Rational Varroa control

It’s the end of July … in the next two to three weeks the first eggs will be laid that will develop into the winter bees that get your colonies through to next spring. Protecting these winter bees is necessary to prevent overwintering colony losses.

I’ve written and lectured extensively on Varroa control and related topics for at least 5 years. The following article is published in August’s BBKA Newsletter and The Scottish Beekeeper. It provides an overview of what I term rational Varroa control.

I define this as effective mite management based upon our current understanding of the biology of bees and Varroa. The goal of this control is to minimise winter losses due to Varroa and viruses.

It is not a recipe with easy to follow if this, then that instructions. Neither does it provide a calendar-based guide of what to do and when to do it.

It does not even tell you what you should use for mite control.

Instead it focuses on the principles … understanding these will enable you to implement control strategies that help your bees, in your environment, survive.

This version is hyperlinked to additional, more expansive, posts on particular topics, is slightly better illustrated than those that appeared in print and contains some additional footnotes with caveats and exceptions.


Despite almost 30 years experience of Varroa in the UK, this ectoparasitic mite of honey bees remains the greatest threat to bees and beekeeping. With the exception of those fortunate to live in mite-free regions, all beekeepers must manage the mite population in their hives or risk losing the colony to the viruses transmitted when Varroa feeds on developing pupae. 

Fortunately, Varroa control is relatively straightforward; there are a range of approved and effective miticides that – used appropriately – reduce mite infestation levels significantly. The key words in that last sentence are ‘approved’, ‘effective’ and ‘used appropriately’. In reality annual colony losses, primarily occurring in the winter, often exceed 20% (Figure 1) and may be significantly higher in long or harsh winters 1. Many of these losses are attributable to Varroa and viruses. It is therefore clear that many beekeepers are not successful in managing Varroa; either they are not treating at all, or they are treating inappropriately.

Figure 1. BBKA winter survival survey – larger studies (COLOSS and BIP) often show much higher losses

This article is primarily aimed at relatively inexperienced beekeepers, but may also help the more experienced who still suffer with high levels of winter losses. It emphasises the importance of two, correctly timed, appropriate miticide treatments per season that should ensure colony survival. It is not going to deal with treatments of questionable or minor efficacy. These include the use of small cell foundation, drone brood culling or sugar dusting. These may reduce mite levels, but insufficiently to benefit colony health. Nor will it discuss the use of any miticides (or application methods) that are not approved by the Veterinary Medicines Directorate. I will also not discuss treatment-free beekeeping, selection of mite-resistant bees or advanced colony manipulations like queen trapping. In my view any or all of these could or should be tried … but only once a beekeeper can routinely successfully overwinter colonies using strategies similar to those described here.

The problem

Varroa is an ectoparasitic mite that feeds on developing honey bee pupae. During feeding it transmits a range of honey bee viruses, the most important of which is deformed wing virus (DWV). DWV is present in honey bees in the absence of Varroa. In our studies, using sensitive PCR-based detection methods, we never detect bees – even those from mite-free regions of Scotland – without DWV. The virus is transmitted horizontally between bees during trophallaxis, and vertically from drones or the queen through sperm or eggs. These routes of transmission are rarely if ever associated with any significant levels of disease and virus only replicates to modest levels (perhaps 1-10 thousand viruses per bee). However, when Varroa transmits DWV the virus bypasses the bee’s natural defence mechanisms and replicates to very high levels in recipient pupae (billions per pupa, 1 – 10 million times higher than in unparasitised pupae). Studies from our laboratory have shown that ~75% of pupae with these high virus loads either do not emerge, or emerge exhibiting the characteristic “deformed wings” that give the virus its name (Figure 2; Gusachenko et al., Viruses 2020, 12, 532; doi:10.3390/v12050532). The ~25% of bees that do emerge and appear ‘normal’ exhibit a range of symptoms including reduced fitness, impaired learning and reduced foraging. However, most importantly they also exhibit reduced longevity. During the summer this is probably not critical; the lifespan of a worker is only ~6 weeks and, assuming the queen is laying well, there are thousands of half-sisters around with more being produced every day.

DWV symptoms

Figure 2. DWV symptoms

But during the winter, brood rearing either stops completely or drops to a very low level. The bees reared from late summer onwards are physiologically very different. These are the ‘winter bees’, also termed the diutinus bees (from the Latin meaning long-lived). Physiologically these bees resemble juvenile workers and they can survive for many months. And they need to … it is these bees that get the colony through the autumn, winter and into the following spring. They protect the queen, they thermoregulate the hive and, usually around the winter solstice, they start to rear small amounts of new brood for the season ahead.

