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This post updates and replaces one published three years ago (which has now been archived).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.

 

Eating my words

I periodically look at the access statistics of this site. It gives me an idea of what’s popular, which subjects might be worth revisiting and which posts have sunk without trace into bottomless void of the internet.

Daily page views are only 50% what they were in June. Maybe it’s the chaos/excitement/disappointment (delete as appropriate) of the US election or the deja vu and crushing inevitably of Lockdown 2.0, but beekeeping appears to be getting less popular.

Or perhaps it just reflects the fact that it’s the end of the season and everyone is frantically catching up on all the tasks they postponed from earlier in the year when they were in the apiary 1.

That’s not to say that there is no beekeeping to do at this time of the year.

Mite corpses

I usually use Apivar for Varroa control. The active ingredient, amitraz, remains effective. I like Apivar as it works even at the lower temperatures we have in Scotland. In addition, the queen continues laying – in contrast to Apiguard for example – at precisely the time the colony needs to be rearing lots of long lived winter bees.

Double brood colony the day before Apivar treatment added

I insert the Apivar strips as soon as the summer honey supers are removed and at the same time as the autumn fondant blocks are added. This year the strips went in on the 28th of August. The mite drop is then monitored over subsequent weeks.

Or should be.

My continued absence on the remote west coast meant that the counts of mite corpses were a bit hit and miss this year 2.

Mite drops – colonies in the bee shed, autumn 2020

The counts were sufficient to determine the relative mite infestation levels and observe how they dropped over time. Unfortunately, they weren’t detailed or frequent enough to see real differences on a day-by-day basis.

I’d hoped to get this to discuss the influence of the reducing laying rate of the queen on apparent mite infestation levels, but that will have to wait until another year.

Mite drop data

The four colonies plotted on the graph above are in our bee shed. They are all within 4 metres of each other, and have been for at least a year. None have had any Varroa management this season 3 other than the Apivar added in late August.

Hives in the bee shed

One of the colonies (#1) has had sealed brood periodically removed for experiments. Hive #2 and #4 are on a double brood box, the other two are on singles. All the hives are Swienty or Abelo (poly) Nationals.

The first thing to notice is that there are very significant differences in cumulative mite drop over the first 40 days after starting treatment. Rather than graph these numbers, here’s a simple list by hive number:

  1. 73
  2. 697
  3. 597
  4. 120

Infestation levels can differ significantly, even in colonies within the same apiary. Or on the same hive stand. Monitoring a single hive as a sentinel for a complete apiary could be very misleading.

Hive #1 counts are probably lower because the colony is a bit weaker than the others (though that’s relatively speaking – many beekeepers would consider it quite strong). However, the drop is not significantly different from #4 which is a very strong colony. 

Throughout the treatment period shown (we stopped counting in October) the average mite drop per day from #1 and #4 never exceeded 5 which is satisfying low. There’s little else to say about these two colonies 4.

The high mite drop from colonies #2 and #3 is about as high as I’ve ever seen in my own hives in Scotland. 

Mite reductions

When I lived in the Midlands I saw higher counts. There’s a much higher density of apiaries and beekeepers there than in Fife, and it was more difficult to manage colonies to routinely have low mite numbers. I’ve always assumed this was due to robbing and drifting – isolation definitely helps – but my Varroa management was also a bit different (in both method and timing).

Hive #3 trace shows a typical reduction week on week over the treatment period. High at the start and negligible after about 40 days.

Colony #2 has a strange increase in mite drop in the third week of treatment. I don’t really understand this. One possibility is that the colony was robbing a nearby heavily-infested colony 5 during this period, with the foragers bringing back phoretic mites as well as the stores they’d robbed out.

In both these “high mite” colonies the mite drop after ~40 days was averaging 5 per day or less, which should be OK. They will be monitored again in mid/late November and after treatment with Api-Bioxal during a broodless period

For reference, colony #1 was broodless when checked on the 13th of October, a few days after the last count on the graph above. 

Apivar strip removal

The approved duration of treatment with Apivar is 6-10 weeks. I usually remove strips after 6 weeks if the mite drop is low and steady. There’s nothing to be gained from overtreating.

However, since I was aware of the high mite drop from colonies #2 and #3 I left the strips in for a bit longer, removing them on the 30th of October (i.e. 9 weeks). 

Used and removed Apivar strips

If beekeepers are to avoid Varroa acquiring resistance to Apivar it is very important that the miticide is used properly. Removing the strips within 10 weeks very important. 

I attended an online Q&A session with Luis Molero (Scotland’s lead Bee Inspector) organised by the SBA. In this he described finding hives on heather moors which still contained Apivar strips. These had presumably been left in the hive after a mid-season treatment, though whether by accident or design is unclear. 

This is poor practice on two counts; continued presence of low levels of the miticide would contribute to selecting amitraz-resistant mites and there is the additional risk of tainting the honey with miticide. 

Reading and writing

I spend a lot of my week stuck in the office reading and writing. Grants, manuscripts, strategy documents, complaints, the BBKA Q&A page, menus (well, OK, not menus … and relatively few complaints) etc.

As a consequence I rarely spend much time reading for pleasure. Months go by without me opening The Scottish Beekeeper, the BBKA Newsletter or ABJ. However, as the beekeeping season draws to a close I have a bit more free time and so periodically binge-read some of these to catch up.

The view from the office … another reason I’m behind on my reading

Usually, by the time I read something, it’s out-of-sync with the season. I find myself reading about queen rearing strategies in late October, or overwintering queens in early February. Much of this is promptly forgotten … unless I make notes and write about it here.

You could consider The Apiarist as a sort of aide memoire for this forgetful beekeeper 😉

However, a few weeks ago I read a letter to the editor in The Scottish Beekeeper on the perils of feeding fondant. I’ll paraphrase here both to avoid copyright issues and because I’ve lost (!) the particular issue the letter appeared in.

The gist of the letter was that the correspondent had lost several colonies when fondant had gone sloppy and dripped down between the frames, killing the colony in the middle of the winter. 

I sent a letter to the editor saying that I’d only seen this when the colony had perished through disease. Healthy colonies, clustering under unfinished fondant blocks, tended to keep nibbling away and so were not swamped by a tsunami of cold, syrupy fondant.

Or words to that effect.

Don’t speak write too soon

I’ve got a couple of Varroa-free colonies on the west coast of Scotland. Both were started from nucs in mid/late summer, built up well and collected a reasonable amount of nectar from the heather. I left this for them, nadiring the partially-filled super and – as I usually do – adding a block of fondant on a queen excluder.

Both colonies are in Abelo poly hives with open mesh floors and a 5cm block of Kingspan insulation under the polystyrene roof. This is typically how my colonies would overwinter 6.

Green thoughts in a green shade

Neither colony used much more than 6 kg of fondant as both brood boxes had ample stores. I therefore intended to remove the unused fondant ‘at some point’. 

For a future post here I wanted a photograph of the typical ‘stripes’ of brood cappings visible on a Varroa tray. Since these west coast colonies brood later in the season than my Fife bees I inserted a tray below one colony a couple of weeks ago.

‘At some point’ turned out to be today (5th of November).

To my surprise. the underside of the fondant block in the hive with the Varroa tray was distinctly soft and sloppy.

