Category Archives: Practice

Biological control with Varroa

Synopsis : Honey bees were eradicated on Santa Cruz Island following the introduction of Varroa. This provides some useful lessons for beekeepers on the importance of controlling Varroa.

Introduction

Honey bees are not native to North America. They were first introduced in March 1622 at Jamestown, Virginia. The bees did well and spread west, following the settlers. They finally arrived on the west coast, in Santa Clara, California, 231 years later in 1853. Of a dozen hives ordered by Christopher Shelton, a Santa Clara botanist and rancher, only one survived the journey from New York via Panama.

Shelton barely had a chance to enjoy his bees 1 as he was unfortunately killed when the steamboat Jenny Lind exploded in mid-April 1853.

Explosion on the steamboat Jenny Lind near San Francisco, California

His bees survived 2 and three hives derived from the original stock were auctioned for $110 each. This was over 20 times the price of hives on the east coast at that time and equivalent to over $4200 today 3.

Californian Channel Islands map

Bees were in demand and they continued to spread – both as feral swarms and as farmers established apiaries to help pollination and for honey production. Having reached the California coast they were then spread to the nearby islands. Bees were transported to Santa Cruz, the largest of the eight Channel Islands near Los Angeles, in the 1880’s. They flourished, but did not spread to the other Channel Islands.

Field station, nature reserves, pigs and bees

Santa Cruz Island is 250 square kilometres in area and lies ~35 km south of Santa Barbara. It is one of the four Northern Channel islands. There is a long central valley lying approximately east-west and the rocky mountainous land reaches 740 m. It has a marine temperate climate; the average low and high temperatures are 9°C and 21°C respectively and it receives about 0.5 m of rain a year. It is a good environment for bees.

From the 1880’s to 1960’s Santa Cruz Island was farmed – primarily for wine and wool, and from the 1940’s for cattle – but, after period of university geology field trips and the establishment of a field station on the island, in 1973 it became part of the University of California’s Natural Reserve System (UC NRS).

In the late 1970’s the Stanton family sold their ranching business on the island to The Nature Conservancy who subsequently bought additional land on the eastern end of the island.

Santa Cruz Island is now jointly owned by The Nature Conservancy, National Parks Service, UC NRS and the Santa Cruz Island Foundation and much of the island is used for scientific research and education.

But what about the bees?

Good question.

As a nature reserve and research station, the presence of non-native species causes a potential problem. Why go to all the expense of managing a remote island research centre if all the same species are present as on the mainland?

The Nature Conservancy therefore initiated a programme of eradicating non-native species. It took 14 months to eliminate the feral pigs, using a combination of trapping, helicopter-based shooting and the release of sterilised radio-tagged pigs to locate the stragglers 4.

But getting rid of the bees took a bit longer …

Save the bees, or not

Why get rid of the bees? Surely they weren’t doing any harm?

The introduction of any non-native species upsets the balance (if there’s ever balance) in the ecosystem. The introduced species competes directly or indirectly with those native to the area and can lead to local extinctions.

Jonathan Rosen has described 5 how honey bee swarms, through occupying tree cavities previously used for nesting, probably played a major role in the extinction of the Carolina parakeet.

Pining for the fjords … a stuffed Carolina parakeet (nailed to its perch)

Competition between honey bees and native pollinators has been well studied. It is not always detrimental, but it certainly can be. Furthermore, it is probably more likely to be detrimental in a small, isolated, island ecosystem. For example, studies showed that the presence of honey bees dramatically reduced visitation of native pollinator to manzanita blossoms on Santa Cruz Island.

As part of the larger programme of non-native plant and animal eradication on Santa Cruz Island plans were drawn up in the late 1980’s to eliminate European honey bees. The expected benefits were to:

  • eliminate competition with native bee species (and presumably other non-bee pollinators, though these rarely get a mention 🙁 )
  • reduce pollination of weed species (some of which were also non-native to Santa Cruz Island)
  • facilitate recovery of native plant species that were reliant on native bee pollination
  • provide a ‘field laboratory’ free from ‘exotic’ honey bees in which comparative studies of native pollinators would be possible

Killer bees

After the plans to eradicate Apis mellifera were approved an additional potential benefit became apparent.

There were increasing concerns about the spread of Africanised honey bees which had recently reached Santa Barbara County. Although there was reasonably compelling evidence that swarms could not cross from the mainland (e.g. none of the other Northern Channel Islands had been colonised by bees) there were concerns that the Santa Ana winds might help blow drones from the mainland.

Had these drones arrived they might mate with the non-native but nevertheless local queens resulting in the spread of the dominant genes for defensiveness and absconding. The resulting swarmy, aggressive Africanised bees would cause problems for visitors and scientists working on the island (as they have for visitors to Joshua Tree National Park).

Aerial view of Santa Cruz Island

Although the introgression of African honey bee genes was used as further justification for the eradication it’s not clear whether drones could actually cross 30-40 km of open sea 6.

As an aside, there’s a current project – the amusingly named Game of Drones – running on the Isles of Scilly investigating whether drones can cross the sea between St Agnes, Tresco, Bryher, St Mary’s and St Martin’s. These are, at most, 11 km apart (northern most tip of St Martin’s to most southerly point of St Agnes) but the individual islands are only separated by 1-2 km. I would be surprised if drones could not cross that distance (at least with a strong following wind).

Killing bees

Adrian Wenner and colleagues set about exterminating the honey bees on Santa Cruz Island (Wenner et al., 2009). The process started in 1988 and ended in 2007, and was divided into four phases:

  1. 1988-1993 – location and elimination of feral colonies
  2. 1994-1997 – biological control and colony demise
  3. 1998-2004 – monitoring residual honey bee activity
  4. 2005-2007 – confirmation of the absence of honey bees

None of this is ’beekeeping’ – actually it’s the exact opposite – so I don’t intend to dwell in much detail on the work that was conducted. However, the ’94-’97 phase includes some sobering lessons for beekeepers which are worth discussing.

By the end of phase 1 the team had identified the existence (if not the location) of at least 200 colonies and eliminated 153 of them.

Remember, none of these were managed colonies in hives. They were all feral colonies occupying natural cavities in trees or rocks etc. Each colony was found using painstaking bee lining techniques similar to those described in Thomas Seeley’s book Following the Wild Bees.

Once located, nests were destroyed with methyl chloroform and the cavity sealed to prevent it being reoccupied.

Some colonies could not be accessed; in these cases acephate-laced sucrose-honey syrup baits were used. This organophosphate has delayed toxicity for bees, allowing foragers to return to the colony which in due course dies. This approach had been partially successful in eliminating Africanised bees on the mainland (Williams et al., 1989), but baits needed to be be monitored to avoid killing the other insects they attracted.

The scientists also deployed swarm traps (aka bait hives) and destroyed any swarms that moved in.

Together these interventions reduced honey bee numbers significantly – as monitored by regular observations at pollen- or nectar-rich plants – but did not eradicate them.

Let there be mite

Heavy rains in January ’93 washed out roads on Santa Cruz Island, thereby severely limiting travel around the island. In addition, the previous removal of cattle had resulted in the near-uncontrolled growth of fennel which now formed dense, impenetrable thickets.

Bee lining became impossible and the scientists had to invent more devious strategies to eliminate the residual feral colonies.

The approach they chose involved the introduction of Varroa.

Varroa was first detected in the USA in 1987 (in Florida) and became widespread over the next 5-8 years. Up until 1994 the honey bees on Santa Cruz Island were free of the ectoparasitic mite.

It was likely that they would have remained that way … there was no beekeeping on Santa Cruz Island and the location was too remote for bees to cross from the mainland (see above).

Varroa was already known to have a devastating impact on the health of honey bee colonies (Kraus and Page, 1995). It was also known that, other than its native host Apis cerana (the Eastern honey bee), Varroa did not parasitise other bee or wasp species (Kevan et al., 1991).

These two facts – host specificity and damage inflicted – suggested that Varroa could be used for biological control (‘biocontrol’) on Santa Cruz Island.

Biological control

Biological control or biocontrol is a method of controlling pests using natural mechanisms such as predation or parasitism.

The pest could be any living thing – from animals to bacterial plant diseases – present where it’s unwanted.

On Santa Cruz Island the pest was the honey bee.

In other studies (covered in a previous post entitled More from the fungi 7 ) biocontrol of Varroa has been investigated.

Control of the pest involves the introduction or application of a biological control agent. The key requirements of the latter have already been highlighted – specificity and damage.

Biological control works well when the specificity is high and the damage is therefore tightly targeted. It can be an abject failure – or worse, it can damage the ecosystem – if the specificity is low and/or the damage is widespread.

The cane toad was introduced to Australia to control infestations of greenback cane beetle (a pest of sugar cane). Cane toads were introduced in 1935 and rapidly spread. Unfortunately, cane toads can’t jump very high and so singularly failed to control the greenback cane beetle which tends to 8 stay high up the cane stems.

Female cane toad (not jumping)

But it gets worse; cane toads have a very catholic diet and so outcompeted other amphibians. They introduced foreign diseases to the native frogs and toads and – because of the poisons secreted from their skin – harmed or killed predators that attempted to eat them.

Oops.

Vertebrates are usually poor biological control agents as they tend to be generalist feeders i.e. no specificity.

But Varroa is specific and so the damage it causes is focused. The likelihood of ecosystem damage was considered low and so the mite was introduced to the island.

Introduction of Varroa

In late 1993 Adrian Wenner caught 85 foraging bees and, to each one, added a single Varroa mite. The bees were then released and presumably flew back to their colonies … taking the hitchhiking mite with them.

