Tag Archives: health

The Autumn of the Matriarch

I’ve previously commented that weak colonies that build up very slowly in Spring are more trouble than they’re worth. The resources they need – syrup, frames of emerging brood, more TLC – are rarely reflected in the subsequent honey yield.

Quite the contrary, they’re often a lost cause and it could be argued that, from a purely efficiency point of view, it would be better if the colony succumbed during the winter than staggered on into the Spring.

Better still, assuming they’re disease free, use the bees in the autumn by sacrificing the queen and uniting the colony with a strong colony. You’ll boost the latter and strong colonies both overwinter better and build up better the following year.

Do as I say, don’t do as I do.

All the above makes perfect sense, but a combination of sentimentality and ill-placed optimism means that it’s not unusual – in late Spring – to find myself being reminded that “weak colonies that build up very slowly in Spring are more trouble than they’re worth”.

And it’s happened again.

One of my colonies was undersized in late autumn and had built up very slowly this Spring. The queen was a little older than most in the apiary but she’d done well in the past and I thought she might have another season in her. Varroa drops in late autumn and mid-winter had been very low and the bees were beautifully tempered, calm, steady on the comb and a pleasure to work with.

But in the first inspection of the year (10th of May) there just weren’t enough of them. The queen was laying, pollen was coming in, there were no signs of disease and the colony behaviour remained exemplary.

Lagging behind

Comparison between colonies is very informative. That’s why it’s easier to maintain two colonies than one. Other colonies in the same apiary were building up well. By late May I was starting swarm prevention measures on these, using pre-emptive vertical splits.

The small colony was largely forgotten or ignored. I peeked through the perspex crownboard a couple of times and could see they were building up.

Slowly.

I got distracted harvesting the early season honey from other colonies, running out of frames and with more swarm prevention and control. I finally completed a full inspection of the colony on the 17th of June, shortly before the summer solstice and the first official day of summer (so still technically Spring).

Queen failure … not epic, but failure nevertheless

The colony had only a couple of frames of brood and covered a frame or two more than that. The temper and behaviour was still very good. The queen was present and laying. She was being attended by a retinue of workers and not being ignored or harassed.

Failing queen ...

Failing queen …

But she was clearly losing her faculties. Many of the cells contained two or more eggs.

Multiple eggs in cells are often seen with laying workers and sometimes seen when a newly mated queen first starts laying. With laying workers the eggs are often placed on the sidewalls of cells and, as they’re unmated, they develop into drones. The brood pattern is scattered randomly around the frame. With newly mated queens the eggs are usually correctly placed in the base of the cell.

Occam’s razor

The colony was clearly doomed. They showed no sign of trying to replace the queen, without which the future was bleak. I needed to rescue something from the situation. The choice depended on my interpretation of what had gone wrong. The options were:

  1. Queen failure, plain and simple
  2. Laying workers in a colony with a failed queen still present (an unusual situation)
  3. A new, recently mated, queen was also present with the old queen (supercedure)

A thorough inspection of the colony failed to find another queen or any evidence of a recently vacated queen cell. Frankly this didn’t take long, the colony was simply too small to ‘hide’ either of these. Option 3 could therefore be discounted. The presence of another queen would be really important if I was considering requeening the colony or uniting it with a queenright hive – both these are likely to go badly if there was a queen still present.

There was no drone brood at all in the colony and the laying pattern was clustered as would be expected from eggs laid by a queen. Option 2 could therefore almost certainly be discounted. Fortunately again as it’s difficult to requeen a colony containing laying workers. As another aside, I can’t remember seeing a colony with laying workers that also contained a (failed) queen.

That left the most likely explanation for the multiple eggs (and the undersized colony) was the simple failure of the queen. For whatever reason, she was laying at a much lower rate than usual and had started laying multiple eggs in cells. Of the three possibilities, this is the most straightforward. Occam’s razor (William of Ockham, ~1287-1347) is the problem-solving principle that states that the simplest explanation is probably the correct one.

Better late than never

The queen was removed from the colony and it was united over newspaper on top of a strong hive in the same apiary. Two days later the Varroa board underneath the colony was covered in shredded paper indicating that the colonies were united successfully.

Successful uniting ...

Successful uniting …

Which is what I should have done in mid-autumn last year.

Better late than never  😉

A few days later I rearranged the colony, placing the two frames of brood into the bottom brood box and putting a clearer board underneath the top brood box. The resulting single colony, now a bit stronger, will be well-placed for the summer nectar flow and the nine frames of drawn comb vacated by the colony will be reused making up nucs for overwintering.


† Interestingly, I’ve never seen several larvae developing in cells after the multiple eggs hatch. Either the excess eggs or larvae must be removed by workers. I presume this means that the workers can’t count eggs, but may be able to count larvae – not literally of course, but by the amount of pheromones produced presumably. If they could count eggs they’d remove the excess and leave only one, making the identification of laying workers (or a recently mated misfiring queen) much more difficult. Something to be thankful for perhaps? They can, of course, identify the origin of eggs – this process is the basis of worker policing which was touched on in discussion of Apis mellifera capensis, and is of relevance to those using grafting for queen rearing.

Colophon

The title of this post is a corruption of The Autumn of the Patriarch, a book by the Nobel laureate Gabriel García Márquez, written in 1975. The book is about the God-like power and status of a dictator, the General, and the awe in which he is held by the people. Of course, this isn’t the situation in matriarchal honey bee colonies, the structure of which is determined as much – if not more – by the workers, the brood and the circulating pheromones.

