Tag Archives: Varroa

The day job

It’s no secret that I have both amateur and professional interests in bees, bee health and beekeeping.

During the weekend I sweat profusely in my beesuit, rushing between my apiaries in Central and Eastern Fife, checking my colonies – about 15 at the autumn census this year – averting swarms, setting up bait hives, queen rearing and carrying bulging supers back for extraction.

Actually, not so much of the latter in 2017¬† ūüôĀ ¬†I did get very wet though, much like all the other beekeepers in Fife.

The BSRC labs

The BSRC labs …

During the week I sit in front of a large computer screen running (or sometimes running to keep up with) a team of researchers studying the biology of viruses in the Biomedical Sciences Research Complex (BSRC) at the University of St. Andrews. Some of these researchers work on the biology and control of honey bee viruses.

During the winter the beekeeping stops, but the research continues unabated. The apiary visits are replaced with trips in the evenings and weekends to beekeeping associations and conventions to talk about our research … or sometimes to talk about beekeeping.

Or both.

This weekend I’m delighted to be speaking at the South Devon Beekeepers Convention in Totnes on the science that underpins rational and practical¬†Varroa¬†control.

Which came first?

I’ve been a virologist my entire academic career, but I’ve only worked on honey bee viruses for about 6 years. I’ve been a beekeeper for about a decade, so the beekeeping preceded working on the viruses of bees.

However, the two are inextricably entwined. Having a reasonable amount of beekeeping experience provides a unique insight into the problems and practicalities of controlling the virus diseases that bees get.

Being able to “talk beekeeping” with beekeepers has been very useful – both for the communication of our results to a wider audience and in influencing the way we approach our research.

Increasingly, the latter is important. Researchers need to address relevant questions, using their detailed understanding of the science to deliver practical solutions to problems1. There’s no point in coming up with a solution if there’s no way it’s implementation is compatible with beekeeping.

Deformed wing virus

DWV symptoms

DWV symptoms

The most important virus for most beekeepers in most years is deformed wing virus (DWV). This virus¬†“does what it says on the tin”¬†because, at high levels, it causes developmental defects in pupae that emerge with shrivelled, stunted wings. There are additional developmental defects which are slightly less obvious, but there are additional (largely invisible) changes which are of greater importance.

DWV reduces the lifespan of worker bees. This is probably not hugely significant in workers destined to live only a few weeks in midsummer. However, the winter bees that get the colony through from September through to March must live for months, not weeks. If these bees are heavily infected with DWV they die at a faster rate. Consequently, the colony dwindles and dies out in midwinter or early Spring. At best, it staggers through to March and then never builds up properly. It’s still effectively a winter loss.

Our research focuses on how¬†Varroa influences the virus population. There’s very good evidence now that DWV transmission by¬†Varroa leads to a significant increase in the¬†amount of virus, and a considerable¬†decrease in the diversity of the virus population.

So what?

Well, this is important because if we want to control the virus (i.e. to¬†reduce DWV-associated disease and colony losses)¬†it must help to know the proper identity of the virus we are trying to control. It will also help us¬†measure how well our control works. We know we’re measuring the right thing.

We’re working with researchers around the world to define the important characteristics of DWV strains that cause disease and, closer to home, with entire beekeeping associations to investigate practical strategies to improve colony health.

Chronic bee paralysis virus

CBPV symptoms

CBPV symptoms

We’re about to start a large collaborative project on the biology and control of chronic bee paralysis virus (CBPV). This virus is becoming a significant problem for many beekeepers and is increasing globally. It’s a particular problem for some bee farmers.

CBPV causes characteristic symptoms of dark, hairless, oily-looking bees that sometimes shiver, dying in large smelly piles at the hive entrance. It typically affects very strong colonies in the middle of the season. It can be devastating. Hives that should be the most productive ones in the apiary fail catastrophically.

Why is a virus we’ve known about for decades apparently increasing in the amount of disease it causes? Are there new virulent strains of the virus circulating? Are there particular beekeeping practices that facilitate it’s spread? We’re working with collaborators in the University of Newcastle to try and address these and related questions.

I’ll write more about CBPV over the next year or so. It won’t be a running dialogue on the research (which would be crushingly dull for most readers), but will provide some background information on what is a really fascinating virus.

At least to a virologist ūüėČ

And perhaps to beekeepers.

Grow your own

As virologists, we approach the disease by studying the virus. Although we maintain an excellent research apiary, we don’t do many experiments in ‘the field’. Almost all the work is done in test tubes in incubators in the laboratory … or in bees we rear in those incubators.

Grow your own

Grow your own …

We can harvest day-old larvae (or even eggs) from a colony and rear them to emergence as adult bees in small plastic dishes in the laboratory. We use an artificial diet of sugar and pollen to do this. It’s time consuming – they need very regular feeding – but it provides a tightly controllable environment in which to do experiments.

Since we can rear the bees, we can therefore easily test the ability of viruses to replicate in the bees. Do all strains of the virus replicate equally well? Do some strains outcompete others? Does the route by which the virus is acquired influence the location(s) in the bee in which the virus replicates? Or the strains it is susceptible to? Or the level of virus that accumulates?

And if our competitors are reading this, the answer to most of those questions is ‘yes’ ūüėČ

We can even ask questions about why and how DWV causes deformed wings.

Again, so what? We suspect that DWV causes deformed wings because it stops the expression of a gene in the bee that’s needed to make ‘good’ wings. If we can identify that gene we might be able to investigate different strains of honey bee for variation in the gene that would render them less susceptible to being ‘turned off’ by DWV. That might be the basis for a selective breeding project.

It’s a simplistic explanation, but it’s this type of molecular interaction that explains susceptibility to a wide range of human, animal and plant diseases.

Bee observant

Bee health is important, and not fundamentally difficult to achieve. There are some basics to attend to … strong hives, good forage, good apiary hygiene etc. However, it primarily requires good powers of observation – does something look odd? Are there lots of mites present? How does the brood look?

If things aren’t right – and often deducing this means comparisons must be made between hives – then many interventions are relatively straightforward.

Not long for this world ...

Not long for this world …

The most widespread problems (though, interestingly, this doesn’t apply to CBPV) are due to high levels of¬†Varroa infestation. There are effective and relatively inexpensive ways to treat these … if they’re used properly.

More correctly, they’re relatively inexpensive whether they’re used properly or not. However, they’re pretty ineffective if not used properly ūüėČ

Regular checks, good record keeping, comparisons between hives and informed observation are what is needed. Don’t just look, instead look for specific things. Can you see bees with overt symptoms of DWV? Are there bees with¬†Varroa riding around on their backs? The photo above has both of these in plain view. Are some hairless bees staggering around the top bars with glossy abdomens, or clinging to the side bars shaking and twitching?

Don’t wait, act

I’ve no doubt that scientists will be able to develop novel treatments to control or prevent virus infections of bees. I would say that … I’m a scientist ūüėČ ¬†However, I’m not sure beekeepers will be able to afford them, or perhaps even want to use them, or that they’d be compatible with honey production or of any use in Warr√© hives¬†etc.

I’m also not sure how soon these sorts of treatments might become available … so don’t wait.

If there are signs of obvious DWV infection you need to do something. ‘Obvious’ because DWV is always present, but it’s usually harmless or at least tolerated by the bees. My lab have looked at thousands of bees and have yet to find one without detectable levels of DWV. However, healthy bees have only about 1/10,000 the level of DWV present in sick bees … and these are the ones that have obvious symptoms.

I’ve discussed¬†Varroa control elsewhere, and will again.

Unfortunately, if your colony has signs of CBPV disease then Varroa control is not really relevant. The virus is transmitted from bee to bee by direct contact. This probably accounts for the appearance of the disease primarily in very strong colonies.

At the moment there’s little you can do to ‘cure’ a CBPV-afflicted colony. I hope, in 2-3 years we will have a better idea on what interventions might work. We have lots of ideas, but there are a lot of basic questions to be addressed before we can test them.

Field work

Field work

Business and pleasure

The half of my lab that don’t work on bee viruses study fundamental mechanisms of virus replication and evolution. They do this using human viruses, some of which are distant relatives of DWV. They work on human viruses as it’s only these that have excellent model systems to facilitate the types of elegant experiments we try to do. They’re also relatively easy to justify in funding applications, and it allows us to tap into a much bigger pot for funding opportunities (human health R&D costs probably total ¬£2 billion/annum, bees might be ¬£2 million/annum).

And no, my lab don’t get anything like that much per year for our research!

Importantly, the two activities on human and honey bee viruses are related. Our experience with the human viruses related to DWV made us well-qualified to tackle the bee virus. They replicate and evolve in very similar ways, we quantify them in the same way and there may be similarities in some ways we could approach to control them.

And with the bee viruses I can mix business with pleasure. If I’m going to the apiary I’ll get to see and handle bees, despite it being officially “work”. It doesn’t happen as much as I’d like as I’m usually sat behind the computer and all of the ‘bee team’ have been trained to work with bees by the ESBA.

However, at least when I talk to collaborators or to the beekeeping groups we’re fortunate to be working with we – inevitably – talk about bees.

And that’s fun¬† ūüėÄ


1¬†Several years ago I delivered an enthusiastic and rather science-heavy talk at a Bee Farmers Association meeting. I thought it had gone reasonably well and they were kind enough to say some nice things to me … and then I got the question from the back of the room which went something like¬†“That’s all very well young man … but what have you made NOW that I can put into my hives to make them healthy?”.

I’m sure my answer was a bit woolly. These days the presentation would have had a bit less science and bit more justification. We’ve also made some progress and it’s possible to now discuss practical strategies to rationally control viruses in the hive. It’s not rocket science … though some of the science it’s based on is reasonably fancy.

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Trick(le) and treat

Tools of the trade

Tools of the trade

This is the third and final post on why, with what, when and how to minimise mite levels in colonies in midwinter.

In the first post I explained why midwinter mite treatment makes sense. In the second I described how oxalic acid-containing solutions should be prepared and stored.

Oxalic acid-containing”¬†solutions includes both Api-Bioxal, the VMD approved treatment, and the unadulterated chemical. All three posts focus on trickling or dribbling – I’ve covered sublimation previously and both are essentially equally effective. Sublimation or vaporisation is currently very fashionable … but trickling is simplicity-itself and requires almost no special equipment.