Adult mites – the dark red ones you see littering the Varroa tray after you treat with Apivar – are mated females.

Due to their incestuous lifestyle a single mite is sufficient to initiate a new infestation.

The mated adult female mite parasitises a honey bee pupa and produces a series of young; the first is male, the remainder are female. You’re probably reading this before the 9 pm watershed so I’ll leave it to your lurid imagination to work out what happens next (or you can read all the sordid details in Know your enemy).

The presence of honey bees – determined by successful swarm trapping or field observation at likely sites – was then regularly monitored over the next four years.

Swarm numbers remained largely unchanged until 1996 and then dramatically decreased.

Numbers of new swarms on Santa Cruz Island 1991 – 2005. Varroa introduction indicated.

It’s worth noting that during ’94-’96 over 70 swarms were found in natural sites or bait hives. There must have been a significant number of established colonies in 1993 to produce this number of swarms.

But, from 1997 it all stopped … only a single swarm was subsequently found, in a natural cavity in 2002.

Monitoring and confirmation of eradication

From 1998 to 2004 the scientists continued to actively monitor the island for honey bees, focusing on 19 areas rich in natural forage. Although honey bees were found – in decreasing numbers – there were too few to attempt bee lining to locate their colonies.

At the sites being monitored, bees were detected 9, 7, 4, 2 and 1 times respectively in the 5 years from 2000 to 2004. After that, despite continued monitoring, no more honey bees were detected.

The final phase of the project (’05-’07) confirmed the absence of honey bees on Santa Cruz Island.

Whilst, as a scientist, I’m a firm believer that ’absence of evidence does not mean evidence of absence’, as a beekeeper I’m well aware that if there are no scout bees, no swarms and no foragers (when I search in likely places) then there are no honey bee colonies.

Lessons for beekeepers

I wouldn’t have recounted this sorry tale – at least from a beekeeping perspective – unless I thought there were some useful lessons for beekeepers.

There are (at least) three.

The first relates to Varroa resistance, the second to Varroa transmission in the environment and the last to ‘safe’ levels of Varroa. All require some ‘arm waving guesstimates’ 9, but have a good grounding in other scientific studies.

Varroa resistance

There wasn’t any.

At a very conservative estimate there were at least 20 colonies remaining on Santa Cruz Island in 1995. I say ‘conservative’ because that assumes each colony generated two swarms that season (see graph above). In studies of other natural colonies only about 75% swarm annually, meaning the actual number of colonies could have been over 50.

The numbers – 20 or 50 – matter as they’re both much higher than the number of colonies most beekeepers manage (which, based upon BBKA quoted statistics, is about 5).

Whether it was 20 or 50, they were all eliminated following the introduction of 85 mites. Colonies did not become resistant to Varroa.

This all took a few years, but – inferring from the swarm numbers above – the vast majority of colonies were killed in just two years, 1994 and 1995. This timing would fit with numerous other studies of colony demise due to mites.

Wenner estimates that only 3 colonies survived until 2001.

Leaving small numbers of colonies 10 untreated with an expectation that resistance – or even tolerance (which is both more likely and not necessarily beneficial) – will arise is a futile exercise.

I’ve discussed this before … it’s a numbers game, and a handful of colonies isn’t enough.

Varroa spread

Wenner doesn’t elaborate on where the foragers were captured before he added the mites. If I was going to attempt this I’d have chosen several sites around the island to ensure as many feral colonies as possible acquired mites … let us assume that’s what he did.

However, with 85 mites piggybacking on returning workers, and somewhere between (my guesstimated) 20 to 50 colonies, I think it’s highly likely that at least some colonies received none of this ’founding’ mite population.

Yet almost all the colonies died within two years, and those that did not subsequently died with no further intervention from the scientists. We don’t know what killed off the last surviving colonies but — and I know I’m sticking my neck out here – I bet it was the mites.

This is compelling evidence for the spread of Varroa throughout the island environment, a process that occurs due to the activities of drifting and robbing.

If a neighbouring apiary to yours has mites some will end up in your hives … unless you are separated by several kilometres 11.

The transmission of mites in the environment is a very good reason to practice coordinated Varroa control.

One mite is all it takes

But, just as I’ve argued that some colonies may have received none of the founding mites, I’m equally sure that others will have acquired very small numbers of mites, perhaps just one.

And one mite is all it takes.

Without exceptional beekeeping skills, resistance in the bee population or rational Varroa control 12 there is no safe level of mites in a colony.

The more you prevent mites entering the colony in the first place, and the more of those that are present you eradicate, the better it is for your bees.

Here endeth the lesson 😉


Note

It’s worth noting that island populations do offer opportunities for the development of Varroa resistant (or tolerant) traits … if you start with enough colonies. Fries et al., (2006) describes the characteristics of the 13 surviving colonies on Gotland after leaving about 180 colonies untreated for several years. I’ve mentioned this previously and will return to it again to cover some related recent studies.

References

Fries, I., Imdorf, A. and Rosenkranz, P. (2006) ‘Survival of mite infested (Varroa destructor) honey bee (Apis mellifera) colonies in a Nordic climate’, Apidologie, 37(5), pp. 564–570. Available at: https://doi.org/10.1051/apido:2006031.

Kevan, P.G., Laverty, T.M. and Denmark, H.A. (1990) ‘Association of Varroa Jacobsoni with Organisms other than Honeybees and Implications for its Dispersal’, Bee World, 71(3), pp. 119–121. Available at: https://doi.org/10.1080/0005772X.1990.11099048.

Kraus, B. and Page, R.E. (1995) ‘Effect of Varroa jacobsoni (Mesostigmata: Varroidae) on feral Apis mellifera (Hymenoptera: Apidae) in California’, Environmental Entomology, 24(6), pp. 1473–1480. Available at: https://doi.org/10.1093/ee/24.6.1473.

Wenner, A.M., Thorp, R.W., and Barthell, J.F. (2009) ‘Biological control and eradication of feral honey bee colonies on Santa Cruz Island, California: A summary’, Proceedings of the 7th California Islands Symposium, pp. 327–335. Available as a PDF.

Williams, J.L., Danka, R.G. and Rinderer, T.E. (1989) ‘Baiting system for selective abatement of undesirable honey bees’, Apidologie, 20(2), pp. 175–179. Available at: https://doi.org/10.1051/apido:19890208.

 

Mellow fruitfulness

Synopsis : Final colony inspections and some thoughts on Apivar-contaminated supers, clearing dried supers, feeding fondant and John Keats’ beekeeping.

Introduction

The title of today’s post comes from the first line of the poem ’To Autumn’ by John Keats:

Season of mists and mellow fruitfulness

The poem was written just over 200 years ago and was the last major work by Keats (1795-1821) before he died of tuberculosis. Although it wasn’t received enthusiastically at the time, To Autumn is now one of the most highly regarded English poems.

The poem praises autumn, using the typically sensuous imagery of the Romantic poets, and describes the abundance of the season and the harvest as it transitions to winter.

That’s as maybe … the last few lines of the first verse raises some doubts about Keats’ beekeeping skills:

And still more, later flowers for the bees,
Until they think warm days will never cease,
 For summer has o’er-brimm’d their clammy cells.

It’s certainly true that there are late summer flowers that the bees can forage on 1. However, he’s probably mistaken in suggesting that the bees think in any sense that involves an appreciation of the future.

And what’s all this about clammy cells?

If there’s damp in the hive in late summer then it certainly doesn’t bode well for the winter ahead.

Clammy is now used mean damp; like vapour, perspiration or mist. The word was first used in this context in the mid-17th Century.

‘Clammy’ honey

But Keats is using an earlier meaning of ’clammy’ … in this case ’soft, moist and sticky; viscous, tenacious, adhesive’, which dates back to the late 14th-Century.

And anyone who has recently completed the honey harvest will be well aware of how apt that definition is 😉 … so maybe Keats was a beekeeper (with a broad vocabulary).

And gathering swallows twitter in the skies

That’s the last line of ’To Autumn’ (don’t worry … you’ve not inadvertently accessed the Poetry Please website). The swallows are gathering and, like most summer migrants, already moving south. Skeins of pink-footed geese have started arriving from Iceland and Greenland.

Skein of geese over Fife

My beekeeping over the last fortnight has been accompanied by the incessant, plaintive mewing of buzzards. These nest near my apiaries and the calling birds are almost certainly the young from this season.

A few nights ago, while hosing the extractor out in the bee-free-but-midge-filled late evening, I was serenaded by tawny owls as the adults evicted their young from the breeding territory in preparation for next season.

These are all signs, together with the early morning mists, that summer is slipping away and the autumn is gently arriving.

Morning mist clearing over the loch

The beekeeping season is effectively over and all that remains is preparing the colonies for winter.

Supers

All the supers were off by the 22nd of August. There was still a little bit of nectar being taken in but the majority was ripe and ready. As it turns out there was fresh nectar in all the colonies when I checked on the 10th of September, but in such small amounts – no more than half a frame – that it wouldn’t have been worth waiting for.

At some point you have to say … enough!

Or, this year, more than enough 🙂 .

Most of the honey was extracted by the end of August. It was a bonanza season with a very good spring, and an outstanding summer, crop. By some distance the best year I’ve had since returning to Scotland in 2015.

Of course, that also meant that there were more supers to extract and return and store for the winter ahead.

Lots of lifting, lots of extracting and lots of buckets … and in due course, lots of jarring.

Storing supers wet or dry?

In response to some recent questions on storing supers wet or dry I tested ‘drying’ some.

