Varroa treatment for honeybees with oxalic acid

In my previous post I mentioned one of the methods I use to get rid of varroa mites; sugar syrup with oxalic acid. I combine two kinds of treatment, both are appropriate at different times of the year. I currently don’t use any other chemical (synthetic or natural) than oxalic acid. Oxalic acid occurs in nature, in rhubarb for example. Although I wouldn’t hope rhubarb tea will do anything for your bees.

The recipe I use to prepare the syrup is:

  • 500g white sugar,
  • 500g distilled water,
  • 33g of oxalic acid crystals and
  • 5ml of 98% ethanol.

I begin by mixing the water and sugar and putting them on a low heat, until the sugar is dissolved. I don’t add the oxalic acid until I’m outside with the sugar water in a pot. Let the mixture cool down before adding to the oxalic acid. The reason why I take care not to allow oxalic acid to heat up much, is because it’s dangerous to inhale it (ingesting it in a concentrated form is toxic) and heating it up is the way to turn it into gas. It’s very unlikely that I’ll get it hot enough to do that on a stove, mixed in water, but it’s best to be extra careful.

 

I pour the syrup over the bees who are mostly gathered in the brood nest. I spray them between the frames. If you have a bottle like the one I’m using, just keep a steady stream pouring out. If you want to do this with a syringe, 10ml per ‘street’, in between the frames should be enough. The bees will lick themselves and others clean, thereby ingesting the syrup and oxalic acid. Mites that are attached to the bees who ingest this will have to let go of the bee and fall down onto the bottom board.

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After I’ve done all my hives, I pour 5ml of 98% ethanol in the remaining mixture. This should prevent it from fermenting before you use it again next month. I use this mixture once every month. You shouldn’t treat hives when they have honey stores you might want to harvest. Remove these before you treat the hive. You should also remove the bottom board out of the hive. I’ve forgotten to do that a couple of times and I can tell you that it gets you a lot of cleaning up to do afterwards.

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Powerful development in spring
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