In The Apiary This Weekend

After a cold spell that meant I couldn't open up the hives for a fortnight, we finally got some warmer weather yesterday.  So - what's been happening?

Starting with Miriam's colony, everything looks fine.  She is laying, there are plenty of bees and there is nectar coming in.  There are two boxes (supers) of honey frames on the hive, and the first one (the one they will use as winter stores) is already full.  The second super is mostly empty at the moment, but there are a couple of frames where the bees have started storing nectar.

Local councillor Ian was helping me with the inspection yesterday, and we were mainly focused on looking for queen cells, as these are a sign the colony is planning to swarm.  We had a good look in Miriam's hive but couldn't see any, so hopefully her colony will stay nice and calm for the next few weeks.

On to Caroline's hive.  This is the one where the queen has been allowed to lay in both the brood-box and the first (bottom) super - an arrangement known as "brood-and-a-half".  It means she has around 60% more laying space than Miriam, which means lots more bees!  The difference is noticeable - Ian and I were greeted with a very busy colony when we opened up.  Unfortunately, there was no time for photos as we had our hands full just checking everything in the hive.

Looking through the brood frames, there were a few empty queen "cups" - these are concave wax structures that face downwards, and are the foundation for a queen cell.  One possibly had an egg in it, but I squished it while I was opening up the cell with my hive tool to get a closer look.

On to the brood-containing super.  The first frame was mostly honey, then two frames full of worker brood.  And then on frame number four, I saw what we were looking for - a queen cup with an egg clearly laid inside it.  This means the colony is starting to make swarm preparations, with the likely swarm date in around 8-9 days time.  I don't want my bees to swarm, so I had two options - either remove the egg, to delay their plans, or remove the queen.  I decided that removing the egg would only delay the inevitable, and I'd rather solve the issue as early as possible in the season.  But what do I do with the queen?

Well, the first thing I needed to do was find her!  Ian and I went back through the brood box for a second time, trying to find the queen.  Believe me, when you are looking through thousands of bees, trying to find one that looks slightly different, this is no easy task.  She made us work for it, too - there are 11 frames in the brood box, and we didn't find her until frame number 9.

So, having now found her, we needed to take her out of the hive and give her a new place to live.  Beekeepers have a piece of equipment for this - a half-width brood box called a "nucleus" (often abbreviated to "nuc").  I have two empty nucleus boxes at the moment, so we brought one down next to the hive, and transferred the frame bearing the queen into it.  A nuc takes 5 frames in total, so I added another frame of bees and brood, plus a frame of bees and honey (they'll need something to eat while they're getting settled into their new home).  I had two partially-drawn (but empty) brood frames that I'd stored over the winter, so I put those in as well - these will give queen Caroline extra space to lay in.  And then put the roof on, and the nucleus was complete.

The now-queenless hive needed three new frames to replace the three I'd just transferred to the nuc.  I found three new frames from my spares box, put them in and then Ian and I re-assembled the hive.  Then there was one last job: the colony had filled both their supers, so we needed to add another one.  I had a spare one ready to go, and added it to the hive, which will give the bees something to work with while they wait for the new queen egg to hatch and grow.

I've been very pleased with the rate of honey collection this year - the bees have started earlier, and collected faster than last year.  There is a great variety of forage around at the moment, including trees and garden flowers.  Here's a picture I took of one of my bees foraging last week on some bluebells round the corner from the hives:

It's always great to see the horse chestnut in flower - the flowers are great forage for bees, and they bring lots of the brick-red pollen into the hive.  Here's a picture taken near Bath Spa railway station, showing the wonderful "candles" of flowers:

A - C - G - T: I Can Make A Honey Bee!

Science warning:  this post contains actual science.  You have been warned...

The Lego bricks of life!
(Wikimedia Commons, Public Domain)

A few weeks ago, I wrote a blog post about drones.  And, despite the cheeky science warning (repeated here!), regular reader Sophie asked this:

"If a male drone is from an unfertilised egg, I assume he is always haploid. However, he must be XY to be male, so where does the extra sex chromosome come from? The egg would presumably always be X, as the queen must be XX. It makes sense that the male would just be Xo because then all the sperm would be X, which accounts for all fertilised eggs developing into females. Can the male spontaneously develop a Y chromosome somehow? Or does Xo present as male in bees?"

