Category Archives: Drifting and robbing

Robbery

Robber

Robber

Another apiculture-flavoured tale of daylight robbery, literally, to follow the post on hive and bee thefts last week.

However, this time it’s not dodgy bee-suited perps with badly inked prison tats offering cheap nucs down the Dog and Duck.

Like other offenders, the robbers this week wear striped apparel, but this time it’s dark brown and tan, or brown and yellow or black and yellow.

I am of course referring to honey bees and wasps (Vespa vulgaris and V. germanica), both of which can cause major problems at this time of year by robbing weak colonies.

Carb loading

The season here – other than for those who have taken colonies to the heather – is drawing to a close. The main nectar sources have more or less dried up in the last fortnight. There’s a bit of rosebay willow herb and bramble in the hedgerows and some himalayan balsam in the river valleys, but that’s about it.

Colonies are strong, or should be. With the dearth of nectar in the fields, the foragers turn their attention to other colonies as a potential source of carbohydrates. Colonies need large amounts of stores to get through the winter and evolution has selected a behavioural strategy – robbing of weaker colonies – to get as much carbohydrate from the easiest possible sources.

Like the nucs you carefully prepared for overwintering 🙁

At the same time, wasps are also wanting to pile in the carbs before winter 1. In the last fortnight the wasp numbers in my apiaries and equipment stores have increased significantly.

Jekyll and Hyde

Within a few days in late summer/early autumn the mood and attitude of colonies in the apiary changes completely.

During a strong nectar flow the bees single-mindedly pile in the stores. They alight, tail-heavy, on the landing board, enter the hive, unload and set out again. There’s a glut and they ignore almost anything other than bingeing on it. Inspections are easy. Most bees are out foraging and they are – or should be – well-tempered and forgiving. 

Laden foragers returning ...

Laden foragers returning …

But then the nectar flow, almost overnight, stops.

Colonies become markedly more defensive. They are packed with bees and they’re tetchy. There’s nothing to distract them, they resent the intrusion and they want to protect their hard-won stores 2.

At the same time, they quickly become more inquisitive, investigating any potential new source of sugar. If you shake the bees off a frame and leave it standing against the leg of the hive stand there will be dozens of foragers – many from nearby colonies – gorging themselves on the nectar.

If you spill unripened nectar from a frame they’re all over it, quickly forming a frenzied mass – probably from several different hives – scrabbling to ‘fill their boots’.

They also closely investigate anything that smells of nectar or honey. Stacks of equipment, empty supers, hive tools, the smoker bellows … anything.

Robbing

And it’s this behaviour that can quickly turn into robbing.

The foragers investigate a small, dark entrance that smells of honey … like a nuc in the corner of the apiary. They enter unchallenged or after a little argy-bargy 3, find the stores, stuff themselves, go back to their colony and then return mob-handed.

Before long, the nuc entrance had a writhing mass of bees trying to get in, any guards present are soon overwhelmed and, in just a few hours, it’s robbed out and probably doomed.

This is the most obvious – and rather distressing – form of robbing. Wasps can do almost exactly the same thing, with similarly devastating consequences.

Prevention is better than cure

Once started (and obvious), robbing is difficult to stop. About the only option is to seal the target hive and remove it to another apiary a good distance away.

Far better to prevent it happening in the first place.

The best way of preventing robbing is to maintain large, strong and healthy colonies. With ample bees there are ample guards and the colony will be able to defend itself from both bees and wasps. Strong colonies are much more likely to be the robbers than the robbed.

For smaller colonies in a full-sized hive, or nucleus colonies or – and these are the most difficult of all to defend – mini-nucs used for queen mating, it’s imperative to make the hive easy to defend and minimise attracting robbers to the apiary in the first place.

The underfloor entrances on kewl floors are much easier to defend than a standard entrance and small entrances are easier to defend than large ones. ‘Small’ might mean as little as one bee-width … i.e. only traversable by a single bee at a time.

