Tag Archives: Correx

Winter covers and colony survival

Synopsis : A recent study shows increased overwinter colony survival of ‘covered’ hives wrapped in Correx and with insulation under the roof. What provides the most benefit, and are the results as clear cut as they seem?

Introduction

A recent talk by Andrew Abrahams to the Scottish Native Honey Bee Society coincided with me catching up my 1 backlog of scientific papers on honey bees. I’d been reading a paper on the benefits of wrapping hives in the winter and Andrew commented that he did exactly that to fend off the worst of the wet weather. Andrew lives on the island of Colonsay about 75 km south of me and we both ‘benefit’ from the damp Atlantic climate.

The paper extolled the virtues of ‘covered’ hives and the data the researchers present looks, at first glance, compelling.

For example, <5% of covered hives perished overwinter in contrast to >27% of the uncovered control hives.

Wow!

Why doesn’t everyone wrap their hives?

However, a closer look at the paper raises a number of questions about what is actually benefitting (or killing) the colonies.

Nevertheless, the results are interesting. I think the paper poses rather more questions than it answers, but I do think the results show the benefits of hive insulation and these are worth discussing.

Bees don’t hibernate

Hibernation is a physiological state in which the metabolic processes of the body are significantly reduced. The animal becomes torpid, exhibiting a reduced heart rate, low body temperature and reduced breathing. Food reserves e.g. stored fat, are conserved and the animal waits out the winter until environmental conditions improve.

However, bees don’t hibernate.

Winter cluster 3/1/21 3°C (insulation block removed from the crownboard)

If you lift the lift the roof from a hive on a cold midwinter day you’ll find the bees clustered tightly together. But, look closely and you’ll see that the bees are moving. Remove the crownboard and some bees will probably fly.

The cluster conserves warmth and there is a temperature gradient from the outside – termed the mantle – to the middle (the core).

If chilled below ~5.5°C a bee becomes semi-comatose 2 and unable to warm herself up again. The mantle temperature of the cluster never drops below ~8°C, but the core is maintained at 18-20°C when broodless or ~35°C if they are rearing brood. I’ve discussed the winter cluster in lots more detail a couple of years ago.

The metabolic activity of the clustered winter bees is ‘powered’ by their consumption of the stores they laid down in the autumn. It seems logical to assume that it will take more energy (i.e. stores) to maintain a particular cluster temperature if the ambient temperature is lower.

Therefore, logic would also suggest that the greater the insulation properties of the hive – for a particular difference in ambient to cluster temperature – the less stores would be consumed.

Since winter starvation is bad for bees (!) it makes sense to be thinking about this now, before the temperatures plummet in the winter.

Cedar and poly hives

I’m not aware of many comparative studies of the insulation properties of hives made from the two most frequently used materials – wood and polystyrene. However, Alburaki and Corona (2021) have investigated this and shown a small (but statistically significant) difference in the inner temperature of poly Langstroth hives when compared to wooden ones.

Poly hives were ~0.5°C warmer and, perhaps more importantly, exhibited much less variation in temperature over a 24 hour period.

Temperature and humidity in poly and wood hives

In addition to the slight temperature difference, the humidity within the wooden hives was significantly higher than that of poly.

The hives used in this study were occupied by bees and the temperature and humidity were recorded from sensors placed in a modified frame in the ‘centre of the brood box’. The external ambient temperature averaged 0°C, but fluctuated over a wide range (-10°C to 20°C) during the four month study 3.

Temperature anomalies

Whilst I’m not surprised that the poly hives were marginally warmer, I was surprised how low the internal hive temperatures were. The authors don’t comment on whether the ‘central’ frame was covered with bees, or whether the bees were rearing brood.

The longitudinal temperature traces (not reproduced here – check the paper) don’t help much either as they drop in mid-February when I would expect brood rearing to be really gearing up … Illogical, Captain.

The authors avoid any discussion on why the average internal temperature was at least 5-8°C cooler than the expected temperature of the core of a clustered broodless colony, and ~25°C cooler than a clustered colony that was rearing brood.

My guess is that the frame with the sensors was outside the cluster. For example, perhaps it was in the lower brood box 4 with the bees clustered in the upper box?

