy.

You’ll need 5ml of oxalic acid-containing solution per seam of bees. In cold weather the colony will be reasonably well clustered and its likely there will be a maximum of no more than 8 or 9 seams of bees, even in a very strong colony.

Hold on … what’s a seam of bees?

Three seams of bees

Looking down on the colony from above, a seam of bees is the row visible between the top bars of the frames.

So, for every hive you need 5ml per seam, perhaps 45ml in total … with an extra 10% to cover inevitable spillages. It’s not that expensive, so don’t risk running out.

And the strength?

The recommended concentration to use oxalic acid at in the UK has – for many years – been 3.2% w/v (weight per volume) in 1:1 syrup. This is less concentrated than is recommended in continental Europe (see comments below on Api-Bioxal).

My advice 7 – as it’s the only concentration I’ve used – is to stick to 3.2%.

Calculators at the ready!

The oxalic acid in Api Bioxal is actually oxalic acid dihydrate. Almost all the powdered oxalic acid you can buy is oxalic acid dihydrate.

The molecular formula of oxalic acid is C2H2O4. This has a molecular weight of 90.03. The dihydrated form of oxalic acid has the formula C2H2O4.2H2O 8 which has a molecular weight of 126.07.

Therefore, in one gram of oxalic acid dihydrate powder (NOT Api Bioxal … I’ll get to Api Bioxal in a minute! Have patience Grasshopper) there is:

90.03/126.07 = 0.714 g of oxalic acid.

Therefore, to make up a 3.2% oxalic acid solution in 1:1 syrup you need to use the following recipe, or scale it up as needed.

  • 100 g tap water
  • 100 g white granulated sugar
  • Mix well
  • 7.5 g of oxalic acid dihydrate

The final volume will be 167 ml i.e. sufficient to treat over 30 seams of bees, or between 3 and 4 strong colonies (including the 10% ‘just in case’).

The final concentration is 3.2% w/v oxalic acid

(7.5 * 0.714)/167 * 100 = 3.2% 9.

Check my maths 😉

Recipe to prepare Api-Bioxal solution for trickling

Warning – the recipe on the side of a packet of Api-Bioxal makes up a much stronger solution of oxalic acid than has historically been used in the UK. Stronger isn’t necessarily better. The recipe provided is 35 g Api-Bioxal to 500 ml of 1:1 syrup. By my calculations this recipe makes sufficient solution at a concentration of 4.4% w/v to treat 11 hives. 

There’s an additional complication when preparing an Api-Bioxal solution for trickling. This is because Api-Bioxal contains two additional ingredients – glucose and powdered silica. These cutting agents account for 11.4% of the weight of the Api-Bioxal. The remaining 88.6% is oxalic acid dihydrate.

Using the same logic as above, 1g of Api-Bioxal therefore contains:

(90.03/126.07) * 0.886 = 0.633 g of oxalic acid.

Therefore, to make up 167 ml of a 3.2% Api-Bioxal solution you need to use the following recipe, or scale up/down appropriately:

  • 100 g tap water
  • 100 g white granulated sugar
  • Mix well
  • 8.46 g of Api-Bioxal

Again, check my maths … you need to add (7.5 / 0.886 = 8.46) grams of Api-Bioxal as only 88.6% of the Api-Bioxal is oxalic acid dihydrate.

Scaling up and down

8.46 g is not straightforward to weigh – though see below – and 167 ml may be too much for the number of hives you have. Here’s a handy table showing the amounts of Api-Bioxal to add to 1:1 syrup to make up the amount required.

Api-Bioxal recipes for 3.2% trickling in 1:1 syrup

The Api-Bioxal powder weights shown in bold represent the three packet sizes that can be purchased.

I don’t indicate the amounts of sugar and water to mix to make the syrup up. I’ll leave that as an exercise for the reader … remember that 100 g of sugar and 100 ml of water make 167 ml of 1:1 (w/v) syrup.

Weighing small amounts of Api-Bioxal

The amount of Api-Bioxal used is important. A few grams here or there matter.

If you are making the mix up for a limited number of hives you will have to weigh just a few grams of Api-Bioxal. You cannot do this on standard digital kitchen scales which work in 5 g increments.

Buy a set of these instead.

Digital scales … perfect for Api-Bioxal (and yeast)

These cost about a tenner and are perfect to weigh out small amounts 10 of Api-Bioxal … or yeast for making pizza dough.

A few words of caution

I don’t want to spoil your fun but please remember to take care when handling or using oxalic acid, either as a powder or when made up as a solution.

Oxalic acid is toxic

  • The lethal dose for humans is reported to be between 15 and 30 g. It causes kidney failure due to precipitation of solid calcium oxalate.
  • Clean up spills of powder or solution immediately.
  • Take care not to inhale the powder.
  • Store in a clearly labelled container out of reach of children.
  • Wear gloves.
  • Do not use containers or utensils you use for food preparation. A well rinsed plastic milk bottle, very clearly labelled, is a good way to store the solution prior to use.

Storage

Storage of oxalic acid syrup at ambient temperatures rapidly results in the acid-mediated breakdown of sugars (particularly fructose) to generate hydroxymethylfurfural (HMF). As this happens the colour of the oxalic acid-containing solution darkens significantly.

This breakdown happens whether you use oxalic acid or Api-Bioxal.

Stored OA solution and colour change

Stored OA solution and colour change …

HMF is toxic to honey bees at high concentrations. Studies from ~40 years ago showed that HMF concentrations below 30 mg/l were safe, but above 150 mg/l were toxic 11.

At 15°C HMF levels in OA solution can reach 150 mg/l in a little over a week. At room temperature this happens much faster, with HMF levels exceeding 150 mg/l in only 2-3 days. In the dark HMF levels build up slightly less quickly … but only slightly 12.

Therefore only make up OA solutions when you need them.

If you must store your oxalic acid-containing syrup for any length of time it should be in the fridge (4°C). Under these conditions HMF levels should remain well below toxic levels for at least one year. However, don’t store it for this long … use it and discard the excess.

Or prepare excess and share it with colleagues in your beekeeping association.

Don’t use discoloured oxalic acid solutions as they’ve been stored incorrectly and may well harm your bees.

Another final few words of caution

I assume you don’t have a fridge dedicated to beekeeping? That being the case please ensure that the bottle containing stored oxalic acid is labelled clearly and kept well out of the reach of children.


Notes

A quick trawl through the Veterinary Medicines Directorate database turns up several oxalic acid-containing solutions for managing Varroa. These include:

  • Oxuvar – approved for trickling or spraying, an aqueous solution of oxalic acid to which you add glucose if you intend to use it for trickling.
  • Oxybee – approved for trickling (and possibly other routes, but the paperwork was a minefield!), contains oxalic acid, glycerol and essential oils and is promoted as having a long shelf life.
  • VarroMed – approved for trickling, contains oxalic acid and formic acid and can be used throughout the year in one way or another.

