If you haven’t yet treated your colonies to reduce Varroa levels before the winter arrives it may well be too late†. High Varroa levels are known to result in the transmission of virulent strains of deformed wing virus (DWV). These replicate to very high levels and reduce the lifespan of bees. If this happens to the ‘winter bees’ raised in late summer/early autumn there’s a significant chance that the colony will die during the winter.
Mite levels in most of my colonies have been very low this year. Partly due to thorough Varroa management in the 2015/16 winter (the only thing I can take credit for), partly due to the relative sparsity of beekeepers in Fife, partly due to the late Spring and consequent slow build-up of colonies and partly due to an extended mid-season brood break when requeening. Most colonies yielded only a small number of mites (<50) during and after a 3 x 5 day treatment regime (to be discussed in detail in a later post) by sublimation.
The low mite drop definitely wasn’t due to operator error or vaporiser malfunction. At the same time I treated a swarm that had moved into a bait hive in early June …
Out, damn’d mite …
This is ~20% of the Varroa tray. Have a guess at the number of mites in this view only. Click on the image to read the full legend which includes the mite count.
The image above was taken on the 18th of September, a day or two after starting the second round of 3 x 5 day treatments. The colony really was riddled. When a colony swarms 35% of the mites in the colony leave with the swarm (or, in this case, arrives with it). For this reason the swarm was treated for mites shortly after it arrived in June. It did have a reasonably high mite load but subsequently built up very quickly and didn’t experience the mid-season brood break my other colonies benefitted from.
The colony now has an acceptable mite drop (<1 per day). Similar colonies are still rearing brood – I’ve not checked this one, but they are bringing in some pollen from somewhere – so there’s a possibility the majority of the remaining mites are tucked away in sealed cells. I’ll keep a close eye on this colony through the next few weeks and will be treating again midwinter to further reduce the parasite burden.
Treat ’em right
If you are treating this late in the season make sure you use a miticide that is appropriate for the conditions. Apiguard (a thymol-containing treatment) is almost certainly unsuitable unless you’re living in southern France as it needs a temperature of 15°C to be effective. MAQS has a recommended temperature minimum of 10°C which may be achievable.
Hard chemicals such as Apivar and Apistan can be used at lower temperatures but there’s little point in treating with Apistan unless you’re certain all your mites are sensitive. They almost certainly are not as Apistan/Bayvarol resistance is very widespread in the UK mite population. Just because you get an increased mite drop in the presence of Apistan does not mean treatment has been effective. Perhaps all you’ve done is killed the sensitive mites in the population, leaving the remainder untroubled. This is what’s known as a bad idea … both for your bees next season and for your neighbours.
† I’m posting this now due to the large number of searches for, and visits to, pages on use of Apiguard or other Varroa treatments. These are currently running second to ‘fondant‘ in one form or another.
This is the last of a short series of related posts on rational Varroa control. It brings together the key points made on the choice of how and when to treat, coupled with a treatment strategy that minimises the influence of bees drifting between colonies. The latter is best summarised in three words … coordinated Varroa treatment.
Coordinated Varroa treatment makes sense
Abandoned hives …
Most beekeepers treat their own colonies together … it’s logical, easier and cost effective. But what about the other beekeepers in the shared association apiary? What about the colonies two gardens away? What about the large row of colonies in the bottom of the adjacent field? What about that abandoned hive in the hedgerow over the road? What about the feral colony in the church tower? All of these are a potential source of reinfestation. After a week or two of miticide treatment your own colonies are likely to be largely free of phoretic mites … but all those nearby untreated (or yet to be treated, or ineffectively treated … or just plain forgotten) colonies can act as a source of mites and viruses from drifting workers and drones. These will infest and infect your colonies. Robbing bees – not the maelstrom of foragers ripping a colony apart that most beekeepers would recognise, but the silent robbing that can occur largely unseen and unsuspected in many apiaries – will bring a smorgasbord of virus-loaded mites and workers to your recently-treated hives. Remember also, your colonies may well be robbing other untreated, mite-infested colonies nearby. If all colonies ‘within range’ (see below) were treated at the same time these bee behaviours (drifting, robbing) that cannot be altered would have far less impact in transferring mites and viruses.