In this post I’ll discuss how to administer the oxalic acid-containing solution.

For readability I’ll use the term OA solution to mean¬†any oxalic acid-containing solution. About 50% of the readers of this site are from outside the UK; local rules may determine what you are or are not allowed to administer to your bees.

Trickling or dribbling

You’ll hear both terms used interchangeably1. The general principle is that you directly administer 5ml of a 3.2% w/v solution of oxalic acid in thin (1:1) syrup per seam of bees in the colony.

Directly‘ because you administer the OA solution to the seam of bees. You don’t count the seams and then simply pour it into the hive. You don’t spread it across the top bars. The idea is that the bees at the top of the seam get coated in the solution and that it dribbles down through the colony, being passed from bee to bee as they feed and groom and move about.

Two seams of bees

Two seams of bees …

During this process any phoretic mites will also get exposed to the oxalic acid. Since mites are readily damaged by the OA solution they fall off and gradually drop out of the bottom of the cluster. Gradually, as it takes a few days for gravity to deliver all the corpses.

You can therefore determine whether mites were present and killed by placing a¬†Varroa tray underneath the open mesh floor of the hive. Note that this doesn’t tell you how¬†effective the treatment has been … for that you’d need to know the mite infestation level before treatment as well.

When to treat

In many ways this is the critical decision. As described previously, maximal benefit occurs when the colony is broodless. Ideally you want an extended cold period late in the calendar year. The colony will cluster tightly and brood rearing will slow down or stop completely.

If the cold period has lasted 2-3 weeks, even better. This will mean that some or all of the brood present will have emerged. The more sealed brood present, the less effective trickling OA solution is as a means of controlling mites.

Choose a calm, cool or cold day. I usually wait for a day with temperatures between 0 and 5¬įC. Much warmer than that and the cluster starts to break up or the bees are more likely to fly about as the crownboard is lifted. Windy or wet days disturb the bees (at least when you prise the crownboard off), so it’s best to avoid those.

I prefer to treat before the year end, rather than after, if I can. From a few irregular midwinter peeks into the cluster I think queens start laying earlier than most beekeepers think.

It pays to be prepared …

Trickle 2 - £1

Trickle 2 Р£1

… Aesop (~620-560BC) was right, though he wasn’t talking about beekeeping.¬†Before treating your colonies there is some preparation needed. Do this properly and it’s a doddle.

Purchase a Trickle 2 container from Thorne’s. These are a measly quid each. You’ll only need one.

Practice with the Trickle 2 container (see below).

Gently warm your pre-prepared OA solution to about 25¬įC. If you made it up in advance and stored it at 4¬įC in the fridge this will take an hour or two. The easiest way is to stand the container (preferably thin-walled … I use a well-rinsed milk carton) in a basin of warm water.

Pour the pre-warmed OA solution into a well-labelled vacuum flask. You can buy these from Tesco for £2.50 with a capacity of 1 litre. The aim here is to take everything you need ready-prepared to the apiary so the treatments take the minimum time possible.

Remember that OA is toxic. Label everything carefully, make sure children can’t get near it and don’t use it again for food/drink purposes.

That’s it … you’re ready. You’ll need a hive tool, a bee suit, thin gloves (to protect you from the OA, not the bees), your vacuum flask of OA solution and the Trickle 2 bottle. By all means take your smoker, but you shouldn’t need it.

I’ve got a 5 ml (or 25 ml) syringe … won’t that do?

Yes … but no.

A Trickle 2 bottle holds 100ml of prepared OA solution. It takes two hands to fill the bottle, but only one hand to use it. That 100ml is sufficient for 20 seams of bees¬†i.e. two completely full colonies (assuming an 11 frame National box). In midwinter the colony is unlikely to occupy 10 seams. A Trickle 2 bottle is also pretty accurate, reproducibly dispensing about 4.6-4.8ml of liquid. That’s close enough to 5ml.

In contrast, a syringe also takes two hands to fill (and refill). However, unless it’s a 5ml syringe, it’s difficult to accurately and reproducibly dispense liquid without using two hands. A 5ml syringe gives you the necessary accuracy, but needs refilling for every seam of bees.¬†This takes time … during which the crownboard is off and the colony is getting chilled.

I’ve done both and can assure you that the Trickle 2 bottle is much better. Just buy one. It’s only ¬£1 and it’ll last ages if one of your association members doesn’t borrow it … or doesn’t return it.

How to use a Trickle 2 bottle

  • Remove the cap and fill to the top of the lower chamber with liquid (practice with water).
  • Replace the cap.
  • Hold the bottle with your thumb and fingers on opposite sides of the lower chamber, with the external ‘pipe’ to the upper chamber next to your palm.
  • Undo the spout about a turn.
  • Gently squeeze the lower chamber. Liquid is forced up the pipe into the upper chamber. Hold it against the light to observe this.
  • Once the upper chamber is full, stop squeezing. Excess liquid drains back into the lower chamber.
  • If you are¬†right handed turn the Trickle 2 bottle anti-clockwise2 using your wrist and gently squeeze the bottle to dispense the liquid in the upper chamber from the spout. If you’re left handed you need to turn the bottle clockwise.

And in practice

The single-handed operation for the Trickle 2 container really pays dividends when treating a colony. You can gently prize up one side of the crownboard, hold it in one hand, administer the OA solution to each seam with the other hand and gently lower the crownboard back down … all in less time than it took me to write that.

Like this:

This is a reasonably sized colony being treated in the second week of January 3 years ago. The video is 1’45” long, but the crownboard is only open for about 50 seconds. And I was chatting with Mick Smith off camera, so could have perhaps gone a bit faster if I’d concentrated … ūüėČ

Here’s a more detailed view of treating a small colony:

33 seconds of warmed, acidic goodness to slaughter the mites and give the colony the best possible start to the upcoming season.

Cautions and considerations

Discard any OA solution that’s not been used. Warming it will have raised the HMF levels and this may be toxic for your bees. However, read footnote 3 for another way to avoid HMF buildup3.

Wash everything carefully – the Trickle 2 bottle, the vacuum flask, gloves¬†etc. Since the OA solution was in syrup everything gets sticky and gummed up. Clean stuff up, make sure it’s labelled and not going to be used in the kitchen and put it away until next year.

Oxalic acid kills mites, but it’s also toxic for unsealed brood. This is perhaps unsurprising considering it has a pH of 1 (i.e. very acidic) and ‘naked’ larvae aren’t protected by the tough exoskeleton that adult bees have. This is another reason to treat during a broodless period in midwinter.

In summer, swarms can also be treated with trickled oxalic acid-containing solutions¬†before they have sealed brood. If a swarm arrives in bait hive, let it settle and start drawing comb on the foundationless frames. A day or so later treat it with oxalic acid by trickling. When I’ve done this I usually wait until late afternoon or early evening, so most of the bees are in the box. The colony obviously won’t be clustered, but the principle is the same – 5ml of syrup down each seam. Easy peasy. Effective.

Swarms have a significant mite load, so it’s well worth treating them before they rear brood and give the phoretic mites somewhere to breed.

Finally, it’s often recommended that a colony is only treated once per year with oxalic acid by trickling or dribbling. I’m not sure where this advice originates, but it’s probably wise.

‘Vaping’¬†vs. trickling

The discussion forums are awash with recommendations to ‘vape’ the colony, rather than trickle. Vaporisation, or more correctly sublimation, is a widely used method and has been in use for two decades. It’s currently very fashionable. I’ll write a more substantial comparison sometime in the future, but the following brief notes might be of interest.

Sublimation can be done repeatedly with brood present (though there’s no peer-reviewed evidence of efficacy) and is both well-tolerated by the colony and is not toxic to unsealed brood. It requires specialised and potentially expensive equipment, both for delivery and personal protection. You¬†can build your own vaporiser, but shouldn’t skimp on protection for the operator. With a well designed vaporiser and hive there’s no need to open the colony to administer treatment.

In contrast, trickling requires only the Trickle 2 bottle and vacuum flask described here. Personal protection is a pair of latex gloves. It should only be conducted when the colony is broodless, should probably only be conducted once and does require the hive to be opened (albeit briefly).

You’ll be told that vaporisation is faster. It isn’t. Watch the videos above. Even my Sublimox – probably the fastest ‘active’ vaporiser on the market – takes well over a minute per colony if you take into account sealing the box, moving the generator about, unsealing the hive¬†etc.

There are reports that sublimation is more effective, but the difference is marginal, and possibly not statistically significant. There is also a report that colonies are stronger in the Spring after sublimation, though this may be due to toxicity to open brood by trickled OA solution. If the colony is broodless this shouldn’t be an issue.

I’ve used both many, many times without a problem. Across the UK I suspect more beekeepers trickle OA, rather than ‘vape’ (a word I dislike), though the vocal ones on the discussion forums currently favour vaporisation.

What’s more important than¬†how you deliver the oxalic acid, is that¬†you do treat. Trickling OA solution is so easy and inexpensive that there’s no reason not to … and your colonies will be much healthier for it.

Get dribbling ūüėČ


1¬†If the beekeeper is of a certain age you’ll hear these terms used in a different context. We’re restricting discussions here to delivering OA ūüėČ

2¬†If you are left handed you need to turn the Trickle 2 bottle clockwise. Actually, to be pedantic, if you are left handed and holding the bottle in your left hand, turn it clockwise. It’ll make sense once you try.

3 In the previous article on preparing oxalic acid solutions Calum posted a comment on preparing the OA in water and only adding and dissolving the required amount of sugar just before use. This has the advantage that there will be no HMF buildup. OA solution in water should be perfectly stable. I’ve not done it this way, but it makes sense and might be worth trying.

Colophon

The title of this article is a twist on the term¬†Trick or treat. This is not entirely inappropriate as Trick or treating is a Halloween (31st October … just a few days away) custom dating back – in various forms – centuries.

The modern usage, essentially North American, dates back to the 1920’s and refers to children in costumes going house to house threatening to play a trick unless the homeowner provides a treat, usually sweets or toys. In Britain these traditions date back to the 16th Century, both of children going house-to-house asking for food and of dressing up in costumes at Halloween.

Closer to home, ‘guising‘ – children in Scotland going from door to door in disguise asking for food, coins or chocolate ¬†– dates back at least a century.