The longevity of the bees in the hive in winter is critical to colony survival. If the winter bees have high DWV levels their longevity is reduced (in addition to the reduced numbers due to overt disease or non-viability). This means that the winter cluster shrinks in size faster than it would do otherwise. With reduced numbers of bees it cannot keep brood warm enough and so the colony fails to expand early the following season. In cold spells it may be unable to reach the food stores resulting in the colony perishing from ‘isolation starvation’. It may not be able to maintain sufficient warmth to protect the queen, or may simply freeze to death.

The goal of rational Varroa control

Successful overwintering requires lots of winter bees. The size of the winter cluster is directly related to its survival chances. Therefore the goal of rational Varroa control is to prevent the winter bees from being exposed to mites and mite-transmitted viruses during their development. Winter bee production is induced by a range of factors including photoperiod, nectar and pollen availability, brood and forager pheromones. Together these induce slowed behavioural maturation of the winter bees. This is not like flicking a switch, instead it is a seamless transition occurring as late summer segues into early autumn (Figure 3). Winter bee production is also influenced by the queen. Young queens lay later into the autumn, so increasing the numbers of winter bees. 

Figure 3. Colony age structure from August to December.

It is important to note that these events are environment-driven, not calendar-driven. It will not happen at precisely the same time each year, or at the same time in different locations (or latitudes) each year.

To protect these winter bees the colony needs to be treated with an effective miticide before the majority of the winter bees are produced. This ensures that the developing winter bee pupae are not parasitised by virus-laden mites and so do not suffer from reduced longevity. 

When are winter bees produced in the UK? 

Unfortunately, I’m not aware of any direct studies of this. Scientists in Bern (49.9°N) in 2007/08, where the average temperatures in November and December were ~3°C, showed that the Varroa- and virus-reduced longevity of bees was first measurable in mid-November, 50 days after emergence. By extrapolation, the eggs must have been laid in the first week of September. 

Doing large scale experiments of Varroa control is time-consuming and subject to the vagaries of the climate (and, as a molecular virologist, beyond me in terms of the resources needed). I have therefore used the well-established BEEHAVE program of colony development (from scientists in the University of Exeter; https://beehave-model.net/) to model the numbers of developing and adult bees, and the mite numbers in a colony. BEEHAVE by default uses environmental parameters (climate and forage) based upon data from Rothamsted (51.8°N). Using results from this model system, the bees present in the hive at the end of December – by definition the diutinus winter bees – were produced from eggs laid from early/mid August (Figure 4).

Whatever the precise date – and it will vary from season to season as indicated above – at some point in September the adult bee population starts to be entirely replaced with winter bees. Large numbers of these need to live until the following February or March to ensure the colony survives and is able to build up again once the queen starts laying.

When to treat – late summer

The numbers of pupae and adult bees present in the colony are plotted in Figure 4 using dashed lines. Adult bee number decrease in early spring until new brood is reared. The influence of the ‘June gap’ on pupal numbers is obvious. Brood rearing gradually tails off from early July and stops altogether sometime in late October or early November. The shaded area represents the period of winter bee production – from early/mid August until brood rearing stops. 

Figure 4. Winter bee production and mite levels – see key and text for further details

Mite levels are indicated using solid lines. The impact on the mite population of treating in the middle of each month from July to November is shown (arrowed and labelled J, A, S, O and N) using the colours green, blue, red, cyan and black respectively. The absolute numbers of bees or mites is irrelevant, but bees (pupae and adults) are plotted on the left, and mites on the right hand axis, so they cannot be directly compared. The miticide treatment modelled was ‘applied’ for one month and was 95% effective, reproducing many licensed and approved products.

Mite levels peak in the colony in late September to October. If treatment does not occur until this time of the season then the majority of winter bees will have been reared in the presence of large amounts of mites. Unsurprisingly, the earlier the treatment is applied, the lower the mite levels during the period of winter bee production. 

Rational Varroa control therefore involves treatment soon after the summer blossom honey is removed from the hive, so maximising the winter bees produced in the presence of low mite numbers. If you leave treatment until mid-September, you risk exposing the majority of winter bees to high levels of Varroa in the hive. If your primary crop is heather honey, which is not harvested until September, you may need to consider treating earlier in the summer – for example during the brood break when requeening or during swarm control.

Why treat in midwinter?

A key point to notice from Figure 4 is that, paradoxically, the earlier the miticide is applied, the higher the mite levels are at the end of the year. Compare the August (blue) and October (cyan) lines at year end for example. This is because mites that survive treatment – and some always do – subsequently reproduce in the small amount of brood reared late in the season. This is what necessitates a ‘midwinter’ treatment. Without it, mite levels increase inexorably year upon year, and cannot be controlled by a single late-summer treatment. Beekeepers bragging on social media that their mite drop after the winter treatment was zero probably applied the summer treatment too late to effectively protect their winter bees.