We’ll never know, but let’s just accept that poly hives – big surprise 😉 – are better insulated. Therefore the bees should need to use less stores to maintain a particular internal temperature.

And, although Alburaki and Corona (2021) didn’t measure this, it did form part of a recent study by Ashley St. Clair and colleagues from the University of Illinois (St. Clair et al., 2022).

Hive covers reduce food consumption and colony mortality

This section heading repeats the two key points in the title of this second paper.

I’ll first outline what was done and describe these headline claims in more detail. After that I’ll discuss the experiments in a bit more detail and some caveats I have of the methodology and the claims.

I’ll also make clear what the authors mean by a ‘hive cover’.

The study was conducted in central Illinois and involved 43 hives in 8 apiaries. Hives were randomly assigned to ‘covered’ or ‘uncovered’ i.e. control – groups (both were present in every apiary) and the study lasted from mid-November to the end of the following March.

Ambient (blue), covered (black) and control (dashed) hive temperatures

There were no significant differences in internal hive temperature between the two groups and – notably – the temperatures were much higher (15°-34°C) than those recorded by Alburaki and Corona (2021).

All colonies, whether covered or uncovered, got lighter through the winter, but the uncovered colonies lost significantly more weight once brood rearing started February. The authors supplemented all colonies with sugar cakes in February and the control colonies used ~15% more of these additional stores before the study concluded.

I don’t think any of these results are particularly surprising – colonies with additional insulation get lighter more slowly and need less supplemental feeding.

The surprising result was colony survival.

Less than 5% (1/22) of the covered hives perished during the winter but over 27% (6/21) of the control hives didn’t make it through to the following spring.

(Un)acceptable losses

To put these last figures into context the authors quote a BeeI Informed Partnership survey where respondents gave a figure of 23.3% as being ’acceptable’ for winter colony losses.

That seems a depressingly high figure to me.

However, look – and weep – at the percentage losses across the USA in the ’20/’21 winter from that same survey 5.

Bee Informed Partnership 2021 winter colony losses (preliminary data)

This was a sizeable survey involving over 3,300 beekeepers managing 192,000 colonies (~7% of the total hives in the USA).

If hive covers reduce losses to just 5% why does Illinois report winter losses of 47%? 6

Are the losses in this manuscript suspiciously low?

Or, does nobody use hive covers?

I don’t know the answers to these questions, but I also wasn’t sure when I started reading the paper what the authors meant by a hive ‘cover’ … which is what I’ll discuss next.

Hive covers

The hives used in this study were wooden Langstroths and the hive covers were 4 mm black corrugated polypropylene sleeves.

This is what I call Correx … one of my favourite materials for beekeeping DIY.

These hive covers are available commercially in the USA (and may be here, I’ve not looked). At $33 each (Yikes) they’re not cheap, but how much is a colony worth?

Significantly more than $33.

I’ve not bothered to make the conversion of Langstroth Deep dimensions (always quoted in inches 🙁 ) to metric and then compared the area of Correx to the current sheet price of ~£13 … but I suspect there are savings to be made by the interested DIYer 7.

However, knowing (and loving) Correx, what strikes me is that it seems unlikely to provide much insulation. At only 4 mm thick and enclosing an even thinner air gap, it’s not the first thing I’d think of to reduce heat loss 8.

4 mm Correx sheet

Thermal resistance is the (or a) measure of the insulating properties of materials. It’s measured in the instantly forgettable units of square metre kelvin per watt m2.K/W.

I couldn’t find a figure for 4 mm Correx, but I did manage to find some numbers for air.

A 5 mm air gap – greater than separates the inner and outer walls of a 4 mm Correx hive cover – has a thermal resistance of 0.11 m2.K/W.

Kingspan

It’s not possible to directly compare this with anything meaningful, but there is data available for larger ‘thicknesses’ of air, and other forms of insulation.

An air gap of 100 mm has a thermal resistance of about 0.17 m2.K/W. For comparison, the same thickness of Kingspan (blown phenolic foam wall insulation, available from almost any building site skip) has a thermal resistance of 5, almost 30 times greater.

And, it turns out, St. Clair and colleagues also added a foam insulation board on top of the hive crownboard (or ‘inner cover’ as they call it in the USA). This board was 3.8 cm thick and has somewhat lower thermal resistance than the Kingspan I discussed above.

