Category Archives: Varroa

Resistance is not futile

Apivar ...

Apivar …

Amitraz-containing miticides are sold in the UK as Apivar and Apitraz.

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) 2 Varroa 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.

Amitraz

Amitraz …

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, resistance 4 is a consequence of two things:

  1. A selective pressure that kills the pathogen
  2. 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.

What 10 is the RMβAOR gene?

I’m glad you asked 😉

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 misuse this 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.


Colophon

Resistance is futile

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 is anything but futile 13.

Resistance – to miticides – gives Varroa a reason to live. Literally.

Let’s not help them 🙂

Survival of the fattest

Winter bees have high levels of vitellogenin, a glycolipoprotein 1, deposited in their fat bodies which act as a food reservoir for the long winter.

These fat winter bees are essential for the successful overwintering of the colony.

Last week I discussed the major points that need attention for overwintering i.e. strong, healthy colonies with ample food in a weathertight hive.

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 ...

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.

Healthy colonies

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

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.

Brrrr 🙁

Winter bee numbers in healthy (blue) and unhealthy (red) colonies

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.

Strong colonies

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 identical 7.

Winter bee numbers in strong and weak colonies.

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.

Mix’n’match

A strong colony with high levels of Varroa and DWV might actually survive less well than a weak but healthy colony.

Strong unhealthy colonies might survive less well than weak healthy colonies.

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.

Simples.

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.

Isolation starvation

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

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.

Prediction

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.


Colophon

Herbert Spencer

Herbert Spencer

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.

Sublimox spares and repairs

Sublimox vaporiser

Sublimox vaporiser …

I’ve been using a Sublimox sublimator (vaporiser) since late 2014. In that time it’s worked faultlessly. There have been only two things that have needed any attention. These are the screws that hold the heat shield in place and replacement of the ‘O’ rings on the nylon cup you load with oxalic acid.

Actually, the other thing that needed attention was the heating chamber that became coated with caramelised glucose when I first used Api-Bioxal … but I’ve posted on that separately.

Screws

The heat shield protects the operator and your easy-to-melt poly hives from the metal heating chamber within which the oxalic acid is vaporised. It’s made out of folded, perforated metal and is held in place with two small retaining screws on the underside.

The heat shield can get a bit of a battering. The sublimator rests on it when the machine is laying on the side. More significantly it can get twisted or pulled if it gets caught on the edge of the hive when inverting it to deliver the oxalic acid. Inevitably, it is also subjected to repeated cycles of heating and cooling.

All of this tends to mean that the grub screws work loose over time. If the machine is cool they can be finger-tightened, but they’ll eventually loosen off again.

Retaining screws ...

Retaining screws …

To rectify this and prevent their permanent loss in the apiary mud I gave them each a dab of Loctite 243 and tightened them up properly 1. This appears to have done the trick and they’ve remained in place without loosening.

O rings

The nylon cup you preload with oxalic acid has an O ring seated in a groove. This provides a gas-tight seal with the metal chamber in which the OA is vaporised.

It’s a tough life being an O ring.

It is subjected to a very harsh environment consisting of both high acidity and high temperatures. With repeated use the O rings become less able to form the gas-tight seal. They get thinner, crack and/or stiffen. Eventually they fail completely.

Once they have failed there’s a significant risk of vaporised oxalic acid escaping. Aside from potentially increasing operator exposure this also means that all that mite-destroying goodness is not being delivered where it does most harm (to the mites in the hive).

Here's two I wrecked earlier ...

Here’s two I wrecked earlier …

Replacement O rings can be purchased from the various suppliers of the Sublimox. Icko used to list them on their website but they appear to have disappeared for the moment. Abelo list them at £2 each.

As an alternative I’ve purchased and am testing some Viton O rings from eBay. Viton 75 is a “DuPont-manufactured fluorocarbon elastomer that exhibit excellent resistance to high temperature and many organic solvents and chemicals over a temperature range of -25°F to +400°F”.