It's a great question.  My initial answers were:  Firstly - yes, drones are haploid. Secondly, the sex determination mechanism in bees (and other hymenoptera) isn't done by a dedicated sex chromosome in the way that it is with mammals - so there is no Y chromosome. 
Thirdly, yes - Xo does indeed present as male in bees. But, it isn't quite as straightforward as saying that "XX is female and Xo is male", even though that is what appears to be going on.

So, if it isn't straightforward, then what is actually going on?  Time to delve right down into the cellular nucleus, and explore the strange world of honey bee genetics...

Firstly, a reminder about the basics in humans.  All our genes are encoded in sequences of DNA.  And the DNA (which is basically a very long molecule) is bundled up in separate packages called chromosomes.  When we started off as a single fertilised egg (which is just one cell), that egg contained 46 chromosomes (occasionally, someone will have 47, which leads to conditions such as Down syndrome and Klinefelter syndrome).  As we grow, cells get copied over and over again, and each new cell gets its own copy of the 46 chromosomes.

23 of the chromosomes came from our mother (from the unfertilised egg) and the other 23 from our father (from the sperm).  And they're not just random - each maternal chromosome has an equivalent paternal chromosome, so they form pairs.  The chromosomes in each pair are similar but not the same - that is to say, if you take a maternal/paternal pair, they will control the same set of genes, but may have different versions of each gene.  So, if we look at chromosome pair 15, we find the gene for eye colour.  The maternal version might be the gene for brown eyes, whereas the paternal version might be the gene for blue eyes.

These two different versions of the same gene are called alleles.  And we'll come back to them later on...

One pair of chromosomes in humans is different - pair 23 is the sex chromosomes.  The one inherited from the mother looks just the same as the other chromosomes, and is referred to as the "X" chromosome.  The one inherited from the father comes in two versions.  Version 1 is also an "X" chromosome (and the father inherited it from his mother).  Version 2 is much smaller, a stubby little chromosome that contains far fewer genes.  This is the "Y" chromosome.  And the simple rule is that if you get two X chromosomes (i.e. you are XX) then you are female, whereas if you get an X and a Y (you are XY) then you are male.  interestingly, pair 23 is the one pair of chromosomes where a gene on one (the X) may not have a match on the other (if it's Y).  For example, the gene that determines colour-blindness is carried only on the X chromosome.

But we digress - this is supposed to be about bees!

There are two big differences in honey bees.  Firstly, there are only 16 pairs of chromosomes.  And secondly, only female bees get their chromosomes in pairs (i.e. a set from both parents for a total of 32).  Male bees only have 16 unpaired chromosomes - all from their mother.  Bee eggs are completely capable of developing into adult bees even if they are unfertilised - and they will always be male in this case.  This process of being able to create children without fertilisation is known as parthenogenesis.  And (male) bees produced through parthenogenesis have half as many chromosomes, so they are referred to as being "haploid".  Female bees, with the full complement of 32 chromosomes, are "diploid".

Now, one of the consequences of this is that there is no Y chromosome.  It's still the case that female bees are XX, but male bees only have one (of each) X chromosome - this is denoted as "Xo" (the "o" denoting "missing" or "absent").

So, one X makes a bee male, two XX makes her female, right?  Well, this is what was thought until 2003, when researchers from the University of California found out it doesn't quite work like that.  They found that sex determination isn't actually done by chromosome count - there's a specific gene that controls it.  The gene is on the 3rd chromosome, and is called the "csd" or "complementary sex-determination" gene.  Now, you might assume that this gene comes in two versions - male and female.  But that would mean that a haploid (Xo) bee could have the "female" version in its one copy of chromosome 3 - in other words, a bee from an unfertilised egg could become female.  But that never happens.  So, what's actually going on?

It comes back to the alleles that we mentioned earlier.  Remember the genes for eye colour in humans?  These come in a number of different versions (blue, brown, green and others).  Each different version of the gene is known as a different allele.  And genes with multiple alleles are referred to as polymorphic - meaning that they come in different forms (poly=multiple, morphic=forms).