Sloppy fondant stuck to the top bars – this hive had the Varroa tray inserted.

In contrast, the other colony was much as I’d expected. No sticky fondant.

No Varroa tray, no sloppy fondant stuck to the top bars.

Clearly, under certain conditions, a fondant block can soften sufficiently to start to dribble down between the frames. It’s worth emphasising the colonies are in the same type of hive (floor, boxes and roof), in the same apiary and are of equivalent strength. The only difference is the presence of a well-fitting Varroa tray in one of them.

Eat my words

I think the explanation for the difference from a) my previous experience, and b) between the two hives pictured above, is straightforward.

It rains a lot on the west coast. In the last fortnight we’ve had 280 mm of rain, with today being the first mainly dry day 7. This was why I’d chosen today to remove the fondant.

With that much rain the humidity levels are also quite high. With the Varroa tray in place I suspect that that humidity levels within the hive were higher still. Under these conditions I suggest that the fondant absorbs water faster than the bees can consume/store it.

These conditions are quite specific and are only likely to be an issue for beekeepers (or bees!) living in areas of high and regular rainfall. The original letter to The Scottish Beekeeper was from a beekeeper in Dumfries and Galloway.

Fife and the Midlands – the only areas I have many years experience of beekeeping in – both have less than 750 mm of rainfall per annum. I’ve had hives with both fondant and Varroa trays in place for weeks without any problems.

In my letter to The Scottish Beekeeper I described the hive insulation but failed to mention the open mesh floor. D’oh!

It’s now time to quickly write a follow up to explain these recent observations.

This example rather neatly demonstrates the influence of local conditions … and the importance of trying to interpret what you see when opening a hive. 

Since I’ve now written about it (my aide memoire for a forgetful beekeeper 😉 ) I’ll hopefully also remember this lesson next winter.

Speaking

It’s turning out to be a busy winter for talks to beekeeping associations.

These are increasingly popular as association members realise the benefits they offer.

You don’t have to negotiate icy roads in the dark to sit for an hour in a draughty church hall. 

No longer do you have to squint at an image projected onto a creamy-yellow wall with an irritating picture hook in the middle of every slide.

You can sit in the comfort of your own lounge (or bath), sipping shiraz and occasionally staring at a nice picture on a high resolution screen.

At least, that’s what I’m doing … as well as talking a bit 😉

I still lament the lack of homemade cakes. 

However, I have taught myself to make pizza during lockdown.

Pizza

If I’m mumbling a bit when I’m talking you’ll know why 😉


 

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.


 

Late season miscellany

I was struggling for a title for the post this week. It’s really just a rambling discourse on a variety of different and loosely related, or unrelated, topics.

Something for everyone perhaps?

Or nothing for anyone?

Beekeeping myths – bees don’t store fondant’

I only feed fondant in the autumn. I discussed how and why a month ago. Inevitably some people question this practice.

I’ve heard that bees don’t store fondant, don’t they just eat it when needed?

‘X’ (a commercial/old/decorated/opinionated beekeeper) assures me that bees do not store fondant.

Many beekeepers, even experienced beekeepers, seem to be under the impression that bees will not store fondant.

All gone!

So, let’s correct that ‘fact’ for starters, and file it forever where it belongs … in 101 Beekeeping Myths.

I added a single 12.5 kg block of fondant to all my colonies on the 28th of August. I checked them again on the 2nd of October (i.e. exactly 5 weeks later). About 80% had completely emptied the bag of fondant. All that remained was the empty blue plastic ‘husk’.

The few that had not completely emptied the bag were ~75% through it and I expect it to be all gone in a week or so.

Blue plastic ‘husks’ from ~60 kg of fondant.

So where has the fondant gone?

There are only two options 1. They’ve either eaten the fondant and used it to rear new brood, or stored it.

That amount of fondant is far more than they could consume and not rear lots of brood. So, it’s gone somewhere …

The weather has been OK. Bees are still gathering pollen and a small amount of late season nectar. They’ve not been locked away for a month just scoffing the fondant to keep warm.

They have been rearing brood – see below – but in ever-diminishing amounts, so this is unlikely to account for those empty blue bags.

But the biggest giveaway is the fact that the hives are now very heavy and almost every frame is packed solid with stores – again, see below.

The hives are actually very much heavier than they were at the end of August.

There’s not enough late season nectar flow to account for this increase in weight. There are also empty fondant bags on the top bars.

Although correlation does not necessarily imply causation, in this case, it does 😉

Bees do store fondant 2. It’s just sugar, why wouldn’t they?

Wall to wall brood stores

Out of interest I opened a couple of colonies to check the levels of stores and brood.

I only did this on colonies that had finished eating storing the fondant. Assuming the hive is heavy enough I remove the empty bag and the queen excluder from these, prior to closing the hive up for the winter. If they are still underweight I add another half block.

And another … all gone!

A 10-frame colony in the bee shed was typical. This was in a Swienty National poly brood box. These colonies are oriented ‘warm way’ and inspected from the back i.e. the opposite side of the hive to the entrance.

The first six frames were packed with capped stores.

Nothing else.

No brood, no gaps, nothing. Solid, heavy frames of nothing but stores.

The seventh frame had a small patch of eggs, larvae and a few open cells. In total an area no larger than my rather modestly sized mobile phone 3. Other than some pollen, the rest of the frame was filled with stores, again all capped.

Frame eight had a mobile-phone sized patch of sealed brood on both sides of the frame, with the remainder being filled with stores.

The ninth frame looked like the seventh and I didn’t bother checking the last frame in the box as the front face of it looked like it was just packed with stores.

I accept that the far side of that frame could have been a huge sheet of sealed brood, but I doubt it. This colony hadn’t been opened for more than a month, so the brood nest had not been rearranged by my amateur fumbling … it’s just as the bees had arranged it.

So, in total, the colony had less brood (eggs, larvae and capped) than would comfortably fit on a single side of one frame i.e. less than one twentieth of the comb area available to them. The rest, almost every cell, was sealed stores.

On the basis that a capped full National brood frame contains ~2.3 kg of stores 4 then this brood box contained about 22 kg of stores, which should be sufficient to get them through the winter.

Apivar strips

I treated all these colonies with Apivar at the same time as I fed them. Apivar needs to be present for 6-10 weeks, so it is still too soon to remove the strips.

However, it’s worth checking the strips haven’t been propolised up, or got embedded into the comb they’re adjacent to.

Apivar strip on wire hanger

Apivar is a contact miticide. The bees need to walk back and forwards over the strips. Therefore, if parts of the strips are gummed up with propolis, or integrated into comb, the bees will not have access.

Apivar strip partially gummed up with wax and propolis

You may remember that I tried hanging the strips on wire twists this season (see photo), rather than using the integrated plastic ‘spike’ to attach them to the comb. These wire hangers have worked well, for two reasons:

  1. The strips are more or less equidistant between the flanking combs. They are therefore less likely to get integrated into the comb 5, consequently …
  2. They are a lot easier to remove 🙂

I checked all the strips, scraping down any with the hive tool that had been coated with wax or propolis. This should ensure they retain maximal miticidal activity until it is time to remove them 6.

