Tag Archives: Varroa

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, 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, 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 – though perhaps only to those with a tendency towards geekiness – to 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 ImageJß. 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 ∞ 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 😉

† 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.

‡ 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.

§ 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.

ß 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

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° 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 🙁 ) 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 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.


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 …

† 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.

‡ 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.


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?



Apistan resistance



In an earlier article I discussed what Apistan is – a pyrethroid miticide – and 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. 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 😉

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. 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.



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 – in the presence of the pyrethroid – is effectively absolute. Without the necessary mutation the mites die, with the mutation they survive.

Bees – and the phoretic mites that are associated with them – are 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.

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 – the 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 … tau-fluvalinate

Apistan® 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 τ-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® and Minadox® – 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. 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.


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.

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.


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 – there 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 – they will collect  less honey – than 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 – in a heavily infected colony – the 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 – see 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°C 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.

 They are not unreliable because they are reported by beekeepers 😉  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.

 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.

2016 in retrospect

The end of another year and another season’s beekeeping. Now is a good time to review what went well and what went badly.

The bee shed in autumn ...

The bee shed in autumn …

In terms of my beekeeping year in Scotland, the end of December isn’t even half way through the winter. Although I didn’t open many hives after mid-September (three and a half months ago), unless we get a warm, early Spring I don’t expect to do any inspections until mid-April. That’s another four and a half months to ruminate on the year passed and plan for the season ahead.

The high points

The great escape ...

The great escape …

This was the first full season using the bee shed and I’m already convinced of the advantages it offers. Colonies built up well in the late Spring, appreciably faster than colonies in the same apiary that didn’t benefit from the protection the shed offers. I was able to inspect whatever the weather. Only really warm days were a problem, and that was because it gets uncomfortably hot. The Up-and-Out™ windows (the bees crawl up and fly out) clear the shed very quickly, making it a good environment for grafting larvae when queen rearing without getting buzzed with bees all the time. It would benefit from power, better lighting, a kettle and an armchair … perhaps something to plan for 2017? It’s never going to resemble the palatial setups in some of those German bee houses, but in terms of secure, weatherproof and sheltered accommodation, it’s hard to beat.

Varroa control has worked well this year. A combination of timely applications of treatment and a significant brood break in the middle of the season, meant that colonies went into the winter with low to very low Varroa levels. Some broodless colonies dropped less than 20 mites after midwinter treatment which is very encouraging.

OSR ... can you believe it?!

OSR … can you believe it?!

I’ve also been pleased with the honey flavour this year. By missing the OSR – too cold (the photo above was taken at the end of April) – the early season honey was a heady mix of goodness knows what, and all the better for it. Great flavour and it has sold well. The switch to square jars with distinctive black lids looks good and, coupled with a very simple DIY label, it’s been popular with repeat customers. My honey is currently available – assuming they haven’t sold out over Christmas – from Mellis Cheese in St. Andrews and Edinburgh, and Luvians in Cupar.

The low points

The most significant problems were all related to queens. Firstly, queens from 2015 were poorly mated (as predicted way back in June 2015) and several gave up (stopped laying) or simply disappeared in May/June. Secondly, my own queen rearing coincided with shortfall and an extended period of very poor weather for queen mating. As a consequence, several hives developed laying workers and needed some significant interventions to rescue them.

Drone laying workers ...

Drone laying workers …

All of these problems – some of my own making, but some unavoidable – meant that production colonies weren’t really strong enough to exploit the summer nectar flow. Honey yields from the summer were the worst I’ve had for half a decade, though the flavour was outstanding. I’ve a couple of 30lb buckets left that I’m hoping to eke out over the next few weeks in the smallest possible portions. To add insult to injury … it was apparently one of the best years for heather honey and, because of the problems detailed above, I was singularly unprepared to take advantage of it. In all honesty, I’m not wildly disappointed about this as I’m not a great fan of heather honey. However, since I’m in Scotland and heather honey is considered by many as the crème de la crème, I feel I’ve missed a golden opportunity.

The new season

With the winter solstice now passed it’s time to make plans for the coming season. I’ll deal with these in the Spring as this article is already longer than intended.