Now, the clue to how this works is in the name of the gene - "complementary sex-determination" gene.  Why complementary?  Simply, that different alleles of csd complement each other - in other words, they work together.  When a bee has two different - complementary - versions of csd, she becomes female.  If a bee has only one version of csd, then he will be male.

So, a quick recap - if a bee is Xo, it can only have one version of csd, so he must be male, and that's exactly what we observe.  And if a bee is XX, and the two versions of csd are different (this is known as being heterozygous), then we get a female.  There are around 20-25 different alleles of csd, so most of the time this is what happens.

But - hang on - it must be possible, even though unlikely, that sometimes an XX (diploid) bee, will have two identical copies of the csd gene?  Indeed it is - in this case the gene is homozygous.  But what happens then?  Well, csd has a secondary effect - when two identical alleles are present, it changes the relative amounts of certain compounds in the skin of the larva when it hatches.  This makes the larva smell different from the others, for around the first three days of its life.  In fact, from a worker bee's perspective, it makes the larva smell delicious.  So she eats it.

This means that adult bees with two identical csd alleles are never present in the hive.  But if a csd-homozygous larva continues to be fed (and isn't eaten!) then it's possible for it to grow into an adult bee.  But what does it become?  Some scientists wanted to find out, so they hatched some csd-homozygous larvae in a laboratory, and fed them.  After three days (when they stopped smelling like a tasty treat) they were returned to the hive where the workers continued to feed them.  And then their cells were capped with wax (by the workers, as normal), the larvae underwent metamorphosis and later emerged as adult bees...  which turned out to be...

Male!  In other words, they are diploid (XX like female workers) but are actually drones.  Having one version (but two copies) of the csd gene has the same effect as having only one copy - i.e. the bee is a male drone.  But there are subtle differences.  They are larger, heavier and have smaller testes.  That last point is important - it means that the drones are, effectively, sterile.  It is theoretically possible to inseminate a queen with diploid (XX) drone sperm to produced triploid (XXX - wowzers!) bees.  But in practice it hasn't been achieved due the the extremely low sperm count of the diploid drones.

So there you have it - a haploid (Xo) bee will be a normal drone.  A diploid (XX), csd-heterozygous bee will be a worker.  And a diploid (XX), csd-homozygous bee will theoretically grow up to be a fat, sterile drone (but will actually be eaten by his sisters just after he hatches).

I'll leave you with one final fun fact.  We've said that there are around 20-25 different alleles of the csd gene.  Interestingly, a queen bee will mate with roughly 20-25 males before she starts laying.  Co-incidence?  I suspect not - it seems that bee mating behaviour has evolved to try to maximise the number of different csd genes, and therefore minimise or eliminate the production of diploid drones in the hive.  Isn't that rather clever?

2017 Bee Visits for Widcome West Residents

I've now set up the calendar of visits for 2017.  So, if you're a resident of the Widcome West area, why not come along and see the hives for yourself?  You'll get to see inside a beehive, hold a frame of honeycomb, and maybe - if you have sharp eyes - you'll spot the queen!

There are a few things you need to know first - all of which are explained on this Information Sheet.

When you're ready, sign up to one of the sessions by clicking this link:  http://tinyurl.com/Bees2017

What a Difference a Year Makes

Yesterday was very exciting - the first day this year that it was warm enough to open up my hives!  Here's an obligatory action shot:

Both hives are doing really well and are very busy.  To compare with last year, here's what both the hives looked like in early May 2016:

... and this was Caroline's hive yesterday:

As you can see, there are lots more bees!  In fact, Caroline's hive is so busy, I had to put another box of frames (super) on to give them more space.  This is the first time I've ever had to add a super to a hive during the first inspection of the year.  It could be a bumper crop this year...!

About... Drones

Science warning:  this post contains actual science.  You have been warned...

Adult themes:  this post contains stuff about sex.  If you're a teenage boy, this will be considerably less exciting than it sounds...

Bees are male and female.  But whenever you see a honey bee, it will almost certainly be a worker bee, and they are all female.  Also, they are sort-of infertile (but not completely, as I'll explain later).

Drones are the males.  And they are most definitely not workers - in fact they don't forage, and don't do any work inside the hive.  They are so lazy that they expect the (female) worker bees to feed them.  In fact, they really only have one purpose - sexy time with a queen bee.