It might provide less insulation than Kingspan, but it’s a whole lot better than Correx.

This additional insulation is only briefly mentioned in the Materials and Methods and barely gets another mention in the paper.

A pity, as I suspect it’s very important.

Perspex crownboard with integrated 50 mm Kingspan insulation

I’m very familiar with Kingspan insulation for hives. All my colonies have a 5 cm thick block present all year – either placed over the crownboard, built into the crownboard or integrated into the hive roof.

Two variables … and woodpeckers

Unfortunately, St. Clair and colleagues didn’t compare the weight loss and survival of hives ‘covered’ by either wrapping them in Correx or having an insulated roof.

It’s therefore not possible to determine which of these two forms of protection is most beneficial for the hive.

For reasons described above I think the Correx sleeve is unlikely to provide much direct thermal insulation.

However, that doesn’t mean it’s not beneficial.

At the start of this post I explained that Andrew Abrahams wraps his hives for the winter. He appears to use something like black DPM (damp proof membrane).

Hive wrapped in black DPM (to prevent woodpecker damage)

Andrew uses it to keep the rain off the hives … I’ve used exactly the same stuff to prevent woodpecker damage to hives during the winter.

It’s only green woodpeckers (Picus viridis) that damage hives. It’s a learned activity; not all green woodpeckers appear to know that beehives are full of protein-rich goodies in the depths of winter. If they can’t grip on the side of the hive they can’t chisel their way in.

When I lived in the Midlands the hives always needed winter woodpecker protection, but the Fife Yaffles 9 don’t appear to attack hives.

Here on the west coast, and on Colonsay, there are no green woodpeckers … and I know nothing about the hive-eating woodpeckers of Illinois.

So, let’s forget the woodpeckers and return to other benefits that might arise from wrapping the hive in some form of black sheeting during the winter.

Solar gain and tar paper

Solar gain is the increase in thermal energy (or temperature as people other than physicists with freakishly large foreheads call it) of something – like a bee hive – as it absorbs solar radiation.

On sunny days a black DPM-wrapped hive (or one sleeved in a $33 Correx/Coroplast hive ‘cover’) will benefit from solar gain. The black surface will warm up and some of that heat should transfer to the hive.

And – in the USA at least – there’s a long history of wrapping hives for the winter. If you do an internet search for ‘winterizing hives’ or something similar 10 you’ll find loads of descriptions (and videos) on what this involves.

Rather than use DPM, many of these descriptions use ‘tar paper’ … which, here in the UK, we’d call roofing felt 11.

Roofing felt – at least the stuff I have left over from re-roofing sheds – is pretty beastly stuff to work with. However, perhaps importantly, it has a rough matt finish, so is likely to provide significantly more solar gain than a covering of shiny black DPM.

I haven’t wrapped hives in winter since I moved back to Scotland in 2015. However, the comments by Andrew – who shares the similarly warm and damp Atlantic coastal environment – this recent paper and some reading on solar gain are making me wonder whether I should.

Fortunately, I never throw anything away, so should still have the DPM 😉

Winter losses

Illinois has a temperate climate and the ambient temperature during the study was at or below 0°C for about 11 weeks. However, these sorts of temperatures are readily tolerated by overwintering colonies. It seems unlikely that colonies that perished were killed by the cold.

So what did kill them?

Unfortunately there’s no information on this in the paper by St. Clair and colleagues.

Perhaps the authors are saving this for later … ’slicing and dicing’ the results into MPU’s (minimal publishable units) to eke out the maximum number of papers from their funding 12, but I doubt it.

I suspect they either didn’t check, checked but couldn’t determine the cause, or – most likely – determined the cause(s) but that there was no consistent pattern so making it an inconclusive story.

But … it was probably Varroa and mite-transmitted Deformed wing virus (DWV).

It usually is.

Varroa

There were some oddities in their preparation of the colonies and late-season Varroa treatment.

Prior to ‘winterizing’ colonies they treated them with Apivar (early August) and then equalised the strength of the colonies. This involves shuffling brood frames to ensure all the colonies in the study were of broadly the same strength (remember, strong colonies overwinter better).

