It’s cold and dark and all is quiet in the apiary. Hives appear somnolent. Colonies are clustered 1 and, other than the odd corpse or two on the landing board, I’ve not seen a bee for at least a fortnight.
The apiary in winter …
Based upon previous experience I suspect colonies are – or very soon will be – broodless. I usually reckon that the first extended (2-3 weeks) period of cold weather 2 in the winter is the most likely time for the colony to be broodless.
Early autumn treatment protects the winter bees but also leaves the long autumn for the residual mites to continue replicating.
And there will be residual mites. No treatment is 100% effective.
So, paradoxically, if you treated early enough in the autumn to really help protect the winter bees, your mite levels will be higher at the end of the year.
Which also means they’ll be higher at the beginning of next year.
Not a good start to the 2019 season 🙁
Convenience or laziness?
Many beekeepers, for convenience, laziness or historical precedent, choose to apply the winter OA treatment between Christmas and New Year. I suspect that this is often too late. If the queen starts laying again around the winter solstice there will be sealed brood – and therefore unreachable Varroa – by the end of the month.
I’d prefer to have a cold and damp afternoon in the apiary slaughtering Varroanow than the convenience of treating them less effectively during the Christmas holiday period.
The latter might be more convenient … the office will be closed, I’ll be replete with turkey and sprouts and it will be a good excuse to ‘escape’ visiting relatives and yet more mince pies 4.
But is it the best time for your bees?
We have the technology
We have a couple of hives with Arnia hive monitors fitted 5. These have a temperature probe inserted into the brood nest. Brood rearing temperature is around 34°C. Here is a trace of one colony over the last month.
Arnia hive monitor temperature
The colony temperature was pretty stable (around 33-35°C) until about the 19th of November and has dropped about 10°C since then. Although I’ve not opened the colony I think that this is additional evidence that the colony is broodless 6.
Beekeeping by numbers
Keeping bees properly involves being aware of the seasons, the available forage and the state of the colony. This varies from month to month and year to year 7.
You can’t mechanically (‘by the numbers’) add supers on the 5th of May and harvest honey on the 15th of June. Sure, it might work some years, but is it the best time to do it?
Similarly, you can’t optimally treat a colony for Varroa on the 30th of December unless the climatic conditions and state of the colony coincide to make that the best time to treat.
It might be, but I suspect that generally it’s a bit late if there is a brood break.
If you’re going to the trouble of preparing the OA treatment, donning the beesuit and disturbing the colony you might as well do it at the right time for the bees.
I’ll be treating in between the predicted sleet showers and sunny periods this weekend.
Time to treat
Isn’t evolution a wonderful thing? This post started with a working title of “Know your enemy” and was on a different topic altogether. I’ll save that for next week.
The above was written at the beginning of the week. Now the weekend is closer it’s clear the weather is going to be cold with heavy snow predicted. Unless the forecast is wrong (and how often does that happen?!) I’ll hold off treating until a) it’s over 5°C, and b) the roads are safe.
Until recently they were only available with a veterinary prescription. I expect – though I have not yet seen data to support this – that their usage in the UK will increase now they are off-prescription. These miticides are now widely available and so there is greater opportunity to use – and misuse – them.
If you’re using Apivar 1 for the first time this year you will soon have to remove the strips from the hive.
That’s assuming you started treating early enough to protect the all-important winter bees from Varroa and its deadly viral payload.
This post is a reminder to remove the strips at the right time. The alternative – leaving them in place until the first Spring inspections – risks help the development of resistance to amitraz, so further reducing our opportunity to control mites effectively.
Leave and let die
Without careful integrated pest management (IPM) 2Varroa levels build up in the hive. Varroa transmits viruses – most important of which is deformed wing virus (DWV) – to developing pupae. High levels of DWV either kills the pupa or results in emergence with or without significant developmental defects. Even those bees that are apparently normally developed have a reduced lifespan 3.
Winter bees with a reduced lifespan prevent the colony from surviving through the winter until the queen starts laying again. I’ve also proposed recently that high levels of DWV, and the resulting increased rate of winter bee die-offs, probably accounts for some cases of isolation starvation.
So … intervention is needed to reduce mite levels, protect your bees and save your colonies.
Follow the instructions!
Apivar is one solution to reduce mite levels. It is an easy-to-apply chemical treatment that is very effective in reducing the Varroa load by ~95%. For a National hive it is applied as two polymer strips, each containing 500mg of slow-release Amitraz. Strips are hung between brood frames for 6-10 weeks and – for maximum efficacy – should be scratched with a hive tool and repositioned half way through the treatment period.
Unlike some other miticides (e.g. Apiguard and MAQS) there are no temperature restrictions for Apivar usage. The colony does not need to be broodless (a requirement for trickled oxalic acid-based treatments) as the treatment period covers multiple brood cycles.
Other than not using it with supers present the only contraindication for Apivar is to not use it if Amitraz-resistant mites are present.
How does resistance develop?
When discussing parasites and pathogens, resistance4 is a consequence of two things:
A selective pressure that kills the pathogen
A population which exhibits genetic diversity
The selective pressure could be anything … heat for example, antibiotics prescribed by your GP, an antiviral against HIV or – of relevance here – Apivar against Varroa.
Killing – at the population level – is not absolute. Some individuals within the population survive longer than others. They could be exposed to a slightly lower dose, or be located in a protected niche for example. However, treat for long enough and the majority will be killed.
But there’s more …
Pathogen populations are not genetically invariant. Actually, many are quite diverse and have replication cycles that – deliberately 5 – generate diversity.
Therefore some pathogens are genetically slightly less resistant and some are genetically slightly more resistant to a selective pressure. We can ignore the former as they’ll rapidly be killed off … but we must be concerned about the more resistant ones.
Keep taking the pills
All of this is a ‘numbers game’, better represented with graphs and equations. However, the take-home message is simple … to effectively control a pathogen you need to treat for long enough and with a high enough dose to kill the vast majority of the population.
That’s why you’re encouraged to “complete the course” of antibiotics … or to remove the Apivar strips after 10 weeks and not leave them in over the winter.
Because both courses of action result in selection of more resistant pathogens.
If you stop taking antibiotics too soon, you won’t have treated for long enough and with a high enough dose. You end up selecting for the more genetically resistant pathogens.
Similarly, if you leave Apivar strips in overwinter you’ll be “treating” the remaining mites 6 with a lower dose of the miticide, which is an ideal situation to favour the growth of the slightly more genetically resistant mites.
How does Amitraz resistance develop?
Resistance to Amitraz in Varroa is well documented. It’s been described in a number of countries including the USA and Europe, Mexico and Argentina 7. Generally resistance is defined in terms of a reduced level of mite killing, or – in laboratory experiments – an increased dose required to kill a certain proportion of mites.
However, I’m unaware of any studies defining the genetic basis of Amitraz resistance in Varroa.
But Amitraz is a widely-used acaricide 8 and the genetic basis of resistance in cattle ticks is well understood. In these, ticks resistant to Amitraz carry a mutation in the RMβAOR gene 9.
This gene encodes the β-adrenergic octopamine receptor protein and readers with good memories will recall that this is one of the targets that Amitraz binds to and inactivates 11.
If the protein carries a mutation the Amitraz cannot bind to it and so the mite – or more correctly the tick as it’s yet to be formally demonstrated in mites – is therefore resistant.
(Bad) practical beekeeping
What does all this mean in terms of practical beekeeping?
It means use the correct number of Apivar strips for the colony and leave them in for the right length of time.
Do not …
Use one strip on a full colony mid-season to ‘knock back the mites a bit’
Re-use the strips in another colony (yes really!)
Use improperly stored strips (or out of date strips) in which the effective Amitraz dose is reduced
I’ve heard examples of these types of misusethis season. All increase the chance of selecting for Amitraz-resitant mites.