I’ve not read the documentation provided with these and so don’t know the precise concentration of oxalic acid they contain. It will be listed as an active ingredient. I have not used these products. As with everything else on this site, I only write about methods or products I am familiar with. I therefore cannot comment on their relative efficacy compared to Api-Bioxal, to Apivar or to careful siting of your hives in relation to ley lines … or 5G phone masts.

 

Smell the fear

With Halloween just around the corner it seemed appropriate to have a fear-themed post.

How do frightened – or even apprehensive – people respond to bees?

And how do bees respond to them?

Melissophobia is the fear of bees. Like the synonym apiphobia, the word is not in the dictionary 1 but is a straightforward compounding of the Greek μέλισσα or Latin apis (both meaning honey bee) and phobos for fear.

Melissophobia is a real psychiatric diagnosis. Although people who start beekeeping are probably not melissophobic, they are often very apprehensive when they first open a colony.

If things go well this apprehension disappears, immediately or over time as their experience increases.

If things go badly they might develop melissophobia and stop beekeeping altogether.

Even relatively experienced beekeepers may be apprehensive when inspecting a very defensive colony. As I have discussed elsewhere, there are certain times during the season when colonies can become defensive. These include when queenless, during lousy weather or when a strong nectar flow ends.

In addition, some colonies are naturally more defensive than others.

Some could even be considered aggressive, making unprovoked attacks as you approach the hive.

A defensive response is understandable if the colony is being threatened. Evolution over eons will have led to acquisition of appropriate responses to dissuade natural predators such as bears and honey badgers.

I’m always careful (and possibly a little bit apprehensive) when looking closely at a completely unknown colony – such as these hives discovered when walking in the Andalucian hills.

If Carlsberg did apiaries ...

Apiary in Andalucia

How do bees detect things – like beekeepers or bears – that they might need to mount a defensive response against?

Ignore the bear

Bees have four senses; sight, smell, touch and taste. Of these, I’ve briefly discussed sight previously and they clearly don’t touch or taste an approaching bear 2 … so I’ll focus on smell.

Could they use smell to detect the scent of an approaching human or bear that is apprehensive of being stung badly?

Let’s forget the grizzly bear 3 for now. At over 200 kg and standing 2+ metres tall I doubt they’re afraid of anything.

Let’s instead consider the apprehensive beekeeper.

Do bees respond to the smell of a frightened human (beekeeper or civilian)?

This might seem a simple question, but it raises some interesting additional questions.

  • Is there a scent of fear in humans?
  • Can bees detect this smell?
  • Have bees evolved to generate defensive responses to this or similar smells?

If two beekeepers inspect the same colony and one considers them aggressive and the other does not, is that due to the beekeepers ‘smelling’ different?

I don’t know the answers to some of these questions, but it’s an interesting topic to think about the stimuli that bees have evolved to respond to.

The scent of fear

This is the easy bit.

Is there a distinctive scent associated with fear in humans?

The Scream by Edvard Munch (1895 pastel version)

Using some rather unpleasant psychological testing researchers have determined that there is a smell produced in sweat secretions that is associated with fear. Interestingly, the smell alone appears not to be detectable. The female subjects tested 4 were unable to consciously discriminate the smell from a control neutral odour.

However, the ‘fear pheromone’ alone caused changes in facial expression associated with fright and markedly reinforced responses to visual stimuli that induced fear.

Females could respond to the fear pheromone produced by males (and vice versa) and earlier MRI studies (involving significantly less unpleasant experiments) had shown that this smell was alone able to induce changes in the amygdala, the region in the brain associated with emotional processing.

So, there is a scent of fear in humans. We can’t consciously detect it, but that doesn’t make it any less real.

Can bees detect it?

Can bees smell the scent of fear?

This is where things get a lot less certain.

I’m not aware that there have been any studies on whether bees can definitively identify the fear pheromone produced by humans.

To conduct this study in a scientifically-controlled manner you would need to know precisely what the pheromone was. It would then be tested in parallel with one or several irrelevant, neutral or related (but different) compounds. In each instance you would have to identify a response in the bee that indicated the fear pheromone had been detected.

All of which is not possible as we don’t definitely know what the fear pheromone is chemically.

We do know it’s present in the sweat of frightened humans … but that’s about it. This makes the experiment tricky. Comparisons would also have to be made with sweat secretions present in the same 5 human when not frightened.

And what response would you look for? Usually bees are trained to respond in a proboscis extension test. In this a bee extends its proboscis in response to a recognised smell or taste.

But, as none of this has been done, there’s little point in speculating further.

So let’s ask the question the other way round.

Would bees be expected to smell the scent of fear?

Smell is very significant to bees.

They have an extremely sensitive sense of smell, reflected in their ability to detect certain molecules as dilute as one or two parts per trillion. Since many people struggle with visualising what that means it’s like detecting a grain of salt in an Olympic swimming pool 6.

Part of the reason we know that smell is so important to bees is because evolution has provided them with a very large number of odorant receptors.

Odorant receptors are the proteins that detect smells. They bind to chemical molecules from the ‘smell’ and these trigger a cellular response of some kind 7. Different odorant receptors have different specificities, binding and responding to the molecules that are present in one or more odours.

Odorant receptor diversity and sensitivity

Bees have 170 odorant receptors, more than three times the number in fruit flies, and double that in mosquitoes. Smell is clearly very important to bees 8.

This is perhaps not surprising when you consider the role of odours within the hive. These include the queen and brood pheromones and the chemicals used for kin recognition 9.

In addition, bees are able to find and use a very wide range of plants as sources of pollen and nectar and smell is likely to contribute to this in many ways.

Finally, we know that bees can detect and respond to a wide range of other smells. Even those present at very low levels which they may not have been exposed to previously. For example Graham Turnbull and his research team in St Andrews, in collaborative studies with Croatian beekeepers, are training bees to detect landmines 10 from the faintest ‘whiff’ of TNT they produce. This deserves a post of its own.

So, while we don’t know that bees could detect a fear pheromone, there’s a good chance that they should be able to.

Evolution of defensive responses

We’re back to some rather vague arm waving here I’m afraid.

In a rather self-fulfilling manner we don’t know if bees have evolved a defensive response to the fear pheromone of humans as – for reasons elaborated above – we don’t actually know whether they do respond to the fear pheromone.

We could again ask this question in a slightly different way.

Might bees be expected to have evolved a defensive response to the fear pheromone?

Long before we developed the poly nuc or the fiendishly clever Flow Hive, humans have been attracted by honey and have exploited bees to harvest it.

The ancient Egyptians kept bees in managed hives over 5000 years ago.

However, we can be reasonably certain that humans provided suitable nesting sites (which we’d now call bait hives) to attract swarms from wild colonies well before that.

But we’ve exploited bees for tens or hundreds of thousands of years more than that.

