Category Archives: Problems

Does DWV infect bumble bees?

Covid (the disease) is caused by a virus called SARS-Cov-2. SARS is an abbreviation of severe acute respiratory syndrome and the suffix ‘Cov’ indicates that it’s a coronavirus. The final digit (2) shows that it’s the second of this type of virus that has caused a pandemic. The first was in 2003, and was caused by a virus we now call SARS-Cov-1. That virus had a case fatality rate of 11%, but only infected ~8500 people worldwide. 

SARS-Cov-2 is not a human virus, by which I mean it’s not a virus that has been present in the human population for a long time. It’s actually a virus that most probably originated in bats.

We’re still not sure how SARS-Cov-2 jumped species from bats to humans.

SARS-Cov-1 made the same transition from bats and we do have a pretty good idea how this happened. Before the virus was found in bats it was detected in palm civets and raccoon dogs, both of which are farmed for food and sold in live game markets. Neither animal shows any symptoms when infected with SARS-Cov-1.

Bats were also sold in the same live game markets in Guangdong province in China and it seems likely that the virus either crossed directly from bats to humans, or went via a third species such as the palm civet.

Pathogen spillover

It’s likely that SARS-Cov-2 followed the same route. We are entering a second – likely extended – period of geographic lockdown due to Covid. Since SARS-Cov-2 made its cross-species jump from bats to humans it has infected at least 41 million people and killed over 1.13 million.

Pathogens that jump from one species to another can have catastrophic consequences for the recipient population 1 or, as in the case of palm civets, might cause no harm whatsoever.

The term ‘pathogen spillover’ is often used to describe the event when a pathogen – whether viral, bacterial or a parasite – escapes or spills over from its natural host to another species. 

CSI in the apiary … motive, opportunity, means

To make the species jump a number of criteria must occur. The pathogen has to be present at a high enough level to be infectious in the ‘donor’ species. For convenience, let’s consider this as the motive to jump species 2.

Secondly, the pathogen needs to have an opportunity to jump species. For example, because the donor and ‘recipient’ species share the same habitat or regularly come into contact.

Finally, it has to have the means to replicate in the recipient. If it cannot replicate it can never get established in the recipient population or cause disease.

In fact, this is an oversimplification. It also needs to be transmissible between individuals of the recipient species (or it will never spread in the recipient species).

So what has all this to do with the bumble bees in the title of this post?

Honey bees get a bad press from some scientists and environmentalists. They compete with native solitary and other bees and pollinators for environmental resources – like pollen and nectar. Increasingly, particularly in agricultural areas, these can be in limiting supply at certain times of the season. For examples, because all the hedgerows have been grubbed up and the wildflower meadows obliterated.

In addition, there are a number of studies that have suggested that honey bee viruses have spilled over into other pollinators, in particular bumble bees, and that this pathogen spillover has contributed to the decline in free-living bee populations.

Do honey bee viruses have the motive, opportunity and means to cause disease in bumble bees?

Are honey bee viruses responsible for the decline in bumble bee populations?

Correlation and causation

There are numerous studies showing that the most widespread honey bee virus, deformed wing virus (DWV), can be detected in wild-caught bumble bees.

Let me pose a quick question … does detection mean ‘replication’?

Deformed wing virus “does what it says on the tin” in honey bees. When transmitted by Varroa it causes developmental defects in pupae that appear as wing deformities in newly emerged workers.

DWV symptoms

DWV symptoms

There’s also one study that implicates DWV in directly causing disease in bumble bees.

This influential paper, published 15 years ago, demonstrated that some bumble bees had the characteristic crippled wings seen in symptomatic emerging honey bee workers. The ‘smoking gun’ was that DWV was also detected in these bumble bees.

Exhibit A : Evidence for DWV infection in bumble bees – click image for full legend.

This is the only figure in the paper and there have been no substantive follow-up papers. For some reason they showed ‘symptomatic’ Bombus terrestris (the buff-tailed bumble bee; panel A, left) and PCR detection data for B. pascorum (the common carder bee).

Nevertheless, this association between presence and symptoms was sufficient for the authors to conclude “we demonstrated that DWV is pathogenic to at least two bumble bee species … causing wing deformity similar to clinically DWV-infected honey bees”.

Here’s a second important question … does the detection of DWV in bumble bees demonstrate it is responsible for the symptoms observed? 3

As a virologist interested in the evolution, replication and transmission of viruses – and a beekeeper – this seemed like a worthwhile topic to explore in a bit more detail.

There might be a correlation between the presence of DWV in bumble bees, but does this account for causation of the DWV-like symptoms seen in the bumble bees?

Motive and opportunity

Let’s get these two out of the way quickly (though we’ll return to opportunity in the notes at the end).

Remember, viruses don’t want to do anything. I’m using motive as a hideously contrived reference to whether the pathogen, DWV, is present at high and infectious levels in honey bees.

It is.

Healthy, mite-naive (but reared in a hive with Varroa) workers can carry as little as ~1000 DWV viruses. Similar levels of DWV are also present in hives from Varroa-free regions – at least of the UK 4. In contrast, after parasitisation by Varroa, symptomatic or asymptomatic adult worker honey bees regularly have more that 109 (one trillion) viruses coursing through their little bodies. 

This virus is highly infectious. When injected into honey bees, as few as 10 viruses are sufficient to start a new infection and are replicated several million-fold within 24-48 hours.

Let’s agree that they have the ‘motive’ … to spread to other hosts.

They also have the opportunity, at least in the broadest sense of the word. Honey bees and bumble bees share the same environment. They collect nectar and pollen from the same flower species. They can even regularly be seen visiting the same flower simultaneously. In addition, it’s not unusual to see bumble bees trying to access honey bee hives to steal nectar.

I’d argue that the virus appears to have ample opportunity to move from one species to the other.

Does DWV replicate in bumble bees?

This is an important question. The data figure (‘Exhibit A’) shown above does not answer this question. Their assay simply detects the presence of DWV, with no indication of whether the virus is replicating.

And the reason this is important is really explained in the section on motive and opportunity above. DWV is ubiquitous and present at extraordinarily high levels in many honey bees. It’s present in honey bee faeces. It can be detected on flowers that honey bees have visited, or in pollen collected from those flowers.

DWV is absolutely everywhere.

So, if it is everywhere, there’s a good chance it might simply contaminate things … like bumble bees that look a bit sick for other reasons.

However, if DWV is involved in causing disease in bumble bees then the virus must replicate in bumble bees.

Virus replication – select for full size and legend.

I’ve used this figure before. To be certain that the virus is replicating you need to identify the intermediate replication products (the negative strand RNA shown as red arrows above).

Almost none of the large number of papers that have reported “DWV infected bumble bees” have identified these intermediate replication products.

Many studies didn’t even bother looking for these critical intermediate products.

So we did

There are two ways we could have investigated this. We could have collected large numbers of bumble bees from the fields and screened them in the lab for these replication intermediates. The problem with this approach is that DWV might be very rare in bumble bees, or might be common, but only replicate rarely. The additional problem is that it involves going out and collecting bees from the environment – that’s hard work 😉 5

An alternative approach is to buy a nest of bumble bees 6 and to inject a few bumble bee pupae and adults with DWV. This is what we did. In parallel, to ‘prove’ the virus used can replicate in honey bees, we injected a few honey bee pupae.

We injected the bees as it’s the definitive way we have of being sure that the virus was present.

‘Gene jockeys’

I’ve got some gifted molecular virologists in my lab. These are scientists who use genetic engineering or biotechnology techniques to address tricky questions (gene jockeys). They are particularly skilled at manipulating nucleic acids, such as the genomes of viruses.

If DWV is so common (it is – see above) how would we know that the replication intermediates were from the virus we injected into the bumble bees, rather than from a virus that was possibly already present?

To solve this puzzle Alex (the lead author on our recent paper) did two things. She engineered a unique genetic marker into the virus which we could look for (and that knew was absent from other similar viruses that might already be present in bumble bees). In addition, she ensured that the virus she injected into the bumble bees contained none of the negative strand RNA that is produced as the intermediate when the virus replicates. 

And … to cut a long story short, we could detect the negative strand RNA replication intermediate in injected bumble bees. In addition, the virus contained the unique genetic marker Alex had engineered into the virus genome, so we were absolutely certain it was the injected virus that was replicating. All of the controls worked exactly as expected.

DWV does replicate in bumble bees … at least under the conditions used in our experiment.

But it does not replicate very fast

The bumble bees we used for these experiments are commercially produced under very clean conditions. When we tested control bumble bees they contained no DWV at all, even using our most sensitive assays.

In contrast to injected honey bee pupae, DWV replicates rather slowly in bumble bees. In honey bees it will amplify a million-fold in 48 hours. However, in bumble bees, in 48 hours we only observed a 100-10,000 fold increase in DWV levels. It was only when we injected large amounts of DWV to bumble bees that we could recapitulate the virus levels seen in symptomatic honey bees.

This was a little puzzling as we’ve assumed that the very rapid replication of DWV in honey bees contributes to pathogenesis. The virus needs to replicate fast to spread through the pupa and infect the particular tissues and organs that, when damaged, result in the characteristic symptoms seen.

If it only replicates slowly in bumble bees how can it cause symptoms?

But hold on … does it cause symptoms?

Not as far as we can tell. 

We never found any injected bumble bees with deformed wings, or any that looked anything like the symptoms seen with DWV in honey bees. The actual quote from the paper is:

Strikingly, none of the eclosed bumble bees showed any signs of the wing deformities that are characteristic of DWV infection of honey bees”. 

Morbidity of DWV in bumble bees

Injected pupae developed until eclosion and were either non-viable, discoloured or apparently normal in appearance (see (c) above). We observed similar numbers of these three types whether the pupae were injected with DWV or mock-injected with buffer alone (see (b) above). What’s more, of those injected with the virus, the level of the virus was the same irrespective of the appearance (or viability) of the bumble bee (see (a) above).

We know that these bumble bees contain replicating DWV but see no evidence for overt disease. I acknowledge that they may have invisible symptoms. However, we see no evidence for the wing deformities reported in the 2005 paper from Genersch and colleagues (‘Exhibit A’, above).

Heavy going? But I’ve only just started … 

So, let’s briefly return to our “motive, opportunity, means” crime analogy and summarise where we’ve got to so far. 

DWV is present at very high levels in at least some honey bees. In addition, bumble bees are likely to regularly come into contact with DWV in the environment. This could happen through contaminated pollen, when attempting to rob hives, or by direct interaction with honey bees when both visit flowers. Finally, and most tellingly, DWV replicates in bumble bees.

So, if I was Peter Falk as Lieutenant Columbo, I’d argue that DWV has the motive, opportunity and means to potentially cause disease in bumble bees.

But, as is apparent from the figure above, it appears not to actually cause disease.

Which is puzzling. 

Just one more thing 7

There’s a major problem with the experiments I’ve discussed so far.

Like all experiments 8 they were tightly controlled, with single variables and lots of statistical analysis to demonstrate our confidence in their reproducibility.

The problem wasn’t technical, it was how well they recapitulated potential transmission in the environment.

We’re not aware of anything that goes around “injecting” bumble bee pupae or adults 9. They are not parasitised by Varroa and, although there are bumble bee mites (such as Parasitellus), they don’t feed on bumble bees in the same way that Varroa feeds on honey bees.

How else might bumble bees acquire DWV?

The obvious route is orally, while feeding. 

There are a few issues with feeding bees DWV. The method is simple enough … you add the virus to sugar syrup and they slurp it down. However, you have little control over how much individual bees consume. Do some bees feed directly and other acquire food when fed by other bees (trophallaxis)? It gets rather difficult control.

In addition, we knew from our studies of honey bees that they are far less susceptible to infection per os (by mouth) than by injection. And by far less I mean tens of thousands of fold less susceptible, at least as adults.

Feeding bumble bees DWV

We chose to investigate two routes of feeding.

The first was to directly feed individual bees in the laboratory. Using this approach we failed to detect any evidence for infection or DWV replication in fed adult bumble bees, even when fed 100 million DWV viruses.

Not an encouraging start. However, larvae generally have increased susceptibility to pathogens, so we also investigated feeding larvae in the laboratory. In these studies we did manage to establish infection. However, to do so we had to add 100 million DWV viruses to he food and only achieved a 50% infection rate. 

The second approach we used was direct feeding of complete bumble bee colonies maintained in the lab.

Bumble bees are easier to keep in the lab than honey bees as they don’t need to be free-flying. Each colony occupies a 30cm3 perforated plastic box, supplied with pollen and syrup. We fed three colonies 100 million DWV per bee per day for 4-6 weeks 10.

That’s a huge amount of virus for a protracted period. Our reasoning here was straightforward. Perhaps there was a particular developmental stage that had increased susceptibility? Perhaps adult bees feeding larvae would – for whatever reason – reduce their resistance to infection via the oral route?

We screened every egg, larva, pupa and adult bee for replicating DWV at the end of the experiment.

There was none present 🙁 ( or perhaps 🙂 , depending upon your viewpoint )

Summary and conclusions

We generated unequivocal evidence that DWV replicates in bumble bees. Specifically in Bombus terrestris, the buff tailed bumble bee. I’d be surprised if it did not replicate in other Bombus species, but that will need to be investigated. 

Infection of adult bees was only possible by injection, with no evidence for infection during feeding.

Bumble bee larvae can be infected with DWV while feeding, but only when fed very large amounts of virus directly. When larvae were reared by a colony supplied with DWV-laced food for several weeks the larvae did not become infected.

These results were recently published in Scientific Reports (Gusachenko et al., 2020) and are freely available. The title of the paper neatly sums up the study “Evidence for and against deformed wing virus spillover from honey bees to bumble bees: a reverse genetic analysis”

What does this mean in terms of our understanding of pathogen spillover from managed honey bee colonies to free living bees? 

If ecologists and environmental scientists are going to make the case that honey bees are threatening the survival of free-living solitary or bumble bees (due to pathogen spillover) they need to:

  1. formally demonstrate that the honey bee virus replicates in the free-living bee
  2. show that this replication is detrimental to the free-living bee
  3. provide evidence for a natural route of transmission by which infection can occur

In my view, and using legal terms again, it’s case proven for the first point in Bombus terrestris 11. In contrast, if I was the judge I’d throw out the other cases due to lack of evidence.