Before we get onto that, it's worth looking at the physiology (and a bit of biology) of the drone.  Firstly, a picture:

They're a little larger than worker bees, and the abdomen is rounder at the end.  This is because they don't have a sting.  Drones also have a larger thorax, to accommodate bigger wing muscles.  Although drones are lazy, they need to be powerful and fast flyers.

The other notable characteristic is a drone's eyes - they are much bigger than a worker bee's eyes, and cover almost the whole head.

So, why the differences?  Since a drone's only job is to try to mate with a queen, he needs to make sure he's good at it.  Drones will first locate a queen by the pheromones she emits.  He then needs to get to her as quickly as possible, as there will be other drones competing with him.  So - bigger wing muscles mean more speed.  Once the queen is in visible range, he uses his visual acuity to make the final approach - hence the big eyes.

But why no sting?  The tip of his abdomen, where the worker bees have their sting, is used for something else on a drone.  It's his bee boy bits.  y'know - his willy.  Actually the proper name for it is an "endophallus".  But it's still his willy, really.

The actual mating act is fairly brief - only a few seconds.  After which the drone departs.  Leaving his willy still stuck inside the queen!!!  Yep - it snaps off.  And, in case you're wondering - yes, that is fatal.  Does he die happy?  one can only hope...

Here's a picture of the underside of a (sadly deceased) drone.  The orange "blob" you can see is the remains of where his endophallus was torn out while mating:

So, that's the physiology.  The genetics are quite fun (you did read the science warning, didn't you?)  If you paid attention in biology class, you'll remember that humans have two sets of chromosomes - one set from their mother, and one set from their father.  And humans are female if they have two X chromosomes (XX), and male if they have an X and a Y (XY).

Bees are different.  Female bees (i.e. workers and queens) still have two sets of chromosomes - a maternal set and a paternal set.  But drones only have one set of chromosomes, all from their mother.  Weirdly, this means than male bees have no father.

This all happens as a consequence of the way fertilisation is done.  When a (poor, doomed) drone mates with a queen, he doesn't fertilise her eggs straight away.  Rather, his sperm is kept inside a special organ in her abdomen (called the spermathecal gland).  Then, each time she lays an egg, one sperm is released from the spermathecal gland to fertilise it - but only if it's to become a female worker.  It's possible for the queen to lay an egg and not release a sperm - in which case the egg will develop into a male drone.

The mechanism for producing fertilised (female) or unfertilised (male) eggs is interesting, because it's under the control of the workers.  Typically, they will make cells in the wax comb that are 5.2mm across.  When the queen lays the egg, her back legs will be on either side of the cell, so they will also be 5.2mm apart.  This particular distance triggers a reflex which releases the sperm.

If however, the workers make the cells slightly larger - around 6.5mm across - then the queen's legs are further apart.  Actually, they are too far apart to trigger the sperm reflex, so when she lays the egg, a sperm isn't released.  The unfertilised egg will have only one set of chromosomes - from the queen.  But in the weird world of bee sex, an unfertilised egg will still develop - it grows up to become a male drone.

I mentioned earlier that (female) worker bees are sort-of, but not completely infertile.  They're not capable of mating, as their "lady parts" aren't fully developed.  And normally they don't lay eggs - partly because the instinct to do so is suppressed by hormones that the queen produces.  However, they are capable of producing eggs, and every so often a worker bee will lay an egg.  These are normally dealt with fairly quickly, because there are worker bees who have the job of tidying up any stray eggs that have been laid by their sister workers.

However, in a hive which has lost its queen, and which also doesn't contain any developing queen cells, things get strange.  The hormone to suppress the laying instinct in workers is absent (because there's no queen to produce it).  So, worker bees start laying eggs - and more than can be tidied up.  Now, remember that none of these workers are capable of mating, so these are all unfertilised eggs.  So, they all develop into drones.  The hive is now in trouble - it's incapable of producing new workers, and instead is creating increasing numbers of drones.  Who will do the work in the hive?  The answer is - after around 6 weeks - nobody, because there will be no workers left.  The hive is doomed.

So, why does evolution allow such a suicidal mechanism to occur?  The drones are the answer.  Once the queen is lost, the hive can't produce workers so it is doomed anyway.  But the mass production of drones in the final few weeks means that the hive has increased its chances of its own bees mating with queens from nearby hives.  Even though these particular bees can't carry on, they can still propagate their genes to other hives, and those genes will build the future workers and drones of those neighbouring colonies.  Life finds a way!