Which sounds ideal for something that needs to work with oxalic acid at a temperature of about 160°C. The documentation from Dupont indicates that Viton has excellent resistance to oxalic acid.

Sublimox nylon cups and O rings ...

Sublimox nylon cups and O rings …

I’ll post on how well these work sometime in the future.

Essential accessories …

Although not really a “spare or repair” it’s worth noting here that the Sublimox requires a 240V supply and so should always be used with an RCD (residual current device). This is particularly important since the apiary in winter is probably a damp (or worse) environment. An RCD, together with a bottle of water for cleaning the vaporiser, can just about be squeezed into the carry case. It’s therefore available whether you use a portable generator or an extension lead to the mains voltage supply.

Spring (or late winter) vigilance

As the season slowly starts, colonies will begin rearing more brood. You don’t need to open the colony up to determine this. Instead, insert a Varroa tray under the open mesh floor and look for thin rows of “biscuit crumbs” that are the cappings from emerging brood.

All is well ...

All is well …

And, while you’re looking at this evidence that the long winter will soon be over, look carefully for any Varroa that have dropped from the colony. Mite drops should be very low if your autumn and midwinter treatment regime was effective.

You need to monitor for at least a week. With low mite numbers in the colony and small amounts of sealed brood the drop can fluctuate a bit.

If the mite drop is not low or non-existent there’s probably no need to treat immediately 2. However, make a note to monitor the colony at regular intervals – both for mites and overt DWV disease – and intervene if necessary.


 

Kick ’em when they’re down

Out, damn'd mite ...

Out, damn’d mite …

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

Is there any need to treat again in midwinter?

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

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

I’ll deal with these in reverse order …

Know your enemy

DWV symptoms

DWV symptoms

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

If developing brood is available the mite can replicate. Under these conditions, newly emerged adult, mated, female Varroa spend a few days as phoretic mites, riding around the colony on young bees. They then select a cell with a late-stage larvae in, enter the cell and wait until pupation occurs. If developing worker brood is available each infested cell produces 1 – 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

Global warming …

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

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

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

Reducing mite levels and minimal mite levels

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

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

Time of treatment and mite numbers

Time of treatment and mite numbers

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

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

This is a good thing.

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

But … look also at mite numbers after treatment

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

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

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

Kick ’em when they’re down

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

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

But not another dose of the same medicine

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

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

Trickle 2 - £1

Trickle 2 – £1

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

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

Be prepared

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

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

More soon …


† 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.

Mid September

Mid September

Counting Varroa

It’s that time of the season again. With the exception of readers in the Southern Hemisphere, Colonsay, the Isle of Man or a few favoured locations in the Highlands of Scotland, 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 ...

Out, damn’d mite …

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

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

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

The scores are on the floors

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

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

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

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

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

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

Objective vs. subjective counting

Easy counting ...

Easy counting …

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

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

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

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

Don’t try this at home

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

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

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

Fiji ...

Fiji …

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

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

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

It does.

Consistently variable

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

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

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

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

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


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

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

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

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

 

Small cell foundation

In a recent monthly newsletter Thorne’s announced they were now supplying small cell foundation. This foundation has a cell diameter of 4.9mm, rather than the standard 5.2-5.4mm. Under the ambiguous heading 4.9 mm foundation for varroa control” they have the following text:

Wired foundation

Wired foundation

“It is claimed varroa mites struggle to reproduce in the slightly smaller cell size. 4.9 mm being close to what bees produce in comb width in nature. Many beekeepers in the USA who have experimented with small cell have reported encouraging results. Moving over to small cell however can be difficult and must be done at the correct time of year. It cannot be done either by simply putting 10 frames of small cell foundation in the hive. The bees must first be subject to regression over a period of several months.”

Do mites struggle to reproduce?

No. There’s compelling scientific evidence that Varroa levels in hives on small cell foundation may actually have higher mite levels than those on standard foundation. These are from properly conducted and controlled studies involving dozens of hives.