And (the real reason for posting this at this time of year) …
Do not leave the strips you added in late summer in the colony throughout the winter
Removing the strips takes seconds. Prize off the crownboard, grab the tab projecting above the top bars, gently withdraw the strip and close the hive up again.
Finally, because of the incestuous lifestyle 12 of Varroa the genetic diversity (and therefore potential presence of more resistant mites) in the population is likely to be increased by the high mite levels that prevail late in the season.
All the more reason to use the effective treatments we currently have in a way that helps ensure they remain effective.
Resistance is futile
Resistance is futile is the title of a 2018 album by the Welsh rock band the Manic Street Preachers.
More specifically, in the context of this post, it was the phrase routinely used by the Borg – the alien cyborgs sharing a collective mind – in the Star Trek franchise. Borgs rarely speak, but when they do they usually include this phrase. For example “We are the Borg. Lower your shields and surrender your ships. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service us. Resistance is futile.” The warning about resistance being futile was usually accompanied by the threat that the target would be “assimilated”.
I’d started writing this post using the title ‘Resistance is futile’ but realised late on that – as far as Varroa are concerned – resistance isanything but futile13.
Resistance – to miticides – gives Varroa a reason to live. Literally.
This week I want to explore the relationship between colony strength, health – specifically with regard to Varroa and deformed wing virus (DWV) – and isolation starvation.
Isolation starvation describes the phenomenon where a small colony of tightly clustered honey bees gets isolated from the honey stores laid down in autumn, resulting – typically during protracted cold periods – in the colony starving to death.
Isolation starvation …
It’s both a pathetic and distressing sight. Bees, with their heads crammed into the bottom of cells searching for food, dying from starvation when literally inches away from capped stores.
Deaths and births
In temperate climates the winter is characterised by low temperatures and little or no forage for the bees. The queen usually stops laying sometime in autumn and starts again around the turn of the year. During the intervening period she may lay intermittently, but generally in limited amounts.
The fat bodied winter bees that are reared in late summer and early autumn are long-lived (about 6 months) and are responsible for getting the colony through the winter. They protect the queen, thermoregulate the hive and they help rear the brood raised in the autumn and through the winter.
In their absence – or if there are just too few of them – the colony will perish.
Winter bees do not all live for 6 months. The usual figure quoted is ~175 days 2. Some live shorter lives, some longer … up to 9 months under certain conditions.
Importantly, in studies I’ve discussed at length previously, high levels of DWV reduces the lifespan of winter bees. We know this because, in Varroa-infested colonies, researchers 3 have shown that the winter bees die off faster 4.
Live fast, die young
Winter bees with high levels of DWV don’t really live fast … but they do die young. In the studies above the average lifespan of winter bees was reduced by 20% in the colonies that died overwinter.
There are a couple of important things to note here. Dainat and colleagues were not looking at bees in the presence or absence of Varroa, or in the presence or absence of high or low levels of DWV. They simply looked at hives that succumbed in the winter or that survived, then measured DWV and Varroa levels. It’s a subtle but important difference. Their surviving colonies still had Varroa and DWV.
From analysis of hives that died or survived, and having marked known numbers of bees in late summer, they could determine the life expectancy of workers – in their surviving colonies it was ~88 days, in those that died it was ~71 days.
The gradual death of bees through the winter coupled with the reduced lifespan of winter bees with high levels of DWV explains why colonies need to be strong and healthy.
The following graphs are based upon modelled data 5, but show the influence of colony size and winter bee lifespan.
The first graph – the least important – simply shows the lifespan of bees. The graph plots the number of bees (on the vertical axis) in a population that die at a particular time (on the horizontal axis) after the start of the experiment. The blue bees have a longer average lifespan than the red bees 6.
Lifespan of winter bees
In the following graphs remember that the blue bees are healthy, with low levels of Varroa and – consequently – low levels of DWV. The red bees are unhealthy and have high levels of Varroa and DWV.
Using this lifespan data we can look at the influence on the total number of winter bees in a colony (on the vertical axis) over time (horizontal). Imagine that the horizontal axis is the long, dark, wet and cold months of winter. Starting in early September and running through until late March.
Winter bee numbers in healthy (blue) and unhealthy (red) colonies
It is clear, and of course entirely predictable, that the numbers of bees in the healthy (blue) colony are higher than those in the unhealthy colony at each time point. If the average lifespan is reduced (by disease) more bees will have died by a particular time point when compared with a healthy colony at the same timepoint.
Finally, consider that the shaded section of the graph represents the lower limit of bee numbers for viability. If the number of bees in the colony drops into this region the colony will perish.
Simplistically – and in reality – starting with similar numbers of bees a healthy colony will survive longer than an unhealthy colony.
Using a similar approach we can also look at the influence of the average lifespan of winter bees on the survival of strong or weak colonies.
The following graph shows the numbers of bees in the colony over time for a strong colony (solid line) and a weak colony (dashed line) where worker bee lifespan is identical7.
Winter bee numbers in large (strong) and small (weak) colonies with the same average lifespan.
The shaded section of the graph again represents colony oblivion.
Large (strong) colonies take longer to drop below the threshold for viability and so – all other things being equal – will survive longer 8.
A strong colony with high levels of Varroa and DWV might actually survive less well than a weak but healthy colony.
Large unhealthy colonies might survive less well than small healthy colonies.
In this graph the weak but healthy colony drops below the ‘viability threshold’ after the strong but unhealthy colony 9.
Winter bees and brood rearing
This is modelled data, but it makes the point clearly. Large and/or healthy colonies retain more of the all-important winter bees and so survive longer.
The differences might not appear marked. However, for convenience 10 I’ve omitted the influence of winter bee numbers on the ability of the colony to rear brood.
If there are more winter bees, the colony is able to thermoregulate the hive better. It’s therefore able to keep any brood present warm. It’s therefore able to rear more brood.
As a consequence, the differences in bee numbers between the large or small, or the healthy and unhealthy, colonies will be much more striking.
Critically 11 the strength of the colony coming out of the winter is often the rate-limiting determinant for spring build-up to exploit early season nectar flows. Weak colonies develop less well.
Finally, returning to that pathetic little cluster of starving bees in the image at the top of the page. What is the relationship between colony health, strength and isolation starvation?
It’s now time to dust off my weak-to-non-existent Powerpoint skills …
Isolation starvation schematic
Again, it’s straightforward. A large (strong) overwintering colony (A above) only has to move a short distance to access stores in midwinter. In contrast, a small (weak) overwintering colony has to move much further.
Consequently, small colonies become isolated from their stores during long, cold periods when the colony is clustered.
Many beekeepers will be familiar with isolation starvation of overwintering colonies.
Most would explain this in terms of “very cold weather and the cluster was unable to reach its stores”.
Some would explain this in terms of “the colony was far too small to reach the stores when clustered”.
Very few would explain this in terms of “the Varroa and DWV levels were too high because of poor disease management last autumn. Inevitably most of my winter bees died off early in the winter, leaving a very small cluster of bees that were unable to reach the stores.“.
I suspect the real cause of isolation starvation is probably disease … specifically poor management of Varroa levels and consequently high levels of DWV in the colony.
Another post, another poor pun in the title. Survival of the fittest encapsulates the Darwinian evolutionary principle that the form of an organism that survives is the one able to leave the most copies of itself in future generations. Darwin didn’t actually use the term until the 5th edition (1869) of his book On the origin of the species. Instead, the phrase was first used by Herbert Spencer in 1864 after reading Darwin’s book. Whilst ‘survival of the fittest’ suggests natural selection, Spencer was also a proponent of the inheritance of acquired characteristics, Lamarckism.
The range of miticides available ‘off the shelf‘ to UK beekeepers has recently been increased by the introduction of Apitraz and Apivar.
‘Off the shelf’ because, until recently, these were only available with a veterinary prescription.
Considering the extensive coverage on this site of oxalic acid-containing miticides and more recent posts about the – regularly ineffective – Apistan, it seemed fair and appropriate to write something on the active ingredient and mode of action of these new products.