The ‘Woman(Man) of Bicorp” honey gathering (c. 8000 BC)

There are examples of Late Stone Age (or Upper Paleolithic c. 50,000 to 10,000 years ago) rock art depicting bees and honey from across the globe, with some of the most famous being in the Altamira (Spain) cave drawings from c. 25,000 years ago.

Survival of the fittest

And the key thing about many of these interactions with honey bees is that they are likely to have been rather one-sided. Honey hunting tends to be destructive and results in the demise of the colony – the tree is felled, the brood nest is ripped apart, the stores (and often the brood) are consumed.

None of this involves carefully caging the queen in advance 🙁

This is a strong selective pressure.

Colonies that responded earlier or more strongly to the smell of an apprehensive approaching hunter gatherer might be spared. These would survive to reproduce (swarm). Literally, the survival of the fittest.

All of this would argue that it might be expected that bees would evolve odorant receptors capable of detecting the fear pheromone of humans.

There’s no fire without smoke

There are (at least) two problems with this reasoning.

The first problem is that humans acquired the ability to use fire. And, as the idiom almost says, there’s no fire without smoke. Humans were regularly using fire 150-200,000 years ago, with further evidence stretching back at least one million years that pre-humans (Homo erectus) used fire.

And, if they were using fire you can be sure they would be using smoke to ‘calm’ the bees millenia before being depicted doing so in Egyptian hieroglyphs ~5,000 years ago.

It seems reasonable to expect that the use of smoke would mask the detection of fear pheromones, in much the same way that it masks the alarm pheromone when you give them a puff from your trusty Dadant.

The other problem is that it might be expected that the Mesolithic honey hunters had probably ‘got the job’ precisely because they weren’t afraid of bees. In extant hunter gatherer communities it’s known that there are specialists that have a particular aptitude for the role. Perhaps these beekeepersrobbers produce little of no fear pheromone in the first place?

What about other primates?

It’s well know that non-human primates (NHP’s), like chimpanzees and bonobo, love honey. They love it so much that they are responsible for an entire research area studying tool use by chimps.

Bonobo ‘fishing’ for termites using a tool (I couldn’t find a suitable one robbing honey)

Perhaps NHP’s produce a fear pheromone similar to that of humans? Since they haven’t learned to use fire (and they are very closely related to humans) bees may have evolved to respond to primate fear pheromone(s), and – by extension – to those of humans.

However, chimpanzees and related primates prefer to steal honey from stingless bees like Meliponula bocandei. The only information I could find suggested they avoided Apis mellifera, or “used longer sticks as tools“.

Perhaps not such a strong selective pressure after all …

More arm waving

A lot of the above is half-baked speculation interspersed with a smattering of evolutionary theory.

Bees clearly respond in different ways to different beekeepers. I’ve watched beekeepers retreat from a defensive colony which – later on the same training day – were beautifully calm when inspected by a different beekeeper.

Trainee beekeepers

Trainee beekeepers

Although this might have been due to differences in the production of fear pheromones, it’s clear that the bees are also using other senses to detect potential threats to the colony.

Look carefully at how outright beginners, intermediate and expert beekeepers move their hands when inspecting a colony.

The tyro goes slow and steady. Everything ‘by the book’. Not calm, but definitely very controlled.

The expert goes a lot faster. However, there’s no banging frames down, there are no sudden movements, the hands move beside the brood box rather than over it. Calm, controlled and confident.

In contrast, although the “knowing just enough to be dangerous” intermediate beekeeper is confident, they are also rushed and a bit clumsy. Hands move back and forwards over the box, movements are rapid, frames are jarred … or dropped. A bee sneaks inside the cuff and stings the unprotected wrist. Ouch!

“That’s an aggressive colony. Better treat it with care.”

You see what I mean about arm waving?

I strongly suspect movement and vibration trigger defensive responses to a much greater extent than the detection of fear pheromones in humans (if they’re detected at all).

Closing thoughts

You’ll sometimes read that bees respond badly to aftershave or perfumes. This makes sense to me only if the scent resembles one that the bees have evolved a defensive response against.

Don’t go dabbing Parfum de honey badger behind your ears before starting the weekly inspection.

Mellivora capensis – the honey badger. Believe me, you’re not worth it.

But why would they react aggressively to an otherwise unknown smell?

After all, they experience millions of different – and largely harmless – smells every day. Bees inhabit an environment that is constantly changing. One more unknown new scent does not immediately indicate danger. There would be an evolutionary cost to generating a defensive response to something that posed no danger.

And a final closing thought for you to dwell on …

Humans have probably been using fire to suppress honey bee colony aggression for hundreds of thousands of years.

Why haven’t bees evolved defensive responses to the smell of smoke? 11

Happy Halloween 🙂


 

Does DWV infect bumble bees?

Covid (the disease) is caused by a virus called SARS-Cov-2. SARS is an abbreviation of severe acute respiratory syndrome and the suffix ‘Cov’ indicates that it’s a coronavirus. The final digit (2) shows that it’s the second of this type of virus that has caused a pandemic. The first was in 2003, and was caused by a virus we now call SARS-Cov-1. That virus had a case fatality rate of 11%, but only infected ~8500 people worldwide. 

SARS-Cov-2 is not a human virus, by which I mean it’s not a virus that has been present in the human population for a long time. It’s actually a virus that most probably originated in bats.

We’re still not sure how SARS-Cov-2 jumped species from bats to humans.

SARS-Cov-1 made the same transition from bats and we do have a pretty good idea how this happened. Before the virus was found in bats it was detected in palm civets and raccoon dogs, both of which are farmed for food and sold in live game markets. Neither animal shows any symptoms when infected with SARS-Cov-1.

Bats were also sold in the same live game markets in Guangdong province in China and it seems likely that the virus either crossed directly from bats to humans, or went via a third species such as the palm civet.

Pathogen spillover

It’s likely that SARS-Cov-2 followed the same route. We are entering a second – likely extended – period of geographic lockdown due to Covid. Since SARS-Cov-2 made its cross-species jump from bats to humans it has infected at least 41 million people and killed over 1.13 million.

Pathogens that jump from one species to another can have catastrophic consequences for the recipient population 1 or, as in the case of palm civets, might cause no harm whatsoever.

The term ‘pathogen spillover’ is often used to describe the event when a pathogen – whether viral, bacterial or a parasite – escapes or spills over from its natural host to another species. 

CSI in the apiary … motive, opportunity, means

To make the species jump a number of criteria must occur. The pathogen has to be present at a high enough level to be infectious in the ‘donor’ species. For convenience, let’s consider this as the motive to jump species 2.

Secondly, the pathogen needs to have an opportunity to jump species. For example, because the donor and ‘recipient’ species share the same habitat or regularly come into contact.

Finally, it has to have the means to replicate in the recipient. If it cannot replicate it can never get established in the recipient population or cause disease.

In fact, this is an oversimplification. It also needs to be transmissible between individuals of the recipient species (or it will never spread in the recipient species).