I’ve stored supers wet for several seasons. I think the bees ‘like’ the heady smell of honey when they are added back to the hives for the spring nectar flow. The supers store well and I’ve not had any problems with wax moth.

However, this year I have over two full carloads of supers, so – not having a trailer or a Toyota Hilux 2 – I have to make multiple trips back to put them in storage 3. These trips were a few days apart.

I added a stack of wet supers to a few hives on the 1st of September and cleared them on the 9th. All these supers were added over an empty super (being used as an eke to accommodate a half block of fondant – see below) topped with a crownboard with a small hole in it (no more than 2.5 cm in diameter, usually less).

Converting wet supers to dry supers – note the crownboard with a small central hole

When I removed the supers on the 10th they had been pretty well cleaned out by the bees. In one case the bottom super had a very small amount of fresh nectar in it.

So, 7-8 days should be sufficient for a strong colony to clean out 3-4 supers and it appears as though you can do it at the same time as feeding fondant … result 🙂 .

Feeding fondant

I only feed my colonies Baker’s fondant. I add this on the same day I remove the honey-laden supers. I’ve discussed fondant extensively here before and don’t intend to rehash the case for its use again.

Oh well, if you insist 😉 .

I can feed a colony in less than two minutes; unpacking the block, slicing it in half and placing it face down over a queen excluder (with an empty super as an eke) takes almost as much time to write as it does to do.

Take care with sharp knives … much easier with a slightly warm block of fondant

But speed isn’t the only advantage; I don’t need to purchase or store any special feeders (an Ashforth feeder costs £66 and will sit unused for 49 weeks of the year). I’ve also not risked slopping syrup about and so have avoided encouraging robbing bees or wasps.

I buy the fondant through my association. We paid £13 a block this year (up from about £11 last year). That’s more expensive than making or buying syrup (though not by much) and I don’t need to have buckets or whatever people use to store, transport and distribute syrup. Fondant has a long shelf life so I buy a quarter of a ton at a time and store what I don’t use.

All gone! 12.5 kg of fondant added on 22/8/22 and photographed on 9/9/22

And, contrary to what the naysayers claim, the bees take it down and store it very well.

What’s the biggest problem I’ve had using fondant?

The grief I get when I forget to return the breadknife I stole from the kitchen … 😉 .

Apivar-contaminated honey and supers

Last season I had to treat a colony with Apivar before the supers came off. This was one of our research colonies and we had to minimise mite levels before harvesting brood.

I’ve had a couple of questions recently on what to do with supers exposed to Apivar … this is what I’ve done/will do.

Apivar

The Apivar instructions state something like ’do not use when supers are present’ … I don’t have a set of instructions to check the precise wording (and can’t be bothered to search the labyrinthine VMD database).

Of course, you’re free to use Apivar whenever you want.

What those instructions mean is that honey collected if Apivar is in the hive will be ’tainted’ and must not be used for human consumption.

But, it’s OK for the bees 🙂 .

So, I didn’t extract my Apivar-exposed supers but instead I stored them – clearly labelled – protected from wasps, bees and mice.

This August, after removing the honey supers I added fondant to the colonies. In addition, I added an Apivar-exposed super underneath the very strongest colonies – between the floor and the lower brood box.

I’ll leave this super throughout the winter. The bees will either use the honey in situ or will move it up adjacent to the cluster.

In spring – if I get there early enough – the super will be empty.

If I’m late they may already be rearing brood in it 🙁 … not in itself a problem, other than it means I’m flirting with a ridiculous ’double brood and a half’.

Which, of course, is why I added it to the strongest double brood colonies. It’s very unlikely the queen will have laid up two complete boxes (above the nadired super) before I conduct the first inspection.

But what to do with the now-empty-but-Apivar-exposed supers?

It’s not clear from my interpretation of the Apivar instructions (that I currently can’t find) whether empty supers previously exposed to Apivar can be reused.

WARNING … my reading might be wrong. It states Apivar isn’t to be used when honey supers are on but, by inference, you can use and reuse brood frames that have been exposed to Apivar.

Could you extract honey from brood frames that have previously (i.e. distant, not immediate, past) been Apivar-exposed?

Some beekeepers might do this 4.

It’s at this point that some common sense it needed.

Just because re-using the miticide-exposed supers is not specifically outlawed 5 is it a good idea?

I don’t think it is.

Once the bees have emptied those supers I’ll melt the wax out and add fresh foundation before reusing them.

My justification goes something like this:

  • Although amitraz 6 isn’t wax-soluble a formamidine breakdown product of the miticide is. I have assumed that this contaminates the wax in the super.
  • I want to produce the highest quality honey. Of course this means great tasting. It also means things like wings, legs, dog hairs and miticides are excluded. I filter the honey to remove the bee bits, I don’t allow the puppies in the extracting room and I do not reuse supers exposed to miticides.
  • During a strong nectar flow bees draw fresh comb ‘for fun’. They’re desperate to have somewhere to store the stuff, so they’ll draw out comb in a new super very quickly. Yes, drawn comb is precious, but it’s also easy to replace.

Final inspections

I conducted final inspections of all my colonies in Fife last weekend 7.

For many of these colonies this was the first time they’d been opened since late July. By then most had had swarm control, many had been requeened and all were busy piling in the summer nectar.

Why disturb them?

The queen had space to lay, they weren’t likely to think about swarming again 8 and they were strong and healthy.

Midsummer inspections are hard work … lots of supers to lift.

If there’s no need then why do it?

Of course, some colonies were still busy requeening, or were being united or had some other reason that did necessitate a proper inspection … I don’t just abandon them 😉 .

I don’t just abandon them … introducing a queen to a nucleus colony

But now the supers were off it was important to check that the colonies were in a suitable state to go into the winter.

I take a lot of care over these final inspections as I want to be sure that the colony has the very best chance of surviving the winter. 

I check for overt disease, the amount of brood in all stages (BIAS; so determining if they are queenright) and the level of stores.

And, while I’m at it, I also try and avoid crushing the queen 🙁 .

Queenright?

I don’t have to see the queen. In fact, in most hives it’s almost impossible to see the queen because the box is packed with bees. If there are eggs present then the queen is present 9.

But, there might not be a whole lot of eggs to find.

Firstly, the queen is rapidly slowing down her egg laying rate. She’s not producing anything like 1500-2000 eggs per day by early autumn.

A National brood frame has ~3000 cells per side. If you find eggs equivalent in area to one side of a brood frame she’s laying at ~1000/day. By now it’s likely to be much less. At 500 eggs/day you can expect to find no more than half a frame of eggs in the hive.

Remember the steady-state 3:5:13 (or easier 1:2:4) ratio of eggs to larvae to pupae? 10

Several of my colonies had about half a frame of eggs but significantly more than four times that amount of sealed brood … clear evidence that the laying rate is slowing dramatically.

The shrinking brood nest – note the capped stores and a little space to lay in the centre of the frame

Secondly, the colony is rapidly filling the box with stores, so reducing the space she has to lay. They’re busy backfilling brood cells with nectar.

Look and ye shall find …

So I focus carefully on finding eggs. I gently blow onto the centre of the frames to move the bees aside and search for eggs.

In a couple of hives I was so focused on finding eggs that – as I prepared to return the frame to the colony – I only then saw the queen ambling around on the frame. D’oh!

Some colonies had only 3-4 frames of BIAS, others had lots more though guesstimating the precise area of brood is tricky because of the amount of backfilling taking place.

I still need to check my notes to determine whether it’s the younger queens that are still laying most eggs … I’d not be surprised.

Stores

Boxes are now heavy but not full. All received (at least) half a block of fondant in late August and more last weekend. There’s also a bit of late nectar. The initial half block was almost finished in a week.

Once the bag is empty I simply peel it away from the queen excluder. If you’re doing this, leave the surrounding super in place. It acts as a ‘funnel’ to keep the thousands of displaced bees in the hive rather than down your boots and all over the floor.

Although the bees were flying well, the bees in and around the super were pretty lethargic. I’ve seen this before and am not concerned. I don’t know whether these are bees gorged with stores, having a kip or perhaps young bees that don’t know their way about yet. However, it does mean that any bees dropped while removing the bag tend to wander aimlessly around on the ground.

I’d prefer they were in the hive, out of the way of my size 10’s.

If you look at many of the frames in the hive they will be partially or completely filled with stores. The outer frames are likely to be capped already. 

An outer frame of capped stores

These frames of stores are heavy. There’s no need to look through the entire box. I simply judge the weight of each frame and inspect any that are lighter than a full frame of stores.

Closer to the brood nest you’ll probably find a frame or two stuffed, wall-to-wall, with pollen. Again, a good sign of a healthy hive with the provisions it needs to rear the winter bees and make it to spring.

Disease

The only sign of disease I saw was a small amount of chalkbrood in one or two colonies. This is a perennial situation (it’s not really a problem) with some of my bees. Quite a few of my stocks have some (or a lot of) native Apis mellifera mellifera genes and these often have a bit of chalkbrood.

I also look for signs of overt deformed wing virus (DWV) damage to recently emerged workers. This is the most likely time of the year to see it as mite levels have been building all season and brood levels are decreasing fast. Therefore, developing brood is more likely to become infested and consequently develop symptoms.

Fortunately I didn’t see any signs of DWV damage and the initial impression following the first week or so of miticide treatment is that mite levels are very low this season. I’ll return to this topic once I’ve had a chance to do some proper counts after treating for at least 8-10 weeks (I use Apivar and, since my colonies all have medium to good levels of brood, the strips need to be present for more than the minimum recommended 6 weeks).

Closing up

Although these were the last hive inspections, they weren’t the last time I’ll be rummaging about in the brood box.