It certainly is claimed that mites struggle to reproduce in small cell foundation. The evidence actually directly contradicts these claims. Undoubtedly beekeepers in the USA have reported encouraging results, but scientists doing side-by-side comparisons clearly demonstrate that mite levels are at best not changed or at worst appreciably higher on small cell foundation.

Actually, it’s not the mites but our bees that struggle to reproduce in small cells. This explains the phrase “subject to regression over a period” above. You have to select smaller bees that can reproduce well in small cell foundation. Once this is done, the bee size is measurably smaller and the density of brood cells in the hive is greater.

Is this is a one-off study – where is the independent verification?

No. They were repeated at least three times by labs at the University of Georgia. Similar studies were conducted by Florida Department of Agriculture and Consumer services. In addition, the Ruakura Research Centre in Hamilton, New Zealand, conducted their own study – using a different experimental format – but achieving the same conclusions. Small cell foundation increased mite levels when compared with conventional or standard diameter foundation. There are now several additional independent studies which essentially reach the same conclusion – small cell foundation does not restrict Varroa replication and may actually increase it.

Has this new research been published?

Apidologie

Apidologie

After all, perhaps Thorne’s aren’t completely up-to-date about these studies? If the work is really new then perhaps they can be excused for trying to flog something for which there’s no compelling evidence of benefit.

Well, it was published … in some cases seven to nine years ago:

  1. Taylor, M.A., Goodwin, R.M., McBrydie, H.M., Cox, H.M. (2008) The effect of honeybee worker brood cell size on Varroa destructor infestation and reproduction. Journal of Apiculture Research 47, 239–242 … summary, a higher proportion of cells from small foundation were mite infested.
  2. Ellis, A.M., Hayes, G.W., Ellis, J.D. (2009) The efficacy of small cell foundation as a Varroa mite (Varroa destructor) control. Experimental and Applied Acarology 47, 311–316 … summary, no difference in mite levels between small cell and conventional foundation.
  3. Berry, J.A., Owens, W.B., Delaplane, K.S. (2010) Small-cell comb foundation does not impede Varroa mite population growth in honey bee colonies. Apidologie 41, 40–44 … summary, small cell colonies had ~40% higher mite infestation levels when compared with conventional foundation.
  4. Seeley, T.D., Griffin, S.R. (2011) Small-cell comb does not control Varroa mites in colonies of honeybees of European origin. Apidologie 42, 526-532 … summary, no difference in mite infestation levels between small cell and conventional foundation.

If you want an accessible and readable account of small cell foundation studies Jennifer Berry has written one for Bee Culture which includes experimental details of the work in references 1-3 above.

In denial

A recent thread on Beesource discussed the reported benefits of small cell foundation and the scientific evidence that contradicts these claims. It’s notable that supporters of small cell foundation generally criticise the ‘agenda’ they claim scientists have, rather than providing scientific evidence that supports the ‘benefits’. I’ve not been able to find a single peer-reviewed and properly controlled study that supports the beneficial claims for small cell foundation.

Hives on small cell foundation may have manageable levels of Varroa. If they do it’s in spite of the use of small cell foundation, not because of it. I am very willing to accept that there are some very competent beekeepers using splits, rational miticide treatment or other strategies and small cell foundation, who have low or manageable Varroa levels. However, it’s their beekeeping skill and experience not the choice of foundation size that is important here.

Indeed, you could argue that the detrimental enhancement to mite reproduction of small cell foundation, means that they must have truly exceptional beekeeping talents.

Or an agenda perhaps 😉

Ambiguous and misleading titles

In the opening paragraph I stated that the title 4.9 mm foundation for varroa control” was ambiguous. The scientific evidence presented above is that small cell foundation does control Varroa. Assuming you use the word ‘control’ when defined as the power to influence or direct the course of events. Small cell foundation does exert control … but almost certainly in the opposite direction to the way implied in the title.

What turns an ambiguous into a misleading title is this implication that small cell foundation reduces Varroa levels. The text that accompanies makes this implication without providing any sort of balanced view based upon the published evidence to the contrary.