Scraped clean Apivar strip … ready for a couple more weeks of mite killing

And, it’s worth stressing the importance of removing the strips after the treatment period ends. Not doing so leaves ever-reducing levels of Amitraz (the active ingredient) in the hive through the winter … a potential mechanism for selecting Amitraz-resistant mites.

Au revoir and thanks for the memories

Other than removing the Apivar strips in a couple of weeks there’s no more beekeeping to do this year. And that task barely counts as beekeeping … it can be done whatever the weather and takes about 15 seconds.

As stressed above, it is an important task, but it’s not really an opportunity to appreciate the bees very much.

It must be done, whatever the weather.

Last Friday was a lovely warm autumn afternoon. The sun was out, the breeze was gentle and the trees were starting to show their fiery autumn colours. The bees were busy, almost self-absorbed, and were untroubled by my visit. It was a perfect way to wrap up the beekeeping year.

Like Fred commented last week, these last visits to the apiaries are always tinged with melancholy. Even in a year in which I’ve done almost no beekeeping, I’ve enjoyed working with the bees. It’s at this time of the season I realise that it’s a long time until April when I’ll next open a hive.

And, when you think about it, the active part of the season is shorter than the inactive part in northern latitudes 🙁

It was reassuring to see strong, healthy colonies showing no defensiveness or aggression. My split them and let them get on with it approach to queen rearing this season seems to have gone OK. With 2020 queens in most of the colonies I’ll hope (perhaps in vain) for reduced swarming next spring. I’m pretty certain that the colonies that were not requeened this year (under non-ideal conditions) generated more honey because there was no brood break while the new queen got out and mated.

Securely strapped up for the winter.

I’m confident that the colonies have sufficient stores and are all queenright. The mite levels are low – some much lower than others as I will discuss in the future – and the hives are securely strapped up for the winter ahead.

There’s no smoke without fire

And now for something completely different.

I’ve acquired a third main apiary this year and, because of its location, cannot carry equipment back and forwards all the time. I’ve therefore had to duplicate some items.

A little smoker

I didn’t want to shell out £60+ on a yet another Dadant smoker so dug out my first ever smoker from the back of the shed. I think this was originally purchased from Thorne’s, though not by me as I acquired it (at least) second hand, and it’s not listed in their catalogue any longer.

It’s a bit small and it has a tendency to go out, either through running out of fuel or simply because the ‘resting’ airflow is rather poor.

Consequently I often have to relight it.

I’m a big fan of using a blowtorch to light a smoker. If you get an auto-start model they work whatever the weather.

Or, more specifically, whatever the wind.

Trying to relight a recalcitrant smoker on a windy day with matches in the presence of a stroppy colony is not my idea of fun.

Of course, my colonies aren’t stroppy, but if they were going to be it would be when all I had was a box of matches in a strong breeze 😉

Rather than buying an additional blowtorch I instead purchased a kitchen or chef’s blowtorch, designed to produce the perfect crème brûlée. It was a ‘Lightning Deal’ for under £7 from Amazon. Even at full price it’s still only half the price of a cheap DIY blowtorch.

Blowtorch

It’s easy to fill, lights first time and immediately produces a focused blue flame. In contrast, my DIY blowtorch needs to warm up for 30 s. to change from billowing yellow 7 to an intense blue flame.

The chef’s blowtorch is also small enough to fit inside the same box I store/carry smoker fuel in. There is a lock to either prevent inadvertent ignition, or to produce an ‘always on’ flame.

If it survives the adverse environment of my bee bag it will be money well spent.

If not, I’ll make some crème brûlée 😉

There’s no smoke without fuel

Thorne’s had a late summer sale a fortnight or so ago. My order was finally shipped and arrived during a week when I was away and it was raining (two facts that are not unconnected … I’d disappeared to check my bees on the other side of the country where the weather was better).

The order sat outside in the rain and looked rather forlorn when I returned. Nothing was water damaged, not least because of the huge amounts of shredded packing protecting the contents.

Drying tonight

This stuff makes good smoker fuel. You just tear a handful off and stuff it in the smoker. It’s easy to light, smoulders well and doesn’t smell too acrid.

At least, once it’s dry it has all those desirable characteristics.

It’s now laid out drying on top of my canoe in the shed. I’m not even sure how they got so much in the delivery box. It looks like several cubic feet laid out like that, possibly enough for all of next year.

Waxworks

Although I’ve singularly failed to cycle a lot of old dark frames out of my colonies this year, I have managed to accumulate a lot of frames that need melting down. Some are old and dark, others are all drone comb in foundationless frames, and some are from a colony with a dud queen. I’d also accumulated quite a bit of burr or brace comb during my few beekeeping days of the season.

There’s not a lot of wax in most brood frames and the wax you can extract is rather dark. However, it’s perfectly acceptable to trade in for fresh foundation and makes very satisfactory firelighters.

Thorne’s Easi-Steam in action

And, after you extract the wax and clean up the frames you can reuse them. Simply add fresh foundation and you save yourself the drudgery of frame making. Result 😉

Or, if you use foundationless frames, you can just reuse them. Even better 🙂

A couple of years ago I treated myself to a Thorne’s Easi-Steam. I bought it without the steam generator as I already had one from my earlier homemade wax extractor 8. With the help of a mate who is a plumber I got the right sort of brass connectors to fit my steam generator to the Easi-Steam and I was ready to go.

Frames and brace comb ready for extraction

The Easi-Steam consists of a metal roof, a deep lower eke and a mesh and metal floor that needs a solid wooden floor underneath (which isn’t provided). You put it all together, add a brood box (almost) full of frames and fire up the steamer … then watch as the wax drips out into a bucket. ‘Almost’ because the brass connector stands proud and fouls the top bars of the frames 9, so you need to leave a gap.

It works well and leaks less than my homemade extractor. The recovered wax is remelted, cleaned up briefly, refiltered and is then ready for trading in or turning into firelighters.

This is all small scale stuff. With an oil drum, a big heater and an old duvet cover you can do much more, much faster. But I don’t need that capacity, or have the space to store the gear for the 363 days of the year it’s not being used.

The finished product

Here’s some I made earlier

There’s a long winter ahead and I think the time invested in wax extraction is more than justified when I …

  • Return from Thorne’s of Newburgh with 200 sheets of premium foundation having ‘paid’ with a just few kilograms of wax
  • Ignite another pile of felled rhododendron logs with a homemade fire lighter
  • Use the time I would have been making frames to do something more enjoyable 10

 

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 🙂

Long distance beekeeping

This post was originally entitled ‘lockdown beekeeping’. I changed it in the hope that, at some point in the future, we’ve all forgotten lockdown and are back to the ‘old normal‘. Instead, long distance beekeeping, better summarises the topic and might rank better in future Google searches …

But before I start, here’s some general advice …

Don’t do as I do, do as I say (elsewhere on this site 😉 )

I don’t think what I’m going to describe below was anything like ideal. In the end it worked out pretty well, but probably as much from luck as judgement. I’d do it again if I had to, but I’d prefer not to. I don’t think it is a workable solution for effective beekeeping in anything other than exceptional circumstances.

But 2020 has been an exceptional circumstance …

Mid-March madness

It was abundantly clear in very early March that a lockdown was inevitable 1 to restrict the spread of Covid-19. All the numbers were going in the wrong direction and other countries were already imposing quite draconian restrictions to control virus transmission 2.

