I’ve just come back from a weekend course at the British Beekeepers Association in Warwickshire. I spent two days in the company of two Master Beekeepers, covering the syllabus for the ‘General Husbandry’ exam which – if I decide to do it this year – will put me through my beekeeping paces.

Exam preparation aside, it was great to pick up so many practical tips from the tutors. Simple but essential things like the right way to pick up queens; how to shake combs with queen cells on them (yes, it is possible) and the right way to give a colony a test comb when you suspect it might be queenless. Plus many more nuggets of information that you only get from beekeepers with a life-time of experience.

Right now I am still thinking about our discussions on the subject of oxalic acid. Having been concerned that I left my oxalic acid treatments too late, I was reminded by the tutors that oxalic acid isn’t just for the broodless periods of Christmas and New Year . . .

Why treat with oxalic acid?

Treating colonies for varroa with oxalic acid sublimation is now pretty standard where I live. When I started beekeeping ten years ago, the norm was to do a ‘trickle’ (or spray) treatment directly over the bees in the cluster during the broodless period roughly between Christmas and New Year.

But then the research done by Professor Ratnieks and his team at the Laboratory of Apiculture and Social Insects (LASI) at the University of Sussex demonstrated that it is more effective to sublimate the crystals (vaporise them using heat).

The LASI research said that 2.25g of oxalic acid applied to broodless winter colonies via sublimation killed 97% of the varroa. Furthermore, these colonies then had 20% more brood in spring than those treated via trickle or spraying, or untreated colonies.

Add to this the fact that you don’t need to disturb colonies when you treat with sublimation, and it seems a no-brainer . . .

From the ridiculous to the sublimation

I have a confession: I get put off by the need for extra equipment and by anything that sounds complicated.  And at first the need for car batteries, cables etc. put me off trying sublimation.  Trickle treatments continued to be the norm in my apiary – and there’s nothing wrong with that, they do work in knocking back varroa levels.

However this year a friend offered to lend me a Sublimox vaporiser. This was an opportunity to try a piece of kit that I couldn’t say no to.

Plenty has been written about this device elsewhere.  Suffice to say that it is compact and efficient to work with.  You can hold it in one hand.  The dose of oxalic acid vaporises when it comes into contact with an integrated heated plate.  You simply invert the device and put the ‘spout’ in the hive entrance, and it administers the does quickly and efficiently.

Sublimox ready for use

Using the Sublimox did make the process of treating all my colonies very quick and easy. There was no waiting around for it to heat up. Even I could handle the car battery/power set up. With a long extension cable I could leave the battery and adaptor in my car and run the power down to my apiary without any fuss. It was brilliant.

He’s wearing a safety mask, you just can’t see it in this photo

If you get the opportunity to try this lovely bee toy, be aware that you absolutely must have a proper full-face mask with breathing filter, because when you stand at the hive entrance and administer the vapour, you are bound to come into contact with some of it. This is very important because oxalic acid is highly toxic to humans.

What about the results of the sublimation? I had a hefty mite drop after each treatment, no surprise there. But as I said earlier, I’ve been wondering if it could have been even higher if I’d treated earlier, when there would have been less brood. I assume so.

Oxalic acid: not just for Christmas

Good news . . . oxalic acid treatments are affective at any time the bees are in a broodless state.

This is because oxalic acid acts on the mites that are attached to the adult bees (the mites in the phoretic stage of their lifecycle), rather than the mites in brood. It is thought that the acid burns their mouthparts, causing them to drop off the bees and out of the hive through the open mesh floor.

Phoretic mites on adult bees

So if you’re planning shook swarms, or swarm control that involves separating the queen and flying bees from the brood and nurse bees, it’s a good opportunity to administer another treatment. I think this will make a huge difference to my own management of varroa throughout the year.

A word of caution about using oxalic acid

Interestingly, oxalic acid has been used by beekeepers to reduce varroa levels for years. It is a naturally-occurring organic acid. But that doesn’t mean it isn’t highly dangerous to work with, requiring precautions and care.

Also, unless you use Api-bioxal (see below), the crystals used in sublimation treatments are not an ‘approved medicine’ in the UK for use with honeybees.

This is important to know about, especially if you sell your honey. There is the potential for any treatment to leave a residue in honey or in other hive products intended for human consumption.  Obviously there was no honey on my hives at the time of treatment.

Api-Bioxal, is the only oxalic acid-based treatment that has been approved for use in the UK for trickle or sublimation (if you do use a Sublimox be aware that you can’t use Api-Bioxal in it because it has sugar in it, and it will mess up your lovely new toy).

You can of course buy oxalic acid crystals in the di-hydrate form and use those. I did and they are slightly cheaper. But when you buy your di-hydrate oxalic crystals and notice that it says ‘hive cleaner’ on the packaging, it’s because they aren’t approved for use as a varroa treatment and legally can only be sold for cleaning purposes.

For chapter and verse about licenced treatments search the National Bee Unit website for its leaflet on bee medicines.

And for further information about how to prepare oxalic acid, see The Apiarist’s blog.

Ultimately the choice as to how you treat your bees is yours. But don’t let indecision stop you treating your bees per se. In my opinion, anything we can do to keep varroa levels down without resorting to chemicals is a good thing.

So I’ll definitely be sublimating again. I just hope I can borrow that Sublimox. If not, it may be back to trickling for me!