Science snippets

Three short and easy-to-digest snippets of science this week. After last weeks’ overly-long DIY extravaganza I thought I’d try and be a little more succinct this time. 

The following triptych is based on three separate papers, two published in the last month or two and one from last year. Individually these incremental advances in our understanding probably do not justify a post of their own. 

The first paper, on sodium butyrate, was included here following a question I was asked during an evening talk to a beekeeping association last week. I don’t think I answered the question particularly well, so thought I’d elaborate here for clarity. The science is cool, but the paper is rather odd.

The other two papers are on a related topic, the bacteria in the gut of bees. The first of these came out last week and had a very catchy title. Reading that paper resulted in my burrowing back a year or two into the literature. While doing this I found a related paper that has got me thinking again about feeding winter bees honey, syrup or fondant.

Sodium butyrate reverses DWV-induced memory loss

All honey bees, perhaps with the exception of those in Australia 1, are infected with deformed wing virus (DWV). Historical studies that report 30% or 60% or whatever virus prevalence were probably using an insensitive assay. Even bees in Varroa-free regions carry DWV. 

And, in the absence of Varroa, DWV is not a problem to the bee 2. It is present at low levels and is apparently not pathogenic.

However, when transmitted by Varroa, the virus levels are amplified about a million times are a range of symptoms are clearly present. These include pupal death or the emergence of workers with overt developmental defects, including the classical ‘does what it says on the tin’ deformed wings.

DWV symptoms

DWV symptoms

In laboratory studies up to 70% of the bees exposed to high levels of virus exhibit these catastrophic symptoms.

However, some bees emerge with high levels of virus, but ‘look’ normal.

But they don’t behave normally.

In particular they have defects in memory and learning. 

Forgetfulness and getting lost

Impairments in memory and learning are bad news for bees. 

Foragers need to be able to learn where sources of nectar and pollen are by interpreting the waggle dance. Perhaps more importantly, they need to remember where the hive is so that they can successfully return from a foraging trip. If they forget where they are going, they’re doomed. 

A social insect like a honey bee cannot become a solitary bee without inevitably becoming a dead bee.

There is a long history of using sodium butyrate (NaB) to either enhance memory, or to reverse memory loss. It belongs to a class of compounds called HDACi’s (histone deacetylase inhibitors) which have been used in medical studies including anti-neural degeneration and anti-Alzheimer’s disease. 

NaB has even been used in studies with honey bees. In these it has been shown to enhance expression of genes involved in the immune response, detoxification and learning/memory. 

In addition, NaB restores learning ability in neonicotinoid-treated bees … it was therefore a logical extension (particularly since this neonic study was conducted by the same Taiwanese researchers) to investigate a role for NaB in counteracting DWV-induced learning and memory loss, the topic of the first paper this week 3 .

CCD and ‘massive disappearance’ of bees

This paper is a bit of a curate’s egg. The science is detailed and appears to be done well. The experiments are logical, mostly well-controlled and involve a combination of detailed molecular studies with monitoring bee behaviour in the field. 

However, the attempted link between memory loss and bee loss, the association with CCD (colony collapse disorder) and the superlatives in the paper make for a rather strange reading experience.

I’m not going to give a detailed account of the science. The key points are as follows:

  • NaB increased honey bee survival after oral DWV challenge 4. Disappointingly they did no virus assays.
  • NaB reversed memory loss in the standard proboscis extension assay (PER)
  • Gene expression studies indicated that NaB (an HDACi) resulted in increased expression of numerous genes, including reversing the suppression of some genes caused by DWV infection. Some of these genes were involved in memory, but many other gene classes were also differentially expressed. NaB was also shown to restore some neurotransmitter activity in the brain.
  • Colonies fed NaB and then fed DWV experienced a much reduced loss of bees than those that just received DWV.

Sodium butyrate reverses bee loss due to DWV (A) in/out ratios and (B) lost bee ratios

I need to re-read some of the methods and data on the in/out ratios (the graph on the left above) as it appears that more bees returned to the hive than left the hive! These field experiments used an automated hive monitoring system , but did not apparently use any form of tagging on the bees. It is not clear how they could be certain that the ‘returning’ bees originated from the monitored hive.

Smells fishy?