It’s been a busy year with posts almost every Friday. This was more than I’d intended at the beginning of the year, but seems to have happened without too much contrivance. Although posted on a Friday, they’re written in the days and weeks preceding (hence explaining the butchered tenses often used).

Keeping it regular

Keeping it regular

I’ve always tried to avoid the diary-like cataloguing of what goes on in the apiary (as there are others who do this much better), instead focusing on a balance between topical items and more expansive posts – often written as separate linked articles (like on Varroa control or queen rearing) – that both reflect my interests and might help others improve their beekeeping … if only by avoiding my mistakes 😉

Page views and visitors

Page views and visitors

Other than a slightly odd dip in July – a belated “June gap”? – visitor numbers and page views showed the expected pattern of increasing interest in mid/late Spring, tailing off again as the season draws to a close. The peak figures in October reflect the interest in feeding fondant and mite treatments. Clearly there’s still some work to do … treating for mites in October is likely to be too late to protect the winter bees from the ravages of deformed wing virus. Over the entire year the original 2014 posting about honey warming cabinets remained the most popular, with articles on feeding fondant, vertical splits, steam wax extractors and foundationless frames getting lots of attention as well.

Search and ye shall find …

Google and most other search engines ‘hide’ the search terms used by viewers to reach a website. This is nominally valuable information, though looking at the terms that do get through the filters makes you wonder … each of the terms below led the viewer to this site (the typos are original) :

circular large 200 frame honey extractor plans … as opposed to a small 200 frame extractor?

wellies with honey bee pucturers on … puctures?

using laser printer in unheated wooden shed … electric heater needed I think

square drones frame homemaking striping images … random word generator?

foundationless sheds … understandable considering foundationless frames and bee sheds

poly queen beekeeping pdf … article on poly queen beekeeping in preparation for 2017

plastic nuc boxes for sale in manitoba … perhaps a little too geographically specialised

simple label design for honey sales in nigeria … see Manitoba

do i feed bees with apiguard … not exactly

is dettol effective against varroa mites … rigorous testing needed and possibly tainted honey?

how to treat a double brood hive with api bioxal … article on beekeeping bankruptcy to follow

houney bees kb shed bnati h or kb kha jays h … yes, that really was a search term

save humanity a topic covered in detail earlier this year

humanity save … there’s a theme emerging here

how do bees save humanity … by pretending to be wasps

Unsocial media

It’s clear that there are whole communities of beekeepers out there with very different online activities – some interchangeably use old-fashioned websites (like this site) and various types of social media, others restrict themselves to Twitter and Facebook. Posts to this site are now also ‘announced’ on Twitter (@The_Apiarist) and Facebook. I still have to get the hang of Facebook as I’ve not previously used it … I don’t even know how to properly link to it 🙁

Anyway … enough for the year. As I write this the winter solstice has now passed, the days will be getting longer and lighter, queens will – particularly now with the warmer winter weather – be starting to lay and mites will be starting to reproduce. There’s very little to do in the apiary, but the new season is definitely on its way …

For 2017 I hope your bees are gentle, your queens are prolific, your supers are heavy and your swarms end up in my bait hives 😉

Happy New Year

Frosty apiary

Frosty apiary


Get dribbling

There has been a prolonged spell of cold weather in Eastern Scotland. Temperatures have rarely risen above 5°C, with hard frosts overnight. However, a warm front moved in on Tuesday night and the last few days have been significantly warmer. The lack of activity at the hive entrances and a quick peek under the insulation through the perspex crownboards (where fitted) indicated the bees were all tightly clustered during the cold spell. Furthermore, the absence of debris on the removable Varroa monitoring trays fitted to many of the open mesh floors, suggested that little or no brood was being reared.

Ridiculous to the sublime

Ridiculous to the sublime

Varroa counts

Varroa trays ...

Varroa trays …

There was another clue that the colonies are likely broodless. I had been recording the natural Varroa drop of a few colonies over the last month. I did this by simply counting Varroa at each visit, calculated on a mites/day basis. Although generally low (and very low in a few colonies), it had been steadily increasing. This is a good indication there were more phoretic mites in the colony … again, presumably due to the absence of suitable brood for them to parasitise.

