Spring Varroa Treatment

We monitor our hives for varroa several times each year, and treat as appropriate, depending on the level of infestation, and the time of year - part of our Integrated Pest Management (IPM) approach.

This year, following a mild winter, we have higher levels of varroa mites in our colonies than we would like (BeeBase Varroa Calculator). Normally a treatment in spring wouldn't be necessary, but we had no option but to treat now - since varroa, like the bees will grow exponentially if left unchecked at this time of year, which could severely hinder colonies later in the year.

At this time of year, there are only a few treatments available - oxalic acid, or drone brood removal/queen trapping. It is still a little early for brood management/drone brood development in our colonies, so this wasn't an option. It is also still too cold to use MAQS strips (formic acid). (For full information on recommended treatments through the year, see: DEFRA: Managing Varroa).

Oxalic is usually not recommended for use outside of winter, since it has no effect on muites in sealed brood frames (which are absent in winter months). Nevertheless, while the effectiveness is reduced, it will still have a strong effect on any phoretic mites within the colony.

There are 2 methods of application of oxalic acid - trickle, or sublimation. The former involves trickling an oxalic-sugar-syrup mixture over the bees - the latter involvbes using a heating device to cause the oxalic acid to sublimate, and then condense on the bees. While we have used trickling in previous years for it's simplicity, recent research at LASI shows that sublimation is actually better for the bees. So we opted for that approach.

It is also worth highlighting that while we are referring to the active substance oxalic acid here - there is an approved version marketed under the name 'ApiBioxal', which we are legally required to use. (Previously, use of pure oxalic was allowed, but now there is a regulated version, this is banned). There are some disadvantages to Apibioxal - namely the cost (around 70p per hive, versus 2p per hive with pure oxalic), and the fact that apiBioxal contains sugars, which burn onto the vaporiser tool, leaving a gummy residue which has to be cleaned off between hives. It will be interesting to see how many apiaries (which have previously treated with pure oxalic will either stop doing so, or stop recording that they are doing so, to avoid prosecution. As such, any signs that varroa is staying well-managed with a drop in winter mite treatments should be taken with a grain of salt over the coming years.

Hopefully, even with a reduction in efficiency, the total mite burden on the hives will be dramatically reduced, and we will be able to fall back to a normal treatment regime (winter ApiBioxal, MAQS as a summer 'backup', and the usual biomechanical methods (open-mesh floor, drone brood removal, etc).