13 March 2015

Dead colony and a WBC

A little while ago I was asked to help a local beekeeper look through a dead colony. They wanted to try to work out two things. First was reassurance that the colony hadn't died of foulbrood, secondly to, if possible, find out what had caused the colony to die - something that isn't always easy.

The colony was in a beautifully appointed cedar WBC - that's the double skinned hive designed by William Broughton Carr way back in the late 1800s. It is a design has stood the test of time, and is used by many British beekeepers.

Colony history, and weather
The queen was in her second year. The colony had been large and thriving going into autumn.

With the help and guidance of a more experienced beekeeper the colony had been treated with a thymol-based varroacide followed by a syrup feed and, around Christmas, had been trickled with oxalic acid.

Weather throughout the winter had been milder than average, but rain had left the local clay soil quite wet.

The hive had been 'hefted', the beekeeper believed there were still plenty of stores.

There had been some activity in early January, but following a short cold spell, none at all. The beekeeper had confirmed their worst fears, then sealed the hive entrance to prevent robbing.

On opening the hive the first thing that was obvious was a lot of faecal staining. All interior woodwork was badly marked - the inner faces of the lifts, the outer face of the hive and frame tops. The colony had clearly suffered from a bad case of diarrhoea/dysentery, which has many possible causes. Here's a quote from MAAREC
Factors leading to this situation include nosema disease, prolonged confinement during winter and early spring consumption of food with a high water content.
Colonies located in moist areas or areas with poor air drainage may often exhibit signs of dysentery.
To prevent dysentery, make sure hives are stocked with high-quality food and are well-ventilated.
If [autumn] feeding is necessary, be sure to do it early enough so that the bees can properly ripen their stores.
Hives should be rainproof and situated in a dry location. Good air circulation is important.
There is no effective treatment for dysentery.
Stores, comb, dead brood and dead bees
Having removed the combi crown/clearer board it was easy to see some newer frames because, even though they were stained with evidence of dysentery, their bright wood stood out amongst the darker coloured, older, frames. It meant nothing at that point.

We began the way most beekeepers begin an inspection, by removing frames closest to one outer wall of the box. The first two frames had a good amount of stores, but then there were the new-looking frames - which turned out to be foundation, undrawn foundation. Adjacent to these new frames, and towards the centre of the brood box, were the first corpses and dead brood - just one or two sealed worker cells in the lower third of the frame along with some dead open brood.

There were more dead bees on the next four frames, a small-looking cluster about 5 inches across, in the upper corner and well away from the small area of dead brood which was, at its' largest, about 3 1/2" (8-9cm) across. All sealed cells were worker, so not a drone-laying queen.

The dead bees were clinging to the comb three or four deep, the innermost ones were so far into the cells that the only thing visible was a hint of their sting - an indication of desperate bees, trying to scrape food from the linings of the cells but dying in situ due to a combination of starvation and cold.

The queen was easily identified by the painted mark on her thorax - she was exactly where she should have been, protected at the centre of the cluster. A beautiful little thing but barely larger than the dead workers because she would have slowly starved to death, and post-mortem dehydration causes shrinking. She is resting in the freezer, to be used as a swarm lure later in the season.

To the other side of the extinct brood area was another undrawn frame of foundation, with a further well-filled frame of sealed stores between it and the outer wall of the brood box.

All frames were badly splattered with faecal matter.

The hive floor was covered with a layer of corpses perhaps two inches deep. These bees would have fallen away from the cluster as they died, hence the appearance of a small cluster. The number indicated quite a large colony. None were mildewed, although a fine dust arose when these  bees were disturbed.

Brood and disease
The bees had clustered on the dwindling stores, abandoning the brood which subsequently chilled. The brood pattern extended across 5 frames.

There were a few cells of chalkbrood, which can be an indicator of a damp site, and a few dead, brown, larvae - EFB negative.

Cells with hollow and/or chewed cappings were probed with matchsticks. Some contained fully developed bees whilst in others there was a dark liquid which didn't rope - which could have been because these cell contents had absorbed atmospheric moisture or these larvae had died during an early stage of metamorphosis. Testing proved negative for AFB.

Hive setup
All roof vents on the outer shell of the WBC were blocked.

The Porter Bee Escape holes in the combi crown/clearer board were sealed with plastic tape.

The varroa-counting tray was in place.

Autumn foundation
The beekeeper had inserted new frames of foundation adjacent to the brood nest as advised by a local, more experienced, beekeeper.

A number of factors contributed to the loss of this colony but we concluded that the bees were stressed by dysentery exacerbated by wet conditions, and had became isolated from their stores during a cold spell.

