Category Archives: Drones

Radar love

The average beefarmer in the UK is probably somewhere in their mid-60’s 1. This means that in 1973, when the Dutch rock band Golden Earring had their only notable chart success Radar love, they were about 18.

Bear with me …

As 18 year olds they probably wore denim flares and loud shirts with spearpoint collars. They would go to the local disco to meet similarly-attired members of the opposite sex (whose shorter hair may have been their only distinguishing feature).

They knew when and where to meet … the weekly Saturday night (obviously 2 ) disco.

There was no point in turning up at 10 in the morning … the disco was closed 🙁

Similarly, despite their ‘cool threads’, wearing them to the launderette would have resulted in almost certain disappointment … the dance partners they were seeking weren’t likely to be found doing the laundry 🙁

No, the disco was the place to go. 

Radar love would have been on the playlist. It reached the top 10 in the charts in many countries.

Hold that thought … we’ll return to Radar love in a few minutes … 3

The birds and the bees

Of course, these young beefarmers didn’t just go to the disco to dance

Oh no.

They had an ulterior motive 😉

They knew that they had a good chance of meeting a like-minded (and similarly attired) member of the opposite sex who was also ‘looking for love’.

These meetings were effectively ritualised … a particular time and place.

Let’s forget the bell bottoms and hippie shirts now … I only added that detail so that any readers who know an ageing beefarmers can have a little giggle imagining them dressed for the disco 😉 

OK, back to the disco … metaphorically.

The disco is not fundamentally dissimilar to the lek used by male grouse 4

Greater sage-grouse at a lek, with multiple males displaying for the less conspicuous females

A lek is defined as a location where males congregate to compete and mate with females. Importantly, there are no direct benefits – such as food or territory – that the females gain from attending the lek 5.

How do the males know where to congregate?

Grouse tend to live for several years 6. Older grouse know where the lek is because they attended last season. Juveniles probably tag along and learn from their elders despite the fact they are too immature to mate, or lack the social dominance (or plumage 7 ) to compete.

As a consequence of this male hierarchy the location of the lek is invariant.

The birds congregate at the same place each year.

One of the features of leks is that males show high levels of fidelity to a single lekking site.

So now we know something about the birds … what about the bees?

Drones congregate in particular – rather ill defined – landscape features called drone congregation areas (DCA’s).

These, like a black grouse lek, are stable from day to day and year to year.

The drones compete (for the queen, though not directly with each other by displaying) and offer the queen no territorial or food benefits … meaning that DCA’s are effectively insect leks 8

Drone congregation areas

There are studies going back well over 50 years on DCA’s. There are no hard and fast rules that define their location (at least to humans … thankfully virgin queens have no problems finding them). However, you can sometimes hear them; they sound like a small swarm, the noise caused by thousands of drones circling 5-40 metres above the ground in a swirling, traffic cone-shaped, perhaps a 100 metres or more in diameter.

How do drones know where to congregate? There is no male hierarchy 9. An individual drone lives for just a few weeks and perishes before winter. 

The location must be somehow ‘hard-coded’ in the environment. Effectively a set of features that – once located – attract the drones back repeatedly until they either mate with a queen, or die trying 10.

Many studies have attempted to identify DCA’s – geographic features on the ground, sheltered from strong winds, a dip in the horizon etc. These have tended to produce rather mixed results.

I don’t think we’re anywhere close to being able to point to an intersection of two hedges and say “Over there … that’s where drones will congregate”.

An alternative approach is to go fishing for DCA’s.

Literally. 

Having identified a number of potential DCA’s from landscape analysis, you can dangle a virgin queen from a helium balloon and sample the drone density in each of the areas.

It sounds a lot simpler than it is … there’s a nice account by Aude Sorel in Bee Culture if you’re interested.

By definition, the drone congregation areas are the ones you trap the most drones in.

Right?

Well, possibly not.

Perhaps the very method used to sample the drones attracted them there in the first place? 

It’s been known since the 1960’s that high concentrations of queen mandibular pheromone can attract drones to almost any location – in one notable example, even 800 metres out to sea 11.

If you use bait, how can you be certain that the areas you define are ‘real’. 

A better way to define a DCA would be to observe individual drones accumulating in a particular area … to watch them leaving the hive, fly the tens or hundreds of metres to the same place they flew to yesterday, and record them ‘strutting their funky stuff’.

Have you ever tried to follow a drone in flight?

They’re strong and fast. They need to be to outcompete other drones when chasing the queen.

It’s almost impossible to track them across the apiary, let alone over the hedge, across two fields and into the lee of a copse.

But scientists can now do exactly that … using a technique called harmonic radar tracking.

The title of this post should now make a bit more sense … it’s the use of radar to find where drones go ‘looking for love’ 😉

Harmonic radar tracking

A harmonic radar system emits a stimulus signal. This signal is picked up by a harmonic tag (the transponder) which uses the low frequency stimulus energy to generate a second harmonic which is then re-radiated back out to a receiving system.

The harmonic signal emitter/receiver is portable … if you’ve got a lorry.

Harmonic radar emitter and detector – with Rothamsted Manor in the background.

Fortunately, the transponder is tiny … small and light enough to be glued to the back of a bee.

Drone with harmonic radar transponder attached.

Harmonic radar has been used to study orientation flights in honey bees 12, to track Asian hornets, and to follow butterfly flight paths 13 (amongst other things).

And now it’s been used to map drone congregation areas by tracking the flights of individual drones from the hive.

Harmonic radar is a relatively short range system. You can’t track transponder-tagged insects flying miles away. The effective range is just a few hundred metres for most systems.

However, for drone congregation areas this shouldn’t be a major limitation. Drones generally fly shorter distances to mate than queens (an evolutionary mechanism to avoid inbreeding) and DCA’s have often been found near to apiaries 14.

Tracking drones by harmonic radar

The study, by Woodgate et al., was published a couple of weeks ago in iScience. The full reference is:

Woodgate et al., Harmonic radar tracking reveals that honeybee drones navigate between multiple aerial leks, iScience (2021), https://doi.org/10.1016/j.isci.2021.102499

It’s available under open access (i.e. free, for anyone) and I recommend you read it if you’re interested.

I’m just going to pick out a few highlights.

During two sequential seasons the authors tracked over 600 flights by at least 78 drones. These included 19 first flights (orientation flights) and – for four drones – 6-8 consecutive flights, including their first ever orientation flight.

Orientation flights were typically observed as multiple loops in different directions, centred on the hive from which the drone originated.

Drone orientation flights

The average duration of these orientation flights was ~13 minutes and the drones observed only took one or two before changing their flight pattern (see below) and seeking drone congregation areas.

Worker bees typically take more (~6) orientation flights than drones. Presumably foragers need to ‘map’ the hive location better because they may end up returning to it (and they’ve failed if they don’t) from any location.

As we’ll see in a minute, drones tend to use particular ‘flyways’ which are probably determined by landscape features. Drones also may return to a different hive to the one they set out from.

Identifying drone congregation areas by harmonic radar tracking

Scientists love ‘heat maps’.

These are a graphical way of depicting levels of activity of one kind or another.

If you overlay the flights by every transponder-tagged drone in each of the two years of this study you generate a map (like C and E shown below). In this study they used a ‘white to red’ scale where the paler the colouration, the more drones were detected in that particular point on the map.

You can easily see the hive location (points 1, 2 and 3) as all flights originated there.

Heat map of the landscape used by drones.

Actually, C and E are a bit confusing because they include the orientation flights which are centred on the hives. If you exclude these you end up with the heat maps D and F on the right.

From these the authors could detect particular areas where the drones tended to concentrate … these are proposed to be the drone congregation areas. There were four within range of the harmonic radar system – A-D above (confusingly labelled on images D and F).