At some point during the period of miticide treatment I’ll reposition the strips (adjacent to the ever-shrinking brood nest) having scraped them to maximise their effectiveness.

Apivar scratch and sniff repositioning studies

However, all that will happen in a month or so when I can be reasonably sure the weather will be a lot less benign. Far better to get the inspections out of the way now, just in case.

So, having added the additional fondant (typically half a block) I closed the hives, strapped them up securely and let them get on with making their preparations for the coming winter.

Goodbye and thanks for the memories

There’s a poignancy about the last hive inspections of the season.

The weather was lovely, the colonies were strong and flying well, and the bees were wonderfully placid. It’s been a great season for honey, disease levels are low to negligible and queen rearing has gone well 11.

But it’s all over so soon 🙁 .

Hive #5 (pictured somewhere above … with the empty bag of fondant) was from a swarm control nuc made up on the last day of May (i.e. a 2021 queen). It was promoted to a full hive in mid-June. At the same time, while the hive they came from (#28) was requeening I’d taken more than 20 kg of spring honey from it. The requeening of #28 took longer than expected as the first was almost immediately superseded. Nevertheless, the two hives also produced almost 4 full supers (conservatively at least 40 kg) of summer honey.

Good times 🙂 .

My notes – for once – are comprehensive. Over the long, dark months ahead I’ll be able to sift through them to try and understand better 12 what went wrong.

That’s because – despite what I said in the opening paragraph of this section – there were inevitably any number of minor calamities and a couple of major snafu’s.

Or ’learning opportunities’ as I prefer to call them.

Last light over Rum and Eigg … not a bad view when visiting an out apiary

But that’s all for the future.

For the moment I have a sore back and aching fingers from extracting for days and the memory of a near-perfect final day of proper beekeeping.

It’s probably time I started building some frames 🙁


 

Tim Toady

Synopsis : The large number of beekeeping methods is both a benefit and – for beginners particularly – a distraction. Learn methods well enough to be confident when you apply them. Understand why they work and their pros and cons.

Introduction

In an earlier life as a junior academic I was generously given a crushingly boring administrative task. The details don’t matter 1 but it essentially involved populating a huge three-dimensional matrix. The matrix had to be re-populated annually … and, when I was allocated the task, manually.

To cut a long story short I taught myself some simple web-database computer programming. This automated the data collection and entry and saved me many weeks of tedious work.

Geek alert …

This minor victory resulted in me:

  • writing lots more code for my admin and research, and for my hobbies including beekeeping and photography. It’s been a really useful skill … and a lot of fun.
  • inevitably being given an additional mundane task to fill the time I had ‘saved’ 🙁 2.

The programming language I used was perl. This is a simple scripting language, which although now superseded in popularity by things like python, remains very widely used. All proper computers 3 still have perl installed.

Perl is perfect for manipulating text-based records. The name is an acronym for ’practical extraction and reporting language’ … or perhaps ’pathetically eclectic rubbish lister’, the latter reflecting its use to manipulate text (‘garbage in, garbage out’ … ) 4.

Perl was (and remains) powerful because it’s a very flexible language. You can achieve the same goal in many different ways.

This flexibility is reflected in the perl motto: ’There’s more than one way to do it’, which is abbreviated to TMTOWTDI.

TMTOWTDI is a mouthful of alphabet spaghetti, so for convenience is pronounced Tim Toady … the title of today’s post.

Why?

Because exactly the same acronym could be applied to lots of things in beekeeping.

Ask three beekeepers, get five answers

But one of the five is wrong because it involves ’brood and a half’.

Anyone who has attended an association meeting and naively asked a simple question will understand the title of this section.

’How do I … [insert routine beekeeping problem here] … ?’

The old and the wise, or perhaps the old or the wise, will recommend a series of solutions. Some will offer more than one.

Each will be different.

Many recommendations will be perfectly workable.

A few might be impractical.

At least one will be just plain wrong.

How do I avoid brace comb?

Confusingly … despite all being proffered solutions to the one question you asked, many will appear contradictory.

Do you move the queen away (the nucleus method) or leave the queen on the same site (Pagden’s artificial swarm) for swarm control? How can they both work if you do such very different things?

Ask twelve beekeepers, get nineteen answers (ONE IN ALL CAPS)

Internet discussion forums (fora?) are exactly the same, but may be less polite. This is due to the absence of the calming influence of tea and homemade cake. At least one answer will include a snippy suggestion to ’use the search facility first’.

Another will be VERY VERY SHOUTY … the respondent either disagrees vehemently or has misplaced the CAPS LOCK key.

Actually, in many ways internet discussion forums are a lot worse … though not for the reasons you might expect.

It’s not because they’re populated with a lot of cantankerous ageing beekeepers and arriviste know-it-alls.

They’re not 5.

There are some hugely experienced and helpful beekeepers online, though they probably don’t answer first or most forcefully.

The internet is worse because the audience is bigger and is spread over a wider geographic area. This is a problem as beekeeping is effectively a local activity.

If you ask at a local association meeting there will be a smaller ‘audience’ and they should at least all have some experience of the particular conditions in your area.

Včelařské fórum … and something you won’t see on the BKF … a whole sub-forum on subsidies

But if you ask on Beesource, Včelařské fórum or the Beekeeping & Apiculture forum the answers may literally be from anywhere 6. The advice you receive, whilst possibly valid, is likely to be most relevant where the responder lives … unless you’re lucky.

On one of the forums I irregularly frequent many contributors have their latitude and longitude coordinates (and sometimes plant hardiness zones) embedded in their .sig.

Geeky perhaps, but eminently sensible … 7

Tim Toady beekeeping

Let’s consider a few of examples of Tim Toady beekeeping. I could have chosen almost any aspect of our hobby here, but I’ll stick with three that are all related to the position or fate of the queen.

Queen introduction

Perhaps this was a bad option to choose first. Queen introduction isn’t only about how you physically get the new queen safely into the hive e.g. in some form of temporary cage. It’s also about the state of the hive.

Is it queenless? How long has it been queenless and/or is there emerging brood present? Is the brood from the previous queen or from laying workers? Is it a full hive or a nuc … or mini-nuc?

Successful introduction ...

Successful introduction …

And it’s about the state of the new queen.

Is she mated and laying, or is she a virgin? Perhaps she’s still in the queen cell? Is the queen the same (or a similar) strain to the hive being requeened? Is she in a cage of some sort? Are there attendants in the cage with her?

And all that’s before you consider whether it’s ‘better’ to use a push-in cage, a JzBz (or similar) cage or to omit the cage and just rely upon billowing clouds of acrid smelling smoke.

Uniting colonies

This blog is nothing if not ’bleeding-edge’ topical … now is the time to consider uniting understrength colonies, or those headed by very aged queens that may fail overwinter.

Uniting two weak colonies will not make a strong colony. However, uniting a strong with a weak colony will strengthen the former and possibly save the latter from potential winter loss (after you’ve paid for and applied the miticides and winter feed … D’oh!). You can always split off a nuc again in the spring.

All the above assumes that both colonies are healthy.

There are fewer ways of uniting colonies than queen introduction, and far fewer than the plethora of swarm control methods.

This is perhaps unsurprising as there are fewer component parts … hive A and hive B, with the eventual product being A/B.

Or perhaps B/A?

United we stand …

But which queen do you keep? 8

And does the queenright hive go on top or underneath?

And how do you prevent the bees from fighting, but instead allow them to mingle gently?

Or do you simply spray them with a few squirts of Sea breeze air freshener, slap the boxes together and be done with it?

Swarm control

If you find queen cells in your colony – assuming they haven’t swarmed already – then you need to take action or the colony will possibly/probably/almost certainly/indubitably 9 swarm.

The primary goals of swarm control are to retain the workforce – the foragers – and the queen.

There are a lot of swarm control methods. Many of the effective ones involve the separation of the queen and hive bees (those yet to go on orientation flights) from the foragers and brood. Some of these methods use unique equipment and most require additional boxes or split boards.

Split board

Split board …

But there are other ways to achieve the same overall goals, for example the Demaree method which keeps the entire workforce together by using a queen excluder and some well-timed colony manipulations.

No landing boards here ...

confused.com

And then there are the 214 individual door opening/closing operations over a 3 week period (assuming the moon is at or near perigee) needed when you use a Snelgrove board 10.

Like any recommendation to use brood and a half … my advice is ‘just say no’.

Just because Tim Toady

… doesn’t mean you have to actually do things a different way each time.

The problem with asking a group – like your local association or the interwebs – a question is that you will get multiple answers. These can be contradictory, and hence confusing to the tyro beekeeper.

Far better to ask one person whose opinion you respect and trust.

Like your mentor.

You still may get multiple answers 😉 … but you will get fewer answers and they should be accompanied with additional justification or explanation of the pros and cons of the various solutions suggested.

This really helps understand which solution to apply.

Irrespective of the number of answers you receive I think some of the most important skills in beekeeping involve:

  • understanding why a particular solution should work. This requires an understanding of the nitty gritty of the process. What are you trying to achieve by turning a hive 180° one week after a vertical split? Why should Apivar strips be repositioned half way through the treatment period?
  • choosing one solution and get really good at using it. Understand the limitations of the method you’ve chosen. When does it work well? When is it unsuitable? What are the drawbacks?

This might will take some time.

More hives, less time

If you’ve only got one colony you’ll probably only get one chance per year to apply – and eventually master – a swarm control method.

With more colonies it is much easier to quickly acquire this practical understanding.

Lots of learning opportunities here

Then, once you have mastered a particular approach you can decide whether the limitations outweigh the advantages and consider alternatives if needed.

