Additions and improvements

I wasn't sure whether to add a question mark to the title of this post.

Both of the things I'm going to discuss this week are possible, but that doesn't mean they're practical or necessarily even desirable. However, either - under certain circumstances - have the potential to offer significant benefits for specific beekeepers, and for those who depend upon the activities of honey bees.

And, even if they don't, they provide some interesting insights into the biology of bees.

But, before diving headlong into the nitty-gritty, let's briefly consider small-scale, amateur beekeeping, with the - fundamentally similar, but so very, very different - large-scale commercial equivalent. Understanding this provides clues to the impetus for these sorts of things I'll discuss in the remainder of the post.

Amateur beekeeping

There are a number of reasons why you might keep bees; you find them fascinating, they help pollinate your apple trees, you enjoy the taste of honey and in producing a few spare jars for friends and family, you like the small additional income honey sales bring, you make prize-winning mead or metheglin, or you want to increase biodiversity and help 'save the bees'.

Most of those reasons are perfectly sound ... but the last two 'not so much'; honey bees do not increase biodiversity, unless you live in a region with no other honey bees, which is unlikely. In reality, the presence of your honey bees might actually be decreasing biodiversity and threatening the survival of other bees (which are actually the ones that need to be saved).

Nevertheless, whatever the reason, you've got a few hives at the end of the garden, or in the corner of a nearby field. They stay there all the time, though you might shift them to the heather moor in late summer if you're feeling particularly confident {{1}}.

Periodically they swarm, or attempt to, and you take advantage of this to requeen them. The queens are 'open mated' with whatever drones are furtively lurking in the neighbourhood. They don't furtively lurk, but it sounded good as I wrote the sentence, so I've left it in.

Some of the resulting queens are great, some are OK, and a few are - quite frankly - rubbish.

Never mind, you'll requeen the colony again next year. The colony might be a bit less productive, but that just means a less extracting to do, and using smaller jars for the Christmas gifts.

Irrespective of the particular motivation, I'd guess that the majority of beekeepers in the country operate like this ... a small scale, enjoyable, fascinating, rewarding (intellectually but probably not financially 😉) hobby.

It describes my beekeeping almost perfectly {{2}}.

Commercial beekeeping

Although the bees are the same, and many of the hive manipulations are recognisably similar, commercial beekeeping is a totally different business. The key difference is the money. Livelihoods are dependent on the bees being successful, either in terms of honey collected or in the pollination activity of the bees. If there's no honey production, the supermarkets will just import yet more rice syrup (henceforth known as pHoney^TM) and most people won't be any the wiser.

Other than the bankrupt bee farmer 😔.

However, with no pollination, there will be no pears in the supermarket, no cider in the pubs and no apple crumble {{3}}.

This might be the end of civilisation as we know it.

About 35% of global food production, and 70% of the leading single crops, are dependent upon animal pollination. The combination of high intensity farming and the reduction of native pollinator numbers (some of which are those bees that really need saving {{4}}) means that successful crop pollination needs pollinator numbers to be artificially increased ... for example, by shipping in a few hundred thousand (and some) colonies of honey bees.

Good levels of pollination are needed to increase both the overall yield and quality of crops like almonds, top fruit (apples, pears) and blueberry.

The Californian almond industry alone is worth about $10bn annually, and produces ~80% of the global almond crop. There are ~1.3 million acres of almond monoculture that need to be pollinated, and this requires ~2 million colonies being shipped to the state in January/February. That's about 75% of the hives in the US.

And not just any colony ... they need to be of a particular size and strength, and when the almonds are over they are moved on for fruit pollination contracts, or honey production, or blueberry or squash or whatever.

It's a tough life ... being a queen in one of those colonies, or a bee farmer.

Queen and colony performance

The quality of the queen is fundamental to the performance of the colony. Generally, bigger queens are better queens. They mate with more drones, they lay more eggs, they head larger colonies, and the fitness (measured by a variety of parameters, for example disease resistance) of those colonies is greater because they are more genetically diverse ... because the queen mated with more drones.

So, although amateur beekeepers might like bigger, better queens, bee farmers depend upon them for their livelihoods ... and the almond farmers depend on them for the improved pollination services that the resulting colonies deliver.

Therefore, it is not surprising that there have been numerous studies on what it takes to make bigger, better queens. I've discussed some of these in a series of posts in Spring 2024.