Coordinated Varroa treatment – over a wide geographic area – hasn’t been widely investigated in the UK. In Europe there have been a number of coordinated treatment trials, for example in isolated mountain valleys, where the geography provides a barrier to bee movement. Due to the unregulated and often undocumented nature of beekeeping in the UK it may well be more difficult to organise effectively. However, this isn’t a reason coordinated Varroa treatment shouldn’t be attempted. There are precedents in the salmon farming industry where all cages within a single water catchment area must be coordinately treated – both in terms of time and (I believe) the compound(s) used for controlling sea lice. This isn’t voluntary because it’s been shown to be effective.
What’s ‘within range‘?
One mile radius …
Drifting of foragers and robbing etc. are distance-dependent activities. The more widely separated colonies are, the less likely they are to be an issue. This was amply demonstrated in the recent comments by Tom Seeley that feral colonies hived and co-located in apiaries succumbed to mite-transmitted virus infections, whereas those sited – individually – at least 30 metres apart had lower mite counts and survived better (Sharashkin, L , ABJ 156:157). So perhaps all colonies within 30 metres should be treated together?
Clearly this is too low a limit. Firstly, we know bees can travel much further and the studies described by Seeley didn’t test whether colonies survived even better if spaced even further apart. Secondly, the feral colonies Seeley studies are naturally located approximately half a mile apart from each other. Whilst this is undoubtedly influenced by the availability of hollow trees it suggests that the range could usefully be extended to at least half a mile. I’ve certainly seen robbing occurring between colonies located at least 500 metres apart.
Since the effective limit over which re-infestation might occur isn’t known it perhaps make sense to throw the net a little more widely … a mile for example? This is a convenient distance … covering most beekeepers within a small village in a rural area, those sharing adjacent fields in farmland or perhaps a number of urban apiaries. It’s also a manageably small area, where personal contact and friendly agreement should be sufficient to coordinate treatment. Do you know the location of all of the colonies within a mile of your own? Google maps can help. So can local association membership, or simply accosting people you see wearing a beesuit. I knew of ~20 hives belonging to 4-5 beekeepers within a mile of my previous home apiary. Of course, with any sort of migratory beekeeping – bringing colonies back from the heather, taking them to orchards – or simply moving nucs from a split colony to a new apiary, there’s a possibility of colonies with low mite levels getting exposed to colonies with a high level of infestation. For proper coordinated treatment these movements would have to be taken account of.
In our bee virus research we’re investigating the benefits of large scale coordinated Varroa treatment by working with all the beekeepers on a large island, where the sea provides a natural barrier to mites entering the test area. Over the next three years we will see how mites, and more importantly the viruses they transmit, are controlled by coordinating Varroa treatment within this defined area.
Coordinated Varroa treatment helps mitigate the effects of drifting and robbing between colonies, activities that are usually underestimated and that are known to transmit mites and (inevitably) viruses and other pathogens. This isn’t rocket science. It’s a logical response to the biology of bees and the pathogens that they carry.
How to treat
Spot the difference …
Use a miticide that is appropriate for the conditions, use it according the manufacturers instructions and keep records of the treatment. There are no hard and fast rules, but it’s worth taking account of the following:
Avoid using pyrethroid-based miticides if there’s any evidence of resistance. Just because you get a high mite drop with Apistan doesn’t mean there isn’t an even larger resistant population left infesting your colony¹ … there are ways of checking this, perhaps you should?
Avoid using Apiguard unless the temperature really is high enough for it to work effectively, which means an average of 15°C for a month. If used at a sub-optimal temperature you’ll be leaving mites behind …
Avoid trickling oxalic acid/Api-Bioxal if there’s brood (sealed or unsealed) in the colony. It’s toxic to unsealed brood and the mites in sealed brood will escape unscathed …
Avoid vaporising Api-Bioxal unless you enjoy cleaning the gunky mess™ from the vaporiser. If vaporising oxalic acid ensure that the colony is broodless, or be prepared to repeat treatment three times at five day intervals to catch both phoretic and emerging mites …
Be aware that some miticides stop the queen from laying. Perhaps try and avoid these when you’re dependent on the colony raising the all-important winter bees that are going to get it through to the following Spring. I don’t actually know how much of an issue this is for colony health and survival, but it always concerned me when the queen went on a go-slow at the very time I wanted her to keep laying strongly through late August/early September.