Beekeepers, particularly beginners, looking for effective ways to reduce their mite levels are not being provided with the facts and are likely to be misled.

But wait … were all these scientific studies flawed?

Thorne’s partly justify the sale of small cell foundation in their newsletter by citing a UK research project that involves its use:

“The University of Reading has just started an exciting new research project examining the highly problematic issue of varroa mites and whether the use of small cell foundation (4.9 mm) can help. This is being carried out with volunteer beekeepers in the local area as well as in an apiary at the University. The study will evaluate the use of small cell foundation alongside regular-sized (5.4mm) foundation and compare the varroa loads during next spring and summer.

This is an interesting topic to research as beekeepers around the world have had success with the use of small cell foundation whereas many others have not. Some previous studies have also found that varroa counts increase in the short term when small cell foundation is first used. The new study will evaluate what happens once the bees have fully adjusted to small cell foundation and if there is a significant impact on varroa loads.”

The implication here is that the previous studies (above) are flawed because they failed to use bees that were properly adapted to small cell foundation. Thorne’s do clearly state that the bees have to be properly adapted – subjected to regression – for several months before benefits are seen (or claimed to be seen). To their credit also, they acknowledge that some studies show increases in mite levels. This text is from the newsletter and unfortunately does not appear on the webpage of their catalogue that describes the foundation.

Call me sceptical …

If it looks like a duck ...

If it looks like a duck …

As you can tell from the tone of this post, I remain sceptical.

If it looks like a duck, if it swims like a duck and if it quacks like a duck … it is a duck. As a scientist I’m influenced by controlled studies, not hearsay or beliefs.

The Berry study (ref 3 above) did use bees reared on small cell foundation for their comparative studies, the other studies did not as far as I can tell. However, remember the original hypothesis about why small cell foundation is beneficial. The mites do not develop properly within the cell as they are ‘crowded’ by the abdomen of the developing honey bee pupa i.e. there’s too little space for the mite.

What does regression lead to? Smaller bees. In the Berry et al., study the weights of adult bees reared on small cell and conventional foundation was 129 and 141 mg respectively. This seems to be contradictory … if properly regressed bees on small cell foundation are significantly smaller than those on conventional foundation how is the space for the mite development restricted? I acknowledge that the cell size is proportionately smaller than the reduction in adult bee weight. Conversely, if small cell foundation is supposed to restrict mite development, why are levels apparently higher when ‘normal’ sized bees are first forced to use smaller cells? Surely there should be a greater reduction in mite reproduction before the bees have regressed?

I hope the study being conducted by the University of Reading is thorough and properly controlled. These are difficult studies to conduct, particularly at the scale needed to be statistically convincing and when not under the direct control of a single beekeeper in a single apiary. I wish them every success with the experiments and look forward to reading about it once it is peer-reviewed and published.

Until then I suggest you save your £11.60 for ten sheets of small cell wired brood foundation … you’d be far better off preparing foundationless frames and controlling Varroa by rational and judicious use of hive manipulations and approved miticides.


Additional reading (far from exhaustive):

The late and still unbeatable Dave Cushman has an article by Philip Denwood reproduced from the 2003 BIBBA magazine on cell size. Recommended for a historical perspective.

A 2013 article from the New Hampsha’ Bees blog Small cell doesn’t work (but please don’t tell my bees describing typical evidence that small cell foundation does work … anecdotal and not controlled, but nevertheless enthusiastic and – unusually – acknowledging the evidence against.

Michael Bush on small cell bees and foundation.

Dee Lusby – one of the originators of the ‘small cell’ movement – in an early article from ABJ reproduced on the Beesource forums. Be warned … there’s some misleading nonsense in this article. For example “it is a known fact that both honey bees and mites have been on this Earth many millions of years together and survived quite nicely”. I don’t disagree that both mites and bees have been around for millennia. However, they have only been together for a century or so. I think I’ll have to write something about natural beekeeping in the future …

It’s notable that top Google ‘hits’ for small cell foundation provide no scientific support for the claims that are made … caveat emptor.