I'm going to look at one further way of improving queen quality in the post today.

But, what if you're a bee farmer, and you've rented your colonies for top fruit pollination ... only to find that there's a huge field of oil seed rape (OSR) in the adjacent field? The bees should be visiting the apple or pear blossom, but instead are going in the opposite direction for the bounteous harvest of nectar and pollen from the OSR.

What about another example ... imagine a mixed orchard of apples and pears (not at all unusual). The apples produce a reasonable amount of nectar (though nothing like that available from a few hundred hectares of OSR) but little pollen, and the pears produce pollen but very little nectar. If the pollen needs of the colony decreases, the bees will abandon the pear blossom, resulting in poor pollination.

Can you do anything to influence where the bees go?

It turns out you can.

And, since you're now thinking about how the bees decide whether to turn left to the OSR, or turn right to the orchard, that's the topic I'll deal with first.

It's not just cost-benefit analysis

Honey bee foraging is complicated ... very complicated.

It might look as simple as flying from the nest to a flower or tree (a 'floral resource' as scientists would call it), collecting the resource - the pollen or nectar {{5}} - and flying back again.

However, there's a bit more to it than that.

It is influenced by the weather, the physiological state of the plants, the community diversity of plants and their dispersion (or clustering) within the landscape. The workers need to make a decision whether the benefits gained outweigh the costs involved. If they didn't, that foraging activity would be detrimental for the colony, and they would eventually be doomed.

Let's consider a couple of very simple examples.

Flowers and trees differ in the quality of the nectar and pollen they produce. If you just think about nectar, the sugar content varies widely between different genera of plants - note the position of apple (Malus) and pear (Prunus) on this graph from Pamminger et al., (2019).

So, at first principles, this would suggest that bees would 'prefer' to visit flowering apple trees rather than pear trees ... for the same number of visits, more sugar would be collected from the apple trees.

Bigger is better

But what if there was a solitary apple tree and an entire field of pear trees? The benefits of a larger patch of forage might then outweigh the reduced sugar concentration of the nectar. There are efficiency gains from foraging on large patches, rather than flying between dispersed patches.

And that's before the distance to the floral resource is considered. A sugar-rich source 3 km away might use so much energy flying there and back that the net gain of the trip is almost zero. Perhaps better to forage closer to home, despite the sugar content of the nectar being lower.

On the other hand, a very extensive, albeit distant, source might well be better than lots of smaller, dispersed, lower quality sources nearer the nest.

The smell of success

I said it was complicated, and that's before you consider the waggle dance recruitment of additional foragers, where the dance reflects the quality of the resource, and the influence of odours on the process.

Odours?

When a bee visits a flower to collect nectar it experiences the odour of the flower and associates it with a reward (nectar). These odour-reward associations create memories that improve foraging efficiency by guiding bees towards the learned stimulus.

For example, when foraging on a dispersed, but high quality floral resource, this "memory of reward" will help guide the forager to find (faster) another small patch of the same type of flowers, rather than randomly flying about, or visiting flowers based on colour alone.

The bees move through the landscape more efficiently, so making their foraging trips more successful.

Bees are surrounded by odours all the time.

I love the warm, heady smell of ripening heather honey when I lift the roof of a colony in early September ... the entire hive smells of heather.

Studies dating back almost 80 years attempted to improve foraging - evidenced in terms of honey or seed yields - by adding scents to the hive. The results were not clear-cut, and the studies joined the never ending list of "nice idea, didn't work" science {{6}}.

But, more recently, Farina and colleagues (Farina et al., 2020) have shown that feeding syrup scented with a synthetic sunflower scent results in increased foraging activity, increased recruitment of foragers to sunflowers and significant gains in sunflower seed yields (i.e. better pollination).

Nice idea, did work 😄.

Getting fruity

The same group have recently turned their attention to a more challenging task ... using scents in mixed orchard settings to favour visits to apple or pear trees.

I've described above why this is a real-world 'beekeeping for pollination' problem. The trees are often grown together or in adjacent fields, and they offer very different rewards in terms of nectar and pollen.

The study involves all sorts of tests to confirm that the bees can detect the synthetic apple- or pear-scents in syrup, that these induced memories that could be recalled, and that the scents could be discriminated from other natural floral scents that they might be exposed to (or get 'false positive' results from).