There are a few obvious features of these proposed DCAs:

  1. They are in approximately (but not exactly) the same position in the two study years.
  2. The frequency with which they were visited changes. A is visited less frequently in the second year (panel F) than in the first (panel D).
  3. The most distant DCA (at least that could be mapped in this study) was ~600 metres from the hive. 
  4. Each DCA had a roughly symmetrical ‘core’ of 30-50 metres, significantly smaller than many drone trapping studies suggest..

One thing that was noticeable by comparison of the orientation flights and the proposed DCAs was that they did not overlap.

So how do the drones ‘find’ the DCA if they don’t discover them on an orientation flight?

Flyways, straight and convoluted flights

Heat maps are cumulative data.

It was also possible to look at the individual flight paths of drones on their way to and from a DCA (in exactly the same way as they mapped orientation flights).

Analysis of these showed that drones adopted two distinct types of flight – an approximately straight, direct flight interspersed with periods of convoluted, looping flight. There are lots of pictures of these in the paper but, rather than showing another published image, here’s my “no expense made spared” diagram of these two patterns of flight.

Drone flight paths showing distinct direct and convoluted elements.

The convoluted flight defines the drone congregation areas. In these the drones showed very distinctive behaviour – the further they were from the centre of the DCA the more strongly they accelerated back towards the centre. 

Drone flight paths (inevitably) overlapped in DCAs.

However, they also overlapped in the straight line flight. Drones tended to use particular flyways from the hives to, and between, the DCAs.

Scientists have previously identified (or at least suggested the existence of) these flyways that drones use to travel to and from the hive and the DCAs 15

However, what they had previously not identified was that drones often visit more than one DCA in a single (potential) mating flight.

In 20% of the flights analysed drones visited more than one DCA. 

Finally, drones tended to only spend about 2 minutes flying around very fast (at ~5 m/s rather than the sedate ~3 m/s they fly around the hive at 16 ) within the proposed DCA.

This suggests that drones might routinely patrol several DCAs in a single flight, moving on unless a queen is present.

Harmonic radar mapping the flights of virgin queens

I’ve often preceded the term ‘drone congregation area’ in the text above with the word ‘proposed’. A DCA has a very specific meaning that describes the places where drones congregate to attempt to mate with a virgin queen.

None of the studies above showed queen mating, or even the presence of a queen.

But, of course, the authors tried that as well.

They transponder-tagged queens (94 in total) and tracked their orientation flights and mating flights (26 in total). The orientation flights were remarkably similar to those of the drones; the average number of these flights was 3 and no queen went on more than 6 orientation flights.

Unfortunately the tracking of queen mating flights was less successful 17.

Queens flew out of range (I’ll return to this shortly), the transponder fell off, or parts of the flight were not picked up by radar. Some of the queens ‘followed’ (or for which tracking was attempted) did get mated, but not apparently in the DCAs identified during the flight tracking of drones.

This type of study clearly needs further work …

Conclusions

Drone congregation areas could be detected using harmonic radar tracking of transponder-tagged drones. Unlike other well-studied lekking areas, males (drones) did not display lek fidelity, but instead visited several in rotation 18.

The DCAs are a consequence of drones exhibiting a convoluted flight pattern in particular locations. The conservation of the flyways – the routes taken by the drones – between DCAs suggest they might contribute to the location of the DCAs.

Understanding what defines these flyways might allow better prediction of DCA locations.

Previous studies have shown that queens tend to fly further to DCAs than drones, presumably to avoid inbreeding. One possibility is that tagged queens in this study might have been more likely to visit the four DCAs identified if they were placed in mating nucs situated further away from this study site.

But, of course, they could have then flown off in a different direction altogether 🙁

Finally, it’s worth noting that a different pattern of queen mating activity had been described for dark, native (Apis mellifera mellifera) and near-native bees. This is apiary vicinity mating (AVM), and is nicely described by Jon Getty on his website

I now have some native black bees. I’m also experiencing the worst spring of my entire beekeeping career for queen mating. I am increasingly interested in AVM as a mechanism for saving the queen from drowning or freezing to death while attempting to reach a DCA 🙁


 

Winter losses

I lost 10% of my colonies this winter.

It’s always disappointing losing colonies, but it’s sometimes unavoidable.

I suspect the two I lost were unavoidable … though, as you’ll see, they weren’t completely lost.

April showers frosts

Late April may seem like mid-season for many beekeepers based in southern England. While they were adding their second super, the bees here in Scotland were only just starting to take their first few tentative flights of the year.

This April has been significantly cooler in Fife 1 than any year ‘since records began’.

However, the records I’m referring to are from the excellent Auchtermuchty weather report 2 which only date back to about 2013 … I like it because it’s local, not because it’s historically comprehensive 😉

The average April temperate has only been 5.5°C with 15 nights with frost in the first three weeks of the month. In contrast, the same month in 2019 and 2020 averaged over 9°C with only 3-4 nights with frosts 3

In both 2019 and 2020 swarming started at the end of April. Several colonies had queen cells when I first inspected them and I hived my first swarm (not lost from one of my colonies 😉 ) on the last day of the month.

First inspections and winter losses

Unsurprisingly, with appreciably lower temperatures, things are less well advanced this season. None of the colonies I inspected on the 19th were making swarm preparations. Instead, most were 2-4 frames of brood down on the strength I’d expect them to have before they started thinking about swarming.

Nevertheless, most were busy on a lovely spring day … lots of pollen (mainly gorse and some late willow by the looks of things) being delivered by heavily-laden foragers, and fresh nectar in some of the brood frames.

Fresh nectar glistening in a brood frame

The first inspection of the season is an opportunity to not only check on the strength and behaviour of the colony, but also to do some ‘housekeeping’. This includes:

  • swapping out old, dark brood frames (now emptied of stores) and replacing them with new foundationless frames
  • removing excess stores to make space for brood rearing
  • removing the first sealed drone brood in the colony to help hold back Varroa replication

And, as the winter is now clearly over, it’s the time at which the overall number of winter losses can be finally assessed.

Winter losses

Winter losses generally occur for one of four reasons:

  • disease – in particular caused by deformed wing virus (DWV) vectored by high levels of Varroa in the hive. DWV reduces the longevity of the diutinus winter bees, meaning the colony shrinks in size and falls below a threshold for viability. There are too few bees to thermoregulate the colony and too few bees to help the queen rear new larvae. The colony either freezes to death, dwindles to the size of an orange, or starves to death because the cluster cannot reach the stores 4.
  • queen failure – for a variety of reasons queens can fail. They stop laying altogether or they only lay drone brood. Whatever the reason, a queen that doesn’t lay means the colony is doomed.
  • natural disasters – this is a bit of a catch-all category. It includes things like flooded apiaries, falling trees and stampeding livestock. Although these things might be avoidable – don’t site apiaries in flood risk areas, under trees or on grazing land – these lessons are often learnt the hard way 5.
  • unnatural disasters – these are avoidable and generally result from inexperienced, or bad 6 , beekeeping. I’d include providing insufficient stores for winter in this category, or leaving the queen excluder in place resulting in the isolation of the queen, or allowing the entrance to be blocked. These are the things that the beekeeper alone has control over. 

The BBKA run an annual survey of winter losses in the UK. This is usually published in midsummer, so the graph below is from 2020.

BBKA winter survival survey

Over the 13 years of the survey the average losses were 18.2% 7. Long or particularly hard winters result in higher levels of losses.

Lies, damn lies and statistics

I’ve no idea how accurate these winter loss surveys are.

About 10% of the BBKA membership reported their losses, and the BBKA membership is probably a bit over 50% of UK beekeepers. 

I would expect, with precious little evidence to back it up, that the BBKA generally represents the more ‘engaged’ beekeepers in the UK 8. It also probably represents a significant proportion of new beekeepers who were encouraged to join while training.