Don’t reduce treatment doses or times … partial treatments are partially effective. This is also a great way to select for miticide-resistant Varroa (though whether they arise depends upon the mechanism of action – resistance to oxalic acid, formic acid and thymol has not been observed).
When to treat
Bee working ivy …
Earlier than you perhaps think to protect the winter bees from viruses. When I lived in the Midlands I would treat immediately after taking the summer honey crop – perhaps mid/late August. There’s later forage available – himalayan balsam and ivy – both of which some beekeepers either like or have a market for, but collecting it risks exposing the developing winter bees to high levels of Varroa and pathogenic viruses. Now I live in Scotland I’m going to have to develop alternative treatment schedules for colonies going to the heather – brood breaks and/or creative use of a vaporiser in June/July.
Treatment is only part of the solution though …
These articles on Varroa control have focused almost exclusively on miticide treatment. There are also a range of beekeeping practices that can contribute significantly to effective Varroa control, reducing the necessity to treat with chemicals. These include enforced brood breaks, shook swarms, drone brood uncapping, queen trapping and others. A proper integrated pest management strategy involves both chemical and beekeeping interventions to prevent the build up of dangerously high mite levels in the colony. Some of these will be covered in more detail during the coming season.
¹I think there’d be a case to ban the sale and use of Apistan for three years out of every four … pyrethroid resistance in mites appears to be detrimental in the absence of selection i.e. resistance is lost if the miticide is not used for a few years. That way, when used it would be devastatingly effective. This compares to the current situation where Apistan resistance is very widespread, and constantly selected for by continuing use of pyrethroids. Of course, there’s no way to enforce this – despite the fact it would probably be a great benefit for bee health – but now we’re back to the unregulated and undocumented nature of UK beekeeping.
When and how do you treat colonies to have the greatest effect in minimising Varroa levels? At the end of this longer than usual post I hope you’ll appreciate that this is a different – and much less important – question than “When is the best time to treat?”.
You probably use one of the treatments licensed and approved by the Veterinary Medicines Directorate (VMD), which include Apistan, Apivar, Apiguard, MAQS and Api-Bioxal. I’ve discussed the cost-effectiveness of these treatments recently. If used correctly, all exhibit much the same efficacy, reducing phoretic mite levels by 90-95% under optimal conditions. That being the case the choice between them can be made on other criteria … the ease of administration, the cost/treatment, the likelihood of tainting the honey crop, the compatibility with brood rearing, whether they mess up your vaporiseretc. After using Apiguard for several years, with oxalic acid (OA) dribbled in midwinter, my current preference – used throughout the 2015 season – is OA sublimation or vaporisation. This change was based on four things – efficiency, cost, ease of administration and how well it is tolerated by a laying queen. The how? you treat is actually reasonably straightforward.
When, not how, is the question
OK, but what about when? Because, if the treatments are all much of a muchness if used correctly, the when is actually the more important consideration. When might be partly dictated by the treatment per se. For example, Apiguard needs an active colony to transfer the thymol throughout the hive so the recommendation is to use it when the ambient temperature is at least 15ºC (PDF guidance from Vita). It’s worth stressing that this is the ambient temperature, not the temperature in the colony, which in places will be mid-30’s even when it’s much colder outside. At low ambient temperatures the colony becomes less active, and in due course clusters, meaning that Apiguard is not spread well throughout the colony, and is therefore much less effective. If you’re going to use Apiguard you must not leave treatment too late.
For readers in Scotland it’s interesting to note that the SBA annual survey by Peterson and Gray shows significant numbers still use Apiguard in September and October, months in which the mean daily maximum temperature is ~14°C and 11°C respectively … so the average daily temperature will be well below the recommended temperature for effective Apiguard use.
However, the when should be primarily informed by the why you’re treating in the first place. It’s not really Varroa that’s the problem for bees, it’s the viruses that the mite transfers between bees when it feeds on developing pupae that cause all the problems. Most important of these is probably Deformed Wing Virus (DWV), but there are a handful of other viruses pathogenic to bees that are also transmitted. DWV causes the symptoms shown in the image above … these bees are doomed and will be ejected from the hive promptly. However, although apparently healthy (asymptomatic) bees have low levels of DWV, it’s been shown by Swiss researchers that DWV reduces the lifespan of worker bees, and that high levels of DWV in a colony are directly associated with – and causative of – overwintering colony losses. Therefore, the purpose of late summer/early autumn treatment is to reduce the Varroa levels sufficiently so that high levels of the virulent strains of DWV are not transmitted to the overwintering bees.When? therefore has to be early enough that this population, critical for overwinter survival, will live through to the spring – however long the winter lasts and however severe it is. However, before discussing when winter bees are reared it’s worth considering what happens if treatment is used early or late.