A WBC is a special type of hive that needs its' own management. It is:-
  • double-skinned, with 'lifts' outside the hive, which means that the brood box is generally well-protected from the elements,
  • almost always on a low stand, meaning that the floor is only a three or four inches (8-10cm) above the ground.*
Neither of the above are a problem on well drained soil, but siting a WBC on wet or waterlogged soil can mean that the air gap between the lifts and brood box will fill with damp, cold, air - hence the cone vents in the roof, which are intended to draw stale air up and away.

The walls of many WBC brood boxes and supers are, these days, made of thinner timber than those of a standard national because manufacturers reason that there is no need to use thicker, and more expensive, wood in a double-skinned hive. However, if those thin walls - which encompass a warm colony of bees - are surrounded by damp air the result can be significant levels of condensation, which in turn can cause mildew and mould to grow on both the inner surface of the lifts and the outer faces of the hive.

Excessive condensation can saturate the thin walls of both brood boxes and supers.

*The WBC hive can be placed on bearers, blocks or bricks to raise it above stale air, but some beekeepers are reluctant to do this because it is not pretty and the extra height can make the hive harder to inspect when supers are being used.

Varroa tray
Should, ideally, be in place only when varroa needs to be counted.

Leaving it in below the mesh floor permanently can detrimentally affect ventilation and will also prevent the bees 'policing' (eating) wax moth eggs and larvae.

It had been wet, the soil waterlogged. The colony was living only a few inches above wet ground in a poorly ventilated, damp, container.

Refer the above hive setup to MAAREC's description of factors causing dysentery and we can see why good ventilation is so important for a WBC, why the WBC's cone vents should never be blocked, why it may be wise to improve land drainage close to low-level hives.

Sick bees are more likely to die early; dysentery causes metabolic stress.

Autumn comb building -
 - can fail if the timing is wrong. If so then the undrawn frames should be either removed or moved to the outer edges of the brood box otherwise, as happened here, the blank frames can block access to stores - more especially in a colony that's already stressed.

Top insulation
I make no secret of the fact that I am a fan of well-insulated hives, am aware that it is becoming popular to add top insulation and leave it in place throughout the year. Doing so is entirely up to the beekeeper - and whether it's needed inside a WBC is open to debate because, unless the WBC hive is on dry ground, stale air between the lifts and thin brood boxes can increase the risk of mould growth, which isn't healthy.

'Hefting' -
- is judging the weight of an overwintering colony by lifting the back of the hive, or by keeping the hive on a set of scales. It is only ever a rough guide, and has to be combined with knowing where the bees are, and ensuring that they are able to access their stores.

Winter stores and space for laying
At each inspection throughout the year the beekeeper should make sure the colony has sufficient stores to last until the next inspection. In autumn this means making sure the colony has enough food to last through to Spring without beekeeper intervention. It can be a bit of a guessing game, but the average colony will need 40-45lbs (c.20kg) of stores to successfully overwinter.

To achieve this many beekeepers will feed a thick (2:1 sugar:water) syrup in early autumn, this strong solution is easier to store at that time of year because there is less water to evaporate. Some will add a slab of fondant instead - either on the top bars, directly above a queen excluder or above the hole in a feeder board - and check the level by looking through the crownboard during the colder months. Some will do no more than rely on leaving brood nest stores intact, and trust the bees will know what to do with the late ivy nectar flow.

The belt and braces approach (which I don't advocate) is to feed both syrup and fondant. They first give a good syrup feed and then add a pack of fondant as described above. If this is done it's very important to check the situation in Spring to make sure the queen doesn't run out of space to lay, otherwise the colony could abscond and leave behind a box full of stores, eggs, larvae and sealed brood - and a very puzzled beekeeper.

Isolation starvation and 'dummying down'
Under normal circumstances a large colony is unlikely to become isolated, because some of the winter cluster will always be in contact with stores - which can then be transferred from bee to bee.

A small colony in a large brood box is more likely to become isolated to one or other side of the chamber, unable to bridge a gap of empty frames to access stores close to the opposite wall of the hive. The solution is to, as part of winter preparation, transfer a small colony to a nuc box, or to dummy down onto six frames in a full-size brood box. Both actions should lessen the risk of isolation.

And finally ...
The beekeeper didn't feel right about closing up all ventilation and wasn't sure about adding the frames of foundation adjacent to the brood, but didn't want to offend the 'older and wiser' beekeeper and so did as advised.

If they had followed this 'gut feeling' or 'instinct', based on nothing more than, "It felt wrong," then perhaps the outcome might have been different.


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