So what has all this to do with the bumble bees in the title of this post?

Honey bees get a bad press from some scientists and environmentalists. They compete with native solitary and other bees and pollinators for environmental resources – like pollen and nectar. Increasingly, particularly in agricultural areas, these can be in limiting supply at certain times of the season. For examples, because all the hedgerows have been grubbed up and the wildflower meadows obliterated.

In addition, there are a number of studies that have suggested that honey bee viruses have spilled over into other pollinators, in particular bumble bees, and that this pathogen spillover has contributed to the decline in free-living bee populations.

Do honey bee viruses have the motive, opportunity and means to cause disease in bumble bees?

Are honey bee viruses responsible for the decline in bumble bee populations?

Correlation and causation

There are numerous studies showing that the most widespread honey bee virus, deformed wing virus (DWV), can be detected in wild-caught bumble bees.

Let me pose a quick question … does detection mean ‘replication’?

Deformed wing virus “does what it says on the tin” in honey bees. When transmitted by Varroa it causes developmental defects in pupae that appear as wing deformities in newly emerged workers.

DWV symptoms

DWV symptoms

There’s also one study that implicates DWV in directly causing disease in bumble bees.

This influential paper, published 15 years ago, demonstrated that some bumble bees had the characteristic crippled wings seen in symptomatic emerging honey bee workers. The ‘smoking gun’ was that DWV was also detected in these bumble bees.

Exhibit A : Evidence for DWV infection in bumble bees – click image for full legend.

This is the only figure in the paper and there have been no substantive follow-up papers. For some reason they showed ‘symptomatic’ Bombus terrestris (the buff-tailed bumble bee; panel A, left) and PCR detection data for B. pascorum (the common carder bee).

Nevertheless, this association between presence and symptoms was sufficient for the authors to conclude “we demonstrated that DWV is pathogenic to at least two bumble bee species … causing wing deformity similar to clinically DWV-infected honey bees”.

Here’s a second important question … does the detection of DWV in bumble bees demonstrate it is responsible for the symptoms observed? 3

As a virologist interested in the evolution, replication and transmission of viruses – and a beekeeper – this seemed like a worthwhile topic to explore in a bit more detail.

There might be a correlation between the presence of DWV in bumble bees, but does this account for causation of the DWV-like symptoms seen in the bumble bees?

Motive and opportunity

Let’s get these two out of the way quickly (though we’ll return to opportunity in the notes at the end).

Remember, viruses don’t want to do anything. I’m using motive as a hideously contrived reference to whether the pathogen, DWV, is present at high and infectious levels in honey bees.

It is.

Healthy, mite-naive (but reared in a hive with Varroa) workers can carry as little as ~1000 DWV viruses. Similar levels of DWV are also present in hives from Varroa-free regions – at least of the UK 4. In contrast, after parasitisation by Varroa, symptomatic or asymptomatic adult worker honey bees regularly have more that 109 (one trillion) viruses coursing through their little bodies. 

This virus is highly infectious. When injected into honey bees, as few as 10 viruses are sufficient to start a new infection and are replicated several million-fold within 24-48 hours.

Let’s agree that they have the ‘motive’ … to spread to other hosts.

They also have the opportunity, at least in the broadest sense of the word. Honey bees and bumble bees share the same environment. They collect nectar and pollen from the same flower species. They can even regularly be seen visiting the same flower simultaneously. In addition, it’s not unusual to see bumble bees trying to access honey bee hives to steal nectar.

I’d argue that the virus appears to have ample opportunity to move from one species to the other.

Does DWV replicate in bumble bees?

This is an important question. The data figure (‘Exhibit A’) shown above does not answer this question. Their assay simply detects the presence of DWV, with no indication of whether the virus is replicating.

And the reason this is important is really explained in the section on motive and opportunity above. DWV is ubiquitous and present at extraordinarily high levels in many honey bees. It’s present in honey bee faeces. It can be detected on flowers that honey bees have visited, or in pollen collected from those flowers.

DWV is absolutely everywhere.

So, if it is everywhere, there’s a good chance it might simply contaminate things … like bumble bees that look a bit sick for other reasons.

However, if DWV is involved in causing disease in bumble bees then the virus must replicate in bumble bees.

Virus replication – select for full size and legend.

I’ve used this figure before. To be certain that the virus is replicating you need to identify the intermediate replication products (the negative strand RNA shown as red arrows above).

Almost none of the large number of papers that have reported “DWV infected bumble bees” have identified these intermediate replication products.

Many studies didn’t even bother looking for these critical intermediate products.

So we did

There are two ways we could have investigated this. We could have collected large numbers of bumble bees from the fields and screened them in the lab for these replication intermediates. The problem with this approach is that DWV might be very rare in bumble bees, or might be common, but only replicate rarely. The additional problem is that it involves going out and collecting bees from the environment – that’s hard work 😉 5

An alternative approach is to buy a nest of bumble bees 6 and to inject a few bumble bee pupae and adults with DWV. This is what we did. In parallel, to ‘prove’ the virus used can replicate in honey bees, we injected a few honey bee pupae.

We injected the bees as it’s the definitive way we have of being sure that the virus was present.

‘Gene jockeys’

I’ve got some gifted molecular virologists in my lab. These are scientists who use genetic engineering or biotechnology techniques to address tricky questions (gene jockeys). They are particularly skilled at manipulating nucleic acids, such as the genomes of viruses.

If DWV is so common (it is – see above) how would we know that the replication intermediates were from the virus we injected into the bumble bees, rather than from a virus that was possibly already present?

To solve this puzzle Alex (the lead author on our recent paper) did two things. She engineered a unique genetic marker into the virus which we could look for (and that knew was absent from other similar viruses that might already be present in bumble bees). In addition, she ensured that the virus she injected into the bumble bees contained none of the negative strand RNA that is produced as the intermediate when the virus replicates. 

And … to cut a long story short, we could detect the negative strand RNA replication intermediate in injected bumble bees. In addition, the virus contained the unique genetic marker Alex had engineered into the virus genome, so we were absolutely certain it was the injected virus that was replicating. All of the controls worked exactly as expected.

DWV does replicate in bumble bees … at least under the conditions used in our experiment.

But it does not replicate very fast

The bumble bees we used for these experiments are commercially produced under very clean conditions. When we tested control bumble bees they contained no DWV at all, even using our most sensitive assays.

In contrast to injected honey bee pupae, DWV replicates rather slowly in bumble bees. In honey bees it will amplify a million-fold in 48 hours. However, in bumble bees, in 48 hours we only observed a 100-10,000 fold increase in DWV levels. It was only when we injected large amounts of DWV to bumble bees that we could recapitulate the virus levels seen in symptomatic honey bees.

This was a little puzzling as we’ve assumed that the very rapid replication of DWV in honey bees contributes to pathogenesis. The virus needs to replicate fast to spread through the pupa and infect the particular tissues and organs that, when damaged, result in the characteristic symptoms seen.