I had speaking engagements with Oban & District BKA on the 12th and at the SNHBS event at Kinross on the 14th and, on the following day, I disappeared to my bolthole on the remote west coast of Scotland. 

The wild west

I decided to simply abandon the bees in Fife for at least a month while the country came to terms with movement restrictions, supermarket food deliveries, protecting the NHS and ‘working from home’.

On the day I left I checked that colonies were not too light, that the entrances were clear and that the roofs were secure and everything was strapped down.

March is too early to do anything with bees in Fife and my first inspections are usually not until mid/late April in a normal year, and even early May if there’s been a cold Spring. I therefore had a month to plan for the season ahead, with the expectation that I would have to manage the bees with the minimum possible number of visits for the next few months.

Planning

The beekeeping season contains a number of ‘moveable fixtures’.

By that I mean that certain things happen every season, but the time when they happen is not fixed. The timing depends upon the weather which, in turn, influences forage availability. It depends upon the strength of the colony, the location of the apiary and – for all I know – the phase of the moon.

Warm springs can lead to swarming by the end of April. Conversely, cold springs delay events. Dry summers generally put paid to the lime nectar and a protracted June gap can leave colonies starving in the middle of the season.

In the previous post I called these moveable fixtures the unknown knowns.

The variable timing of these moveable fixtures influences colony management by the beekeeper; this includes the spring honey harvest, swarm control and the summer honey harvest. In addition, it includes more mundane things like comb exchange, feeding the colony up for winter and Varroa management.

Bees and beekeeping are influenced by the environment, not the calendar 3.

The UK government imposed a nationwide lockdown on the 23rd of March 2020. Movement restrictions were imposed, including the distance you could travel from where you live.

Exemptions were made for allowed activities and, after lobbying from national associations and others, beekeeping was included as an exempt activity. Notwithstanding this, it was not going to be practical to conduct the usual weekly inspections from April until late July.

First inspections

I returned to Fife to conduct the first inspections in the third week of April. The spring was well advanced and the strong colonies were really booming. The overwintered nucs had built loads of brace comb in the space over the top bars and urgently needed to be moved to a full hive.

Overwintered nuc with brace comb

There were about 20 colonies spread between my two main apiaries. All were checked for space/strength, temper and the presence of a laying, marked and clipped queen 4. I didn’t have time to mollycoddle any weak colonies so these (having checked they were healthy) were united with nearby strong colonies.

Safely back in the hive

In addition, I didn’t have the luxury of time to see if poorly behaved colonies might pick up later in the season. To be frank, I had more colonies than I needed (or could easily cope with). With the need for swarm control looming, I decided to reduce colony numbers by uniting de-queened aggressive colonies with others in the same apiary. There were only a couple of these (identified the previous season and seemingly unimproved after the winter) … but every little bit helps.

United colonies, three supers, strapped up well … 25th April 2020

Finally, with the oil seed rape about to flower, I added three supers to the majority of the colonies. In a normal season these would have been added incrementally as needed. This year I had to assume (or hope) they might need them.

Swarm control

On my return to the west coast the spring was warming up. The primroses were looking fantastic and we had several weeks of outstanding weather.

Primroses – late April 2020

I enjoyed the good weather and spent the time fretting about the timing of swarm control.

My colonies tend to make swarm preparations between mid-May and the first week of June – a good example of a moveable fixture.

A priority this year was not to lose any swarms.

I did not want to inconvenience other beekeepers (or civilians’ 5) with swarms I managed to lose by ineptly doing my beekeeping from the other side of the country.

With most people trying to keep themselves isolated, 30,000 bees moving into a chimney would be a lot more than unwelcome.

Even in a normal year I do my very best not to lose swarms, and this was anything but a normal year.

I therefore decided to conduct pre-emptive swarm control on every colony in the third week of May. ‘Pre-emptive’ meaning that, whether the colonies showed any signs of swarming or not, I’d remove the queen and let them rear another.

Colonies do not swarm every year. Every now and again a strong colony of mine will show no inclination to swarm. These are great … I just pile another super or two on top and am thankful not to have to intervene.

However, strong colonies are more than likely to swarm and I didn’t feel I had the luxury of waiting around to find which wanted to and which didn’t.

A swarm in May (and how I avoided it … )

With the exception of a couple of our research colonies that seemed to be on a ‘go slow’ I treated all my colonies in the same way.

I used the nucleus method of swarm control. I removed the queen and one frame of emerging brood and put them into a 5 frame nuc box with a frame of foundation or drawn comb and a frame of stores. To ensure there were sufficient bees in the box I then shook in another frame of bees before sealing them up for transport.

All the nucs were moved to distant apiaries so there was no risk of bee numbers being depleted as they returned to the original hive.

And then there were three … nucs for pre-emptive swarm control

The parental colonies were left for 6 days and then checked for queen cells.

Ideally this should have been 7 days. By this time there would be no larvae young enough to generate additional queen cells from. However, there was a large storm moving in from the west and it was clear that there would be no possibility of doing any beekeeping while it moved through.

I therefore checked on the sixth day, knocked back all the queen cells, leaving just one good one, and then scarpered back to the west coast (meeting the storm en route).

However, before I disappeared I also checked all the nucs. All were doing fine. There was a good nectar flow and they had already drawn and laid up the frame out I’d given them. I therefore added two foundationless frames flanking the central frame. With frames either side these are usually drawn straight and true.

New comb with queen already laying it up

If you give the bees lots of foundationless frames together, particularly if the hive isn’t perfectly level, they will often make a real mess of drawing the comb out. By interleaving the new frames with those that were already drawn the bees are forced to maintain the required bee space on either side, so usually draw the frame out satisfactorily.

Getting the timing right … at least partly

When I left Fife on the 22nd of May the OSR was in full flower. It would finish sometime in early June.

My next dilemma was to time the following visit for the spring honey harvest. Too soon and the frames wouldn’t be capped. Too late and, being OSR, it might start to crystallise in the comb.

But I also wanted to deal with all the requeening colonies during the same visit and all of the nucs.

I’ve previously discussed the time it takes for a new queen to develop, emerge, mature, mate and start laying. It always takes longer than you’d like. The absolute minimum time is about two weeks, but it usually takes longer. Ideally I wanted to go through all the requeening colonies, find, mark and clip the queens or re-unite (with the nuc) those that had failed.

At the same time, with a strong nectar flow and a strongly laying queen, there was a real risk that the nucs were going to get overcrowded very fast. The longer they were left, the more chance that they would think about swarming.

I employed a number of local spies (beekeeping friends in the area) and queried them repeatedly 6 about the state of the OSR. Shortly after it finished, I returned to take off the spring honey.

A minor catastrophe

It was the 10th of June; this was exactly 20 days since leaving the requeening colonies with a single freshly-sealed queen cell.

I’ve previously mentioned that one of my apiaries is rather exposed to strong westerlies. Despite the wind-reduction netting and the rapidly growing willow hedge, this apiary had been really hammered by the storm on the 22nd/23rd of May.

Nuked nucs

Two nucs had lost their lids and crownboards and a full strapped-up hive had been blown over, denting the fence on its descent but remaining more or less intact.

How is the queen supposed to find the entrance?