Mites on drone pupae …
Conveniently, because the active ingredient is identical, these can be dealt with together in a single post. The similarities don’t end there. The amount of the active ingredient is the same and the way it is administered is very similar. They are different commercial products; Apitraz is distributed by Laboratorios Calier, SA and sold by BS Honeybees, Amitraz is distributed by Veto Pharma and sold by Thorne’s. The strips have a different appearance and a slightly different mechanism by which they are hung in the hive.
They even cost about the same – a single packet of 10 strips (sufficient to treat 5 hives) costs £30.50 and £31 respectively for Apitraz and Apivar.
The active ingredient in both Apitraz and Apivar is Amitraz.
Yes … I find these three names confusing similar as well 😉
Amitraz is a synthetic acaricide – a pesticide that kills mites and ticks. It was discovered and developed almost 50 years ago by the Boots Co. (the drug development predecessor of the Boots the Chemist 1 found in most high streets). Amitraz is the active ingredient in a range of medicines approved by the Veterinary Medicine Directorate, including Aludex and Certifect, both of which are used to treat mange in dogs.
For completeness I should add that Amitraz used to be used by US beekeepers and was sold as a generic pesticide under the name Taktic, though this was withdrawn in about 2014. I believe that Apivar is now available as a slow-release Amitraz-containing Varroa treatment in the US.
Mechanism of action
Amitraz has to be metabolised (essentially ‘modified’) before it is active. This modification occurs much less well in bees than in mites. In fact, the toxicity of Amitraz for bees has been determined to be about 7000 times less than in mites.
Once converted into an ‘active’ form the most important mechanism of action for Amitraz is through interaction with the alpha-adrenoreceptor and octopamine receptors of Varroa2.
OK, since you asked … octopamine receptors normally bind a neurotransmitter called – rather unimaginatively – octopamine. Quelle surprise as an apiculteur would say. It’s likely that occupancy of these receptors by Amitraz triggers a series of so-called downstream events that change the behaviour of Varroa. Similarly, amitraz also acts as an agonist 3 when binding to the alpha-adrenoreceptor which normally interacts with catecholamines. This results in neurotoxicity and preconvulsant effects.
That all sounds a bit vague. Essentially, amitraz binds and activates receptors that are critically important in a range of important aspects of the Varroa activity and behaviour. Remember here that the mite is entirely dependent upon proper interaction with the bee to complete the life cycle. For example, if the mite fails to enter a cell at the correct time or doesn’t hitch a ride on a passing nurse bee for a few days, it will likely perish.
Amitraz changes behaviour and so exhibits miticidal activity. It has additional activities as well … these multiple routes of action may explain why resistance to amitraz is slow to develop. More on this later.
Usage of Apitraz and Apivar
Both Apitraz and Apivar are formulated as plastic strips impregnated with amitraz. The bees must come into contact with the strips to transmit the amitraz around the hive. Two strips are therefore placed between frames approximately one-third of the way in from each side of the brood box – typically between frames 4 & 5 and 7 & 8 of an 11 frame box. This assumes the bees occupy the entire box. If they don’t, arrange the strips in the appropriate part of the box with 2 frames separating them. Both types of amitraz-containing strips have a means of securing them hanging between the frames.
The recommended treatment period is 6 (Apitraz, or Apivar with little/brood present) to 10 weeks (Apivar with brood present). As with Apistan, treatment should not be applied during a honey flow or when honey supers are present. Further details are included on the comprehensive instructions provided with both products. There’s also a reasonable amount of information on this New Zealand website for Apivar.
This is the good bit … very, very effective. When used properly, amitraz-containing miticides can kill up to 99% of the Varroa in a colony.
Toxicity and wax residues
The good news first. Amitraz does not accumulate in wax to any significant extent. It is not wax-soluble. This is in contrast to Apistan which is found as a contaminant in most commercially-available beeswax foundation.
And now the bad news. Beekeepers also have alpha-adrenoreceptors and octopamine receptors. So do dogs and fish and bees. Although amitraz has increased specificity for the receptors in mites and ticks, it can also interact with the receptors in other organisms. Consequently, amitraz can be toxic. In fact, if you ingest enough it can be very toxic. Symptoms of amitraz intoxication include CNS depression, respiratory failure, miosis, hypothermia, hyperglycemia, loss of consciousness, vomiting and bradycardia.
And it can kill you.
Admittedly, the doses required to achieve this are large, but it’s worth being aware of what you’re dealing with. Amitraz-containing strips should be used only as described in the instructions for use, handled with gloves and discarded responsibly after use.
Multiple modes of action makes it much more difficult for resistance to evolve. But it can and does. Resistance to amitraz is well-documented and is understood at the molecular level. However, this is in cattle ticks, not Varroa.
At least, not yet, though there are numerous anecdotal reports of Varroa resistance.
I’ll deal with resistance in a separate post. It’s an important subject and avoiding it is a priority if amitraz-containing compounds are going to remain effective for Varroa control.
When you purchase a couple of packets of Apivar – enough for 10 colonies – it might feel expensive 5. However, it’s worth remembering that this is still less than the likely ‘profit’ on a couple of jars of your fabulous local honey per colony per year, which seems pretty reasonable in the overall scheme of things.
And, if you look after your colonies well, you are maximising the potential yield of honey in the future … so you’ll be able to afford it 😉
Not Whether to treat? … to which the answer is yes. Instead, a poor pun on the choice of how I use temperature as an indication of when to treat colonies in midwinter …
Midwinter OA-based treatments
Oxalic acid-based treatments for midwinter Varroa control are most effective when colonies are broodless†. This is because oxalic acid (OA) treatments only kill phoretic mites and are ineffective against mites in sealed cells. They are therefore ideal for use on swarms, packages and broodless colonies in midwinter.
How can you tell whether your colonies are broodless in midwinter?
On a warm, sunny, Spring afternoon this takes just a couple of minutes … remove the roof, crack off the crownboard, gently lift out the dummy board and the adjacent frame, look carefully at the mass of bees covering the top bars, aim for about the middle and gently prise apart those two frames, lift out a frame from one side of the ‘gap’ and – Hey presto – brood.
Just writing that in early December makes me hanker for much warmer days …
Memories of midseason
Actually, you can do exactly the same in midwinter. There are videos on the internet showing an experienced and (in)famous Finnish beekeeper opening his colonies at -10ºC.
I’ve opened and briefly inspected colonies at low temperatures (though not sub-zero). The bees are usually pretty torpid, reluctant to fly – or simply too cold to – and you can be in and out in just a minute or so. Bees cope pretty well with this. It undoubtedly disturbs them a bit and it breaks the propolis seal on the crownboard, but – done carefully and quickly – it’s the only foolproof way to determine whether a colony is broodless in midwinter.
But what if they’ve got brood and it’s therefore not the optimal time to treat? Do you go back and repeat the entire process in 1-2 weeks? What if it’s snowing next time, or there’s a howling gale blowing?
An alternative approach is needed∞.
The annual brood rearing cycle
As the colony moves from summer to autumn the egg laying rate of the queen drops. It goes on dropping, although not necessarily smoothly, as the days shorten further, the temperature drops and the sources of pollen and nectar disappear. If the queen stops laying altogether then the colony will become broodless about 21 days later.
At some point, perhaps early in the New Year, the queen starts laying again. Slowly at first, but at increasing levels as the season starts. Once foraging starts in earnest the egg laying rate increases markedly and peaks sometime in June.
The precise timing of all these changes cannot be predicted. It’s likely to be dependent on a range of factors – nectar and pollen availability, the strain of bee, day length (and whether it’s increasing or decreasing) and temperature.
Of these, temperature probably has the greatest influence.
Generalised annual brood and worker numbers …
Here’s a quick’n’dirty graph put together with BEEHAVE showing a generalised annual cycle of total brood (blue) and adult bee (red) numbers. Under the conditions in this model the colony is broodless for ~30 days at the end if the year.