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 …  😉

 

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 …

Save the bees, save humanity

I’ve used this poster in talks a couple of times to make a distinction between colony collapse disorder (CCD) in the US and colony losses due to disease in the UK.

Save the bees ...

Save the bees …

It’s a rather striking poster … although it carries the website address www.nrdc.com (which appears to belong to the National Realty and Development Corp.), the logo and the subject are much more likely to be associated with the Natural Resources Defense Council (www.nrdc.org). Whatever … the message is clear, without bees there will be pollination shortages for many important and valuable fruit and vegetable crops. The term CCD, a still incompletely understood phenomenon where hives are abandoned by workers, was first used in 2006 in the USA and similar types of colony losses have been reported in a number of European countries, though not in the UK. Prior to 2006 there were a range of other names given to apparently similar phenomena – spring dwindle, May disease, fall dwindle disease [PDF] etc.

The ‘Save humanity’ statement possibly refers to the the apocryphal quote attributed to Albert Einstein “If the bee disappears from the surface of the earth, man would have no more than four years to live” … though it’s highly unlikely Einstein ever actually said this. It’s also a rather questionable statement. Certainly honey bees provide important pollination services, but so do many other insects (and not just insects). There are certain crops for which honey bees are important – such as almonds – at least on the scale they grow them in California. However, on a visit-by-visit basis, honey bees can be relatively poor pollinators. For examples, solitary bees such as Osmia sp. are much more efficient pollinators of apples. The inefficiency of honey bees is more than compensated though by their numbers and our ability to move hives to crops that need pollinating.

So, if honey bees are so important, why does the picture above show a wasp?  😉

 

 

When to treat?

Preparing Apiguard

Preparing Apiguard …

When and how do you treat colonies to have the greatest effect in minimising Varroa levels? At the end of this longer than usual post I hope you’ll appreciate that this is a different – and much less important –  question than “When is the best time to treat?”.

You probably use one of the treatments licensed and approved by the Veterinary Medicines Directorate (VMD), which include Apistan, Apivar, Apiguard, MAQS and Api-Bioxal. I’ve discussed the cost-effectiveness of these treatments recently. If used correctly, all exhibit much the same efficacy, reducing phoretic mite levels by 90-95% under optimal conditions. That being the case the choice between them can be made on other criteria … the ease of administration, the cost/treatment, the likelihood of tainting the honey crop, the compatibility with brood rearing, whether they mess up your vaporiser etc. After using Apiguard for several years, with oxalic acid (OA) dribbled in midwinter, my current preference – used throughout the 2015 season – is OA sublimation or vaporisation. This change was based on four things – efficiency, cost, ease of administration and how well it is tolerated by a laying queen. The how? you treat is actually reasonably straightforward.

When, not how, is the question

DWV symptoms

DWV symptoms

OK, but what about when? Because, if the treatments are all much of a muchness if used correctly, the when is actually the more important consideration. When might be partly dictated by the treatment per se. For example, Apiguard needs an active colony to transfer the thymol throughout the hive so the recommendation is to use it when the ambient temperature is at least 15ºC (PDF guidance from Vita). It’s worth stressing that this is the ambient temperature, not the temperature in the colony, which in places will be mid-30’s even when it’s much colder outside. At low ambient temperatures the colony becomes less active, and in due course clusters, meaning that Apiguard is not spread well throughout the colony, and is therefore much less effective. If you’re going to use Apiguard you must not leave treatment too late.

For readers in Scotland it’s interesting to note that the SBA annual survey by Peterson and Gray shows significant numbers still use Apiguard in September and October, months in which the mean daily maximum temperature is ~14°C and 11°C respectively … so the average daily temperature will be well below the recommended temperature for effective Apiguard use.

However, the when should be primarily informed by the  why you’re treating in the first place. It’s not really Varroa that’s the problem for bees, it’s the viruses that the mite transfers between bees when it feeds on developing pupae that cause all the problems. Most important of these is probably Deformed Wing Virus (DWV), but there are a handful of other viruses pathogenic to bees that are also transmitted. DWV causes the symptoms shown in the image above … these bees are doomed and will be ejected from the hive promptly. However, although apparently healthy (asymptomatic) bees have low levels of DWV, it’s been shown by Swiss researchers that DWV reduces the lifespan of worker bees, and that high levels of DWV in a colony are directly associated with – and causative of – overwintering colony losses. Therefore, the purpose of late summer/early autumn treatment is to reduce the Varroa levels sufficiently so that high levels of the virulent strains of DWV are not transmitted to the overwintering bees. When? therefore has to be early enough that this population, critical for overwinter survival, will live through to the spring – however long the winter lasts and however severe it is. However, before discussing when winter bees are reared it’s worth considering what happens if treatment is used early or late.

What happens if you treat early?