What happens if you treat early?
Mid June treatment …
For example, mid-season or after the first honey crop comes off. Nothing much … other than slaughtering many of the phoretic mites. This is what most beekeepers would call “a result” 😉 Aside from possible undesirable side effects of treatment – like tainting honey, or preventing the queen from laying or even, with some treatments, queen losses – early treatment simply reduces mite levels. It’s important to remember that the levels may well not be reduced sufficiently to negate the need for a treatment later in the season … as long as there is brood being raised the mites will be reproducing (for example, look at the mid-June treatment generated using BEEHAVE modelling – image above). Furthermore, avoiding those undesirable side effects might require some ‘creative’ beekeeping (for example, clearing the supers and moving them to another hive) and will certainly inform the choice of treatment but, fundamentally, if the mite levels are high then treating earlier than is usual will benefit the colony, at least temporarily. If the mite levels – estimated from the disappointingly inaccurate mite drop perhaps – are dangerously high you should treat the colony.
What happens if you treat late in the season?
Isolation starvation …
In midsummer workers only live for ~40 days. If mite levels are high, virus transmitted to these workers will shorten their lives, so reducing the colonies’ foraging ability and – possibly – ability to defend itself against wasps or robbing late in the season. However, if you delay treatment until very late the lifespan of bees raised at the end of the season – the overwintering bees – will be reduced with potentially more devastating consequences. The usual winter attrition rate of workers will be higher. The cluster size of the colony will shrink faster than a colony with low mite levels. At some point the colony will cross a threshold below which it becomes non-viable. The cluster is too small to move in cold periods to new stores, resulting in the beekeeper finding a pathetic little cluster of bees in a colony that’s succumbed to isolation starvation. A larger cluster, spread across a greater area and more frames, is much more likely to span an area of sealed stores and be able to exploit it.
When are winter bees reared?
In the Swiss study referred to above they looked at the longevity of winter bees. The title of the paper is “Dead or alive: deformed wing virus and Varroa destructor reduce the life span of winter honeybees”. We can use their data to infer when winter bees start to be reared in the colony and when mite treatments should therefore have been completed to protect these bees. Their studies were conducted in Bern, Switzerland, in 2007/08 where the average temperature in November/December that year was 3ºC. They first observed measurable differences in winter bee longevity (between colonies that subsequently succumbed or survived) in mid-November. This was 50 days after bees emerged and were marked to allow their age to be determined. By the end of November these differences were more pronounced. Therefore, by mid-November Varroa and virus-exposed winter bees are already exhibiting a reduced lifespan. Subtracting 50 days from mid-November means these bees must have emerged in late September. Worker development takes ~21 days, so the eggs must have been laid in the first week of September, and the developing larvae capped in mid-September.
To protect this population of overwintering bees in these colonies, mite treatments would have had to be completed by the middle of September, so that mite levels were sufficiently low that the developing larvae weren’t capped in a cell with a Varroa mite carrying a potentially lethal payload of DWV. For Apiguard treatment (which takes 2 x 14 days) this means treatment should have been started in mid-August. For oxalic acid vaporisation (which empirical tests suggest is best conducted three times at five day intervals) treatment would need to start no later than early September and preferably earlier as it is effective for up to a month.
Of course, these figures and dates aren’t absolute – the weather during the study would have influenced when the larvae would be raised as winter bees, with the increased fat deposits and other characteristics that are needed to support the colony survival through the winter. Despite the study being based in Switzerland my calculations on dates are probably broadly relevant to the UK … for example, the temperature during their study period is only about 1ºC lower than the 100 year average for Nov/Dec in Eastern Scotland where I now live.
That was all a bit protracted but it hopefully explains why it’s important to be selective about when you administer Varroa treatments. Chucking in a couple of trays of Apiguard in mid-August or mid-October has very different outcomes:
in mid-August the phoretic mite population should be decimated, reducing the transmission of virulent DWV to the all-important winter bees that are going to get the colony through the winter. This is a good thing.
in mid-October the mite population will be reduced (not decimated, as it’s probably too cool to effectively transfer the thymol around the hive – see above) but many of the winter bees will already have emerged, probably with elevated levels of DWV to which they will succumb in December or January. This is a bad thing.