The conclusions of the paper end with the sentence a diet incorporating histone deacetylase inhibitors could be used to maintain the overall wellbeing of the bees and integrity of the colony”.

Well … perhaps.

I’d argue that prevention is always better than cure.

It is preferable to minimise DWV levels in the hive – by killing Varroa – than it is to try and counteract the deleterious effects of DWV by adding additional chemicals. Studies from my lab and others show that effective Varroa control results in very low virus levels.

But if you are going to feed them HDACi’s, then it probably should not be sodium butyrate. 

The ‘butyrate’ bit of the name is derived from butyrum meaning ‘butter’ in Latin. Sodium butyrate is a fatty acid and is famously smelly. It reeks of spoiled milk, or sour butter, and is the compound that gives vomit that distinctive ‘smell-it-a-mile-off’ odour.

Hmmmm …. nice 🙁

So, although it doesn’t smell fishy … it certainly does smell. 

Possibly not something you’d want anywhere near hives producing honey 😉

Chicken eating bees

I wrote recently about how important catchy titles are to scientific papers. The title of this next paper was the only thing that made me read the study …

Why Did the Bee Eat the Chicken? Symbiont Gain, Loss, and Retention in the Vulture Bee Microbiome by Figuerosa et al., (2021) mBio 12:e02317-21

How could you not want to read a paper with a title like that?

Well, one reason might be that you don’t know the words symbiont or microbiome.

Let’s see if we can change that … 😉

Vulture bees

Honey bees, along with all other bees, are classified with the sawflies, wasps and ants as members of the Hymenoptera. Of these, bees are wasps that switched to a vegetarian lifestyle, eating pollen and nectar.

Vulture bees dining out on chicken

However, some stingless bees also dine on carrion (literally ‘the decaying flesh of dead animals’) and a few species – the aptly named vulture bees – only feed on carrion for protein and no longer collect pollen.

You are what you eat

The microbiome is a collective term for the all the bacteria 5 in a particular environment.

For example, the gut microbiome or the skin microbiome. 

In the gut, these microbes help the host exploit novel food resources. For example, honey bees have bacteria (Gilliamella apicola) that help them digest toxic sugars 6.

The host (bee) benefits from the presence of the bacteria, and the bacteria benefits from the protection and food provided by the host … which is exactly what the term symbiotic means.

You are what you eat is, of course, not meant literally 7.

However, it is certainly true that the symbiotic microbiome is significantly influenced by diet. And the symbiotic microbiome also influences what can be consumed.

The Figuerosa et al., study compared the gut microbiome of a variety of stingless bees from Costa Rica. Some of these bees were pollenivorous and others were facultatively or obligately necrophagous.

Eh?

  • Pollenivorous – pollen eating
  • Facultatively – some of the time 
  • Obligately – all of the time / only
  • Necrophagous – feeding on corpses or carrion

The microbiome of vulture bees

By analysing the microbiome of these different types of bees the authors determined that reversion to a purely necrophagous lifestyle had resulted in the acquisition of a unique range of additional bacterial species.

Gut microbial communities in pollen-eating (absent), or facultatively or obligately necrophagous stingless bees.

However, the gut microbiome was not entirely unique. Many species were also found in facultative necrophagous bees, or in the pollenivorous species. 

It’s not yet clear what all these new species actually ‘do’ in the gut of these carrion eating ‘vulture’ bees. Further studies will be needed to determine this.

And, of course, this study begs the additional question.

Which came first, the chicken or the bacteria? 8

Did the microbiome change in response to a change in diet, or was the change in diet enabled by the change in the microbiome?

And, the topic of changes in the microbiome is the topic of the third paper … which, you’ll be relieved, is on honey bees.

The microbiome of summer and winter bees

I really used the ‘vulture bees’ paper to introduce the concept of the symbiotic microbiome.

In honey bees, the microbiome has been extensively studied over the last decade or so.

A striking feature is that it includes relatively few species of bacteria, and is dominated by less than 10 in total 9. These species are conserved regardless of geography, life stage (nurse bee, forager etc.) or season.

Almost every study of the honey bee microbiome has been a qualitative one. By that I mean the scientists determine the species present, but ignored the quantities of the different bacteria. 

In comparison, a quantitative study would have determined the amounts of some or all of the core species in the microbiome. 