Mid June

Mid June treatment …

For example, mid-season or after the first honey crop comes off. Nothing much … other than slaughtering many of the phoretic mites. This is what most beekeepers would call “a result” 😉  Aside from possible undesirable side effects of treatment – like tainting honey, or preventing the queen from laying or even, with some treatments, queen losses – early treatment simply reduces mite levels. It’s important to remember that the levels may well not be reduced sufficiently to negate the need for a treatment later in the season … as long as there is brood being raised the mites will be reproducing (for example, look at the mid-June treatment generated using BEEHAVE modelling – image above). Furthermore, avoiding those undesirable side effects might require some ‘creative’ beekeeping (for example, clearing the supers and moving them to another hive) and will certainly inform the choice of treatment but, fundamentally, if the mite levels are high then treating earlier than is usual will benefit the colony, at least temporarily. If the mite levels – estimated from the disappointingly inaccurate mite drop perhaps – are dangerously high you should treat the colony.

What happens if you treat late in the season?

Isolation starvation ...

Isolation starvation …

In midsummer workers only live for ~40 days. If mite levels are high, virus transmitted to these workers will shorten their lives, so reducing the colonies’ foraging ability and – possibly – ability to defend itself against wasps or robbing late in the season. However, if you delay treatment until very late the lifespan of bees raised at the end of the season – the overwintering bees – will be reduced with potentially more devastating consequences. The usual winter attrition rate of workers will be higher. The cluster size of the colony will shrink faster than a colony with low mite levels. At some point the colony will cross a threshold below which it becomes non-viable. The cluster is too small to move in cold periods to new stores, resulting in the beekeeper finding a pathetic little cluster of bees in a colony that’s succumbed to isolation starvation. A larger cluster, spread across a greater area and more frames, is much more likely to span an area of sealed stores and be able to exploit it.

When are winter bees reared?

The apiary in winter ...

The apiary in winter …

In the Swiss study referred to above they looked at the longevity of winter bees. The title of the paper is “Dead or alive: deformed wing virus and Varroa destructor reduce the life span of winter honeybees”. We can use their data to infer when winter bees start to be reared in the colony and when mite treatments should therefore have been completed to protect these bees. Their studies were conducted in Bern, Switzerland, in 2007/08 where the average temperature in November/December that year was 3ºC. They first observed measurable differences in winter bee longevity (between colonies that subsequently succumbed or survived) in mid-November. This was 50 days after bees emerged and were marked to allow their age to be determined. By the end of November these differences were more pronounced. Therefore, by mid-November Varroa and virus-exposed winter bees are already exhibiting a reduced lifespan. Subtracting 50 days from mid-November means these bees must have emerged in late September. Worker development takes ~21 days, so the eggs must have been laid in the first week of September, and the developing larvae capped in mid-September.

To protect this population of overwintering bees in these colonies, mite treatments would have had to be completed by the middle of September, so that mite levels were sufficiently low that the developing larvae weren’t capped in a cell with a Varroa mite carrying a potentially lethal payload of DWV. For Apiguard treatment (which takes 2 x 14 days) this means treatment should have been started in mid-August. For oxalic acid vaporisation (which empirical tests suggest is best conducted three times at five day intervals) treatment would need to start no later than early September and preferably earlier as it is effective for up to a month.

Of course, these figures and dates aren’t absolute – the weather during the study would have influenced when the larvae would be raised as winter bees, with the increased fat deposits and other characteristics that are needed to support the colony survival through the winter. Despite the study being based in Switzerland my calculations on dates are probably broadly relevant to the UK … for example, the temperature during their study period is only about 1ºC lower than the 100 year average for Nov/Dec in Eastern Scotland where I now live.

In conclusion

That was all a bit protracted but it hopefully explains why it’s important to be selective about when you administer Varroa treatments. Chucking in a couple of trays of Apiguard in mid-August or mid-October has very different outcomes:

  • in mid-August the phoretic mite population should be decimated, reducing the transmission of virulent DWV to the all-important winter bees that are going to get the colony through the winter. This is a good thing.
  • in mid-October the mite population will be reduced (not decimated, as it’s probably too cool to effectively transfer the thymol around the hive – see above) but many of the winter bees will already have emerged, probably with elevated levels of DWV to which they will succumb in December or January. This is a bad thing.

Perhaps perversely, treating early enough to prevent the expected Varroa-mediated damage to developing winter bees is not be the best way to minimise mite numbers in the colony going into the winter. Using BEEHAVE I modelled the consequences of treating in the middle of each month between August and November¹. I used the default BEEHAVE setup as described previously. Figures plotted are the average of 3 simulations, each ‘primed’ with 20 mites at the start of the year.

Time of treatment and mite numbers

Time of treatment and mite numbers

There’s a lot on this graph. To show colony development I plotted numbers of eggs, larvae and pupae (left axis) as dotted red, blue and black lines respectively. Mite numbers are shown in solid lines – treated with a generic miticide in mid-July (black), mid-August (blue), mid-September (brown), mid-October (cyan) and mid-November (green). In each case the miticide is considered to be 95% effective at killing phoretic mites. The gold arrowhead indicates the period during which winter bees are developing in the colony, based upon the data from Dainat.

Oxalic acid trickling

Oxalic acid trickling

Treating at or before mid-August controls the late-summer build up of mites in the colony – look how the blue line changes direction. Mites that are not killed go on to reproduce in late September and early October, resulting in levels of ~200 at the year end. Remember that mites present in midwinter can, in the absence of sealed brood, be effectively controlled by trickling or vaporising oxalic acid (Api-Bioxal), and that this Christmas miticide application is particularly important if the autumn treatment has not been fully effective. In contrast, treating as late as October and November (cyan and green lines) exposes the developing winter bees to the highest mite levels that occur in the colony doing the year, and only then decimates the phoretic mite numbers, with those that remain being unable to reproduce effectively as the brood rearing period is almost over. Starting treatment in mid-September isn’t much different, in terms of exposing the winter bees to high mite levels, than starting later in the year.