Part of the problem with being definitive about the annual brood cycle is the temperature variation with latitude. Temperate regions stretch – in Europe – from Northern Finland to Southern Spain. Bees are kept throughout this range, but obviously experience wildly different climates.
And then there’s the year to year variation.
So if you can’t predict when the colony is going to be broodless, perhaps you can observe the weather – and in particular the temperature – and make an educated guess.
Watch the weather
Over the last few years I’ve applied my midwinter treatment soon (<6 days) after the end of the first extended cold period of the season. This is generally earlier than most beekeepers, who often treat between Christmas and New Year, or early in January.
So, how do we reasonably accurately monitor the weather for a suitable time to treat?
Ho ho ho
Most of us live in centrally-heated splendour, protected from the day-to-variation of temperature by heated car seats, air conditioning, hot water bottles, Thinsulate and wood-burning stoves. Do you know what the temperature was today? Rather than trust the wildly-variable (in accuracy) national‡ weather reports for the actual temperature near my apiaries, I instead use very much more local data from Weather Underground.
There are hundreds of ‘amateur’ weather stations across the country that upload data to wunderground.com. Most of these provide current and historic data, including temperature (max, min and average). Here’s one for Auchtermuchty in Fife (on wunderground.com) and directly from the weather station.
Once the weather cools I keep an eye on the average temperature over an extended period of a fortnight or so. If it remains low I wait a bit more … but I then treat as soon as practical after it warms up to 8-10°C or so.
I didn’t open my colonies, but others opened on the same day nearby were all broodless. The 7th was chosen as it was the first warm (relatively!) day after a 19 day window in which the average temperature had barely climbed above 5°C.
These treated colonies went into the New Year with vanishingly low Varroa levels.
And again …
This year appears to be repeating a very similar pattern. We’ve had frosts most nights since the 10th of November. It started to warm up significantly in early December as storm Caroline bore down on Scotland and I treated most of my colonies on the 6th …
… by the light of a head torch, in light rain and strengthening wing at 7pm after work.
No, I didn’t open any of the hives to check if they were broodless 😉
It was over 11°C in the apiary when I treated, the barometer was plummeting and the forecast was for near-zero temperatures within 24 hours and remaining that way for another 10 days.
Some of my hives have perspex crownboards. These allow me to check both the state of the colony and if the vapour from my Sublimox has permeated to every corner of the hive. All the colonies were very loosely clustered, with a few bees even wandering out briefly onto the landing board in the dark as I bumbled around preparing things.
The Varroa trays will now be checked in a week or so to work out the mite infestation levels. In the meantime, I can start planning for the coming season knowing I’ve done the best I can to reduce virus levels in the colonies, so giving them a good start to the year.
A Hi tech solution?
Colonies rearing brood maintain a higher, and stable, broodnest temperature (32-35°C) than colonies without brood. It is therefore possible to determine whether a colony has brood by monitoring the temperature directly, rather than trying to infer it from the ambient temperature.
Brood rearing starts …
Arnia make hive monitors that allow this sort of thing to be measured. It would be interesting to relate the brood temperature to the ambient temperature (described above) to determine how accurate or otherwise simply ‘watching the weather’ is. Of course … what you’d really want to do is monitor when brood rearing stops and treat soon after that.
I treated colonies in our research apiary the following day – the 7th – with dribbled Api-Bioxal. The temperature had dropped almost 7°C since the previous evening and colonies were again beginning to cluster tightly. Under these conditions I’m never confident that the OA vapour penetrates fully, so prefer to trickle treat.
I briefly checked one strong colony in a poly hive for brood.
It was broodless, as I’d hoped 🙂
Of course, this doesn’t guarantee all the others are also broodless, but it does give me some confidence that I’d chosen the correct weather to treat.
† This article, like most on this site, discuss beekeeping issues relevant to temperate climates. It’s important to make this clear now as most of what follows is irrelevant to readers from warmer regions.
∞ Even if there is brood in midwinter, it’s going to be in pretty small amounts. The rate at which this brood emerges is going to be low. The chances of determining what’s going in the colony by ‘reading the tea leaves’ from the debris falling through the mesh floor of the hive is therefore not great. It would probably also require repeated visits to the apiary.
ß This needs qualifying … in midseason, when the temperature varies but it’s not generally cold, the nectar flow is probably the rate-limiting step for brood rearing. The June gap is regularly associated with the queen shutting up shop for a while. However, in late autumn and early winter I’m sure the plummeting temperatures is a major influence on egg laying by the queen.
‡ National … Ha! Most are only national if you live within the M25. Anywhere else and you’re usually much better off accessing some data from closer to home. It’s worth noting that the sort of ‘amateur’ weather stations I discuss do vary in data quality. For example, they’re a bit dodgy recording temperatures in full sun (they tend to over-read). However, if you find a local one, check the temperature in comparison to a thermometer in your apiary, you’ll find it’s a useful way to monitor what might be happening in the hives.
§ I don’t routinely generate these graphs – I have a life (!) – but did specifically to illustrate this post. It’s sufficient to simply monitor the average temperature.
Whether the weather be fine Or whether the weather be not, Whether the weather be cold Or whether the weather be hot, We’ll weather the weather Whatever the weather, Whether we like it or not.
This is the third and final post on why, with what, when and how to minimise mite levels in colonies in midwinter.
In the first post I explained why midwinter mite treatment makes sense. In the second I described how oxalic acid-containing solutions should be prepared and stored.
“Oxalic acid-containing” solutions includes both Api-Bioxal, the VMD approved treatment, and the unadulterated chemical. All three posts focus on trickling or dribbling – I’ve covered sublimation previously and both are essentially equally effective. Sublimation or vaporisation is currently very fashionable … but trickling is simplicity-itself and requires almost no special equipment.
In this post I’ll discuss how to administer the oxalic acid-containing solution.
For readability I’ll use the term OA solution to mean any oxalic acid-containing solution. About 50% of the readers of this site are from outside the UK; local rules may determine what you are or are not allowed to administer to your bees.
Trickling or dribbling
You’ll hear both terms used interchangeably1. The general principle is that you directly administer 5ml of a 3.2% w/v solution of oxalic acid in thin (1:1) syrup per seam of bees in the colony.
‘Directly‘ because you administer the OA solution to the seam of bees. You don’t count the seams and then simply pour it into the hive. You don’t spread it across the top bars. The idea is that the bees at the top of the seam get coated in the solution and that it dribbles down through the colony, being passed from bee to bee as they feed and groom and move about.
Two seams of bees …
During this process any phoretic mites will also get exposed to the oxalic acid. Since mites are readily damaged by the OA solution they fall off and gradually drop out of the bottom of the cluster. Gradually, as it takes a few days for gravity to deliver all the corpses.
You can therefore determine whether mites were present and killed by placing a Varroa tray underneath the open mesh floor of the hive. Note that this doesn’t tell you how effective the treatment has been … for that you’d need to know the mite infestation level before treatment as well.
When to treat
In many ways this is the critical decision. As described previously, maximal benefit occurs when the colony is broodless. Ideally you want an extended cold period late in the calendar year. The colony will cluster tightly and brood rearing will slow down or stop completely.
If the cold period has lasted 2-3 weeks, even better. This will mean that some or all of the brood present will have emerged. The more sealed brood present, the less effective trickling OA solution is as a means of controlling mites.
Choose a calm, cool or cold day. I usually wait for a day with temperatures between 0 and 5°C. Much warmer than that and the cluster starts to break up or the bees are more likely to fly about as the crownboard is lifted. Windy or wet days disturb the bees (at least when you prise the crownboard off), so it’s best to avoid those.
I prefer to treat before the year end, rather than after, if I can. From a few irregular midwinter peeks into the cluster I think queens start laying earlier than most beekeepers think.