And that is exactly what Kešnerová et al., (2020) did in their study entitled Gut microbiota structure differs between honeybees in winter and summer 10.

Multi-year, multi-hive studies

As you would expect from a paper in the ISME Journal 11 this is a thorough study, involving sampling of one hive on a monthly basis for 24 months, and fourteen hives in two different locations in the summer and winter. Each sampling involved multiple individual bees that were analysed. There are some additional experiments on colonisation of the gut that I’m going to largely ignore here.

The authors qualitatively and quantitatively studied only five of the core species and two non-core species from the gut microbiome. The names don’t really matter, but are shown in the figures below.

The gut microbial community differs between summer foragers and winter bees

There’s a huge amount of date in this figure.

However, simply by looking at the monthly changes (A), or the community composition (B), it is clear that summer foragers and winter bees have significantly different microbial populations within the gut.

In addition, the overall levels of many of the species tested (C) were significantly increased in the winter bees population.

Summer bees, nurse bees and winter bees

From a physiological and dietary point of view, there are some similarities between nurse bees and the long-lived winter bees. The authors therefore tested the bacterial population the gut of each contained in summer (foragers and nurse bees) and winter (winter bees).

Bacterial load and community composition in foragers, nurse and winter bees

Nurse bees and winter bees contained at least 10 times the population of bacteria as present in the gut of foragers (A, above). Of these, nurse bees were intermediate in the range of species between the foragers – which had a greater range – and the winter bees which contained fewer species.

Finally, detailed statistical analysis of the populations in the three bee types indicated that they were distinct (C), despite conservation of several of the core microbiome species. This latter analysis showed that, whilst each was distinct, all of the populations were similarly variable within a particular bee type i.e. none of the dots are more clustered/scattered in the third panel above.

Diet and the microbiome

Numerous studies have shown that diet influences the bacteria in the gut – of honey bees, vulture bees, flies, mice and men. It’s therefore very likely that the diet of nurse and winter bees at least partly accounts for the differences in the bacterial community present in their gut.

Foragers need an energy-rich diet and mainly feed on nectar and honey. In contrast, nurse bees and winter bees also consume pollen.

In studies I don’t have time to discuss, Kešnerová et al., (2020) also showed that feeding gnotobiotic bees 12 pollen and syrup resulted in significant increases in the amount and levels of bacterial colonisation i.e. they resembled nurse or winter bees. In contrast, bees fed syrup alone developed a gut microbiota that resembled that of foragers.

All of which made me think about feeding bees syrup/fondant for the winter vs. feeding/leaving them honey.

Honey is better for bees in the winter … really?

Beekeepers who leave their bees with a super or so of honey are often convinced of the benefits to the colony.

When pressed they unfortunately provide little evidence to support their expensive decision 13

I’m not aware of a single study that convincingly i.e. statistically, demonstrates that colonies are more successfully overwintered on a diet of pure honey, rather than a colony fed syrup or fondant. 

I’ve discussed this before – for example, see my response to this comment in the post entitled ‘Cut more losses’. 

Is the microbiome a marker of colony health?

However, this paper on the winter bee microbiome got me wondering whether – in the absence of evidence supporting better overwintering survival – bees fed syrup/fondant or honey have a different bacterial population.

It would be very interesting if they did.

Furthermore, as scientists further untangle the role of these bacteria, we would be able to tell whether syrup/fondant was better, worse or neutral in terms of the changes it induced in the bacteria that inhabit the winter bee gut.

Unfortunately, the Kešnerová et al., (2020) study has no details whatsoever of the hive management regime. The work was done in Lausanne, Switzerland, but it doesn’t say how or what they were fed for the winter.

Nor is there any mention of whether the diet was supplemented with sodium butyrate 14. This will also need to be studied as butyrate is a natural product of some gut microbes and there is evidence that – in humans at least – it is involved in communication between the gut and the brain.