So, like Amazon reviews, I treat the results of the survey with quite a bit of caution. I suspect beekeepers who have low losses complete it enthusiastically to ‘brag’ about their success (despite its anonymity), while those with large losses either keep quiet or are happy to share their grief. 

Unlike Amazon reviews, I’d be surprised if there are many fake submissions to the BBKA and I’m not aware there’s a living to be made from selling fake colony survival reviews in bulk online.

For comparison, the Bee Informed Partnership in the USA runs a similar survey every year.

Bee Informed Partnership loss and management survey

This survey covers about 10% of the colonies in the USA. Again it is voluntary and likely subject to the same inherent biases that may affect the BBKA survey.

The USA winter colony losses average ~28% over the same 13 year survey period.

Are US beekeepers less good at keeping their colonies alive than beekeepers in the UK?

Perhaps the US climate is less suited to honey bees?

Or, possibly, US beekeepers are simply more honest than their UK counterparts?

I doubt it 9.

Running on empty

My two colony losses were due to queen failures.

Old winter bees and no brood

In the first colony there was no evidence the queen had laid any brood since the previous autumn. There were about 6 seams of bees in the hive, but the outer 2-3 frames were solid with untouched winter stores.

Unused winter stores

This is usually a dead giveaway … literally. The colony hasn’t used the stores because they’ve not had any hungry mouths to feed. With no new brood the colony is doomed.

This queen appears to have simply run out of sperm and stopped laying. She was present (a 2019 marked queen and the same one I’d seen in August last year) and ambling around the frame, but she wasn’t even going through the pretence of inspecting cells before laying.

I removed the queen and united what remained of the colony over a nearby strong colony.

Strong colony ready for uniting

Assuming the queen stopped laying at the end of year all the bees in the hive – and there were a good number – were old, winter bees. These won’t survive long, but will provide a temporary boost to the colony I united them with. 

Every little bit helps 🙂

Even more valuable than the bees were the frames they were on.

Most of the comb in the colony with the failed queen was relatively new. By uniting them I can quickly swap out the old comb (from the stronger hive #34) when I next inspect the hive. At the same time I’ll rescue the frames of sealed stores for use when making up nucs during queen rearing.

Drone laying queen

The second failure was a drone laying queen (DLQ).

These are usually unmistakeable … the brood is clustered, with drone pupae occupying worker brood cells. If the queen has been drone laying for some time there may be lots of undersized ‘runt’ drones present in the hive as well.

Drone laying queen ...

Drone laying queen …

Again, this colony was doomed. With no new queens available and a lot of pretty old bees in the hive they could not be restored to a functioning colony.

However, many of the bees could be saved …

The colony wasn’t overrun with drones. Going by the amount of stores consumed it had probably been rearing worker brood since the winter solstice.

The queen was unmarked and unclipped. I strongly suspect she was a late-season supersedure queen who was very poorly mated.

The 3-4 weeks of drone brood rearing 10 had wrecked quite a few of the frames, but the bees were worth saving.

Under these circumstances I decided to shake the colony out.

When I do this I like to move the original hive and the stand it’s on. If you don’t move the stand the displaced bees tend to cluster near the original hive entrance, festooned from the hive stand. 

In poor weather, or late in the afternoon, this can lead to lots of bees unnecessarily perishing.

However, the stand was shared with two other colonies, so couldn’t be removed. It was also late morning and the weather was excellent.

I moved the hive away and shook the bees out. 

Sure enough … they returned to their original location.

They then marched along the hive stand to the entrance of the adjacent hive.

This way sisters!

And, by the time I left the apiary in mid-afternoon there were only a few diehard bees clustered near where the original hive entrance was.

Why didn’t I just unite them as I’d done with the other failed queen?

Drone brood is a Varroa magnet

Varroa replicate when feeding on developing pupae. The longer development time of drone pupae (when compared with worker pupae) means that you get ~50% more Varroa from drone brood 11

Unsurprisingly perhaps (or not, because that’s the way evolution works) Varroa have therefore evolved to preferentially infest drone brood. When given the choice between a drone or worker pupa to infest, Varroa choose the drone about 10 times more frequently than the worker.

And that ~10:1 ‘preference ratio’ increases when drone brood is limiting … as it is early in the season.

What this means is that the first burst of drone brood production in a colony is very attractive to Varroa.

Unless there are compelling reasons to keep this very early drone brood – for example, a colony with stellar genetics I’d like to contribute as much as possible to the local gene pool – I often try and remove it.

Drone-worker-drone

Drone-worker-drone …

If you use foundationless frames this is often as easy as simply cutting out a single panel of drone brood.

But, in the case of this drone laying queen, it meant that the logical action was to discard all of the drone brood to ensure I discarded the majority of the Varroa also present in the colony 12.

Which is why I shook the colony out, rather than uniting them 🙂

Boxes of bees

Several colonies in one apiary went into the winter on double brood colonies. Inevitably, with the loss of bees during the winter months, the colony contracts and the queen almost invariably ends up laying in the upper box.

The first inspection of the season is often a good time to remove the lower box. It can be removed altogether, or replaced (above the other box) for a Bailey comb change if the weather is suitable.

At this stage of the year the lower box is often reasonably empty of bees and totally empty of brood. 

Emptying a box of bees

If the comb in the lower box is old and dark (see the picture above) I place the upper box on the original floor and add an empty super on top. I then go through the lower box, shaking the bees into the empty super. Good frames are retained, the rest are destined for the wax extractor and firelighters.

Using an empty super helps ‘funnel’ the bees into the brood box.

Sometimes the queen has already laid up a frame or so in the lower box. Under these circumstances – particularly if the comb is relatively new – I’ll simply reverse the boxes, placing the lower box on top of the upper one. This results in the queen quite quickly moving up and laying up the space in the upper brood chamber.

It’s then time to add a queen excluder and the first super.

The beekeeping season has definitely started 🙂


Notes

I commented a fortnight ago about the apparent lateness of the 2021 spring. I’m adding this final note on the afternoon of the 23rd and have still yet to see or hear either cuckoo or chiffchaff on the west coast. Last year they were here in the middle of the month. This, combined with the temperature data (see above) show that everything is a week or two behind events last year.

Which means I can expect to start doing some sort of swarm prevention and control in the next fortnight.

The million drones fiasco

Accidents happen.

Sometimes they are due to stupidity, sometimes to forgetfulness, or sometimes they are just the result of plain dumb luck.

They’re also often caused or at least exacerbated by ‘local’ factors – like a rainstorm or a cancelled train preventing timely inspections. 

Or a countrywide lockdown necessitated by a global viral pandemic.

With the exception of the cancelled train my excuse for what follows is “all of the above” 😉

Social distancing

Beekeeping, like other activities involving livestock management, has been a permitted activity during lockdown. Beekeepers have been allowed to travel to their apiaries and to move bees for pollination etc

I was away when lockdown was imposed and opted 1 to stay where I was. For the first half of the season I’ve had to forego weekly colony inspections. I’ve not had the pleasure of watching the colonies build up, of queen rearing or of sweating profusely when shifting nectar-filled supers 🙁

Instead all my beekeeping – the first inspection of the season, the swarm prevention and the swarm control – have been squeezed into two visits, each of a few frantically busy days, in late April and mid-May.

And, inevitably, mistakes have been made.

Well, one mistake … that I’m currently aware of.

First inspections and swarm prevention

We’re late starters in Fife.

It’s not unusual to delay the full first inspection until the very end of April in this part of Scotland. A couple of years ago we had knee-high oil seed rape (OSR) ankle deep in snow at the end of April.

There seems little point in disturbing the colony if it’s too cold to have a leisurely look through the brood box. The bees get tetchy, the brood gets chilled and you don’t have time to look for the important things – like disease, or that elusive queen you failed to mark last autumn.