The apiary hadn’t been checked since my last visit, so I’m assuming the damage happened during the storm in late May. That being the case, the nucs would have been open to the elements for about 18 days. Amazingly, both still contained laying queens and – despite looking a little the worse for wear – eventually recovered.

In contrast, the strapped up hive was not ‘open to the elements’. It had fallen entrance-first onto the ground. I think a few bees could fly from a gap where the ground didn’t quite block the entrance, but I was more concerned about getting them upright again to check too carefully.

Despite my best efforts I failed to find a queen in this hive. My frames are arranged ‘warm way’, so all the frames had slid together when the hive fell and it’s possible the queen didn’t survive 7.

Spring honey, nucs and queens

The spring honey harvest went well. The OSR frames were mostly capped. Those that weren’t could still be extracted as the honey would not shake out of the frame.

A fat frame of spring honey

It was my best year for spring honey since returning to Scotland in 2015. With the exception of that one big storm the weather had been pretty good and the bees had had ample opportunity to be out foraging.

However, although a few of the colonies had newly mated and laying queens, the majority did not. In most of them I found evidence that there would be a laying queen sometime soon … I usually infer this from the presence of ‘polished’ cells in the centre of the one or two of the central frames in the hive. This gave me confidence that there was likely to be an unmated, or just mated, queen in the box. There’s nothing much to be gained from actually finding her, so I would have to be a bit more patient.

Just as these things cannot be rushed, an overcrowded nuc cannot be ignored.

Almost all the nucs were fast running out of space. I therefore removed 2-3 frames of brood from each and replaced them with fresh frames. I used the frames of brood to boost the honey production colonies that were ‘busy’ requeening.

Mid-June and the foxgloves are in flower

By the 14th of June I was back on the west coast.

Late June rearrangements

I returned a fortnight later for a very busy couple of days of beekeeping.

By this time the summer nectar flow was starting. The nucs, even those ‘weakened’ by removing brood, were busy filling spaces with brace comb.

Comb in feeder

All of the requeening colonies were checked for a laying queen. A handful had failed, disappeared or whatever and now looked queenless. These were requeened by uniting them with a nuc containing the ‘saved’ queen from earlier in the season.

What could be simpler? That’s one of the main attractions of this method of swarm control.

The colonies with the first of the new laying queens were doing really well, with lovely fresh frames of wall-to-wall brood. It’s only after a queen has laid up a full frame or two that you get a proper impression of her quality. I can never properly judge this in the tiny little frames of a mini-mating nuc, so – despite the extra resources (bees, frames, boxes) needed – prefer to get queens mated and laying in hives with full-sized frames.

Good laying pattern

The remaining ‘unused’ nucs were all expanded up to full hives and given a super. All the strong colonies in the apiaries were again given three supers and left to get on with things.

Expanded nucs on the left, production hives on the right

It was a backbreaking few days, particularly because I spent the evenings jarring honey 8, but it left the apiaries in a good state for the summer nectar flow.

Summer honey

The only beekeeping I did in July was on the west coast of Scotland. I moved a couple of nucs up to full hives and, since the heather wasn’t yet in full flower, I gave them each a gallon or so of thin syrup to encourage the bees to draw comb to give the queen space to lay.

Welcome to your new home … nuc ‘promoted’ to hive with contact feeder in place

I finally returned to Fife to take the summer honey off in late August. I’ve recently posted a brief description of clearing supers during Storm Francis so won’t repeat it here.

In four days I removed all the supers and extracted the honey, fed and treated the bees for the winter, and left the colonies strapped up securely for … goodness knows when.

The summer honey harvest was unusual. One of my apiaries did fantastically well, more than the last two seasons combined, and by far my best year since 2015.

The other apiary was just slightly worse than … utterly pathetic.

This second apiary is usually very reliable. The forage in the area has been dependable and, in some years, the lime has yielded very well. However, not this year and, since I wasn’t about, I don’t know why.

I did it my way … but it wasn’t very satisfying

That last paragraph rather neatly sums up the 2020 beekeeping season.

Overall the season must be considered a success; I didn’t lose any swarms, the majority of colonies were requeened successfully, all of the colonies are going into the winter strong, fed and treated, and the overall honey crop was very good.

However, it’s all been done ‘remotely’, both literally and figuratively. I’ve not felt as though I’ve been able to watch the season and the colonies develop together. I don’t feel as though I was ‘in tune’ with what was happening in the hives. I can’t explain why some things worked well and other things – like the apiary with no honey 🙁 – failed miserably.

My notes are perfunctory at best, “+3 supers, Q laying well”, and contain none of the usual asides about what’s happening in the environment. There’s no indication of what was flowering when, whether the year was ‘early’, ‘late’, or ‘about normal’, when the migrant birds arrived or left.

I’ve done less beekeeping this year than in any year in at least a decade. Since I rather like beekeeping, this means it has been a bit of a disappointment. Since I’ve spent less time with the bees, and I’ve been so rushed when I have been working with them, I feel as though I’ve learnt less this year than normal.

What didn’t get done?

With irregular and infrequent visits some things were simply ignored this season.

I did very little Varroa monitoring. With the Apivar strips now in it’s clear that some hives have higher Varroa counts than I’ve seen in the last few years 9. However, not all of them. Some colonies appear to have extremely low mite loads.

We finally managed to check the levels of deformed wing virus in our research colonies quite late in the season once the labs partially reopened. The levels were reassuringly low. This strongly suggests that the mite levels are not yet at a point threatening the health of the colonies.

I’ve singularly failed to do much in the way of brood comb exchange this season. This means I’m going to have to take a bit more care next year to cycle out the old, dark frames and replace them with brand new ones.

Here’s one I did manage to replace

Again, not the end of the world, but ‘bad beekeeping’ all the same.

As I’m putting the finishing words together for this post the government is re-introducing further curfews and restrictions … maybe next year will be more of the same?


 

Trees for bees

The pollen and nectar sources available to bees depend upon the time of the year and the area of the country. The bees will enthusiastically exploit what’s available, but will struggle if there’s a dearth of either.

For much of this year I’ve been living on the remote west coast of Scotland, in an area with a very low population density and an even lower density of beekeepers … by my calculations less than 1 per 25 km2.

It’s very different from Fife (on the east coast of Scotland). It’s warmer and wetter here and there is almost no arable farming. One or two of the crofts on the coast might grow a bit of barley or wheat, but the few fields tend to be used for grazing and hay production. There’s probably no oil seed rape within 50 miles.

And there’s also no Varroa 🙂 … but I’ll discuss that another time.

Trees – in this case providing shelter from the westerlies – and bees

It goes without saying, since I’m spending so much time here, I now have bees here 🙂

Triffids and mad honey

The primary nectar source for honey is heather, which doesn’t yield until August. I have less than zero experience with heather honey – other than on toast – so have a lot to learn.

The land is on the edge of moorland with a mix of larch and scots pine, with a shrubby understorey of birch and some rowan. It’s awash with wildlife; pine marten, eagles, crossbills and the elusive Scottish wildcat 1.

Pine marten raiding the bird table

However, at least until a year or two ago, much of the land was covered in a triffid-like invasive mass of rhododendron. Swathes of the west of Scotland and Ireland are blighted by this shrub which was first introduced as an ornamental plant in the 18th Century.