 

 

 

CSI: Forensics in Fife

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

It’s the viruses wot done it … probably.

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

Introduction

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

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

Mollycoddling weak colonies in the Spring … a wasted effort?

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

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

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

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

Learning from your losses

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

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

For example …

A life in the year of a June swarm

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

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

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

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

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

The autopsy

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

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

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

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

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

Elementary, my dear Watson

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

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

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

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

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

The damage was already done …

Miss Scarlett in the ballroom with the lead piping

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

DWV symptoms

DWV symptoms

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

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

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

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

Learning from my mistakes

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

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

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


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

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

Take one for the team

You know it makes sense

You know it makes sense

… would have been a much better title for an interesting recent paper on the impact of Varroa on honey bee colonies. More specifically, the snappily titled “Social apoptosis in honey bee super organisms” (Page et al., 2016 Scientific Reports 6: 27210 doi:10.1038/srep27210) attempts to answer how and why the natural host of Varroa, the Eastern honey bee (Apis cerana), copes with mite infestation whereas ‘our’ bees (Apis mellifera), the Western honey bee, succumbs within 2-3 years without mite-control? The paper is Open Access so you don’t need to pay to read it and you can find it here.

Only the good damaged die young 

The authors demonstrate that A. cerana mite-associated pupae die before they emerge, whereas those of A. mellifera do not. As a consequence of this the mite levels are unable to build up to damaging levels in the colony. Essentially the pupae on which the mites feed die very quickly, meaning the mite also dies. They determined this by uncapping and examining age-matched pupae one day before natural emergence (see below) in Varroa-infested or uninfested colonies. Varroa-associated pupae (upper row in the image below) had all died during pupation.

Infested (above) and control (below) A. cerana pupae

Infested (above) and control (below) A. cerana pupae

In an extension to this study the authors showed that puncturing pupae with a sterile glass needle and then re-sealing the cell (you can do this with gelatin) also results in the pupae dying. The needle used had the same diameter as the chelicerae of the Varroa mite, so this treatment recapitulated the physical damage caused by the mite. Since the needle was sterile it was unlikely that the pupae were dying from exposure to the viruses (or other pathogens) transmitted by the Varroa mite. Instead, it seems that the Eastern honey bee has evolved mechanisms of “self-sacrifice” in response to wounding that result in the death of damaged pupae before the infesting mite has had a chance to multiply. Clever.

Social apoptosis

Apoptosis is the term used by cell biologists to describe a series of events that are also called programmed cell death seen, for example, in virus-infected cells. If a cell detects that it is virus infected, a cascade of signalling events result in it undergoing apoptosis (it dies), so preventing the infecting virus from replicating properly and spreading to neighbouring cells in the organism. Social apoptosis is a similar process, the death of an infected – or infested – member of the superorganism, the honey bee colony.

Immunity is a term meaning ‘having resistance to’, for example immunity to measles due to prior vaccination or infection. Generally, immunity is a reflection of strength of the recipient or exposed to the ‘abuse’ caused by the infectious agent. In contrast, the mechanism described for A. cerana is the opposite of this, instead being a form of immunity through weakness or susceptibility.

A. cerana has additional resistance mechanisms that help it combat Varroa infestation including enhanced grooming, removal of mites from unsealed brood, entombing multiply mite-associated drone brood (it’s not clear to me whether this is the same mechanism as the social apoptosis reported here), increased hygienic behaviour and shorter developmental cycles. These will have evolved over the millennia that the mite and bee have associated.

Any chance A. mellifera will evolve a similar mechanism?

Possibly, but I’m not holding my breath. There are already hygienic strains of A. mellifera – for example, VSH bees developed by the USDA group at Baton Rouge. These typically uncap and discard Varroa-associated pupae. This isn’t the same process as the social apoptosis reported here in A. cerana. The latter pupae die prematurely, thereby preventing mite reproduction. While we’re on the subject of Varroa and genetic resistance – do VSH A. mellifera strains open and discard mite-associated pupae … a) early enough to prevent significant levels of mite replication, and b) without releasing progeny mites from the cells they were raised in? I’m aware of the rates at which they clear out Varroa infested cells, but not either the timing of these events or the fate of any Varroa released at the same time.