It pays to be prepared …
Trickle 2 – £1
… Aesop (~620-560BC) was right, though he wasn’t talking about beekeeping. Before treating your colonies there is some preparation needed. Do this properly and it’s a doddle.
Practice with the Trickle 2 container (see below).
Gently warm your pre-prepared OA solution to about 25°C. If you made it up in advance and stored it at 4°C in the fridge this will take an hour or two. The easiest way is to stand the container (preferably thin-walled … I use a well-rinsed milk carton) in a basin of warm water.
Pour the pre-warmed OA solution into a well-labelled vacuum flask. You can buy these from Tesco for £2.50 with a capacity of 1 litre. The aim here is to take everything you need ready-prepared to the apiary so the treatments take the minimum time possible.
Remember that OA is toxic. Label everything carefully, make sure children can’t get near it and don’t use it again for food/drink purposes.
That’s it … you’re ready. You’ll need a hive tool, a bee suit, thin gloves (to protect you from the OA, not the bees), your vacuum flask of OA solution and the Trickle 2 bottle. By all means take your smoker, but you shouldn’t need it.
I’ve got a 5 ml (or 25 ml) syringe … won’t that do?
Yes … but no.
A Trickle 2 bottle holds 100ml of prepared OA solution. It takes two hands to fill the bottle, but only one hand to use it. That 100ml is sufficient for 20 seams of bees i.e. two completely full colonies (assuming an 11 frame National box). In midwinter the colony is unlikely to occupy 10 seams. A Trickle 2 bottle is also pretty accurate, reproducibly dispensing about 4.6-4.8ml of liquid. That’s close enough to 5ml.
In contrast, a syringe also takes two hands to fill (and refill). However, unless it’s a 5ml syringe, it’s difficult to accurately and reproducibly dispense liquid without using two hands. A 5ml syringe gives you the necessary accuracy, but needs refilling for every seam of bees. This takes time … during which the crownboard is off and the colony is getting chilled.
I’ve done both and can assure you that the Trickle 2 bottle is much better. Just buy one. It’s only £1 and it’ll last ages if one of your association members doesn’t borrow it … or doesn’t return it.
How to use a Trickle 2 bottle
Remove the cap and fill to the top of the lower chamber with liquid (practice with water).
Replace the cap.
Hold the bottle with your thumb and fingers on opposite sides of the lower chamber, with the external ‘pipe’ to the upper chamber next to your palm.
Undo the spout about a turn.
Gently squeeze the lower chamber. Liquid is forced up the pipe into the upper chamber. Hold it against the light to observe this.
Once the upper chamber is full, stop squeezing. Excess liquid drains back into the lower chamber.
If you are right handed turn the Trickle 2 bottle anti-clockwise2 using your wrist and gently squeeze the bottle to dispense the liquid in the upper chamber from the spout. If you’re left handed you need to turn the bottle clockwise.
And in practice
The single-handed operation for the Trickle 2 container really pays dividends when treating a colony. You can gently prize up one side of the crownboard, hold it in one hand, administer the OA solution to each seam with the other hand and gently lower the crownboard back down … all in less time than it took me to write that.
This is a reasonably sized colony being treated in the second week of January 3 years ago. The video is 1’45” long, but the crownboard is only open for about 50 seconds. And I was chatting with Mick Smith off camera, so could have perhaps gone a bit faster if I’d concentrated … 😉
Here’s a more detailed view of treating a small colony:
33 seconds of warmed, acidic goodness to slaughter the mites and give the colony the best possible start to the upcoming season.
Cautions and considerations
Discard any OA solution that’s not been used. Warming it will have raised the HMF levels and this may be toxic for your bees. However, read footnote 3 for another way to avoid HMF buildup3.
Wash everything carefully – the Trickle 2 bottle, the vacuum flask, gloves etc. Since the OA solution was in syrup everything gets sticky and gummed up. Clean stuff up, make sure it’s labelled and not going to be used in the kitchen and put it away until next year.
Oxalic acid kills mites, but it’s also toxic for unsealed brood. This is perhaps unsurprising considering it has a pH of 1 (i.e. very acidic) and ‘naked’ larvae aren’t protected by the tough exoskeleton that adult bees have. This is another reason to treat during a broodless period in midwinter.
In summer, swarms can also be treated with trickled oxalic acid-containing solutions before they have sealed brood. If a swarm arrives in bait hive, let it settle and start drawing comb on the foundationless frames. A day or so later treat it with oxalic acid by trickling. When I’ve done this I usually wait until late afternoon or early evening, so most of the bees are in the box. The colony obviously won’t be clustered, but the principle is the same – 5ml of syrup down each seam. Easy peasy. Effective.
Swarms have a significant mite load, so it’s well worth treating them before they rear brood and give the phoretic mites somewhere to breed.
Finally, it’s often recommended that a colony is only treated once per year with oxalic acid by trickling or dribbling. I’m not sure where this advice originates, but it’s probably wise.
‘Vaping’ vs. trickling
The discussion forums are awash with recommendations to ‘vape’ the colony, rather than trickle. Vaporisation, or more correctly sublimation, is a widely used method and has been in use for two decades. It’s currently very fashionable. I’ll write a more substantial comparison sometime in the future, but the following brief notes might be of interest.
Sublimation can be done repeatedly with brood present (though there’s no peer-reviewed evidence of efficacy) and is both well-tolerated by the colony and is not toxic to unsealed brood. It requires specialised and potentially expensive equipment, both for delivery and personal protection. You can build your own vaporiser, but shouldn’t skimp on protection for the operator. With a well designed vaporiser and hive there’s no need to open the colony to administer treatment.
In contrast, trickling requires only the Trickle 2 bottle and vacuum flask described here. Personal protection is a pair of latex gloves. It should only be conducted when the colony is broodless, should probably only be conducted once and does require the hive to be opened (albeit briefly).
You’ll be told that vaporisation is faster. It isn’t. Watch the videos above. Even my Sublimox – probably the fastest ‘active’ vaporiser on the market – takes well over a minute per colony if you take into account sealing the box, moving the generator about, unsealing the hive etc.
There are reports that sublimation is more effective, but the difference is marginal, and possibly not statistically significant. There is also a report that colonies are stronger in the Spring after sublimation, though this may be due to toxicity to open brood by trickled OA solution. If the colony is broodless this shouldn’t be an issue.
I’ve used both many, many times without a problem. Across the UK I suspect more beekeepers trickle OA, rather than ‘vape’ (a word I dislike), though the vocal ones on the discussion forums currently favour vaporisation.
What’s more important than how you deliver the oxalic acid, is that you do treat. Trickling OA solution is so easy and inexpensive that there’s no reason not to … and your colonies will be much healthier for it.
Get dribbling 😉
1 If the beekeeper is of a certain age you’ll hear these terms used in a different context. We’re restricting discussions here to delivering OA 😉
2 If you are left handed you need to turn the Trickle 2 bottle clockwise. Actually, to be pedantic, if you are left handed and holding the bottle in your left hand, turn it clockwise. It’ll make sense once you try.
3 In the previous article on preparing oxalic acid solutions Calum posted a comment on preparing the OA in water and only adding and dissolving the required amount of sugar just before use. This has the advantage that there will be no HMF buildup. OA solution in water should be perfectly stable. I’ve not done it this way, but it makes sense and might be worth trying.
The title of this article is a twist on the term Trick or treat. This is not entirely inappropriate as Trick or treating is a Halloween (31st October … just a few days away) custom dating back – in various forms – centuries.
The modern usage, essentially North American, dates back to the 1920’s and refers to children in costumes going house to house threatening to play a trick unless the homeowner provides a treat, usually sweets or toys. In Britain these traditions date back to the 16th Century, both of children going house-to-house asking for food and of dressing up in costumes at Halloween.
Closer to home, ‘guising‘ – children in Scotland going from door to door in disguise asking for food, coins or chocolate – dates back at least a century.