If it only replicates slowly in bumble bees how can it cause symptoms?

But hold on … does it cause symptoms?

Not as far as we can tell. 

We never found any injected bumble bees with deformed wings, or any that looked anything like the symptoms seen with DWV in honey bees. The actual quote from the paper is:

Strikingly, none of the eclosed bumble bees showed any signs of the wing deformities that are characteristic of DWV infection of honey bees”. 

Morbidity of DWV in bumble bees

Injected pupae developed until eclosion and were either non-viable, discoloured or apparently normal in appearance (see (c) above). We observed similar numbers of these three types whether the pupae were injected with DWV or mock-injected with buffer alone (see (b) above). What’s more, of those injected with the virus, the level of the virus was the same irrespective of the appearance (or viability) of the bumble bee (see (a) above).

We know that these bumble bees contain replicating DWV but see no evidence for overt disease. I acknowledge that they may have invisible symptoms. However, we see no evidence for the wing deformities reported in the 2005 paper from Genersch and colleagues (‘Exhibit A’, above).

Heavy going? But I’ve only just started … 

So, let’s briefly return to our “motive, opportunity, means” crime analogy and summarise where we’ve got to so far. 

DWV is present at very high levels in at least some honey bees. In addition, bumble bees are likely to regularly come into contact with DWV in the environment. This could happen through contaminated pollen, when attempting to rob hives, or by direct interaction with honey bees when both visit flowers. Finally, and most tellingly, DWV replicates in bumble bees.

So, if I was Peter Falk as Lieutenant Columbo, I’d argue that DWV has the motive, opportunity and means to potentially cause disease in bumble bees.

But, as is apparent from the figure above, it appears not to actually cause disease.

Which is puzzling. 

Just one more thing 7

There’s a major problem with the experiments I’ve discussed so far.

Like all experiments 8 they were tightly controlled, with single variables and lots of statistical analysis to demonstrate our confidence in their reproducibility.

The problem wasn’t technical, it was how well they recapitulated potential transmission in the environment.

We’re not aware of anything that goes around “injecting” bumble bee pupae or adults 9. They are not parasitised by Varroa and, although there are bumble bee mites (such as Parasitellus), they don’t feed on bumble bees in the same way that Varroa feeds on honey bees.

How else might bumble bees acquire DWV?

The obvious route is orally, while feeding. 

There are a few issues with feeding bees DWV. The method is simple enough … you add the virus to sugar syrup and they slurp it down. However, you have little control over how much individual bees consume. Do some bees feed directly and other acquire food when fed by other bees (trophallaxis)? It gets rather difficult control.

In addition, we knew from our studies of honey bees that they are far less susceptible to infection per os (by mouth) than by injection. And by far less I mean tens of thousands of fold less susceptible, at least as adults.

Feeding bumble bees DWV

We chose to investigate two routes of feeding.

The first was to directly feed individual bees in the laboratory. Using this approach we failed to detect any evidence for infection or DWV replication in fed adult bumble bees, even when fed 100 million DWV viruses.

Not an encouraging start. However, larvae generally have increased susceptibility to pathogens, so we also investigated feeding larvae in the laboratory. In these studies we did manage to establish infection. However, to do so we had to add 100 million DWV viruses to he food and only achieved a 50% infection rate. 

The second approach we used was direct feeding of complete bumble bee colonies maintained in the lab.

Bumble bees are easier to keep in the lab than honey bees as they don’t need to be free-flying. Each colony occupies a 30cm3 perforated plastic box, supplied with pollen and syrup. We fed three colonies 100 million DWV per bee per day for 4-6 weeks 10.

That’s a huge amount of virus for a protracted period. Our reasoning here was straightforward. Perhaps there was a particular developmental stage that had increased susceptibility? Perhaps adult bees feeding larvae would – for whatever reason – reduce their resistance to infection via the oral route?

We screened every egg, larva, pupa and adult bee for replicating DWV at the end of the experiment.

There was none present 🙁 ( or perhaps 🙂 , depending upon your viewpoint )

Summary and conclusions

We generated unequivocal evidence that DWV replicates in bumble bees. Specifically in Bombus terrestris, the buff tailed bumble bee. I’d be surprised if it did not replicate in other Bombus species, but that will need to be investigated. 

Infection of adult bees was only possible by injection, with no evidence for infection during feeding.

Bumble bee larvae can be infected with DWV while feeding, but only when fed very large amounts of virus directly. When larvae were reared by a colony supplied with DWV-laced food for several weeks the larvae did not become infected.

These results were recently published in Scientific Reports (Gusachenko et al., 2020) and are freely available. The title of the paper neatly sums up the study “Evidence for and against deformed wing virus spillover from honey bees to bumble bees: a reverse genetic analysis”

What does this mean in terms of our understanding of pathogen spillover from managed honey bee colonies to free living bees? 

If ecologists and environmental scientists are going to make the case that honey bees are threatening the survival of free-living solitary or bumble bees (due to pathogen spillover) they need to:

  1. formally demonstrate that the honey bee virus replicates in the free-living bee
  2. show that this replication is detrimental to the free-living bee
  3. provide evidence for a natural route of transmission by which infection can occur

In my view, and using legal terms again, it’s case proven for the first point in Bombus terrestris 11. In contrast, if I was the judge I’d throw out the other cases due to lack of evidence.

Monkey puzzles

There are viruses everywhere. Every living species has one or more viruses that infect it. Inevitably, because viruses replicate to very high levels, species other than the natural host may become exposed.

But almost always this has no consequences at all …

And to illustrate that I’ll briefly describe a study of monkey viruses infecting humans in Cameroon from several years ago. HIV is one of a very large group of viruses called immunodeficiency viruses. The ‘H’ stands for human, though the virus originated in chimpanzees and is very closely related to the simian immunodeficiency viruses (SIV).

A study of hunters living in the forests of Cameroon showed evidence for exposure to multiple different SIV isolates in tribespeople who hunted non-human primates or who were involved in butchering them or preparing them for market or cooking. There was no evidence these viruses were spreading in the human population, or that there was any sickness or disease associated with prior exposure. 

Environmental exposure happens all the time, and is relatively easy to detect. That’s exactly what had happened with these monkey viruses.

But evidence for environmental exposure, whilst easy to get, is not sufficient to support a claim that the virus causes disease at the level of the individual, or that it threatens an entire population.

As a virologist I think it’s interesting that DWV replicates in Bombus terrestris. However, I’ve yet to see any convincing evidence that DWV spillover from honey bees is responsible for the decline in wild bee populations.

Circumstantial evidence is not the same as convincing evidence.


Notes

What are the missing experiments that we didn’t do?

A key one is to determine whether long-term infection of bumble bees with DWV results in disease. We didn’t see overt deformed wing disease, but it’s possible that infection for weeks could have caused this or other symptoms. 

