When I looked out of the bathroom window this morning I could just see the tops of the trees through the fog. I went out to open the hen house armed with a jug of hot water to de-ice their galvanised drinker, and found I didn't need it and needn't have set the glasshouse heaters last night for it was not actually freezing. There was still a thick crust of ice on the pond, and when I looked out after giving the cats their breakfast I saw Mr Fluffy and Mr Fidget sliding about on it. I tried to coax them off, but Mr Fluffy thought that running on the spot was a great game. It was still too thick for them to fall through, but before the end of the afternoon the Systems Administrator broke it up with a stake.
The sun soon burnt off the mist and had real warmth in it while there was no wind at all, so I decided it was time to dose the bees for varroa. I'd normally have aimed to do this between Christmas and the New Year, since you want to pick a time when there is as little brood as possible in the hive. The varroa mites spend some of their life cycle inside the capped brood cells with the bee larvae, and any that are sealed away when you apply the treatment will be protected by their wax covering. I'd been in no fit state to mess around with bees then, though, and for the past few days it has been so savagely cold I didn't want to open the hives at all, but today was perfect. I didn't want it to be too warm, since you are supposed to trickle a measured amount of treatment over each seam of bees, meaning you want them to be clustered together into a nice tight ball. If they break the cluster and start wandering all over the place you don;t know where to direct the treatment, and it's important not to overdose them.
When I started beekeeping it was not long since the varroa mite had arrived in the UK, and the recommended course of treatment was to hang strips impregnated with pyrethroids inside the beehive. The pyrethroids were more lethal to the mites than the bees, and so a good measure of control was achieved. Over the next few years the mites developed drug resistance, which was pretty much inevitable. If you try to eradicate a pest chemically using only one class of chemicals, and beekeepers only had one class of chemical, any individual pests that happen to have an unusually high tolerance to that chemical will survive and breed, and in due course you will have selectively bred a resistant population of pests. That is why at Writtle we were taught that a basic principle if using chemical crop protection is to rotate between different classes of chemical treatment so that any pests that survive the first round will with any luck be done for in a subsequent one
There was a suggestion when resistance began to appear that beekeepers were partly to blame for using the pyrethroid strips incorrectly, leaving them in the hives for too long or reusing them and so exposing the varroa to sublethal doses that allowed them to build up resistance, but I'm not sure that follows. Even if an individual mite could develop higher tolerance through prolonged low exposure, like a human being building up tolerance to arsenic or alcohol, would it be heritable? Either way, I was always careful to use my strips properly because I was brought up to be respectful of medicines, but the time came when there was no point in applying them any more.
No other single treatment has been as effective as the pyrethroid strips used to be. I tried applying trays of a thymol based gel for a couple of seasons, the idea being that the thymol was more objectionable to the mites than the bees, but gave up, partly because some friends who used them reported that their bees disliked it so much they had simply absconded, and partly because it meant I had to change the hive floors specially for the treatment. When I started beekeeping hives came with solid wooden floors, then somebody hit on the notion that if you used a fairly fine wire mesh then any varroa mites that fell off the bees would drop through the floor and out of the hive before they could climb back on. The open mesh floor would not offer total control, but could help as part of an integrated pest management system, which has been the buzzword for a few years now in beekeeping as well as horticulture.
You can't use a thymol gel varroa treatment on an open mesh floor, though, because the fumes need to build up in the hive as the gel evaporates and as they are heavier than air they would sink out through the floor. I leave my bees on the open mesh floors all year round, after some initial uncertainty about whether it would be too cold in the winter, and have found that works fine, if anything better than the solid floor because condensation can't collect in puddles inside the hive. Damp is worse for bees than cold. My general view on beehives after many years of beekeeping is that I don't pull them around and take them apart more than I have to. It stresses the bees, and a stressed colony is a disease prone and unproductive colony. And changing floors is a fiddle. The brood box is heavy to lift when full of stores, and once the bees start coming out of the bottom it is very difficult to put it down on its new floor without squashing some of them. And getting the entrance block into the gap between floor and brood box is another fiddle where it is only too easy to squash your bees. Sometimes you want to look at the floor, to check for problems, but I didn't want to have to change every floor in the apiary and then change them back each time I treated for varroa.
For the past few years I've been trickling a solution of oxalic acid over the bees. The legal status of oxalic acid as a veterinary medicine was slightly obscure, but the big beekeeping suppliers sold it and the bee inspectors turned a blind eye or decided the ambiguity in the beekeepers' favour, because we had to treat the bees with something and there wasn't a lot out there. Now there is a licenced treatment available in the UK, called Api-Bioxal, and a government email arrived before Christmas warning that it was illegal to use oxalic acid and that we must buy the authorised product. That's what I did, being one of those people who always reads the leaflet and finishes courses of antibiotics. The Api-Bioxal crystals are dissolved in sugar syrup and trickled over the bees at the rate of five millilitres per seam of bees, which means all the bees huddled together between two adjacent combs, at a maximum of ten per hive, and the fastest way to do it so as to not have the hive open for longer than necessary is to fill ten plastic syringes before you open the hive and use as many as you need to. I forgot to buy any syringes when I ordered the chemical because I was feeling distinctly sub par, but fortunately we had some in the kitchen drawer, a legacy of some past pet's illness, and if we hadn't then the SA has them for railway modelling.
I feel pretty irritated, though, because I read the instructions on the back of the packet several times very carefully to make sure I applied it correctly, and as far as I can see the active ingredient is hydrated oxalic acid, which is according to Wikipedia a commonly encountered form. Oxalic acid is not a new active molecule, on the contrary it has been around for millennia. You will find it in rhubarb leaves and spinach. The Systems Administrator lent me a pair of small scales capable of measuring accurately to the last fraction of a gramme, because I wanted to split the contents of the packet instead of wasting sugar making up a full half litre of treatment when I only wanted a maximum of two hundred millilitres, and as I opened the packet I remarked that according to the instructions I ought to be wearing gloves and a protective mask, and the SA said oxalic acid wasn't that toxic, he used to use it to scrub rust stains off the boat.
And it's true, it is still sold for that purpose. A kilo of oxalic acid sold as a wood bleach will set you back £11.75 including VAT. The smallest packet I could buy in the form licenced as Api-Bioxal cost £10.99 for 35 grammes. That was sufficient to treat ten hives, which was twice as much as I wanted and more than most hobby beekeepers would need. When I was treasurer of my local beekeeping association I handled the bee disease insurance premiums, and so saw how many hives each member expected to have during the year. Relatively few had more than five, and a lot didn't admit to more than three. The instructions on the Api-Bioxal packet said that it was good until 2019 unopened, but once opened it had a shelf life of only three months, so it's not as though anybody can save the other half or two thirds of the packet until the next season. And not everybody has scales capable of weighing to the last gramme. Why can't the manufacturers at least break it down into smaller ten gramme sachets so that customers don't have to open the whole packet at once? I would not dream of trying to treat my bees with wood bleach, but I do feel that hobby beekeepers are being mugged, forced to pay over the odds for a chemical that's been around for donkey's years and to buy it in uneconomically large sizes.