Perhaps perversely, treating early enough to prevent the expected Varroa-mediated damage to developing winter bees is not be the best way to minimise mite numbers in the colony going into the winter. Using BEEHAVE I modelled the consequences of treating in the middle of each month between August and November¹. I used the default BEEHAVE setup as described previously. Figures plotted are the average of 3 simulations, each ‘primed’ with 20 mites at the start of the year.
Time of treatment and mite numbers
There’s a lot on this graph. To show colony development I plotted numbers of eggs, larvae and pupae (left axis) as dotted red, blue and black lines respectively. Mite numbers are shown in solid lines – treated with a generic miticide in mid-July (black), mid-August (blue), mid-September (brown), mid-October (cyan) and mid-November (green). In each case the miticide is considered to be 95% effective at killing phoretic mites. The gold arrowhead indicates the period during which winter bees are developing in the colony, based upon the data from Dainat.
Oxalic acid trickling
Treating at or before mid-August controls the late-summer build up of mites in the colony – look how the blue line changes direction. Mites that are not killed go on to reproduce in late September and early October, resulting in levels of ~200 at the year end. Remember that mites present in midwinter can, in the absence of sealed brood, be effectively controlled by trickling or vaporising oxalic acid (Api-Bioxal), and that this Christmas miticide application is particularly important if the autumn treatment has not been fully effective. In contrast, treating as late as October and November (cyan and green lines) exposes the developing winter bees to the highest mite levels that occur in the colony doing the year, and only then decimates the phoretic mite numbers, with those that remain being unable to reproduce effectively as the brood rearing period is almost over. Starting treatment in mid-September isn’t much different, in terms of exposing the winter bees to high mite levels, than starting later in the year.
So, within reason, treating earlier rather than later both reduces the maximum mite levels and helps protect the winter bees from virus exposure. Of course, treating as early as mid/late August may not be compatible with your main honey crop (particularly if you take hives to the heather) … but that’s another issue and one to be addressed in a future post.
STOP PRESS There is a very important follow-up article to this. Kick ’em when they’re down describes why it’s so important to treat during a broodless period in midwinter to minimise mite numbers at the start of the following year. Just treating in late summer is not sufficient … you’ll protect your winter bees, only for them to be targeted by mites the following Spring.
¹BEEHAVE makes a distinction between ‘infected’ and ‘uninfected’ Varroa, the proportions of which can be modified. This might (no pun intended) not accurately reflect the reality in the hive, where Varroa-mediated transmission of DWV results in the preferential amplification of virulent strains of the virus. I need to roll my sleeves up and delve into the code to see if the model can be altered to fully reflect our current understanding of the biology of the virus. This might take quite a while …
My recent comments on the cost of Api-Bioxal prompted me to look in a little more detail at the cost of miticides routinely available to beekeepers. The figures quoted below are the best prices listed by one of three leading beekeeping suppliers in the UK (E.M. Thorne, Maisemore’s and C. Wynne Jones – there are lots of other suppliers, but I’ve used these three and been satisfied with their service). I made the following assumptions: the beekeeper is purchasing sufficient to treat three single-brooded full colonies for three years (i.e. something with a reasonable shelf-life) with as little left over as possible. Costs per colony treatment were calculated for 9 colonies (3 x 3 years) only … any ‘spare’ can therefore be considered as free. This means that for Apiguard, available in packs of ten trays (5 colony treatments) or a 3kg tub (30 colonies), the cost is calculated per colony from two packs of 10 trays as a full course of treatment for one colony requires two trays. Obviously, buying in bulk – for example through a co-operative purchasing scheme in your beekeeping association – should reduce these costs significantly. No postage costs were included.
Apiguard – two boxes of 10 trays (C. Wynne Jones) = £41 = £4.55/colony
Apistan – two packs of 10 strips (C. Wynne Jones) = £41 = £4.55/colony
MAQS – one 10 dose tub (all suppliers) = £57.60 = £6.40/colony
Oxalic acid (OA) crystals – one 300g tub (Maisemore’s) = £4.32 = £0.48/colony
Note that this simplistic comparison hides a number details.