Smaller is better ...

Smaller is better …

You can even combine the two; insert a 9mm thick piece of stripwood into the Kewl floor entrance to reduce the space to be defended to a centimetre or two. If – as happened tonight when returning wet supers to the hives – I don’t have a suitable piece of stripwood in the apiary I use a strip of gaffer tape to reduce the entrance 4.

Gaffer tape is also essential to maintain the integrity of the hive if some of the supers are a bit warped. Wasps can squeeze through smaller holes than bees and the quick application of a half metre along the junction between boxes can save the day 5.

The poly nucs I favour have a ridiculously large entrance which I reduce by 90% using foam blocks, dried grass, gaffer tape, wire mesh or Correx.

Correx, the beekeepers friend ...

Correx, the beekeepers friend …

Don’t tempt them

Finally, reduce the inducement robbers – whether bees or wasps – have to investigate everything in the apiary by not leaving open sources of nectar, not spilling honey or syrup, clearing up brace comb and ensuring any stored equipment is ‘bee proof’.

You don’t need to inspect as frequently at this time of the season. The queen will have reduced her laying rate and colonies are no longer expanding. With no nectar coming in they should have sufficient space in the brood nest. There’s little chance they will swarm.

If you don’t need to inspect, then don’t. The ability to judge this comes with experience.

If you do have to inspect (to find, mark and clip a late-season mated queen for example 6 do not leave the colony open for longer than necessary. Any supers that are temporarily removed should be secured so bees and wasps cannot access them.

Wet supers

If you’re returning wet supers after extraction, do it with the minimum disruption late in the evening. These supers absolutely reek of honey and attract robbers from far and wide. Keep the supers covered – top and bottom – gently lift the crownboard, give them a tiny puff of smoke, place the supers on top, replace the roof and leave them be.

Returning wet supers

Returning wet supers …

In my experience wet supers are the most likely thing to trigger a robbing frenzy. I usually reduce the entrance at the same time I put the wet supers back and try to add wet supers to all the colonies in the apiary on the same evening 7.

I generally don’t inspect colonies until the supers are cleaned out and ready for storage.


 

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 🙂


 

If Carlsberg did apiaries …

How about this for an apiary in a truly stunning location?

If Carlsberg did apiaries ...

If Carlsberg did apiaries …

I discovered this apiary while out walking in the Andalucian hills in Southern Spain in mid-May. It was at the end of a forest track, miles from anywhere, with breathtaking views over the cork oak woods South towards the Strait of Gibraltar. It was a bit hazy that afternoon, but on a good day you can clearly see across the Strait to the Rif mountains in Morocco (~100 miles distant), with the faintest trace of the Middle Atlas beyond them.

Not just a pretty view

The photo doesn’t really do justice to the location of the apiary. Yes, the view was great, but what was at least as impressive was the amount of wildflowers around. It’s not an arable area. Most of the farmland was olive trees or lemons, with large areas of wildflower meadow and mixed deciduous woodland. Much of this was cork oak, but it was interspersed with Corsican pines and a variety of other things I couldn’t name.

Wildflower meadow Andalucia

Wildflower meadow Andalucia

I’d be surprised if any of it ever sees a spray of any kind, and the only grazing is by horses, a few feral goats and the elusive wild boar 1. The scene on the right is typical and the road verges were the same, with acres and acres of these beautiful “weeds” everywhere.

Unsurprisingly, the other thing missing from these pictures is the noise.

Everywhere I walked – even on days when I barely left the fringes of the village – I was accompanied by the incessant drone of insects. There were bees everywhere and – again unsurprisingly – the local mixed floral honey was fantastic.

From a beekeeping point of view it really did seem idyllic. Perhaps the only issue would be the temperature. In Spring the midday temperatures were in the mid-20’s (°C) and – going by my experience of working colonies in the bee shed – that can get pretty hot and tiring in a bee suit.

