Sublimation
January is a time of year when it is difficult to do anything for your bees due to low temperatures. However, it could be worth putting the inspection board in for a week and seeing what sort of ‘dead mite drop’ you are getting. Bad news if you are getting ten or more. That is because those dead varroa you are seeing on your inspection board are what are called a ‘natural dead mite drop’. They are the indication that there are a lot of live phoretic mites on the bees.

What does this mean for your colony?
In early January in mild winters (so far, we have had a very mild winter) colonies start raising brood after a short brood break between mid-December to early January. If you have the inspection board in you will see debris falling out the hive where the bees have been uncapping their honey. They have been doing this in order to raise the temperature in the brood nest. It is the honey that is fuelling this rise in temperature and allowing new young bees to be raised. However, at this time of year the brood nest is a small one and this can be where the problem is. If you have a heavy varroa load on the bees, and the Queen starts to come into lay again, what happens? The female varroa mites have not been able to breed for a month or so, and so when young larvae are about to be capped the female varroa will dive into the cells, perhaps several breeding female varroa mites to each cell. The implication of this is that the feeding site established on the developing pupa will be being used by the offspring of several mites and the consequent damage to the pupa will be detrimental, and she will emerge with damaged wings soon to be removed by her sisters as no better than a piece of expendable debris.

But I can hear Peter Coxon saying to me that he no longer treats for varroa and that the bees are still doing well. Probably if you have a super strong colony, they will cope but you will have fewer bees in the Spring. The danger will be for smaller units which cannot afford to raise damaged bees that cannot contribute to the life of the colony. It may also be that if you go for no treatment over a number of years colonies will just gradually get weaker. Beekeepers who say they are not treating are probably controlling varroa by other methods. Drone brood uncapping for instance. Or as Andrew Vestrini does at Mount Camphill letting the bees swarm, and then collecting the swarms (swarms leave a lot of varroa behind in the brood box). Or as Colin Stocks does, religiously dusting his bees with icing sugar every week in the summer months (icing sugar knocks off varroa mites).Or as Stuart Goddard does, using ‘hive alive’ on the colony and spraying them with it (this damages the varroa and they fall off).

There is, however, another possibility. Norman Beresford, Chris Chandler and some others in the association have for the last couple of year sublimated their bees. Professor Ratnicks at LASI (laboratory of apiculture and social insects at Sussex university) recommends using a vaporiser which you attach to a car battery. In the vaporiser you place oxalic acid crystals and this when heated becomes a cloud of smoke. This is placed underneath the hive (I hope my pictures will show you how this is done) and this cloud of smoke knocks off the phoretic mites on the bees. Boy is it effective. Be warned however. It is nasty stuff and if, perchance, you breathe in any of the smoke you will seriously damage your lungs. It is not difficult to do but hive types vary, and this may make it more complicated for some to do. I have wooden deep nationals i.e. 14*12 brood boxes.
Below is a picture of some of the brood from hives that were treated 3 times with oxalic acid by sublimation. I did this at the trout farm 2 winters ago. The resultant brood frames the following summer were great with few gaps (this particular picture was of a buckfast colony).

Brood frame

It seems incredible but sublimating oxalic acid does not seem to harm the bees very much and it is quite possible to do it 3 times with no ill effect (not the case if you use the trickle method). The reason for doing it three times is in order to cover a brood cycle. The smoke cannot penetrate a capped cell and if there are varroa mites breeding within the cells (and there will be) they will emerge to reinfect the bees. Hence sublimating the bees three times. Norman says you do the sublimation at 5-day intervals. Although this does not add up to 21 (a brood cycle) these are the time intervals that need to be respected otherwise it is possible that some female varroa will be able to get into a capped cell without having been dosed with your oxalic acid smoke. And then these mites would reinfect the colony. And this would destroy the whole point of the exercise!

Steve with mask

Back of hive and vaporiser

Inspection board and dead mites

What you need.
• A car battery
• A vaporiser
• Oxalic acid crystals (Apibioxal is the licensed product and costs £10 for a sachet to treat 10 colonies. You can see I used something else but of course I am not telling you about that and you did not hear it from me - cost about 2p per colony)
• Sponges to block entrances and the backs of the hive
• A watch to time the process
• A mask to prevent inhalation of fumes (use your common sense and don’t go near the hive when smoke is emerging)
• A bucket of water (after each treatment, cool down the vaporiser in the water ; not a good idea to put oxalic acid crystals on a hot vaporiser thereby creating noxious vapour immediately)
• An inspection board or boards
• Goggles

Oxalic acid crystals

Inspection board

How to proceed
• Introduce wooden inspection board into hive upside down
• Block front entrance of hive with a sponge
• Place a sponge in the back of hive as shown in photo
• Place 1/2 a teaspoon oxalic acid crystals onto vaporiser
• Introduce vaporiser into gap between inspection board and the open mesh floor
• Stuff sponge around stem of vaporiser to seal up the back of hive
• Connect leads of battery to vaporiser
• Stand back and leave for three minutes (after 2 minutes smoke will start to leak out)
• Disconnect and leave for a further 1minute
• Remove vaporiser and dunk in water
• Leave hive sealed up for 10-15 minutes
• Remove all sponges
• Examine inspection board but leave in place to better monitor varroa drop
Malcolm Wilkie 16th January 2018