These various treatments should be broadly similar in their efficacy (see below) in reducing the mite population, but must be used according to the manufacturers instructions for maximum efficiency. Under optimal conditions all quote at least 90% reduction in mite levels. However, Apistan (and Bayvarol, not listed) is pyrethroid-based and resistant mite populations are very widespread. In the presence of totally or partially resistant mites, Apistan will be of little or no benefit. Interestingly, Apistan resistance (which, like resistance to pyrethroids in other species, is due to a single amino acid substitution, so readily selected) appears to be detrimental to the mite in the absence of selection. This means that it may be possible to use Apistan effectively every 3-5 years as part of an integrated pest management as long as other beekeepers in the area follow the same regime. During the years Apistan is not used the pyrethroid-resistant mites should reduce in number, so restoring the efficacy of the treatment. I’m not aware that this idea has been properly tested, but it might be worth investigating.
Only the first four treatments are approved for use in the UK by the VMD.
Both the oxalic acid-containing treatments – Api-Bioxal and OA crystals – require preparation before use, or specialised equipment for delivery. OA vaporisation (sublimation) also necessitates both care and personal protection equipment to prevent exposure to the chemical which is a lung irritant. The costs indicated do not include these additional requirements.
The treatments are not equivalent or necessarily interchangeable. For example, a) only MAQS should be used when honey supers are present, b) Apiguard is moved around the hive by active bees, so treatment is recommended when average daytime temperatures are above 15ºC , and c) there are reports on discussion forums of repeated OA vaporisation treatment – 3 at 5 day intervals – for colonies with brood present. The costs indicated above assume a single treatment (in midwinter or of a swarm/shook swarm in the case of OA) with any of the listed compounds.
Finally, the ‘excess’ amount spare after treating the colonies over three years differs significantly. The first four have sufficient left over for one further treatment. The OA crystals will have enough left over for a further 190 colonies … and buying a 300g tub is probably about the most expensive way to purchase OA per gram 🙂
Bang for your buck
As indicated above, all of the Varroa treatments listed should give 90+% knockdown in mite numbers if used properly. This means following the manufacturers’ instructions – in terms of dose, time and duration of application. A key point to remember is that the mite is only susceptible when outside the capped cell and that 80% or more of the Varroa in a colony at any one time will be inside capped cells if there is brood present. For this reason, it is preferable to treat during natural (or induced e.g. a shook swarm) broodless periods. It has even been suggested that the midwinter OA treatment should be preceded by destruction of any brood present. Although this makes sense, I can understand why some beekeepers might be reluctant to open a colony to destroy brood in the middle of winter. There have been numerous reviews of individual and comparative efficacy of the various Varroa treatments – for example this well-referenced article on mite treatment in New Zealand from 2008. If used properly there’s little to choose between them in terms of efficacy, so the choice should be made on the grounds of suitability, convenience and cost.
‘Suitability’ is a bit of a catch-all, but requires you broadly understand how and when the treatment works – for example, Apistan is a pyrethroid so works well against sensitive mites, but is pretty-much useless against resistant populations, and resistance is widespread in the UK. ‘Convenience’ is generally high in the ready-prepared commercial treatments – it takes seconds to insert a tray of Apiguard – and much lower if the compound has to be prepared or you have to get dolled up in protective gear. In this regard, the absence of a pre-mixed liquid version of Api-Bioxal is a disappointment. Thorne’s still supply (at the time of writing) Trickle 2, a very convenient pre-mixed 3.2% w/v OA treatment for mid-winter trickling, but for how much longer? Similarly, the gloves, mask, goggles and power needed to treat a colony by OA sublimation makes it far from convenient for a single treatment.
Closing thought …
1 lb jar of honey …
Despite the great differences between the cost/treatment/colony it’s worth noting that even the most expensive is not a lot more than the price of a 1 lb jar of top quality local honey … just like the stuff your bees produce 😉 So, in the overall scheme of things, Varroa treatment is relatively inexpensive and very important to maintain colony health and to reduce overwintering colony losses.
See also Managing Varroa (PDF) published by the Animal and Plant Health Agency
The short days of late December and early January are a time for working in the shed, drinking copious mugs of scalding tea and preparing for the coming season. I haven’t done a full colony inspection since late August and don’t expect to start until late March or early April (usually about when the ornamental current, RIbes, is in full flower). Other than feeding fondant in the autumn and ensuring the hives are weathertight and woodpecker-proof there’s little to do.