The term Trick or treat only entered common usage in the UK in the 1980’s.
This is the second of three articles on midwinter treatment of colonies with oxalic acid to minimise Varroa levels. In a recent post I explained why a midwinter treatment was necessary, even if you’d treated three months earlier. Essentially this is because:
midwinter is the time when brood levels are at a minimum, so most mites will be phoretic and readily accessible to the miticide treatment
Midwinter is the time to use oxalic acid-containing treatments. It can be delivered in a variety of ways; by sublimation (vaporisation), spraying or trickling (dribbling).
Trickling or dribbling
This post is about the preparation and storage of oxalic acid-containing solutions for trickling. Sublimation is covered elsewhere and spraying is not approved or widely used in the UK.
The process for trickling is very straightforward. You simply trickle a specific strength oxalic acid solution in thin syrup over the bees in the hive. The oxalic acid kills the mites. How isn’t entirely clear – it’s thought to corrode the mouthparts and soft tissue. It’s more than 90% effective in killing phoretic mites when used like this.
Beekeepers have used oxalic acid for years as a ‘hive cleaner’, as recommended by the BBKA and a range of other official and semi-official organisations. All that changed when Api-Bioxal was licensed for use by the Veterinary Medicines Directorate (VMD).
Oxalic acid and Api-Bioxal, the same but different
To trickle or dribble oxalic acid-containing solutions you’ll need to prepare it at home, store it appropriately and administer it correctly.
I’ll deal with how it is administered next time. This is all about preparation.
The how much is easy. You’ll need 5ml of oxalic acid-containing solution per seam of bees. In midwinter the colony will be reasonably well clustered and its likely there will be a maximum of only 8 or 9 seams of bees, even in a very strong colony.
Hold on … what’s a seam of bees?
Two seams of bees …
Looking down on the colony from above, a seam of bees is the row visible between the top bars of the frames.
Remember to prepare ~10% more than you think you need. You’ll inevitably spill some when using the Trickle 2 bottle to administer it to the colony. It’s not that expensive, so don’t risk running out.
And the how strong? The recommended concentration to use oxalic acid at in the UK has – for many years – been 3.2% w/v (weight per volume) in 1:1 syrup. This is less concentrated than is recommended in continental Europe (see comments below on Api-Bioxal).
My advice – as it’s the only concentration I’ve used – is to stick to 3.2%.
Listen very carefully, I shall say zis only once†
A bit of basic chemistry coming up. Skip to the warning in red below and then the recipes if you want, but this explains some important things about working out how much to use.
The molecular formula of oxalic acid is C2H2O4. The molecular weight of oxalic acid is 90.03 g/mol. However, the oxalic acid you purchase – including Api-Bioxal – is the dihydrated form of oxalic acid.
Di as in two, hydrated as in water.
The molecular formula of oxalic acid dihydrate is C2H2O4.2H2O and oxalic acid dihydrate has a molecular weight of 126.07 g/mol.
Therefore the weight of oxalic acid in 1 g of oxalic acid dihydrate is 90.03/126.07 = 0.714 g.
Oxalic acid is toxic
The lethal dose for humans is reported to be between 15 and 30 g. It causes kidney failure due to precipitation of solid calcium oxalate.
Clean up spills of powder or solution immediately.
Take care not to inhale the powder.
Store in a clearly labelled container out of reach of children.
Do not use containers or utensils you use for food preparation. A carefully rinsed plastic milk bottle, very clearly labelled, is a good way to store the solution prior to use.
Recipes : oxalic acid
The standard recipe is 100 g water plus 100 g white granulated sugar. Mix well and then add 7.5 g of oxalic acid. The final volume will be 167ml i.e. sufficient to treat over 30 seams of bees, or between 3 and 4 strong colonies (including the 10% ‘just in case’).
This final concentration is 3.2% w/v oxalic acid … (7.5 * 0.714)/167 * 100 = 3.2. Check my maths.
0.01 g to 500 g
If you have more colonies to treat, or have trouble weighing 7.5g, scale everything up ten-fold. Or buy a small, accurate set of digital scales – like these for £9 which work very well. 1 kg of sugar plus 1 kg (1 litre) of water requires 75 g of oxalic acid and makes 1.67 litres … enough to treat all the colonies in the association apiary.
Which is not such a bad idea. Make it up carefully once and share it with your fellow beekeepers. Storage details are provided below.
Recipes : Api-Bioxal
Warning – the recipe on the side of a packet of Api-Bioxal makes up a much stronger solution (4.4% w/v) of oxalic acid than has historically been used in the UK. Stronger isn’t necessarily better. The recipe provided is 35 g Api-Bioxal to 500 ml of 1:1 syrup. By my calculations this recipe makes sufficient solution at a concentration of 4.4% w/v to treat 11 hives.
To make a 3.2% Api-Bioxal-based oxalic acid-containing solution using the 35 g pack of Api-Bioxal you need to mix the entire contents of the pack with 691 ml of 1:1 syrup.
Here’s the maths:
35 g of Api-Bioxal contains only 22.14 g of oxalic acid. 88.6% of the 35 g is oxalic acid dihydrate (the remainder is cutting agents like glucose and powdered silica) and so the oxalic acid content is ((35 * 0.886) * 0.714) = 22.14 g.
To calculate the volume of syrup you need to divide it by the final percentage required i.e. (22.14 / (3.2/100)) = 691 ml. I don’t know the exact amount of sugar and water needed to make this amount … it’ll be about 430 g of each (I think).
A 35 g packet of Api-Bioxal is therefore sufficient to treat about 15 colonies (assuming 5 ml per seam, 8 seams per hive and 10% ‘just in case’) at the recommended concentration of 3.2% w/v.
Api-Bioxal is sold in three pack sizes (35 g, 175 g and 350 g). If you are wealthy enough to be able to purchase the larger pack sizes you’ve probably got your own beekeeper (or mathematician). Relax on your yacht while they do the calculations‡ for you 😉
On the other hand … if you have a smaller number of colonies either make a full 35 g packet up and share it, or use accurate scales and the following table:
Api-Bioxal recipes for 3.2% OA trickling
Storage of oxalic acid syrup at ambient temperatures rapidly results in the acid-mediated breakdown of sugars (particularly fructose) to generate hydroxymethylfurfural (HMF). As this happens the colour of the oxalic acid-containing solution darkens significantly.
This breakdown happens whether you use oxalic acid or Api-Bioxal.
Stored OA solution and colour change …
HMF is toxic to honey bees at high concentrations. Studies from ~40 years ago showed that HMF concentrations below 30 mg/l were safe, but above 150 mg/l were toxic1. HMF buildup is one way overheated honey is detected.
At 15°C HMF levels in OA solution can reach 150 mg/l in a little over a week. At room temperature this happens much faster, with HMF levels exceeding 150 mg/l in only 2-3 days. In the dark HMF levels build up slightly less quickly … but only slightly 2,3.
Only make up OA solutions when you need them.
If you must store your oxalic acid-containing syrup for any length of time it should be in the fridge (4°C). Under these conditions HMF levels remain well below toxic levels for at least one year. However, don’t store it for this long … use it and discard the excess. Don’t use discoloured oxalic acid solutions as they’ve been stored incorrectly and may well harm your bees.
Please re-read the comments above about the toxicity of oxalic acid. If you are going to store it in the fridge it must be very clearly labelled and there must be no chance that children can reach or open the container.
Api-Bioxal is the least expensive VMD-approved miticide and powdered oxalic acid is much, much cheaper. Both contain the same active ingredient, oxalic acid, which is highly effective against phoretic mites.
In midwinter, with very low levels (or no) of brood, a single oxalic acid-containing treatment minimises mite levels for the coming season.
Oxalic acid-containing solutions are easy to prepare. I recommend you make sufficient for your own colonies and those of your beekeeping friends and association members. My previous BKA used to distribute litres of the stuff for use in midwinter. Use this solution in midwinter and then discard any that is unused.