So, within reason, treating earlier rather than later both reduces the maximum mite levels and helps protect the winter bees from virus exposure. Of course, treating as early as mid/late August may not be compatible with your main honey crop (particularly if you take hives to the heather) … but that’s another issue and one to be addressed in a future post.


¹BEEHAVE makes a distinction between ‘infected’ and ‘uninfected’ Varroa, the proportions of which can be modified. This might (no pun intended) not accurately reflect the reality in the hive, where Varroa-mediated transmission of DWV results in the preferential amplification of virulent strains of the virus. I need to roll my sleeves up and delve into the code to see if the model can be altered to fully reflect our current understanding of the biology of the virus. This might take quite a while …

References

Overwintering honey bees: biology and management from the Grozinger lab.

Managing Varroa (PDF) by the National Bee Unit

 

The Drifters cont.

The Drifters ...

The Drifters …

Not the legendary American doo-wap/R&B vocal group but instead a quick follow-up to a recent post on drifting in honey bees. I discovered an interesting article in a 2011 issue of American Bee Journal in which Wyatt Mangum (Mangum, W. [2011] Varroa immigration and resistant mites ABJ 151:475) quantified mites introduced with bees from other colonies. The experiment was straightforward and quite clever … a number of colonies were prepared with very low mite numbers, overwintered and then miticides (unspecified, but from the remainder of the article I’m assuming Apistan) were applied continuously for the rest of the season. This would kill all the mites present. With a Varroa tray in place it was therefore possible to count newly introduced mites throughout the season. These must arrive with drifting workers, drones (not sure if drones ‘drift’ as such … perhaps there’s a better term for their itinerant wandering?), bees that have abandoned other colonies or potentially robbers. The newly infesting mites would of course be killed by the miticide after introduction and before reproduction. They could therefore easily be counted on the Varroa tray under the open mesh floor.

The results were striking … in one year between mid-May and early October an average of 1415 and 1001 mites were introduced to each of the seven ‘recipient’ colonies in two separate apiaries. Mite arrivals weren’t evenly spread, but peaked during a late summer dearth of nectar … perhaps, as suggested by the author, as other colonies started to run out of stores. The source colonies were not identified, but were not within the test apiaries. Whatever the cause, this represents a very significant influx of up to 7-10 mites per day. In Mangum’s experiment these mites could not replicate (due to the miticide that was always present). Had they been able to do so the impact on the recipient colony, in terms of numbers of mites transmitting viruses within the hive, would have been much greater.

The impact of drifting and mite reinfestation

The impact of drifting and mite reinfestation

Using BEEHAVE this impact can be modelled. In untreated colonies (solid lines), primed with 20 mites at the beginning of the year (and default conditions as previously described), the average mite level at the year end is ~430 (n=3) having reached a maximum of ~600. Using the same infestation period as reported by Mangum¹, with a mite infestation rate of 7/day (the lowest he observed), the average mite levels at the year end were ~2700 (n=3), with maximum levels reaching ~3800 in late summer (dotted lines). In this simulation the introduced mites can reproduce. Therefore, within just a few months, phoretic mites carried on workers and drones from other colonies, have the potential to raise mite levels in the recipient colony to dangerously high levels – significantly higher than the maximum recommended level of 1000/colony. This is potentially of fundamental importance in strategies to effectively control Varroa.  It should be noted that in a repeat of his study this large scale infestation was not observed. This suggests that this type of infestation – from outwith the apiary – may only be a problem in certain years or under specific conditions. One possibility that comes immediately to mind would be a collapsing feral colony or abandoned (or potentially not abandoned, but just completely ignored and untreated … or ‘abandoned‘ as some might say 😉 ) hive within foraging distance.

Ample opportunity ...

Ample opportunity …

Interestingly, a recent study has looked at the influence of a number of honey bee pathogens on drifting (or inter-colonial transmission as they rather long-windedly call it) behaviour. Of the viruses, Varroa and Nosema tested, only the presence of high mite levels influenced drifting … but not in the direction that might be expected. Distance between colonies in an apiary was the major factor that influenced drifting and ~17% of tested workers had drifted (with a third to half of these being apparently unrelated to other colonies in the test apiary). Surprisingly, colonies with high Varroa levels were more likely to acquire drifting workers, though the mechanism for this was unclear. The increased mixing through drifting would ensure that these colonies would likely end up with a greater diversity of viral and other pathogens though whether these colonies could, later in the season, act as a source rather than a sink for mites was not tested.

Drone

Drone …

Finally, returning to the subject of drifting bees and the ABJ … in the February 2016 issue there’s an interview with Tom Seeley (of Honeybee democracy fame … Sharashkin, L [2016], ABJ 156:157) in which he states that, when quantified, 34% of drones in his apiary colonies were from other hives. This article – on Surviving without Treatments: Lessons from Wild Bees – also discusses the importance of colony separation to coping with Varroa. The feral colonies Seeley studies are located at least half a mile apart in woodland. When recovered and relocated together in apiaries (‘beeyards’ as they’re called in the US) they rapidly succumb to mite-transmitted viral diseases, whereas those maintained some distance apart (30+ metres) survive. Seeley makes the point that pathogens evolving in closely-spaced colonies are likely to be more virulent, whereas those that are in distantly spaced colonies should be less virulent (or they’ll kill the host colony before being transmitted). Seeley is referring to the virulence of Varroa but I think his comments apply better to the viral payload carried by the mite. This is a relatively minor distinction but these observations further emphasise that drifting in honey bees is clearly a major factor in mite, and consequently disease, transmission … and therefore needs to be considered in control.