A follow-up Varroa check in mid-October showed that mite levels were still at 3.5% (i.e. 10.5 phoretic mites/300 bees) and so all colonies were treated with vaporised oxalic acid (OA).

Sublimox vaporiser

Sublimox vaporiser … phoretic mites don’t stand a chance

In early November, mite levels were down to a more acceptable 0.7%. Colonies received a second OA treatment in early January.

For whatever reason, the Apivar treatment appears to have been ineffective.

When colonies are treated for 6-10 weeks with Apivar (e.g. early August to mid-October) mite levels should be reduced by >90%.

Mite infestation levels of 3.5% suggest to me that the Apivar treatment did not work very well. That being the case, the winter bees being reared through August, September and early October would have been exposed to high mite levels, and so acquired high levels of DWV.

OA treatment in mid-October would kill these remaining mites … but the damage had already been done to thediutinus’ winter bees.

That’s my guess anyway.

An informed guess, but a guess nevertheless, based upon the data in the paper and my understanding of winter bee production, DWV and rational Varroa management.

In support of this conclusion it’s notable that colonies died from about week 8, suggesting they were running out of winter bees due to their reduced longevity.

If I’m right …

It raises the interesting question of why the losses were predominantly (6 vs 1) of the control colonies?

Unfortunately the authors only provide average mite numbers per apiary, and each apiary contained a mix of covered and control hives. However, based upon the error bars on the graph (Supporting Information Fig S1 [PDF] if you’re following this) I’m assuming there wasn’t a marked difference between covered and control hives.

I’ve run out of informed guesses … I don’t know the answer to the question. There’s insufficient data in the paper.

Let’s briefly revisit hive temperatures

Unusually, I’m going to present the same hive temperature graph shown above to save you scrolling back up the page 13.

Ambient (blue), covered (black) and control (dashed) hive temperatures

There was no overall significant difference in hive temperature between the control and covered colonies. However, after the coldest weeks of the winter (7 and 8 i.e. the end of February), hive temperatures started to rise and the covered colonies were consistently marginally warmer. By this time in the season the colonies should be rearing increasing amounts of brood.

I’ve not presented the hive weight changes. These diverged most significantly from week 8. The control colonies used more stores to maintain a similar (actually – as stated above – marginally lower) temperature. As the authors state:

… covered colonies appeared to be able to maintain normal thermoregulatory temperatures, while consuming significantly less stored food, suggesting that hive covers may reduce the energetic cost of nest thermoregulation.

I should add that there was no difference in colony strength (of those that survived) between covered and control colonies; it’s not as though those marginally warmer temperatures from week 9 resulted in greater brood rearing.

Are lower hive temperatures ever beneficial in winter?

Yes.

Varroa management is much easier if colonies experience a broodless period in the winter.

A single oxalic acid treatment during this broodless period should kill 95% of mites – as all are phoretic – leaving the colony in a very good state for the coming season.

If you treat your colonies early enough to protect the winter bees there will inevitably be some residual mite replication in the late season brood, thereby necessitating the midwinter treatment as well.

I’m therefore a big fan of cold winters. The colony is more likely to be broodless at some point.

I was therefore reassured by the similarity in the temperatures of covered and control colonies from weeks 48 until the cold snap at the end of February. Covered hives should still experience a broodless period.

I’m off for a rummage in the back of the shed to find some rolls of DPM for the winter.

I don’t expect it will increase my winter survival rates (which are pretty good) and I’m not going to conduct a controlled experiment to see if it does.

If I can find the DPM I’ll wrap a few hives to protect them from the winter weather. With luck I should be able to rescue an additional frame or two of unused stores in the spring (I often can anyway). I stack this away safely and then use it when I’m making up nucs for queen mating.

I suspect that the insulation over the crownboard provides more benefit than the hive ‘wrap’. As stated before, all my colonies are insulated like this year round as I’m convinced it benefits the colony, reducing condensation over the cluster and keeping valuable warmth from escaping. However, wrapping the hive for solar gain and/or weather protection is also worth considering.


References

Alburaki, M. and Corona, M. (2022) ‘Polyurethane honey bee hives provide better winter insulation than wooden hives’, Journal of Apicultural Research, 61(2), pp. 190–196. Available at: https://doi.org/10.1080/00218839.2021.1999578.