Rhododendron as far as the eye can see – now cleared and planted with hazel and rowan

I’m biased, but I’d argue that rhododendron has no redeeming features. It seeds itself everywhere and smothers all other groundcover, leaving a near sterile environment. It’s terrible for wildlife. The flowers are briefly showy but not hugely attractive, either to me or to bees – whether wild or managed.

Oh yes, and the nectar produces hallucinogenic honey. I’ve even less experience of this than I do of heather honey … but in this case I have no desire to learn more.

So, I’ve been slowly clearing the rhododendron and replanting the cleared areas.

Trees for Life

A friend who used to keep bees in this are a few years ago commented that there was a shortage of early season pollen, meaning that colonies could sometimes struggle to build up. A colony that fails to build up well early in the season will struggle to reproduce i.e. swarm.

Of course, like most beekeepers, I don’t really want my bees to swarm.

However, I do want my colonies to be strong enough to want to swarm. That way, there will be loads of foragers to exploit the heather from late July. In addition, I’m particularly interested in queen rearing and building my stocks up, and for both these activities I need the colonies to have good access to pollen and nectar … and to be big and strong.

With no agriculture to speak of there are also no pesticides. Perhaps as a consequence of this there are a very large number of bumble bees about. These give me hope that there might actually be sufficient pollen, but more can only be beneficial.

And more will certainly be helpful if I end up with a reasonable number of colonies that could compete with the native bees for environmental resources 2.

I’m therefore busy planting trees in some of the areas cleared of rhododendron. Not quite on the same scale as the Trees for Life rewilding at Dundreggan, but every little bit helps 😉

Why trees?

Partly because they’ll take the longest to grow, so need to go in first, and partly because many of them are excellent sources of early season pollen and nectar.

It’s also the sort of epic-scale ‘gardening’ involving chainsaws and brushcutters, huge bonfires, cubic metres of firewood and lots of digging that I have an affinity for. I don’t have the patience for pricking-out and growing on bedding plants, or weeding the herbaceous border 😉

Native trees

I’m keen to re-plant with native trees and shrubs. I know they’ll do well in this environment and they can be readily sourced, either locally or at little expense.

As will become clear shortly, the ‘expense’ part is a not an insignificant consideration with the grazing pressure from deer in this area.

I’ve initially focused on just six species; alder, hazel, wild cherry (gean), poplar, willow and  blackthorn.

Of these I’ll skip over the blackthorn (Prunus spinosa). Although the white spring flowers produce nectar, I chose it to make a spiky hedge and for the distant opportunity of making sloe gin. However, I’m going to have to try again as the bareroot whips I planted last winter have done almost nothing.

Alder

Alder (Alnus glutinosa) produces large amounts of early season pollen. It also thrives in damp ground and we have plenty of that. I’ve planted quite a bit of alder and it’s all doing pretty well. There is already a lot along the banks of nearby streams and in boggy areas at the side of the loch, so I know it will do well in this area. In fact, the few dozen I’ve planted are insignificant in comparison to what’s growing locally, but I wanted to create an area of mixed alder and willow carr 3. I planted 30 cm bareroot whips last winter and those that have survived the deer have doubled or trebled in height.

Alder

Alder, once established, seems reasonably resistant to browsing by deer, presumably because they find it relatively unpalatable. The long-term plan is to coppice the alder – it makes good firewood when properly dried. It has also historically been used to make clogs, but I’ll be cutting it back before it’s grown enough for anything but the tiniest feet.

Hazel

Like alder, hazel (Corylus avellana) is a good source of early season pollen. Most readers will be familiar with the catkins which appear as early as mid-February. The area shown in a picture (above), now cleared of rhododendron, has been planted with hazel. It’s a south-facing slope with thin soil but most seem to be doing OK so far.

Hazel

There are a couple of mature hazel nearby and I managed to find a few seedlings which I transplanted, however the majority went in as bareroot whips.

Hazel is popular with deer and with the red squirrels. The fact I needed to buy barerooted trees probably reflects the fact that the squirrels get most of the nuts, and those that do germinate are then eaten by the deer. It’s a tough life.

Gean

Gean is the Scottish name for the wild cherry (Prunus avium) 4. It flowers in April and is a great source of nectar and pollen for the bees. I’ve only planted a few of these, in scattered groups of three, or along the side of the track. Despite gean not really flourishing in acid, peaty soil they seem to have established well and are already approaching shoulder height. Gean, like rowan 5, is also great for the birds and the thrushes will probably get the majority of the fruit that sets.

Poplar or aspen

Poplar or aspen (Populus tremula) is a favourite of mine. The leaves have pale undersides and are held on long, flattened petioles. As a consequence they flutter in the faintest of breezes and are a wonderful sight, particularly planted against a backdrop of dark brooding conifers.

Poplar or aspen (Populus tremula)

In fact, poplar is so attractive I’d have planted it even if it was of no interest to the bees.

Poplar is wind pollinated and the bees probably only get a little pollen from it. Some species also produce early season sap that is a major component of propolis apparently. Finally, poplar are susceptible to a rust or fungus called Melampsora, and the bees collect the spores if they need protein and there’s no pollen to be found.

Inaccessible aspen

The standard way to propagate poplar is by root cuttings. There is relatively little poplar around here, and none I could have easily grubbed up the roots from. However, after a bit of searching I discovered Eadha Enterprises in Lochwinnoch, near Glasgow. Eadha is derived from the old gaelic word for aspen. They are a social enterprise specialising in aspen production from stocks of known provenance. The cell-grown saplings I received, which are going in this winter, are derived from trees on the Isle of Arran.

Willow

In contrast to the relative difficulty of propagating aspen, you have to try hard not to propagate willow. A foot long, pencil-thick cutting – taken more or less any time of the year – will root very quickly. Even if left in a bucket of water for a fortnight.

Willow cuttings ready for planting

I’ve planted a lot of willow from local trees (probably goat willow, Salix caprea, but they hybridise so freely you can never be certain) and planted it in variously boggy bits of ground, alongside some of the alder. Willow is generally dioecious (male or female) and you need to plant male trees for the pollen. I planted some female as well as they both produce nectar.

Willow male catkins

In addition to just planting them directly, I grew a few on in tubs in potting compost. These developed good root systems and grew better.

Pot grown cutting ready for planting

However, willow is a favourite of deer and the cuttings I’ve planted have periodically been hammered by both red and roe deer.

Sabre planting and oversize cuttings

The obvious way to prevent deer damage is to build a 6 foot high fence but, because of the rocky nature of the ground, this is impractical (which is an easier way of saying eye-wateringly expensive).

If you visit the Scottish highlands you’ll be familiar with the site of small burns cascading down gulleys in the hillside. Often the the sides of the gulleys have dense growth of alder, birch or willow.

This is not just because of the nearby water supply. After all, much of the land receives 2000 mm of rain or more a year.

The other reason the trees are there (and not on the open moor) is that the gulley is steep sided and the trees therefore experience less grazing pressure. You can recapitulate this by so-called sabre planting 6. In this you plant trees of 1m+ height perpendicular on slopes of at least 40°. The slope makes the growing tips less accessible and they gradually grow out and away, straightening up as they do.