However, this season started well and I should have started colony inspections in the second week of April.

But by that time the world had changed dramatically …

I finally snatched a couple of days around the 25th of April to do the first inspections and swarm prevention all rolled into one … and coupled this with reducing my colony numbers by 50% to make management over the coming months easier 2.

I’ll discuss how I did all this in a couple of full-on days some other time. The end result was about a dozen united colonies, each topped with three supers, containing a good marked laying queen. Many of the colonies were very strong, with up to 15 frames of brood after uniting 3.

The colonies were strong and healthy. All were headed by a laying queen. I saw all but a couple of the queens 4 and clipped and marked all those I found that weren’t already 5.

Safely back in the hive

Three supers were overkill for the usual spring nectar flow. However, there was already a reasonable flow on and I wanted to give the colonies a good amount of space in the hope of delaying swarm preparations. 

Swarm control

Colonies usually start making clear their intent to swarm in the second half of May here. It varies a bit depending upon how advanced or otherwise the season is – one of those unknown knowns.

I kept in email contact with beekeeping friends about their own colony build up. By the time I received the first email saying charged queen cells were present (~16th of May) I was travelling back to do my own swarm control.

I decided to use the nucleus method whether queen cells were present on not.

Effectively I was going to implement preemptive swarm control on some colonies. By taking the queen out into a nuc the colonies would be forced to requeen, I’d then leave a single charged/capped queen cell and let them get on with it.

All looking good …

And for eleven of the colonies that’s precisely what happened. 

I removed the queen on a frame of emerging brood and shook some of the bees from a second frame into the nuc box. These were to be relatively small nucs but made sure each had a full frame of capped stores (saved from colonies at the first inspection). I also added a frame of drawn comb and two foundationless frames.

I sealed the nucs and moved them to another apiary.

Three of many … and hive number 29

Most of the brood boxes had play cups with eggs and about 50% had charged queen cells. There were no capped cells. I marked frames containing promising looking charged cells and closed the boxes up.

… and still looking good six days later

Six 6 days later I went carefully through every frame in the de-queened colonies.

One good queen cell, an old play cup and some rather old comb

All the boxes had good looking queen cells and I made sure I left just one in each colony. 

The nucs also all looked great when I checked them on the same day. 

New comb with queen already laying it up

The queens were laying well and the bees were drawing new comb. They would be fine for another few weeks. 

Come in Number 29, your time is up

One of the colonies proved more problematic.

Hive #29 … this had been left as a strong single brood colony on the 25th of April.

Three weeks later it was – unsurprisingly – still a strong single brood colony. The bees were busy and the supers were already filling nicely 7.

What was missing from the brood box in mid-May were eggs, larvae or capped brood 🙁

Had I inadvertently killed the queen 8 at the last inspection? The 21-22 day interval would have meant that all worker brood would have matured and subsequently emerged 9.

However, the temperament of the colony suggested it wasn’t queenless. The bees were calm, they were foraging well and bringing in good amounts of OSR pollen.

With a sense of dread I had a look in the supers …

Let there be drones

About 75% of my many super frames are drawn on drone cell foundation. For the same amount of wax – by weight – you store more honey. I also think there may be advantages when spinning it out in terms of honey recovery 10.

In addition, if you use drone cell comb immediately over the brood box, you dissuade a strong colony from storing an arch of pollen over the brood nest in the super … 

Drone comb in super

… though they do often leave cells empty, ready for the queen to lay.

But she can’t do that because she’s trapped under the queen excluder. 

Right?

Wrong 🙁

The middle few frames of the lower couple of supers were wall to wall capped drone brood and drone larvae. The queen was busy laying up some of the remaining space that wasn’t already filled with nectar.

I found the marked and clipped queen on the very first super frame I removed.

Sod it.

Snatching victory from the jaws of defeat

Perhaps.

Here was the dilemma. Hive #29 was strong and healthy but effectively queenless. Time was against me. I didn’t have the luxury of simply plonking her beneath the QE and checking the colony didn’t make swarm preparations in another three or four weeks 11

I’d already united all my other colonies and made up the nucs. I didn’t want to disassemble any of these to accommodate this colony.

With bad weather approaching in a few days I decided to make up a nuc with the queen and, in due course, donate a queen cell from another colony.

Which is what I did. 

An adjacent colony helpfully raised several very good looking cells which I knew were charged. One of these, on a frame holding a sideplate-sized patch of brood, was added to the colony just before the rain arrived.

Open the box, open the box

But on the same day I added the queen cell I also checked the supers thoroughly.

I wanted to make sure that every frame was drone foundation and that I’d not missed a queen cell drawn from any worker comb in the supers. That might have resulted in a virgin queen running about in my supers and, knowing my luck, squeezing through the QE and slaughtering the queen from the cell I’d just introduced. 

There were lots of “queen cells” in the supers. However all were little more than play cups drawn along the top edge of the drone comb, against the top bar. 

Lots of drone brood … but no real queen cells

None contained eggs. It was as though the bees, sensing the colony was now truly queenless, had known what to do but had no primary material to work with.

Over the next fortnight or so this hive was going to generate hundreds thousands lots of drones. Not in itself a bad thing – this was a good colony and the positve influence on local bee genetics might be beneficial.

However, all the drones would emerge in the supers and be prevented from exiting the hive due to the queen excluder.

When this happens the drones die in their droves stuck half way through the excluder.

This is a distressing sight and, for a drone, a demoralising experience (I would imagine 12).

Under normal circumstances I would simply return every 3-4 days, pop the lid off the hive and release them. This wasn’t possible living four hours away … 

… so I played the ‘get out of jail free’ card by adding a thin eke and upper entrance.

Upper entrance

When I next check the colony I expect the drone brood to have all emerged and, largely, left the supers. I hope there’s a mated laying queen in the bottom box and there should be some capped worker brood.

What there’s unlikely to be is three full supers of honey 🙁

With no worker brood being reared for at least 5 weeks the foraging workforce will be significantly depleted. I hope they manage to defend what they’ve already collected … time will tell.

What went wrong?

After finding the supers full of drone brood I wrote “dodgy” on both sides of the queen excluder frame as I replaced it with a plastic spare.

I assumed the queen had found a bent wire and   s  q  u  e  e  z  e  d  her way through to have a field day – actually three weeks – in the supers.

However, I think the explanation is more prosaic than that 13.

My notes indicated I’d not seen the queen in this hive during the April inspection. In this instance evidence of absence was not absence of evidence … there were lots of eggs and brood in all staged. The colony was queenright and the queen was in the right place.

At least before I opened the hive 😉

And this is where stupidity, forgetfulness and plain dumb luck played their part. I … 

  • stupidly botched the inspection, taking the strength and health of the colony as the most important signs that all was well, but …
  • forgot that the next inspection – when I would be making up nucs – would also need worker eggs in the brood box to rear new queens from.
  • There’s more … I also presumably forgot to thoroughly inspect the queen excluder before laying it to the side, allowing …
  • dumb luck to intervene when the queen scooted around to the other side of the excluder and so end up trapped in the supers when I reassembled the hive.

Mea culpa.

That’s my best guess anyway.

Did I do the right thing?

Hive #29 was the last to be inspected after a hard day of beekeeping in late April.

Coincidentally it was also the last to be checked in mid-May 14

This limited my options somewhat and I made a judgement call as to the best course of action. Doing what I describe above risks the queen failing to emerge or mate. It also potentially risks the box being robbed as the workforce diminish, particularly with the upper entrance I’ve added.

Both of these could lead to the loss of the hive, but the loss/problem would be all mine. At the time, standing there swearing sweating in my beesuit, gasping for a beer, it seemed like the safest bet. It also seemed like the responsible course of action in the middle of a global pandemic.