Monkey puzzles

There are viruses everywhere. Every living species has one or more viruses that infect it. Inevitably, because viruses replicate to very high levels, species other than the natural host may become exposed.

But almost always this has no consequences at all …

And to illustrate that I’ll briefly describe a study of monkey viruses infecting humans in Cameroon from several years ago. HIV is one of a very large group of viruses called immunodeficiency viruses. The ‘H’ stands for human, though the virus originated in chimpanzees and is very closely related to the simian immunodeficiency viruses (SIV).

A study of hunters living in the forests of Cameroon showed evidence for exposure to multiple different SIV isolates in tribespeople who hunted non-human primates or who were involved in butchering them or preparing them for market or cooking. There was no evidence these viruses were spreading in the human population, or that there was any sickness or disease associated with prior exposure. 

Environmental exposure happens all the time, and is relatively easy to detect. That’s exactly what had happened with these monkey viruses.

But evidence for environmental exposure, whilst easy to get, is not sufficient to support a claim that the virus causes disease at the level of the individual, or that it threatens an entire population.

As a virologist I think it’s interesting that DWV replicates in Bombus terrestris. However, I’ve yet to see any convincing evidence that DWV spillover from honey bees is responsible for the decline in wild bee populations.

Circumstantial evidence is not the same as convincing evidence.


Notes

What are the missing experiments that we didn’t do?

A key one is to determine whether long-term infection of bumble bees with DWV results in disease. We didn’t see overt deformed wing disease, but it’s possible that infection for weeks could have caused this or other symptoms. 

Although we fed bumble bee nests for weeks with DWV we saw no evidence of larval infection. This was despite previously demonstrating that larvae could be infected with high levels of DWV orally. One possibility is that DWV is inactivated by adult bees. I think it would be interesting to look at the level of infectious DWV in larval food.

Are there natural routes of exposure to DWV that result in bumble bee infection?

Does DWV ever cause environmental contamination at a high enough level to naturally infect bumble bees? For example, is the level of DWV in honey bee faeces high enough and does it ever contaminate pollen?

We are not going to do these studies so it will be interesting to see if others do … or whether simply the presence of the virus (whether replicating or not) will be proof’ that honey bee viruses are responsible for the decline in free-living bee populations.

Diutinus bees

Diutinus is Latin for long-lasting.

Diutinus bees are therefore long-lasting bees. These are the bees that, in temperate regions, maintain the colony through the winter to the warmer days of spring.

I’ve discussed the importance of these bees recently., and I’ve regularly made the case that protecting these ‘long-lived’ bees from the ravages of Varroa-vectored viruses is critical to reduce overwintering colony losses.

Winter is coming …

In most cases the adjective diutinus is replaced with ‘winter’, as in winter bees; it’s a more familiar term and emphasises the time of year these bees are present in the hive. I’ll generally use the terms interchangeably in this post.

Diutinus does not mean winter

From a scientific standpoint, the key feature of these bees is that they can live for up to 8 months, in contrast to the ~30 days a worker bee lives in spring or summer. If you are interested in what induces the production of long-lived bees and the fate of these bees, then the important feature is their longevity … not the season.

Furthermore, a proper understanding of the environmental triggers that induce the production of long-lived bees might mean they could be produced at other times of the season … a point with no obvious practical beekeeping relevance, but one we’ll return to in passing.

It’s worth emphasising that diutinus bees are genetically similar to the spring/summer bees (which for convenience I’ll refer to as ‘summer bees’ for the rest of the post). Despite this similarity, they have unique physiological features that contribute to their ability to thermoregulate the winter cluster for months and to facilitate spring build-up as the season transitions to spring.

What induces the production of winter bees? Is it a single environmental trigger, or a combination of factors? Does summer bee production stop and winter bee production start? What happens at the end of the winter to the winter bees?

Segueing into winter bee production 

The graph below shows the numbers of bees of a particular age present in the hive between the end of August and early December.

Colony age structure from August to December – see text for details

Each distinct colour represents bees reared in a particular 12 day ‘window’. All bees present before the 31st of August are blue. The next 12 day cohort of bees are yellow etc. The area occupied by each colour indicates the number of bees of a particular age cohort.

Note that egg laying (black) is negligible between early October and late November when it restarts.

The graph shows that that there is no abrupt change from production of summer bees to production of winter bees.

For example, about 95% of the blue bees have disappeared by December 1. Of the yellow bees, which first appeared in mid-September, about 33% are present in December. Finally, the majority of the lime coloured bees, that first put in an appearance in early October, are present at the end of December.

The colony does not abruptly stop producing short-lived summer bees on a particular date and switch to generating long-lived ‘diutinus’ winter bees. Instead, as late summer segues into early autumn, fewer short lived bees and more long lived bees are produced. 

Note that each cohort emerge from eggs laid 24 days earlier. The orange cohort emerging from 24/09 to 05/10 were laid within the first two weeks of September. This emphasises the need to treat early to reduce mite levels sufficiently to protect the winter bees.

Winter bees are like nurse bees but different

Before we consider what triggers the production of diutinus bees we need to discuss how they differ from summer bees, both nurses and foragers.

Other than being long-lived what are their characteristics?

Interaction of key physiological factors in nurse (green), forager (red) and winter bees (blue). Colored disks indicate the relative abundance of each factor.

The four key physiological factors to be considered are the levels of juvenile hormone (JH), vitellogenin (Vg) and hemolymph proteins and the size of the hypopharyngeal gland (HPG).

As summer nurse bees transition to foragers the levels of JH increases and Vg decreases. This forms a negative feedback loop; as Vg levels decrease, JH levels increase. Nurse bees have high levels of hemolymph proteins and large HPG, the latter is involved in the production of brood food fed to larvae.

So if that describes the summer nurse bees and foragers, what about the winter bees?

Winter bees resemble nurse bees in having low JH levels, high levels of VG and hemolymph proteins and large HPG’s. 

Winter bees differ from nurse bees in being long lived. A nurse bee will mature into a forager after ~3 weeks. A winter bee will stay in a physiologically similar state for months.

There have also been time course studies of JH and Vg levels through the winter. In these, JH levels decrease rapidly through October and November and are at a minimum in mid-January, before rising steeply in February and March.

As JH levels rise, levels of Vg and hemolymph proteins decrease and the size of the HPG decreases i.e. as winter changes to early spring winter bees transition to foragers.

Now we know what to look for (JH, Vg levels etc) we can return to think about the environmental triggers that cause these changes.

No single trigger

In temperate regions what distinguishes winter from autumn or spring? 

Temperatures are lower in winter.

Daylength (photoperiod) is shorter in winter.

There is less pollen and nectar (forage) available in winter.

Under experimental conditions it’s quite difficult to change one of these variables without altering others. For example, shifting a colony to a cold room (i.e. lowering the ambient temperature to <10°C) leads to a rapid decrease in JH levels (more winter bee-like). However, the cold room was dark, so perhaps it was daylength that induced the change? Alternatively, a secondary consequence of moving the colony is that external forage was no longer available, which could account for the changes observed.

And forage availability will, inevitably, influence brood rearing.

Tricky.

Reducing photoperiod alone does induce some winter bee-like characteristics, such as increases in the protein and lipid content of the fat bodies. It also increases resistance to cold and starvation. It can even cause clustering at elevated (~19°C) temperatures. However, critically, a reduced photoperiod alone does not appear to make the bees long lived. 

Remember also that a reduced photoperiod will limit foraging, so reducing the nutritional status of the colony. This is not insignificant; pollen trapping 2 in the autumn accelerates the production of winter bees.

But again, this may be an indirect effect. Reduced pollen input will lead to a reduction in brood rearing. Feeding pollen to broodless winter colonies induces egg-laying by the queen.

Brood, brood pheromones and ethyl oleate

One of the strongest clues about what factor(s) induces winter bee production comes from studies of free-flying summer colonies from which the brood is removed. In these, the workers rapidly change to physiologically resemble winter bees 3.

How does the presence of brood prevent the generation of diutinus bees?

There are some studies which demonstrate that the micro-climate generated in the colony by the presence of brood – elevated temperature (35°C) and 1.5% CO2 – can influence JH levels. 

However, brood also produces pheromones – imaginately termed brood pheromone – which does all sorts of things in the colony. I’ve discussed brood pheromone previously in the context of laying workers. The brood pheromone inhibits egg laying by worker bees.

Brood pheromone also contributes to a enhancement loop; it induces foraging which results in increased brood rearing and, consequently, the production of more brood pheromone.

One way brood pheromone induces foraging is by speeding the maturation of middle-aged hive bees into foragers. Conversely, when raised in the absence of brood, bees have higher Vg levels, start foraging later and live longer.

But it’s not only brood that produces pheromones.

Workers also produce ethyl oleate, a pheromone that slows the maturation of nurse bees, so reducing their transition to foragers.

A picture is worth a thousand words

All of the above is quite complicated.

Individual factors, both environmental and in the hive, have direct and indirect effects. Experimentally it is difficult to disentangle these. However, Christina Grozinger and colleagues have produced a model which encapsulates much of the above and suggests how the production of winter bees is regulated. 

Proposed model for regulation of production of winter bees.

During autumn there is a reduction in forage available coupled with a reduced daylength and lower environmental temperatures. Consequently, there is less foraging by the colony. 

Since more foragers are present within the hive, the nurse bees are exposed to higher levels of ethyl oleate, so slowing their maturation.

There’s less pollen being brought into the colony (reduced nutrition), so brood production decreases and so does the level of brood pheromone. The reduced levels of brood pheromone also reduces nurse bee maturation.

As shown in the diagram, all of these events are in a feedback loop. The reduction in levels of brood pheromone further reduces the level of foraging … meaning more foragers are ‘at home’, so increasing the effects of ethyl oleate.

All of these events have the effect of retarding worker bee maturation. The workers remain as ‘nurse-like’ long-lived winter bees.

Is that all?

The difference between nurse bees and winter bees is their longevity … or is it?

In the description above, and in most of the experiments conducted to date, the key markers of the levels of JH, Vg and hemolymph proteins, and the size of the HPG, are what has been studied. 

I’d be astounded if there are not many additional changes. 

Comparison of workers and queen bees have shown a large range of epigenetic changes induced by the differences in the diet of young larvae 4. Epigenetic changes are modifications to the genetic material that change gene expression.

I would not be surprised if there were epigenetic changes in winter bees, perhaps induced by alteration of the protein content of their diet as larvae, that influence gene expression and subsequent longevity. Two recent papers suggest that this may indeed happen; the expression of the DNA methyltransferases (the enzymes that cause the epigenetic modifications) differs depending upon the demography of the colony 5 and there are epigenetic changes between the HPG in winter bees and bees in spring 6.

Clearly there is a lot more work required to fully understand the characteristics of winter bees and how they are determined.

Don’t forget …

It’s worth emphasising that the local environment (forage and weather in particular) and the strain of the bees 7 will have an influence on the timing of winter bee production.

Last week I discussed a colony in my bee shed that had very little brood on the 2nd of October (less than one side of one frame). When I checked the colonies last weekend (11th) there were almost no bees flying and no pollen coming in. A colleague checked an adjacent colony on Monday (13th) and reported it was completely broodless. These bees are ‘local mongrels’, selected over several years to suit my beekeeping.

Early autumn colonies

In contrast, my colonies on the west coast are still busy. These are native black bees. On the 14th they were still collecting pollen and were still rearing brood. 

The calendar dates in the second figure (above) are therefore largely irrelevant.

The transition from summer bees to the diutinus winter bees will be happening in your colonies, sooner or later. I suspect it’s already completed in my Fife bees.

Whether genetics or environment has a greater influence on winter bee production remains to be determined. However, I have previously described the good evidence that local bees are better adapted to overwintering colony survival.

To me, this suggests that the two are inextricably linked; locally selected bees are better able to exploit the environment in a timely manner to ensure the colony has the winter bees needed to get the colony through to spring.


 

Preparing for winter

The beekeeping season is fast receding into the distance as the first frosts of autumn appear and, finally, the wasp numbers start to diminish. By now colonies should be heavy with stores, either collected by the bees or provided by the beekeeper.

Winter is coming … be prepared

There is relatively little actual beekeeping to be done this late in the year.

Colonies do not need to be disturbed unnecessarily. They certainly don’t require the usual weekly inspection … they’re not going to swarm, you’ve already applied your miticide of choice and fed them with fondant or syrup 1.

Late queen mating

With temperatures during the day in the low to mid-teens (°C) it is still warm enough to open a colony if you need to.

One of the few reasons I’d open a colony in very late September/early October would be to check if a new queen that had emerged at the end of August had successfully mated. If she had, then all is good. She will continue to lay late into the autumn and should produce sufficient winter bees to get the colony through to the following Spring.

When I lived in the Midlands I would regularly get queens successfully mated in early/mid September. It was pretty dependable, and in good years I’d be actively queen rearing through much of August.

Now, back in Scotland, late queen mating is not something I would want to rely on. I’m certain it happens now and again, but only in very exceptional years.

It’s a tough life being a drone in late August … but not for much longer

This year, many of my colonies turfed their drones out a month ago, and queen mating is not going to happen unless there are plenty of drones about.

A quick peek

It takes just minutes to check whether the queen is mated and laying. Although you don’t need to see the queen, it’s worth using just a whiff of smoke so you have the option of searching for her if needed. If you smoke the colony heavily she’ll end up rushing about or buried under a mass of disturbed bees.

Just a whiff …

You will need to remove the feeder (if using syrup) or the queen excluder and fondant block. Place these aside gently and remember that there are likely to be large numbers of bees adhering to the underside, so balance them on the rim of an upturned roof. This is the time you realise the benefit of using framed rigid wire QE when feeding fondant … removing the block on a flexible plastic QE is a right palaver.

The hive should be busy with bees. Gently remove the dummy board and outer frame. This should be full, or in the process of being filled, with stores. There’s no need to shake the bees off. Just stand it aside out of the way.