Signs of Spring

The weather has been a little variable over the last few days, but there have been some sunny periods and the bees have been making the most of it.  Here they are, a couple of weeks ago, on their first busy day after winter:

This worker bee has found a nice flower to forage on, at our local garden centre:

Further afield, up in Birmingham, I took this photo of a bee foraging on some heather:

... And even further away, I was at a cactus garden in Lanzarote last week, and saw this solitary bee foraging on a cactus flower!

There's plenty of blossom out now, which means nectar and - more importantly - pollen.  The bees will be raising this year's first generation of new workers, and they need the protein from the pollen to feed the new brood.

If the weather gets warm enough by the end of next week, I may be able to open the hives for the first time and see how well the queens are laying.

About... Propolis

I mentioned propolis in a couple of blog entries last year, and you may have heard it mentioned in newspaper/magazine articles about bees.  One company is even adding it as an ingredient to shampoo(!)  So what exactly is it?

Well, from the beekeeper's point of view, it's a very sticky, general purpose brown "gunk" that bees use.  And it looks like this:

Propolis has a couple of important jobs in the hive:

Job one is as a disinfectant for brood cells.  One of the properties of propolis is that it inhibits the growth of pathogens.  Bees make use of this - every time a bee finishes the process of metamorphosis, and emerges for the first time as an adult bee, it leaves an empty cell ready to be re-used.  But before the queen lays a new egg in the cell, it needs to be "cleaned".  One of the worker bees (specifically a house bee - one of the younger bees which has not yet started foraging) enters the cell, and lines it with a thin layer of propolis.  This (partially) inhibits any pathogens passing through the wax into the cell, so after the queen has laid an egg and it hatches and starts to grow, it reduces the chances of the larva picking up any infections.

The second job is a general-purpose filler.  Bees don't like gaps in the hive walls, and they notice the small cracks between the stacked boxes that make up the hive.  So they tend to stick them together with propolis.  They also like to stick the frames together where they touch.  Basically, bees will fill any gap between two non-wax surfaces, that is less than 4mm, with propolis.  This is particularly important for the hive walls, as it prevents draughts and also prevents small intruders (such as wax moth) from entering the hive.

The third job is, again, related to hygiene.  Normally, if bees find something inside the hive that they don't like (for example, a dead wasp - quite possibly one that they've just killed) they'll carry it out through the hive entrance and dump it away from the hive.  This prevents mould and diseases, if it starts to decompose.  But sometimes, the thing will be too big to remove.  The best example I heard was a mouse that had got inside a hive (not one of mine) to try to hibernate over the winter.  For some reason, the mouse had died during the winter.  When the beekeeper came to open the hive in spring, the bees had been unable to remove the mouse from the hive because, of course, it was just too big.  So the bees had instead encased the dead mouse in a layer of propolis, and mummified it...!

So, where does propolis come from?  It's basically a mix of resins and wax.  Bees will use various sources of resins, but the most common are tree sap and the sticky stuff that is secreted by some leaf buds.

I've taken a couple of photographs so that you can get a sense of what propolis actually looks like when the bees are using it:

This is a strip of propolis that Miriam's bees added to the bottom corner of one of the brood frames.  They did this to a number of brood frames last summer.  I must admit, I'm not entirely sure what the function of this is, though I suspect it's related to airflow/ventilation in the hive.

This photo was taken from a solid board that I was using as a temporary hive floor last summer while I was doing some work on the hive stand.  I'm almost certain it's a wax-moth caterpillar which has been encased in propolis and mummified.  Normally, I'd expect the bees to kill the caterpillar and then remove it.  However, it may be that it was pupating and the cocoon was too difficult for the bees to remove, so they just covered it in propolis instead.

I was very lucky to get this photo - and very pleased!  It's a worker bee who has recently been out to collect resin for making propolis.  You can see that she has attached a blob of resin to each of her back legs (in the same place where she would carry pollen) so that she can bring it back to the hive.  After I've re-assembled the hive, she will mix the resin with wax to make propolis, and then probably use it to fill a crack between the boxes.