St. Clair, A.L., Beach, N.J. and Dolezal, A.G. (2022) ‘Honey bee hive covers reduce food consumption and colony mortality during overwintering’, PLOS ONE, 17(4), p. e0266219. Available at: https://doi.org/10.1371/journal.pone.0266219.

Less is more

The season here started late after a a long, cold spring, and it’s giving every impression of ending early. A couple of low pressure systems have slowly drifted in from the west, replacing the settled calm weather with something a lot more changeable.

On the west coast of Scotland the heather has still to really get started. That is if it’s going to get started at all 🙁

It was so dry earlier in the summer that the recent rain may be too little, too late. I’m not unduly worried as I’m busy making bees rather than making honey this year.

Although the temperature hasn’t dropped much 1 it’s starting to feel quite autumnal. 

Siskin

The mixed woodland around us is now quiet most of the time, with very few small birds about. When you do see them, siskin and goldfinch are starting to form large jittery flocks, bounding away at the slightest provocation. The longer nights 2 are busy with the calls of tawny owls as the young leave the nest.

My infrequent visits to the east coast are short and packed with beekeeping and work commitments so I see much less wildlife. However, it’s very clear that the season is ‘all over bar the shouting’. The bees are getting defensive, there are lots of wasps about and the nectar flow is finished.

Let the heavy lifting begin … and Correx

On my last visit to Fife I cleared the supers and removed them for extraction.

I’ve described my clearer boards before 3. They have no moving parts, a deep lower rim providing space for the bees to clear to, and two well-separated exits.

Clearer boards

Clearer boards …

I usually try and clear all the hives in a single apiary at once. It increases the workload, but it saves making more than two visits. This of course means that I need sufficient clearer boards for every hive in the apiary … and on this trip I didn’t 4.

At the last minute I therefore built a few extra using Correx, some butchered rhombus escapes, spare ekes and gaffer tape. 

Quick fix clearer board – hive side

If you’re going to do this here are a couple of tips:

  1. Do not use standard 3M gaffer tape as sold in the ‘Middle of Lidl’ and elsewhere. It can’t cope with the warmth and humidity of the hive – at least when stuck to Correx – and the escape usually detaches within 24 hours. Unsurprisingly these things work a whole lot less well (i.e. not at all) without the rhombus escape. The best gaffer tape I’ve found for Correx is Unibond Power Tape (which is waterproof and very long lasting).
  2. Don’t try and save time/save rhombus escapes/cut corners by using only one exit hole and half a rhombus escape. The hives I tried this with still had hundreds of bees in the supers. Don’t say I didn’t warn you 😉

I have to transport all my supers to the west coast for extraction. Emptying them of bees, keeping the wasps away and loading them into my little car was a fraught and exhausting process.

More Correx

Whatever the opposite of a hot hatchback is … is what I drive.

It’s a great little car and very economical 5.  However, it’s not really ideal as a beemobile. I can only get a maximum of about 16 supers in it whilst still being able to see out of at least some of the windows.

To save the already filthy upholstery from contaminating all that lovely honey in the supers I use more Correx …

The multi-purpose Correx hive roof

… in this case an upturned Correx hive roof.

These are simplicity itself to construct using Correx and more Unibond Power Tape. Correx is remarkably UV resistant and I have roofs originally built in 2013/14 still going strong. A single 1.2 x 2.4 m sheet of Correx will yield half a dozen roofs and cost you the grand sum of about £1.70 each 6.

When you’re clearing and transporting supers these lightweight roofs/trays are invaluable. They keep the wasps out of the top of the stack and stop the honey dripping out of the bottom.

And a bit more Correx

It’s much easier to extract honey if it’s warm. I therefore stack the supers on top of my honey warming cabinet until I’m ready to do the extracting … or until my back recovers after lifting all those supers off the hives and into the car.

Honey supers waiting to be extracted

I built my honey warming cabinet several years ago. It is probably one of the most useful (and used) pieces of beekeeping ‘stuff’ I’ve got. It’s got excellent temperature control and I’ve even used it to incubate queen cells. However, it is primarily used for honey and every bucket I process and jar goes through it, often more than once 7.

Because of the size of available plywood sheet, the depth needed to house the element and insulation, coupled with a generous helping of my incompetence, I built the cabinet slightly too small. 