And I think my gut is telling my brain that it would like some pizza …


 

Footnotes

  1. Discuss …
  2. Though I suppose there’s the question about “how can you tell if they are all infected … where’s the negative control?”, which is a valid point.
  3. Tang et al., Real-time monitoring of deformed wing virus-infected bee foraging behavior following histone deacetylase inhibitor treatment, iScience (2021), https://doi.org/10.1016/j.isci.2021.103056.
  4. Though it’s worth noting that the bees they used appeared very susceptible to oral challenge with DWV … strange.
  5. And viruses and other microbes etc., though it’s usually used to only refer to the bacteria.
  6. Zheng H, Nishida A, Kwong WK, Koch H, Engel P, Steele MI, Moran NA. 2016. Metabolism of toxic sugars by strains of the bee gut symbiont Gilliamella apicolamBio 7:e01326-16.
  7. Or I’d be a large pizza.
  8. Which is the title I’d have used for the paper.
  9. More accurately, these are phylotypes, not species, based upon their genetic relatedness of ≥97% … which is not quite the same, but for our purposes will do.
  10. The ISME Journal 14:801-814, in the following discussion you can consider that the term microbiota = the microbiome, though it is probably subtly different.
  11. Which is part of the Nature Springer stable and describes itself as a multidisciplinary journal of microbial ecology.
  12. Bacteria-free bees … or at least hugely reduced. Gut bacteria were at ~10,000 times lower levels.
  13. As I’ve said before, It’s a free world … and the more that do this, the less competition there is for those of us who sell honey. I don’t care what they do, but I do care if they make claims that are unsupported … there’s too much of that in beekeeping already.
  14. Unsurprisingly …

16 thoughts on “Science snippets

  1. Dave Pehling

    Hi David,
    I very much enjoy reading your blog. I think your climate is quite like ours NE of Seattle in the foothills.
    Regarding the benefits of honey vs. sugar for overwintering, we have at least a couple annual surveys here in the U.S. “Bee Informed Partnership” is nationwide. For my local, we have the “PNW Honey Bee Survey” at https://pnwhoneybeesurvey.com/survey-results/2019-20-survey-reports/
    On that particular page, the survey results are as follows:

    “Individuals statewide that fed sugar syrup had a 7% lower loss level (average for the 4 years). Those feeding honey (as frames or liquid) had lower loss only during the 2018 and this past winter overwinter period. Individuals feeding non–liquid sugar (in any of the forms) had lower losses all four past winter seasons, with 5 or 6 percentage point improvement from overall losses. Dry sugar feeders had slightly better survival all 4 winters (average= 39%) while hard candy feeders had a much improved survival all 4 winters (=31% average survival); fondant feeders had better survival 3 of the 4 winters (37% 4-year average).”

    Of course, this is a voluntary survey so there are any number of variables involved that could skew the data…but it’s something to consider in the discussion.

    Reply
    1. David Post author

      Hi Dave

      Many thanks for that link … very interesting. Over 1300 hives as well, so a reasonably good sized survey. There’s a lot in the report and I’ve only skim read it for now, but will read it carefully in due course.

      As you say, all sorts of variables, not least of which would be Varroa management differences. I would guess that those that feed honey alone might be more likely to minimise treatments or use no treatment at all (though perhaps I’m jumping to conclusions here). That being the case, you’d expect higher losses from mites/viruses in the honey-fed colonies … so only a 7% difference isn’t huge. I’m rubbish at statistics, but it might be interesting to crunch some numbers and work out what’s noise and what are real differences … for example, there may not be a real difference in 31 – 39% range if the hive numbers are relatively small.

      I think you’re right about climate. Moist and maritime most of the time here on the west coast. Colder and drier on the east coast, but not much colder and drier. I’m going to write something about weather next year as it’s something that affects all beekeepers and that I’ve started to take a bit more note of recently.

      Enjoy the winter … only another 4 months to go now 😉

      Cheers
      David

      Reply
  2. Archie McLellan

    Hi David

    I noticed ‘There’s a huge amount of date in this figure’ – but no prune or apricot? 🙂

    Thanks for the science, and for making it accessible. ‘Facultatively’ has made a long journey to mean ‘some of the time’, helped along its way by occasions like this. Very hard to see the point of using it – except as jargon (members only please).

    Vulture bees eating carrion is not the same as honey bees in the nest consuming large amounts of eggs and some larvae. Even so, does this challenge the notion that they are vegetarian? Or do they eat very young bees not for their diet, but solely to clear the hive of unhealthy or superfluous brood?