Although we fed bumble bee nests for weeks with DWV we saw no evidence of larval infection. This was despite previously demonstrating that larvae could be infected with high levels of DWV orally. One possibility is that DWV is inactivated by adult bees. I think it would be interesting to look at the level of infectious DWV in larval food.

Are there natural routes of exposure to DWV that result in bumble bee infection?

Does DWV ever cause environmental contamination at a high enough level to naturally infect bumble bees? For example, is the level of DWV in honey bee faeces high enough and does it ever contaminate pollen?

We are not going to do these studies so it will be interesting to see if others do … or whether simply the presence of the virus (whether replicating or not) will be proof’ that honey bee viruses are responsible for the decline in free-living bee populations.

Diutinus bees

Diutinus is Latin for long-lasting.

Diutinus bees are therefore long-lasting bees. These are the bees that, in temperate regions, maintain the colony through the winter to the warmer days of spring.

I’ve discussed the importance of these bees recently., and I’ve regularly made the case that protecting these ‘long-lived’ bees from the ravages of Varroa-vectored viruses is critical to reduce overwintering colony losses.

Winter is coming …

In most cases the adjective diutinus is replaced with ‘winter’, as in winter bees; it’s a more familiar term and emphasises the time of year these bees are present in the hive. I’ll generally use the terms interchangeably in this post.

Diutinus does not mean winter

From a scientific standpoint, the key feature of these bees is that they can live for up to 8 months, in contrast to the ~30 days a worker bee lives in spring or summer. If you are interested in what induces the production of long-lived bees and the fate of these bees, then the important feature is their longevity … not the season.

Furthermore, a proper understanding of the environmental triggers that induce the production of long-lived bees might mean they could be produced at other times of the season … a point with no obvious practical beekeeping relevance, but one we’ll return to in passing.

It’s worth emphasising that diutinus bees are genetically similar to the spring/summer bees (which for convenience I’ll refer to as ‘summer bees’ for the rest of the post). Despite this similarity, they have unique physiological features that contribute to their ability to thermoregulate the winter cluster for months and to facilitate spring build-up as the season transitions to spring.

What induces the production of winter bees? Is it a single environmental trigger, or a combination of factors? Does summer bee production stop and winter bee production start? What happens at the end of the winter to the winter bees?

Segueing into winter bee production 

The graph below shows the numbers of bees of a particular age present in the hive between the end of August and early December.

Colony age structure from August to December – see text for details

Each distinct colour represents bees reared in a particular 12 day ‘window’. All bees present before the 31st of August are blue. The next 12 day cohort of bees are yellow etc. The area occupied by each colour indicates the number of bees of a particular age cohort.

Note that egg laying (black) is negligible between early October and late November when it restarts.

The graph shows that that there is no abrupt change from production of summer bees to production of winter bees.

For example, about 95% of the blue bees have disappeared by December 1. Of the yellow bees, which first appeared in mid-September, about 33% are present in December. Finally, the majority of the lime coloured bees, that first put in an appearance in early October, are present at the end of December.

The colony does not abruptly stop producing short-lived summer bees on a particular date and switch to generating long-lived ‘diutinus’ winter bees. Instead, as late summer segues into early autumn, fewer short lived bees and more long lived bees are produced. 

Note that each cohort emerge from eggs laid 24 days earlier. The orange cohort emerging from 24/09 to 05/10 were laid within the first two weeks of September. This emphasises the need to treat early to reduce mite levels sufficiently to protect the winter bees.

Winter bees are like nurse bees but different

Before we consider what triggers the production of diutinus bees we need to discuss how they differ from summer bees, both nurses and foragers.

Other than being long-lived what are their characteristics?

Interaction of key physiological factors in nurse (green), forager (red) and winter bees (blue). Colored disks indicate the relative abundance of each factor.

The four key physiological factors to be considered are the levels of juvenile hormone (JH), vitellogenin (Vg) and hemolymph proteins and the size of the hypopharyngeal gland (HPG).

As summer nurse bees transition to foragers the levels of JH increases and Vg decreases. This forms a negative feedback loop; as Vg levels decrease, JH levels increase. Nurse bees have high levels of hemolymph proteins and large HPG, the latter is involved in the production of brood food fed to larvae.

So if that describes the summer nurse bees and foragers, what about the winter bees?

Winter bees resemble nurse bees in having low JH levels, high levels of VG and hemolymph proteins and large HPG’s. 

Winter bees differ from nurse bees in being long lived. A nurse bee will mature into a forager after ~3 weeks. A winter bee will stay in a physiologically similar state for months.

There have also been time course studies of JH and Vg levels through the winter. In these, JH levels decrease rapidly through October and November and are at a minimum in mid-January, before rising steeply in February and March.

As JH levels rise, levels of Vg and hemolymph proteins decrease and the size of the HPG decreases i.e. as winter changes to early spring winter bees transition to foragers.

Now we know what to look for (JH, Vg levels etc) we can return to think about the environmental triggers that cause these changes.

No single trigger

In temperate regions what distinguishes winter from autumn or spring? 

Temperatures are lower in winter.

Daylength (photoperiod) is shorter in winter.

There is less pollen and nectar (forage) available in winter.

Under experimental conditions it’s quite difficult to change one of these variables without altering others. For example, shifting a colony to a cold room (i.e. lowering the ambient temperature to <10°C) leads to a rapid decrease in JH levels (more winter bee-like). However, the cold room was dark, so perhaps it was daylength that induced the change? Alternatively, a secondary consequence of moving the colony is that external forage was no longer available, which could account for the changes observed.

And forage availability will, inevitably, influence brood rearing.

Tricky.

Reducing photoperiod alone does induce some winter bee-like characteristics, such as increases in the protein and lipid content of the fat bodies. It also increases resistance to cold and starvation. It can even cause clustering at elevated (~19°C) temperatures. However, critically, a reduced photoperiod alone does not appear to make the bees long lived. 

Remember also that a reduced photoperiod will limit foraging, so reducing the nutritional status of the colony. This is not insignificant; pollen trapping 2 in the autumn accelerates the production of winter bees.

But again, this may be an indirect effect. Reduced pollen input will lead to a reduction in brood rearing. Feeding pollen to broodless winter colonies induces egg-laying by the queen.

Brood, brood pheromones and ethyl oleate

One of the strongest clues about what factor(s) induces winter bee production comes from studies of free-flying summer colonies from which the brood is removed. In these, the workers rapidly change to physiologically resemble winter bees 3.

How does the presence of brood prevent the generation of diutinus bees?

There are some studies which demonstrate that the micro-climate generated in the colony by the presence of brood – elevated temperature (35°C) and 1.5% CO2 – can influence JH levels. 

However, brood also produces pheromones – imaginately termed brood pheromone – which does all sorts of things in the colony. I’ve discussed brood pheromone previously in the context of laying workers. The brood pheromone inhibits egg laying by worker bees.

Brood pheromone also contributes to a enhancement loop; it induces foraging which results in increased brood rearing and, consequently, the production of more brood pheromone.