I chose not to just dump the queen back into the brood box, add the upper entrance and leave them to it. Had the colony subsequently swarmed 15 the problem might then have been someone else’s

Did I do the right thing?

We’ll know soon enough … 😉


 

Who’s the daddy?

I’ve recently discussed the importance and influence of polyandry for honey bee colonies. Briefly, polyandry – the mating of the queen with multiple (~12-18) drones – is critical for colony fitness e.g. ability to resist disease, forage efficiently or overwinter successfully.

Hyperpolyandry, for example resulting from instrumental insemination of the queen with sperm from 30+ drones, further increases colony fitness and disease resistance.

How do you measure polyandry?

Essentially, you genetically analyse the worker bees in the colony to determine the range of patrilines present. Patrilines are genetically distinct offspring fathered by different drones. Essentially they are subfamilies within the colony.

With a finite number of patrilines – which there must be, because the queen does not mate with an infinite number of drones – there will be a point at which the more workers you screen the fewer new patrilines will be detected.

Search and ye shall find – detecting rare patrilines

The more you screen, the more you are likely to have detected all the patrilines present.

However, the queen uses sperm randomly when fertilising worker eggs. This compounds the difficulty in determining the full range of different patrilines present in a population. In particular, it makes detecting very rare patrilines difficult.

For example, if 20% of workers belong to one patriline you don’t need to sample many bees to detect it. In contrast, if another patriline is represented by 0.0001% of randomly selected workers you would probably have to screen thousands to be sure of detecting it.

Consequently, rare patrilines in the honey bee worker population are very difficult to detect. Inevitably this means that the number of drones the queen mates (~12-18) with is probably an underestimate of the actual number 1.

Half-sisters and super-sisters

Worker bees are often described as ‘half sisters’ to each other. They share the same mother (the queen), but different fathers.

Actually, as you should now realise, that’s an oversimplification because – with only ~12-18 different fathers contributing to the genetics of the colony – some workers are going to be more related to each other because they share the same father and mother.

Half-sisters share the same mother but have different fathers and share about 25% of their genes.

Super-sisters share the same mother and father and so share about 75% of their genes (25% from the queen and 50% from the drone).

Super-sisters are more likely to help each other in the colony 2.

Emergency queens and nepotism

What’s the most important decision a colony makes?

If the queen is killed (or removed) the workers rear new queens under the so-called ’emergency response’. They feed selected young larvae copious amounts of Royal Jelly to rear a replacement queen.

Arguably, the most important decision the workers make is the selection of the day-old larvae to rear as new queens.

If they get it wrong the colony is doomed. If they get it right the colony will flourish 3.

But as described above, workers are more or less related to each other genetically.

To ensure the continued propagation of at least some of their genes it might be expected that the nurse bees making this selection 4 would choose larvae more closely related to themselves.

Do worker bees exhibit nepotism when rearing emergency queens?

If workers were nepotistic you’d expect the most common patrilines in the nurse/worker bee population would also predominate in the queens reared.

However, for at least 20 years evidence has been accumulating that indicates bees are not nepotistic. On the contrary, emergency queens appear to be reared from some of the rare patrilines in the colony.

A recent paper from James Withrow and David Tarpy has provided some of the best evidence for the existence of these so-called royal patrilines in honey bee colonies 5.

Royal patrilines

Evidence for these goes back to at least 1997 6, with about half a dozen publications in the intervening period. Essentially all used broadly the same approach; they genetically screened worker bees and the emergency queens they reared to determine which patrilines were present in the two groups. 

With certain caveats (size of study, number of microsatellites screened, colony numbers etc.) all concluded that colonies rear emergency queens from some of the rarest patrilines in the colony.

The recent study by Withrow and Tarpy is well explained and probably the most comprehensive, so I’ll use that to flesh out the details.

Experimental details

Six double-brood colonies were each split into a three separate colonies; a queenright single-brood colony and two five-frame nucs. The latter contained eggs and young larvae and so reared emergency queens.

Seven days later the developing emergency queens were all harvested for future analysis. One or two frames from the nucs were then exchanged with frames containing eggs and day-old larvae from the matched queenright colony.

The nucs then started rearing new queens … again.

And again … and again.

This process was repeated until the nucs failed.

In total over 500 queens were reared (to 7 days old) from these six original colonies. These queens were analysed genetically by microsatellite analysis, as were over 500 workers from colonies.

Within the 6 experimental colonies the authors identified a total of 327 patrilines (or subfamilies as Withrow and Tarpy describe them), ranging from 34-77 per colony. 108 patrilines (4-40 per colony) were exclusively detected in worker bees and 130 patrilines (5-55/colony) were exclusively detected in queens.

Cryptic “royal” subfamilies

Over 40% of queens raised per colony were produced from the patrilines exclusively detected in the queen population.

Subfamily distribution per colony.

As shown in the figure above, many queens (black bars) were reared from subfamilies (patrilines) not represented in the worker bee population (grey bars, sorted left to right by abundance).

Since there were different numbers of patrilines per colony (34-77), the bias towards the rarer patrilines is more apparent if you instead split them into tertiles (thirds) based upon worker abundance.

Are the queens predominantly reared from the most common tertile, the intermediate tertile or the rarest tertile?

Frequency distribution of subfamilies.

It’s very clear from this graph that workers select queens from the rarest patrilines within the colony.

It is therefore very clear that worker bees do not exhibit nepotism when choosing which larvae to rear emergency queen from.

Implications for our understanding of honey bee reproduction

Two points are immediately apparent:

  • there is a cryptic population of queen-biased patrilines that have largely been overlooked in genetic studies of honey bee polyandry
  • honey bee queens mate with more drones than conventional studies of worker bee patrilines indicate

Colony 5 had at least 77 distinct subfamilies (there might have been more detected had they screened more than the 94 workers and 135 queens from this colony). By extrapolation it is possible to determine that the effective queen mating frequency (me; the number of drones the queen had mated with) was ~32 if all the samples (worker and queen) were taken into account. If only the worker or queen samples were used for this calculation the effective queen mating frequency would be ~12 or ~65 respectively.

The average effective queen mating frequency over the six colonies was ~33 (total), significantly higher than the oft-quoted (including at the top of this page) me of ~12-18.

So perhaps honey bees really are hyperpolyandrous … or even extremely hyperpolyandrous as the authors suggest.

It’s worth noting in passing that routine mating frequencies over 30 are almost never quoted for honey bees 7, but that the ‘normal’ me ~12-18 is rather low when compared with other species within the genus Apis. The giant honey bee, Apis dorsata, exhibits mating frequencies of greater than 60.

Who’s the daddy?

So, when it comes to emergency queens , although we might not know precisely who the daddy is, we can be pretty certain the particular patriline selected by the workers is most likely to be one of the rare ones in the colony.

Mechanistically, what accounts for this?

Are these larvae selected solely because they are rare?

That seems unlikely, not least because it would require some sort of surveying or screening by nurse bees. Not impossible perhaps, though I’m not sure how this would be achieved.

Perhaps it is not even worker selection?

An alternative way to view it is larval competition. A better competing larvae would be fed Royal Jelly and would be much more likely to pass on her genes to the next generation.

We don’t know the answers to these questions … yet.

Or whether they’re the wrong questions entirely.

Swarming and supercedure

The colony rears a new queen under three conditions; enforced queenlessness (as described above) which induces emergency queen rearing, prior to swarming and during supersedure.

These are fundamentally different processes in terms of the larvae used for queen rearing.

During swarming and supersedure 8 the queen lays the egg in a ‘play cup’ which is subsequently engineered into a queen cell in which the new queen develops.

Play cups

However, it is known that the patrilines of queens reared during the swarming response are similar to those of workers in the same colony 9, implying that there is no overt selection by the workers (or the parental queen).