Oxalic acid-containing solutions are inexpensive and easy to administer by trickling. As I shall demonstrate next time.
Please re-read the safety instructions highlighted in red above.
† Listen very carefully, I shall say zis only once was a catchphrase used by “Michelle of the Resistance” in the 1980’s comedy ‘Allo ‘Allo! Michelle (Dubois) was rarely seen without a trench coat and beret, had a corny French accent and was played by Kirsten Cooke.
‘Allo ‘Allo! ran for 85 episodes in the decade from 1982 on BBC one. It was about a café in Nazi-occupied France and the French Resistance, just about. It mixed bawdy humour with gross stereotypes (posh British twits, sex-obsessed French) and was a parody of ITV’s series Secret Army (’77-’79).
Early episodes had obvious and rather dull titles. In the later series the individual episodes had some quite good puns like Awful Wedded Wife.
Michelle – Listen very carefully, I shall say zis only once
René – Well, in that case, could you please speak slowly?
You had to be there … 😉
‡ Oh alright then, since you insist. The 175 g pack of Api-Bioxal (~£39) needs to be made up in 3.459 litres of 1:1 syrup and the 350 g pack (~£65) 6.919 litres of 1:1 syrup. Determining how much water and sugar to mix to make these amount is, as they say, an exercise for the reader. Assuming a 3.2% solution and 8 seams of bees per colony Api-Bioxal costs between 63p and 41p per hive (see note below), depending upon the pack size you purchase. I know that beekeepers moan on and on about the outrageous cost of Api-Bioxal (as do I), but is 63p per colony really an unreasonable amount to spend on VMD-approved medicines to keep your colony as clear of Varroa as possible? I don’t think so.
Note – the costs in the paragraph were calculated using the lowest prices I could currently find for Api-Bioxal. C Wynne Jones has the 35g packets for £9.50 and Maisemores have the 350g packets for £64.79. Prices correct on 9/10/17.
1Jachimowich T., El Sherbiny G., Zur Problematik der verwendung von Invertzucker für die Bienenfüttering, Apidologie6 (1975) 121-143.
3Prandin, L., Dainese, N. , Girardi, B., Damolin, O., Piro, R., Mutinelli, F. A scientific note on long- term stability of a home-made oxalic acid water sugar solution for controlling varroosis Apidologie, 32:) 451-452
Why bother treating colonies in midwinter to reduce Varroa infestation? After all, you probably treated them with Apiguard or Apivar (or possibly even Apistan) in late summer or early autumn.
Is there any need to treat again in midwinter?
Yes. To cut a long story short, there are basically two reasons why a midwinter mite treatment almost always makes sense:
Mites will be present. In addition, they’ll be present at a level higher than the minimum level achievable, particularly if you last treated your colonies in late summer, rather than early autumn.
The majority of mites will be phoretic, rather than hiding away in sealed brood. They’re therefore easy to target.
I’ll deal with these in reverse order …
Know your enemy
The ectoparasite Varroa feeds on honey bee pupae and, while doing so, transmits viruses (in particular DWV) that can completely mess up the development of the adult bee. Varroa cannot replicate anywhere other than on developing pupae. It’s replication cycle, and the resulting mite levels in the colony, are therefore tightly linked to the numbers and availability of hosts … honey bee pupae.
If developing brood is available the mite can replicate. Under these conditions, newly emerged adult, mated, female Varroa spend a few days as phoretic mites, riding around the colony on young bees. They then select a cell with a late-stage larvae in, enter the cell and wait until pupation occurs. If developing worker brood is available each infested cell produces 1 – 2 new mites (drone cells produce 3+) and mite numbers increase very rapidly in the colony.
In contrast, if there’s no developing brood available, the mites have to hang around waiting for brood to become available. They do this as phoretic mites and can remain like this for weeks or months if necessary.
Therefore, when brood is in abundance and the queen in laying freely mites can replicate to very high levels. In contrast, when brood is limiting and the queen has reduced her egg laying to a v e r y s l o w r a t e the mite cannot replicate and must be predominantly phoretic.
When does this happen?
Lay Lady Lay … or don’t
Ambient temperature, day length and the availability of nectar and pollen likely influence whether the queen lays eggs. When it’s cold, dark and there’s little or no pollen or nectar coming into the hive the queen slows down, or even stops, laying eggs.
About 8 days after she stops laying there will be no more unsealed brood in the colony. About 13 days after that all the sealed brood will have emerged (along with any Varroa). Therefore, after an extended cold period in midwinter, the colony will have the lowest level of sealed brood … and the highest proportion of the mite population will be phoretic.
Under normal (midsummer) circumstances about 10% of the mite population is phoretic. It’s probably unnecessary to state that, if there’s no brood available, 100% of the mites must be phoretic.
All licensed miticides work extremely well against phoretic mites†.
Caveats, guesstimates, global warming and the Gulf Stream
Global warming …
Whatever the cause, the globe is warming (irrespective of what Donald Trump tweets). Long, hard winters are getting less common (or perhaps even rarer, as they were never particularly common in the UK). In Central, Southern or Eastern Britain it’s possible that the colony will have some brood present all year. In parts of the West, warmed by the Gulf Stream, I’d be surprised if a colony was ever broodless. Only in the North is it likely that there will be a brood break in midwinter.
Most of the paragraph above is semi-informed guesswork. I don’t think anyone has systematically analysed colonies in the winter for the presence of sealed brood. Sure, many (including me) have opened colonies for a quick peek. Others will have peered intently at the Varroa board to search for shredded wax cappings that indicate emerging brood. The presence of brood will vary according to environmental conditions and the genetics of the bees, so it’s not possible to be dogmatic about these things.
However, it’s safe to say that in midwinter, sealed brood – within which the mites can escape decimation by miticides – is at a minimal level.
However, I will re-present the graph that illustrates the modelled (using BEEHAVE) mite levels‡.
Time of treatment and mite numbers
The gold arrow(days 240-300i.e. September and October) indicates when the winter bees are being reared. These are the bees that need to be protected from mites (and their viruses).Mite numbers (starting with just 20 in the hive on day zero) are indicated by the solid coloured lines. The blue, black, red, cyan and green lines indicate modelled mite numbers when the colony is treated with a miticide (95% effective) in mid-July, August, September, October or November respectively.
The earlier you treat, the lower the mite levels are when the winter bees are being reared. Study the blue and black lines.
This is a good thing.
In contrast, by treating very late (the cyan and green lines) the highest mite numbers of the season occur at the same time as the winter bees are being reared. A bad thing.
But … look also at mite numbers after treatment
Look carefully at the mite numbers predicted to remain at the end of the year. Early treatment leaves higher mite levels at the start of the following year.
This is simply because mites escaping the treatment at the end of summer have had an opportunity to reproduce during the late autumn.
This is why the additional midwinter treatment is beneficial … it kills residual mites and gives the colony the best start to the new calendar year§.
Kick ’em when they’re down
Early treatment protects winter bees but risks exposing bees the following season to unnecessarily high mite numbers. However, in midwinter, these residual mites are much more likely to be phoretic due to a lack of brood in the colony. As I stated earlier, phoretic mites are relatively easy to target with miticides.
So, give the mites a hammering in late summer with an appropriate and effective miticide and then give those that remain another dose of the medicine in midwinter¶.
But not another dose of the same medicine
Since the majority of mites in a colony with little or no brood will be phoretic, you can easily reduce their numbers using a single treatment containing oxalic acid. This can be administered by sublimation (vaporisation) or by trickling (dribbling).
There’s no need to use any treatment that needs to applied for a month. Indeed, many (Apiguard etc.) are not recommended for use in winter because they work far less well on a largely inactive colony.
Trickle 2 – £1
I’ve discussed sublimation previously. However, since this requires relatively expensive (£30 – £300) specialised delivery and personal protection equipment it may be inappropriate for the two hive owner. In contrast, trickling requires almost no expensive or special equipment and – reassuringly – has been successfully practised by UK beekeepers for many years. I did it for years before I bought my Sublimox vaporiser.