This should be an informed evolution of your beekeeping methods.

What you should not do is use a different method every year as – unless you have a lot of colonies – you never get sufficient experience to understand its foibles and the wrinkles needed to ensure the method works.

Informed evolution

If you consider the three beekeeping techniques I mentioned earlier – queen introduction, uniting colonies and swarm control – my chosen approach to two of them is broadly similar to when I started.

However, as indicated above, there are still lots of subtle variations that could be applied.

With both queen introduction and uniting colonies I’ve more or less standardised on one particular way of doing each of them. By standardising there’s less room for error … at least, that’s the theory. I now what I’m doing and I know what to expect.

In contrast, I’ve used a range of swarm control methods over the years. After a guesstimated 250+ ‘hive years’ I now almost exclusively 11 use one method that I’ve found to be extremely reliable and fits with the equipment and time I have available.

It’s not perfect but – like the methods I use for queen introduction and uniting colonies – it is absolutely dependable.

I think that’s the goal of learning one method well and only abandoning it when it’s clear there are better ways of achieving your goal. By using a method you understand and consider is absolutely dependable you will have confidence that it will work.

You also know when it will work by, and so can meaningfully plan what happens next in the season.

So, what are the variants of the methods I find absolutely dependable?

Queen introduction

99% of my adult queens – whether virgin or mated – are introduced in JzBz cages. I hang the queen (only, no attendants) in a capped JzBz cage in the hive for 24 hours and then check to see if the queenless (!) colony is acting aggressively to her.

If they are not I remove the cap and plug the neck of the cage with fondant. The bees soon eat through this and release the queen.

Checking for aggression

I used to add fondant when initially caging the queen but have had one or two queens get gummed up in the stuff (which absorbs moisture from the hive). I now prefer to add it after removing the cap. The queen needs somewhere ‘unreachable’ in the cage to hide if the colony are aggressive to her.

It’s very rare I use an alternative to this method. If I do it’s to use a Nicot pin on cage where I trap the queen over a frame of emerging brood 12.

Nicot queen introduction cages

I use this method for real problem colonies … ones that have killed a queen introduced using the JzBz cage or that may contain laying workers.

Doing the latter is a pretty futile exercise at the best of times 🙁 .

Uniting colonies

Almost all colonies are united over newspaper. A sheet to two of an unstapled newspaper is easy to carry and uniting like this is almost always successful.

The brood box being moved goes on top. I want bees from the moved box to realise things have changed as they work their way down to the hive entrance. That way they’re more likely to not get lost when returning.

An Abelo/Swienty hybrid hive ...

An Abelo/cedar hybrid hive … uniting colonies in midsummer

I don’t care whether the queen is in the upper or lower box and, if there’s any doubt that one of the colonies isn’t queenless, I use a queen excluder over the newspaper. I then check the boxes one week later for eggs.

I’m not absolutely certain one of the colonies is queenless

At times I’ve used a can of air freshener and no newspaper. This has worked well, but it’s one more bulky thing to carry. I also prefer not to expose my bees to the chemical cocktail masquerading as Sea breeze, Summer meadow or Stale socks.

Since uniting doesn’t necessitate a timed return visit there’s little to be gained from seeking alternatives to newspaper in my view. Perhaps if I lived in a really windy location I’d have a different opinion … placing the newspaper over the brood box can be problematic in anything more than a moderate breeze 13.

Swarm control

Like many (most?) beekeepers I started off using the classic Pagden’s artificial swarm. However, I quickly ran out of equipment as my colony numbers increased – you need two of everything including space on suitably located hive stands.

I switched to vertical splits. These are in essence a vertical Pagden’s artificial swarm, but require only one roof and stand. If you plan to merge the colonies again i.e. you don’t want to ’make increase’, vertical splits are very convenient. However, they can involve a lot of lifting if there are supers on the colony.

Vertical split

Vertical split – day 7 …

Now I almost exclusively use the nucleus method of swarm control. Used reactively (i.e. after queen cells are seen) it’s almost totally foolproof. Used proactively (i.e. before queen cells are produced) also works well. In both cases the timing of a return visit to reduce queen cells is important, and you need to use good judgement in deciding how strong to make the nuc.

Here's one I prepared earlier

Here’s one I prepared earlier

The nucleus method has a couple of disadvantages for my beekeeping. However, its ease of application and success rate more than make up for these shortfalls.

Tim Toady is ‘a good thing’

I love the flexibility of perl for programming. I can write one-liners to do a quick and dirty file conversion. Alternatively I can craft hundreds of lines of well-documented code that is readable, easy to maintain and robust.

Others, in the very best tradition of Tim Toady, might write programs to do exactly the same things but in a completely different way.

The flexibility to tackle a task – the three used above for example, or miticide treatment, queen rearing, uncapping frames or any of the hundreds of individual tasks involved in beekeeping – in different ways provides opportunities to choose an approach that fits with your diary, manual dexterity, available equipment, preferences, ethics or environment.

In this regard it’s ‘a good thing’.

Choice and flexibility are beneficial. They make things interesting and, for the observant beekeeper, they provide ample new opportunities for learning.

… and a distraction

However, this flexibility can also be a distraction, particularly for beginners.

That is why I emphasised the need to learn the intricacies of the method you choose by understanding the underlying mechanism, and the subtleties needed to get it to work absolutely dependably.

Don’t just try something once and then do something totally different the next year 14. Use the method for several years running (assuming it’s an annual event in the beekeeping calendar), or at least on a lot of different colonies.

Choose a widely used and well-documented method in the first place 15. Read about it, understand it and apply it. Tweak it until it either works exactly as you want it to i.e. reliably, efficiently, quickly or whatever, or choose a different widely used and well-documented method and start over again.

Get really competent at the methods you choose.

Once your beekeeping is built upon a range of absolutely dependable methods you have the foundations to be a little bit more expansive.

You can then indulge yourself.

Explore the options offered by Tim Toady.

Things might fail, but you always have a fallback that you know works.


Note

The Apiarist is moving to an upgraded server in the next few days, If the site is temporarily offline then I’ve either pressed the wrong button, or the site will be back in a few minutes … please try again 😉

Mini-nucs: tips and tricks

Synopsis : More discussion of modifying and maintaining mini-nucs for queen mating; judging queen quality, repeat queen mating, season’s end and overwintering mini-nucs.

Introduction

A couple of weeks ago I described some of the basics of using mini-nucs for queen mating. I’ll try and avoid overlaps with that post in the following discussion of ‘tips and tricks’, effectively a rag-bag collection of stuff I failed to cover last time, interspersed with some typical problems that might be encountered.

Inevitably some of the discussion will be about specific modifications to the particular mini-nucs I use (Kieler or Warnholz polystyrene mating nucs). I settled on these because I needed a dozen one season, I had zero experience in using any so had nothing to compare and I couldn’t afford Apidea’s.

Kieler mini-nucs: four topbar frames and an integral feeder

Overall I’ve been reasonably satisfied with the choice my younger, poorer 1 and (even more) ill-informed self made. Over a decade later I’m using the same mini-nucs and I’ve not been tempted to try anything else 2.

Nevertheless, despite a Kieler-centric flavour to some of the comments below, most still apply directly (or with a little finagling) to other makes of mini-nuc.

Finally, I’ll repeat the point I made last time … mini-nucs are ’high maintenance’. They are not ’fit and forget’ beekeeping. Unless placed in the shade they may well abscond on a lovely day 3. Late in the season, without care and attention, they can get robbed out by wasps in hours. If there’s no nectar flow they will need feeding.

But, looked after carefully, they can be an efficient way to get queens mated .

Painting and decorating

Any poly hive needs painting to protect it from UV degradation. Most of my mini-nucs were first painted with el cheapo masonry paint. This has a matt finish and has been reasonably hard wearing.

More recently, I’ve started painting – or overpainting – them with Hammerite garage door paint. This is an oil or solvent based gloss paint. It causes the surface of the polystyrene to melt (very slightly) and therefore bonds extremely well. The Swienty brood boxes I painted several years ago look as good now as they did then. The Hammerite paint comes in a range of colours, including a rather nice green or blue.

Hammerite Oxford blue, since you asked

Successful queen mating needs reasonable weather (and patience). However, it also needs the returning mated queen to successfully find the mini-nuc she set out from. It therefore makes sense to either place the mini-nucs in separate and distinctive locations, or (perhaps that should be and/or) to paint them in distinctive colours.

Red ‘Wilko’ masonry paint and ‘bin end’ yellow gloss

I tend to place mine in pairs and so often have a plain and coloured one on the same stand, facing in opposite directions to further help the queen discriminate between entrances.

Entrances and exits

Kieler-type mini-nucs have a rotatable entrance with three or four options – blanked off, ventilation, a queen excluder or fully open. I shouldn’t need to mention that, if there’s a virgin queen in the hive (that you want mated), the entrance must be fully open.

But I will 😉

Entrance discs for mini-nucs

You can purchase replacement entrance disks like those in the photo above from a range of suppliers (or eBay, which is significantly less expensive). Using these may help queens return to the correct mini-nuc after orientation or mating flights.

Oops, almost forgot … bees have a tendency to nibble away at the polystyrene around the entrance of these Kieler nucs (or at the ‘under entrance’ which I’ve never used) while confined. It’s therefore worth painting the entrance tunnel as well as the outside.

Crownboards

Apidea’s and several other mini-nucs I’ve looked at are sold with clear semi-rigid plastic crownboards. Some have integral flaps for adding the queen cell or feeding the mini-nuc without letting clouds of bees escape (admittedly small clouds, as they’re only primed with a few hundred millilitres of bees).