This resulted in the classic ‘good news and bad news’.

The good news is that I don’t need to be absolutely precise in terms of positioning the edge of the supers on the thin upper edges of the cabinet. Any mistakes here would result in the insulation getting crushed. 

The bad news is that some supers can leave a slight gap at the bottom through which heat escapes. This depends upon the particular design of the supers. Paradise/Denrosa poly supers and Abelo supers are reasonably flat on the underside, but red cedar boxes leave lots of unwanted gaps.

Correx gap-filler on the honey warming cabinet

A simple shim of Correx is an easy solution to this issue. As an added benefit, this also stops the upper edges of the cabinet from getting sticky.

A wheely useful trolley

A honey warming cabinet takes up quite a bit of space when not in use. Mine conveniently fits onto a robust ‘trolley’ that allows me to easily wheel it out of the way when needed.

Wheely useful trolley under the honey warming cabinet

When pre-warming supers for extraction it has to be moved off this onto the floor. The 18 supers in the picture above probably weigh over 300 kg. Neither the tiled floor nor the castors would be able to support this.

However, when just warming a couple of buckets of OSR honey prior to creaming this allows me to tuck the cabinet out of the way until needed.

I’ve got a couple of these trolleys. I stack the empty supers on them after extraction and so can move them about without excess bending and lifting.

Extracting

I uncap supers using a hot air gun. This is fast and efficient. The cappings melt almost instantaneously but can generate wax ‘shrapnel’ which tends to fly off in all directions. I strongly recommend wearing an apron to avoid getting peppered with tiny specs of molten wax.

A 10 frame super … but I actually squeezed the bottom one in from another box.

Almost all my supers are arranged to contain 9 frames. I start them with 11, reduce them to 10 once the comb is drawn, and take one more frame out once they start fattening up. Drawn super comb is reused year after year and it’s always nice to see a frame dated a decade or more ago going though the extractor. 

The 9 frames in a super conveniently fills my 9 frame extractor (funny that). Of course, sometimes the bees fail to completely fill the outer frames, so there may be a little juggling to try and get the machine reasonably well balanced before starting the run.

It’s surprising how quickly you learn to judge the weight of a filled frame and to calculate where it should be placed in the extractor to achieve the best balance.

‘Best’ as in ‘best that can be achieved with these 9 frames without spending an interminable amount of time shifting the frames about’.

Thank goodness for extractors on castors 🙂

Rubber-wheeled castor with brake

An unbalanced extractor on castors gently wiggles back and forth, rather than walking boldly across the room. Leave the castors unbraked during use.

My extractor is pretty basic. On/off and speed control. No timed runs or other snazzy settings. Because some honey extracts more easily (perhaps because it was lower down in the stack of warming supers?) I use an LED headtorch 8 to look down the inner sidewall of the machine to judge when I should stop the run.

Extractor and headtorch

You can see the drops of honey hitting the sidewall as tiny pinpricks of reflected light. Once they’ve reduced to almost nothing I reverse the machine for a minute or two, or remove the frames and reload it.

Why is less more?

As I suggested in the opening paragraph, this has felt like a very short season. Because of my move to the west coast I’ve also got far fewer honey production colonies this year than any time in the last decade.

Nevertheless, it’s been an outstanding year for honey 🙂

My total crop is the best I’ve had since returning to Scotland in 2015, though this was largely due to a fantastic spring harvest. I’m also hopeful there may be a little bit of heather honey before the end of the season … we’ll see.

The priority now is to ensure that the bees are given sufficient fondant to store for the winter ahead, and that the mites are treated promptly and effectively. I’ll write about these important aspects of preparing for winter in the next week or three.

But before I go …

With all those winter bees to rear over the next couple of months the colony will need lots of pollen. 

The United colours of Benetton pollen in one of my hives

This frame made me smile. I counted just 20 developing larvae in the centre, surrounded by a pointillist sea of different pollen types. These will be well-nourished bees 🙂

Although not absolute, the bees tend to store similar pollens in individual cells. Since it takes many corbiculae-full to fill one cell this must involve a degree of ‘sorting’ by the bees during pollen storage. This all happens in the dark, so presumably is based upon a characteristic other than the colour of the pollen.