The term Trick or treat only entered common usage in the UK in the 1980’s.

 

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Oxalic acid preparation

This is the second of three articles on¬†midwinter¬†treatment of colonies with oxalic acid to minimise¬†Varroa levels. In a recent post I explained¬†why a midwinter treatment was necessary, even if you’d treated three months earlier. Essentially this is because:

  • there will still be some residual¬†Varroa, particularly if you treated in late summer rather than early autumn (and this post explains why early treatment is preferable)
  • midwinter is the time when brood levels are at a minimum, so most mites will be¬†phoretic and readily accessible to the miticide treatment

Midwinter is the time to use oxalic acid-containing treatments. It can be delivered in a variety of ways; by sublimation (vaporisation), spraying or trickling (dribbling).

Trickling or dribbling

This post is about the preparation and storage of oxalic acid-containing solutions for trickling. Sublimation is covered elsewhere and spraying is not approved or widely used in the UK.

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. The oxalic acid kills the mites. How isn’t entirely clear – it’s thought to corrode the mouthparts and soft tissue. It’s more than 90% effective in killing phoretic mites when used like this.

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

Spot the difference ...

Spot the difference …

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

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) which actually makes it much less suitable for sublimation.

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’ll deal with how it is administered next time. This is all about preparation.

The how much is easy. You’ll need 5ml of oxalic acid-containing solution per seam of bees. In midwinter the colony will be reasonably well clustered and its likely there will be a maximum of only 8 or 9 seams of bees, even in a very strong colony.

Hold on … what’s a seam of bees?

Two seams of bees

Two 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.

Remember to prepare ~10%¬†more than you think you need. You’ll inevitably spill some when using the Trickle 2 bottle to administer it to the colony. It’s not that expensive, so don’t risk running out.

And the how strong? The recommended concentration to use oxalic acid at in the UK has Рfor many years Рbeen 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 – as it’s the only concentration I’ve used – is to stick to 3.2%.

Listen very carefully, I shall say zis only once†

A bit of basic chemistry coming up. Skip to the warning in red below and then the recipes if you want, but this explains some important things about working out how much to use.

The molecular formula of oxalic acid is C2H2O4. The molecular weight of oxalic acid is 90.03 g/mol. However, the oxalic acid you purchase – including Api-Bioxal – is the dihydrated form of oxalic acid.

Di as in two, hydrated as in water.

The molecular formula of oxalic acid dihydrate is C2H2O4.2H2O and oxalic acid dihydrate has a molecular weight of 126.07 g/mol.

Therefore the weight of oxalic acid in 1 g of oxalic acid dihydrate is 90.03/126.07 = 0.714 g.

Caution

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 carefully rinsed plastic milk bottle, very clearly labelled, is a good way to store the solution prior to use.

Recipes : oxalic acid

The standard recipe is 100 g water plus 100 g white granulated sugar. Mix well and then add 7.5 g of oxalic acid. The final volume will be 167ml¬†i.e. sufficient to treat over 30 seams of bees, or between 3 and 4 strong colonies (including the 10% ‘just in case’).

This final concentration is 3.2% w/v oxalic acid … (7.5 * 0.714)/167 * 100 = 3.2. Check my maths.

0.01 g to 500 g

0.01 g to 500 g

If you have more colonies to treat, or have trouble weighing 7.5g, scale everything up ten-fold. Or buy a small, accurate set of digital scales – like these for ¬£9 which work very well. 1 kg of sugar plus 1 kg (1 litre) of water requires 75 g of oxalic acid and makes 1.67 litres … enough to treat all the colonies in the association apiary.

Which is not such a bad idea. Make it up carefully once and share it with your fellow beekeepers. Storage details are provided below.

Recipes : Api-Bioxal

Warning – the recipe on the side of a packet of Api-Bioxal makes up a much stronger solution¬†(4.4% w/v) 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.¬†

To make a 3.2% Api-Bioxal-based oxalic acid-containing solution using the 35 g pack of Api-Bioxal you need to mix the entire contents of the pack with 691 ml of 1:1 syrup.

Here’s the maths:

  • 35 g of Api-Bioxal contains only 22.14 g of oxalic acid. 88.6% of the 35 g is oxalic acid dihydrate (the remainder is cutting agents like glucose and powdered silica) and so the oxalic acid content is ((35 * 0.886) * 0.714) = 22.14 g.
  • To calculate the volume of syrup you need to divide it by the final percentage required¬†i.e. (22.14 / (3.2/100)) = 691 ml. I don’t know the exact amount of sugar and water needed to make this amount … it’ll be about 430 g of each (I think).

A 35 g packet of Api-Bioxal is therefore sufficient to treat about 15 colonies (assuming 5 ml per seam, 8 seams per hive and 10% ‘just in case’) at the recommended concentration of 3.2% w/v.

Api-Bioxal is sold in three pack sizes (35 g, 175 g and 350 g). If you are wealthy enough to be able to purchase the larger pack sizes you’ve probably got your own beekeeper (or mathematician). Relax on your yacht while they do the calculations‚Ä° for you ūüėČ

On the other hand … if you have a smaller number of colonies¬†either make a full 35 g packet up and share it, or use accurate scales and the following table:

Api-Bioxal recipes for 3.2% OA trickling

Api-Bioxal recipes for 3.2% OA trickling

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 toxic1. HMF buildup is one way overheated honey is detected.

At 15¬įC 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 2,3.

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¬įC). Under these conditions HMF levels remain well below toxic levels for at least one year. However, don’t store it for this long … use it and discard the excess. Don’t use discoloured oxalic acid solutions as they’ve been stored incorrectly and may well harm your bees.

Please re-read the comments above about the toxicity of oxalic acid. If you are going to store it in the fridge it must be very clearly labelled and there must be no chance that children can reach or open the container.

Conclusions

Api-Bioxal is the least expensive VMD-approved miticide and powdered oxalic acid is much, much cheaper. Both contain the same active ingredient, oxalic acid, which is highly effective against phoretic mites.

In midwinter, with very low levels (or no) of brood, a single oxalic acid-containing treatment minimises mite levels for the coming season.

Oxalic acid-containing solutions are easy to prepare. I recommend you make sufficient for your own colonies and those of your beekeeping friends and association members. My previous BKA used to distribute litres of the stuff for use in midwinter. Use this solution in midwinter and then discard any that is unused.

Oxalic acid-containing solutions are inexpensive and easy to administer by trickling. As I shall demonstrate next time.

Please re-read the safety instructions highlighted in red above.


Michelle Dubois

Michelle Dubois

‚Ƭ†Listen very carefully, I shall say zis only once was a catchphrase used by “Michelle of the Resistance” in the 1980’s comedy ‘Allo ‘Allo!¬†Michelle (Dubois) was rarely seen without a trench coat and beret, had a corny French accent and was played by Kirsten Cooke.

‘Allo ‘Allo! ran for 85 episodes in the decade from 1982 on BBC one. It was about a caf√© in Nazi-occupied France and the French Resistance, just about. It mixed bawdy humour with gross stereotypes (posh British twits, sex-obsessed French) and was a parody of ITV’s series Secret Army (’77-’79).

Early episodes had obvious and rather dull titles. In the later series the individual episodes had some quite good puns like Awful Wedded Wife.

Michelle –¬†Listen very¬†carefully, I shall say zis only once

Ren√© –¬†Well, in that case, could you please speak slowly?

You had to be there … ūüėČ

‚Ä°¬†Oh alright then, since you insist. The 175 g pack of Api-Bioxal (~¬£39) needs to be made up in 3.459 litres of 1:1 syrup and the 350 g pack (~¬£65) 6.919 litres of 1:1 syrup. Determining how much water and sugar to mix to make these amount is, as they say, an exercise for the reader. Assuming a 3.2% solution and 8 seams of bees per colony Api-Bioxal costs between 63p and 41p per hive (see note below), depending upon the pack size you purchase. I know that beekeepers moan on and on about the outrageous cost of Api-Bioxal (as do I), but is 63p per colony really an unreasonable amount to spend on VMD-approved medicines to keep your colony as clear of¬†Varroa as possible? I don’t think so.

Note Рthe costs in the paragraph were calculated using the lowest prices I could currently find for Api-Bioxal. C Wynne Jones has the 35g packets for £9.50 and Maisemores have the 350g packets for £64.79. Prices correct on 9/10/17.

1¬†Jachimowich T., El Sherbiny G., Zur Problematik der verwendung von Invertzucker f√ľr die¬†Bienenf√ľttering, Apidologie 6 (1975) 121-143.

2 Bogdanov S., Kilchenman V., Chamere J.D.. Imdorf A. (2001) available online.

3 Prandin, L., Dainese, N. , Girardi, B., Damolin, O., Piro, R., Mutinelli, F. A scientific note on long- term stability of a home-made oxalic acid water sugar solution for controlling varroosis Apidologie, 32:) 451-452

 

Kick ’em when they’re down

Out, damn'd mite ...

Out, damn’d mite …

Why bother treating colonies in midwinter to reduce Varroa infestation? After all, you probably treated them with Apiguard or Apivar (or possibly even Apistan) in late summer or early autumn.

Is there any need to treat again in midwinter?

Yes. To cut a long story short, there are basically two reasons why a midwinter mite treatment almost always makes sense:

  1. Mites¬†will be present. In addition, they’ll be present at a level higher than the minimum level achievable, particularly if you last treated your colonies in late summer, rather than early autumn.
  2. The majority of mites will be phoretic, rather than hiding away in sealed brood. They’re therefore easy to target.

I’ll deal with these in reverse order …

Know your enemy

DWV symptoms

DWV symptoms

The ectoparasite¬†Varroa feeds on honey bee pupae and, while doing so, transmits viruses¬†(in particular DWV) that can completely mess up the development of the adult bee.¬†Varroa¬†cannot replicate anywhere other than on developing pupae. It’s replication cycle, and the resulting mite levels in the colony, are therefore tightly linked to the numbers and availability of hosts … honey bee pupae.

If developing brood is available the mite can replicate. Under these conditions, newly emerged adult, mated, female Varroa spend a few days as phoretic mites, riding around the colony on young bees. They then select a cell with a late-stage larvae in, enter the cell and wait until pupation occurs. If developing worker brood is available each infested cell produces 1 Р2 new mites (drone cells produce 3+) and mite numbers increase very rapidly in the colony.