Queen rearing

Does this insight into how bees rear new queens have any implications for how beekeepers rear new queens?

There are about as many queen rearing methods as there are adult workers in a double-brood colony in late June. Many  exploit the emergency queen rearing response by a colony rendered temporarily or permanently queenless.

Beekeepers often comment on the differential ‘take’ of grafted larvae presented to queenless cell raising colonies.

Sometimes you get very good acceptance of the grafted larvae, other times less so.

Of course, we only show the ones that worked well!

3 day old QCs ...

3 day old QCs …

Differential ‘take’ is often put down to the state of the cell raising colony or the nectar flow (or the cackhandedness of the grafter, or the phase of the moon, or about 100 other things).

I have never heard of beekeepers comparing the ‘take’ of larvae originating from the cell raising colony with those from another colony. The latter are always going to be ‘rare’ if you consider the patrilines present in the cell raising colony. However, grafts taken from the same colony as used for cell raising 10 are likely to reflect the predominant patrilines.

Are these accepted less well by the nurse bees?

I suspect not … but it is testable should anyone want to try.

My expectation would be that the presentation of larvae in a vertically oriented cell bar frame would likely override any genetic selectivity by the colony. They’re desperate to raise a new queen and – thank goodness – here’s a few that might do.

Alternatively, differential acceptance is more likely to reflect use of larvae of an unsuitable age, or that have been damaged during grafting.

As I listen to the wind howling outside it seems like a very long time until I can test any of these ideas … 🙁


Colophon

Ray Winstone (as Carlin) 1979

Who’s the daddy? is British slang for who, or what, is the best. It originated in a line by Ray Winstone’s character Carlin from the 1979 film Scum. This was not a romantic comedy and I’m certainly not recommending viewing it. Nevertheless, the phrase became widely used over the subsequent couple of decades and seemed appropriate here because the colony is dependent on selecting high-quality larvae for colony survival.

Polyandry and colony fitness

Honey bees are polyandrous. The queen mates with multiple drones during her mating flight(s). Consequently, her daughters are of mixed paternity.

In naturally mated queens there is a relationship between the number of patrilines (genetically distinct offspring fathered by different drones) and the ‘fitness’ of a colony.

Colony fitness

A ‘fit’ colony is one that demonstrates one or more desirable traits (those that benefit the colony … and potentially the beekeeper) such as better population growth, weight gain, resistance to pathogens or survival.

If you analyse the molecular genotype of the worker offspring you can determine which patriline they belong to. If you genotype enough workers you start to see the same patrilines appearing again and again. The more patrilines, the more drones the queen mated with 1.

Shallow depth of field

One of many …

Naturally mated queens mate with ~13 drones. Depending upon the study a range from as low as 1 to as high as 40 (and exceptionally into the high 50’s) has been demonstrated, though different studies all tend to produce an average in the low- to mid-teens.

There is a well-established link between polyandry and colony fitness 2. Essentially, the more genetically diverse a colony i.e. the larger the number of patrilines, the fitter that colony is.

The benefits of polyandry

Why should colonies with increased genetic diversity be fitter?

There are a number of hypotheses that attempt to explain why intracolonial genetic diversity is beneficial. These include the increased behavioural repertoire of the worker bees, a reduced production of diploid drones (which would otherwise be produced due to the single-locus sex determination system) and an increased resistance to a wide range of parasites and pathogens 3.

Parasites and pathogens are an extremely effective evolutionary selective pressure. Several studies from David Tarpy and Thomas Seeley have shown that increased polyandry results in better resistance to chalkbrood and American foulbrood.

But what about Varroa? It’s a new pathogen (evolutionarily speaking) to honey bees and there is evidence that the resistance mechanisms observed are genetically determined 4.

Does polyandry contribute to Varroa resistance? 

Would increased polyandry result in improved resistance to mites?

Limits of polyandry and natural resistance

Why is the average number of drone matings in the low teens?

If polyandry is beneficial – and there’s no doubt it is – then surely more patrilines (hyperpolyandry) would be even more beneficial?

How could this be tested?

Naturally mated queens only very rarely exhibit 30+ drone matings. Not only are these colonies hard to find, but they are so rare that doing any sort of statistical analysis of the improved (or otherwise) fitness is probably a non-starter.

Perhaps there’s an alternative way to approach the question? Rather than look at individual colonies within a mixed population, why not study the overall level of polyandry within a population that demonstrates resistance?

For example, do queens that head colonies of untreated feral bees that exhibit a demonstrated enhanced resistance to Varroa, the most important pathogen of honey bees, exhibit higher levels of polyandry?

Two relatively recent scientific papers have tackled these questions. Both have produced clear answers.

Drones : if more is better, is lots more better still?

Yes.

Keith Delaplane and colleagues used instrumental insemination (II) of virgin queens to produce queens ‘mated’ with 15, 30 or 60 drones. Sperm was collected from 1, 2 or 4 drones from 15 donor colonies, mixed thoroughly and used for queen insemination.

Full-sized colonies were requeened with the II queens and left for 6 weeks 5 after which sampling started. Over two seasons a total of 37 colonies (with 11, 13 and 13 colonies respectively headed by queens ‘mated’ with 15, 30 and 60 drones) were tested at approximately monthly intervals.

Testing involved visual analysis of colony strength 6 and comb construction. Mite levels were measured using standard alcohol wash of ~300 bees at mid- or late-summer timepoints.

Brood frame with a good laying pattern

The results of this study are commendably brief … just 8 lines of text and two tables. I’ll summarise them in just a couple of sentences.

Colonies headed by queens ‘mated’ with 30 or 60 drones produced significantly more brood than the colony headed by the queen ‘mated’ with only 15 drones. Conversely, significantly more colonies headed by queens mated with only 15 drones had a higher level of mite infestation 7.

Natural Varroa resistance and polyandry

One of the best studied populations of feral bees co-existing with Varroa are those in the Arnot Forest in New York State. These are the bees Thomas Seeley and colleagues study.

These colonies live in natural holes in trees at low density through the forest. The colonies are small and they swarm frequently. Their spatial distribution, size and swarminess (is that a word?) are all evolutionary traits that enable resistance, or at least tolerance, to Varroa and the pathogenic viruses the mite transmits.

I’ve discussed Seeley’s studies of the importance of colony size and swarming previously. I don’t think I’ve discussed his work on spatial separation of colonies, but I have described related studies by Delaplane and colleagues.

Essentially, by being well-separated, mite transmission between colonies (e.g. during robbing) is minimised. Similarly, by existing as small colonies that swarm frequently Iwith concomitant brood breaks) the mite population is maintained at a manageable level.

Marked queen surrounded by a retinue of workers.

Her majesty …

Do the Arnot Forest Varroa-resistant 8 bees exhibit especially high levels of polyandry, suggesting that this contributes their survival?

No.

Seeley and colleagues determined the number of patrilines in 10 Arnot Forest colonies using the same type of genotyping analysis described earlier. They compared these results to a similar analysis of 20 managed honey bee colonies located nearby.

On average, Arnot Forest queens had mated with ~18 drones (17.8 ± 9.8) each. In contrast, queens in managed colonies in two nearby apiaries had mated with ~16 and ~21 drones. These figures are not statistically different from each other or from the natural mating frequencies reported for honey bees in other studies.

Hyperpolyandry and colony fitness

The first of the studies confirms and extends earlier work demonstrating the polyandry (and in this instance hyperpolyandry i.e. at an even greater level than seen normally) increases colony fitness – at least in terms of colony strength and Varroa resistance.