    In the little reading I’ve done, there seems to be a wide range of opinion on what makes winter bees. I think people used to think that one cause was a pollen-rich diet, but now opinion and research seems to lean to the opposite.

    As you are a bread-maker, can I take it you make your own pizza?

    Reply
    1. David Post author

      Hi Archie

      Data of course, not date. D’oh! Serves me right for writing at daft o’clock.

      I’ve ‘simplified’ the scientific meaning of facultatively somewhat. It perhaps more correctly means ‘optionally’. Unfortunately, from a biology perspective, it gets used quite a bit. A facultative anaerobe is a bacterium that can live anaerobically but doesn’t need to, or can do if it has to. Typically, if oxygen were present it would use aerobic respiration though.

      I think the ‘carnivorous’ activity of honey bees involved in destroying eggs or larvae during a severe nectar dearth, or during worker policing, is probably a housekeeping activity, rather than proper carnivorous activity. It’s probably easier to just munch up eggs or young larvae rather than go to the hive entrance and discard them there.

      I’ve written about the forces driving winter bee development, though I think they have still to be completely defined. Brood pheromones are important.

      I certainly do make my own pizzas … Ken Forkish (he of the Flour, Water, Salt, Yeast bread fame has written an excellent book called The Elements of Pizza which is pretty much foolproof. Only a couple of days ago I was standing outside, 4°C in the spitting rain, making pizza for lunch in a wood-fired oven …

      Here's one I made earlier

      It wasn’t that pizza, but you get the general idea 😉

      Cheers
      David

      Reply
  3. Elaine Robinson

    Hi David, I’m sure I’ve read from one of your earlier posts that the cost of proving whether honey is beneficial vs sugar syrup would cost £50k for a scientifically robust trial. Which researchers have this sort of £ to spare? So I guess the argument will rumble on, depending on whether you do or you don’t leave honey on for the bees.
    Personally until otherwise proven, I buy into the lady of ‘Honeylands ‘ mantra, “one for me and one for you”. Seems only fair to attribute human values and share the crop, given their hard work in collecting it and as a minimum, give the bees a good start in the spring, with a few trace elements, vitamins and amino acids 😉

    Reply
    1. David Post author

      Hi Elaine

      I think the £50k was a ‘off the top of my head’ guesstimate. No researchers have that sort of money to spare 🙁 Well, some might, but this researchers certainly does not.

      A standard 3 year research grant for one post-doctoral scientist and the necessary consumables (not pizza … but chemicals, plasticware, time on the microscopes or whatever) – at least doing the sort of research I do – is about £500,000. The sugar/honey experiment ‘argument’ would cost less than that … but if the differences are as close as Dave Pehling states in his comment elsewhere on this post, you would need to study a lot of hives to be certain there were statistically significant differences one way or another, and do it over two or three winters. It’s a very time consuming thing to determine. The same management, mite treatments, hive strength etc.

      It’s probably not actually worth doing. What irks me is constantly being told that honey is better, when it’s usually based upon assumptions and anecdotes … neither of which make for statistically compelling evidence (I know, as I’ve attempted to publish several manuscripts that were accused of an overdose of both 😉 ).

      Actually, going back to Dave Pehling’s comment … a really good survey, either of lots of beekeepers, or a smaller number of unwaveringly honest beekeepers, might be able to get some relevant answers, though they might have to agree on a limited range of feeding/mite/management strategies to avoid too many variables.

      And getting beekeepers to agree on something like that is probably harder than winning a million pound research grant 😉

      If you’re happy and your bees are happy, then I’m happy 🙂

      Cheers
      David

      Reply
  4. Maccon Keane

    Dear David
    Apologies for this question after the really nice 3 science paper blog but it is a question they has been niggling at me since the ‘Contact Killer’ blog of 4 weeks ago and ignited again by the picture of the DWV infected bee. You mentioned previously that you think Oxalic Acid in Autumn isn’t as effective as other mitecides at that time of year but I don’t know if you showed any data. I am assuming this is even when reapplied to cover a whole brood cycle. Have you any data / comparators for outcomes from the different mitecides used in Autumn? PS I have used Na Butyrate to differentiate breast cancer cells in vitro – and as I am sure you are aware as an untargeted HDAC inhibitor it has major effects in gene expression across the whole genome leading to a bunch of unintended consequences. While it is a nice model system, at a first principles level it wouldn’t be my first choice as a whole organism – in this case whole bee treatment / supplement for anything. Maccon