I almost always treat colonies with oxalic acid in midwinter, irrespective of whether the colony was treated with Apiguard in the autumn. I did this a week or so ago during a period of cold, settled weather. The weather was ideal, 3ºC with no wind. Together this ensures that the bees are clustered tightly and are discouraged from flying. I prepare 3.2% oxalic acid solution in 1:1 w/v syrup (for a dozen or so colonies 500g sugar, 500ml water and 37.5g oxalic acid dihydrate should be ample), warmed to about 30ºC and transported in a well-labelled Thermos flask. I use a Trickle 2 dispenser from Thorne’s to deliver 5ml per seam of bees. The colony must be opened gently and there’s usually no need to use smoke. I always wear a beesuit for protection just incase they’re more lively than expected. However, the low temperature usually means they are both clustered tightly and less likely to fly – both make the task of application easier. The entire process takes under a minute per colony and hardly disturbs the bees, as shown in this video I prepared last year for a talk on Varroa.
There is an additional video showing treatment of a larger colony and use of the Trickle 2 dispenser. While the crownboard is off I scan the tops of the visible comb for remaining sealed stores. I carefully close the colony up and insert a Varroa tray to monitor mite drop over the following few days.
Of the colonies treated this year, all but one had a mite drop of <30 in the first 24 hours. This included a couple of nucs that were not treated with Apiguard. The mites continue to drop over the next 2-4 weeks and I usually monitor for a maximum of about 5 days, by which time the daily drop should be tailing off significantly. The number that drop is related to the number in the colony accessible to treatment … in turn this must be due to the number present in the colony after the autumn Apiguard treatment, the amount of brood rearing that has gone on subsequently and the amount of sealed brood present at the time OA was added. I therefore keep the mite drop records and look carefully at colonies with high winter levels during the spring build up. These may be candidates for a shook swarm – to give a brood break – in due course.
Routine winter checks
I only infrequently check my colonies over the winter. I ensure the entrances of the hives with Kewl floors are clear using a bent piece of wire (I lost a double brood colony a few years ago after the entrance got blocked with corpses during a very long cold spell). I sometimes check the movement of the cluster by peering through the Perspex crownboard. Finally, I “heft” the colony to check there are sufficient stores present. This is a rather inexact process – particularly with a mix of equipment and colonies on single brood or brood and a half – and so I’ve started weighing colonies using a set of digital luggage scales. There are 6mm holes each side of the floor into which a bolt – attached to the scales – can be pushed (see pictures) allowing the colony to be gently lifted, one side at a time, recording the sum of the weights. This is largely to record the rate they are using stores, rather than identify dangerously light colonies. Stores usage should increase once they start rearing new brood early in the season.
All of these checks take only a few minutes per apiary, meaning I can get back to the warmth of shed for more tinkering (and another cup of tea) for the season ahead.
Deformed wing virus (DWV) is probably the most important viral pathogen of honeybees. In the presence of Varroa the virus is amplified to very high levels in the colony, resulting in newly emerged workers – those that survive long enough to emerge – exhibiting the classic symptoms familiar to most beekeepers. These include deformed or atrophied wings, a stunted abdomen, additional deformities or paralysis of appendages and (not visible) learning impairment. There is a clear association between high Varroa levels, high levels of DWV symptomatic bees and overwintering colony losses.
Classic DWV symptoms
These images are of workers from a colony treated for a month with Apiguard to reduce mite numbers. Many bees remained with symptoms. I suspect the high levels of mites pre-treatment resulted in the amplification of virulent strains of DWV which continued to cause disease even after the mite numbers were reduced. This emphasises the need to monitor mite numbers and treat appropriately with Apiguard, oxalic acid or – during the season – other appropriate integrated pest management practices such as drone brood culling.
A guaranteed way of reducing winter losses is to only overwinter colonies that are strong and healthy. Although colony losses can occur for several reasons (e.g. starvation) researchers in Switzerland have shown that high levels of the parasitic mite Varroa and deformed wing virus (DWV), which the mite transmits, are the primary cause of overwintering colony losses. It is therefore important to minimise mite numbers in the colony in early autumn, preferably by treating with a miticide early enough for the queen to have time to lay up more frames before the weather gets too cold. Many mite treatments (e.g. Apiguard and MAQS) stop queens laying.