Delaplane and colleagues hypothesise that the increased mite resistance in hyperpolyandrous (30 or 60 drones) colonies may be explained by either:

  • the importance of extremely rare alleles (gene variants), which would only be present in colonies in which the queen had mated with a very large number of drones.
  • the presence of beneficial non-additive interactions between genetically-determined traits e.g. grooming and hygienic behaviour and reduced mite reproduction.

Neither of which are mutually exclusive and both fit at least some of the extant data on natural mite resistance. Discriminating between these two hypotheses and teasing apart the variables will not be straightforward.

Absence of hyperpolyandry in naturally mite-resistant colonies

At first glance, the absence of the hyperpolyandry in the mite-resistant Arnot Forest bees studied by Thomas Seeley and colleagues appears to contradict the studies using the instrumentally inseminated queens.

The Arnot Forest bees exhibit the same level of polyandry as nearby managed colonies, and for that matter, as colonies studied elsewhere. They are mite-resistant but the queen has not mated with an increased number of drones.

In other studies 9, naturally mated colonies exhibiting different levels of polyandry (within the normal range) showed no correlation between Varroa levels and queen mating frequency.

Perhaps it’s surprising that the Arnot Forest queens hadn’t mated with fewer drones considering the extreme separation of the colonies (when compared with managed colonies). The colony density within the Forest is approximately one per square kilometre.

However, at least during the peak swarming and mating period in the season, drone availability is rarely limiting.

This is because drones are not evenly spread in the environment. Instead, they accumulate in drone congregation areas (DCA) to which the queen flies for mating.

What limits polyandry?

Polyandry is beneficial and, apparently, hyperpolyandry is more beneficial. However, queens mate with 10 – 20 drones, rather than 50 or more. Why is this?

Queen mating is a risky business. The queen has to fly to the DCA, mate with multiple drones and then return to the hive. She may make one or several mating flights.

I’ve discussed how far drones and queens fly to reach the DCA previously. Most drones fly less than 3 miles and 90% of matings occur within about 5 miles of the virgin queen’s hive. The queen probably flies further to the DCA.

All the time she is travelling to and from the DCA, and all the time she is present within it mating, she’s potentially at risk from hungry house martins, swallows, bee eaters (!) or from thunderstorms.

Or simply from getting lost.

Additionally, a number of honey bee pathogens are transmitted between drones and queens during mating. Hyperpolyandrous queens 10 are therefore at risk from these sexually transmitted diseases 11.

It’s therefore likely that the level of polyandry observed in honey bees has evolved as a consequence of the beneficial pressures polyandry brings balanced by the risks associated with mating multiple times.

Practical beekeeping

Although the two studies described here don’t have an immediate relevance to day-to-day practical beekeeping, it’s worth remembering that poor queen mating is regularly blamed for queen failures e.g. queens that develop into drone layers during the winter.

I’m going to write about drones later this year so for the moment will just make these points:

  • drone production is maximised to generate sexually mature drones for the swarming season
  • after eclosion, drones need to mature before being able to mate
  • drones live about 30 days and their sperm volume, though not necessarily viability, decreases as they age

Together this means that late in the season – perhaps late July or early August (though this will vary depending upon location) – the number of drones will decrease.

More significantly, the drones will be ageing.

In turn this means that late-mated queens may not mate with as many drones, or that the matings may not result in insemination.

Most beekeepers will be aware of queens that apparently ‘run out of sperm’ and become drone layers.

However, there may be less obvious problems with late-mated queens. I’m not aware of any studies on seasonality of queen mating and polyandry. However, I would not be at all surprised if they exhibited a reduced level of polyandry.

And, as described above, these colonies are likely to exhibit reduced fitness.

Something else to consider when deciding whether to unite a colony late in the season or hope the last of your virgin queens mates successfully …


 

Women without men

The title of the post last week was The end is nigh which, looking at the fate of drones this week, was prophetic.

Shallow depth of field

Watch your back mate … !

After the ‘June gap’ ended queens started laying again with gusto. However, there are differences in the pattern of egg laying when compared to the late spring and early summer.

Inspections in mid/late August 1 show clear signs of colonies making preparations for the winter ahead.

For at least a month the amount of drone brood in colonies has been reducing (though the proportions do not change dramatically). As drones emerge the cells are being back-filled with nectar.

Seasonal production of sealed brood in Aberdeen, Scotland.

The data in the graph above was collected over 50 years ago 2. It remains equally valid today with the usual caveats about year-to-year variation, the influence of latitude and local climate.

Drones are valuable …

Drones are vital to the health of the colony.

Honey bees are polyandrous, meaning the queen mates with multiple males so increasing the genetic diversity of the resulting workers.

There are well documented associations between colony fitness and polyandry, including improvements in population growth, weight gain (foraging efficiency) and disease resistance.

The average number of drones mating with a queen is probably somewhere between 12 and 15 under real world conditions. However studies have shown that hyperpolyandry further enhances the benefits of polyandry. Instrumentally inseminated queens “mated” with 30 or 60 drones show greater numbers of brood per bee and reduced levels of Varroa infestation.

Why don’t queens always mate with 30-60 drones then?

Presumably this is a balance between access, predation and availability of drones. For example, more mating would likely necessitate a longer visit to a drone congregation area so increasing the chance of predation.

In addition, increasing the numbers of matings might necessitate increasing the number of drones available for mating 3.

… and expensive

But there’s a cost to increasing the numbers of drones.

Colonies already invest a huge amount in drone rearing. If you consider that this investment is for colony reproduction it is possible to make comparisons with the investment made in workers for reproduction i.e. the swarm that represents the reproductive unit of the colony.

Comparison of the numbers of workers or drones alone is insufficient. As the graph above shows, workers clearly outnumber drones. Remember that drones are significantly bigger than workers. In addition, some workers are not part of the ‘reproductive unit’ (the swarm).

A better comparison is between the dry weight of workers in a swarm and the drones produced by a colony during the season.

It’s worth noting that these comparisons must be made on colonies that make as many drones as they want. Many beekeepers artificially reduce the drone population by only providing worker foundation or culling drone brood (which I will return to later).

In natural colonies the dry weight of workers and drones involved in colony reproduction is just about 1:1 4.

Smaller numbers of drones are produced, but they are individually larger, live a bit longer and need to be fed through this entire period. That is a big investment.

Your days are numbered

And it’s an investment that is no longer needed once the swarming season is over. All those extra mouths that need feeding are a drain on the colony.

Even though the majority of beekeepers see the occasional drone in an overwintering colony, the vast majority of drones are ejected from the hive in late summer or early autumn.

About now in Fife.

In the video above you can see two drones being harassed and evicted. One flies off, the second drops to the ground.

As do many others.

There’s a small, sad pile of dead and dying drones outside the hive entrance at this time of the season. All perfectly normal and not something to worry about 5.

Drones are big, strong bees. These evictions are only possible because the workers have stopped feeding them and they are starved and consequently weakened.

A drone’s life … going out with a bang … or a whimper.

An expense that should be afforded

Some of the original data on colony sex ratios (and absolute numbers) comes from work conducted by Delia Allen in the early 1960’s.

Other colonies in these studies were treated to minimise the numbers of drones reared. Perhaps unexpectedly these colonies did not use the resources (pollen, nectar, bee bread, nurse bee time etc) to rear more worker bees.

In fact, drone-free or low-drone colonies produced more bees overall, a greater weight of bees overall and collected a bit more honey. This strongly suggests that colonies prevented from rearing drones are not able to operate at their maximum potential.

This has interesting implications for our understanding of how resources are divided between drone and worker brood production. It’s obviously not a single ‘pot’ divided according to the numbers of mouths to feed. Rather it suggests that there are independent ‘pots’ dedicated to drone or worker production.

Late season mating and preparations for winter

The summer honey is off and safely in buckets. Colonies are light and a bit lethargic. With little forage about (a bit of balsam and some fireweed perhaps) colonies now need some TLC to prepare them for the winter.