STOP PRESS – A recent Bee-L post highlighted a further study on the influence of re-infestation. Greatti et al., (1992) showed that ~2-14 mites/day/colony were acquired in their test apiary during June-August, and that this number rose to up to 75 mites/day/colony in September and October². This type of re-infestation can occur by drifting as already discussed, or by workers in the sentinel colonies robbing out mite-infested collapsing nearby hives or feral colonies.


¹In the Mangum study the mites did not infest the sentinel colonies at an even rate of 7+/day. Instead there was a marked peak in mid-season. I’ve not attempted to model this. Clearly if mites don’t arrive earlier in the season the overall levels would be lower (as they wouldn’t have the chance to reproduce). However, an influx of mites in mid/late-season might just arrive at the wrong time to damage the all-important winter bees … the topic of a future post.

²Greatti, M., Milani, N. and Nazzi, F., (1992). Reinfestation of an acaricide-treated apiary by Varroa jacobsoni Oud. Exp. Appl. Acarol., 16: 279-286

Time to BEEHAVE

BEEHAVE ...

BEEHAVE …

I’ve been dabbling with BEEHAVE, a computer simulation of a honeybee colony. It’s not beekeeping, but it’s about as close as you can get in the middle of winter. BEEHAVE was developed by Matthias Becher in the University of Exeter and the paper that describes the model is published and Open Access [PDF]. The model includes a wealth of user-modifiable variables such as forage availability, climate, beekeeping activities and pathogens, and outputs information on colony size, speed of development, age structure, honey stores etc. The BEEHAVE simulation is implemented in the open source language NetLogo and is freely available. The parameters that influence colony development – egg laying rate, drone/worker ratios, forage (nectar and pollen) availability, mite replication rate etc. are all based on measured and published data (or logically extrapolated from this if they don’t exist) so that the in silico performance is a fair reflection of what might be expected in the field.

If you can, do … if you can’t, simulate it 🙂

I’m interested in the rational and effective use of miticides to control Varroa-mediated transmission of DWV (and other viruses) in the hive. Using BEEHAVE and a standardised set of conditions allows predictions to be made of how effective a particular Varroa control might be. For example, here’s a simple question we can try and answer:

How important is a midwinter mite treatment if you’ve treated earlier in the year?

Using BEEHAVE set to all the default conditions and ‘priming’ the colony with just 20 mites on the 1st of January it’s possible to see what happens if no treatments are applied over one or more years. It’s then possible to repeat the predictions with the inclusion of a Varroa treatment. For the purpose of this brief introduction to BEEHAVE I’ve used a miticide which is applied and active for a total of 28 days and which kills 95% of phoretic mites. This might broadly reflect Apiguard treatment (2 x 14 days) or vaporised oxalic acid (OA; 3 treatments at 5 day intervals, but documented to kill mites for up to one month). I’ve additionally looked at the application of a single treatment with oxalic acid in midwinter, again killing 95% of phoretic mites, the sort of effect that OA trickling might achieve if there’s no brood present.

No treatment … they’re doomed

No treatment

No treatment

BEEHAVE modelling is based on a series of underlying probabilities (e.g. likelihood of a developing pupa to become mite associated, likelihood of that being a drone or worker pupa) so doesn’t produce the same results every time it is run¹. For example, the graph above shows adult bee numbers (left axis, blue lines) in an untreated colony for three simulations of up to five years each (horizontal axis), together with the associated mite number (right axis, red lines). Mite number build up strongly as new brood is reared each spring, with mite numbers peaking at ~24,000 in the fourth summer. In the third and fourth winters mite number per bee range from 2-4. The default conditions of 20 mites, coupled with a minimum viable colony size of 4000 bees, results in one colony succumbing in the fourth winter and the two remaining dying in the fifth winter (bee numbers drop to zero). Real studies – with untreated hives in the field – have shown similar outcomes (Martin, 1998 [PDF]) though colonies tend to die between winters 2 and 3, presumably because the input mite populations are higher². In all subsequent graphs the data plotted is the average of three simulations.

One treatment … better than nothing

It’s worth remembering at this point that the advice from the National Bee Unit is that mite numbers in the colony should be maintained below 1000 (Managing Varroa [PDF]). To try and achieve this we need to investigate the influence of applying miticides in the simulation – in mid-June (left graph), mid-September (middle) or late December (right). I appreciate mid-June is very early in the season, but it emphasises an important point.