‘Guesstimate’ the approximate centre of the brood nest, based upon the density of bees in the seams. Gently lever the frames apart a centimetre or so, then release one of the frames adjacent to the gap you’ve created from its neighbours.

Lift the frame and look for sealed brood, open brood and eggs. By knowing the development cycle of workers bees (3E,5L,13P 2) you can determine approximately when the queen started laying 3.

If she started laying …

Snatching victory from the jaws of defeat

… if there are no eggs or larvae by very late September I would assume that the queen had failed to mate.

You need to use your judgement here. If the weather was poor in the first half of September, but excellent since then, it remains a distant possibility that she has only just mated and has yet to start laying.

Look carefully for polished cells where the centre of the broodnest should be.

And cross your fingers.

Polished cells are a sign that the nurse bees are preparing the comb for egg laying. However, in my experience, they do this even if the queen remains unmated, so it is not a reliable sign that all is well.

You therefore need to use your judgement and be realistic.

Miracles do happen, but you can’t depend upon them 4.

If the weather has been consistently poor – windy, low temperatures (for queen mating, which really needs ~18-20°C) or wet – then assume the worst and ‘save’ the colony by uniting it with a nearby strong colony.

A colony without a laying queen in late autumn will not survive the winter in any state that will make it a viable colony the following year 5.

In Scotland, I routinely unite colonies that do not have a laying queen at the end of August. As described in the last couple of weeks, I do my final colony checks with feeding and miticide treatment.

I know the chances of a queen getting successfully mated after that are effectively zero.

Quick uniting – air freshener

If you need to unite two colonies quickly, without the usual week long wait while they gently mingle after stacking them separated by a sheet of newspaper, you can use a few squirts of household air freshener.

  • Open the queenright recipient colony, removing the feeder and carefully placing it aside to avoid crushing bees (see above)
  • Find the unmated/unlaying/uncooperative queen in the broodless box and remove her (permanently I’m afraid)
  • Spray the top of the recipient colony with a a few squirts of air freshener
  • Do the same with the underside of the now queenless broodless colony
  • Stack the latter on top of the recipient colony
  • Add the feeder back, again giving a squirt or two of air freshener at the interface to stop the bees from fighting

The air freshener masks the distinctive pheromone ‘smell’ of the two colonies, allowing the bees to mingle without fighting.

That’s it.

Job done.

Caveat emptor

Like everything else on this site, I only write here from direct experience. I have successfully united quite a few colonies like this, though nothing like the number I’ve united using newspaper 6.

Given time and the choice I’d always use newspaper 7.

But this late in the season you might not have time.

A day after uniting with air freshener you can, if needed, revisit the hive and go through the double brood box to reduce it to a single box for the winter.

Does it matter which air freshener you use?

I have no idea.

I use Glade Citrus Sunny Beat as it was the cheapest I could find at the time I needed it 8.

Securing the queenright overwintering colony

If you consult the COLOSS records for overwintering colony losses they include a small percentage that are lost to ‘natural disasters’. COLOSS record queen failures and things like that separately, and – in an earlier paper – they define natural disasters as:

… rather loosely defined, as the causes can be very different in participating countries, including fire, storm, flooding, vandalism, bears, martens, woodpeckers, falling trees, suffocation from snow and many more.

The small percentage (0.1 – ~5%) lost to natural disasters vary from country to country, and from year to year.

What is notable about several of these natural disasters is that they should be avoidable.

If your colonies are strong and queenright, and if you’ve fed and treated them to give them the best chance of surviving the winter, it makes sense to do what you can to avoid these natural disasters.

The hive

I use a combination of polystyrene and cedar hives. Sometimes I even combine the two together in a single hive. The majority of my poly hives are from Abelo or Swienty which, for reasons explained elsewhere, are compatible with all the woodenware I own.

The apiary in winter ...

The apiary in winter …

I see no difference in the overwintering colony success between poly and cedar hives.

This doesn’t mean there isn’t one.

I’ve only run about 20 colonies for the last decade. That’s ~200 overwintered colonies. If there were wildly different survival rates I would have noticed. Since I haven’t noticed it either means there is no difference or there is a subtle difference but my sample size is too low 9.

All my colonies overwinter on open mesh floors, usually with the Varroa tray removed. The hives in the photo above are being monitored for mite drop in early December following oxalic acid treatment.

DIY insulation over a perspex crownboard

In addition, all of my hives have a 50 mm thick block of Kingspan under the roof, integrated into the roof, or integrated into the crownboard. In the bee shed my hives have no roof, and are just capped with a block of Kingspan over the crownboard.

Look, no roof … but insulation present all year round

Make sure the stack of boxes in the hive are stable and secure. If the apiary is exposed, strap everything together securely. A colony might survive a week or two of summer showers with no roof, but will surely perish if exposed for any length of time to cold, wet winter weather.

Apiary security

It is unlikely that you will visit the apiary much in the winter. Once a fortnight is more than enough.

It might therefore be worth considering whether it is sufficiently secure from the attention of unwanted human visitors. Unfortunately, incidents of vandalism occur throughout the season, but a hive kicked over in midwinter has less chance of being detected quickly.

Or of surviving.

Although it should probably be included within the ‘Varmints’ section below, large animals – cows, deer, elk, bear, rhino, kangaroo 10 – might also inadvertently, or deliberately, overturn a hive.

Apiary gate

Safe and secure

Fences, either a couple of strands of barbed wire, an electric fence or a full-blown razor-wire topped security barrier, are usually sufficient to keep large two and four-legged visitors at bay.

COLOSS mention both falling trees and flooding as natural disasters.

Winter storms can and do wreak havoc in some years, though I always associate the summer with storm-toppled trees because they’re in full leaf and therefore offer more resistance. It’s certainly worth looking to see if trees adjacent to your apiary might threaten the hives.

Where did Noah keep his bees? In his Ark hive.

Where did Noah keep his bees? In his Ark hive.

Flooding appears to be on the increase. I have experienced minor flooding in one of my apiaries. None of the hives were threatened, but it made access inconvenient for weeks at a time. Again, it’s worth imagining the worst and preparing for it.

Hives often float, but not necessarily the right way up 🙁

Varmints

Having dealt with the threat of large animals 11 it’s also worth considering the damage some small animals can do to hives.

The two main culprits are woodpeckers and mice. Both can be a menace once the frosts set in, but rarely before that.

Woodpeckers, and specifically green woodpeckers (yaffles 12), can learn that beehives contain a wonderful bounty of pupae and larvae. It is learned behaviour. Some green woodpeckers never go near hives, others routinely target them.

In Warwickshire, hives needed to be protected from yaffles. Here in Fife the bird is very much less common and I’ve never had any hives targeted.

Wrapped for winter

Wrapped for winter …

Protection is straightforward. If needed, I simply wrap the hives in a single sheet of DPM (damp proof membrane), pinned in place with drawing pins. The bird need to cling onto the vertical side of the hive to easily burrow through to the brood. The DPM stops them doing this. Leaving bits of the roof or sides of the floor exposed is therefore not a problem 13.

Pixie or Dixie?

Pixie or Dixie?

Mice access hives through overly large entrances. I only have problems with the stupidly cavernous maw of my preferred Everynuc. Mice eat pollen and stores, destroy the brood and wee everywhere 🙁  Thoroughly unpleasant.

Everynuc entrance

Open wide …

A standard mouseguard pinned in place throughout the coldest months of the winter prevents them accessing the hive. Alternatively, on a full-sized colony, the kewl-style underfloor entrances are very effective at excluding rodents.

Kewl open mesh floor showing L-shaped entrance slot

Kewl floor entrance …

That’s not the end of winter-related tasks, but it’s just about all you need to do for your colonies before winter proper starts.

There are some midwinter checks that are needed, but we’ll deal with them nearer the time.


Note

We also have pine martens at one of my apiaries. They are reported to vandalise hives and steal honey (and presumably brood) in late winter. Pine martens are incredibly agile and no fence exists that could keep them out. Time will tell whether they are a problem.

In the meantime, here’s one living up to its name, stealing a pine offcut used to slow down the rate at which they empty the squirrel feeder of peanuts 🙂

Winter bee production

There are big changes going on in your colonies at the moment.

The summer foragers that have been working tirelessly over the last few weeks are slowly but surely being replaced. As they die off – whether from old age or by being eaten by the last of the migrating swallows – they are being replaced by the winter bees.

Between August and late November almost the entire population of bees will have changed. The strong colonies you have now (or should have) will contain a totally different workforce by the end of the year.

Forever young

The winter bees are the ones responsible for getting the colony from mid/late autumn through to the following spring. They are sometimes termed diutinus bees from the Latin for “long lived”.

These are the bees that thermoregulate the winter cluster, protecting the queen, and rearing the small amounts of brood during the cold, dark winter to keep the colony ticking over.

Midwinter cluster

A midwinter colony

Physiologically they share some striking similarities with so-called hive or nurse bees 1 early in the summer.

Both hive bees and winter bees have low levels of juvenile hormone (JH) and active hypopharyngeal glands. Both types of bee also have high levels of vitellogenin, high oxidative stress resistance and corpulent little bodies.

But early summer nurse bees mature over a 2-3 week period. Their JH levels increase and vitellogenin levels decrease. This induces additional physiological changes which results in the nurse bee changing into a forager. They sally forth, collecting nectar, pollen and water …

And about three weeks later they’re worn out and die.

Live fast, die young

And this is where winter bees differ. They don’t age.

Or, more accurately, they age   v  e  r  y    s  l  o  w  l  y.

In the hive, winter bees can live for 6 months if needed. Under laboratory conditions they have been recorded as living for up to 9 months.

They effectively stay, as Bob Dylan mumbled, forever young.

Why are winter bees important?

Although not quite eternal youth … staying forever young is useful as their longevity ensures that the colony does not dwindle and perish in the middle of winter.

With little or no nectar or pollen available in the environment the colony reduces brood rearing, and often stops altogether for a period.

But what about the kilograms of stores and cells filled with pollen in the hive? Why can’t they use that?

Whilst both are present, there’s nothing like enough to maintain the usual rate of brood rearing. If they tried the colony would very quickly starve.

Evolution has a very effective way of selecting against such rash behaviour 🙁

If you doubt this, think how quickly hives get dangerously light during the June gap. With no nectar coming in and thousands of hungry (larval) mouths to feed the colony can easily starve to death during a fortnight of poor weather in June.

The winter bees ‘hold the fort’, protecting the queen and rearing small amounts of brood until the days lengthen and the early season pollen and nectars become available again.

And, just as the winter bees look after the viability of the colony, the beekeeper in turn needs to look after the winter bees … we rely on them to get the colony through to spring.

Lots of bees

Can you identify the winter bees?

But before we discuss that, how do you identify and count the winter bees? How can you tell they are present? After all, as the picture above shows 2, all bees look rather similar …

Counting the long lived winter bees

The physiological changes in winter bees, such as the JH and vitellogenin levels, are only identifiable once you’ve done some rather devastating things to the bee. These have the unfortunate side effect of preventing it completing any further bee-type activities 🙁

Even before you subject them to that, their fat little bodies aren’t really sufficiently different to identify them visually.

But what is different is their longevity.

By definition, the diutinus or winter bees are long lived.

Therefore, if you record the date when the bee emerged you can effectively count back and determine how old it is. If it is more than ~6 weeks old then it’s a winter bee.

Or the queen 😉

And, it should be obvious, if you extrapolate back to the time the first long lived bees appear in the hive you will have determined when the colony starts rearing winter bees.

The obvious way to determine the age of a bee is to mark it upon emergence and keep a record of which marks were used when. Some scientists use numbered dots stuck to the thorax, some use combinations of Humbrol-type paint colours.

I’m not aware that anyone has yet used the barcoding system I discussed recently, though it could be used. The winter bee studies I’m aware of pre-date this type of technology.

Actually, some of these studies date back almost 50 years, though the resulting papers were published much more recently.

This is painstaking and mind-numbingly repetitive work and science owes a debt of gratitude to Floyd Harris who conducted many of the studies.

Colony age structure – autumn to winter

Here is some data showing the age structure of a colony transitioning from late summer into autumn and winter. There’s a lot in this graph so bear with me …

Colony age structure from August to December - see text for details

Colony age structure from August to December – see text for details

The graph shows the numbers and ages of bees in the colony.

The ages of the bees is indicated on the vertical axis – with eggs and brood (the youngest) at the bottom, coloured black and brown respectively. The adult bees can be aged between 1 and ~100 days old 3. The number of bees is indicated by the width of the coloured bar at each of the nine 12 day intervals shown.

All of the adult bees present in the hive at the end of August are coloured blue, irrespective of their age. There are a lot of these bees at the end of August and almost all of them have disappeared (died) by mid-November 4.

The remaining colours indicate all the bee that emerge within a particular 12 day interval. For example, all the bees that emerge between the 31st of August and the 12th of September are coloured yellow.  Going by the width (i.e. the numbers of bees of that age) of the yellow bars it’s clear that half to two-thirds of these bees die by mid October, with the rest just getting older gracefully.

But look at the cohort that emerge between the end of September and early October, coloured like this 5. The number of these bees barely changes between emergence and early December. By this time they are 72 days old i.e. an age that most summer bees never achieve.

Brood breaks and climate

In the colony shown above the queen continued laying reduced numbers of eggs – the black bars – until mid-October and then didn’t start again until the end of November. During this period the average age of the bees in the colony increased from ~36 days to ~72 days and the strength of the colony barely changed.

The figure above comes from a BeeCulture article by Floyd Harris. The original data isn’t directly referenced, but I suspect it comes from studies Harris conducted in the late 70’s in Manitoba, some of which was subsequently published in the Journal of Apicultural Research. In addition, Harris co-authored a paper presenting similar data in a different format in Insectes Sociaux which describes the Manitoban climate as having moderate/hot summers and long, cold winters.

My hives in Scotland, or your hives in Devon, or Denmark or wherever, will experience a different climate 6.

However, if you live in a temperate region the overall pattern will be similar. The summer bees will be replaced during the early autumn by a completely new population of winter bees. These maintain the colony through to the following spring.

The dates will be different and the speed of the transition from one population to the other may differ. The timing of the onset of a brood break is likely to also differ.