It’s worth noting that the natural mite drop is a notoriously unreliable method of accurately determining mite levels in a colony. For example, it’s dependent upon the amount of sealed brood in the colony. With no sealed brood all mites must be phoretic. In contrast, with limitless sealed brood 80-90% of the mites are within cells. However, although estimates from mite drop are not hugely accurate, they are a lot better than doing nothing. The National Bee Unit has published a Varroa calculator. This allows you to use a combination of the mite drop per day, the time of year, length of season and level of drone brood to predict the total numbers of mites in the colony. For some inexplicable reason this asks for the level of drone brood in December … with 0% not being an available option  🙁

Time to treat

With little or no brood in the colonies, now is a perfect time to treat with an oxalic acid-containing preparation to hammer down the remaining mite population. I’ve previously discussed the importance of this midwinter treatment (see Two treatments … a double whammy). In many ways it’s preparation for the season ahead, rather than for the protection of the bees already present in the colony. The lower the mite levels are at the beginning of the season, the longer it will take for the mite population to reach dangerously high levels.



You can model these events using BEEHAVE. This is an interesting in silico model of a beehive. With mite numbers of ~10 at the beginning of the year, maximum levels reached are low to mid-hundreds by late summer, reducing to a couple of hundred the following winter. This assumes no intervening treatment and runs the model using all the default settings. In contrast, using the same parameters but starting the year with ~100 mites, levels peak at between 3000 and 4000 mites, returning to about 1800 in December.

Remember that the National Bee Unit recommends mite levels should not exceed 1000 or there is a risk of “significant adverse effects on the colony”. Therefore, the midwinter treatment is an important preparation for the year ahead, delaying the point at which these dangerously high mite levels are achieved.

Have your hives got less than 100 mites in them now?

Remember also that, with no sealed brood, midwinter is also the ideal time to expose as many mites as possible to the treatment. With the exception of prolonged treatment with hard chemicals like Apistan or Apivar, it’s probably the only time you’ll achieve greater than 95% reduction in mite numbers. With little or no brood present there’s nowhere for the mites to hide.

Dribbling or vaporisation?

An oxalic acid-containing treatment is recommended in midwinter. This can be delivered by dribbling or sublimation (vaporisation). Under optimal conditions, efficacy of the two methods is broadly similar (90%+) though there is some evidence that dribbled oxalic acid is slightly detrimental to colonies (when compared with sublimation, but not when compared to doing nothing).

Sublimox in use

Sublimox in use …

Api-Bioxal is the VMD-approved oxalic acid-containing treatment. If used for dribbling be aware that the suggested concentration on the side of the packet is higher than conventionally used in the UK. It’s also worth noting that it’s not available pre-mixed so has to be made up from powder. In this regard it’s a less useful product than the pre-mixed oxalic acid solution that Thorne’s (and possibly other suppliers) sold each winter. The one- or two-hive beekeeper needs to weigh out very small amounts accurately, or get together with others to make a large batch. Hardly what I’d call progress. Furthermore, the inclusion of glucose and powdered silica (as an anti-caking agent) in Api-Bioxal means it leaves a caramelised mess if used for vaporisation. Although a scouring pad and elbow grease will get rid of this mess, it’s another example of how the “approved” commercial product is actually less good – and no more effective – than the oxalic acid dihydrate that beekeepers have been using for 20 years or more.

Notwithstanding these negative comments, Api-Bioxal works well and is less expensive (per treatment) than most of the other VMD-approved Varroa treatments.

Don’t delay, get out and get dribbling …

The forecast for the next 7-10 days is for significantly warmer temperatures. This means that the queen – if she was having a break from egg-laying – will start laying again. There will be open brood by this weekend and sealed brood in your colonies by about the 15th of December. Dribbled oxalic acid is detrimental to – and may kill – open brood so if this is your preferred method of treatment then don’t delay. If you sublimate you’ve got a few days leeway, but don’t delay any longer than that.

Here are a couple of old videos showing trickling (dribbling) oxalic acid onto a large and small colony in the middle of winter. The Trickle bottle from Thorne’s makes administering the treatment very quick and easy.