It’s difficult to imagine a practical strategy to select for A. mellifera honey bee pupae that are more sensitive to Varroa infestation … our bees are currently too robust.


Billy Joel wrote Only the good die young which appeared on his 1977 album The Stranger. “[Not] so much anti-Catholic as pro-lust” Joel explained when it was censored, inevitably ensuring its chart success. The song has more to do with the birds and the bees …  😉

 

Same time, next year

About this time last year a swarm arrived in a bait hive in my back garden in Fife. Almost exactly one year later a different bait hive in the same spot was occupied by another swarm … or, possibly, a very good-sized cast.

The bait hive was being investigated by scout bees for a few days but on 6th, which was a very warm day here in Fife, the numbers increased markedly from a couple of dozen to a hundred or more. On my return from work on the following day the swarm was in residence. My neighbour reported seeing a ‘huge swarm arriving’ at about 11am.

Foundationless frames and bait hives

The hive contained a single old, dark brood frame and about five foundationless frames, together with a cotton bud dipped in lemongrass oil. I’ve previously described why I think foundationless frames are so convenient for bait hives – they provide the bees with guides to build new comb without taking up significant space in the box. It’s worth remembering that the scout bees are seeking out a sheltered, south facing, bee-smelling (ideally), empty space of about 40 litres volume i.e. about the same as a single National brood box. Foundationless frames take up little space, but mean that an arriving swarm can start building new comb immediately … and they do.

I posted a photo last week of a swarm from the bee shed that had clustered because the queen was clipped and so unable to fly. I dealt with the swarm within a couple of hours of it settling. Once cleared, the wall of the bee shed was dotted with small crescents of wax as the bees had already started to build new comb. In the bait hive, when checked on the evening of the 8th (less than 48 hours after the bees arrived) they were well on their way to drawing out the first three foundationless frames, with the first of these being half full of nectar, presumably from the dregs available in the nearby OSR fields.

Mite treatment be needed?

Almost certainly … and there’s no better time. When swarms leave a hive they take with them up to 35% of the Varroa population as phoretic mites. A large swarm from a heavily infested hive can therefore introduce an unhealthy dose of virus-riddled mites to your apiary. These will rapidly spread to your other hives. I therefore routinely treat swarms with suitable miticides soon after they arrive, well before any brood is sealed. I don’t look for DWV symptoms or bother searching for signs of phoretic mites, I just treat. Due to work commitments this swarm had to be treated on the third day after arrival, before I was even certain whether the queen was laying or not. Within the first 24 hours after treatment (with sublimated oxalic acid) there were about 40-50 mites on the board, with more falling over the next couple of days. It’s far easier and more effective to treat when there’s no brood present and so give the colony the very best chance of getting well established without a pathogenic virus load.

Finally, after a day of heavy rain, I took advantage of the bees being all ‘at home’, sealed the entrance and relocated them to another apiary to make space for a replacement bait hive on the same spot … on the off chance that swarming here isn’t over yet.

If it is, then there’s always the same time, next year.


Same time, next year was a 1978 romantic comedy starring Alan Alda and Ellen Burstyn about a couple, married to others, who meet by chance, develop an “instant rapport” or at least “really hit it off” (one of the quotes from the film) and then meet again, year after year, both gradually changing, ageing and dealing with life’s crises.

Keep your distance

A recent paper by Nolan and Delaplane (Apidologie 10.1007/s13592-016-0443-9) provides further evidence that drifting/robbing between colonies is an important contributor to Varroa transmission. In the study they established multiple pairs of essentially Varroa-free colonies 0, 10 or 100 metres apart and then spiked one of the pair with a known number of Varroa. They then monitored mite build-up in the paired colonies over several months. By comparison of the relative mite increases in colonies separated by different distances they showed that the more closely spaced, the more likely they were to acquire more Varroa, presumably through robbing or drifting.