However, the population changes will be broadly similar.

And, it should be noted, the dates may differ slightly in Manitoba (and everywhere else) from year to year, depending upon temperature and forage availability.

Colony size and overwintering survival

Regular readers might be thinking back to a couple of posts on colony size and overwintering survival from last year.

One measured colony weight, showing that heavier colonies overwintered better 7. A second discussed the better performance of local bees in a Europe-wide study of overwintering survival. In this, I quoted a key sentence from the discussion:

“colonies of local origin had significantly higher numbers of bees than colonies placed outside their area of origin”

I can’t remember when during the season those studies recorded colony size, but I’m well aware that large colonies in the winter survive better.

The colonies that perish first in the winter are the pathetic grapefruit-sized 8 colonies with ageing queens or high pathogen loads.

In contrast, the medicine ball-sized ‘boomers’ go on and on, emerging from the winter strongly and building up rapidly to exploit the early season nectar.

But what the graph above shows is that the bees in a strong colony in late summer are a completely different population from the bees in the colony in midwinter.

The strength of the midwinter colony is determined entirely by when winter bee rearing starts and the laying rate of the queen, although of course both may be indirectly influenced by summer colony strength.

The influence of the queen

Other than this potential indirect influence, it’s possibly irrelevant how large the summer colony is in terms of winter colony size (and hence survival).

After all, even if the summer bees were three times as numerous, their fate is sealed. They are all going to perish six weeks or so after emergence.

Are there ways that beekeepers can influence the size of the overwinter colony to increase its chances of survival?

I wouldn’t pose the question if the answer wasn’t a resounding yes.

It has been known for a long time 9 that older queens stop laying earlier in the autumn than younger queens. As explained above, the longer the queen lays into the autumn the more winter bees are going to be produced.

Mattila et al., 10 looked at the consequences of late season (post summer honey harvest) requeening of colonies. In these they removed the old queen and replaced her with either a new mated or virgin queen, or allowed the colony to requeen naturally.

Using the ’12 day cohort’ populations explained above, the authors looked at when the majority of the winter bees were produced in the colony, and estimated the overall size of the winter colony.

The influence of new queens on winter bee production.

The influence of new queens on winter bee production. Note shift to the right in B, C and D, with new queens.

With the original old queen, 53% of winter bees were produced in the first two cohorts of winter bees. With the requeened colonies 54-64% of the winter bees were produced on average 36 days later, in the third and fourth cohorts of winter bees.

This indicates that young queens produce winter bees later into the autumn.

This is a good thing™.

In addition, though the results were not statistically significant, there was a trend for colonies headed by new queens to have a larger population of bees overwinter.

Perhaps one reason the requeened colonies weren’t significantly larger was that the new queens delay the onset of winter bee rearing. I’ll return to this at the end.

The influence of deformed wing virus (DWV)

Regular readers will know that this topic has been covered extensively, and possibly exhaustively, elsewhere on this site … so I’ll cut to the chase.

DWV is the most important virus of honey bees. When transmitted by Varroa destructor there is unequivocal evidence that it is associated with overwintering colony losses. The reason DWV causes overwintering losses is that it reduces the longevity of the winter bees.

The virus might also reduce the longevity of summer bees but,

  1. there’s so many of them to start with
  2. there’s loads more emerging every day, and
  3. they only survive a few weeks anyway,

that this is probably irrelevant in terms of colony survival.

Dainat et al., (2012) produced compelling evidence showing that DWV reduces the longevity of winter bees 11. The lifespan was reduced by ~20%.

A consequence of this is that the winter bees die off a little faster and the colony shrinks a little more. At some point it crosses a threshold below which it cannot thermoregulate the cluster properly, further limiting the ability of the colony to rear replacement bees (assuming the queen is able to lay at a low rate).

This colony is doomed.

Even if they stagger through to the longer days of spring they contain too few bees to build up fast. They’re not dead … but they’re hardly flourishing.

Winter bees and practical beekeeping

I think there are three ways in which our understanding of the timing of winter bee production should influence practical beekeeping:

Firstly … The obvious take-home message is that winter bees must be protected from the ravages of DWV. The only way to do this is to minimise the mite population in the colony before the winter bee rearing starts.

The logical way to do this is to treat using an approved miticide as soon as practical after the summer honey is removed 12.

I discuss the importance of the timing of this treatment in When to treat?, which remains one of the most-read posts on this site.

Secondly … Avoid use of miticides (or other colony manipulations) that reduce the laying rate of the queen in early autumn.

When I used to live at lower latitudes I would sometimes use Apiguard. This thymol-containing miticide is very effective if used when the temperature is high enough. However, in my experience a significant proportion of queens stop laying when it is being used. Not all, but certainly more than 50%.

I don’t know why some stop and others don’t. Is it genetic? Temperature-dependent?

Whatever the reason, they stop at exactly the time of the season you want them to be laying strongly.

Thirdly … consider requeening colonies with young queens after the summer honey is removed. This delays the onset of winter bee production and results in the new queen laying later into the year. The later start to winter bee production gives more time for miticides to work.

A win-win situation.


 

Weed and feed

Weed and feed is a generic term that describes the treatment of lawns to simultaneously eradicate certain weeds and strengthen the turf.

It seemed an appropriate title for a post on eradicating mites from colonies and feeding the bees up in preparation for the winter ahead.

Arguably these are the two most important activities of the beekeeping year.

Done properly they ensure you’ll still be a beekeeper next year.

Ignored, or done too little and too late, you’ll join the unacceptably large number of beekeepers who lose their colonies during the winter.

They think it’s all over

In Fife, on the east coast of Scotland, my beekeeping season effectively finishes with the midsummer ‘mixed floral’ nectar sources. This is a real mix of lime, blackberry, clover and Heinz nectars 1 … many of which remain to be identified.

There’s no reliable late nectar flow from himalayan balsam around my apiaries are and not enough rosebay willowherb (fireweed) to be worthwhile, though in a good year the bees continue to collect a bit from both into early September.

But by then the honey supers are off and extracted. Anything the bees find after that they’re welcome to.

The contrast with the west of Scotland is very marked. Over there my bees are still out collecting reasonable amounts of late heather nectar, though the peak of the flow is over.

Storing supers

Once the honey supers are extracted they can be returned to the colonies for the bees to clean up prior to storing them overwinter. However, this involves additional trips to the apiary and usually necessitates using the clearer boards again to leave them bee-free before storage.

I used to do this and quite enjoyed the late evening trips back to the apiary with stacks of honey-scented supers. More recently I’ve stopped bothering and instead now store the supers ‘wet’. The main reasons for this are:

  • laziness lack of time
  • unless you’re careful it can encourage robbing, by wasps or bees. You need to return supers to all the colonies in the apiary and if you have the hives open too long it can induce a frenzy of robbing 2
  • the honey-scented supers encourage the bees to move up faster when they’re used the following season

If you do store the supers ‘wet’ make sure the stacked boxes are bee and wasp-tight. Mine go in a shed with a spare roof on the top. If there are any gaps the wasps, bees or ants will find them and it then becomes very messy. 

I know many beekeepers who wrap their supers in clingfilm. Not the 30 cm wide roll you use in the kitchen but the sort of metre wide swathe they used to wrap suitcases in at London Heathrow.

Dated super frames

The drawn super comb is a really valuable resource and can be used again and again, year after year. I usually record the year a frame was built on the top bar. Many are now over a decade old and have probably accommodated at least 80 lb of honey in their lifetime 3.

The timing of late season Varroa management

During the brood rearing season the Varroa levels in the colony will have been rising inexorably. Without intervention the mites will continue to replicate on developing pupae that would otherwise emerge as the all-important overwintering bees. These are critical to get the colony through to the following spring.

When Varroa feeds on a developing pupa it transmits the viruses – primarily deformed wing virus – it acquired from the last bee is fed on. These viruses amplify by about a million-fold within 24-48 hours. Pupae that do not die before eclosion may have developmental defects. Importantly, those that appear normal have a reduced lifespan.

The overwintering bees should live for months, but might only live for weeks if their virus levels are high.

And if enough overwintering bees have high viral loads and die prematurely, the probability is the the colony will perish in the winter.

You therefore need to reduce mite levels before the overwintering bees are exposed to Varroa

The full details and justification are in a previous post logically entitled When to treat?

TL;DR 4late August to early September is the best time to treat to protect the winter bees from the worst of the ravages of mite-transmitted DWV.

Use an appropriate treatment

You need to reduce the mite levels in the colony by at least 90% to protect the winter bees.

To achieve this you need an appropriate miticide used properly. 

I use Apivar

Apivar is an Amitraz-containing miticide. Although there are reports of mite resistance in some commercial apiaries, the pattern is very localised (individual hives within an apiary, which is difficult to understand) and in my view it is currently the best choice.

What are the alternates?

  • MAQS – active ingredient formic acid – poorly tolerated at high temperatures, but can be used with the supers present
  • Apiguard – active ingredient thymol – ineffective at lower temperatures (it needs an ambient temperature of 15°C to work – that’s not going to happen in Scotland in September).
  • Apistan – active ingredient a synthetic pyrethroid – unsuitable as there is widespread resistance in the mite population.

Using Apivar

Apivar treatment is temperature-independent. It cannot be used when the honey supers are present. You simply hang two strips in the hive for 6 to 10 weeks and let them do their work. The bees tolerate it well and, unlike MAQS or Apiguard, I’ve not seen any detrimental effects on the queen who continues to lay … making more of those important winter bees.

Apivar strips

Each strip consists of an amitraz-impregnated piece of plastic tape with a V-shaped tab that can be pushed into the comb to hold it in place. 

This generally works well as the frames are usually not moved much as there’s no need for inspections this late in the season.

Apivar strip pushed into comb

However, the strips can be a little fiddly to remove (or fall off during frame handling) and some of our research colonies will continue to be used for at least another month. I’ve therefore used a short piece of bent wire to hang the strips from in these hives.

Apivar strip on wire hanger

I place the strips in opposite corners of the hive, set two frames in from the sides. 

Apivar, wax and honey contamination

Although Amitraz is not wax soluble 5 there are recent reports on BEE-L that one of its breakdown products are, including one that has some residual miticide activity 6

I therefore try and get all the bees into the brood box before starting treatment (I described nadiring supers with unripe honey last week).

Very rarely I’ll leave the bees with a super of their own unripe honey. Usually this happens when the brood box is already packed with stores and overflowing with bees. In this case I’ll mark the super and melt down the comb next season rather than risking tainting the honey I produce.

I attended a Q&A session by the Scottish Beekeeping Association last month in which the chief bee inspector discussed finding Apivar strips in honey production hives. He described the testing of honey for evidence of miticide contamination and potential subsequent confiscation.

This is clearly something to be avoided.

Remember to record the batch number of Apivar used and note the date in your hive records. I just photograph the packet for convenience. The date is important as the strips must be removed after 6 weeks and before 10 weeks have elapsed. 

It’s finally worth noting that the instructions recommend scraping the strip with a hive tool part way through the period if they are being used for the full ten week course of treatment. The strips usually get propolised into the frame and the scraping ‘reactivates’ them to ensure that the largest possible number of mites are killed off.

And, after all, that’s what they’re being used for.

Apivar is expensive

Well … yes and no.

Yes it feels expensive when walking out of Thorne’s of Newburgh clutching one small foil packet and being £31 poorer. 

But think about it … that packet is sufficient to treat 5 colonies.

Is £6.20 too much to spend on a colony?

My 340 g jars of honey cost more than £6.20 and my productive colonies produce at least one hundred times that amount of honey. 

I don’t think 1% of the honey value is too much to spend on protecting the colony from mites and the viruses they carry.

Mite drop

Varroa killed by the miticide 7 fall to the bottom of the hive. If you have an open mesh floor (OMF) they fall through … onto the ground or the intervening neatly divided Varroa tray, enabling you to easily count them

Varroa trays ...

Varroa trays …

Remember that amitraz, the active ingredient of Apivar, works by direct contact. This is why you place the strips diametrically opposite one another so that as many bees as possible contact them. Unlike Apiguard, it makes no difference whether the Varroa tray is present or not.

It is useful to ‘count the corpses’ to get an idea of the infestation level and the efficacy of the treatment.

I’m going to discuss what you might expect in terms of mite drop in the winter (I need to plot some graphs first). However, this is something you could think about before then … knowing Apivar kills mites in less than three hours after exposure, what do you think the mite drop should look like over the 6-10 weeks of treatment?

Enough weeding, what about feeding?

I treat and feed colonies on the same day.

I also do the final hive inspection of the season. At this I look for evidence of a laying queen, the general health of the colony, the amount of brood present and the level of stores in the brood box. 

If the colony is queenless (how did that happen without me noticing earlier?) I simply unite the colony with a strong, healthy queenright colony. I don’t bother testing it with a frame of eggs … time is of the essence.

It’s too late to get a queen mated (at least in Fife … when I lived in the Midlands I got a few September queen matings but they could not be relied upon) and I rarely, if ever, buy queens.

I only feed with fondant in the autumn.

Convenience food

I described fondant last week as a convenience food

A spade's a spade ...

A spade’s a spade …

I’ve described in detail many of the benefits of fondant in numerous previous posts. Essentially these can be distilled to the following simple points:

  • zero preparation; no syrup spillages in the kitchen, no marital strife.
  • bucket- and feeder-free; no need to carry large volumes of syrup to the apiary and no feeders to store for the remaining 11 months of the year. All you need to feed fondant is a queen excluder and an empty super … and you’ve got those already.
  • easy to store; unopened it keeps for several years 8.
  • super speedy; I can feed a colony, including cutting the block in half, in less than 2 minutes.
  • good for queen and colony; perhaps that’s stretching it a bit. What I mean is that the bees take the fondant down more slowly than syrup, consequently the queen continues to lay uninterrupted as the brood nest does not get backfilled with stores. This is good for the colony as it means the production of more winter bees.
  • an anti-theft device; you can’t spill fondant so there is much less chance of encouraging robbing by neighbouring bees or wasps.
  • useful boxes; the empty boxes are a good size to store or deliver jarred honey in – each will accommodate sixteen 1 lb rounds.