And when is midwinter?

Historically beekeepers apply the ‘midwinter’ treatment between Christmas and New Year. This is probably too late. The usual miticide used at this time is oxalic acid, a ‘one shot’ treatment that is ineffective against mites in capped cells. For maximum efficacy this must be applied when the colony is broodless. Brood rearing usually starts (if it ends at all, again this is climate-dependent) around the winter solstice. By delaying treatment until a lull in the Christmas festivities or even early January some mites will already be inaccessible in capped cells. 

Figure 5. Biscuit coloured (or a bit darker) cappings indicating brood rearing in this colony

I check my colonies for brood – either by looking for biscuit-coloured cappings on the Varroa tray (Figure 5) or by quickly inspecting frames in the centre of the cluster – and usually treat in November or very early December. If I cannot check visually I apply the treatment during the first extended cold spell of the winter. By treating when the colony is broodless I can be certain my intervention will have maximal effect.

What to treat with?

I have deliberately avoided – other than mentioning oxalic acid – specific miticides. Rational Varroa control involves the choice of an appropriate miticide and its correct application. Examples of incorrect or inappropriate miticide choice include; use of Apistan when resistance is known to be very widespread, use of Apiguard when the average ambient temperature is below 15°C (which makes Apiguard of little use for effective control in much of Scotland) or the use of Api-Bioxal when there is capped brood present. In addition, use of a half-dose or a reduced period of application will both reduce efficacy and potentially lead to the selection of resistance in the mite population. Used correctly – the right dose at the right time and for the right duration – the majority of the currently licensed miticides are be capable of reducing mite levels by over 90%. If they do not, use one that does. Miticide choice should be dictated by your environment and the state of the colony.

All together now

Most beekeepers grossly underestimate the movement of bees (and their phoretic mites) between colonies. Numerous studies have shown that drifting and (to an even greater extent) robbing can result in the transfer of large numbers of mites from adjacent and, in the case of robbing, more distant colonies. 

Gaffer tape apiary

Figure 6. Gaffer tape apiary …

Rational Varroa control therefore involves treating all colonies within an apiary, and ideally the wider landscape, in a coordinated manner. In communal association apiaries (Figure 6), where beekeeping experience and therefore colony management and health can vary significantly, this is particularly important. Coordinated treatment is only relevant in late summer when bees are freely flying.


Swarms originating from unmanaged or poorly managed colonies will have high mite levels. The bee population in a swarm is biased towards younger bees; these are the bees that phoretic mites preferentially associate with. Studies have shown that ~35% of the mite population of a colony leaves with the swarm.

Figure 7. Varroa treatment of a new swarm in a bait hive…

Since swarms contain no sealed brood until ~9 days after they are hived oxalic acid is the most appropriate treatment. I usually treat them using vaporised oxalic acid late in the evening soon after they are hived (Figure 7). Even casts get this treatment and I have not experienced any issues with the queen not subsequently mating successfully. I’d prefer to have a queenless low-mite colony than a queenright one potentially riddled with Varroa.

Midseason mite treatment

The text above describes the mite management strategies I have used for several years. I apply Apivar immediately the summer honey is removed and treat with oxalic acid when broodless before the end of the year. Doing this has almost never required any additional midseason treatments; if mite levels are sufficiently low at the beginning of the season they cannot rise to dangerous levels before the late summer treatment. I still get winter colony losses, but they are almost always due to poor queen mating and rarely due to Varroa and viruses.

Figure 8. Queenright splits and the window(s) of opportunity

However, if midseason treatments are required – either because there are signs of overt infestation, because regular mite counts have shown there is a problem, or to have low mite colonies after the heather honey is collected – then there are two choices. Treat with MAQS which is approved for use when there are supers on the hive and, more importantly, is effective against mites in capped cells 2. Alternatively, treat during swarm control. With care, the majority of splits (e.g. the Pagden artificial swarm or the nucleus method) can be performed to give a broodless period for both the queenright (Figure 8) and queenless partitions. That being the case, a single application of an oxalic acid-containing miticide can be very effective in controlling the mite population.


Many beekeepers complain about the cost of licensed and approved miticides. However, some perspective is needed. A colony with low levels of mites will be more likely to survive overwinter, so reducing the costs of replacement bees. In addition, a healthy colony will be a stronger colony, and therefore much more likely to produce a good crop of honey (and potentially an additional nuc). Over the last 5-6 years my miticide costs are equivalent to one jar of honey per colony per year. This is an insignificant amount to pay for healthy colonies.