In contrast, if there’s no developing brood available, the mites have to hang around waiting for brood to become available. They do this as phoretic mites and can remain like this for weeks or months if necessary.

Therefore, when brood is in abundance and the queen in laying freely mites can replicate to very high levels. In contrast, when brood is limiting and the queen has reduced her egg laying to a   v  e  r  y     s  l  o  w     r  a  t  e     the mite cannot replicate and must be predominantly phoretic.

When does this happen?

Lay Lady Lay … or don’t

Ambient temperature, day length and the availability of nectar and pollen likely influence whether the queen lays eggs. When it’s cold, dark and there’s little or no pollen or nectar coming into the hive the queen slows down, or even stops, laying eggs.

About 8 days after she stops laying there will be no more unsealed brood in the colony. About 13 days after that all the sealed brood will have emerged (along with any¬†Varroa). Therefore, after an extended cold period in midwinter, the colony will have the lowest level of sealed brood … and the highest proportion of the mite population will be phoretic.

Under normal (midsummer) circumstances about 10% of the mite population is phoretic. It’s probably unnecessary to state that, if there’s no brood available, 100% of the mites must be phoretic.

All licensed miticides work extremely well against phoretic mites†.

Caveats, guesstimates, global warming and the Gulf Stream

Global warming

Global warming …

Whatever the cause, the globe is warming (irrespective of what¬†Donald Trump tweets). Long, hard winters are getting less common (or perhaps even rarer, as they were never particularly common in the UK). In Central, Southern or Eastern Britain it’s possible that the colony will have some brood present all year. In parts of the West, warmed by the Gulf Stream, I’d be surprised if a colony was ever broodless. Only in the North is it likely that there will be a brood break in midwinter.

Most of the paragraph above is semi-informed guesswork. I don’t think anyone has systematically analysed colonies in the winter for the presence of sealed brood. Sure, many (including me) have opened colonies for a quick peek. Others will have peered intently at the¬†Varroa board to search for shredded wax cappings that indicate emerging brood. The presence of brood will vary according to environmental conditions and the genetics of the bees, so it’s not possible to be dogmatic about these things.

However, it’s safe to say that in midwinter, sealed brood – within which the mites can escape decimation by miticides – is at a minimal level.

Reducing mite levels and minimal mite levels

Within reason, the earlier you apply late summer miticides, the better you protect the all-important overwintering bees from the ravages of viruses, particularly deformed wing virus. This is explained in excruciating detail in a previous post, so I won’t repeat the text here.

However, I will re-present the graph that illustrates the modelled (using BEEHAVE) mite levels‡.

Time of treatment and mite numbers

Time of treatment and mite numbers

The gold arrow (days 240-300 i.e. September and October) indicates when the winter bees are being reared. These are the bees that need to be protected from mites (and their viruses). Mite numbers (starting with just 20 in the hive on day zero) are indicated by the solid coloured lines. The blue, black, red, cyan and green lines indicate modelled mite numbers when the colony is treated with a miticide (95% effective) in mid-July, August, September, October or November respectively.

The earlier you treat, the lower the mite levels are when the winter bees are being reared. Study the blue and black lines.

This is a good thing.

In contrast, by treating very late (the cyan and green lines) the highest mite numbers of the season occur at the same time as the winter bees are being reared. A bad thing.

But … look also at mite numbers after treatment

Look carefully at the mite numbers predicted to remain at the end of the year. Early treatment leaves higher mite levels at the start of the following year.

This is simply because mites escaping the treatment at the end of summer have had an opportunity to reproduce during the late autumn.

This is why the additional midwinter treatment is beneficial … it kills residual mites and gives the colony the best start to the new calendar year¬ß.

Kick ’em when they’re down

Early treatment protects winter bees but risks exposing bees the following season to unnecessarily high mite numbers. However, in midwinter, these residual mites are much more likely to be phoretic due to a lack of brood in the colony. As I stated earlier, phoretic mites are relatively easy to target with miticides.

So, give the mites a hammering in late summer with an appropriate and effective miticide and then give those that remain another dose of the medicine in midwinter¶.

But not another dose of the same medicine

Since the majority of mites in a colony with little or no brood will be phoretic, you can easily reduce their numbers using a single treatment containing oxalic acid. This can be administered by sublimation (vaporisation) or by trickling (dribbling).

There’s no need to use any treatment that needs to applied for a month. Indeed, many (Apiguard etc.)¬†are not recommended for use in winter because they work far less well on a largely inactive colony.

Trickle 2 - £1

Trickle 2 Р£1

I’ve discussed sublimation previously. However, since this requires relatively expensive (¬£30 – ¬£300) specialised delivery and personal protection equipment it may be inappropriate for the two hive owner. In contrast, trickling requires almost no expensive or special equipment and – reassuringly – has been successfully practised by UK beekeepers for many years. I did it for years before I bought my Sublimox vaporiser.

Therefore, in two further articles this autumn (well before you’ll need to treat your own colonies) I’ll describe the preparation and storage of oxalic acid solutions and its use.

Be prepared

If you want to be prepared you’ll need to beg, borrow or steal the following – sufficient oxalic acid (or Api-Bioxal), a Trickle 2 bottle sold by Thorne’s, a cheap vacuum flask (Tesco ¬£2.50), granulated sugar and a pair of thin disposable gloves.

Do this soon. Don’t leave it until midwinter. You need to be ready to treat as soon as there’s a protracted cold spell (when brood will be at a minimum). Over the last few years my records show that this has been anywhere between the third week in November and the third week in January.

More soon …


‚Ƭ†Only MAQS is effective against mites sealed in cells. This is why most miticides are used for extended periods in the late summer or early autumn … the miticide must be present as¬†Varroa emerge from sealed cells.

‚Ä°¬†I’ll repeat the caveat that this is an¬†in silico simulation of what happens in a beehive. Undoubtedly it’s not perfect, but it serves to illustrate the point well. It’s freely available, runs on PC and Mac computers, and is reasonably¬†well-documented.¬†In the simulations shown here the virtual colony was ‘primed’ with 20 mites at the beginning of the year. BEEHAVE was run using all the default settings – climate, forage etc. –¬†with the additional application of a miticide (95% effective) in the middle of the months indicated. Full details of the modelling have already been posted.

¬ß¬†The National Bee Unit recommend¬†Varroa levels are maintained below 1000 throughout the season. Without treatment, 20 mites at the start of the season can easily replicate to ~750 in the autumn. If you start the season with 200 mites then levels are predicted to reach ~5000 in the following summer. The colony will almost certainly die that season or the next. There’s a more detailed account of the consequence of winter brood rearing and the level of mite infestation written by Eric McArthur and reproduced on the Montgomeryshire BKA website¬†that’s worth reading.

¬∂¬†The cumulative (year upon year) effect of late summer treatment¬†with no midwinter treatment has been discussed previously. I’ll simply re-post the relevant figure here – 5 years of bee (in blue, left axis) and mite (in red, right axis) numbers with only one treatment per season applied in late September. Within two years the higher mite numbers that are present at the start of the year reproduce to dangerously high levels.

Mid September

Mid September

Counting Varroa

It’s that time of the season again. With the exception of readers in the Southern Hemisphere, Colonsay, the Isle of Man or a few favoured locations in the Highlands of Scotland‚Ć, miticide treatments should be on to reduce¬†Varroa levels.

For reasons explained elsewhere, it’s important that this is done¬†before the winter bees are exposed to the smorgasbord of viruses that¬†Varroa trasmits when it feeds.

It’s not sufficient to just treat. You also need to have some idea that the treatment is reducing the numbers of¬†Varroa in the colony.

Counting by numbers

It has been determined that only 10-20% of mites in a colony are phoretic i.e. attached to emerged workers‡. The majority of treatments (MAQS is the current exception) only target these mites. Therefore, treatments are usually applied over a period of several weeks to ensure that mites newly emerged from capped cells are also exposed.

There are a couple of obvious ways to determine the mite load before and after treatment. These include:

  • conducting an alcohol wash test, or a sugar-roll equivalent, of workers to quantify the phoretic mites.
  • uncap a known amount of worker brood (drone brood is almost certainly absent from colonies this late in the season) to quantify mite infestation.

However, both are pretty intrusive and – with the exception of the sugar-roll – involve the sacrifice of bees or brood, so perhaps not ideal at this stage of the season. However these are the most accurate way of measuring things.

Counting the corpses

Out, damn'd mite ...

Out, damn’d mite …

Alternatively, and this is what most beekeepers do, apply the treatment and count the mite drop.

To count the mites you need some way of catching the mites. Open mesh floors (OMF) can easily be fitted with a sheet of closely-fitting (most usefully white) Correx onto which the mites drop. Restrict the access of ants and other creepy crawlies to the tray or they may steal some of the corpses. Check these on a regular basis during treatment and you have a simple way of determining whether the treatment is working.

The treatment may be working, but has it been effective?

The scores are on the floors

If you count thousands of dropped mites and that number doesn’t diminish during treatment¬†i.e.¬†the drop per day early and late in treatment is broadly similar, then the treatment is working, but it’s not effective or finished as there are loads of mites still left.

What you need to observe is a reduction in mite drop when comparing early and late counts.

Depending upon the treatment, the first days’ drop isn’t necessarily indicative of whether the miticide is working (or of the phoretic mite load of the colony). It may take a day or two for the treatment to achieve maximum kill. Vaporised oxalic acid often gives a better drop after 24-48 hours, and continues to work over about 5 days.

As indicated in the footnote‚Ä°, the numbers of brood emerging per day will expose ‘new’ mites to the miticide, increasing the count. If emerging brood levels vary, so will the mite drop … but also remember that the efficacy of the miticide also varies over time.

What you’re looking for is a hugely reduced count of mites dropped per day at the end of the full treatment period when compared with the beginning.

I usually carefully monitor the first week or two and the last week. Simples.

Objective vs. subjective counting

Easy counting ...

Easy counting …

Some beekeepers count each and every mite that appears on the trays. Others just look for ‘lots’ at the beginning and ‘almost none’ at the end. I consider >50/day is ‘lots’ and only count smaller numbers.