That’s a bit better 🙂 These plots show the averages of adult bee and mite numbers (using the format shown above, blue for bees, red for mites). None of the in silico colonies expired during the simulation though the mite numbers are dangerously high irrespective of the treatment during the mid/late summer months. Note that range of the scale on the right hand (mite numbers) axis differs in each graph. Treatment in mid-June (left) delays the summer exponential rise in mite numbers and, in terms of overall impact on mite numbers (and consequent adult bee losses) is measurably better than only treating in midwinter (right). Of the conditions tested, mid-September (centre) is clearly the best … Varroa levels are reduced at the same time as the colony starts to contract, leaving the remaining mites less opportunity to reproduce. Maximum colony size remains about the same year on year and Varroa numbers never reach more than one third of those seen in either mid-summer or midwinter treatments. However, not everything is rosy … Varroa levels are dangerously high from the third summer on, and levels are increasing each winter. Remember that these simulations were started with just 20 mites in the colony².

Do your colonies have only ~20 mites in them this winter?

Two treatments … a double whammy

Two optimal treatments

Two optimal treatments

It’s only when you combine early autumn and midwinter treatments that mite numbers are really well controlled. Under the highly optimised conditions – both treatments were set to be 95% effective against phoretic mites – Varroa numbers remain below the NBU recommended maximum of 1000 for the duration of the simulation. Clearly the combination of the mid-September slaughter of phoretic mites, coupled with a midwinter mopping up – when there’s little or no brood present – provides really tight control of Varroa levels. However, the importance of this is perhaps even more apparent when you consider the consequences of a sub-optimal mid-September treatment.

The graph on the left shows the consequences of using a miticide that achieves only 85% efficacy … perhaps reflecting Apiguard usage when the ambient temperature is too low for the thymol to be spread throughout the colony. Under these conditions mite numbers rapidly get out of control. Compare that with the graph on the right which includes an additional midwinter treatment where mite numbers are far better controlled … though only to about the same level as is seen with a 95% knockdown of mites in mid-September (centre graph in the ‘one treatment only’ section, above).

And the answer is …

Occupied bait hive

Occupied bait hive …

Although the majority of miticides are broadly similar in their maximum published efficacy, I suspect that they are often used in a way or under conditions that do not routinely achieve these maxima. For example, the 30 year average September temperature in England is just below 13°C, much lower than the temperatures in which Apiguard efficacy reached the reported maximum of 99%, and lower than the Vita-recommended minimum temperature (15°C). Therefore, the answer to the original question (which was How important is a midwinter treatment if you’ve treated earlier in the year?) is … if there’s any chance the late summer/early autumn treatment was sub-optimal then a midwinter treatment is very important to prevent Varroa levels building up in the colony, resulting in the spread of virulent strains of DWV and other viruses. The other broad conclusion is that miticides are much more effective – in terms of impact against the total mite population – when brood levels are low or absent. That’s why brood breaks coupled with miticide treatments e.g. applying vaporised oxalic acid to a recently hived swarm or one that has moved in to a bait hive, are a very powerful combination to reduce the impact of mites, and the viruses they transmit, on the colony.

There are additional considerations which influence the choice and timing of miticide treatments. In a future post I’ll address the timing of the autumn treatment and the critical development of the overwintering bees that get the queen and the colony through to the following Spring.


¹BEEHAVE provides the ability to model colony development based upon measured and measurable parameters within a honeybee colony. Of course, in the real world a host of factors influence our bees – climate, forage availability, bad beekeeping, good beekeeping, integrated pest management, swarming, queen longevity etc. These are all variable within BEEHAVE but have been left unaltered from the defaults for the purpose of this post in which only the timing and efficacy of miticide treatment was altered. All the data for this post were generated using the rather verbosely numbered BEEHAVE_BeeMapp2015 version.

²Mite levels were deliberately started at a very low level to emphasise how quickly they build up if not controlled. Running the simulations with a higher mite input simply shifts all the graphs to the right e.g. increasing input mites to 200 (not an unreasonable number for many midwinter colonies) with no treatment, results in the virtual colony dying in early December of the third year, with mite levels having reached ~5300 in the first summer and ~19000 in the second.

This is the second in a series of related posts about Varroa control. The first was on drifting in honeybees. I’ve created a separate page that lists these and other posts on the how, why and when of Varroa treatment.

Drifting in honeybees

During previous research on deformed wing virus (DWV) biology and its transmission by Varroa I’ve moved known Varroa-free colonies (sourced from a region of the UK which the mite has yet to reach and maintained totally mite-free) into apiaries in the countryside. Within 2-3 weeks Varroa was detectable in sealed brood, showing that mite infestation occurs very readily. I know other researchers who have made very similar observations. Where do these mites come from?

They’re not all ‘your’ bees

The obvious source would be the phoretic mites transported on workers ‘drifting’ from nearby infested colonies, or on drones which are known to travel quite long distances and may be accepted by almost any colony. If you want to see how frequent this is try marking a few dozen drones with a dab of paint. To avoid confusion use the colour used to mark queens next year. There are unlikely to be 4+ year old queens in the apiary and the drones will all perish before the end of the current season. Over the next few days and weeks the drones will appear in adjacent colonies, and some will likely leave the apiary and be accepted in your neighbours colonies.

How to encourage drifting ...