I’ve fed nothing but fondant for about a decade and can see no downsides to its use.

Money, money, money

I’ve never used anything other than commercially purchased “baker’s” fondant … don’t believe the rubbish (about ‘additives’) some of the bee equipment suppliers use to justify their elevated prices.

You should be paying about £1/kg … any more and you’re being robbed. This year (2020) I paid less than 90p/kg.

Do not use the icing fondant sold by supermarkets for Christmas cakes. I’m sure there’s nothing much wrong with it, but – at £2/kg – you’ll soon go bankrupt. 

Tips for feeding fondant

Fondant blocks are easier to slice in half if they are slightly warm.

Use a sharp bread knife and don’t slice your fingers off. 

You can cut the blocks in half in advance in the warmth of your kitchen and then cover the cut faces with clingfilm to prevent them reannealing, but I just do it in the apiary.

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

Alternatively, use a clean spade 9.

Always place the block cut face down on a queen excluder directly over the top bars of the brood frames. With a full block, it’s like opening a book and laying it face down. Do not place it above a crownboard with a hole in it.

You want the bees to have unfettered access to the open face of the fondant block.

Fondant on queen excluder with eke

Ideally, use a framed wire queen excluder.

These are easier to lift off should you need to go into the colony.

Which you don’t 😉

There’s no need to continue inspections this late into the season. Go and enjoy a week or two away in Portugal … or perhaps not 🙁

If you need to store an unused half block of fondant wrap the cut face in clingfilm.

All my colonies get one full block (12.5 kg) and many get a further half block, depending upon my judgement of the level of the stores in the hive.

Insulation

The bees will take the fondant down over 2 – 4 weeks. They do store it, rather than just using it as needed. By late September or early October all that will remain is the blue plastic husk. The photo below is from mid-October. This colony has had a ‘topup’ additional half block after already storing a full block of fondant.

They fancied that fondant

With cooler days and colder nights, you want to reduce heat loss by the colony and minimise the dead space above the bees into which the heat escapes.

Although bees take fondant down at lower temperatures than they do syrup, there’s no point in giving the colony more additional space to heat than they need.

Poly super and fondant ...

Poly super and fondant …

Depending upon the availability of equipment I do one or a combination of the following:

  • use a poly super to provide space for the fondant
  • compress the fondant (use your boot) into as little space as possible and you squeeze it into a 50 mm deep eke, which (conveniently) is the same depth as the rim on my insulated polcarbonate/perspex crownboards 10.
  • use an eke and an inverted perspex crownboard with no need to compress the fondant
  • add a 50 mm thick block of insulation above the crownboard, under the roof (which may also be insulated)

Fondant block under inverted perspex crownboard – insulation block to be added on top is standing at the side

Oh yes … before I forget … completely ignore any advice you might read on using matchsticks to provide ventilation to the hive 11.

They think it’s all over … it is now

That’s the end of the practical beekeeping for the season 🙁

If your colonies are strong and healthy, if the mite levels are low and they have sufficient stores, there’s almost nothing to do now until March 12

Now really is a good time for a beekeeper to take a holiday.

Make a note in your diary on the date you need to remove the Apivar strips

Write up your notes, pour a large glass of Shiraz and make plans for next season 🙂


 

More gentle beekeeping

I’ve done less beekeeping this year than any time in the past decade. The Covid-19 lockdown enforced changes to the way we live and work, meaning my contact with the bees has been ‘big and infrequent’ rather than ‘little and often’. 

‘Big and infrequent’ meaning a day or three of intense activity every month or so. I’ll write about this once the season is over as it has meant that the season has, in many ways, been very unrewarding … 🙁

… but nevertheless quite successful 🙂

23,000 iced buns

With the season winding to a close, now is the time to remove the supers of summer honey and prepare to feed the colonies for winter. 

Which means a couple of days of very heavy lifting.

I buy fondant in bulk as it stores well until it is needed. This year ‘bulk’ meant over 400 kg which, based upon this recipe, is enough for over 23,000 iced ‘finger’ buns 1. That’s too much to fit in my car (fondant or finger buns 😉 ), so entailed two trips and manhandling the boxes twice – from the pallet to the car and from the car to the shed.

Load 1 of 2 … there’s more in the passenger footwell!

During all that lifting and carrying I focus on the thought that fondant has a lower water content than syrup (~78% sugar vs ~60% for syrup) so I need to feed less weight to get the same amount of sugar into the hive.

And there’s no preparation needed or fancy (expensive) feeders to store for the rest of the year. 

As convenience foods go, it’s very convenient.

But after a dozen or two blocks, also very heavy 🙁

Beekeeper’s back

There’s a bittersweet irony to the honey harvest.

The more backbreakingly exhausting it is, the better it is. 

Not so much there’s no gain without pain” as “the more pain, the more gain”.

I have two main apiaries about 15 miles apart in Fife. I checked the hives in the first apiary and was disappointed to find the supers were mostly empty. This is a site which usually has good summer forage. The OSR had yielded well in the spring, but the colonies had then all had pre-emptive splits for swarm control, before being united back prior to the main flow.

Which appears not to have happened 🙁

I put clearers on the hives and returned the following day to collect a pathetically small number of full supers. There were some uncapped and part-filled frames, some of which contained fresh nectar 2 which I pooled together in the smallest number of supers possible.

I placed these above the floor but underneath the brood boxes.

This is termed nadiring, which isn’t actually a real word according to the OED. Nadir means the lowest point, but in the 17th Century (now obsolete and probably only used by beekeepers) nadir meant a point directly beneath an object.

The hope and expectation here is that the bees will find the stores beneath the cluster and move it up into the brood box, prior to me treating and feeding them up for winter.

Quick fix clearer board – hive side

On the same day I placed clearers underneath the (much heavier) supers in my second apiary. Actually, under about half the hives as I don’t have enough clearers for all the hives at once, even with a few Correx and gaffer tape bodged efforts to supplement them (shown above).

Clearing supers

I’ve discussed these clearers previously. With no moving parts and a deep rim on the underside the bees move down quickly. It’s not unusual to find the full 5cm depth full of bees the following morning.

Lots of bees

These bees have to be gently shaken back into the hive before replacing the crownboard and roof. This is easy on a calm, warm day with placid bees, but can be a little traumatic for everyone concerned if those three key ingredients are missing.

More lifting 🙁

Filled supers usually weigh between 37 and 50 lb (17-23 kg) each 3. Therefore, moving a dozen from the hives to the car and the car to the honey warming cabinet involves manually lifting about half a metric tonne. 

And that doesn’t include shaking off the few remaining bees which remain on individual frames. It’s not only my back that aches after this, but my fingers as well. Beekeeping, not such a gentle art as some might think.

I’ve previously noticed that more bees tend to remain in the supers if the colony is queenless.

This year the only queenless colony I found was also honeyless 🙁 

There was no need for the bees to remain in the supers … and no real evidence they’d been there in the first place.

This colony had a late queen mating fail (or perhaps lost on a mating flight) so I’ll unite it with a strong colony at the same time as I feed them and treat them for mites.

There’s obviously no point in feeding and treating before uniting or I’d jeopardise the reputation some beekeepers (including me 😉 ) have for being incredibly mean financially astute.

Lugless …

While shaking bees off one frame a lug broke. It’s a lovely frame of capped lime honey. Not close to show quality but pretty respectable all the same. I could scrape it back to the mid-rib and filter the honey or cobble together some sort of nail in place of the lug so I could spin it in the extractor. Instead I’m going to give it to friends who love honey direct from the comb … I’ll let them work out how to hang or stand it at the breakfast table.

The recovered supers were stacked on my honey warming cabinet set to 40°C. By the time heat losses are taken into account this maintains the supers at about 35°C, making the honey much easier to extract.

I usually rotate the stacks top to bottom and bottom to top a day before extracting. More lifting 🙁

Back in the apiary, the freed up clearers were placed under the supers on the remaining hives for collection the following day.

Storm Francis

Storm Francis only really arrived on the east coast of Scotland on Tuesday. It was windy and wet, but nothing like the pounding west Wales received. 

However, on early Tuesday morning when I arrived at the apiary it was wet.

Very wet.

There are few more demoralising sights than an apiary in really grey, wet and miserable conditions.

It was wetter and more miserable than this photo suggests …

There’s work to do and hives to open. Every single bee is ‘at home’. You know you’re going to get wet. It’s too blustery to use an umbrella and, anyhow, social distancing means there’s no-on there to hold one. 

Cold, clammy and heavy … a wet bee suit

The one saving grace is that the bees were incredibly calm.

I’d like to think they’ve been selectively bred over the years to be placid and well behaved, and that my skills as a beekeeper have been honed to the point where they barely know I’m there.

Hogwash.

It was so wet that they caused as little trouble as possible so that I got the roof back on the hive with the minimal delay 😉

Stings

Joking aside, these bees are calm and well behaved. Despite the flow being effectively over they haven’t become defensive. The majority of the colonies are very strong and they’re not being troubled by wasps, though these are searching out spilt honey and stores wherever possible. 

Our colonies in the bee shed are used for research and used to provide larvae and pupae for experiments. Members of my research team harvest brood when needed and, because they aren’t hugely experienced beekeepers, it’s important that the bees are not stroppy.

During the week I commented to a friend that I didn’t think I’ve been stung all season.

There may have been one of those glancing blows to a nitrile glove, but nothing that actually caused any pain or inconvenience.

Partly this is because I’ve done less beekeeping, but it also reflects repeated replacement of queens from stroppy colonies with selected calmer bees over past seasons. 

Aggressive bees do not collect more nectar. They are a menace to non-beekeepers and thoroughly unpleasant to work with. Fortunately, aggression is a relatively easy trait to select against and you can quickly see an improvement in colonies over just a couple of seasons.

Of course, I spoke too soon …

I lifted the lid on a stack of boxes containing old brood frames for melting down. To my complete surprise and considerable pain, I was greeted by a frenzied blitzkrieg of angry wasps.

Bang, bang, bang, bang, bang … BANG!

Five stings in less time than it takes to say it.

The final BANG was self inflicted as I hit the side of my head to try and squish a wasp before it burrowed into my ear and stung me.

Partial success … I crushed the wasp, but only after it had stung me on the cartilaginous pinna of my ear 🙁

I don’t know which hurt more … the sting or the blow to the side of my head.

These days I no longer bother setting wasp traps in my apiaries, instead relying on strong colonies (and reduced entrances or kewl floors) for defence. However, I’ve discovered that a strong washing up detergent spray is a good deterrent if wasps are getting into stacks of stored boxes. Spray the stripy blighters, stand back and let it do its work before blocking access with whatever you have to hand 4.

More bittersweet season endings

After about four days of intense beekeeping I’d removed all the supers, extracted the honey, collected the fondant, fed and treated all the colonies.

I’ll deal with feeding and treating next week (if I remember) but now need to rest my weary back and fingers … over the week I estimate I’ve lifted a cumulative total of 1200 kg of fondant and at least the same amount again of supers. 

The hives are now busy chucking out drones so they have fewer mouths to feed over the winter.

It’s a tough life being a drone in late August … but not for much longer

But to end on a more uplifting note, the honey crop was pretty good this summer 🙂


 

Orientation flights

Part of the reason for the success of honey bees is the division of labour between workers of different ages. Young workers (hive bees) clean the cells, nurse larvae and look after the queen. Older workers are foragers, collecting pollen and nectar (and water) from across the landscape.

To be successful, foragers need to know where to look and how to return.

The ‘where to look’ is partly accounted for by the well-known waggle dance 1.

In this post I’m going to discuss the second component of successful foraging – the homing ability of foragers.

More specifically, I’m going to discuss how the bee first learns about the location of the hive. 

Orientation flights

Bees do not instinctively know where the hive (or the tree they are nesting in for a wild colony) is located. They have to learn this before embarking on foraging trips to collect nectar or pollen.

This learning takes the form of one (or usually several – as we shall see) orientation flights. These enable the bee to memorise the precise location of the hive with relation to geographic landmarks. On subsequent foraging flights the bees use these landmarks to return to the hive.

Orientation flight have a characteristic appearance …

… and are very nicely described in the introduction to a paper by Capaldi and Dyer 2:

An orientation flight at the nest entrance begins as a departing bee turns and hovers back and forth, turning in short arcs, apparently looking at the hive entrance. Then, the bee increases the size of the arcs until, after a few seconds, she flies in circles while ascending to heights of 5–10 metres above the ground. This spiraling flight takes the bee out of sight of human observers. She returns a few minutes later, always without nectar or pollen.

Which I couldn’t have written any better, so have reproduced verbatim.

There are a number of features of the orientation flight that are immediately obvious from this description (which all beekeepers will recognize). These include:

  • A ‘local’ component, in the immediate vicinity of the hive
  • Wider ranging flight at a greater altitude and a longer distance
  • Direct observation does not allow the location, duration or track of these distant flights to be monitored
  • The bee returning from the orientation flight does not bring pollen or nectar with her

Do orientation flights allow orientation?

How do we know that these flights enable the bee to learn where the hive is located?

Early studies conducted by Becker (1958) showed that bees captured after a single orientation flight and then re-released up to 700 metres away from the hive could find their way ‘home’. In contrast, bees that had not gone on an orientation flight before were, by definition, disoriented and did not return to the hive.

However, the percentage that returned after undertaking a single orientation flight was related to the distance of the release point, and was never more than ~60% (at 200 metres). 

In contrast, reorienting older foragers (for example, as happens after moving a hive to a new location) were much better (~90%) at returning to the hive after a single reorientation flight. 

Capaldi and Dyer extended these early studies by Becker to investigate the impact of the visibility of local landmarks on orientation and reorientation, and also measured the speed with which bees returned after being displaced.

Landmarks

These studies showed that a single orientation flight allowed bees to identify the landmarks in the immediate vicinity (100 – 200 m) of the hive. When released from more distant locations, returning flights were faster and more successful (i.e. fewer lost bees) when the bees had sight of the landmarks in the vicinity of the hive.