One way brood pheromone induces foraging is by speeding the maturation of middle-aged hive bees into foragers. Conversely, when raised in the absence of brood, bees have higher Vg levels, start foraging later and live longer.

But it’s not only brood that produces pheromones.

Workers also produce ethyl oleate, a pheromone that slows the maturation of nurse bees, so reducing their transition to foragers.

A picture is worth a thousand words

All of the above is quite complicated.

Individual factors, both environmental and in the hive, have direct and indirect effects. Experimentally it is difficult to disentangle these. However, Christina Grozinger and colleagues have produced a model which encapsulates much of the above and suggests how the production of winter bees is regulated. 

Proposed model for regulation of production of winter bees.

During autumn there is a reduction in forage available coupled with a reduced daylength and lower environmental temperatures. Consequently, there is less foraging by the colony. 

Since more foragers are present within the hive, the nurse bees are exposed to higher levels of ethyl oleate, so slowing their maturation.

There’s less pollen being brought into the colony (reduced nutrition), so brood production decreases and so does the level of brood pheromone. The reduced levels of brood pheromone also reduces nurse bee maturation.

As shown in the diagram, all of these events are in a feedback loop. The reduction in levels of brood pheromone further reduces the level of foraging … meaning more foragers are ‘at home’, so increasing the effects of ethyl oleate.

All of these events have the effect of retarding worker bee maturation. The workers remain as ‘nurse-like’ long-lived winter bees.

Is that all?

The difference between nurse bees and winter bees is their longevity … or is it?

In the description above, and in most of the experiments conducted to date, the key markers of the levels of JH, Vg and hemolymph proteins, and the size of the HPG, are what has been studied. 

I’d be astounded if there are not many additional changes. 

Comparison of workers and queen bees have shown a large range of epigenetic changes induced by the differences in the diet of young larvae 4. Epigenetic changes are modifications to the genetic material that change gene expression.

I would not be surprised if there were epigenetic changes in winter bees, perhaps induced by alteration of the protein content of their diet as larvae, that influence gene expression and subsequent longevity. Two recent papers suggest that this may indeed happen; the expression of the DNA methyltransferases (the enzymes that cause the epigenetic modifications) differs depending upon the demography of the colony 5 and there are epigenetic changes between the HPG in winter bees and bees in spring 6.

Clearly there is a lot more work required to fully understand the characteristics of winter bees and how they are determined.

Don’t forget …

It’s worth emphasising that the local environment (forage and weather in particular) and the strain of the bees 7 will have an influence on the timing of winter bee production.

Last week I discussed a colony in my bee shed that had very little brood on the 2nd of October (less than one side of one frame). When I checked the colonies last weekend (11th) there were almost no bees flying and no pollen coming in. A colleague checked an adjacent colony on Monday (13th) and reported it was completely broodless. These bees are ‘local mongrels’, selected over several years to suit my beekeeping.

Early autumn colonies

In contrast, my colonies on the west coast are still busy. These are native black bees. On the 14th they were still collecting pollen and were still rearing brood. 

The calendar dates in the second figure (above) are therefore largely irrelevant.

The transition from summer bees to the diutinus winter bees will be happening in your colonies, sooner or later. I suspect it’s already completed in my Fife bees.

Whether genetics or environment has a greater influence on winter bee production remains to be determined. However, I have previously described the good evidence that local bees are better adapted to overwintering colony survival.

To me, this suggests that the two are inextricably linked; locally selected bees are better able to exploit the environment in a timely manner to ensure the colony has the winter bees needed to get the colony through to spring.


 

Preparing for winter

The beekeeping season is fast receding into the distance as the first frosts of autumn appear and, finally, the wasp numbers start to diminish. By now colonies should be heavy with stores, either collected by the bees or provided by the beekeeper.

Winter is coming … be prepared

There is relatively little actual beekeeping to be done this late in the year.

Colonies do not need to be disturbed unnecessarily. They certainly don’t require the usual weekly inspection … they’re not going to swarm, you’ve already applied your miticide of choice and fed them with fondant or syrup 1.

Late queen mating

With temperatures during the day in the low to mid-teens (°C) it is still warm enough to open a colony if you need to.

One of the few reasons I’d open a colony in very late September/early October would be to check if a new queen that had emerged at the end of August had successfully mated. If she had, then all is good. She will continue to lay late into the autumn and should produce sufficient winter bees to get the colony through to the following Spring.

When I lived in the Midlands I would regularly get queens successfully mated in early/mid September. It was pretty dependable, and in good years I’d be actively queen rearing through much of August.

Now, back in Scotland, late queen mating is not something I would want to rely on. I’m certain it happens now and again, but only in very exceptional years.

It’s a tough life being a drone in late August … but not for much longer

This year, many of my colonies turfed their drones out a month ago, and queen mating is not going to happen unless there are plenty of drones about.

A quick peek

It takes just minutes to check whether the queen is mated and laying. Although you don’t need to see the queen, it’s worth using just a whiff of smoke so you have the option of searching for her if needed. If you smoke the colony heavily she’ll end up rushing about or buried under a mass of disturbed bees.

Just a whiff …

You will need to remove the feeder (if using syrup) or the queen excluder and fondant block. Place these aside gently and remember that there are likely to be large numbers of bees adhering to the underside, so balance them on the rim of an upturned roof. This is the time you realise the benefit of using framed rigid wire QE when feeding fondant … removing the block on a flexible plastic QE is a right palaver.

The hive should be busy with bees. Gently remove the dummy board and outer frame. This should be full, or in the process of being filled, with stores. There’s no need to shake the bees off. Just stand it aside out of the way.

‘Guesstimate’ the approximate centre of the brood nest, based upon the density of bees in the seams. Gently lever the frames apart a centimetre or so, then release one of the frames adjacent to the gap you’ve created from its neighbours.

Lift the frame and look for sealed brood, open brood and eggs. By knowing the development cycle of workers bees (3E,5L,13P 2) you can determine approximately when the queen started laying 3.

If she started laying …

Snatching victory from the jaws of defeat

… if there are no eggs or larvae by very late September I would assume that the queen had failed to mate.

You need to use your judgement here. If the weather was poor in the first half of September, but excellent since then, it remains a distant possibility that she has only just mated and has yet to start laying.

Look carefully for polished cells where the centre of the broodnest should be.

And cross your fingers.

Polished cells are a sign that the nurse bees are preparing the comb for egg laying. However, in my experience, they do this even if the queen remains unmated, so it is not a reliable sign that all is well.

You therefore need to use your judgement and be realistic.

Miracles do happen, but you can’t depend upon them 4.

If the weather has been consistently poor – windy, low temperatures (for queen mating, which really needs ~18-20°C) or wet – then assume the worst and ‘save’ the colony by uniting it with a nearby strong colony.

A colony without a laying queen in late autumn will not survive the winter in any state that will make it a viable colony the following year 5.