I’ve only discovered this strategy recently 7 and will be trying it in a couple of locations.

An alternative strategy, particularly suitable for willow, is to plant ‘cuttings’ that are already too big for the deer to reach the growing tips.

A ‘big’ willow cutting – there’s a game trail 2m from this that’s used every night.

To avoid grazing by red deer this means at least 1.5-1.8 m in height. The technique is almost the same as planting the foot long, pencil-thick cuttings … you just push them into the ground. It’s worth noting that you need to push them a good distance into the ground and stake them. About 50% of the big cuttings I’ve planted have apparently rooted. I’m pretty certain that those that didn’t failed because they were not staked firmly enough. This makes sense … as the leaves sprout they become wind-resistant and gales will quickly damage the developing root system through simple leverage.

Gimme Shelter

I’ve planted trees for bees before. We planted lots of goat willow and mixed hedging around our research apiary in Fife in early 2018. The combination of a major fire in my research institute the following year, and Covid this year, meant that the trees have been just left to get on with it.

Mixed hedging and willow and wildflowers (aka weeds, but the bees don’t know that)

And they have. This was a bare earth bank in February 2018. We still need a windbreak, but even that can probably be dispensed with in a year or so. Not all the trees have thrived, but I’m more than satisfied considering the neglect they received.

Oh deer

Scotland is overrun with deer. A review over 50 years ago stated that the optimum number of red deer the land could maintain was ~60,000. They defined ‘optimum’ in terms of avoiding agricultural damage, while allowing natural regeneration with no necessity for fencing. This would also ensure that there’s enough food for the deer during the winter months.

The current estimate is that there are over 450,000 red deer in Scotland. As a consequence there are many areas with no natural tree regeneration without installing expensive and intrusive fencing. In addition, the deer are often in lousy condition and/or starve to death in hard winters.

If you look carefully you can see a couple more coming down the track. There’s also a beehive in the video above, though it’s tricky to spot.

In addition to red deer we also have a smaller number of roe deer … equally attractive and almost equally destructive.

Don’t get me wrong, I love deer … particularly braised slowly with a good quality, full-bodied red and winter vegetables.

Not beekeeping?

OK, in terms of specifics, not beekeeping. However, I’d argue that beekeepers have a responsibility to maintain and protect their environment. This includes ensuring that their charges do not impact negatively on the native wildlife.

This area is towards the extreme north-west corner of the country and the introduction of a quarter of a million bees (~5 hives) will inevitably impact the pollen and nectar available for the established native pollinating insects.

I could choose to avoid the latter by ‘not beekeeping’, but I’ve instead chosen to try and improve the resources available in the environment. Time will tell if there is a shortage of pollen and if my bees thrive.

If they don’t, at least there will be a bit less bloody rhododendron 😉


Notes

If you’re interested in native trees I thoroughly recommend the Handbook of Scotland’s Trees by Reforesting Scotland. It has lots of good advice about collecting seed and planting, but also has details of uses for trees and folklore. Whilst it focuses on Scotland’s trees (the clue is in the title), most grow elsewhere as well, and it’s packed with information. If you are interested more generally in the history, uses and planting of woodlands it’s probably worth reading all 16,452 pages (a slight exaggeration, but it is a magnum opus) of Oliver Rackham’s Woodlands which is a masterpiece.

 

Winter bee production

There are big changes going on in your colonies at the moment.

The summer foragers that have been working tirelessly over the last few weeks are slowly but surely being replaced. As they die off – whether from old age or by being eaten by the last of the migrating swallows – they are being replaced by the winter bees.

Between August and late November almost the entire population of bees will have changed. The strong colonies you have now (or should have) will contain a totally different workforce by the end of the year.

Forever young

The winter bees are the ones responsible for getting the colony from mid/late autumn through to the following spring. They are sometimes termed diutinus bees from the Latin for “long lived”.

These are the bees that thermoregulate the winter cluster, protecting the queen, and rearing the small amounts of brood during the cold, dark winter to keep the colony ticking over.

Midwinter cluster

A midwinter colony

Physiologically they share some striking similarities with so-called hive or nurse bees 1 early in the summer.

Both hive bees and winter bees have low levels of juvenile hormone (JH) and active hypopharyngeal glands. Both types of bee also have high levels of vitellogenin, high oxidative stress resistance and corpulent little bodies.

But early summer nurse bees mature over a 2-3 week period. Their JH levels increase and vitellogenin levels decrease. This induces additional physiological changes which results in the nurse bee changing into a forager. They sally forth, collecting nectar, pollen and water …

And about three weeks later they’re worn out and die.

Live fast, die young

And this is where winter bees differ. They don’t age.

Or, more accurately, they age   v  e  r  y    s  l  o  w  l  y.

In the hive, winter bees can live for 6 months if needed. Under laboratory conditions they have been recorded as living for up to 9 months.

They effectively stay, as Bob Dylan mumbled, forever young.

Why are winter bees important?

Although not quite eternal youth … staying forever young is useful as their longevity ensures that the colony does not dwindle and perish in the middle of winter.

With little or no nectar or pollen available in the environment the colony reduces brood rearing, and often stops altogether for a period.

But what about the kilograms of stores and cells filled with pollen in the hive? Why can’t they use that?

Whilst both are present, there’s nothing like enough to maintain the usual rate of brood rearing. If they tried the colony would very quickly starve.

Evolution has a very effective way of selecting against such rash behaviour 🙁

If you doubt this, think how quickly hives get dangerously light during the June gap. With no nectar coming in and thousands of hungry (larval) mouths to feed the colony can easily starve to death during a fortnight of poor weather in June.

The winter bees ‘hold the fort’, protecting the queen and rearing small amounts of brood until the days lengthen and the early season pollen and nectars become available again.

And, just as the winter bees look after the viability of the colony, the beekeeper in turn needs to look after the winter bees … we rely on them to get the colony through to spring.

Lots of bees

Can you identify the winter bees?

But before we discuss that, how do you identify and count the winter bees? How can you tell they are present? After all, as the picture above shows 2, all bees look rather similar …

Counting the long lived winter bees

The physiological changes in winter bees, such as the JH and vitellogenin levels, are only identifiable once you’ve done some rather devastating things to the bee. These have the unfortunate side effect of preventing it completing any further bee-type activities 🙁

Even before you subject them to that, their fat little bodies aren’t really sufficiently different to identify them visually.

But what is different is their longevity.

By definition, the diutinus or winter bees are long lived.

Therefore, if you record the date when the bee emerged you can effectively count back and determine how old it is. If it is more than ~6 weeks old then it’s a winter bee.

Or the queen 😉

And, it should be obvious, if you extrapolate back to the time the first long lived bees appear in the hive you will have determined when the colony starts rearing winter bees.

The obvious way to determine the age of a bee is to mark it upon emergence and keep a record of which marks were used when. Some scientists use numbered dots stuck to the thorax, some use combinations of Humbrol-type paint colours.

I’m not aware that anyone has yet used the barcoding system I discussed recently, though it could be used. The winter bee studies I’m aware of pre-date this type of technology.

Actually, some of these studies date back almost 50 years, though the resulting papers were published much more recently.

This is painstaking and mind-numbingly repetitive work and science owes a debt of gratitude to Floyd Harris who conducted many of the studies.