The less frequently you count the more difficult it is to discriminate dead mites from all the other detritus that accumulates on the trays. The cell cappings, the pollen that’s being dropped, the wax scales and various other bits of bee, all make spotting the mites more tricky.

The larger the area you’re counting the more likely it is to either double-count or miss mites. Make life a bit easier by ruling a simple grid onto the tray and counting square by square.

Scrape the tray clean after counting the mites … if you leave the tray dirty you’ll end up double counting¬†and struggling to spot mites that are knee-deep in the crud that’s fallen through the OMF.

Don’t try this at home

Varroa are a pretty regular size and shape. And colour for that matter. At least adult mites are. This raises the possibility Рthough perhaps only to those with a tendency towards geekiness Рto try and count mites automagically§.

Rather than stand around the apiary squinting through myopic eyes at tiny reddish ovals you could simply photograph the tray and then process the image later.

Been there, done that … or at least tried to.

Fiji ...

Fiji …

There’s a freely-available, well-supported, image analysis package called ImageJ (also distributed sometimes as the auto-referential Fiji … Fiji is just ImageJ). It’s possible to count objects using ImageJ having set criteria that define them.

As an exercise in near-futility I’ve attempted to do this for¬†Varroa. You first need to ensure the Varroa¬†are of a standardised size and shade by¬†scaling the image appropriately and correcting the colour. This can be done by using a photographers grey card of a known size, placed to the side of the¬†Varroa tray. You then use this as a reference to scale the image and define the white balance.

Finally, you define the size, roundness and shade of a¬†Varroa and process the image in ImageJ√ü. It counts the mites and provides an overlay with each identified mite numbered. You’re then able to check whether it’s missed any.

It does.

Consistently variable

This is the point I’ve got stuck at … the accuracy is all over the place but it’s clearly not impossible. Problems include:

  • It overlooks mites lying on their ‘edges’, perhaps propped up on a speck of pollen or fragment of wax. Better colour definition and a wider range of ‘ovality’ might sort this out.
  • It misses mites lying immediately next to another mite – these look like 8 or¬†‚ąě rather than a simple solid oval. I’ve no clear solution to this other than counting lower densities of mites.
  • It ignores some mites that appear as ‘doughnuts’ because of reflection from the shiny carapace. Don’t use flash for the photography.
  • It counts some ovalish, reddish lumps of pollen that are about the right size as mites. D’oh!

At best the accuracy is above 80%, but it’s variable. The lack of consistency is the major issue. If it was¬†always 80% it would be perfectly acceptable and a very fast way to record mite numbers. At worst – usually when the tray is messy and mite numbers are relatively low – it’s well below 50%.

This is an intriguing beekeeping-related task for long winter nights. If you’re a geek. My ambition is to take a quick smartphone photo, scrape the Correx tray clean and then (automagically!) do the counting at home with a cup of tea and piece of cake.

I’ll keep persevering … particularly with the tea and cake ūüėČ


‚Ƭ†It’s currently Spring in the Souther Hemisphere, so the wrong time to treat. The remaining locations (and Australia) have no¬†Varroa so have no need to treat. Lucky blighters.

‚Ä°¬†This is a gross oversimplification. Obviously, a broodless colony will¬†only have phoretic mites. Swarms that issue from colonies take 35% of the mites with them, leaving 65% on the remaining bees (or capped in cells). The actual number of phoretic mites likely depends upon the prior history of egg laying by the queen. It also is probably influenced by the overall level of mites in the colony (or ratio of uncapped brood to mites perhaps). I’m not sure if anyone has modelled this successfully, though it might be possible to do this with BEEHAVE.

¬ß¬†Automagically¬†is¬†pretty obviously a concatenation of automatic and magic. It is usually defined as “(especially in relation to the operation of a computer process) automatically and in a way that seems ingenious, inexplicable, or magical”. Interestingly, the term was first used in the 1940’s, well before the advent of computers.

√ü¬†Once I’ve got this working better I’ll provide some instructions … in the meantime the menus that you need to use are¬†Analyse … Set Measurement and¬†Analyse … Count Particles. Image scaling needs to be done first in ImageJ. Currently I do the white balance in Adobe Lightroom (which is overkill, but convenient as all my images go through this software).

 

That’s all folks

That's all Folks

That’s all Folks

It’s late August and the end of my least successful beekeeping year ever. That sounds very negative, so perhaps it should be qualified. It’s the end of my least successful beekeeping year in terms of honey production.

However, in terms of the satisfaction I’ve got from my beekeeping, it’s been a pretty good year. Let’s examine these two things separately, dealing with the bad news first.

Tell ’em about the honey, mummy‚Ć

My production colonies only generated about 25lb each of Spring honey. Some of this was clearly oil seed rape (OSR) as there were fields just about in range, but much of it was essentially mixed hedgerow and tree nectar, and none the worse for that. This was all extracted in late May or early June and is now stored, set, in buckets. Later in the year, once the temperature drops, I’ll prepare soft set honey for sale or distribution to friends and family.

25lb is firmly at the bottom end of the averages over the last few years though – in fairness – It’s only my second Fife Spring, so I don’t have much recently to compare it with. Colonies were doing well when I first inspected them, but in some cases that wasn’t until early May. The active beekeeping season is only 4-5 months long here (latitude 56.3¬į N).

June started well, with clear weather and high temperatures.

And then it started to rain. And continued for almost the entire month.

Lime can yield well in July

Lime can yield well in July …

None of my full-size colonies needed feeding, but most reduced their brood rearing. July nectar flows were poor. The lime yielded a small amount of very high quality honey, but for whatever reason – poor weather, colonies not strong enough, patchy flows – pretty-much nothing else. The summer honey was extracted in mid-August and is already disappearing fast.

I didn’t take any colonies to the heather as I was abroad for a chunk of July when I’d need to be preparing and shifting them to the moors. And, in all likelihood, they probably weren’t strong enough anyway.

And that was it … like last year, all over much sooner than expected.

There’s some balsam in central Fife along the River Eden that might give some late-season nectar and there’s ivy (but that is some way off flowering yet) but I usually let the bees keep anything they collect once the summer honey is extracted.

Flowering ivy

Flowering ivy

And the good news is

Beekeeping isn’t¬†all about honey. There’s also tremendous satisfaction to be gained from working with the colonies, improving your stock and feeling that – although perhaps not in complete control – you’ve got a pretty good grasp of what’s happening and how things are going.

In this regard, 2017 was a success.

I know I lost one swarm (actually a cast from the queenless half of a split). I got a call to say that the apiary was thick with bees but they’d long gone by the time I extricated myself from meetings and got home. In itself this wasn’t a success. However, I learned my lesson and managed to hive a second cast that issued from the same colony a day or two later. I also had success with my bait hives.

With a couple of exceptions my vertical splits went well, with the resultant queens both laying well and heading well-behaved colonies. The couple that didn’t work developed into (drone) laying workers and were dealt with successfully by uniting.

In retrospect, considering the weather in early/mid-June I’m astounded any queens managed to get out and mate. By late July colonies headed by these newly mated queens were developing well, with frame after frame of brood exhibiting a pretty respectable laying pattern.

That'll do nicely

That’ll do nicely …

Throughout the season I had a pretty good idea what was happening in most of my colonies. There were no big surprises …¬†“Oops, a virgin queen, where did she come from?”, or¬†“Grrrr … no queen, no eggs and no swarm cells, I’m stumped”.

Colonies behaved in a thoroughly predictable manner. Strong ones were caught before they swarmed, split and were merged back to a double brood box. Nucs developed pretty well, though they needed close attention and some emergency feeding through June. No drama, no panic.

The end of the summer season, other than the truly woeful honey yield, has left me with a good number of nicely behaved and generally very strong colonies. As always there’s one exception, but I’ll unite that weakling late this week if things haven’t picked up.

All the gear, no some idea

Split board ...

Split board …

Gradually equipment standardisation is starting to pay dividends. I ran out of almost nothing (I certainly didn’t run out of supers ūüôĀ ) and managed to mix’n’match as needed to leave colonies secure, watertight and with the proper bee space when needed. Homemade split boards ended up being pressed into service as floors and it’s clear I’ll have to make some additional kewl floors this winter.

Bamboo-strengthened foundationless frames were a great success. Furthermore, I prepared a second batch mid-season and never got round to using them, so have plenty to start the season next year. Result! However, it’s sobering to realise that one of the reasons they weren’t used was that the nectar flow simply wasn’t strong enough to get them drawn properly.

Finally, whilst we’re on the subject of equipment, I’ve used about half a dozen Abelo poly hives this year in addition to the usual Swienty boxes with homemade floors and roofs. First impressions of the Abelo boxes are pretty positive and I’ll write something up later in the year on them.

Season’s end … or the start of the new season?

Late summer and autumn is an important time in the beekeeping year. Some even consider it the start of the next season, as success in the subsequent year is very dependent upon the preparation in the preceding autumn.

Feed'n'treat ...

Feed’n’treat …

All my colonies are scarfing‚Ä° down large quantities of fondant at the moment. They’ll all get another few kilograms as the autumn progresses. Unless there’s good reason to, it’s unlikely any colonies will be inspected again until Spring.

Varroa treatment is ongoing and the mite drop from most colonies is reassuringly low. I count the mites from each colony over a two week period. Over the first 5 days, some dropped just single figures …

All colonies are coordinately treated to maximise decimation of the mite population at a time when bees have a tendency to drift more and/or rob adjacent colonies – both being well-documented routes by which¬†Varroa can be transmitted between hives. I’ve also helped a neighbouring beekeeper (with colonies within range of my own apiary) by loaning out my Sublimox so that, together, the mite population at a landscape-scale is reduced.

This is simple common sense. I don’t want my (nearly) mite-free colonies infested from neighbouring apiaries and I also don’t want the colonies I do have with appreciable mite levels (~50+ after 5 days treatment) to infest others.

2018

It’s far too soon for much serious thought about 2018. However, I already know there are going to be some major changes to my beekeeping. The local Council have just announced that they will shortly (Spring next year) build a new road literally through the middle of my bee shed and apiary … finding a new location and getting things rebuilt is my major focus at the moment.

And finally … it’s harvest time and raining again …

Mainly dry ...