    Reply
    1. David Post author

      Hello Maccon

      I’ve done no side by side comparisons of any miticides … at least none when I’ve done accurate mite quantifications before and afterwards. I do know that Apivar can clear huge mite (phoretic) levels in 7-10 days. Apivar is now the miticide I use in autumn – it fits in with my beekeeping year and my availability in the latter parts of the season. I have previously discussed repeat OA treatment, but haven’t done it for several years now. One off treatment is not a problem, but repeated treatments every 5 days, 3-4 times for ~20 hives, is a lot of work.

      We’ve also used NaB for cell differentiation in the lab. Considering the ‘reversal’ of neonic-induced learning impairment by NaB the results presented above weren’t too surprising, but it’s clearly not a practical solution for DWV. Partly for the reasons you mention, but also because it’s so much easier and more practical to simply hammer down the mite population and – as a consequence – reduce the viral load by orders of magnitude.

      Cheers
      David

      Reply
  5. Michael

    Hi David
    Interesting snippets. Thank you.
    Amazingly last weeks Economist (Nov 27th) printed an article on Varroa management but by bees – not beekeepers. It was research on how colonies behaviour changes depending on the levels of varroa in the hive. The study was by Michelina Pusceddu of The University of Sassari in Italy It was published In Science Advances with the long title of Honey Bees increase social Distancing when facing the ectoparasite Varroa Destructor. Have you seen it?

    Reply
    1. David Post author

      Hello Will

      I’d not seen that article but know some of those quoted in it. I’ll have a read. I see at the end they conflate 40+% colony losses a year reported by the Bee Informed Partnership and poor nutrition. Whilst I have no doubt that nutrition contributes to this figure, I suspect disease is a much greater contributor.

      Your IP address suggests that ‘here’ is Maine. I assume the ash is from forest fires? I tried planting some goldenrod this year for my bees but it never appeared and I fear that the deer ate it all 🙁

      Cheers
      David

      Reply
      1. Will

        Hi David,
        Greetings again from the state of Maine, USA specifically an island off the coast. The ash I am referring to is in the nectar/honey and can contribute to digestion problems due to higher than normal undigestibles. And winter is not the time for that. Most of New England is prime area for goldenrod/aster. The deer do not bother with it though. One of my favorite times entering a bee yard is when they are on a good flow of goldenrod. The fragrance is, in my opinion quite nice. Although last year there wasn’t a fall flow and this year it was minimal.
        I do not recall where I read or heard about the goldenrod though. I think through our state apiarist.

        Reply
        1. David Post author

          Thanks Will … must be one of the few things that the damned deer don’t eat!
          Thanks also for the link sent separately which I’ve added to my (extensive) ‘to read’ list.
          Cheers
          David

          Reply
  6. Ann

    Hello David, Just a quick comment on leaving honey stores v feeding bees sugar syrup/fondant for winter stores. I very much doubt that anyone has researched this to come up with scientific proof that one way is better than the other, but I have left the bees with their own stores for the 17 winters that I have kept 4-12 colonies. I have only had 2 colonies perish at the start of the new season from the queen not being properly mated. I’ve never lost a colony to starvation or anything else. Best wishes, Ann (Beelistener)

    Reply
    1. David Post author

      Hello Ann

      I’m sure there are many other experienced beekeepers who can report similarly good overwintering success. I also suspect the majority of these beekeepers are also very good at mite control, as I’m sure you are. It therefore becomes extremely difficult to ascribe better overwintering success to feeding honey rather than anything else.

      Of course, in the overall scheme of things, it doesn’t matter. Whatever helps prepare strong, healthy, well fed colonies in late autumn, that overwinter successfully and build up quickly the following spring, then that’s what should be done. However, I do think it’s important that new beekeepers understand the priorities … it doesn’t matter what you feed them on if they’re riddled with mites and viruses, and a super or two of honey will not compensate for poor mite management.

      Poorly mated queens are another issue altogether. I’ve not been keeping bees long enough, but know that some ‘old timers’ report that they are significantly poorer than 25-30 years ago.

      Best Wishes
      David

      Reply

Leave a Reply

Your email address will not be published.