Kieler’s are sold without a crownboard. Don’t let that put you off. A thick piece of clear plastic works just fine as a crownboard and you can easily engineer (i.e. cut) a small flap to add the queen cell between the topbar frames. I use a small piece of tape to hold in down.

Plastic crownboard. Note flaps for adding the queen cell and (above the feeder) adding syrup

You can put an additional small flap above the feeder that allows you to add syrup without any bees escaping. This only needs to be a few millimetres square and doesn’t need taping down. Even if you don’t think you’ll be feeding syrup – which you do using a small funnel – this modification takes seconds and won’t be in the way (but you’ll be glad it is there if you need it).

Hold the crownboard in place with drawing pins. That way there’s less chance it will blow away should you open the box on a windy day. It also means the crownboard stays stuck to the brood body, rather than being removed with the tightly-fitting roof.

Feeder mods

The Kieler integral feeder has some good and bad points.

It’s a good size, so reducing the chance of the mini-nuc starving if left for an extended period. However, this inevitably cuts into the space available for bees and brood, meaning that retention of the feeder can lead to rapid overcrowding.

You win some, you lose some!

The feeder is easy to remove and only fits in one orientation. Irritatingly it is too deep to fit into the ‘second storey’ extension (see below). It also has no cover or queen excluder and the queen can sometimes end up in the feeder, particularly if the bees build comb there.

Feeder with queen excluder

I therefore usually fit a small rectangle of plastic queen excluder, balanced on map pins stuck into the inner walls of the feeder. This stops the queen entering the feeder, but doesn’t necessarily stop the bees building comb there.

Be thankful for small victories … 😉

If you need more brood space you can easily replace the integral feeder with a homemade frame feeder designed to feed fondant. I build these shorter than the integral feeder so that they can be used interchangeably in the ‘second storey’ extension.

Kieler frame feeders

These work well, cost pennies to make and can be quickly exchanged when needed. When I’ve overwintered queens in these mini-nucs I’ve always used these fondant frame feeders in the upper storey, with frames filling the entire lower level. This reduces disturbance when you need to feed them.

Frames

The Kieler is a mini-topbar hive. Each topbar has a longitudinal slot cut into its underside designed to take a strip of foundation. They also have a ‘pinched’ central area, so that a queen cell can be easily inserted between two adjacent bars.

The bars themselves are just 15 x 8 mm softwood. Purchased separately they cost 36 p each (Yikes! … and those don’t even appear to have the central pinched indent).

If you need more (and you will … to replace losses and for the the upper storey should you buy one) just make your own with some wood from the store, a metal ruler, a Stanley knife and some antiseptic cream and Elastoplast.

And, while you’re at it, don’t go fiddling about with little strips of foundation held in place with melted wax. I did this for years. They work perfectly well, but they are fragile. The foundation in unused topbar frames will get bent or broken, and then you’ll have to start all over again.

Instead, eat as many Fruit Splits, Rocket lollies or Twister’s as you can stomach 4 and keep the sticks. Split these lengthwise and glue them into the longitudinal slot in the Kieler topbar using normal wood glue and 5 never re-wax them again.

Kieler mini-nuc topbar frames – no need for foundation or waxing

And, no, you don’t need to cover them in melted wax or anything else. All the bees need is a guide to help them draw the comb in the right place.

I’m sure there’s stuff I’ve forgotten about, but that lot will do for the moment. Let’s move on to four specific practical aspects of using mini-nucs.

Judging queen quality

You can’t … or at least I can’t.

I don’t think you can meaningfully determine the quality of the queen in a mini-nuc. The time between when she starts laying and when she runs out of comb is sometimes too short to even check whether she’s producing worker brood.

I usually leave her in the box until there’s some capped worker brood present and then – ideally – move her to a 2-5 frame nucleus colony. At the same time I clip and mark her. As long as she’s laying one egg per cell (and she sometimes starts laying more than this, but should slow down after a day or so) and the brood develops into worker brood then things should be OK.

However, it’s not until she’s laid a full frame or three of brood that you can judge the laying pattern (remembering that the laying pattern may also depend upon the bees in the box with her).

Brood frame with a good laying pattern

Furthermore, to properly judge her you need to observe the behaviour of the bees that develop from the eggs she lays.

Are they well tempered? Are they steady on the comb? Do they have the other traits you are keen to promote? Frugality? Good pollinators? Preferential collection of avocado nectar (Afik et al., 2010).

OK, perhaps not the last of those, but you’d be surprised about the traits some beekeepers favour.

Queen introduction

I remove the mated queen from the mini-nuc, place her in a JzBz cage without attendants and introduce her in the usual way to a queenless full-frame nucleus colony; I leave the sealed cage hanging between frames overnight and – assuming there are no signs of aggression to the caged queen – I remove the plastic cap and leave the workers to eat their way in through the fondant-plugged entrance/exit tube.

If there are signs of aggression, leave it another 24 hours.

Checking for aggression

A well designed introduction cage has some protection for the queen so she can avoid aggressive workers that can otherwise damage her feet. I’ve had considerable success with the JzBz cages (and happen to have inherited a bucket full and so don’t use anything else 😉 ).

I’ve inadvertently left a queen trapped in one of these cages for 6 days with no ill effects. Don’t rush things.

Rear some spares

What do you think happens with commercially reared queens, many or most of which are mated from mini-nucs?

Exactly … nothing, other than being popped into a shipping cage and having a £40 price tag attached.

In contrast, you have the opportunity to check your queens more thoroughly.

Rear a few more than you need, check out their performance, keep the best and donate the unwanted to one of the many, many beekeepers clamouring for queens – particularly late in the season. Even the also-rans are likely to be OK 6. Not necessarily great, but more than good enough to get the colony through to the next season 7.

Queen rearing diary; automagically populates days and events

And finally, make sure you keep good records. The first couple of times you do this you’ll think you will be able to remember the key points the following year; the dates of emergence, the time it took to have mated queens, the origin of the queen cell used to prime the mini-nuc etc.

But you probably won’t. The notes will be very useful for planning your queen rearing the following season.

Keeping things going

Populating mini-nucs early in the season is often a thankless and unpleasant task. The weather is cool, the bees are tetchy and – as described a fortnight ago – you may have had to shake through the colony twice to get the young workers.

That’s not the sort of task I like to repeat if I can possibly avoid it.

If you’re rearing queens all through the summer you can simply remove one mated queen and, shortly afterwards (within a few hours), add a new mature queen cell. This is the ideal situation and, with good organisation, good weather and good mating success, you can get three or four queens out of a single mini-nuc in one season.

Mainly good organisation.

You need to ensure you have a succession of mature queen cells ready at the about right time, remembering that queen mating often takes longer than expected (or wanted).

Scrub ‘caretaker’ queens

If that’s not possible, or if you want (or have) to interrupt queen cell production (e.g. your queenright cell starter swarms or a round of grafting fails) you can remove the mated queen from the mini-nuc and allow the bees to rear a ‘scrub’ queen.

A well populated mini-nuc will readily do this. The resulting queen is usually a bit on the small side, but she will keep the worker population ticking over and ready to accept a new mature queen cell in due course. In addition, the enforced brood break while they rear the scrub queen helps prevent the mini-nuc from getting too overcrowded.

These ‘caretaker’ queens are reared under the emergency response and – assuming there are suitable eggs in the little colony – emerge about 15 days after you remove the mated queen (remember, the bees preferentially choose 3 day old eggs to rear queens under the emergency response). A fortnight or so later the queen should be mated and laying. This approach therefore means you can take 4-6 weeks off if needed.

The end of the queen rearing season

What do you do with the contents of the mini-nuc after you’ve taken the last of the mated queens out? The little hive may well be bursting with bees, with all 4-6 combs containing brood.

Many beekeepers shake the bees out in front of a strong hive. The majority of the workers will be accepted, but the brood is wasted.

To avoid this I’ve used ‘zip’ ties to secure two Kieler topbar frames into a standard brood frame. At the very least these can be placed into a full sized hive for the brood to emerge. Usually, by the time of year I get round to this the bees have stopped drawing comb. Once the brood has emerged I move the frame to the side of the brood box and remove it.

Dave Cushman has details of some clever frame modifications that allow Kieler-type (he calls them Kirchhain mating hives) frames to be drawn at the beginning of the season and used to accommodate brood-filled frames at the end.

Unsurprisingly, when I’ve done this it’s been a lot more ’Heath Robinson’. The Kieler topbar frames are a little too long to fit end-to-end in a National frame. I therefore built some with a scrap 8 mm thick spacer (shown in black below) tacked under one side of the frame. I then use zip ties to hold everything more or less in place.

Using mini-nuc brood frames

Despite being a total bodge this has generally worked well. I’m pleased not to waste the brood.

Now I know the air freshener trick (described in this 2020 post) I’d probably just add the frames as shown in the diagram above together with the adhering bees, and give them and the recipient colony a quick blast of ’Sea breeze’ before uniting them.

Overwintering mini-nucs

Alternatively, with a little care you can overwinter queens in mini-nucs. This saves you the faff of emptying them at the end of the season, and means they are ready for queen cells the following year (after removing the queen of course) 8.

I’ve overwintered queens successfully quite a few times but certainly don’t consider myself an expert at it. There’s quite a high attrition rate. Remember how small these colonies are, how limited the space is for stores and the relatively small population of bees present to stop the colony freezing in the winter.

I think every mini-nuc I’ve overwintered successfully has been a double-decker, with the standard Kieler brood box underneath an additional extension brood body. These almost double the volume of the mini-nuc.