Rational Varroa control requires an understanding of the goals of treatment – protecting the winter bees and minimising mite levels for the beginning of the following season – and an appreciation of how this can best be achieved using miticides appropriate for the environment and the state of the colony. Like so much of beekeeping, it involves judgement of the colony and will vary from season to season and your location. I’ve applied my midwinter treatment as early as the end of October or as late as mid-December, reflecting variation in timing of the broodless period. Rational Varroa control also involves an understanding of the biology of bees and an awareness of the influence of beekeeping (e.g. crowding colonies in apiaries which increases mite and disease transmission) on our bees. However, none of this is difficult, expensive or time consuming … and the benefits in terms of strong, healthy, productive colonies are considerable.



  1. Caveat … small scale surveys of 1-2% of beekeepers are likely to be under-representative of true losses, suffering also from the “Amazon review” factor where those with particularly good, or bad, experiences dominate the responses.

    Bee Informed Partnership annual colony losses

    The large scale BIP survey in the USA has reported annual losses of over 40% (or winter losses averaging over 30%) in 6 of the last 8 years.

  2. Note – I have no experience using MAQS but am aware there are major problems using it when temperatures are high.

33 thoughts on “Rational Varroa control

  1. Trish the Beekeeper

    So…. what are your typical mite counts (% please, save me some math) in spring, summer and fall?

    I’m in Northeast OH in the US, and we have significant brood Feb-Oct. Typical mite counts in spring are 0 (threshold is 1 mite in 300 bees), summer varies between 0 and 10% (if that hive recently found a dying hive, for example, and was robbing it in the summer). Late summer will vary between 0 and 6% ( I treat at 4%, formic pro). 15-20 colonies.

    What are your threshold levels? for us, with real winter, pretty strict is the way to go.
    May check: 1 mite in 300 is above threshold
    Aug check: 13 mites in 300 is above threshold

    1. David Post author

      Hello Trish

      I don’t calculate them like that but instead monitor individual uncapped brood and virus levels by qPCR. Mite drop over 6 weeks at the end of the season is usually less than 500 in total (Apivar), and often significantly less. Mite drops after OA treatment in ‘midwinter’ (which usually means late November during a broodless period) are one tenth that at most. In both cases I’m expecting to kill about 90-95% of the mites in the colony. We’ve only intervened with one colony this season and that’s because virus levels were creeping up and the colony were needed for brood harvesting for experiments. Had that been a honey production colony I wouldn’t have treated. Although I’ve not got the numbers for this year, we’ve previously uncapped ~3000 cells and found just one or two mites in total.

      It’s worth noting that this season has been a “low mite” year, probably due to the relatively long, cold spring. Mite levels in uncapped drone brood are now increasing and treatment will be needed in mid/late August. However, what’s described in the post above is exactly what I’ve done for the best part of a decade.


  2. Dave Stokes

    Hi David,
    Thanks for another informative post; our local association has enrolled a lot of new members this yearso I’ll be sending out a link to them.
    One question, although I am aware of DWV being a major problem, I see very little evidence of it but am aware of a significant number of bees walking up my garden path. They look healthy, apart from the obvious inability to fly, so I assume it’s a paralysis virus. What is your opinion, please?

    1. David Post author

      Hi Dave

      How did they get to your garden path? What I mean is, did they walk there from the hive, or did they fly there and get chilled or something like that?

      There’s quite a bit of chronic bee paralysis virus about this year – more than I’ve been aware of before in Scotland and definitely more south of the border than the last couple of seasons. However, the symptoms you describe are not typical for CBPV. The two other paralysis viruses are acute BPV and slow BPV. Neither are well characterised I’m afraid. I think both are Varroa-transmitted. Most of the paralysis viruses are associated with some sort of shivering, shaking or trembling symptoms, which you don’t describe …

      It’s clear reading back over my answer that I’ve not been much help 🙁


  3. Dave Stokes

    They appear to walk from the hives which are on a small paved area the length of the path which is about 20 metres; they become invisible if they venture onto the uncut lawn. I first noticed it when I brought my best hives home from the apiary just before we first went into lock-down as I was anticipating not being allowed to travel to the apiary. I think it’s has been too warm for them to be chilled and there is no sign of shivering, shaking or trembling. I assume that they either don’t have the energy to fly, or the nervous system is compromised.
    I wouldn’t notice this at the apiary because it is in a field though I have to assume it’s there as I regularly move hives between the two sites.

    Even “I don’t know” is a useful answer; thanks.

    1. David Post author

      Hi Dave

      I still don’t know, but would additionally comment that it’s not unusual to see bees crawling some distance away from the hive when the area around the boxes is paved. I used to see this in my little courtyard garden in Fife. The absence of shivering, shaking or trembling symptoms might suggest that a paralysis virus is not involved.