The hive itself was effectively invisible except at very short ranges. This makes sense for a tree-nesting animal. One tree looks much the same as another 3, but if you learn that the nest is in the tree between the very tall conifer and the long straight hedgerow – two features visible from hundreds of metres distant – then orientation is straightforward.

This suggests that apiaries located near distinctive landscape features may be preferable in terms of increased returning forager rates.

“Distinctive” as far as an orienting worker bee is concerned, which may not be the same as distinctive to the beekeeper of course 😉

Reorienting bees (compared to first flight bees) took longer to explore the environment and were better at returning. Either these bees learn differently (a distinct possibility) or their prior experience in the wider landscape gives them an advantage when the hive is relocated.

Where do you go to my lovely?

The early studies by Becker and those by Dyer and colleagues defined many of the parameters that characterise orientation flights. What they did not do is show where the bees actually go during the orientation flights?

Do they just zoom around randomly?

Do they fly ever-increasing spirals?

Perhaps they perform some sort of grid search, exploring individual landscape features carefully for future reference?

Recent developments with harmonic radar have allowed tracking of individual bees during orientation flights over hundreds of metres. These have provided further insights into the process.

Because harmonic radar is also relevant to other studies of honey bee flight – for example, the impact of neonicotinoids on foraging ability – I’ll digress slightly from orientation flights to describe the technology.

Harmonic radar

Harmonic radar has revolutionised tracking studies of insects in much the same way as GPS tags have provided unique insights into bird migration (or, for that matter, shark migration).

The radar system has two components. The insect is tagged with a tiny antenna attached to a Schottky diode (together termed the transponder). The transmitter/detector is a ground-based scanner that transmits the radar signal. This is used as the energy source by the diode which re-emits a harmonic of the original signal which can then be detected.

Tagged bumble bee (left) and harmonic radar detector (right)

The transponder weighs less than a normal pollen load, though presumably there is some wind resistance from the antenna. In studies of bees with and without transponders fitted the orientation flights were of a similar duration, suggesting any wind resistance didn’t appreciably impact the flying ability of the bee.

Orientation (a-c) and foraging (d) flights monitored by harmonic radar.

 

Orientation flights 4 were taken by bees between 3 and 14 days post-emergence, with the mean onset of foraging being 14 days post-emergence.

Bees took between 1 and 18 orientation flights, though there wasn’t a direct relationship between the number of flights and the age of the bee, suggesting they may learn at different rates.

Initial orientation flights were generally in the immediate vicinity of the hive. Older workers – pre-foraging – ventured further afield. More recent studies have addressed this in greater detail (see below).

Orientation flights were distinctly different from foraging flights. The former were slower and less direct. The ground speed of orienting bees was ~3.6 m/s in contrast to foragers who flew at ~5.6 m/s and, as shown in D above, foraging flights were very much ‘there and back’ straight lines.

Venturing forth …

A more recent study 5 has used harmonic radar to investigate multiple orientation flights by individual bees, effectively analysing how the bee explores the landscape as it ages towards a forager.

This was a remarkable study. It involved addition and subsequent removal of the transponder from 115 individual bees during 184 orientation flights. When the orienting bee returned they recaptured it, removed the transponder and allowed it to reenter the hive. When it reappeared for another orientation flight they reattached the transponder.

Anyone complaining about their inability to mark queens 6 should do this as a training exercise 😉

The scientists also recorded several foraging flights of a smaller number of the same bees, to allow comparison with their behaviour during orientation flights.

Orientation and foraging flights of five individual bees.

Flights were defined as short or long range, but long range orientation flights were still significantly shorter than foraging flights.

  • Short range flights were made in poor weather and familiarised the bees with the immediate vicinity of the hive.
  • Consecutive long range flights reduced in duration as the bees learnt about the immediate hive vicinity i.e. the long range flights included some local exploring at first as well.
  • Orientation flights explored different areas of the landscape, rather than focusing on one sector.
  • Subsequent foraging flights involved areas that the bees may have never visited during orientation flights.
  • Some very long duration foraging flights may involve a degree of exploration, though it’s not clear whether this is truly orientation, or actual scouting activity.

Not all bees performed short and long range flights though early long range lights did involve local exploration as well. 

Ground clues and conclusions

The final part of this study investigated the influence of visual landscape features on orientation flights. This deserves a post in its own right as the techniques are quite involved.

Essentially they generated heat maps of the flights overlaid onto the geography. Using this approach they determined that some features visible from the air e.g. borders between grassland and a track, influenced the direction of flight and hence the orientation flights. 

There are additional studies of the influence of visible landmarks on bee flight which I’ll return to at some point in the future.

Again, like the comment made above about visible landmarks, it suggests to me that apiaries situated near such distinctive features may aid orientation and subsequent homing flights by honey bees.

When you next stand by your hive entrance on a warm, sunny afternoon and watch young workers flying to and fro across the entrance before spiralling up and away out of sight, you’ll know that it is an essential component of their training to be effective foragers.

They don’t forage for long – perhaps three weeks at most – but they are very effective, partly because they know where to return to.


Notes

Where do you go to my lovely? was the title of a rather syrupy (my blog, my opinion! … Apologies if it’s a favourite of yours 😉 ) song by Peter Sarstedt in 1969. It’s notable for some quite clever rhyming lyrics and a particularly dodgy mustache he sports in the YouTube video. (I’m just linking it, rather than embedding just because of the mustache).

It has nothing to do with bees.

 

The gentle art of beekeeping

High summer.

The swarm season had been and gone. The June gap was over. Grafts made at the peak of the swarm season had developed into lovely big fat queen cells and been distributed around nucleus colonies for mating.

That was almost six weeks ago.

From eclosion to laying takes a minimum of about 8 days. The weather had been almost perfect for queen mating, so I was hopeful they’d got out promptly, done ‘the business’, and returned to start laying.

That would have been about a month ago.

Good queens

I’d spent a long morning in the apiary checking the nucs and the colonies they were destined for. In the former I was looking for evidence that the queen was mated and laying well. That meant looking for nice even frames of sealed worker brood, with some – the first day or two of often patchy egg laying – now emerging.

Brood frame with a good laying pattern

It was warming up. More significantly, it was getting distinctly close and muggy. I knew that thunderstorms were predicted late in the afternoon, but by late morning it already had that oppressive ‘heavy’ feel to the air. Almost as though there wasn’t quite enough oxygen in it.

Never mind the weather, the queens were looking good. 90% of them were mated and laying well.

Just one no-show. She’d emerged from the cell, but there was no sign of her in the nuc, and precious few bees left either.

Queenless nucs often haemorrhage workers to nearby queenright colonies (or nucs), leaving a pathetic remainder that may develop laying workers. There’s no point in trying to save a colony like that.

Actually, it’s not even a colony … it’s a box with a few hundred abandoned and rapidly ageing workers. Adding resources to it – a new queen or a frame of eggs and young larvae – is almost certainly a waste of resources. They’d better serve the colonies they were already in. The remaining workers were probably over a month old and only had another week or two before they would be lost, ‘missing in action’, and fail to return from a foraging flight.

If you keep livestock, you’ll have dead stock.

These weren’t dead stock, but they were on their last legs, er, wings. I shook the workers out in front of a row of strong colonies and removed the nuc box so there was nowhere for them to return. The workers wouldn’t help the other colonies much, but it was a better fate than simply allowing them to dwindle.

Spare queens

Most of the nucs were going to be used to requeen production colonies. A couple had been promised to beginners and would be ready in another week or so.

Midseason is a good time to get a nuc to start beekeeping. The weather – the predicted (and seemingly increasingly imminent) afternoon thunder notwithstanding – is more dependable, and much warmer. The inevitably protracted inspections by a tyro won’t chill the brood and nucs are almost always better tempered than full colonies. In addition, the new beekeeper has the pleasure of watching the nuc build up to a full colony and preparing it for winter. This is a valuable learning experience.

Late season bramble

Late season bramble

It’s too late to get a honey crop from these midseason nucs (usually, there may be exceptional years) but that’s probably also good training for the new beekeeper. An understanding that beekeeping requires a degree of patience may be a tough lesson to learn but it’s an easier one than discovering that an overcrowded nuc purchased in April, swarms in May, gets really ratty in June and needs a new queen at the beginning of July.

But, after uniting the nucs to requeen the production hives it turned out that I had one queen spare.

Which was fortunate as I’d been asked by a friend for an old leftover queen to help them improve the behaviour of their only colony. Rather than give them one of the ageing queens she could have the spare one from this year.

A queen has a remarkable influence over the behaviour and performance of the colony. Good quality queens head calm, strong colonies that are a pleasure to work with. But it’s not all good genes. You can sometimes detect the influence of a good new queen in a poor colony well before any of the brood she has laid emerges. I assume this is due to pheromones (and with bees, if it’s not genetics or pheromones I’m not sure what else could explain it – ley lines, phase of the moon, 5G masts nearby?).

Go west, young(er) man

My friend lived about 45 minutes away. I found the queen in the nuc, popped her into a marking cage and placed her safely in light shade at the back of the apiary while I rearranged the nuc for uniting over a strong queenright colony.

Handheld queen marking cage

Handheld queen marking cage

A few minutes later I’d recovered the queen, clipped her and marked her with a white Posca pen. I alternate blue and white (and sometimes yellow if neither of those work or can be found) and rely on my notes to remind me of her age should I need to know it. I’m colourblind and cannot see – or at least distinguish – red and green, either from each other or from lots of other colours in the hive.

I transferred the marked queen into a JzBz queen cage and capped the exit tube. Of all the huge variety of queen introduction cages that are available these are my favourite. They’re also the only ones I was given a bucket of … something that had a big part to play in influencing my choice 🙂

JzBz queen cages

JzBz queen cages

I put the caged queen in the breast pocket of my beesuit, extinguished the smoker and tidied up the apiary. It was warm, dark and humid in the pocket – for an hour or so she would be fine.

Actually, it was getting increasingly humid and the heaviness in the air was, if anything, getting more oppressive.

What I’d really like now would be a couple of large mugs of tea … I’d inspected a dozen large colonies and nearly the same number of nucs. The colonies that needed requeening had been united with the nucs (having found and removed the ageing queens) and I’d neatly stacked up all the empty nuc boxes in the shed. Finally, I’d retuned all the supers, some reassuringly heavy, and left everything ready for the next inspection in a fortnight or so 1.

That’s a lot of lifting, carrying, bending, squinting, prising, turning, rearranging and then gently replacing the crownboard and the roof.

Not really hard work, but enough.

Actually, quite enough … I’d really like that cuppa.

Was that thunder? Way off to the west … a sound so faint I might have imagined it. There were towering cumulus clouds building along the horizon.

Cloud

Threatening

Time to get a move on.

With the car packed I lock the apiary gate and set off.

West.

Leaving the flat agricultural land I climbed gently into low rolling hills. The land became more wooded, restricting my view of the thunderheads building, now strongly, in the direction I was heading. The sun was now intermittently hidden between the wispy clouds ahead of the storm front.

Could you do me a favour?

The bad weather was still a long way off. I’d have ample time to drop the queen off, slurp down a cuppa and be back home before any rain arrived. If my friend was sensible she’d just leave the new queen hanging in her cage in a super. The workers would feed her until the weather was a little more conducive to opening the hive and finding the old queen.

I pull into the driveway and my friend comes out to meet me. We share beekeeping chat about the weather, forage, the now-passed swarm season, the possibility of getting a nuc for next season 2.

“Could you perhaps requeen the colony? I’m really bad at finding the queen and they’ve been a bit bolshy 3 recently. I’ll put the kettle on while you’re doing it.”

I did a quick mental calculation … weighing up the positives (kettle on) and the negatives (bolshy, the distant – but approaching – thunder) and was surprised to find that my yearning for a cuppa tipped the balance enough for me to agree to do it.

I returned to the car for my smoker and some queen candy which I used to plug the neck of the JzBz cage. At the same time I also found a small piece of wire to hang the cage between the frames from.

“They’re in the back garden on the bench by the gate to the orchard.”

I look through the kitchen window across the unkempt lawn (was the mower broken?). Sure enough, there was a double brooded National hive topped with two supers on a garden bench about 30 metres away.

“I’ll stay here if you don’t mind … they gave me a bit of a fright when I last checked them.”

Sure. No problem. I’ve done this a hundred times. White, no sugar and, yes, I’d love a cookie as well.

Be properly prepared

I stepped into the back garden and fired up the smoker. It was still warm from being used for my own bees and the mix of cardboard, woodshavings and dried grass quickly started smouldering nicely. A couple of bees had come to investigate but had just done a few laps of my head and disappeared.

But they returned as I walked across the lawn.

And they brought reinforcements.

By the time I was half way across the lawn I’d been pinged a couple of times. Not stung, but the sort of glancing blow that shows intent.

A shot across the bows, if you like.

I didn’t like.

I pulled the veil over my head and zipped it up quickly, before rummaging through my pockets to find a pair of gloves. Mismatched gloved. A yellow Marigold for my left hand and a thin long-cuff blue nitrile for my right. It’s an odd look 4 but an effective combination. The Marigold is easy to get on and off, and provides ample protection.

Nitriles ...

Nitriles …

The nitrile is a bit of a nightmare to get on when it’s still damp inside. Another couple of bees dive bomb my veil, one clinging on and making that higher pitched whining sound they make when they’re trying to get through. I brushed her off with the Marigold, turned the nitrile inside out, blew into it to inflate the fingers, and finally got it on.

Why two different gloves? Two reasons. I’d lost the other Marigold and because nitriles are thin enough to easily pick a queen up with, and that’s what I’d been doing most of the morning.

And hoped to do again shortly when I found the old queen in the agitated colony.

Opening hostilities

I approached the hive. It was a strong colony. Very strong. It was tipped back slightly on the bench and didn’t look all that stable 5. I gave them a couple of puffs of smoke at the entrance and prised the supers up and off, placing them propped against the leg of the bench.

I was faintly aware of the smell of bananas and the, still distant, sound of thunder. It probably wasn’t getting any closer, but it certainly wasn’t disappearing either.

The thunder that is.

The smell of bananas was new … it’s the alarm pheromone.