How to encourage drifting …

Beekeepers are usually aware that colonies at the ends of rows often ‘accumulate’ bees that have drifted when returning to the hive. In shared association apiaries some crafty beekeepers will site their colonies at the ends of rows to take advantage of the ‘generosity’ of other colonies. However, many beekeepers probably do not appreciate the extent to which drifting occurs. Pfeiffer and Crailsheim (1998) report that 13-42% of the population of a colony are ‘alien’ i.e. have drifted from adjacent hives, depending upon the time of season. Remember that drifting occurs in both directions simultaneously, so the overall numbers of bees in a colony may not be adversely affected (or boosted). In other studies Sekulja and colleagues (2014) showed that ~1% of marked bees drifted between colonies over a three day observation window. Interestingly, American foulbrood (AFB) infected bees drifted slightly more than uninfected bees. Spread of foulbroods during drifting is one reason the bee inspectors check nearby apiaries when there is an outbreak. These studies were all on workers where drifting primarily occurs during orientation flights before the bees become foragers. Drones drift two to three times more than workers (Free, 1958).

The likelihood of drifting must be closely related to the separation of hives and apiaries. Although workers will forage up to 2-3 miles from the hive I suspect the proportion of bees that drift this distance is extremely small. However, unless you’re very isolated I expect there are other apiaries within a mile or so of your own. Drones are known to fly up to about five miles to reach drone congregation areas for queen mating and are accepted by all colonies. I’ve regularly found drones appearing in (relatively) isolated mini-nucs. I’m not aware of studies that have formally tested drifting between apiaries (though it is reported in passing in the Sekulja et al., 2014 paper cited above).

Consequences of drifting

So, your hives probably contain workers and drones from other nearby colonies, and you can only really be sure that they’re all “your” bees if you live – as the sole beekeeper – on an isolated island. Not only does your neighbour generously exchange bees with you, he or she also kindly shares the phoretic mites those bees are carrying, the viral payload the bees and mites are infected with and – if you’re really unlucky – the Paenibacillus larvae spores responsible for causing AFB infection (and vice versa of course).

There are lessons here that should inform the way we conduct our integrated pest management to maintain healthy colonies. 

This post provides background information for an article (“Viruses and Varroa: Using our current controls more effectively” by David Evans, Fiona Highet and Alan Bowman) in the December 2015 issue of Scottish Beekeeper, the monthly magazine for members of the Scottish Beekeepers Association.

More later …

 

Winter checks for kewl floors

Kewl floor

Kewl floor …

The majority of my full colonies are on kewl floors. Some call these ‘floors with underfloor entrances‘, which is a bit more of a mouthful. These floors have narrow ‘L’ shaped entrances; the bees are forced to access the brood box through a 8-9mm high or wide slot, negotiating a 90º bend en route. For the majority of the season these offer more than enough advantages to easily outweigh their slightly more difficult construction (though you can buy something broadly similar if needed). These advantages include:

  • integral (and readily replaceable) Correx landing board
  • no need for mouseguards – even determined mice can’t negotiate an 8mm right angle
  • guard bees can occupy both the landing board and brood box entrance so far fewer problems with robbing or wasps (and if these are really a problem a simple 9mm lathe can be pushed into the entrance leaving a single bee gap at one end)
  • easy to seal for transport

Other users of these floors also claim the absence of draughts is a benefit but, since they also have open mesh floors, I don’t think this is likely to make much of a difference.

I’m only aware of three disadvantages of this type of floor.

  • they are not suited to the Varrox-type OA vaporisers i.e. the passive heating pan that is designed to be pushed through the hive entrance. This is not an issue if you use a Sublimox-type ‘active’ vaporiser I’ve described previously
  • bees can be confounded by the gap under the landing board when reorientating to these floors, though there are quick’n’dirty fixes to this and it’s only ever an issue for a few days. For the same reason, clipped queens might – on returning to the hive – miss the entrance and end up underneath the floor (though this happens with floors and normal entrances)
  • during long cold winters the entrance can become blocked with bee corpses – the only really significant problem and easily avoided

Bring out your dead

Blocked Kewl floor

Blocked Kewl floor …

There can be a high loss of bees from the colony during long cold winters. This is generally not an issue during the depths of winter, but as the weather warms slightly and the colony becomes more active – and, inevitably, the overwintering bees get older – the attrition rate rises. If the weather still isn’t warm enough for the corpses to be removed they can end up blocking the entrance. Twice in recent years I’ve had colonies trapped inside. In both cases these went into the winter as strong double-brood colonies and – due to work commitments – weren’t checked for 4-6 weeks in late January-early March. In both cases I managed to save the colonies, but they were severely stressed by the situation, with signs of Nosema, and needed mollycoddling for several weeks at the start of the season proper.

Fortunately there’s an easy solution. On your weekly apiary winter checks (or however frequent they are) push a bent piece of wire into the entrance, turn it to project up through the vertical part of the entrance slot and slide it along the full width of the hive to ensure the entrance is clear. Any old piece of wire should be suitable as long as it it short enough not to foul the bottom of the frames. For a few years I used an easily-lost piece of wire coat hanger. More recently I added a handle to a stainless steel bicycle spoke … with a little hook so it can hung up in a “safe place” (which, of course, is no guarantee whatsoever that it won’t be lost 🙁 ).

Kewl floor unblocker ...

Kewl floor unblocker …

Miticide cost effectiveness

There goes a few pence ...