The mini-nuc needs to be strong in mid/late autumn, almost certainly boosted by combining the contents of two separate mini-nucs. You can unite them over paper in the same way you’d treat a full sized hive.

Unfortunately, the upper and lower brood boxes have different depths, so comb drawn in the bottom box needs to be trimmed to fit in the upper box. A messy and irritating task.

I replace the lower integral feeder with additional brood frames and place one or two fondant frame feeders in the upper chamber – usually one at either end to ensure the mini-cluster is near to one of them.

Place the box somewhere sheltered, leave the entrance open to allow the bees to fly for cleansing flights and cross your fingers …

Gimme shelter

I’ve not overwintered mini-nucs since returning to Scotland, though I know several beekeepers here who do this successfully. In the Midlands we often had quite harsh winter weather – certainly much colder than we usually get here on the north-west coast of Scotland.

Two double decker mini-nucs overwintered successfully in an unheated greenhouse

A decade ago, well before my bee shed experiments, I was successfully overwintering mini-nucs in an unheated greenhouse with entrance tunnels from the hive to the outside. These worked surprisingly well and got queens through some really hard weather (note the snow in the picture above – late March 2013).

Tunnel entrances to overwintered mini-nucs

If the winter was particularly severe I would cover the mini-nucs with a thick layer of bubble wrap to try and retain as much warmth as possible. The levels of stores needs to be checked regularly, particularly once brood rearing starts in earnest. These little colonies can starve surprisingly quickly 🙁 . It takes seconds and causes minimal disruption to swap out those fondant frame feeders.

With a little luck and the normal amount of good judgement it was sometimes possible to remove the overwintered queen to make up a nuc in mid/late April, replacing her with a queen cell from the first round of grafting.

Of course, it rarely worked quite as smoothly as that … 😉 9

Finally

The one thing I would not recommend you try is allow the mini-nuc to build up to a full-sized nuc without supplementing it with additional brood and bees. A mini-nuc is too small and it will take too long rearing a few hundred bees at a time to make even a five frame nuc. I’ve tried and it’s a waste of effort.


References

Afik, O. et al. (2010) ‘Selection and breeding of honey bees for higher or lower collection of avocado nectar’, Journal of Economic Entomology, 103(2), pp. 228–233. Available at: https://doi.org/10.1603/ec09235.

Shook swarms and miticides

Synopsis : Combining a shook swarm with miticide treatment removes most mites in the colony and dramatically reduces DWV levels. The application of this strategy for practical beekeeping is discussed.

Introduction

Why does Varroa have such a devastating impact on colony health?

Feeding on haemolymph – or the abdominal fat body – by Varroa is probably detrimental. Furthermore, during feeding the mite induces immunosuppressive responses which make the bee both more susceptible to bacterial infections and compromises its nutritional status (Aronstein et al., 2012 1 ).

But if that wasn’t enough, the real damage is caused by transmission of viruses – in particular deformed wing virus (DWV) – from the mite to the developing pupa (and adult worker, as mites probably also feed on newly eclosed workers during the misnamed phoretic stage of the life cycle).

In the absence of Varroa, DWV is seemingly inconsequential for honey bees. Varroa-free colonies – including mine on the remote west coast of Scotland – carry DWV, but virus levels are very low and there is never any overt disease.

But Varroa infested colonies, particularly at this time of the season, often have very high levels of DWV.

Individual pupae parasitised by Varroa can develop stratospherically high DWV levels – reaching over a million times higher levels than seen in unparasitised bees (which can be similar to those recorded in Varroa-free bees). In the mite-exposed pupae the virus levels can kill the developing bees, or result in the characteristic symptoms (primarily deformed wings but also stunted abdomens and discolouration) that give the virus its name.

Worker bee with DWV symptoms

Worker bee with DWV symptoms

But bees not directly exposed to Varroa also have higher DWV levels in mite-infested colonies, particularly as the season progresses. Presumably this is due to horizontal transmission of the virus during larval feeding or trophallaxis.

What happens to these elevated virus levels after the removal of Varroa using a miticide such as Apivar?

Who cares? … I mean, Why could that matter?

The clue is in the section above.

Here it is again:

But bees not directly exposed to Varroa also have higher DWV levels [ … snip … ] presumably this is due to horizontal transmission of the virus during larval feeding or trophallaxis.

If you remove mites the virus levels in the treated adult bees are often surprisingly high 2. That makes sense because the miticide is only removing the vector for the virus … the bees with high levels of virus infection are unaffected.

If, during larval feeding or trophallaxis, these elevated levels of DWV result in yet more bees acquiring high DWV levels then the health of the colony will remain compromised.

The real reason that DWV is a problem for honey bees is that high levels of the virus result in the reduced longevity of bees. This isn’t an issue for the short-lived summer foragers 3. However, reducing the longevity of the winter bees – the so-called diutinus bees – can be fatal for the colony. These are the bees that support the queen in winter, thermoregulating the hive and that rear the first brood of the following season.

Their importance to successful overwintering cannot be overemphasised.

So, the question remains. What happens to the virus levels in the hive after the removal of Varroa?

Of course, the reason I’m posing this question is that we now know … 😉 .

Two easy-to-understand potential outcomes

It seemed to us that there were at least two likely outcomes.

  1. The virus levels in the hive drop very quickly after mite removal (red dashed line, below) and return to some sort of basal level. How quickly and to what basal level? We didn’t know.
  2. Virus levels remain elevated for a long period after Varroa is removed (red solid line, below). How long and to what elevated level? Yes – you guessed it – we didn’t know 😉 .

Of course, biology isn’t binary. There are any number of alternative outcomes … it’s just that those two seemed the most likely.

Two possible outcomes for virus levels after mite removal (black vertical dashed line)

What’s more, they’re the easiest to understand … and to explain.

Why might virus levels remain high if Varroa are removed?

Surely the short lifespan of adult bees means these would soon be lost from the colony … particularly if they have reduced longevity?

Yes, but …

We published a paper a couple of years ago that clearly demonstrated that honey bee larvae fed high levels of DWV became infected with the fed virus. The latter, which we could distinguish from any DWV already present in the larvae, replicated to similar high levels seen in a mite-infested hive (Gusachenko et al., 2020).

This observation perhaps suggested that the second scenario outlined above could occur. All the mites are slaughtered, but the remaining bees with high levels of DWV feed developing brood which consequently also go on to develop high levels of DWV.

Although it’s always good to remove mites this would not be the best outcome for the colony.

Virus quantification

Before I explain how we tested which, if any, of these two possibilities is correct I need to say a few things about virus ‘levels’.

For a variety of reasons I don’t have time, space or energy to explain, we don’t actually count viruses, instead we count copies of the virus’s genetic material (the genome).

All the magic happens in one of these machines – a Bio-Rad CFX96 Touch Real Time PCR system.

The virus genome is made of ribonucleic acid (RNA) and we can therefore use fantastically expensive sensitive and accurate diagnostic methods to measure how many copies are present in a particular sample – for example, in a worker bee, or a developing pupa.

Still with me?

Good.

To complicate things a little, we can’t meaningfully express the number of virus genomes present as an absolute number (like one million, or 2,478) because bees are different sizes; larvae are tiny, pupae are bigger, drones are larger still.

In addition, different workers are different sizes, larvae grow etc.

Therefore we express it as genomes per unit of total RNA extracted from the sample. That’s a bit of a mouthful, so we abbreviate it to GE / μg 4.

Phew!

And finally, to put some numbers on the low and high levels of DWV I discussed earlier, a bee from a Varroa-free colony contains ~1,000 – 10,000 GE / μg (103 – 104) of DWV whereas a pupa parasitised by Varroa regularly has 10,000,000,000 to 1,000,000,000,000 GE / μg (1010 – 1012).

That’s a lot of virus 🙁 .

The experiments

Experiments plural because we did these studies in both 2018 and 2019. ‘We’ are Luke (a then PhD student and now post-doctoral fellow in my laboratory, and the first author on the paper) together with our friends and collaborators, Craig, Ewan and Alan (in Aberdeen) and Giles (in Newcastle). The work was published a few days ago in the journal Viruses and is ‘open access’ (Woodford et al., 2022). This means that anyone feeling particularly masochistic or suffering from sleep deprivation can read all the gruesome details at their leisure.

Not ‘breaking rocks in the hot sun’ … but it sometimes feels like that

The paper covers more than just the one experiment I’m going to discuss here. We also looked at how the virus population changes when mite-free bees become infested with Varroa.

I’ll save that for another post 5  … it’s a good story in its own right.

Most mites are in capped cells

It’s been known for at least three decades that the majority of the Varroa population in a brood rearing colony are within capped cells, feasting on developing pupae.

Nom, nom, nom!

Precisely what percentage of the population is the majority varies a bit 6, but a figure of 90% is often quoted as typical for midseason.

% of mites in capped cells

The percentage of mites in capped cells (this is predicted, not actual data)

We reasoned that the best way to quickly remove all 7 the Varroa in a colony was to combine treatment of the phoretic mites with removal of all the brood … where the majority of the mites are lurking.

And to remove the brood (and associated mites) we conducted a shook swarm.

The shook swarm

Many beekeepers will be familiar with the technique called a shook swarm.

Shook swarm setup. Note Apivar strips in the open hive. Returning foragers already clustering at the entrance

This involves shaking all the adult bees into a new hive with frames containing fresh foundation. All the old frames and brood from the original hive are discarded.

We modified this by including Apivar strips in the hive into which we shook the adult bees.