      1. Duncan

        Birds walk when they can, I think because it’s got a lower energy budget than flying. Could the same be true of bees when the surface is easy-going like a paved area?

        1. David Post author

          I’d be surprised … but that wouldn’t be the first time. I guess it depends whether the bees Dave refers to were clearly walking to and fro his hive, or just randomly wandering about.

          I’m sure if I knew more about the energetics of flight vs. walking and the relative risk of predation etc etc etc I could produce a more scientific answer.

          But don’t hold your breath 😉

  4. Denry

    Hi David,

    Great article, thanks. I’m a first year beekeeper living in Snowdonia. We’re still got loads of nectar coming in (Bramble’s are still going strong, rosebay willowherb and himalayan balsam also prolific). There’s also a lot of Heather, both Bell and Ling, in the area. My neighbour who keeps bees tells me that she often has supers on the hive until the end of August, and some years into mid-September.

    I had bought a box of Apiguard to use when the supers come off, but hadn’t realised that it’s not effective below 15 degrees C. By September up here it’s very likely to be below that on average.

    What would be my best strategy for treating to cover the start of the winter bee production? Would MAQS be an option?

    Thanks very much,


    1. David Post author

      Hello Denry

      The Apiguard instructions include reference to temperature. It works at lower temperatures, but less well. I’m not sure how quickly efficacy drops, but there’s little point in treating with something that you know isn’t going to give the best chance of killing the mites. I gave up using Apiguard when I moved back to Scotland … and I’ve always been a bit wary of it because so many queen stop laying when the trays are in the hive. That treatment period is exactly when the queen should be laying eggs for the winter bee production.

      This article is about preventing the bees succumbing to Varroa and viruses … it completely ignores local nectar flows. There’s no easy answer to the question you ask. Firstly, it depends upon how good the late season nectar flows are. Do they contribute 10% or 80% of the honey collected. If the former, perhaps protecting the bees is more important. Secondly, your neighbour may leave the supers on to late September, but do they need to? Perhaps the majority of the flow is finished by then, but that fits with their holiday schedule, innate procrastination or whatever. Does your neighbour suffer from high winter losses? If so, perhaps don’t replicate their strategy. What do they treat with? Do they treat midseason, so mite levels are low throughout these late season nectar flows?

      In Fife, the main summer honey is usually finished by mid-August. Sure, there’s stuff available after that but it’s insignificant in terms of overall honey production. I take the supers off and start treating. If the bees collect a bit more then they’re welcome to it.

      If the September nectar is critical you need to develop a strategy to control mites before then. Lots of the commercial beekeepers do this when taking bees to the heather. There are opportunities when you do your swarm control.

      MAQS is an option, but it’s not something I have experience of. Read the instructions very carefully. At elevated temperatures it’s often not well tolerated.

      On a more general point … many inexperienced beekeepers lose colonies through poor mite management, get frustrated and eventually drift away and do something else with their spare time instead. This is obvious from the numbers trained vs. the slower increase in number of beekeepers, and in the ‘churn’ in association membership. Lots join, far fewer of these renew their membership. I’d argue that it would be better to get slightly less honey and successfully overwinter more colonies.

      Good luck

  5. Adam Darling

    Your article is timely; I have always tried to get varroa treatment on as soon as possible after the honey comes off – usually in July – so there is a good chance of having a healthy colony going into winter. Many people have the message that varroa treatment is an “autumn” treatment which is incorrect – autumn is too late and your article explains why.
    With the late season for many of us this year, there are going to be late-treated bees. I hope this doesn’t correlate with high winter losses reported next year.

    1. David Post author

      Hello Adam

      I – like many other beekeepers – was taught that there’s an ‘autumn’ treatment and a ‘midwinter’ treatment. That miight be the case, but I expect it’s the exception rather than the rule. Autumn and midwinter are too late. Autumn should more usually be late summer to protect the winter bees. Midwinter should be whenever there’s a brood break at the end of the season. I’ve treated in ‘midwinter’ as early as mid/late October as I knew the colonies were broodless.

      The start of the season was late, but it seems about on track now … though, of course, this depends where you are located.

      One thing you can be certain of though is that winter losses will be significantly higher than they need to be 🙁


  6. Denry

    HI David,

    Thanks very much for the reply. I hadn’t thought of it in those terms of the balance between ekeing out a small amount of extra honey, against the greater risk to colony health. Though as I’m learning in beekeeping, everything is a balance in some way. I’ll ask my neighbour a bit more about her past experience and practice. If there is a substantial late August flow, then maybe I need to plan for it and have some hives managed specifically for that flow.

    For this season, it sounds like I could take the supers off mid August, and then treat. In that case, what would be the best option of treatment? I’m keen to avoid apivar of possible and stick to the non-synthetic miticides, although I realise that it’s a pragmatic choice. Would an oxalic acid dribble or vape be a good solution once the supers come off, then another in early to mid December?