I'm going to let you read about all of those proboscis extension assays rather than regurgitate them here. Enjoy yourself ... or just accept that they could detect the synthetic odour, could discriminate it from other odours, and that it induced memory.

Shortly before the apple or pear trees began to bloom, colonies were fed syrup laced with either the apple (AM) or pear mimic (PM) scents for 2-3 days. Control colonies just received unflavoured syrup.

Since apple and pear trees provide different floral resources (you're getting the hang of this now 😉) - specifically nectar or pollen respectively - it was necessary to measure the impact, if any, of the scent in different ways. For the apple scent, foraging activity (returning bees at the hive entrance) was measured for 8-9 days after feeding. For the pear scent, they quantified the weight of pollen on returning foragers, and the proportion of pollen from pear trees.

The proof of the pudding

Finally, a further set of studies at a larger scale - more trees, more hives - was conducted to investigate whether the apple or pear scent mimics influenced crop yield ... which is, after all, the "proof of the pudding" if you'll excuse the mixed metaphors.

Compared to control colonies, those fed the AM (apple mimic) scent exhibited increased foraging activity, which was significantly (statistically speaking) greater 7-9 days after feeding the scented syrup. The pear mimic (PM) fed colonies did not show greater foraging activity, but they did collect more pollen, and more of that pollen was from pear trees.

Finally, the yield of fruits per tree (of apples or pears), was significantly increased when the colonies were fed AM- or PM-scented syrup compared with those fed syrup only.

There are additional results in the paper which are worth reading, but I've covered the main points.

It's clear that in-hive odours influence foraging behaviour, and these in-hive odours could be manipulated to enhance pollination of less attractive crops, or to potentially boost pollination of such crops in an environment with competing - more attractive - natural floral resources.

I think that's a pretty exciting result that has clear commercial application (the apple and pear mimic scents are patented, with some of the authors being co-inventors on the patents).

Even bigger, better queens

But all of those improvements suppose that the colony is strong enough, with sufficient foragers, to visit the millions of individual flowers in an orchard. Just adding a few 'pear drops' to a mediocre colony will produce, at best, mediocre results.

And since the strength of the colony is predominantly due to the egg-laying rate of the queen, and that the size of the queen is a good measure of her quality, let's quickly look at ways to produce even bigger, better queens.

Quickly, because this is supposed to be the last post in November, not the first post in December 😉.

The size of the queen - measured in terms of things like wet weight, thoracic width, wing length - correlates with her mating success, and her attractiveness to drones on mating flights {{7}}.

Queen rearers like to use big strong cell raising colonies to ensure developing queens are well-fed ... this is because the size of the queen is largely determined by her diet of royal jelly during her development.

However, additional studies have shown that juvenile hormone (JH) early in the larval phase is required for good ovarian development, and that the quantity of the sugars in the diet are also important.

The cell raising colony provides all these ... but what happens if more are added? Is queen quality already maximised, or can larger queens be produced by supplementing their diet with additional JH and/or sugar?

Feeding queens

In the apples and pears study the entire colony was transiently fed supplementary syrup. In contrast, in this study of diet supplements for queens, the scientists added JH or additional sugar directly to individual queens developing from grafted larvae.

Time-consuming certainly, but very specific ... no need to worry whether the cell raiser had given one queen more than one of her sisters.

You can purchase synthetic JH from companies like Sigma. 10 mg costs about £185.

This research was published a few years ago by De Souza et al., (2019) and is Open Access.

1 or 3 day old larvae were grafted and fed JH or additional sugars, or both. For the JH, 1 µl of JH solution at 2 µg/µl was pipetted directly onto the developing larvae ... by my calculations, this would costs about 4 pence, a small price to pay if you get a bigger, better queen.

Do you?

The scientists had to establish separate cell raising colonies for the 1 and 3 day larvae, as cell raisers containing 1 day old grafts tended to reject older larvae. This made me think about my own grafting ... if I get poor 'take' is it not because I damaged the smallest larvae when transferring them, but instead because I also selected some older larvae that were considered a poor choice by the colony (and promptly eaten)? Remember also that a high proportion of emergency queen cells - which may be started from older larvae - are torn down by the colony.

Well, do you?

OK, I'm getting to that bit.

1 day old grafted larvae produced significantly larger queens than the 3-day-old larvae. We knew this already as there are studies going back to the 50's or earlier than showed similar results.