This isn’t rocket science. However, it’s a nicely-conducted study and emphasises the importance of colony spacing on the transmission of phoretic mites between infested and uninfested colonies – through the normal colony activities such as robbing and drifting – as a primary cause of deformed wing virus (DWV) disease spread in the honey bee population. The paper only studies mite levels, but the association with DWV transmission is well established and unequivocal.

Related studies on the influence of colony/apiary separation

The introduction to the paper provides a good overview of the prior literature on the impact of drifting on disease and Varroa transmission, some of which has already been discussed here. However, some of these studies have not previously been mentioned and deserve an airing, for example:

  • Sakofski et al., (1990) showed that there was no difference in mite migration between colonies in closely-spaced rows from those located up to 10m apart.
  • Frey and Rosenkranz (2014) showed that high-density colonies (>300 within flight range [2.5 km] of the sentinel colonies) experienced approaching 4-fold greater inbound mite migration than when located in areas containing a low-density of treated colonies. Over a 3.5 month period the difference was 462 +/- 74 vs. 126 +/- 16 mites. This would have a very significant impact if allowed to subsequently replicate in the recipient colonies.
  • Frey et al., (2011) previously investigated mite transfer between colonies located 1m to 1500m apart. Strikingly, in this study (which was conducted during a dearth of nectar) mite transmission was effectively distance-independent, with the recipient colonies acquiring 85 – 444 mites over a 2 month period.
Frey and Rosenkranz (2014) Mite invasion ...

Frey and Rosenkranz (2014) Mite invasion …

What can we conclude from these studies?

  1. Closely-spaced colonies – for example, the sort of distances used to separate colonies in an apiary – should really be viewed as a single location as far as mite infestation is concerned. A single heavily-infested colony in an apiary will quickly act as a source of mites to all other colonies.
  2. High densities of beekeepers – assuming the usual range in both the timing and vigour with which Varroa control is practised – is probably detrimental to maintaining low mite levels in your own bees.
  3. Significant mite transmission occurs over distances of at least 1.5 km … not just between hives in a single apiary. How many colonies are there within 1.5 km of your own apiary? Even if you are careful about controlling mite levels, what about all the beekeepers around you?
  4. Colonies wth uncontrolled levels of mite infestation, abandoned colonies (or swarms that occupy abandoned hives) and feral colonies located at least 1.5 km away are potential sources from which your carefully-maintained hives get re-infested …

Recent experience with high and low density beekeeping

One mile radius ...

One mile radius …

I’ve moved in the last year from the Midlands to Fife. Beebase and my involvement with local beekeepers suggest that these represent areas of high and low colony-density respectively. For comparison, Beebase indicates that there were over 230 apiaries within 10 km of my home apiary in the Midlands and that there are currently 20 within a similar range in Fife. In the Midlands I was aware of at least 25 colonies (in several different apiaries) within a mile of one of my apiaries. Furthermore, apiaries might contain lots of hives … one of those previously within 10 km of my home apiary was our association apiary which held up to 30 colonies from ~15 beekeepers. In contrast, the closest beekeeper to my current home apiary is almost 3km away … though I acknowledge there may well be hives “under the radar” belonging to beekeepers that are not members of the local association or have not bothered to registered on Beebase (why not?). It’s far too early to be definitive but mite levels in my colonies have been reassuringly low this season. This includes uncapping hundreds of drone pupae – the preferred site for Varroa to replicate – without detecting a single mite. I’d like to think this was due to timely and effective Varroa control, but it is undoubtedly helped because my neighbours are further away … and perhaps better at controlling the mite levels in their own colonies.

This study provides further compelling evidence of the importance of either keeping colonies isolated (which may not be possible) and ensuring that all colonies in the same and adjacent apiaries are coordinately treated during efforts to control mite numbers.

Gaffer tape apiary

Gaffer tape apiary …