    One other question regarding mite counts. I did a mite wash as described by Randy Oliver, which showed 0 and 1 mites per 300 bees in each of my 2 hives respectively. I am happy to do monthly or so counts and treat at some threshold. Maybe followed by another mite count to evaluate the efficacy. Would this be a good way of going forward to monitor and treat for mites?

    Thanks again.

    1. David Post author

      Hi Denry

      You need to read up a bit on the requirements for effective miticide treatment. There’s a large number of posts on this site – look under Varroa on the Problems pages. Oxalic acid is not suitable in late summer. It has no effect against mites in sealed brood. At best you’ll be targeting 10-20% of the mite population.

      It’s your choice what to treat with. Apivar works well … but if you’ve chosen to use organic treatments then it’s not suitable.

      Monthly mite counts before and after (if treated) will certainly tell you lots about the mite levels in the hive. However, it’s probably overkill. Mite levels will vary as I’ve previously indicated. Your numbers are low, but it’s a bit meaningless as I don’t know when the counts were done (earlier will be lower) or whether the queen was laying frantically, or had stopped laying a fortnight ago. I’d suggest thinking in more detail about what you’re trying to count, what affects that count, and being as observant as possible – uncap a few drone pupae as they’re the most attractive to mites.

      I know some beekeepers want recipes for treating on particular schedules … almost beekeeping by rote. Some of the US beekeepers promote this type of threshold-based treatment, but don’t really discuss what influences mite levels. You can have relatively low mite counts in late May, a prolonged June gap, a significant rise in mite counts (because there’s no brood) and feel that treatment is urgently required … in practice, there are no more mites in the hive than there were in late May as the mites have had nowhere to reproduce, it just looks as though there are.


  7. Paul Lindstrom

    Good reminder to act. All 4 colonies now have the inspection boards in to check the mite levels. This year I’ll probably use VarroMed if needed to treat the colonies, and then vap them with Oxalic acid early in December.

    1. David Post author

      Hi Paul

      I’ve no experience with VarroMed but know it’s a dribbled mix of oxalic and formic acids. I’ve seen their efficacy data and it looks surprisingly high … that’s not to say it’s wrong, but I’d really like to see the primary data. If it wasn’t for the fact that I’ve just ordered my Apivar and that 50% of my colonies are now Varroa-free ( 🙂 ) I’d give it a try.


      1. Paul Lindstrom

        Thanks David. Several of my fellow beekeepers here in High Weald BKA use it, and is pleased with it. For me it will be the first time I use it. But since you are supposed to switch what type of brand you use now and then, I’ll give it a go.

      2. Margaret Cowley

        I’ve used VarroMed several times and have been pleased with the ease and flexibility of use, and the results. The only problem is that you are supposed to use it before 30 days after opening which could result in high wastage. We have got round that by a group of us in the same village sharing a bottle.


        1. David Post author

          Hello Margaret

          Presumably the relatively short shelf life is because of the oxalic acid content. If stored at room temperature this rapidly produces HMF which is toxic to bees. Storage at 4°C should slow this process (see the Storage paragraph at the bottom of this post on Api-Bioxal preparation).

          That’s very useful to hear you have had success using it …

          With thanks

  8. Denry

    Thanks very much for the reply. I didn’t really grasp how each treatment has such specific conditions in which it is effective, has its own specific down-sides and also how mite levels (both in sealed brood and on adult bees) are so variable at different times of the year. There’s so much to learn in beekeeping and I’m only just starting to learn about mite management. I suppose I’m just trying to get my head around the numerous variables which are important to make a decision on how and when to treat. I’ll have a read through some more of your articles on the various methods, strategies and timings.

    One last question then to clarify things in my head. This is for a late summer treatment to protect the developing winter bees, low ambient temperatures at 200m altitude in Snowdonia and taking into account the timing of the treatments and the possible side-effects associated with some of these treatments. Apiguard is out due to temperature and reduced laying. Oxalic dribble is out due to ineffectiveness on sealed brood and toxicity to unsealed brood.

    So the options are: a) MAQS, with the possibility of keeping supers on for potential Heather flow, but risking queen problems/loss; b) remove supers and do oxalic sublimation with several treatments some days apart to cover the brood cycle and get more of the mites from the sealed brood as they emerge; or c) apivar strips – synthetic, but simple to apply – do they cover the sealed brood?

    And am I right in thinking all of these options need to be followed up with OA dribble/vape in the early winter brood break?

