Beekeeping notes from Amanda Millar
Oxalic Acid Vapourisation:
Well, I have finally done it, after holding off for a while to see the results from other people. I am talking about Oxalic Acid vapourisation (OAV). I had been put off by a number of aspects all of which I have resolved to my satisfaction, and have assessed the treatment and results for the first couple of weeks. I will let you know in the spring how the colonies have fared over winter.
Not in any particular order, one of my reservations had been the risk to the operator of OA vapour blowing about and the need for respirator, goggles, gloves etc. However, a vapouriser mounted on a board inserted under the mesh floor, as designed by my bee-friend Tony, seems to have reduced the loss of fumes to the outside. This also makes it more efficient and the full dose reaches where it is supposed to. After Tony kindly demonstrated on the four Divisional colonies using his board, I built one to his design and used it last week without any obvious risk to me. It simply consists of a thick board (I used 21mm marine ply) in which we cut a recess to fit the Varrox heat wand, the board width was cut to the under-floor width of my narrowest floor (my floors have come from a range of manufacturers including home-made, so vary in width by as much as 1cm), and somewhat longer than the depth. The board is pushed hard over to one side and the gap at the other side, when used on my wider floors, is made up with a length of plywood pushed over to cover the gap, and I found very little vapour escaped. The rear of the board has a strip of wood which acts as a handhold and holds down the wand handle securely. The gap round the wand was filled with silicone sealer and a damp cloth (or length of sponge if you prefer) is draped over and stuffed into the gap at the back between the board and the mesh floor. See picture. December BBKA news also showed a picture of a vapourisor board, pg 403, but I think Tony's design is superior, with my wood strip to accommodate floors of different sizes, resulting in a much tighter seal and less vapour lost and little risk if you stand upwind when it is turned on. The wand has a long cable so you can operate the battery from a couple of metres away.
This board also overcame another reservation I had, which was the disturbance to the colony if the wand is inserted through the entrance as sometimes recommended. At the very least this would require mouse guard and/or entrance block to be removed, angry bees might fly around before the wand can be inserted and sealed off and at worst any bees landing on the very hot wand would be cooked or have their feet or wings burned off, especially if your cluster was hanging below the frames. This under-mesh board means that no bees will be harmed as the mesh floor keeps them clear of the direct heat. The entrance is blocked with sponge before starting so it was not necessary to wear a bee suit (unless it is warm enough for them to be flying before I managed to get to the apiary!). Only a tiny amount of the OA condensed on the mesh floor immediately above the heating element and this had fallen into the insert the next day. (See picture).
Varroa on board after Oxalic Acid Vap
Which brings me to my third reservation, I was unsure how safe it was for the bees, but having read several recent research papers it appears they are not harmed (with the correct dose) and were actually stronger in the spring than the controls and no queen loss was found. I dare say it is most affective if done when there is no brood as it only gets the phoretic mites, but as I would rather not disturb my bees so much at the turn of the year by scraping out any brood beforehand as LASI recommends, nor wait that long when I knew I had to deal with the varroa bomb which was taking too long to resolve with icing sugar. As I was pretty sure all but one had brood, but not wanting to disturb them by looking, I decided to treat three times at 5 day intervals as several researchers have done, to span one full mite brood cycle. It is supposed to be between 95-97% effective on phoretic mites.
My final reservation was the cost; needing a battery and heating element. Tony recommends a leisure or marine battery rather than a car if buying from new, and I already had a spare aircraft battery which seems to work. The better Varrox wand appears to be very expensive but keeping an eye on eBay might pay dividends.
To operate we inserted the board part way in, I weighed out the appropriate amount of OA related to volume of hive not number of bees. So the one on a single shallow had one 1g, those on two boxes or a brood and a half had 2 or 2.1g and those on 3 boxes had 2.3g. (I decided to err on the cautious side until I saw how it worked as the manufacturers recommend 2.3g without stating hive size) On all 2.5 mins was ample to vapourise all the OA, the battery was disconnected then it was left sealed up for a further 8 mins, to allow the OA to condense, before quickly replacing the board with a plastic insert with cloth block at the back, and 10 mins later I quickly removed the sponge from the entrance. Unfortunately, because of the glucose content in the ApiBioxal, this leaves a black deposit which needs to be scraped out between hives, perhaps one day we will be able to buy pure OA legally. It was 12 degrees C but overcast the first time and a dozen milled about the entrance but did not fly, the second time it was 7 degrees and none even appeared at the entrance, although I could hear a bit of fanning going on. The minimum recommended temperature is 4 degrees.
Oxalic Acid Treatment
The results so far are interesting, although I will not have the full cycle until next month. An example from the worst affected Divisional colony which had dropped 2500 over a period of 6 weeks during icing sugar dusting; they dropped 798 mites in the five days after the first OA treatment and a further 999 mites after the second dose. For most of the colonies treated the main drop seemed to come on the second day ie after 48 hours, with day one and three not far behind, fewer on day 4 although still significant but by day 5 the drop had fallen right off but not yet down to baseline. If there is brood present the mites will keep hatching, and every day there were pale juvenile mites, but the mother mite is only out of circulation from day 7 (one day before the bee larva is sealed over) until the bee hatches on day 21, ie 14 days later. Treating 3 times at 5 day intervals should expose them all at some point. I am very happy with the results so far and OAV is now going to be a regular part of my Integrated Pest Management.
Oxalic Acid Equipment
The weather has turned cold now and I shall have to put my woodpecker netting on as we have had one or two frosts. I have also put some strips of cellotex cut to fit the handhold rebates on my smaller colonies to improve the insulation properties of these thin-walled hives. The colonies on just one shallow box have a relatively larger surface area than the colonies on two or even three boxes. Better insulated walls will reduce the risk of isolation starvation and may reduce the amount of stores they need to eat to maintain their cluster temperature. I was surprised to find I had three cream crocus in flower on 10th December along with my Viburnham bodnantense and a few days later journeying west on the A272 saw several patches of (confused?) oil seed rape in flower so if the bees feel it is warm enough to venture forth they might find something to eat.
Research and news:
Trump is planning to reduce the size of two National Parks in Utah by 47% and 85% to favour his buddies in development and mining. These parks are hotspots for bee biodiversity, many of the 660 species, some of which have not been studied, will now be threatened as it is feared that habitat loss will quickly follow and many of the species lie outside the remaining protected area. Recent research in Vermont, USA has shown half of their 17 bumble bee species are endangered or extinct.
I hope you all have a very Happy, Restful Christmas