Colony age structure – autumn to winter

Here is some data showing the age structure of a colony transitioning from late summer into autumn and winter. There’s a lot in this graph so bear with me …

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

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

The graph shows the numbers and ages of bees in the colony.

The ages of the bees is indicated on the vertical axis – with eggs and brood (the youngest) at the bottom, coloured black and brown respectively. The adult bees can be aged between 1 and ~100 days old 3. The number of bees is indicated by the width of the coloured bar at each of the nine 12 day intervals shown.

All of the adult bees present in the hive at the end of August are coloured blue, irrespective of their age. There are a lot of these bees at the end of August and almost all of them have disappeared (died) by mid-November 4.

The remaining colours indicate all the bee that emerge within a particular 12 day interval. For example, all the bees that emerge between the 31st of August and the 12th of September are coloured yellow.  Going by the width (i.e. the numbers of bees of that age) of the yellow bars it’s clear that half to two-thirds of these bees die by mid October, with the rest just getting older gracefully.

But look at the cohort that emerge between the end of September and early October, coloured like this 5. The number of these bees barely changes between emergence and early December. By this time they are 72 days old i.e. an age that most summer bees never achieve.

Brood breaks and climate

In the colony shown above the queen continued laying reduced numbers of eggs – the black bars – until mid-October and then didn’t start again until the end of November. During this period the average age of the bees in the colony increased from ~36 days to ~72 days and the strength of the colony barely changed.

The figure above comes from a BeeCulture article by Floyd Harris. The original data isn’t directly referenced, but I suspect it comes from studies Harris conducted in the late 70’s in Manitoba, some of which was subsequently published in the Journal of Apicultural Research. In addition, Harris co-authored a paper presenting similar data in a different format in Insectes Sociaux which describes the Manitoban climate as having moderate/hot summers and long, cold winters.

My hives in Scotland, or your hives in Devon, or Denmark or wherever, will experience a different climate 6.

However, if you live in a temperate region the overall pattern will be similar. The summer bees will be replaced during the early autumn by a completely new population of winter bees. These maintain the colony through to the following spring.

The dates will be different and the speed of the transition from one population to the other may differ. The timing of the onset of a brood break is likely to also differ.

However, the population changes will be broadly similar.

And, it should be noted, the dates may differ slightly in Manitoba (and everywhere else) from year to year, depending upon temperature and forage availability.

Colony size and overwintering survival

Regular readers might be thinking back to a couple of posts on colony size and overwintering survival from last year.

One measured colony weight, showing that heavier colonies overwintered better 7. A second discussed the better performance of local bees in a Europe-wide study of overwintering survival. In this, I quoted a key sentence from the discussion:

“colonies of local origin had significantly higher numbers of bees than colonies placed outside their area of origin”

I can’t remember when during the season those studies recorded colony size, but I’m well aware that large colonies in the winter survive better.

The colonies that perish first in the winter are the pathetic grapefruit-sized 8 colonies with ageing queens or high pathogen loads.

In contrast, the medicine ball-sized ‘boomers’ go on and on, emerging from the winter strongly and building up rapidly to exploit the early season nectar.

But what the graph above shows is that the bees in a strong colony in late summer are a completely different population from the bees in the colony in midwinter.

The strength of the midwinter colony is determined entirely by when winter bee rearing starts and the laying rate of the queen, although of course both may be indirectly influenced by summer colony strength.

The influence of the queen

Other than this potential indirect influence, it’s possibly irrelevant how large the summer colony is in terms of winter colony size (and hence survival).

After all, even if the summer bees were three times as numerous, their fate is sealed. They are all going to perish six weeks or so after emergence.

Are there ways that beekeepers can influence the size of the overwinter colony to increase its chances of survival?

I wouldn’t pose the question if the answer wasn’t a resounding yes.

It has been known for a long time 9 that older queens stop laying earlier in the autumn than younger queens. As explained above, the longer the queen lays into the autumn the more winter bees are going to be produced.

Mattila et al., 10 looked at the consequences of late season (post summer honey harvest) requeening of colonies. In these they removed the old queen and replaced her with either a new mated or virgin queen, or allowed the colony to requeen naturally.

Using the ’12 day cohort’ populations explained above, the authors looked at when the majority of the winter bees were produced in the colony, and estimated the overall size of the winter colony.

The influence of new queens on winter bee production.

The influence of new queens on winter bee production. Note shift to the right in B, C and D, with new queens.

With the original old queen, 53% of winter bees were produced in the first two cohorts of winter bees. With the requeened colonies 54-64% of the winter bees were produced on average 36 days later, in the third and fourth cohorts of winter bees.

This indicates that young queens produce winter bees later into the autumn.

This is a good thing™.

In addition, though the results were not statistically significant, there was a trend for colonies headed by new queens to have a larger population of bees overwinter.

Perhaps one reason the requeened colonies weren’t significantly larger was that the new queens delay the onset of winter bee rearing. I’ll return to this at the end.

The influence of deformed wing virus (DWV)

Regular readers will know that this topic has been covered extensively, and possibly exhaustively, elsewhere on this site … so I’ll cut to the chase.

DWV is the most important virus of honey bees. When transmitted by Varroa destructor there is unequivocal evidence that it is associated with overwintering colony losses. The reason DWV causes overwintering losses is that it reduces the longevity of the winter bees.

The virus might also reduce the longevity of summer bees but,

  1. there’s so many of them to start with
  2. there’s loads more emerging every day, and
  3. they only survive a few weeks anyway,

that this is probably irrelevant in terms of colony survival.

Dainat et al., (2012) produced compelling evidence showing that DWV reduces the longevity of winter bees 11. The lifespan was reduced by ~20%.

A consequence of this is that the winter bees die off a little faster and the colony shrinks a little more. At some point it crosses a threshold below which it cannot thermoregulate the cluster properly, further limiting the ability of the colony to rear replacement bees (assuming the queen is able to lay at a low rate).

This colony is doomed.

Even if they stagger through to the longer days of spring they contain too few bees to build up fast. They’re not dead … but they’re hardly flourishing.

Winter bees and practical beekeeping

I think there are three ways in which our understanding of the timing of winter bee production should influence practical beekeeping:

Firstly … The obvious take-home message is that winter bees must be protected from the ravages of DWV. The only way to do this is to minimise the mite population in the colony before the winter bee rearing starts.

The logical way to do this is to treat using an approved miticide as soon as practical after the summer honey is removed 12.

I discuss the importance of the timing of this treatment in When to treat?, which remains one of the most-read posts on this site.

Secondly … Avoid use of miticides (or other colony manipulations) that reduce the laying rate of the queen in early autumn.

When I used to live at lower latitudes I would sometimes use Apiguard. This thymol-containing miticide is very effective if used when the temperature is high enough. However, in my experience a significant proportion of queens stop laying when it is being used. Not all, but certainly more than 50%.

I don’t know why some stop and others don’t. Is it genetic? Temperature-dependent?

Whatever the reason, they stop at exactly the time of the season you want them to be laying strongly.

Thirdly … consider requeening colonies with young queens after the summer honey is removed. This delays the onset of winter bee production and results in the new queen laying later into the year. The later start to winter bee production gives more time for miticides to work.

A win-win situation.