Pollen close up

I don’t know how they do this but will read a bit more during the winter and report back. This was one of the outer frames in the colony. Most of the rest are still packed with brood, ensuring the colonies will be strong going into the winter.

Wasps are starting to pester the hives. On the west coast I have several colonies recently promoted from nucs to a full hive. Most are in hives with kewl floors 9 which have an L-shaped tunnel entrance, making them easier to defend.

However, to improve things further I often add an entrance reducer. The ‘roof’ of the horizontal part of the L-shaped entrance has two small screws set into it 10 which act as ‘stops’ for the entrance reducer which I build out of the bottom bar of a frame.

A case of misdirection …

My quality control is a bit shonky and these reducers sometimes fit rather poorly. To make them a better fit I added a few wraps of gaffer tape. Initially I used black tape. However, it was clear that this looked sufficiently like the dark entrance to the hive that the bees were getting ‘misdirected’ away from the real entrance to the black tape.

That’s better …

To avoid further confusion I added an overwrap of a lighter coloured tape. All of which resulted in me revisiting some of the scientific literature on bee vision … which I’ll save for another day.


 

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).

 

Split boards

Since moving to Scotland my DIY activities have been restricted – by lack of time, by lack of space and by lack of any major shortages in the equipment I use. However, a couple of spare sheets of Correx became available after some non-bee projects and I decided to use them to knock up a few split boards for swarm control and requeening this season.

As an aside … I love Correx. It makes great roofs, temporary floors and landing boards.

Split boards are simple square boards with beespace both sides and – usually – a single entrance. With an entrance door (rather than a simple gap) closed they can double up as crownboards or can be used to stack supers late in the season.

They can also be built with mesh panels to allow the warmth and smell of the lower colony to spread through the hive. However, in this instance these were to be about as simple as possible so I omitted the mesh.

Opposing entrances

For additional flexibility you can provide two opposing entrances with doors. With these the split board is starting to look dangerously like a cut down Snelgrove board. The vertical split method I use involves turning the hive 180° on the seventh day. With opposing entrances on the split board (and a corresponding double-entrance floor) it’s possible to avoid any heavy lifting – simply close the front door and open the rear door on the split board and vice versa on the floor.

Split board ...

Split board …

Assembly instructions

Really? How simple could it be?

I don’t have a table saw (or space to hide store it) so asked the nice people at Haldane’s in Glenrothes to generate some 20mm x 9mm strip wood. They did this from oak (!) offcuts for about a tenth the price one of the DIY chain stores would charge for equivalent softwood. The latter would have been preferable, not least because I got some wicked splinters from the oak, but it was what they had to hand and would have otherwise gone to the wood burner.

The Correx I had was 4mm thick. I’d have preferred 6mm, but as this was ‘spare’ from another project, I had to make do. I was originally going to use two sheets arranged at 90° to each other to provide rigidity. However, the first single-sheet prototype I built was plenty rigid enough so I stuck with that design.

Corner detail ...

Corner detail …

I cut the oak strips to 44cm in length, arranged them around the periphery of the 46 x 46cm Correx sheet and nailed all but two – on opposing sides of the top face – in place. ‘Overlap’ the corners (see image right) to provide additional strength. It’s worth noting here that my nail gun was only just strong enough to penetrate ~20mm of oak. The few nails that protruded were driven home with a hammer, brute force and a lot of ignorance. With care, frame nails (gimp pins) can easily be used instead.

Doors

In preparing the wood for the last two sides I made two slanting cuts to create the ‘doors’, nailed everything down and added a simple hinge from a gimp pin. It’s worth noting that it’s much easier to place the door ‘hinge’ (pivot?) centrally, rather than at one end of the door. Firstly, there’s less chance the end of the door will foul the adjacent wood. Secondly, to open the door you just need to push one end inwards with the hive tool; there’s no need to add a handle (a screw or nail that protrudes) to open the door outwards. This means there’s nothing to protrude and catch on clothing, on adjacent stacked boxes or on the lower lip of the roof when you’re using it as a crownboard. Finally, the bees won’t care.

Doors closed ...

Doors closed …

I gave the wood a couple of coats of (ironically) One Coat Ronseal Fence Life which should protect it from the elements.