High levels of DWV …
I completed Apiguard treatment of my colonies by mid-September but noticed that one still contained lots of bees showing the characteristic symptoms of DWV infection – atrophied wing development, stunted abdomens and a generally dark coloration. In the photograph (right) there are at least 5 bees visible with these symptoms, one of which also has a phoretic mite attached (lower right hand corner). This colony had failed to build up after a mid-season setback. It was only taking limited amounts of fondant down and the flying bees were bringing back only small amounts of pollen (in marked contrast to neighbouring colonies that – now the Apiguard is off – are piling in huge amounts of pollen for the winter). There were also signs of sacbrood virus which often requires re-queening to eradicate. The queen was still laying, but there was only a frame and a half of sealed brood.
At this stage in the season there is no real chance this colony could build up sufficiently to overwinter successfully. It’s not simply dependent upon the size of the colony, it’s also the vigour. After all, it’s reasonably straightforward to overwinter Apidea or Kieler mini-nucs with a bit of care. These have far fewer bees present than the colony photographed above.
Shake them out …
If the colony had been healthy, but small, I would have united it with another over newspaper. However, I wanted to minimise exposure of other colonies to the brood so instead removed the queen, moved the colony to another corner of the apiary and shook all the bees out. The healthy flying bees should be able to get accepted by another colony. The symptomatic bees would be lost. Although there was a risk that bees carrying phoretic mites would get back to other colonies I carefully checked the frames before shaking them out and saw almost no mites. In due course I’ll treat these remaining colonies with oxalic acid. I subsequently uncapped a frame or so of brood and found almost 50% of capped pupae were mite-associated.
Figures collected and published by the BBKA indicate that, on average in England, ~20% of colonies are lost each winter. In particularly hard winters, such as 2012/13, losses can be significantly higher than this, reaching over 50% in certain regions of the country.
Annual colony losses
Aside from ensuring adequate stores are present in late autumn, with hives in good condition to provide protection from the elements, the best way to minimise overwintering losses is to not try and overwinter weak or diseased colonies. Sometimes you have to be cruel to be kind …
In mid- to late-August the forage here is pretty-much finished, with the exception of himalayan balsam in some of the damper areas and along streams. In my main out-apiary stores are running really low in the hives now that the honey supers have been removed. During a recent check by the regional bee inspector (clean bill of health, other than a little chalkbrood) most colonies appeared to have undergone a natural break in brood rearing, with little or no capped brood but clear signs that the queen was laying again. This is a good opportunity to start Apiguard treatment and winter feeding.
Preparing Apiguard …
I use Apiguard for autumn Varroa treatment, either the individual trays which are convenient and easy to handle, or the stuff bought in bulk and spread on bits of card. The 3kg tubs contain sufficient to treat 30 colonies – more than I have, but it has a reasonable shelf-life – and is much more economical. Through my association co-operative purchasing scheme an annual treatment with Apiguard trays costs £3.70/colony, whereas it’s only £2.50/colony a year for the stuff bought in tubs … a big enough saving to justify juggling with the messy spatula and scoop while ladling it out onto the cards.
The almost total absence of sealed brood in most of my colonies at the moment means that any mites present are likely to be phoretic, so they should be more susceptible to these thymol-based treatments. Apiguard treatment requires two successive two-week treatments and needs temperatures of over 15oC to work properly. Therefore, treat as early as possible … not only does this ensure the temperature will be higher but it also leaves more of the autumn for raising brood to overwinter. Many queens stop laying when the Apiguard is added, so the earlier it is finished the greater the chance that it will still be warm enough to rear those all-important ‘winter bees’ that will get the colony through to the following spring.
Small entrances and Apiguard
There are lots of wasps about at the moment so the entrances on my colonies are restricted to 1-2 cm wide … the kewl floors I use provide better protection against wasps, but a simple strip of 9 mm softwood gives even less area for the guards to defend (as an aside, I predicted those DPM ‘skirts’ would still be present at the end of the season back in April). Bees sometimes ‘beard’ outside the entrance of hives with Apiguard on in hot weather – the thymol vapour can get a bit overpowering and can be smelt downwind of the apiary. Being a bank holiday weekend the weather here isn’t warm enough to cause this bearding … the bees in the hive on the left are simply queueing to get in.