When these 1 day old larvae were also fed JH and additional sugars almost all the morphological features measured were larger - wet weight, thorax width, head width and wing length. Not all the increases were statistically significant, but many were.

Queen quality

It was notable that the JH/sugar supplementation did not 'rescue' the poorer quality 3 day old grafted larvae and make them into 'good' queens ... by the criteria measured, they were still less good than those from 1 day old larvae who did not receive any diet supplements.

The virgin queens that weren't subjected to all sorts of measurements (one of which involved removal and measurement of the legs from the humanely killed queen) were put into mini-mating nucs and allowed to mate. Disappointingly, the mating success rate - of both control and JH/sugar-fed queens - was almost as poor as mine was this year, but they ended up with 3 mated control queens, and four mated 'fed' queens.

Once the mated queens started laying, they were culled and the ovaries dissected out for analysis. The JG/sugar fed queens contained a significantly higher sperm count and greater count of viable sperm (than those not supplemented).

The assumption here was that these larger queens mate with more drones and physically store more sperm ... these are both desirable features, resulting in a queen potentially able to lay more eggs (or lay at the same rate for longer), and head a colony with better fitness because of the increased genetic diversity.

It should be noted that most of the last paragraph were assumptions ... they didn't measure how many drones the queen mated with, her egg laying rate or duration, or the genetic diversity of her progeny. Nevertheless, the assumptions are reasonable, and it certainly warrants further research.

So, it seems you can make bigger, better queens if you supplement their diet with additional sugars and some JH.

The authors finish the conclusions that these studies may benefit the commercial pollination industry that rely on the queen breeders to regularly replace their queens ... which neatly takes us back to where we started.

Final thoughts

Neither of these studies probably has practical application for amateur beekeepers. Most of us don't have pollination contracts to fulfil and instead want to avoid feeding additional syrup unless absolutely necessary (as it will taint the honey which is our primary goal). Similarly, the majority of amateur beekeepers do their queen rearing - if it's done actively at all (rather than simply letting nature take its course) - without grafting day old larvae.

Nevertheless, I think both studies are interesting, and they provide some insights into fascinating aspects of the lives of honey bees. Even though we might not need this type of technology, understanding how and why it works helps us understand out bees a little better.

Note

A regular reader contacted me and reminded me of Piers Moore Ede's book Honey and Dust (2005). In it, Ede describes a beekeeper in a hot, dry country placing a cloth in front of the hive soaked in the 'juice' of the desired crop to encourage the bees to seek it out and preferentially forage there. I read this book years ago but had completely forgotten this part. About half the book is on the search for honey in the Middle East, so I'll seek out the relevant reference when I get a chance and add it here.

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References

De Souza, D.A., Hartfelder, K.H., and Tarpy, D.R. (2019) Effects of larval Age at Grafting and Juvenile Hormone on Morphometry and Reproductive Quality Parameters of in Vitro Reared Honey Bees (Hymenoptera: Apidae). Journal of Economic Entomology 112: 2030–2039 https://doi.org/10.1093/jee/toz148.

Farina, W.M., Arenas, A., Díaz, P.C., Martin, C.S., and Barcala, M.C.E. (2020) Learning of a Mimic Odor within Beehives Improves Pollination Service Efficiency in a Commercial Crop. Current Biology 30: 4284-4290.e5 https://www.cell.com/current-biology/abstract/S0960-9822(20)31172-6.

Pamminger, T., Becker, R., Himmelreich, S., Schneider, C.W., and Bergtold, M. (2019) The nectar report: quantitative review of nectar sugar concentrations offered by bee visited flowers in agricultural and non-agricultural landscapes. PeerJ 7: e6329 https://peerj.com/articles/6329.

{{1}}: Usually misplaced confidence, I'm afraid 😜.

{{2}}: Including the absence of a heather crop most years 😢.

{{3}}: Hint ... substitute porridge oats for the flour in the crumble ... even better.

{{4}}: The irony being that the high intensity farming involves landscape fragmentation, pesticides, pollution and agrochemicals which are some of the major reasons that native pollinator numbers have nosedived.

{{5}}: Or honeydew, or tree resin, or water or whatever ...

{{6}}: I've got quite a few things of my own on that list.

{{7}}: This deserves a post of its own ...