Of course, sublimation using an active vaporiser like a Sublimox is even faster and doesn’t involve opening the colony. Here’s an example showing treatment of a recently hived swarm in midsummer … I could have removed the Sublimox after about 30 seconds.

The Daily Mail may be predicting the coldest winter since the last ice age (so perhaps there will be another broodless period§) but I wouldn’t rely on them to influence something as important as the midwinter treatment for reducing Varroa levels.

Here’s a perfect example of the problems encountered by the ‘topical blogger’. I wanted to write about midwinter Varroa treatment in the middle of winter, at a time when others – particular new beekeepers – should be treating their own colonies. Typically these treatments are made in late December or early January. However, the long-range (10 day) forecast in late November suggested the second week of December might be suitable. Some of this was therefore written in very late November, the Varroa drop comments added once I’d completed counting around the 4th to the 6th, and the post finished off the following day once I’d treated my own colonies.

This assumes that the queen started laying on the 7th, the first full day with elevated temperatures.

§ I didn’t open any colonies to confirm they were broodless. I was happy enough to take the clues from the increased mite drop on the Varroa trays and the absence of debris indicating uncapping of brood cells. However, I was told by friends that other colonies they opened on the 7th were broodless.


Out, damned mites

Sublimox vaporiser

Sublimox vaporiser …

Today was very mild, slightly damp and breezy after a prolonged cold spell (at least here in Scotland). The long, cold spell means that colonies are broodless. Now is an ideal time to apply your midwinter Varroa treatment. Don’t wait until the Christmas holidays, don’t wait until the weekend after next … colonies will probably have sealed brood again by then. For maximum effect treat while the colony is broodless and decimate the phoretic mite population.

I treated all my colonies late this afternoon and evening. I finished the last using a headtorch for illumination and tidied up under bright moonlight. The bees looked good and it was great to be doing some beekeeping again, if only briefly.

 A longer post justifying why the colonies were considered broodless and why it is so important to treat when they are broodless will appear this Friday.

The rather weak title is a variant of Shakespeare’s “Out, damned spot” from the play Macbeth. The words are spoken by the sleepwalking Lady Macbeth who is going insane with guilt after her husband killed Duncan (the King of Scotland). The spot refers to Duncan’s blood. Mites on the Varroa tray look like tiny spots of blood …


Helensburgh & District BKA talk

DWV symptoms

DWV symptoms

I’m very pleased to be speaking on the 24th of November (this Thursday) to members of the Helensburgh and District BKA. The talk will be at the rather splendid looking Rhu Parish Church at 7.15pm. The title of the talk is “Bees, viruses and Varroa: the biology and control of deformed wing virus (DWV)”. I’ll discuss aspects of the biology of DWV, particularly relating to its transmission by Varroa, and will then explore potential ways in which bees could be ‘protected’ using either high-tech or low-tech approaches. If you’re attending please introduce yourself when we’re all having a cuppa at the end of the evening … don’t leave it too late though, I’ve got a 2 hour drive home afterwards.


The drive from the east coast to Helensburgh was stunning, with a fantastic pink-tinged sunset lighting up the snow-covered hills around Crainlarich (Stuc a’ Chroin, Ben Vorlich and Ben Ledi). It was bitterly cold and clear.

Stuc a' Chroin and Ben Vorlich ...

Stuc a’ Chroin and Ben Vorlich …

There was a slight delay due to an absentee projector. During this we discussed oxalic acid-containing treatments for Varroa control and the problems caused by the lack of a ready-mixed preparation of Api-Bioxal. Once the projector arrived we were up and running and I covered viruses and Varroa, why we treat when we treat (or perhaps more correctly ‘when should we treat for maximum effect?’) and the influence of drifting and robbing on parasite and pathogen transmission between colonies. That’s quite a lot to get through in an hour … and I didn’t. The audience were rewarded for their patience with a well-earned cup of tea and a question and answer session.

The return trip was less visually pleasing other than a great view of a barn owl ghosting along the verges of the A977 near Rumbling Bridge. With thanks to Cameron Macallum and colleagues for their hospitality and a very enjoyable evening.