Actually, it’s one of the alarm pheromones. Importantly, it’s the one released from the Koschevnikov gland at the base of the sting. This meant that one or two bees had already pressed home a full attack and stung me. Felt nowt. Presumably they’d hit a fold in the beesuit or the cuff of the Marigold.

Or my adrenaline levels were sufficiently elevated to suppress my pain response.

I was increasingly aware of the number of really unpleasant bees that were in the hive.

And, more to the point, coming out of the hive.

But I was most aware that I was only wearing a single thickness beesuit in the presence of 50,000 sociopaths with a thunderstorm approaching. Under the suit I had a thin short sleeved shirt and a pair of shorts.

It might be raining in half an hour … this could get ugly.

It was late July, it was a hot day, my bees are calm. I wasn’t dressed appropriately for these psychos.

I felt I needed chain mail … and an umbrella.

Time for a rethink

I gave the hive a couple of larger puffs from the smoker and retreated back to the car, ducking under and through – twice – some dense overhanging shrubs to deter and deflect the bees attempting to hasten my retreat.

Ideally I’d have put a fleece on under the beesuit. That makes you more or less impervious to stings.

Did I mention it was a warm day in July? No fleece 🙁

However, I did have a beekeeping jacket in the car. This is what I wear for most of my beekeeping (unless I’m wearing shorts). I removed the jacket hood and put it on over the beesuit, remembering to transfer the queen to the outer jacket pocket. I also found another nitrile glove and put it on to be double gloved.

“The queen’s not marked”, my friend shouted to me as I walked back across the garden, “Sorry!”

Now you tell me …

I See You Baby

I See You Baby

I returned to the hive. To reduce the immediate concentration of bees, I split the two brood boxes off the floor, placing each several metres away on separate garden chairs. I balanced the supers on the original floor to allow returning foragers and the increasing maelstrom of flying bees to have somewhere to return if needed.

And then I found the unmarked queen.

As simple as that.

Amazingly, it was on the first pass through the second brood box.

Each box was dealt with in the same way. I gently split the propolis sealing the frames together – first down one side of the box, then the other. I removed the outer frame, inspected it carefully and placed it on the ground leaning against the chair leg. With space to work I then methodically went through every frame, calmly but quickly.

I didn’t expect to find her so easily. I wasn’t sure I’d be able to find her at all.

It helped that she was huge and pale. It helped that she was calmly ambling around on the frame, clearly confident in the knowledge that there were 50,000 acolytes willing to lay down their lives to protect her.

Her confidence was misplaced 🙁

Veiled threat

And then a bee got inside the veil.

This happens now and then. I suspect they sneak through the gap where the zips meet at the front or the back. There are little Velcro patches to hold everything together, but it was an old suit 6 and the Velcro was a bit worn.

There are few things more disconcerting that 50,000 psychos encouraging a Ninja worker that’s managed to break through your defences and is just in your peripheral vision. Or worse, in your hair. With a calm colony you can retreat and deal with the interloper. You have to take the veil off. Sometimes you have to take the suit off.

Removing the veil would have been unwise. Perhaps suicidal. I retreated a few yards and dealt with the bee. It was never going to end well for one of us 🙁

Reassemble in the reverse order

Returning to the original bench, I removed the supers that were now festooned with thousands of bees, balancing them against the leg again. I found a pencil-thick twig and used it under one corner of the floor to stop everything wobbling. Both brood boxes were returned, trying to avoid crushing too many bees at the interface. A combination of a well aimed puff or two of smoke, brushing the bees away with the back of my hand and placing the box down at an angle and then rotating it into position reduced what can otherwise cause carnage.

I hung the new queen in her cage between the top bars of the central frames in the upper box, returned the queen excluder and the supers and closed the hive up.

It took 15 minutes to avoid and evade the followers before I could remove the beesuit safely. I’d been stung several times but none had penetrated more than the suit.

I finally got my cup of tea.

Confidence

This was several years ago. I took a few risks towards the end with the queen introduction but got away with it. The colony released the queen, accepted her and a month or so later were calm and well behaved.

I was lucky to find the queen so quickly in such a strong colony. I didn’t have to resort to some of the tricks sometimes needed to find elusive queens.

Ideally I’d have left the queen cage sealed to see if they were aggressive to her, only removing the cap once I was sure they’d accept her. This can take a day or two, but you need to check them.

There was no way I was going back into the hive and my friend definitely wasn’t.

The rain and thunder never arrived … like many summer storms it was all bluster but eventually dissipated as the day cooled.

This was the worst colony I’ve ever handled as a beekeeper. At least for out and out, close quarter, bare knuckle aggression. By any measure I’d have said they were unusable for beekeeping. I’ve had colonies with followers chase me 300 metres up the meadow, though the hive itself wasn’t too hot 7. This colony was an order of magnitude worse, though the followers were less persistent.

I suspect that aggression (or, more correctly, defensiveness) and following have different genetic determinants in honey bees.

Lessons

  • Knowing when to retreat is important. Smoking them gently before I returned to the car for a jacket helped mask the alarm pheromone in the hive and gave me both time to think and renewed confidence that I was now better protected.
  • Confidence is very important when dealing with an unpleasant hive. It allows you to be unhurried and gentle, when your instincts are screaming ‘get a move on, they’re going postal’.
  • Confidence comes with experience and with belief in the protective clothing you use. It doesn’t need to be stingproof, but it does need to protect the soft bits (my forearms, ankles and face react very badly when stung).
  • Indeed, it might be better if it’s not completely stingproof. It’s important to be aware of the reactions of the colony, which is why I prefer nitrile gloves to Marigolds, and why I never use gauntlets.
  • Many colonies are defensive in poor weather or with approaching thunderstorms. If I’d known just how defensive this colony were I’d have planned the day differently.
  • The unstable ‘hive stand’ would have agitated the bees in windy weather or during inspections.

Bad bees

It turned out the colony had been purchased, sight unseen, as a nuc the year before. By the end of the season it had become unmanageable. The supers had been on since the previous summer and the colony hadn’t been treated for mites.

They appeared healthy, but their behaviour was negatively influencing their management (and the upkeep of the garden). Beekeeping isn’t fun if you’re frightened of the bees. You find excuses to not open the hive, or not mow the lawn.

The story ended well. The new queen settled well and the bees became a pleasure to work with. My friend regained her confidence and is happy to requeen her own colonies now.

She has even started using proper hive stands rather than the garden bench … which you can now use for relaxing on with a mug of tea and a cookie.

While watching the bees 🙂


 

A virus that changes bee behaviour

Particle physicists might not agree, but I think that evolution is the most powerful force in the universe. It is responsible for the fabulous diversity of life, for everything from the 6,000,000 kg Pando clonal colony of quaking aspen covering 43 hectares of the Fishlake National Forest in Utah, to the teeniest of tiniest of viruses.

As a microbiologist I’m acutely aware of the role evolution has played in the genetic arms race between hosts and pathogens. This is what is responsible for the multi-faceted immune system higher organisms carry – the antibodies, the lymphocytes, the complement and interferon responses, and everything else.

In turn, the fast replicating bacteria and viruses have evolved countermeasures to subvert these immune mechanisms, to switch them off entirely or to decoy them into targeting the wrong thing. This ‘arms race’ has gone on since well before the evolution of multicellular organisms (~600 million years ago) … and continues unabated.

Evolution is powerful for one simple reason; if a particular genetic combination 1 ‘works’ it will be passed on to the progeny. If a virus evolves a way to resist the immune response of the host, or to spread between hosts more efficiently, then the trait will be inherited.

Molecular mechanisms and behavioural changes

Some of changes work at the molecular level, invisible without exquisitely sensitive in vitro analysis; protein A binds to protein B and, in doing so, stops protein B from doing whatever it should have be doing. These are important but often very subtle.

Rabies: Slaying a mad dog, 1566 illustration from Wellcome Images

Other changes are far more obvious. Take rabies for example (or don’t, it’s not recommended as it has a near-100% case fatality rate) … the primary host of the rabies virus are carnivorous mammals. Infection causes gross behavioural changes that facilitate virus transmission. The animal becomes bolder and much more aggressive, resulting in virus transmission through biting.

Recent studies have elegantly demonstrated that this (also) is an example of protein A binding to protein B at the molecular level, it’s just that the phenotype 2 is very much more marked.

A protein on the surface of the virus resembles a snake venom toxin and has the ability to bind to nicotinic acetylcholine receptors present in the central nervous system of the mammalian host. These receptors ‘do what they say on the tin’ and bind the neurotransmitter acetylcholine. If the virus protein binds the receptor the response to acetylcholine is blunted and this, in turn, leads to hyperactivity, one of the key behavioural responses caused by rabies viruses.

That’s enough about mad dogs.

If virus-induced behavioural changes are so obvious, why haven’t lots of different examples already been identified and characterised?

Sniffles

Part of the problem is the blurring of distinctions between overt behavioural changes and the direct symptoms induced due to the virus replicating.

Human rhinovirus, the aetiological agent of the common cold, causes upper respiratory tract infections. You get a runny nose and you sneeze a lot.

Gesundheit

Your behaviour changes.

However, it’s generally accepted that the sneezing and runny nose are a result of the physiological response to infection, rather than a virus-induced behavioural response to facilitate transmission.

It’s worth noting that all that “stuff” that comes out of your nose contains infectious virus, so it’s perhaps an artificial distinction between the general symptoms of sickness and evolutionarily-selected host behavioural changes caused by the virus.

Which in a roundabout way …

… allows me to finally introduce the topic of bee viruses that cause host behavioural changes involved in their transmission.

Or, rather, one bee virus that does this … though I’m certain that there will be more.

Israeli Acute Paralysis Virus (IAPV) is an RNA virus transmitted horizontally by direct contact between bees, or while feeding on developing pupae, by the parasitic mite Varroa destructor. It was implicated as a causative agent of Colony Collapse Disorder (CCD), though really compelling evidence supporting it as the primary cause never materialised.

It’s a virus UK beekeepers should be aware of, but unworried by, as it is extremely rare in the UK.

A recent paper has shown two behavioural changes in response to IAPV infection in honey bees. One of them – that facilitates horizontal transmission between colonies – is also partially explained at the molecular level.

The paper was published a couple of months ago:

Geffre et al., (2020) Honey bee virus causes context-dependent changes in host social behavior. Proc. Natl. Acad. Sci. USA 117:10406-10413. 3

I’m going to focus on the results, rather than the methods, though the methods are rather cool. They used barcoded bees to allow the automated image analysis of every bee in a colony for some of the studies where they had introduced known IAPV infected individuals.

Responses of nestmates to IAPV infected bees

Imagine watching a few hundred waggle dances and being able to recount the position, distance and response of every bee ‘watching’ 4 the dance, and then being able to summarise the results.

Over five days.

Non-stop.

Including nights (and yes, bees do still waggle dance at night – a subject for the future).

The scientists orally infected groups of 30 bees with a sub-lethal dose of IAPV, marked them and released them into an observation hive. They then recorded their movements around the hive and their interactions with other bees in the colony. In particular, they focussed on trophallaxis interactions where one bee ‘feeds’ another.

Trophallaxis is also considered to be a method of communication in the hive and has been implicated in disease transmission.

The authors love their whisker plots and statistical analysis.

Who doesn’t? 😉

However, they generally make for rather underwhelming images in a bee blog for entertaining reading. Here .. see what I mean …

Number of trophallaxis interactions per hour.

Suffice to say that the results obtained were statistically significant.

They showed that the infected bees in the colony actually moved about the colony more than their nestmates. Conversely, they were engaged in fewer trophallaxis interactions i.e. it appeared as though they were being ‘ignored’ by their nestmates.

Were they really being ignored altogether or did their nestmates approach them, detect something was amiss and move away?

Antennation

Antennation is the mechanism by which bees recognise nestmates. They use the sensitive chemoreceptors on their antenna to detect cuticular hydrocarbons (CHC) which are distinctive between bees from different hives.

Antennation is a precursor to trophallaxis.

After all, bees do not want to feed a foreigner, or exchange chemicals involved in communications, or even potentially risk being exposed to a new pathogen.

Good as the barcoding and camera system is, it’s not good enough to record antennation within the observation hive. To do this they manually 5 recorded antennation events between IAPV-infected bees and nestmates in cages in the laboratory 6.

In these studies IAPV-infected bees were engaged in the same number of antennation events as control bees. This strongly suggests that the nestmate could detect there was something ‘wrong’ with the IAPV-infected individuals. In support of this conclusion, the authors also demonstrated that bees inoculated with a double stranded RNA (dsRNA) stimulator of the honey bee immune response were also also antennated equally, but engaged in less trophallaxis interactions.

Therefore, these studies appear to show that nestmates exhibit a behavioural response to IAPV-infected bees (and bees with elevated immune responses, recapitulating their response to pathogen infection) that is likely to be protective, reducing the transmission of horizontally acquired viruses.

It’s worth noting two things here.

  1. There were no virus transmission studies conducted. It’s assumed that the lack of trophallaxis reduces virus transmission. That still needs to be demonstrated.
  2. This response is not induced by the virus on the host. It’s a response by nestmates of the host to virus infected individuals (or individuals that present as ‘sick’). As such it’s not the same as the rabies example I started this post with.

Virus-induced behavioural responses

But do the IAPV-infected bees behave differently when they come into contact with other bees who are not their nestmates?

After all, IAPV is a pathogenic virus and its continuing presence within a population (not just a single hive) depends upon it being spread from hive to hive.

For a highly pathogenic virus this is very important. If you spread from bee to bee within a hive and kill the lot you also go extinct … this partly explains the mechanism by which highly virulent viruses become less virulent over time.

But back to IAPV. What happens when IAPV-inoculated bees interact with bees from a different hive?

For example, what would happen if they drifted from one hive to another in a densely populated apiary? Drifting is a significant contributor to the spread of bees between adjacent colonies – studies show that 1% of marked bees drift to adjacent hives over a 3 day window. This partially accounts for the genetic mix of workers (up to 40% are unrelated to the queen that heads the colony) in a hive, a fact generally unappreciated by beekeepers.

The authors first showed that IAPV-infected bees could apparently leave and return to the hive with a similar frequency as uninfected foragers. Their flying was not compromised.