Mainly dry …


‚Ƭ†Tell ’em about the honey, mummy was a catchphrase from a TV advert for Sugar Puffs breakfast cereal. The advert aired from 1976 to ’85 and featured the Honey Monster and¬†Henry McGee (from the Benny Hill show).

Henry is the one on the right.

They don’t make advertising like that any longer.¬†For obvious reasons.

‚Ä°¬†Scarf is American slang meaning to ‘eat voraciously’. It’s probably a bastardisation of the word scoff.¬†Scarf has other meanings and I strongly suggest you don’t look these up.

Colophon

That's All Folks

That’s All Folks

The phrase That’s all folks dates back to 1930 when it was used on the closing screen of a Warner Bros. Looney Tune cartoon.

Over the years many different characters used this line on both Looney Tunes and Merrie Melodies cartoons. Mel Blanc (1908-’89), the actor who voiced (stuttered) the most famous version …¬†Th-th-th-that’s all folks! has the engraving That’s All Folks on his gravestone.

There’s a 1949 Merrie Melodies cartoon called¬†The Bee-Deviled Bruin with the Three Bears, a colony of bees and a shortage of honey for breakfast. Typical slapstick ensues. It ends with¬†That’s all folks”.

Size matters

Anyone reading the beekeepingforum.co.uk will be aware that there are a number of contributors there that enthusiastically recommend the treatment of colonies with vaporised (or, perhaps more accurately, sublimated) oxalic acid to reduce Varroa levels.

There goes a few pence ...

There goes a few pence …

Although vaporised oxalic acid (OA) has been used by some for many years, the speed with which it has recently been embraced by many UK beekeepers (at least those that contribute to discussion forums and, perhaps to a lesser extent, those I speak to in associations over the winter) probably reflects two or three things:

  • an awareness of just how effective oxalic acid is as a treatment
  • the increased availability of commercial oxalic acid vaporisers (or Heath Robinson-like plans to build-your-own)
  • the huge price-differential between oxalic acid and most other treatments

There are almost as many homegrown or imported vaporisers as there are treatment regimes to hammer down the mite levels. Of course, there’s the contentious point that¬†oxalic acid is not approved by the VMD (Veterinary Medicines Directorate), despite having been in routine use for decades. Api-Bioxal is, but is probably unsuitable for sublimation¬†due to the inert (as far as Varroa are concerned)¬†additives it contains. Api-Bioxal can be vaporised but leaves a caramelised residue in the vaporiser pan that is hard to clean.

Out, damn'd mite ...

Out, damn’d mite …

‘Vaping’ is also popular in the US. Randy Oliver has covered it extensively on his scientificbeekeeping.com site and it’s also regularly¬†discussed on Beesource. OxaVap make/supply a¬†vaporiser¬†that appears very similar to the Sublimox I use. The OxaVap model has a useful temperature display that I would find much easier to read than the red/green diodes on the Sublimox … I’m red/green colourblind.

Active and passive vaporisers

The Sublimox and OxaVap vaporisers are ‘active’ … they blow out a dense cloud of OA-containing vapour through a relatively narrow diameter nozzle (the video below uses water to demonstrate this process). This provides advantages both in terms of ease and speed of delivery. These vaporisers simply need a 7mm hole drilled through the sidewall of the floor (see photo at the top of the page), or through an eke placed over the colony. The OA-containing vapour is ‘squirted’ in, permeates all corners of the hive within seconds and you can then move on to the next hive. The vaporiser doesn’t need cooling between treatments and the dose administered is tightly controlled.

Big Daddy

However, OA dosage isn’t critical. It has been shown to be well-tolerated by bees in studies from groups in the UK and Germany.¬†If the dose isn’t critical and speed really is important then perhaps consider the vmVaporizer. At $3600 it’s about ten times the price of a Sublimox.

vmVaporizer ...

vmVaporizer …

The manufacturers claim you can treat 300 hives an hour with one of these … one every 12 seconds. For comparison, the Sublimox takes 20-30 seconds per hive. However, what takes the time is sealing the hive, moving the generator about, unsealing the hive etc. so you’d need a team of (well protected) helpers and some closely spaced hives to achieve a similar rate. The vmVaporizer is mains (110V) powered so would also need a generator or inverter.

The video above demonstrates the vmVaporizer in action. It produces copious amounts of oxalic acid vapour, albeit less ‘forcefully’ than the Sublimox. It seems the only way to control how much is delivered is by changing the duration the hive is exposed for.

Undoubtedly this is overkill for the majority of readers of this site, but it’s interesting to see what the commercial beekeeping community are using (much like browsing the decapping or bottling machines in the Swienty catalogue).¬†There’s at least one satisfied UK-based beekeeper quoted on the vmVaporizer site so … Mark, if you happen to read this I’d be interested in how well the machine works and whether you can achieve the quoted hive treatment every 12 seconds?

And, does it work with Api-Bioxal?

ūüėČ

 

Apistan resistance

Apistan

Apistan

In an earlier article I discussed what Apistan is Рa pyrethroid miticide Рand the consequences of using it. These include decimation of the mite population if it is susceptible, coupled with the accumulation of long lasting residues in wax. These residues may adversely effect queen and drone development. I also discussed ways to avoid build-up of Apistan residues in comb.

The key phrase in the paragraph above is ‘if it is susceptible’. Unfortunately, resistance to Apistan and the related tau-fluvalinates develops very quickly. To understand why we’ll need to look in a little more detail at how Apistan and other pyrethroids work.

How does Apistan work?

Apistan, like other pyrethroids, works by blocking the activity of voltage gated sodium channels (VGSC) resulting in paralysis because the axonal membrane cannot repolarise.

What on earth does that mean?

Action potential

Action potential

Nerve transmissions – like the signal from the¬†Varroa brain to tell the¬†Varroa legs to move – travel along axons. These are usually very long thin cells. In the adjacent image¬†the ‘brain’ is on the left and the leg muscles on the ‘right’. The nerve impulse (the moving arrow) travels down the axon ‘driven’ by¬†a change in polarity (charge) across the membrane of the axon. In the resting state, when there is no impulse, this is positively charged on the outside and negatively charged on the inside. Sodium – remember the ‘S’ in the acronym VGSC – is positively charged and¬†crosses the¬†membrane (out to in) via a small pore or hole as the impulse passes. This makes the inside of the axon transiently positive‚Ć. The pore or hole is the VGSC.

Top view of a VGSC

Top view of a VGSC

The VGSC is a transmembrane protein. It actually crosses the membrane multiple times and assembles to form a very narrow channel through which the sodium passes. The cartoon on the right shows the top view of a VGSC, looking “down” the pore into the inside of the axon. The blue bits can move to open or close the pore, allowing sodium to traverse – or not – the membrane into the axon. Apistan binds to the transmembrane protein and prevents the pore¬†from closing. As a consequence, sodium continues to pass from the outside to the inside of the axon, the nerve cannot repolarise and no further impulses can be transmitted. As a consequence,¬†Apistan paralyses the¬†Varroa.

But I don’t suppose many beekeepers will feel much sympathy for the mite ūüėČ

Why isn’t the beekeeper paralysed as well?

Nerve impulses in¬†Varroa and humans are transmitted in essentially the same way. We also have VGSC’s that operate¬†in a similar manner. Why doesn’t Apistan also paralyse careless beekeepers? More generally, why are pyrethroids the most widely used insecticides, available in all garden centres and supermarkets?

Two factors are at work here. The first is the specificity of binding. The VGSC is a protein. Proteins are made from building blocks termed amino acids. The precise sequence, or order, of amino acids is usually critical for protein function. However, two proteins with a similar function can exhibit differences in the amino acid sequence. Although the¬†human and mite VGSC have a similar function¬†they have a¬†different amino acid sequence. Apistan binds much better to the mite VGSC than the human VGSC (this also explains why bees aren’t also paralysed by Apistan … the miticide is specific for the mite VGSC and binds poorly to the honey bee VGSC). In addition, many mammalian species have a number of detoxifying enzymes which deactivate pyrethroids, rendering them ineffective. Together, this explains the specificity of Apistan and other pyrethroids, and the low level of toxicity to humans.

So now you know how Apistan works we can address the much more important question …

Does Apistan work?

Unfortunately, usually not. Since the late-1990’s there have been a large number of publications¬†of Apistan- or fluvalinate-resistant mites from many countries, including the¬†USA (1998, 2002), Israel (2000), UK (2002), Spain (2006), Korea (2009) and Poland (2012). The National Bee Unit used to report¬†Varroa resistance¬†test results by geographic region in England and Wales.¬†Resistance was first reported in mites from Cornwall and Devon (in 2001 and 2002). By 2006 resistance was very widely distributed throughout England. By then approximately a¬†third of all mite samples tested were resistant. The number of tests conducted (or at least reported) then dwindled and there have been none reported since 2010. Not no resistance … no tests. Presumably it’s no longer worth reporting as resistance is so widespread.

The most up-to-date map on the distribution of Apistan resistance I could find is in the NBU booklet on Managing Varroa [PDF; page 28 of the 2015 edition], though the data presented is from 2009.

However, bee equipment suppliers continue to sell Apistan (even Vita, the manufacturer, states that resistance is widespread) and beekeepers continue to use it. Many do so without first testing whether the mite population in their colonies is sensitive to the miticide. How should this be done?

Testing for resistance

Vita suggest two tests. Their first (the “rule of thumb test”) is deeply flawed in my view. It suggests simply looking for a drop of 100’s of mites in the first 24 hours after treatment starts as indicative of a sensitive population.

This isn’t good enough. What if there were thousands of mites present? Perhaps 20% of the population are sensitive, with the remainder resistant‚Ä°. 20% of 5000 mites is 1000 … so you might expect a drop of 100-200 (the majority of the phoretic population) within the first 24 hours. Some might consider this drop indicates a sensitive population … it doesn’t.

It’s not sufficient to¬†count the corpses … you need to know how many mites were unaffected by the treatment.

The second Vita-recommended test is a cut-down version of the “Beltsville” pyrethroid resistance test which is fully described in an¬†NBU pamphlet (PDF). This is much more thorough. Essentially this treats ~300 bees with Apistan, counts the mites that are killed in 24 hours and then¬†counts the unaffected mites remaining on the bees. It’s only by knowing the total number of mites at the start and by determining the percentage of mites sensitive that you can be sure that the treatment is effective.

