Rhubarb, Rhubarb

Varroa - Courtesy Of The Animal and Plant Health Agency (APHA) Crown Copyright
Varroa Mites On A Bee – Courtesy Of The Animal and Plant Health Agency (APHA) Crown Copyright

Beekeepers are getting hot under the collar about an academic study which compares the different methods of applying oxalic acid (derived from rhubarb leaves) to a hive to combat the pernicious varroa mite. Oh yes.

It seems a little inopportune of Professor Francis Ratnieks, head of Laboratory of Apiculture and Social Insects (LASI) at the University of Sussex to have published a research paper unequivocally recommending oxalic acid (OA) sublimation to the exclusion of other methods of applying this chemical in the week before Christmas.

Let me explain: sublimation is when OA is vapourised inside the hive using an electrically heated tool. Professor Ratnieks’ team has found that, on grounds of both efficacy and bee-health, it  is preferable to the pair of other application methods and to say that beekeepers should cease using the other two methods (“trickling” and “spraying”, in which a dilute solution of OA is used) as they are harmful to the bees and less effective at killing the varroa mite. But still a lot better than not treating the bees.

Here is a video of me “trickling” Abbey Hive on Christmas Day 2014. And everyone agrees that the ideal period for applying OA is around today’s winter solstice, when British hives should normally be broodless, meaning that the varroa mites are all to be found on the bees themselves, and vulnerable to the effect of OA. (The mild weather this year may mean that hives are not currently taking a brood break, so the mites may shelter away from the OA, in the sealed brood cells, where they reproduce. Beekeeping isn’t quite as simple as it looks.)

5 Varroa Mites Killed By Oxalic Acid Trickle
5 Varroa Mites Killed By Oxalic Acid Trickle

While I agree that sublimation is the best method of introducing OA to a hive, I’m against setting this cat amongst the beekeeping pigeons at this crucial time of year for treating bees against the parasitic varroa mite. Varroa is by far the biggest killer of British bees. (Whatever 38 Degrees’ neonicotinoids petition may have led you to believe to the contrary).

I offer this practical advice to beekeepers:

  • The important thing for your bees is that you treat them with some form of OA in the next two or three weeks (when they are most likely to be broodless). Do not be put off trickling or spraying in late 2015 or early 2016 by this article if you already have purchased the OA trickling or spraying products!
  • The important thing for human beings is to be aware that inhalation (or absorption through the skin) of OA is extremely toxic and that sublimation should be ideally performed by practiced people taking proper precations, not raw recruits.

Yes, when you use OA spray or diluted liquid, you should expect a few bees to be killed by direct contact with it. I always say that if you have dead bees outside your hive, it means that you have bees alive inside the hive (“undertaker” bees carry out the dead bees from natural causes or from a soaking with OA). On the other hand, no dead bees outside the hive can mean that there are no bees alive inside the hive. Not one for the squeamish, but a good rule of thumb nonetheless.

Rhubarb Leaves
Rhubarb, Rhubarb

So do not be deflected from applying rhubarb acid onto your bees in next few weeks – whichever way you do it. And consider sublimation next year.

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