Yes, I’m going to go on about varroa mites again. What percentage of beekeepers carry out an alcohol wash on their colonies to understand the mite loads of those colonies? I reckon it’s a low number, maybe below 5%. A small, but possibly growing slice of the people who don’t monitor with an alcohol wash, also think that being a non-treater is a noble pursuit. In a possible contrarian way, I am considering treating my bees three times per year instead of two.
Natural Mite Drop
Incidentally, monitoring the natural mite drop onto a board under a mesh floor has been shown to be a less than ideal way of tracking the number of mites in a colony. Most of my floors are not made of mesh, so that approach is irrelevant anyway. However, the ‘counting fallen mites on a board’ method is good at seeing how many mites you had, after treatment with a varroacide. If you apply a treatment, and numerous mites fall onto the board, then you clearly had plenty of mites in your colony. A sticky board would certainly be better than a shiny, smooth one.
This year, the season of 2023, was busier than normal for me, as we were expanding our colony numbers. To my shame and regret, I completely missed doing any alcohol washes throughout the season. I don’t like it because I have to rely on guesswork that my treatments worked, and that the bees that are now hunkering down for winter are relatively free of mites.
Mite Loads Really Matter
The mite load of colonies really does matter, a lot. Once you have provided a safe shelter for your bees (a hive), and ensured that they have plenty of food (pollen and nectar/honey/sugar), the next most important thing is to manage the varroa mites. Those mites cause the death of more colonies each year than anything else, apart from, perhaps, extreme weather events. What’s worse, you can look at your bees and not see anything wrong, even when it is. By the time you see deformed wings, and mites on bees, your colony is in big trouble.
Proactive Not Reactive
The point of beekeeping is not to react to events, but to foresee them and proactively deal with risks before they turn into disasters. If you know that a dearth is coming, check your hives and get ready to feed them if necessary. If a storm is coming, secure the hives and do a tour of your apiaries afterwards to check for damage (hives blown over, roofs blown off). With varroa mites, the only way to really know your ‘mite status’ is to do the alcohol wash and count them.
It is not unreasonable, in the absence of alcohol wash data, to simply assume that your bees have mites, and follow a planned treatment regime. That is fine, but when something goes wrong, you won’t know about it until your bees are in trouble. An example of this would be treating bees with oxalic acid in winter under the assumption that there is little or no brood in the colony. What if there is some brood? What if you accidentally missed a hive, or the treatment was of a suboptimal concentration? Stuff happens.
Every Colony Is Different
In the past, I have carried out mite washes on my bees – all hives, so I have seen the wide range of mite loads from hive to hive. The bees to be sampled come from the frames at the edge of the brood nest, and make sure you don’t get the queen (!). It is perfectly possible to find low mite levels in nine colonies, but the tenth is riddled with them. I have seen plenty of ‘zeros’ when doing mite washes in June, but some colonies can be as high as 16. That’s a 5% infestation, or something like 2,000 mites in the colony. Such a colony will not do well, and will probably be dead before the autumn. The majority of mine generally fall between 3–8 mites per half-cup of bees (1% to 2.7% infestation). The National Bee Unit brochure ‘Managing Varroa‘ suggests that we aim to keep mite numbers in the hive below 1,000.
Using a Varroa Model
Why am I considering treating three times next season? I shall use an example, a hive in one of my apiaries, which I call ‘Hive 19’ (H19). Imaginative, eh? On 17th June 2022 the mite count was 8, which you can see in the chart below (Randy Oliver’s Varroa Model). The main things to look out for on this chart are the blue line (number of mites per 300 bees sampled), the red line (number of mites in the colony), and the yellow coloured cells , which show treatments being applied.
Eight mites from 300 bees was too high, so I immediately squirted some VarroMed along the seams of bees in the brood nest. I returned a week later with Formic Pro, and gave them the full two pad blast of formic acid. Then, in mid-August, they got Thymovar, and in December, they received the oxalic acid trickle. The varroa model for H19 for 2022 looks like this:
Even with what appears to be a considerable assault on the mites in H19, the model shows the colony ending the year with 193 mites, having started it with 110. The Thymovar treatment in August was a half-dose. I don’t know why, but they got a 3-week treatment rather than 6 weeks, which can’t have helped.
Have I Left It Too Late?
Moving into 2023, these bees have so far only had a full thymol treatment in August, using Thymovar and following the instructions correctly. I have assumed that the effectiveness of this treatment was 90% as per the varroa model recommendation (I used the Apiguard number). Looking at the chart, you can see why I am worried. Without mite wash data from 2023 I have to rely on this forecast from the model. In the past, I have found that some colonies do not follow the model at all; unsurprising as it is an average over many colonies, and each colony is different. If mite levels really did get over 10,000 then they could well be toast; even if I get mites down, the virus levels will be high.
Amitraz In Early March
I will be treating with oxalic acid in late November, but maybe I will be too late for H19. I just don’t know. Consider the impact of a pre-emptive strike of an amitraz treatment (Apivar or Apitraz) in early March. It is not temperature dependant, and does not slow down the egg laying of the queen. Using the 95% effectiveness suggested in the model, it’s like a comfort blanket. I have not used amitraz for several years, so it is unlikely that my bees have resistance to it.
The answer seems to be this: if I perform alcohol washes in June I can treat some colonies twice per season (August and Nov/Dec), and for others they will need a June formic acid treatment if mites are too high. However, if I don’t do mite washes in June, the safety-first policy is three treatments per season. That would be Amitraz in spring, thymol or formic pads at the end of summer, and oxalic acid in winter. It seems a lot, but I want my bees to be healthy and thriving, not burdened with the torture of mites and associated viruses. Hitting the mites early, in spring, makes such a big difference. One mite in March can become 100 mites in October.
Multiple Oxalic Vapes
Some people have had great success using a series of oxalic acid treatments in the winter by sublimation rather than trickling. Typically, they will ‘vape’ the hive three or four times, with a gap of four days between treatments. The idea is that any mites under cappings at the first treatment will be exposed to the acid at some point, so the effectiveness should be, say, 95%. I can’t bring myself to ever assign more than 95% to anything (born pessimist). It is a lot of work to get around every hive three or four times, and some say that repeated treatments may affect the queen. I don’t know about that, but presumably, if it kept killing queens people would not be using it.
If you are getting a 95% knock down in winter, the chances are pretty good that only two treatments per year (August & December in my area) will be plenty. And, if you do your mite washes, you will know for sure how things are going.