There goes a few pence …

My recent comments on the cost of Api-Bioxal prompted me to look in a little more detail at the cost of miticides routinely available to beekeepers. The figures quoted below are the best prices listed by one of three leading beekeeping suppliers in the UK (E.M. Thorne, Maisemore’s and C. Wynne Jones – there are lots of other suppliers, but I’ve used these three and been satisfied with their service). I made the following assumptions: the beekeeper is purchasing sufficient to treat three single-brooded full colonies for three years (i.e. something with a reasonable shelf-life) with as little left over as possible. Costs per colony treatment were calculated for 9 colonies (3 x 3 years) only … any ‘spare’ can therefore be considered as free. This means that for Apiguard, available in packs of ten trays (5 colony treatments) or a 3kg tub (30 colonies), the cost is calculated per colony from two packs of 10 trays as a full course of treatment for one colony requires two trays. Obviously, buying in bulk – for example through a co-operative purchasing scheme in your beekeeping association – should reduce these costs significantly. No postage costs were included.

Apiguard – two boxes of 10 trays (C. Wynne Jones) = £41 = £4.55/colony

Apistan – two packs of 10 strips (C. Wynne Jones) = £41 = £4.55/colony

MAQS – one 10 dose tub (all suppliers) = £57.60 = £6.40/colony

Api-Bioxal – one 35g sachet (C. Wynne Jones) = £8.20 = £0.91/colony

Oxalic acid (OA) crystals – one 300g tub (Maisemore’s) = £4.32 = £0.48/colony

Note that this simplistic comparison hides a number details.

  1. These various treatments should be broadly similar in their efficacy (see below) in reducing the mite population, but must be used according to the manufacturers instructions for maximum efficiency. Under optimal conditions all quote at least 90% reduction in mite levels. However, Apistan (and Bayvarol, not listed) is pyrethroid-based and resistant mite populations are very widespread. In the presence of totally or partially resistant mites, Apistan will be of little or no benefit. Interestingly, Apistan resistance (which, like resistance to pyrethroids in other species, is due to a single amino acid substitution, so readily selected) appears to be detrimental to the mite in the absence of selection. This means that it may be possible to use Apistan effectively every 3-5 years as part of an integrated pest management as long as other beekeepers in the area follow the same regime. During the years Apistan is not used the pyrethroid-resistant mites should reduce in number, so restoring the efficacy of the treatment. I’m not aware that this idea has been properly tested, but it might be worth investigating.
  2. Only the first four treatments are approved for use in the UK by the VMD.
  3. Both the oxalic acid-containing treatments – Api-Bioxal and OA crystals – require preparation before use, or specialised equipment for delivery. OA vaporisation (sublimation) also necessitates both care and personal protection equipment to prevent exposure to the chemical which is a lung irritant. The costs indicated do not include these additional requirements.
  4. The treatments are not equivalent or necessarily interchangeable. For example, a) only MAQS should be used when honey supers are present, b) Apiguard is moved around the hive by active bees, so treatment is recommended when average daytime temperatures are above 15ºC , and c) there are reports on discussion forums of repeated OA vaporisation treatment – 3 at 5 day intervals – for colonies with brood present. The costs indicated above assume a single treatment (in midwinter or of a swarm/shook swarm in the case of OA) with any of the listed compounds.
  5. Finally, the ‘excess’ amount spare after treating the colonies over three years differs significantly. The first four have sufficient left over for one further treatment. The OA crystals will have enough left over for a further 190 colonies … and buying a 300g tub is probably about the most expensive way to purchase OA per gram 🙂

Bang for your buck

As indicated above, all of the Varroa treatments listed should give 90+% knockdown in mite numbers if used properly. This means following the manufacturers’ instructions – in terms of dose, time and duration of application. A key point to remember is that the mite is only susceptible when outside the capped cell and that 80% or more of the Varroa in a colony at any one time will be inside capped cells if there is brood present. For this reason, it is preferable to treat during natural (or induced e.g. a shook swarm) broodless periods. It has even been suggested that the midwinter OA treatment should be preceded by destruction of any brood present. Although this makes sense, I can understand why some beekeepers might be reluctant to open a colony to destroy brood in the middle of winter. There have been numerous reviews of individual and comparative efficacy of the various Varroa treatments – for example this well-referenced article on mite treatment in New Zealand from 2008. If used properly there’s little to choose between them in terms of efficacy, so the choice should be made on the grounds of suitability, convenience and cost.

‘Suitability’ is a bit of a catch-all, but requires you broadly understand how and when the treatment works – for example, Apistan is a pyrethroid so works well against sensitive mites, but is pretty-much useless against resistant populations, and resistance is widespread in the UK. ‘Convenience’ is generally high in the ready-prepared commercial treatments – it takes seconds to insert a tray of Apiguard – and much lower if the compound has to be prepared or you have to get dolled up in protective gear. In this regard, the absence of a pre-mixed liquid version of Api-Bioxal is a disappointment. Thorne’s still supply (at the time of writing) Trickle 2, a very convenient pre-mixed 3.2% w/v OA treatment for mid-winter trickling, but for how much longer? Similarly, the gloves, mask, goggles and power needed to treat a colony by OA sublimation makes it far from convenient for a single treatment.

Closing thought …

1 lb jar of honey

1 lb jar of honey …

Despite the great differences between the cost/treatment/colony it’s worth noting that even the most expensive is not a lot more than the price of a 1 lb jar of top quality local honey … just like the stuff your bees produce 😉 So, in the overall scheme of things, Varroa treatment is relatively inexpensive and very important to maintain colony health and to reduce overwintering colony losses.

See also Managing Varroa (PDF) published by the Animal and Plant Health Agency