They then resorted again to recording interactions in the laboratory between IAPV-infected bees or control dsRNA-inoculated bees and workers from a different hive.

This was where it gets particularly interesting.

Hello stranger

The dsRNA-immunostimulated bees (remember, these induce a generalised immune response characteristic of a ‘sick’ bee) were treated aggressively by unmatched workers from a different hive.

In contrast, the IAPV-infected bees (which were ‘sick’ and would have been undergoing immunestimulation caused by the IAPV infection) experienced significantly less aggression than both uninoculated workers (which induced an intermediate response) and the dsRNA-inoculated.

This strongly suggests that IAPV is somehow able to modulate the appearance or behaviour (and one often determines the other) of the host to make it more acceptable to an unmatched worker.

They extended this study to conduct “field-based assays at the entrances of three normally managed honey bee colonies”, monitoring whether IAPV-infected bees were more likely to be accepted by the guard bees at the entrance of the hive.

They were. The IAPV-infected bees received a less aggressive reception and/or entered the hives much more easily than the controls.

But what about proteins A and B?

Good question.

The behavioural alterations described above must be explainable in terms of the molecular changes that IAPV induces in the bees. By that I mean that the virus must make, or induce the making of, a chemical or protein or other molecule, the presence of which explains their acceptance by the foreign guard bees.

And the obvious candidates are the cuticular hydrocarbons (CHC) that are recognized during antennation, which I introduced earlier.

And here the story leaves us with some tantalising clues, but no definitive answer.

The scientists demonstrate that there were marked differences between the CHC profile of IAPV-infected and control bees. Again, they used their favoured whisker plots to show this, but collated all of the CHC data into an even more difficult to explain scatter plot of linear discriminant analysis.

CHC profiles (relative abundance) shown using linear discriminant analysis.

The key take home message here is that for each of the CHC’s analysed there were differences in both the quality and relative abundance between the control bees, bees immunestimulated with dsRNA and the IAPV-infected bees.

These differences were so marked that you can see distinct clustering of points in the analysis above … these bees ‘look’ 7 different to the guard bees that antennate them.

This is a great story.

It’s as yet incomplete. To complete the understanding we will need to know which of those CHC’s, or which combination, when suppressed (or overrepresented) induce the guard bees to say “Welcome, step this way … “.

We’ll then of course need to find out how IAPV induces the change in CHC profile, which takes us right back to protein A and protein B again.

Ever the pedant

Much as I like this science I’d perhap argue that, again, the virus isn’t directly inducing a behavioural change in the host.

What it’s doing is inducing a behavioural change in the response to the infected host (by the guard bee). So perhaps this again isn’t quite the same as the rabies example we kicked off with.

A behavioural change in the host might include IAPV-infected bees drifting more, or drifting further. Alternatively, perhaps a colony with widespread IAPV infection could more easily indulge in robbing neighbouring colonies as they would experience less aggression from guard bees.

Smaller is better ...

Reduced entrance to prevent robbing …

I can see immediate evolutionary benefits to a virus that induced these types of behavioural changes. It’s not an original idea … the late Ingemar Fries suggested it in a paper two decades ago 8.

I’m also certain that researchers are looking for evidence supporting these types of directly-induced behavioural changes caused by viral pathogens in honey bees.

All religion, my friend, is simply evolved out of fraud, fear, greed, imagination, and poetry

Edgar Allen Poe may or may not have said this.

However, while we’re on the thorny subject of pathogen-induced behavioural changes in the host, it might be worth mentioning a couple of more controversial areas in which it has been proposed.

In the snappily titled paper “Assortative sociality, limited dispersal, infectious disease and the genesis of the global pattern of religion diversity” Fincher and Thornhill argue 9 that the wide diversity of religions in the tropics (compared to temperate regions) is driven by infectious disease selecting for three anti-contagion behaviours; in-group assortative sociality; out-group avoidance; and limited dispersal. It’s an interesting idea and I’m pleased I don’t have to test it experimentally. Their argument is that these three behavioural changes select for fractionation, isolation and diversification of the original culture … and hence the evolution of religions.

Conversely, perhaps microorganisms induce religious behaviours (rather than religion per se) that facilitate their transmission. This is exemplified in the entertainingly titled paper “Midichlorians – the biomeme hypothesis: is there a microbial component to religious rituals?” by Panchin et al., (2014). They argue that microbes – and they are really thinking about the gut microbiota here – might be able to influence their hosts (humans) to gather for religious rituals at which both ideas (memes) and infections are more easily transmitted.

Perhaps something to think about when mindlessly spinning out all that summer honey in the next few weeks?

Party, party

I think it’s fair to say that both the papers in the section above have some way to go until they achieve mainstream acceptance … if they ever do.

Furthermore, the general area in which parasites, bacteria and viruses, induce changes in the behaviour of their hosts’ is really in its infancy. We are aware of a lot of behavioural changes, but few are understood at the molecular level 10. As such, we often don’t know whether the association is correlative or causative.

Evolution is certainly a powerful enough selective force to ensure that even extremely subtle benefits to the pathogen may become a genetically-fixed feature of the complex interaction it has with the host.

Respiratory viruses, such as the common cold, Covid-19 and influenza infect millions of people globally and are readily transmitted by direct or indirect contact.

That’s why most of the readers of this post have a face mask nearby and a bottle of hand sanitizer ‘at the ready’. Or should.

Direct transmission benefits the virus as it does not have to survive on a door handle, milk bottle or petrol filling pump.

But direct transmission requires that people meet and are in close contact.

And a paper 10 years ago demonstrated that infection with influenza virus resulted in increased social interactions in the 48 hours post-exposure, compared with the same period pre-exposure 11.

It’s amazing what viruses can do … or might do … or (just look around you) are doing.


 

Barcoding bees

Every jar of honey I prepare carries a square 20mm label that identifies the apiary, batch, bucket and the date on which is was jarred. The customer can scan it to find out about local honey … and hopefully order some more.

The label looks a bit like this:

Scan me!

This is a QR code.

You’ll find QR codes on many packaged goods in the supermarket, on bus stop adverts, on … well, just about anything these days.  QR codes were first used in 1994 and are now ubiquitous.

QR is an abbreviation of quick response.

It’s a machine-readable two-dimensional barcode that is used to provide information about the thing it’s attached to.

QR codes contain positional and informational content. In the image above the three corners containing large squares allow the orientation to be unambiguously determined.

Within the mass of other, much smaller, black and white squares are several alignment points, an indication of the encoding 1 and the ‘information payload’. 

Large QR codes can contain more information and more error correction (so they can be read if damaged 2 ). Conversely, small QR codes contain reduced amounts of information and less error correction, but can still be used to uniquely identify individual things in a machine-readable manner.

A barcoded bee and barcode diagram.

And those ‘things’ include bees.

I am not a number 3

I had intended to write a post on how pathogens alter honey bee behaviour. This has been known about in general terms for some time, but only at a rather crude or generic level. 

To understand behavioural changes in more detail you need to do two things:

  • observe bees in a ‘natural setting’ (or at least as natural as can be achieved in the laboratory)
  • record hundreds or thousands of interactions between bees to be able to discriminate between normal and abnormal behaviour. 

And that isn’t easy because they tend to all look rather similar.

Lots of bees

How many of the bees above are engaging in trophallaxis?

Does the number increase or decrease over the next five minutes? What about the next hour?

And is it the same bees now and in an hour?

And what is trophallaxis anyway? 

I’ll address the last point after describing the technology that enables these questions to be answered.

And, since it’s the same technology that has been used to monitor the behavioural changes induced by pathogens, I’ll have to return to that topic in a week or two. 

Gene Robinson and colleagues from the University of Illinois at Urbana–Champaign have developed a system for barcoding bees to enable their unique identification 4.

Not just a few bees … not just a couple of dozen bees … every bee in the colony.

Though, admittedly, the colonies are rather small 😉

Each barcode carries a unique number, readable by computer, that can be tracked in real time.

So, unlike Patrick McGoohan, these bees are a number.

bCode

The scientists designed a derivative of the QR code that could be printed small enough to be superglued to the thorax of a worker bee. They termed these mini-QR-like codes bCodes 5. The information content of a bCode was limited by its size and the reference points it had to carry that allowed the orientation of the bee to be determined.

In total the bCode could carry 27 bits of data. Eleven bits (each essentially on or off, indicated by a black or white square) encoded the identification number, allowing up to 2048 bees to be uniquely numbered. The remaining 16 bits were the error-correction parity bits that had to be present to ensure the number could be accurately decoded.

If you’re thinking ahead you’ll realise that the maximum number of bees they could therefore simultaneously study was 2048. That’s about 1/25th of a very strong colony at the peak of the season, or the number of bees covering both sides of a two-thirds full frame of sealed brood.

It’s enough bees to start a one frame nucleus hive, which will behave like a mini-colony 6 and, in due course, expand to be a much larger colony.

And if you’re thinking a long way ahead you’ll realise the every barcode must be affixed to each bee in the same orientation. How otherwise would you determine whether the bees were head to head or abdomen to abdomen?

Labelling bees

This is the easy bit.

Each bCode was 2.1mm square and weighed 0.6mg i.e. ~0.7% of the weight of a worker bee. Honey bees can ‘carry’ a lot more than that. When they gorge themselves before swarming they ingest ~35mg of honey. 

The bCode therefore should not be an encumbrance to the bee (and they confirmed this in an exhaustive series of control studies).

A single frame of sealed brood was incubated and the bees labelled within a few hours of emergence. Typically, two batches of ~700 bees each were labelled from a single frame for a single experiment.

Each bee was anaesthetised by chilling on ice, the bCode glued in place (remember … in the same orientation on every bee) and the bee allowed to recover.

Labelling a single bee took 1-2 minutes.

Labelling 1400 bees takes several people a long time.

I said it was easy.

I didn’t say it was interesting.

Smile for the camera

I’ve not yet discussed the goal of the study that needed barcoded bees. It’s not really important while I’m focusing on the technology. Suffice to say the scientists wanted to observe bees under near natural conditions.

Which means a free-flying colony, on a frame of comb … in the dark.

Free-flying because caged bees do not behave normally.

On a frame of comb because they were interested in the interactions between bees under conditions in which they would normally interact.

And in the dark because that’s what it’s like inside a beehive (and it’s one of the features that scout bees favour when selecting a site for a swarm).

Camera and hive setup.

The scientists used an observation hive with a difference. It had an entrance to allow the bees to fly and forage freely and it contained a single sided, single frame. In front of the frame was a sheet of glass separated by 8mm from the comb. This prevented the bees from clambering over each other, which would have obscured the bCodes 7. Behind the frame was an 850nm infrared lamp to increase contrast, and the front was illuminated by several additional infrared lamps.

Bees cannot see light in the infrared range, so they were effectively in the dark.

The camera used (an Allied Vision Prosilica GX6600 … not your typical point and shoot) recorded ~29MP images every second. A typical experiment would involve the collection of about a million images occupying 4-6 terabytes of hard drive space 8.

The recorded images were processed to determine the temporal location of every bee with a visible (and readable) bCode. This was a computationally interesting challenge and involved discarding some data – e.g. barcodes that moved faster than a bee can walk or barcodes that fell to the bottom of the hive and remained motionless for days (i.e. dead bees). About 6% of the data was discarded during this post-processing analysis.

Trophallaxis

Which finally gets us to the point where we can discuss trophallaxis. 

Honey bees and other social insects engage it trophallaxis.

It involves two insects touching each other with their antennae while orally transferring liquid food. It occurs more frequently than would be required for just feeding and it has been implicated in communication and disease transmission

bCoded bees and trophallaxis

So, if you are interested in trophallaxis, how do you determine which bees are engaging in it, and which are just facing each other head to head?

In the image above the two bees in the center horizontally of the insert 9 are engaged in trophallaxis. The others are not, even those immediately adjacent to the central pair.

Image processing to detect trophallaxis – head detection.

This required yet more image processing. The image was screened for bees that were close enough together and aligned correctly. An additional set of custom computer-vision algorithms then determined the shape, size, position and orientation of the bees’ heads. To be defined as trophallaxis the heads had to be connected by thin shapes representing the antennae or proboscis.

And when I say the image … I mean all million or so images.

Bursty behaviour

And after all that the authors weren’t really interested in trophallaxis at all.

What they were really interested in was the characteristics of interactions in social networks, and the consequences of those interactions.

This is getting us into network theory which is defined as “Well out of my depth”

Transmission of things in a network depends upon interactions between the individuals in the network.

Think about pheromones, or honey, or email … or Covid-19.

It’s only when two individuals interact that these can be transmitted between the individuals. And the interaction of individuals is often characterised by intermittency and unpredictable timing. 

Those in the know – and I repeat, I’m not one of them – call this burstiness. 

If you model the spread of ‘stuff’ (information, food, disease) through a bursty human communication network it is slower than expected.

Is this an inherent characteristic of bursty networks?

Are there real bursty networks that can be analysed.

By analysing trophallaxis Gene Robinson and colleagues showed that honey bee communication networks were also bursty (i.e. displayed intermittent and unpredictable interactions), closely resembling those seen in humans.

However, since they had identified every trophallaxis interaction over several days they could follow the spread of ‘stuff’ through the interacting network.

By simply overlaying the real records of millions of interactions over several days of an entire functional community with an event transmitted during trophallaxis they could investigate this spread..  

For example, “infect” (in silico) bee 874 in the initial second and follow the spread of the “infection” from bee to bee through the real network of known interactions.

In doing this they showed that in a real bursty network, interactions between honey bees spread ‘stuff’ about 50% faster than in randomised reference networks. 

Why isn’t entirely clear (certainly to me 10, and seemingly to the authors as well). One obvious possibility is that the topology of the network i.e. the contacts within it, are not random. Another is that the temporal features of a bursty network influence real transmission events. 

Scientists involved in network theory will have to work this out, but at least they have a tractable model to test things on …

… and at a time when some remain in lockdown, when others think it’s all a hoax, when social distancing is 2m 11, when some are wearing masks and when prior infection may not provide protective immunity anyway, you’ll appreciate that ‘how stuff spreads’ through a network is actually rather important.

Stay safe