Cheapy, cheapy

The Correx was about a tenner a sheet – delivered 5+ sheets at a time – from which I could cut sufficient for 10 split boards, with useful offcuts to build nuc crownboards or landing boards from. The hardwood strip wood was about £2 per board. Therefore, aside from a few nails, the finished boards cost about £3 each. This compares very favourably with the £28-36 charged by most suppliers for a Snelgrove board. Of course, I appreciate that the latter are more complicated and offer additional confusion functionality, but these are perfectly serviceable for a vertical split and there’s a lot of pleasure to be gained by using something you’ve bodged lovingly crafted yourself 😉

By the time this appears these boards might even be in use …


There’s a good explanation of split board construction in a post by Calluna4u on the SBAi discussion forum (“the thinking beekeepers web forum”). Calluna4u has a wealth of experience as a commercial beekeeper and prepares these boards in industrial quantities. His design differs slightly as it’s for use with hives arranged four to a palette. His post contains links to suppliers for 6mm pre-cut Correx in Dundee which might be useful to Scottish-based beekeepers.

A late start …

After a couple of false alarms, the season finally feels like it’s about to start, with temperatures predicted to be consistently into the (low) teens by this time next week. It’s been a punishing Spring as far as my beekeeping has been concerned with lots of queen failures due to poor mating success last year. I therefore need to expand my current stocks in time for the summer nectar flow – ever hopeful! – but am pretty-much resigned to not being able to exploit the oil seed rape (OSR) that is just about starting to flower in the fields nearest my out apiary (it’s already flowering well in other parts of the county – out of foraging range for my bees though).

OSR 30th April 2015 ...

OSR 30th April 2015 …

Go forth and multiply

It’s not all doom and gloom though … colonies that are queenright are expanding well despite the weather. Those in the bee shed are doing particularly well, with part-filled supers (dandelion perhaps?) and colonies expanding up to a double brood box. As an aside, I’d estimate that these colonies are at least 2-3 weeks further advanced than those ‘outside’ … I’ll discuss this in more detail in a later post. Furthermore, the colonies that haven’t developed DLQ’s include some beautifully docile bees, very steady on the comb even when inspecting them in less than ideal conditions, of which we’ve had lots this Spring. With the expectation (or at least hope) of much better weather by the end of the month I’ll be setting up some vertical splits. This is an easy way of either requeening or making increase, involving a minimum of equipment and almost no interventions in terms of hive manipulations. This is queen rearing made easy … simply dividing a suitable colony and giving each half an opposing entrance, then turning the colony through 180° after 7 days. I’ve also sourced a couple of Snelgrove boards to try this year, but work commitments mean these will have to wait until later in the season as they need a little more attention than a simple split board.

Split board

Split board …

Covet thy neighbours bees … or at least catch his swarms

With the assumption that other strong colonies are at least as well advanced as mine I’ve also set out a number of bait hives. Each of these contains an old dark brood frame – importantly containing no stores or you just attract robbers – pushed against the back wall and several (6-9) foundationless frames. The top bar of the old brood frame gets a few drops of lemongrass oil (this stuff ‘eats’ poly hives, which is what my bait hives are made from, so make sure you keep it restricted to the wooden frame). Bait hives should also have solid floors and small entrances – so I cover the OMF with a few scraps of Correx. Finally, to save on equipment I also often use a simple square of heavy duty polythene sheeting as a crownboard.

I set bait hives out every year, catching a few swarms that would otherwise disappear into the church tower, someones loft space or perish in a thunderstorm. It’s always a bit hit and miss in terms of the quality of bees that are attracted … of course, other than when I catch a swarm from my own colony 😉 The peak swarming season extends over the next 6-8 weeks and the bees are always useful, if only to act as willing recipients for queens raised next month when I’ll start grafting.

Bait hives ...

Bait hives …

New queens

Finally, I’ve ordered a couple of queens from a reputable (UK-based) queen breeder to improve the genetics of my stocks. One of my apiaries is in a region with predominantly black ‘native’-type bees in the area, and with local beekeepers keen to keep it that way. I’ll requeen colonies in this apiary with these queens – and in due course their daughters – to be both a good neighbour and to see whether these ‘native’ bees perform better than my Heinz (57 varieties) local mongrels.