Last week, I treated all my colonies with oxalic acid before the winter solstice on 22nd December. After that, the queens will start laying again increasing production as the days lengthen. So, there is unlikely to be much brood just now and it is a good time to kill off the phoretic mites (those that are being carried around on worker bee bodies). In the past, I’ve trickled a solution of oxalic acid over the brood frames but I now prefer the less invasive method of heating the oxalic acid crystals and sublimating the bees. Trickled oxalic acid can kill any open brood present. When the crystals are heated they are converted to vapour which penetrates the hive and winter cluster of bees. The vapour kills the varroa but doesn’t harm the bees. However, I don’t sublimate when the ambient outside temperature is lower than 5 degrees Celsius because the bees will be a tighter cluster at low temperatures and the vapour may not penetrate the cluster suffiently.
Oxalic acid is dangerous for humans, and if vapour is inhaled it can reform as crystals and severely damage lungs. I never take chances and I wear an appropriate face mask that conforms to EN14387 standards. It has ABEK1 filters. Protective gloves are necessary.
Monitoring Varroa Infestions.
During the late spring and summer I use the sugar roll test as explained in a previous blog. I treat the colony if test results show more than 2% varroa in my sample of 300 bees. If varroa levels are high then I use formic acid. I remove the honey supers for the period of treatment. After removing the honey supers at the end of the season, I sublimate using oxalic acid if varroa levels have increased. I used to monitor the natural varroa drop regularily using the BeeBase varroa calculator to work out when treatment was needed. https://secure.fera.defra.gov.uk/beebase/public/BeeDiseases/varroaCalculator.cfm However, I now don’t believe that measuring the natural drop is as reliable as performing a sugar roll or alcohol wash test. So, in winter I routinely treat all colonies with oxalic acid sublimation since it it well tolerated by honey bees. I count dead varroa post-treatment but don’t base winter treatment on natural varroa drop.
More About Gas-Vap at Bridge Cottage.
Until Fred Mollison told me about his Gas-Vap, I’d been using a Varrox sublimator that hooked up to car/wheelchair battery and heated the oxalic acid crystals. It worked fine on wooden hives but it was impossible to insert into a poly hive so I worked from underneath the open mesh floor rather than through the front entrance. So, it may not have been so efficient. I’m really pleased with the Gas-Vap because it has an extension that fits well into the poly hive entrance without heating and melting the hive. Also, it is very quick in comparison with the Varrox method. The detachable caps get hot and I used a cloth to remove them to avoid melting my gloves. The cloth scorched so I shall find some heat resistant material to carry in my kit. The metal that fits onto the torch gets hot too so I will rest the Gas-Vap on a piece of wood on the landing boards of my poly hives in future.
Gas-Vap Review: A Year On, 18/01/21.
Where this gadget is excellent in terms of getting into hives with wasp deterrent floors, I’ve found that the attachments have fallen off the blowtorch once it heats up now. A year on and I am wondering if it is such good value. It is cheap in comparison with most other products but I need to rely on something that will be easy to manipulate and safe. The caps are difficult to remove sometimes without using pliers and the lighter fuel leaks out frequently when I am filling the torch. I’ve asked another beekeeper who tells me that the same thing happens for him, apart from the attachments falling off. He tells me that he there is a screw on the attachment of his kit which is not present on mine. I haven’t noticed the long nozzle blocking but my beekeeper friend has had to unblock his. A long wire should solve this.
If you are thinking of buying this product, it might be worth asking around and getting more feedback and opinions first. I know someone who has no complaints at all about it. Although I wear the correct PPE and mask, I don’t want to be exposed to any vapours at all. This can happen if the kit falls apart after the oxalic acid crystals have been heated and sublimated. I’ve contacted the manufacturer following my recent problems and I have been told that the latest models have an adjustable screw so this should not happen now.