Hives

There were about 20 hives in the apiary, lined up on pallets all in full sun. Unlike other apiaries in the area there was no registration number displayed, so it might have been a temporary site from which the hives would be moved in high summer.

Andalucian apiary

Andalucian apiary

To a beekeeper familiar with the stackable boxes of a National or Langstroth, the hives were unusual. The majority were single boxes, with hinged lids and one or two entrances low down at the front.

Layens hive

Layens hive

These are Layens hives, a single large, deep box containing 15 or more frames. Each frame is about the same width as a British National brood frame, but is almost twice as deep. Georges de Layens, who invented the hive in the 19th Century, designed it for minimal management beekeeping.

No weekly inspections, no overt swarm control, simply give the bees sufficient room in a well-insulated hive and return to harvest the honey at the end of the season.

Can it really be that simple?

Well, it certainly could be that simple.

However, Layens developed the hive long before Varroa appeared on the scene, and monitoring and managing disease in a hive with no removable or open mesh floor – particularly with only a couple of inspections a season – seems an unlikely recipe for success to me 2.

It’s reported that there are still more than a million Layens hives in use in Spain and the hive design has some strong supporters in the US 3. The hive design also lends itself to migratory beekeeping as there are no teetering stacks to be strapped together for transport.

Spanish readers of this site represent less than 0.5% of the annual visitors … if you are one of them please add a comment on the practicalities of beekeeping using the Layens hive.

But it’s not all sunshine and roses

Derelict Spanish apiary

Derelict Spanish apiary

I’ve visited this area of Andalucia for several years. Near the village is an apiary that has – year by year – slowly been falling into disrepair. There were originally ~20 hives in lightly shaded woodland surrounded by wildflower meadows. It was a lovely spot, just off a little-used track, protected from the midday sun, secure yet accessible … though the view wasn’t a patch on the one at the top of the page.

Five years ago most hives – all Layens again – were busy with bees and I remember being surprised by the number of hornets hawking around. The apiary carried a registration number and the hives were scruffy, but functional.

Year by year the number of hives on their side, open, damaged or otherwise clearly defunct has gradually increased. Corners of the apiary filled with broken and discarded frames or other rubbish.

By this Spring it was all over. There were still about 20 hives in the apiary, but none of them were upright and functional. The few that were upright were non-functional and the only one containing bees was badly damaged and on its side, with the bees gaining access from a split in the corner.

It appeared as though the apiary had been abandoned by just about everything other than the Jabalí … and they’d had a field day ransacking the hives.

Ransacked Layens hive ...

Ransacked Layens hive …

Abandoned hives, robbing and mites

Of course, I don’t know the back story … an ageing beekeeper unable to cope any longer, hives inherited by someone without sufficient interest or beekeeping skills, or simply an unproductive apiary that was forgotten.

Bees entering an abandoned Layens hive

Bees entering an abandoned Layens hive

The hives were largely stripped out, but at one point must have posed a disease risk for neighbouring colonies. Unless mite levels were controlled the colonies would eventually succumb to Varroa-transmitted viruses. As the colony weakens it is likely to get robbed-out by strong colonies from nearby apiaries.

The robbers returning to their colonies carry honey and hitchhiking phoretic mites. This is what the Americans call a “mite bomb”.

There’s good evidence that this route of mite transmission peaks late in the season during a dearth of nectar. This is one of the reasons that justifies coordinated mite treatments at the correct time of the year to protect the winter bees.


Colophon

I have no imagination … I’ve used the “If Carlsberg did …” prefix a couple of times already, when discussing smokers and vaporisers. I’ll try and think of something a little more original for the future. In my defence I have spent 50% of the last four weeks abroad, successfully controlled swarming (by vertical splits or Pagdens’) in over half of the ~25 colonies I’m currently managing, run out of supers, brood boxes and frames (D’oh!) and been involved in some exciting new plans for going Varroa-free in the future. Watch this space.

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 …

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

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 …