Shook swarmed colony strapped up for transport … we wait for all the bees to enter the hive before moving it

The ‘shook swarm and miticide’ experiment – which we conducted in May – therefore involved the following steps (we used three strong double brood hives per season, each containing similar amounts of bees and brood):

  1. We quantified DWV in emerging brood in hives in which no Varroa management was conducted.
  2. The queen was removed, caged and kept safe for a few hours.
  3. All adult bees were shaken into a new brood box containing 11 frames of fresh foundation and two strips of Apivar 8.
  4. The shook swarms were relocated to a quarantine apiary.
  5. The queen was returned to the shook swarmed colonies and they were fed ad libitum with syrup to encourage them to draw fresh comb.
  6. Mite drop was recorded at 5 day intervals, increasing to longer intervals, until October when brood rearing ceased.
  7. DWV levels were quantified on a monthly basis from June to October.

As you can see, a very simple experiment.

The results

The mite levels in the ‘donor’ hives were much higher in 2019 than 2018. It’s not unusual to see this type of year to year variation in mite levels. In this instance the mean temperature in February and March 2018 had been several degrees colder than 2019 (remember the Beast from the East?).

The Beast from the East ...

The Beast from the East …

This almost certainly reduced early season brood rearing and so delayed mite replication. Brood rearing was strong by late Spring, but the mite levels in 2018 had yet to catch up.

The results of the experiment in both years were essentially the same. However, for clarity I’ll just present the 2019 data as the mite infestation numbers were so dramatic.

Mite drop after conducting the shook swarm

The cumulative mite drop from Apivar-treated shook swarms ranged from ~500 to ~3000 in the first 5 days. After that the daily mite drop remained at extremely low levels until recording stopped in October.

Mite drop following shook swarm and Apivar treatment

If you assume that only 10% of mites were phoretic at the time we conducted the shook swarm, this means that the total number of mites in some of these colonies was about 30,000. Even the colony with the lowest mite drop may have been hiding an additional 4,500 mites in capped cells.

Remember … the National Bee Unit guidance states that if mite levels exceed 1,000 then treatment is strongly recommended ’to avoid Varroa causing significant adverse effects to the colony’.

I think this part of the study shows just how effective Apivar is. After the first 5 days of treatment the cumulative drop – the Apivar strips still were left in place for 8 weeks – was extremely low for each fortnightly sampling period.

Of course – other than the very high numbers – none of this was particularly surprising. We know Apivar kills Varroa.

Perhaps you’re thinking ”My hives drop more Varroa during the autumn treatment, and for longer.”

When you treat a colony with brood present the mite drop is high in the first few days, but then often remains significant over the next 2-3 weeks while the mite-infested brood emerges. 

In our case, all the mites were on adult bees. By killing these mites in the first few days before there was new sealed brood in the colony we ensured the majority of the new brood did not become infested.

Virus levels before and after the shook swarm

In each colony we sampled a dozen emerging workers, once before the shook swarm and then on a monthly basis until brood rearing stopped. By testing emerging brood we could be certain they had been reared in the test colony, rather than drifting in from elsewhere. 

Before the shook swarm virus levels ranged from 105 to 1010 per worker, with an average of around 5 x 107 GE / μg. For those of you unfamiliar with scientific notation that is 50 million virus genomes.

Virus quantification in individual workers from colonies before and after the shook swarm and Apivar treatment

Strikingly, from the June sample onwards, virus levels dropped to an average of about 104 GE / μg (10,000 virus genomes, a 5,000-fold reduction). This average obscured a range of individual levels, from about 102 to 106.

These reductions are statistically significant … always reassuring 😉 .

The 2018 data showed a similar marked reduction in virus levels. The pre-treatment levels were marginally lower (remember, it was a ’low Varroa’ season), but the levels dropped to an average of only 1,000 GE / μg, a slightly higher fold-reduction and again highly statistically significant.

If you remove the majority of the Varroa the virus levels drop very fast to levels seen in mite-free colonies, or colonies with very low mite counts.

Tough love?

Some beekeepers consider that a shook swarm is tough on the colony. 

I’m not sure I agree.

How and when the shook swarm is done matters a lot.

It can be tough, but it shouldn’t be.

The bees need to draw new comb. For this they need ample feeding, lots of bees and warm weather. By conducting shook swarms on strong colonies in late May and giving them a few gallons of syrup we achieved all this.

‘I know I put that caged queen down here … somewhere’

Doing a shook swarm on a weak colony, too early (or late) in the season or omitting feeding is a recipe for disaster. The colony will struggle to draw comb, its brood rearing will be limited and it will be playing ’catch up’ for the remainder of the year.

Our shook swarmed colonies were booming by late July and entered the winter very strong. All overwintered successfully.

I’d argue that a shook swarm is a lot less tough on a colony than the disease burden caused by thousands of mites … 🙁 .

Why Apivar?

It’s worth emphasising that this was a scientific experiment to investigate the consequences for the virus population of removing almost all of the Varroa.

It was not designed as an example of how a beekeeper would necessarily choose to manage a honey production colony.

Our choice of Apivar was considered and deliberate. Application is straightforward, toxicity – at the levels we used – is undetectable and, critically for these studies, it remains active for weeks.

Apivar strip on wire hangar

Of course, Apivar cannot be used when there are honey supers on the hive 9. Any supers added for the summer nectar flow were not extracted.

Additionally, feeding gallons of syrup when there are honey supers present is also not recommended 😉 .

What else could we have used?

The two obvious choices were MAQS or oxalic acid. Both are effective against phoretic mites, though perhaps less so than Apivar. However, both are only active for a short period in the hive; the treatment period for MAQS is 7 days and the activity of oxalic acid – trickled or vaporised – is probably less than a week.

Neither could be relied upon to slaughter the maximum number of mites, a necessity to produce an understandable result 10. We were additionally concerned about problems with queens or absconding had we used MAQS (both of which would have invalidated the study), and we were keen to avoid the need for repeat treatments with oxalic acid (not least because this is not an approved application method).

With thousands of mites we wanted to ensure that the majority were killed quickly … and, as important, that any that survived the first few days of miticide treatment were also more than likely to be killed later 11.

Application to practical beekeeping

The main aim of this experiment was to investigate the levels of DWV in the colony after the majority of Varroa are removed. However, we were also mindful that the method may be useful for a beekeeper who discovers his/her colony has damagingly high mite levels mid-season, or for someone who inherits abandoned hives with high mite loads.

In these scenarios, assuming there are sufficient bees, some nice warm weather and lashings of syrup available, the combination of a shook swarm and simultaneous miticide application is probably the fastest way to restore colony health.

I am not suggesting that beekeepers routinely conduct a shook swarm and miticide application mid-season. It might not be tough on the colony, but that doesn’t mean it’s not very disruptive. If it’s not needed (because mite levels are well controlled, for example) then it’s a waste of brood … and syrup.

However, there are times when I could imagine it might be useful.

If your primary crop is heather honey you’ll know that the hives sometimes don’t come back from the hills until late-September. That’s late to be applying miticides to protect the winter bees. In an area with an extended June gap (which often starts in May) it might be possible to effectively rid the hives of Varroa in June and have a strong colony to take to the moors in early August.

This is probably a better approach than using a half dose of Apivar in June (as some do) which probably doesn’t kill all the mites anyway, risks contributing to amitraz resistance in the mite population and may result in Apivar strips being left in the hive during the heather flow 12.

Conclusions

Miticides kill mites … big deal.

However, it’s the viruses – in particular deformed wing virus – that kill colonies.

We have now shown that removing the majority of the mites from a colony (including those associated with sealed brood) results in the levels of DWV in the hive dropping very quickly.

The speed with which this happens – four weeks or less – is probably accounted for by the lifespan of the adult bees in the colony following the shook swarm.

This suggests that high levels of virus are not horizontally transmitted or (and this is subtly different) that horizontal transmission, through feeding, of large amounts of virus does not result in elevated levels of virus replication in the recipient bee (larva or adult).

All sorts of questions remain. Would oxalic acid be a suitable replacement for Apivar? How much virus is transferred from a worker to a larva during brood rearing, or between workers during trophallaxis? Is this below a threshold for efficient infection? Do virus levels drop as dramatically when treating a broodless colony (e.g. after caging the queen for three weeks)?

In the meantime just remember that ”the only good mite is a dead mite” … and, if you kill the mites, you also quickly reduce virus levels to a level at which they do not damage the colony.

And a straightforward way to achieve that is to combine a shook swarm with an effective miticide.

Result!


References

Aronstein, Katherine A., Eduardo Saldivar, Rodrigo Vega, Stephanie Westmiller, and Angela E. Douglas. ‘How Varroa Parasitism Affects the Immunological and Nutritional Status of the Honey Bee, Apis Mellifera’. Insects 3, no. 3 (27 June 2012): 601–15. https://doi.org/10.3390/insects3030601.

Gusachenko, Olesya N., Luke Woodford, Katharin Balbirnie-Cumming, Ewan M. Campbell, Craig R. Christie, Alan S. Bowman, and David J. Evans. ‘Green Bees: Reverse Genetic Analysis of Deformed Wing Virus Transmission, Replication, and Tropism’. Viruses 12, no. 5 (May 2020): 532. https://doi.org/10.3390/v12050532.

Woodford, Luke, Craig R. Christie, Ewan M. Campbell, Giles E. Budge, Alan S. Bowman, and David J. Evans. ‘Quantitative and Qualitative Changes in the Deformed Wing Virus Population in Honey Bees Associated with the Introduction or Removal of Varroa Destructor’. Viruses 14, no. 8 (August 2022): 1597. https://doi.org/10.3390/v14081597.