What is the molecular basis of resistance?

We’re almost there … specific pyrethroids, like Apistan, bind to specific parts of the VGSC. The VGSC is a protein made up of a long connecting chain of amino acids. The binding of the pyrethroid requires an interaction with a small number of¬†specific amino acids in the VGSC. If these particular amino acids change – through mutation for example – then the pyrethroid will no longer bind. If the pyrethroid does not bind the VGSC can open and close again, so the axon repolarises and the mite is not paralysed. The mite is resistant and can then go on to rear lots more resistant baby mites … which, in due course, transfer the viruses that kill your bees.

And that’s exactly what happens.

Leucine

Leucine

A single mutation that causes a substitution of amino acid number 925 in the Varroa¬†VGSC, which is usually a leucine, to either a valine, a methionine or an isoleucine, is sufficient to prevent Apistan and other tau-fluvalinates from binding. At least 98% of mites resistant to¬†Apistan have one of these substitutions. Apistan resistant mites with substitutions at¬†position 925 have been found in the UK, eastern Europe and several sites in South-Eastern USA. It wouldn’t be surprising if the remaining ~2% of resistant mites had a mutation at one of the other amino acids involved in pyrethroid binding. Further studies will confirm¬†this (there are alternative mechanisms that cause¬†resistance, but the one described here is the most frequently seen).

Why aren’t all¬†Varroa mites resistant to tau-fluvalinates?

Apistan resistance has clearly been demonstrated for the last two decades. Resistance is easy to acquire and selection Рin the presence of the pyrethroid Рis effectively absolute. Without the necessary mutation the mites die, with the mutation they survive.

Bees Рand the phoretic mites that are associated with them Рare moved around the place all the time, by migratory beekeepers, by importers and through robbing and drifting between colonies.

Why therefore aren’t all¬†Varroa mites now resistant to Apistan and other tau-fluvalinates?

The answer to that is interesting and suggests strategies that could make Apistan an effective treatment again¬†… but I’ll save that for another time.


‚Ć Only transiently as the charge is reversed shortly afterwards by a¬†similar, though not identical, ¬†mechanism that does not use the VGSC. However, life is simply too short to describe this bit as it’s not needed to understand pyrethroid – or Apistan – activity and resistance.

‡ The incestuous life cycle of the Varroa mite is important here. This post is already too long to fully elaborate on this but the size of the mite population relative to available open brood (and whether you get single or multiple occupancy of cells) will likely influence the proportion of resistant, partially resistant and sensitive mites in a population.

Credits Рthe action potential GIF was created by Laurentaylorj from Wikipedia.

 

Apistan and residues

This is the first of two or three posts on Apistan, a widely used yet often ineffective miticide sold¬†for Varroa control.¬†I was originally going to title this post¬†“Don’t do this at home” and restrict discussion to Apistan misuse and resistance in the UK. However, having drafted¬†the article it was clear there was more than could be covered in a single post (or at least comfortably read).

I’ve therefore split it up; the first focuses on what Apistan is, how it’s used and the consequences of use for the hive. Next time – though possibly not next week – I’ll cover the molecular mechanism of activity¬†and¬†mite resistance.

What is Apistan

Apistan

Apistan … tau-fluvalinate

Apistan¬ģ is a miticide used to kill Varroa. It is a registered tradename used in the UK and other parts of the world. The active ingredient is a synthetic pyrethroid tau-fluvalinate (or sometimes¬†ŌĄ-fluvalinate). Synthetic in this instance means it is not a natural compound, but is produced using a chemical process. Other miticides containing the same active ingredient include Klartan¬ģ and Minadox¬ģ¬†– precise compositions may vary, but the important component is the tau-fluvalinate.¬†In the UK, Apistan is supplied by Vita (Europe) Ltd. and sold by all the leading beekeeping equipment suppliers. I’ll use the name fluvalinate and Apistan interchangeably in the remaining text.

Instructions for use

Apistan can be used at any time of year but its use is recommended in late summer after the honey harvest. The active ingredient, fluvalinate, is supplied as impregnated polymer strips, two of which are hung vertically in the brood box, between frames 3 & 4 and 7 & 8. It is a contact miticide and needs to be located near the centre of the colony to get trampled through the broodnest. Nucs and weak colonies only should be treated with one strip. The treatment period is 6 to 8 weeks i.e. a minimum of two full brood cycles. The instructions specifically state that it should not be used for less than 6 weeks, or more than 8 weeks. This is to avoid the selection of a resistant mite population. Apistan should not be used when there is a nectar flow.

How effective is Apistan?

On susceptible mite populations Apistan is fantastically effective. Cabras and colleagues in Italy reported greater than 99% efficacy in studies published in 1997.

Fluvalinates and foundation

Importantly, because of its chemical formula, Apistan is fat soluble, meaning it is readily absorbed into or dissolves in fats¬†… like beeswax. It is also a very stable compound. In a relatively recent study by Jeff Pettis and colleagues all 21 samples of¬†commercial foundation¬†tested were¬†contaminated with fluvalinates. This was a US study and I’m not aware of an equivalent analysis of UK foundation suppliers. However, there is an international trade in beeswax and fluvalinates are used globally‚Ć. I’d be very surprised¬†if any¬†commercially-purchased foundation – perhaps other than the certified organic stuff¬†– was ¬†not¬†contaminated with fluvalinates.

Are fluvalinates in wax foundation a problem?

These studies are difficult to conduct using field-realistic levels of miticides. Nevertheless, despite the fact that the absolute¬†toxicity of fluvalinates for honey bees is very low (i.e.¬†a lot is needed to kill the bees – the compound has a high LD50 0%)¬†there is compelling evidence that sub-lethal levels are probably detrimental. Drones reared in fluvalinate-treated hives exhibit increased mortality, reduced bodyweight and decreased sperm production. Similarly, queens reared in treated colonies exhibited lower body weight. More recent studies¬†by Keith Delaplane and colleagues tested emergence weight, memory, learning and longevity of workers exposed to fluvalinates and did not show any significant differences between treated and untreated colonies. In contrast, coumaphos – an organophosphate used for¬†Varroa control – was clearly detrimental in these studies. Perhaps the most significant result in this study was that mite levels in treated and untreated colonies were unaffected¬†… there was no evidence that the Apistan worked. I’ll discuss resistant in a future post.

Avoiding fluvalinate residues in comb

There are a variety of ways to avoid fluvalinates in comb. The first would be to use certified organic wax foundation. Thorne’s sell this for about twice the price of their standard worker brood foundation. This foundation is manufactured from beeswax sourced from New Zealand. Although certified organic, it’s not clear whether the wax has been tested for the presence of fluvalinates (an expensive process … so I’d be surprised if it had been). For reasons that will become clear shortly, just because the colonies used to source the wax had not been treated does not mean that there are no fluvalinates present in the comb from which the wax was rendered. Apistan was licensed for use in New Zealand seventeen years ago, shortly after Varroa was imported to the country.

An obvious way to reduce¬†fluvalinates in comb is to use foundationless frames. Even if commercial foundation contains traces of the chemicals, by using only thin starter strips you can significantly reduce contamination. Perhaps even better, by making your own starter strips from wax recovered from your own brace comb, cappings or foundationless frames, you can exclude the need for commercial foundation – and all the ‘extra goodies’ it contains – completely. I’m also investigating the use of unwaxed wooden starter strips this season, removing any chance of initial contaminants (note that this is not my primary reason for trying these).

And now the bad news …

Unfortunately, avoiding commercial foundation of any sort and¬†letting the bees draw comb directly from unwaxed starter strips still might¬†not prevent¬†the appearance and accumulation¬†of fluvalinates in your hives. In the Delaplane study they used brand new hives and foundationless frames with plastic starter strips. After one year they compared¬†treated and untreated colonies for the presence of fluvalinates in drawn comb. Unsurprisingly, treated colonies contained high levels of residual Apistan. However, untreated colonies also contained statistically significant levels of Apistan, four times higher than their detection limit. Coumaphos was also detectable at significant levels in untreated colonies. The authors suggest that the presence of both Apistan and Coumaphos¬†was due to drifting of bees from treated colonies carrying the miticide into the untreated colonies. Therefore, even if you don’t use Apistan, if your neighbour does you are likely to get low levels of fluvalinates accumulating in comb – even when using foundationless frames.

The Delaplane study appeared in 2013. An earlier article¬†appeared in¬†Bee Culture in 2009 which described the fluvalinate contamination of both commercial foundation and comb supplied by¬†‘chemical free’ beekeepers. It’s much easier reading than the data-rich Delaplane article.

Conclusion

If used appropriately, at the right time of the season on a susceptible mite population, Apistan is very effective at killing Varroa. If used like this, Apistan levels will accumulate in the beeswax in the colony. This may be detrimental for drones or queens reared in the colony, but current studies indicate is probably has negligible effects on the worker bees.

However, widespread use of Apistan has resulted in the rapid and¬†widespread¬†selection of resistance in the mite population … meaning that Apistan often has negligible effects on¬†Varroa. I’ll discuss this in more detail in another post.


‚Ć What do you think happens to all the reclaimed beeswax¬†traded with Thorne’s and other companies? It’s recycled into new sheets of foundation.¬†You might not use fluvalinates, but many beekeepers do and this will be generously divided up across¬†all the new sheets of pressed foundation.

CSI: Forensics in Fife

This is a long post. If you can’t be bothered to read it in its entirety the conclusion is …

It’s the viruses wot done it …¬†probably.

But the take home message is that you can learn from colonies lost in midwinter.

Introduction

I always have mixed feelings about midwinter hive losses, or deadouts as they’re called in the US. Of course, I regret losing the colony and wonder whether I could have managed them differently, or prepared them better, to increase their chances of survival. At the same time I’d much prefer a weak colony perishes in midwinter rather than having to mollycoddle them through the spring.

Winter colony losses in the UK vary from year to year but have averaged about 20% over the last decade (BBKA figures and SBA data). Whether these accurately reflect real losses is unclear to me Рthere are no statistics and they are usually by self-selected beekeeper reporting, so possibly unreliable†.

Mollycoddling weak colonies in the Spring … a¬†wasted effort?