    Thanks again,


    1. David Post author

      I’ve been keeping bees for several years and am still learning … that’s part of the beauty of the hobby 😉

      MAQS … queen problems should not be significant if the temperature is reasonable. It’s high temperatures when problems occur.
      Multiple OA sublimations is not a VMD approved method so I cannot recommend it … which doesn’t mean it doesn’t work. The late Pete Little determined that 3-4 treatments at 5 day intervals was probably optimal. Again, this is not an endorsement of the method.
      Apivar … if used according to the instructions (which you should) takes 6-10 weeks depending upon the amount of brood in the colony.

      And, yes, for the reasons clearly laid out in the post above, you should do a winter oxalic acid treatment.


  9. Denry

    Great stuff! Thanks very much for a very interesting discussion. It’s certainly clarified some things in my mind, and challenged me to read up on more!

    Keep the posts coming, they’re great!


  10. vince poulin

    David – I’m pleased your persistent in discussing mite treatments, schedules and the importance of this being well understood by every bee keeper. The problem with mites is they sneak up on you and why a strategy is key to retaining healthy hives. I lost 7-hives last year despite beginning treatments as early as that first week of August. This truly caught me off-guard because I thought – I was particularly “pro-active”. However, those treatments Failed! It was a huge high, mite year and I was not alone in loosing hives – most keepers lost hives due to it being an exceptional year. Frankly – I think you can not talk enough about mites. Keep hammering us! We need to hear it. OK – this year. There are fewer mites around – perhaps due in part by our 70% hive losses last year. But they are still here and we know will come. I uncapped n=1,420 drone cells by July 15, with no mites. I then began removing summer honey and replacing with as much drone come as I had available. With that now complete I ran alcohol washes on 4-hives. Results: hive 1, n=289 bees tested, n=2 mites (0.7%), Hive 2, n=288 bees tested, n=2 mites (0.7%); Hive 3, n=317 bees tested, n=0 mites; and lastly Hive 4, n=286 bees tested, n=0 mites. These results look quite good. But – mites are here and I know more coming. How good are these results? This is not perfect science. What is a single or even two frame sample of 300 bees worth in the world of statistics where mites may well not have decided to populate that frame or those frames???? Killing 300 bees is OK but 600 or 900 is hard to do. Now – alcohol vs drone uncapping? I like drone uncapping, I think a great method but very time consuming. I looked for capped drone cells during the alcohol tests but unfortunately all the drone comb I planted in early July was filled with honey and not used for drone brood. My mistake was not putting the trap comb in the lowest brood box – I went for ease of placement and inspection and had the frames placed too high. But did get some to sample. In Hive 2 I uncapped 69 cells – this hive had 2 mites in the alcohol wash. In the drone cells I found 8 mites for an 11% infestation rate. In hive 4 – I uncapped 22 drone cells. In this hive had no mites in the drone cells and none in the alcohol wash. Over all this does look good but it is not perfect science – if science at all. My results do show the importance of multiple sample methods and to never become complacent about mites. I’m heading off for 2-weeks soon – when I return I will repeat the tests immediately and uncap as many drone cells as I can find. I want to treat only if necessary but my threshold for treatment is very low. I lost 7-hives last year and doggedly do not want see that repeated again.

    1. David Post author

      Hi Vince

      Frankly – I think you can not talk enough about mites. Keep hammering us! … I’m not sure what else I can say without repeating myself ad nauseam 😉

      It’s clear there are broadly two types of readers of posts here; 1) regulars who have subscribed for some time and are often quite experienced beekeepers, and 2) new beekeepers, or at least new readers, who dip in for a few posts and then disappear. Despite the search facility and as many cross-links and summary pages (Problems, Practice etc) many of this second group probably miss some of the Varroa control posts, but if I write more (and start repeating myself) I’ll probably end up losing some/all of the first group.

      However, your numbers sound pretty good. As we approach the end of the season it’s always a bit of a balancing act between getting the last of the nectar flows before the mite numbers explode. It looks like a low mite year as well, so I think we’ll be OK.

      The autumn treatment is undoubtedly the most important for successful overwintering. It has to be administered in a timely manner and must be effective … there’s no point in using an ineffective treatment (e.g. Apistan [tau-fluvalinate]) at the right time, or using an effective treatment at the wrong time (e.g. oxalic acid when there’s lots of sealed brood).

      I’ll be using Apivar later this month and oxalic acid in the winter (as I generally do these days) … but also enjoying not treating some colonies that are mite-free because of our geography and isolation 🙂


  11. John Eaden

    I shall be recommending your post to members of my Association Aston every opportunity! I notice it a,so is in BBKA News.
    I found your explanation of the timing of laying for winter bees most useful. I will now be taking the honey off sooner than usual. There has been a good lime flow and there’s a lot of capped honey. Persuading Association members to do the same will be more difficult as many enjoy the late and heavy Himalayan Balsam flows we have around here in Manchester.
    Question – when do you place your Varroa trays in the colonies to monitor for the brood break – I find that left too,long there’s a lot of debris to confuse the assessment.
    Question – are there circumstances in which you wouldn’t open a colony for a quick brood check in November?