In Scotland, I routinely unite colonies that do not have a laying queen at the end of August. As described in the last couple of weeks, I do my final colony checks with feeding and miticide treatment.

I know the chances of a queen getting successfully mated after that are effectively zero.

Quick uniting – air freshener

If you need to unite two colonies quickly, without the usual week long wait while they gently mingle after stacking them separated by a sheet of newspaper, you can use a few squirts of household air freshener.

  • Open the queenright recipient colony, removing the feeder and carefully placing it aside to avoid crushing bees (see above)
  • Find the unmated/unlaying/uncooperative queen in the broodless box and remove her (permanently I’m afraid)
  • Spray the top of the recipient colony with a a few squirts of air freshener
  • Do the same with the underside of the now queenless broodless colony
  • Stack the latter on top of the recipient colony
  • Add the feeder back, again giving a squirt or two of air freshener at the interface to stop the bees from fighting

The air freshener masks the distinctive pheromone ‘smell’ of the two colonies, allowing the bees to mingle without fighting.

That’s it.

Job done.

Caveat emptor

Like everything else on this site, I only write here from direct experience. I have successfully united quite a few colonies like this, though nothing like the number I’ve united using newspaper 6.

Given time and the choice I’d always use newspaper 7.

But this late in the season you might not have time.

A day after uniting with air freshener you can, if needed, revisit the hive and go through the double brood box to reduce it to a single box for the winter.

Does it matter which air freshener you use?

I have no idea.

I use Glade Citrus Sunny Beat as it was the cheapest I could find at the time I needed it 8.

Securing the queenright overwintering colony

If you consult the COLOSS records for overwintering colony losses they include a small percentage that are lost to ‘natural disasters’. COLOSS record queen failures and things like that separately, and – in an earlier paper – they define natural disasters as:

… rather loosely defined, as the causes can be very different in participating countries, including fire, storm, flooding, vandalism, bears, martens, woodpeckers, falling trees, suffocation from snow and many more.

The small percentage (0.1 – ~5%) lost to natural disasters vary from country to country, and from year to year.

What is notable about several of these natural disasters is that they should be avoidable.

If your colonies are strong and queenright, and if you’ve fed and treated them to give them the best chance of surviving the winter, it makes sense to do what you can to avoid these natural disasters.

The hive

I use a combination of polystyrene and cedar hives. Sometimes I even combine the two together in a single hive. The majority of my poly hives are from Abelo or Swienty which, for reasons explained elsewhere, are compatible with all the woodenware I own.

The apiary in winter ...

The apiary in winter …

I see no difference in the overwintering colony success between poly and cedar hives.

This doesn’t mean there isn’t one.

I’ve only run about 20 colonies for the last decade. That’s ~200 overwintered colonies. If there were wildly different survival rates I would have noticed. Since I haven’t noticed it either means there is no difference or there is a subtle difference but my sample size is too low 9.

All my colonies overwinter on open mesh floors, usually with the Varroa tray removed. The hives in the photo above are being monitored for mite drop in early December following oxalic acid treatment.

DIY insulation over a perspex crownboard

In addition, all of my hives have a 50 mm thick block of Kingspan under the roof, integrated into the roof, or integrated into the crownboard. In the bee shed my hives have no roof, and are just capped with a block of Kingspan over the crownboard.

Look, no roof … but insulation present all year round

Make sure the stack of boxes in the hive are stable and secure. If the apiary is exposed, strap everything together securely. A colony might survive a week or two of summer showers with no roof, but will surely perish if exposed for any length of time to cold, wet winter weather.

Apiary security

It is unlikely that you will visit the apiary much in the winter. Once a fortnight is more than enough.

It might therefore be worth considering whether it is sufficiently secure from the attention of unwanted human visitors. Unfortunately, incidents of vandalism occur throughout the season, but a hive kicked over in midwinter has less chance of being detected quickly.

Or of surviving.

Although it should probably be included within the ‘Varmints’ section below, large animals – cows, deer, elk, bear, rhino, kangaroo 10 – might also inadvertently, or deliberately, overturn a hive.

Apiary gate

Safe and secure

Fences, either a couple of strands of barbed wire, an electric fence or a full-blown razor-wire topped security barrier, are usually sufficient to keep large two and four-legged visitors at bay.

COLOSS mention both falling trees and flooding as natural disasters.

Winter storms can and do wreak havoc in some years, though I always associate the summer with storm-toppled trees because they’re in full leaf and therefore offer more resistance. It’s certainly worth looking to see if trees adjacent to your apiary might threaten the hives.

Where did Noah keep his bees? In his Ark hive.

Where did Noah keep his bees? In his Ark hive.

Flooding appears to be on the increase. I have experienced minor flooding in one of my apiaries. None of the hives were threatened, but it made access inconvenient for weeks at a time. Again, it’s worth imagining the worst and preparing for it.

Hives often float, but not necessarily the right way up 🙁

Varmints

Having dealt with the threat of large animals 11 it’s also worth considering the damage some small animals can do to hives.

The two main culprits are woodpeckers and mice. Both can be a menace once the frosts set in, but rarely before that.

Woodpeckers, and specifically green woodpeckers (yaffles 12), can learn that beehives contain a wonderful bounty of pupae and larvae. It is learned behaviour. Some green woodpeckers never go near hives, others routinely target them.

In Warwickshire, hives needed to be protected from yaffles. Here in Fife the bird is very much less common and I’ve never had any hives targeted.

Wrapped for winter

Wrapped for winter …

Protection is straightforward. If needed, I simply wrap the hives in a single sheet of DPM (damp proof membrane), pinned in place with drawing pins. The bird need to cling onto the vertical side of the hive to easily burrow through to the brood. The DPM stops them doing this. Leaving bits of the roof or sides of the floor exposed is therefore not a problem 13.

Pixie or Dixie?

Pixie or Dixie?

Mice access hives through overly large entrances. I only have problems with the stupidly cavernous maw of my preferred Everynuc. Mice eat pollen and stores, destroy the brood and wee everywhere 🙁  Thoroughly unpleasant.

Everynuc entrance

Open wide …

A standard mouseguard pinned in place throughout the coldest months of the winter prevents them accessing the hive. Alternatively, on a full-sized colony, the kewl-style underfloor entrances are very effective at excluding rodents.

Kewl open mesh floor showing L-shaped entrance slot

Kewl floor entrance …

That’s not the end of winter-related tasks, but it’s just about all you need to do for your colonies before winter proper starts.

There are some midwinter checks that are needed, but we’ll deal with them nearer the time.


Note

We also have pine martens at one of my apiaries. They are reported to vandalise hives and steal honey (and presumably brood) in late winter. Pine martens are incredibly agile and no fence exists that could keep them out. Time will tell whether they are a problem.

In the meantime, here’s one living up to its name, stealing a pine offcut used to slow down the rate at which they empty the squirrel feeder of peanuts 🙂