If there’s any reason to delay feeding it’s important that colonies are not allowed to starve. We had a week of bad weather in mid-August. One or two colonies became dangerously light and were given a kilogram of fondant to tide them over until the supers were off all colonies and feeding and treating could begin. I’ll deal with these important activities next week.

In the meantime there are still sufficient drones about to mate with late season queens. The artificial swarm from strong colony in the bee shed was left with a charged, sealed queen cell.

Going by the amount of pollen going in and the fanning workers at the entrance – see the slo-mo movie above – the queen is now mated and the colony will build up sufficiently to overwinter successfully.


Colophon

Men without Women

Men without women was the title of Ernest Hemingway’s second published collection of short stories. They are written in the characteristically pared back, slightly macho and bleak style that Hemingway was famous for.

Many of these stories have a rather unsatisfactory ending.

Not unlike the fate of many of the drones in our colonies.

Women without men is obviously a reworking of the Hemingway title which seemed appropriate considering the gender-balance of colonies going into the winter.

If I’d been restricted to writing using the title Men without Women I’d probably have discussed the wasps that plague our picnics and hives at this time of the year. These are largely males, indulging in an orgy of late-season carbohydrate bingeing.

It doesn’t do them any good … they perish and the hibernating overwintering mated queens single-handedly start a new colony the following spring.

Sphere of influence

How far do honey bees fly? An easy enough question, but one that is not straightforward to answer.

The flight range of the honeybee ...

The flight range of the honeybee …

Does the question mean any honey bee i.e. workers, drones or the queen? As individuals, or as a swarm?

Is the question how far can they fly? Or how far do they usually fly?

Why does any of this matter anyway?

Ladies first …

Workers

The first definitive experiments were done by John Eckert in the 1930’s. He located apiaries in the Wyoming badlands at increasing distances from natural or artificial forage 1. Essentially the bees were forced to fly over a moonscape of rocks, sand, sagebrush and cacti to reach an irrigated area with good forage. He then recorded weight gain or loss of the hives located at various distances from the forage.

Wyoming badlands

Wyoming badlands …

The original paper can be found online here (PDF). The experiments are thorough, explained well and make entertaining reading. They involved multiple colonies and were conducted in three successive years.

Surprisingly, Eckert showed that bees would forage up to 8.5 miles from the colony. This means they’d be making a round trip of at least 17 miles – and probably significantly more – to collect pollen and nectar.

However, although colonies situated within 2 miles of the nectar source gained weight, those situated more than 5 miles away lost weight during the experiments.

Gain or loss in hive weight ...

Gain or loss in hive weight …

Therefore, bees can forage over surprisingly long distances, but in doing so they use more resources than they gain.

John Eckert was the co-author (with Harry Laidlaw) of one of the classic books on queen rearing 2. His studies were probably the first thorough analysis of the abilities of worker bees to forage over long distances. Much more recently, Beekman and Ratnieks interpreted the waggle dance (PDF) of bees to calculate foraging distances to heather. In these studies, only 10% of the bees foraged ~6 miles from the hive, although over 50% travelled over 3.5 miles.

Queens

Queens don’t get to do a lot of flying. They go on one or two matings flights, perhaps preceded by shorter orientation flights, and they might swarm.

Heading for a DCA near you ...

Heading for a DCA near you …

I’ll deal with swarms separately. I’ll also assume that the orientation flights are no greater than those of workers (I don’t think there’s any data on queen orientation flight distance or duration) at no more than ~300 metres 3.

On mating flights the queen flies to a drone congregation area (DCA), mates with multiple drones and returns to the colony. DCA’s justify a complete post of their own, but are geographically-defined features, often used year after year.

There are a number of studies on queen mating range using genetically-distinguishable virgin queens and drones in isolated or semi-isolated locations. They ‘do what they say on the tin’, drone congregate there and wait for a virgin queen

In the 1930’s Klatt conducted studies using colonies on an isolated peninsula and observed successful mating at distances up to 6.3 miles

Studies in the 1950’s by Peer demonstrated that matings could occur between queens and drones originally separated by 10.1 miles 4. These studies showed an inverse relationship between distance and successful mating.

More recently, Jensen et al., produced data that was in agreement with this, with drone and queen colonies separated by 9.3 miles still successfully mating 5.

However, this more recent study also demonstrated that more than 50% of matings occurred within 1.5 miles and 90% occurring within 4.6 miles.

Just because they can, doesn’t mean they do 🙂

Drones … it takes 17 to tango …

Seventeen of course, because that’s one queen and an average of 16 drones 😉

There’s a problem with the queen mating flight distances listed above. Did the queen fly 9 miles and the drone fly just a short distance to the DCA?

Or vice versa?

10 miles ... you must be joking!

10 miles … you must be joking!

Or do they meet in the middle?

Do queens choose 6 to fly shorter distances because it minimises the risk of predation and because they are less muscle-bound and presumably less strong flyers than drones?

Alternatively, perhaps drones have evolved to visit local DCAs to maximise the time they have aloft without exhausting themselves flying miles first?

Or getting eaten.

It turns out that – at least in these long-distance liaisons – it’s the queen that probably flies further. Drones do prefer local DCAs 7 and most DCAs are located less than 3 miles from the ‘drone’ apiary 8.

Swarms

I’ve discussed the relocation of swarms recently. Perhaps surprisingly (at least in terms of forage competition), swarms prefer to relocate relatively near the originating hive. Metres rather than miles.

The sphere of influence

Effective foraging – in terms of honey production (or, for that matter, brood rearing) – occurs within 2-3 miles of the hive. This distance is also the furthest that drones usually fly to occupy DCAs for mating.

Queens can fly further, but it’s the law of diminishing returns. Literally. The vast majority of matings occur within 5 miles of the hive.

In fact, other than under exceptional circumstances, a radius of 5 miles from a colony probably represents its ‘sphere of influence’ … either things that can influence the colony, or that the colony can influence.

Why does this matter?

Worker flight distances are relevant if you want to know the nectar sources your bees are able to exploit, or the pollination services they can provide. In both cases, closer is better. It used to also be relevant in trying to track down the source of pesticide kills, though fortunately these are very much rarer these days.

Closer is better ...

Closer is better …

Workers not only fly to forage on plants and trees. They also fly to rob other colonies. I don’t think there are any studies on the distances over which robbing can occur, but I’ve followed bees the best part of a mile across fields from my apiary to find the source of the robbing 9.

All of these movements can also transport diseases about, either in the form of phoretic Varroa mites piggybacking and carrying a toxic viral payload, or as spores from the foulbroods.

Drone and queen flight distances are important if you’re interested in establishing isolated mating sites to maintain particular strains of bees. My friends in the Scottish Native Honey Bee Society have recently described their efforts to establish an isolated queen mating site in the Ochil Hills.

And I’m interested as I now have access to a site over 6 miles from the nearest honey bees in an area largely free of Varroa.

It’s not the Wyoming badlands, but it’s very remote 🙂


 

Last of the drones

At the inspections last weekend there was only one colony with obvious numbers of drones present. We’ve had nearly a full month with no appreciable nectar flow and the colonies have almost all ejected the drones. Here’s one of the few that were left:

Last of the drones

Last of the drones

 

Not long mate until you too are chucked out during the autumn purge. Watch your back!

This colony was a swarm that was attracted to a bait hive in early June. I don’t know whether bee genetics influences the time when drones are ejected from the hive, but it’s notable that almost all the other queens in the apiary are half sisters (unrelated to the queen from the swarm) and there wasn’t a drone to be seen in half a dozen hives. The other notable thing about this colony is that the Varroa levels remain stubbornly high despite three treatments by sublimation. I’m just starting a second series of treatments to get the numbers down to a more acceptable level.