    Your suggestion that leaving Oxalic Acid based treatment till after Christmas is too late is one I saw last year – this year I plan to follow your example and monitor brood and apply the treatments earlier. Whether I can change the long established tradition of the Association to treat in January is the $64k question.

    Keep sending the messages out on importance of Varroa control – we need constant reminders.

    1. David Post author

      Hello John

      It’s also in the Scottish Beekeeper this month … 😉

      Why don’t you get association members to monitor colony losses and time of treatment … see if there’s a relationship. Colony losses have to be through disease or starvation (which I suspect is usually disease anyway), not queen failure. Perhaps that might persuade some to either forego the fireweed flow, or to treat before midseason to have healthy colonies to exploit the late season nectar.

      I’ve written extensively about ‘midwinter’ mite treatment not actually being in the midwinter over the last 5 years. For example, this post from 2017. I suspect it will be difficult to get established association members to change their ways. It’s almost become a ritual to treat between Christmas and the New Year. Some associations even prepare bulk amounts of oxalic acid for dribbling, but don’t distribute it until far too late in the year (or early in the New Year!). I’ve treated when broodless as early as late October … if the colony is broodless there is nothing to be lost. Other than mites.

      I leave the tray in for a few days during cold spells in the winter and can usually ‘read’ the resulting pattern. I’ve written a bit about this here. The colony will be inactive and the amount of debris will be limited in very cold weather … but if bees are emerging they must leave some dropped cappings.

      Quick brood checks … I wouldn’t do it in a thunderstorm 😉 . More seriously, I generally only open a colony in the winter for confirmation of broodlessness. I don’t routinely check each week. I’ll often only check one in each apiary, and only then if I’m in doubt.

      I usually watch the weather carefully and focus on the first extended (say 2-3 weeks) cold period of the winter. As soon as it warms to high single figures I usually treat as experience shows that my bees are usually broodless at this time.

      It’s probably easier to time the winter treatment in more northerly latitudes …

      As I replied to someone else recently, I’m not sure there’s much else I can write about Varroa. There are no quick fixes. Treatment is simple, quick and cheap. The key thing is timing it properly … if you don’t, you (almost) might as well not bother.


  12. John Eaden

    Thanks David for such a speedy and detailed reply.
    I think your comment about northerly latitude might be key. I suspect that winter brood breaks are more common in Scotland than further South.

    1. David Post author

      I’m sure they are … but when I lived in the Midlands there were brood breaks in the winter and the graph in the post above is based upon environmental data from Rothamsted, and also includes a brood break.

      Even if there’s no brood break, the best time to treat in the winter will be when there’s the minimal amount of brood. I suspect this happens earlier in the winter than many people assume.


  13. Gareth Ritchie

    Hi David,

    I am a new beekeeper and have just started with two hives this year. I am really enjoying reading your blog posts and the large back catalogue. I have found your scientific and practical information invaluable.

    I have followed your advice and have purchased some Apivar, I searched a good bit to get one with a expiry date that would cover next years treatment so as to save wasting 6 strips. They arrived today but on reading the package it seems that storage is impossible once the seal has been broken. Have you any advice on the possibility of storing these strips?

    Many thanks


    1. David Post author

      Hello Gareth

      Amitraz (the active ingredient in Apivar) is pretty unstable and readily oxidises. I have used them from a previously opened packet (stored tightly wrapped in clingfilm and kept cool) but was sufficiently unconvinced of their efficacy that I wouldn’t do it again.

      You have two options … get more hives so you can use a full packet each season or share the packet with neighbouring beekeepers.

      Either option is highly recommended 😉

      More hives should increase your honey production, improve local pollination or generate more wax/propolis/royal jelly (or whatever you’re interested in) and will give you some flexibility should one go queenless or swarm. Sharing the Apivar should ensure your ‘neighbours’ bees are also relatively mite-free so reducing the risk of diseases being transmitted through drifting or robbing.


      1. Dorothie Jones

        Hi David
        I there evidence of Amitraz resistance appearing in the US? I heard a rumour but not been able to find anything.

  14. Gareth Ritchie

    Thank you David,

    I suspected that storage was ill advised, but at least now I know for certain. I think I will donate them to the local association this year and plan to expand in the coming years to utilize these better (along with all the other benefits of expansion).

    Thank you again for all your excellent posts they really are invaluable!



Leave a Reply

Your email address will not be published. Required fields are marked *