The reality is that weak colonies in the spring require a lot of support¬†and still may not survive. Even if they do, there’s little chance they will be strong enough to exploit anything other than the late season nectar flows.

If the¬†colony is¬†weak because of queen problems then they are likely to need re-queening. This requires a spare queen early in the season – not impossible, but it needs planning or is likely to be expensive. In my view you’d be better off using the ‘spare’ queen to make up a nuc from a prolific colony, rather than trying to rescue what might be a basket case.

If the colony is weak because of disease then having them limp on through the spring is a potential disaster for your other colonies. If it doesn’t recover quickly it’s likely¬†that neighbouring colonies will rob it out, both destroying the weak colony and transferring whatever it was ailing¬†from around the apiary.

Finally, the colony might be weak due to poor management e.g. insufficient stores in the early spring when the queen was gearing up to lay again. In this case you might be able to rescue the situation by boosting it with syrup, brood and bees. However, care is needed not to weaken your other colonies. Two half-strength colonies are more work and much less use Рthey will collect  less honey Рthan one full strong colony.

Learning from your losses

So, rather than pampering weak colonies in Spring – particularly if they’re struggling because of disease or queen problems – I’d prefer they expired in the winter. That sounds cruel but isn’t meant to. The reality is that a proportion of all colonies are likely to be lost in the winter … on average ~20%, but significantly more in long hard winters (or perhaps with more accurate surveys!). As beekeepers, all we can do is manage them in ways to minimise these losses – keep strong, healthy colonies and provide them with sufficient stores – and learn from those that are lost.

How do you learn from the losses? By examining the ‘deadout’ and trying to work out what went wrong. You then use this information in subsequent seasons to try and avoid a repeat performance.

For example …

A life in the year of a June swarm

Sometime in early/mid January a colony of mine died.

The colony was alive in early December when treated for mites. It was suspiciously quite at the end of that month when other colonies were flying. It looked moribund by mid-January on a quick visit to the apiary.

I took the hive apart on the 30th of January to see what might have gone wrong.

But before the autopsy, here’s the history of the deceased …

  • 7th June – a small to medium sized swarm arrives in a bait hive. The bait hive had foundationless frames so it¬†was¬†difficult to estimate the amount of bees in terms of ‘frames covered’. My notes state ” … 4-5 frames of bees (ish) …”.
  • 8th June – very brief inspection, two frames nearly drawn. Queen not seen.
  • 9th June – vaporised¬†with an oxalic acid-containing treatment. 21 mites dropped in the first 24 hours. Not monitored after that as I replaced the solid floor of the bait¬†hive with an open mesh floor.
  • 19th June – unmarked queen laying well. My notes state¬†“… suspect this is a 2015 Q on account of the lousy weather we’ve had …”. There was already sealed brood present.
  • 27th June – clipped and marked the queen blue. At this point there were over¬†7 frames of brood in all stages – eggs, larvae and sealed brood – present.
  • Between then and mid-August the colony continued to build up¬†very well … so well I ‘harvested’ three¬†frames of brood and bees to make up nucs for circle splits.
  • In mid/late August I treated three¬†times at five day intervals with a vaporised oxalic acid-containing miticide. My notes in August state¬†” … KEEP AN EYE ON THIS ONE … very high mite levels …” and¬†(after a second round of treatment)¬†in late September,¬†” … mite levels still high …”. Actual mite counts weren’t recorded.
  • In late September/early October the colony was fed with fondant. An additional block of fondant was left on into the late autumn.
  • Further miticide treatment was added in early December. Mite drop was high but not outrageous¬†– about 44/day averaged over the first 5 days, dropping to 3/day over the subsequent five day period.
  • By late December the mite drop was less than one per day … however, by this time I was beginning to be concerned as there was very little activity from the colony on the warm days around Christmas.

The autopsy

I took the roof off the hive and removed the remaining fondant. Some of the fondant had dripped down between the frames but, in taking these apart, it was clear there were sufficient stores present.

The frames were clean. There were no sign of Nosema, which usually appears as distinctive faecal smearing and marking on the top bars, the face of the frames and Рin a heavily infected colony Рthe front of the hive.

The frames were almost devoid of bees. There were a hundred of so clinging to the middle pair of frames. I brushed these away to reveal a dozen or so corpses stuck headfirst down in the cells. This is characteristic of starvation. These particular bees likely died of starvation, but the majority did not (or they would have also been wedged headfirst into the comb).

Having removed the frames the few hundred dead bees lying on the open mesh floor could be seen. Amongst these was the blue marked and clipped queen. The bees on the floor weren’t showing any obvious signs of disease – no characteristic shrivelled wings seen with overt deformed wing virus¬†infection for example.

I’d walked to the apiary so couldn’t take the hive away with me. I therefore sealed up the entrance to prevent any robbing just in case there was¬†disease present that could be transmitted to another colony. In due course I’ll burn old frames, I’ll treat some of the good drawn comb with acetic acid fumes and I’ll clean and sterilise the hive.

Elementary, my dear Watson‡

There’s no really obvious smoking gun, but there are some reasonably¬†strong clues. I’m pretty sure why and how this colony succumbed.

But first, what didn’t kill off the colony? Well,¬†Nosema didn’t and nor did starvation. Sure, a handful of bees in the middle frame died of starvation, but the majority were on the floor and there were ample stores in the hive and some fondant remaining. It had also been warm enough to move about within the colony to get to these stores.

It’s not possible to deduce much about the queen. The colony was strong in late August but not fully inspected after that. My notes state that brood levels were low in late September, but they were in all the colonies I peaked in at that time.¬†She could have failed catastrophically soon afterwards. If she had I might have expected to find signs of attempted replacement¬†e.g.¬†a queen cell, as there were a few warm periods in the autumn. The fact that she was still present is far from conclusive, but suggests to me that she didn’t fail outright. The colony wasn’t full of drones late in the season suggesting she was poorly mated, though there are plenty of other ways the queen can fail. At least until late August she was laying very well.

I think the two main clues are the Varroa levels in autumn and December, coupled with the small number of bees present on the floor of the colony. Taking those in reverse order. There were far fewer bees than I would have expected from a colony that entered the autumn with about 8 frames of brood. This suggests to me that the bees were dying off at a faster rate than expected. Many bees that died off earlier in the winter would have been carried out and discarded on the warmer days.

The Varroa levels were very high in autumn¬†and quite high (at least for my colonies) in December. In the autumn¬†I didn’t¬†record the numbers. A couple of hundred dropped after treatment in December isn’t huge … but I suspect that the colony was much reduced in size by now meaning the percentage infestation was likely significant.

The damage was already done …

Miss Scarlett in the ballroom with the lead piping

I think this colony died due to the viruses transmitted by Varroa, in particular deformed wing virus (DWV). DWV is known to shorten the life of overwintering honey bees Рsee this study by Dainat et al., for full details.

DWV symptoms

DWV symptoms

Why are there no symptomatic bees visible in the carpet of bees littering the floor of the hive? That’s easy … you only get these symptoms in very young bees that have emerged from¬†Varroa-infested brood. In the winter there’s little or no brood (and there certainly wasn’t for some time in this colony). Any bees in this colony that had emerged with DWV symptoms would have been discarded from the colony months earlier. The colony was inspected every 7-10 days¬†from mid-June to late July but there were no obvious signs of DWV symptomatic bees. They might have been missed, but I’m reasonably experienced at spotting them.

My interpretation is that the colony arrived with high¬†Varroa levels and that – despite treatment shortly after¬†arrival – these persisted through to mid-August. The mites transmitted the usual cocktail of pathogenic DWV strains within the colony. High¬†Varroa levels are known to result in the massive amplification of virulent DWV strains in exposed bees. This late summer/early autumn period is a critical time for a colony. It’s when the overwintering bees are being reared. I discuss this at length in¬†When to treat?. These overwintering bees, now infected with virulent strains of DWV, subsequently died off at a higher rate than normal. Despite the colony appearing reasonably strong in late August, many of the bees were carrying a lethal viral payload.

Bees that died in late autumn would have been carried out of the hive and discarded in the usual manner. Overall bee numbers continued to dwindle, leaving just a few hundred and the queen by the year end. We’ve had some hard frosts in the last month. The expired colony is in the same apiary as the bee shed¬†which has a¬†max/min thermometer inside. The lowest temperature seen was -6¬įC during this period. This probably finished them off.

So no crime scene … just another reminder that the viruses will get you if the Varroa levels are allowed to get too high.

Learning from my mistakes

I think I made one big¬†mistake with this colony … way back on the 10th of June, just three days after it moved into the bait hive. I treated for mites, monitored mite drop after 24 hours and then left the colony with an open mesh floor. I should have monitored for longer (mite drop after vaporisation is often greater¬†after the first 24 hours). I would have then realised how badly infested they were and could have taken greater care to reduce mite levels. By mid/late August mite levels were probably¬†catastrophically¬†high. They were hammered down with miticides but the damage was already done. I suspect that this is also a good example of why the timing of treatment is critical.

It’s sobering that an apparently minor oversight in midsummer probably resulted in the loss of the colony in midwinter.

If you got this far, well done. It wasn’t my intention to write so much. Swarms are a significant source of potential disease and carry a disproportionately high mite load … something I’ll discuss¬†in the future.


‚Ƭ†They are not unreliable because they are reported by beekeepers ūüėČ ¬†Not entirely anyway. They are unreliable because they are generally a self-selecting group that report them. The BBKA or SBA ask for beekeepers to complete a survey. Some do, many do not. The BBKA do not report – at least in their press releases – the number of respondents. Self-selecting bias in surveys means they may not be entirely (or at all) accurate. The SBA surveys by Magnus Peterson and Alison Gray are more thorough. For their 2014 report for example the sample size was 350, with a total of 213 respondents (for comparison, there are about 4000 beekeepers in Scotland). With this information, coupled with some additional data – for example, knowing that only 87% of respondents were actually keeping bees during the survey period! – you can determine how representative the survey is.

‚Ä°¬†Sherlock Holmes never uses this phrase in any of the books by Conan Doyle though he does use a number of similar expressions. The phrase¬†“Elementary, my dear Watson” was first used by PG Wodehouse in Psmith, Journalist which was published contemperaneously (1909). The actor Clive Brook used the phrase in the 1929 film¬†The return of Sherlock Holmes.