Therefore, in two further articles this autumn (well before you’ll need to treat your own colonies) I’ll describe the preparation and storage of oxalic acid solutions and its use.
If you want to be prepared you’ll need to beg, borrow or steal the following – sufficient oxalic acid (or Api-Bioxal), a Trickle 2 bottle sold by Thorne’s, a cheap vacuum flask (Tesco £2.50), granulated sugar and a pair of thin disposable gloves.
Do this soon. Don’t leave it until midwinter. You need to be ready to treat as soon as there’s a protracted cold spell (when brood will be at a minimum). Over the last few years my records show that this has been anywhere between the third week in November and the third week in January.
More soon …
† Only MAQS is effective against mites sealed in cells. This is why most miticides are used for extended periods in the late summer or early autumn … the miticide must be present as Varroa emerge from sealed cells.
‡ I’ll repeat the caveat that this is an in silico simulation of what happens in a beehive. Undoubtedly it’s not perfect, but it serves to illustrate the point well. It’s freely available, runs on PC and Mac computers, and is reasonably well-documented. In the simulations shown here the virtual colony was ‘primed’ with 20 mites at the beginning of the year. BEEHAVE was run using all the default settings – climate, forage etc. – with the additional application of a miticide (95% effective) in the middle of the months indicated. Full details of the modelling have already been posted.
§ The National Bee Unit recommend Varroa levels are maintained below 1000 throughout the season. Without treatment, 20 mites at the start of the season can easily replicate to ~750 in the autumn. If you start the season with 200 mites then levels are predicted to reach ~5000 in the following summer. The colony will almost certainly die that season or the next. There’s a more detailed account of the consequence of winter brood rearing and the level of mite infestation written by Eric McArthur and reproduced on the Montgomeryshire BKA website that’s worth reading.
¶ The cumulative (year upon year) effect of late summer treatment with no midwinter treatment has been discussed previously. I’ll simply re-post the relevant figure here – 5 years of bee (in blue, left axis) and mite (in red, right axis) numbers with only one treatment per season applied in late September. Within two years the higher mite numbers that are present at the start of the year reproduce to dangerously high levels.
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 transmits 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 …
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 …
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.
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.
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).
In February 2016 I posted an article on “When to treat“ colonies with miticides. It was read by subscribers, generated a bit of discussion – in particular on Apiguard use – and then disappeared into the howling wilderness that is the interwebs …
Google hides the searches that drives most of the website traffic to this site. However, it has been found … as is clear from the access stats (below), it is now being accessed extensively.
This reflects the change in the seasons as beekeepers turn their thoughts from harvesting honey to protecting their colonies from the ravages of Varroa and the viruses it transmits.
‘When to treat’ stats …
It’s worth reiterating it here, though this won’t be news to regular readers, Varroa itself is probably not the problem. The problem is the smorgasbord of viruses that Varroa transmits when feeding on the haemolymph (blood) of honey bee pupae.
Benign and virulent
Most important of these viruses is deformed wing virus (DWV). This virus has a sort of Jekyll and Hyde personality. It’s probably present in all honey bees, transmitted between bees while larvae are being reared and during trophylaxis (the regurgitation of liquid food between bees). Under these conditions, and in the absence of Varroa the virus is probably benign.
Of course, it’s difficult to test whether it is really benign as there probably aren’t any bees that lack DWV. Even bees that have never been exposed to Varroa, such as the black bees on Colonsay, have DWV. Let’s assume that, even if not benign, it has minimal detrimental effect on the bees.
Varroa changes the route by which DWV is transmitted. Instead of being orally transferred – a route the bees have probably evolved to cope with – Varroa bypasses any defence mechanisms by ‘injecting’ DWV directly into the blood. Under these conditions DWV reproduces rampantly – for reasons that have yet to be determined – causing the ‘deformed wing’ symptoms most beekeepers are familiar with.
Symptomatic adult, or recently emerged, bees can contribute little or nothing to the colony.
Live fast, die young†
But there’s more bad news. Asymptomatic adult bees with high levels of DWV have a shorter lifespan and die prematurely. This is perhaps not an issue during the heady days of summer when the turnover of worker bees is at its height – the queen is laying well, perhaps 1500-2000 eggs per day, the colony is bulging and individual workers “live fast and die young” after about 6 weeks.
Formally, I don’t think it’s been shown that mid-season workers have a shorter life span when they have high levels of DWV. What is known, and what is much more important, is that winter bees die prematurely if their DWV levels are high.
Winter bees are the ones with high levels of fat in their bodies. These are the bees that get the colony through the winter. Some might live for 5-6 months in the UK, and it’s known they can live for up to 9 months. If these bees die early, in the absence of any significant brood rearing, the colony dwindles and dies.
Preventing the inevitable
Varroa transmits DWV and results in high levels of DWV. High levels of DWV in winter bees shortens their lifespan and results in colony losses. How can you prevent the inevitable?
In the absence of ways to directly control DWV levels (these are in development but you’re then tackling the symptom, not the cause) the only way to do this is to prevent the transmission of DWV to the winter bees by Varroa in the first place.
And you do this by applying effective miticides early enough that the winter bees are protected from exposure to Varroa, and the viruses it transmits.
How early is early?
I discussed this in the earlier article and am working on a more nuanced version at the moment. Essentially – and I’m writing this in mid-August – the answer is now or very soon.
In the definitive publication demonstrating the premature death of winter bees by DWV, Peter Neumann and colleagues detected a measurable reduction in longevity as early as November in the colonies they studied. These bees were age-marked and had emerged 50 days earlier. The eggs had therefore been laid in the first week of September … and been capped (together with any Varroa) as pupae in mid-September.
Therefore, treatments to reduce Varroa should be completed by mid-September to protect the winter bees. Since many treatments take ~4 weeks the time to treat is right now.
There’s climatic variation between parts of the UK and Bern, where the study by Peter Neumann was conducted. There’s also seasonal variation year on year.
In the balmy South the dates will be later than in the frigid North. In cool years with an early autumn they will be earlier, whereas an Indian summer will delay the need to treat.
Treatments are generally incompatible with a honey flow. If you take your bees to the heather you have to balance collecting a late heather crop with protecting the bees from the ravages of Varroa.
it’s not possible, or wise, to be dogmatic about precise dates … other than to say that miticide treatment is generally required earlier than you think to protect the winter bees from DWV.
Better late than never?
Well, yes, but the damage may well have been done.
The annual survey of beekeepers in Scotland regularly includes significant numbers using Apiguard in October. Close, but no cigar‡ (actually, not even close) … it’s probably too late to reduce Varroa levels in a meaningful way, and it’s unlikely to be effective anyway as Apiguard needs average temperatures around 15°C.
All of the comments above on the timing of treatment make the assumption that the treatment is effective – the right dose, the right duration, the absence of resistanceetc.
Finally, it’s worth noting that starting treatment in mid/late August does not reduce Varroa levels to the lowest achievable levels. Treating later in the year does this, because more mites are phoretic and ‘reachable’ by the treatment. To reduce mite levels to the minimum you also have to also treat midwinter … something for another post.
† Live fast, die young was the title of a biography of the actor James Dean by James Gilmore. It’s a popular phrase, being used for a movie and several song titles. The extended version Live fast, die young and have a good looking corpse, often wrongly attributed to James Dean, actually came from the 1947 book Knock on Any Door by Willard Motley.
‡ Close but no cigar is a mid-20 phrase from the USA. It dates back to the time when fairground stalls gave out cigars as prizes.
Right here, right now is a song released in April ’99 by Fatboy Slim (Norman Cook) from the album You’ve come a long way, baby‘. If you appreciate evolution you’ll enjoy the video …
… but you’ll need to like beat/dance music to appreciate the track.