Managing the Mighty Mites

Gosh, it’s been a long time since I wrote a blog post. Perhaps I have some sloth DNA somewhere in me. Maybe long ago a wayward walrus mated with a sloth and generations later the characteristics of our three-toed slow-moving friends popped up in me. It’s surprising how many people like sloths, perhaps because we can always feel quite busy and useful compared to them, or maybe they are just cute.

A Sloth
A Sloth

I had a brilliant Summer with the bees this year. I have lots of delicious honey; I raised eight new mated queens who now head colonies in my apiaries (yes, I grafted them myself!), and even though wasps are pestering the bees they seem to be coping quite well. The bees are currently working on Himalayan Balsam which is an excellent source of food for them at this time of the year. I can tell that they are on balsam by the white stripes down their backs, caused by pollen which they pick up as they move deep into the flowers. I plan to step up the queen rearing next year and, who knows, I might be able to sell some to cover a tiny portion of my burgeoning travel expenses. It’s terrific fun raising queens anyway, regardless of any potential income stream.

I’m delighted to be visiting Randy Oliver in Grass Valley, California, in October, where I shall be doing my very best not to look and sound like a jet-lagged fool. This will not be easy, because I will be jet lagged, and compared to the legends of beekeeping that I am interviewing for my book, Mr Oliver included, I am, if not a complete fool, at least a bit of a novice. The only way to be the best is to learn from the best, so that is what I’m doing.

One of the significant challenges of beekeeping is keeping bees alive, and one of the main culprits indicated in killing them is the Varroa mite. Randy Oliver has done a considerable amount of research into this beastie and thanks to his efforts we now have access to his super cool excel spreadsheet model. The chart plots the population of bees, brood and varroa mites over time and can be used to test multiple scenarios. It is based on a lot of research and was built by somebody who knows far more about this than me, so while I accept that it won’t be perfect, it is an excellent tool for looking at the effects of various varroa treatments and their timings. I tweaked it to more accurately match the bees in my location, which is different from those in California (different climate, forage etc.) and played around with it to see what I could learn.

It sounds obvious, but one of the most critical things that a beekeeper can do is to ensure a low mite level going into Winter. In my case, I have about 14,000 bees in a typical hive on 1st January, dropping to under 10,000 in early March before the rapid Spring buildup. According to the model, if I have 500 mites in that hive at that time, it will crash; it will die out and be recorded as a Winter loss. I think that a lot of Winter losses are related to higher than ideal varroa levels in Winter. When the queen starts laying again in February/March the mites, which have been phoretic over Winter, jump into the brood, and it has no chance because nearly all of the brood will have varroa feeding on it.

Randy Oliver Varroa Model
Varroa Model: start year with 300 mites

In Randy’s model, the thing that causes the colony to collapse is the percentage of brood that is infested with varroa mites. Once it reaches 30%, the hive is history; you are too late to save it. In my hives, if I had 300 mites on 1st January, then the colony would crash in late July. That is too early for me to use any treatment other than formic acid because there is honey in the hive which I want to harvest in August. What we need to achieve is a really low mite level going into Winter, so that treatment in August/September is not too late for the bees to be able to survive. If I had 40 mites in my hive on 1st January, the colony would not collapse until mid-October. That is much more manageable than having to deal with heavy mite loads in the middle of Summer.

There are other factors which make a big difference to how well a colony can cope with varroa. Some bees have a trait called Varroa Sensitive Hygiene (VSH) which means that they remove larvae from the hive that are infested with varroa mites, which curtails the mites’ ability to reproduce rapidly. If this trait were widespread across our honeybee populations, the need for treatments would be less, and survival of colonies would be higher. However, queen breeders tend to be more focused on other traits, like gentleness and honey production, which are very important too.

Another factor can be the influx of mites from a heavily infested colony to one that has very few mites in it. This is why all colonies need to be treated at the same time, and varroa levels need to be monitored. If a colony begins to dwindle due to a heavy varroa load, it will be robbed by bees from nearby colonies, and those robbers will bring mites back to their homes where they can wreak havoc. I have to confess that I am not very diligent on the mite monitoring front and need to perfect the art of the sugar shake or alcohol wash. There’s always something…

Varroa Model: two treatments
Thymol or Amitraz in August then Oxalic in November

Randy Oliver also preaches the rotation of varroa treatments from year to year to minimise the chances of the mites becoming resistant to them. In America, there are early signs of resistance to Amitraz, which has been one of the primary treatments over there for many years. He seems to be keen on thymol, oxalic acid and formic acid. Whatever the treatment, the key to knocking mite levels right down is to either treat them when they are broodless (generally mid Winter) or to keep the product in the hive for 6 – 8 weeks so that mites are killed as they emerge from sealed brood. Basically, follow the instructions!

I am taking delivery of a Sublimox device next month, which is a contraption which sublimes oxalic acid (turns it straight from solid crystals to vapour) and is becoming very popular with many commercial beekeepers. I shall be giving my bees a series of three vapes at six-day intervals sometime in October, which should ensure that the mighty mites are at a very low level going into Winter. I used to dissolve the oxalic acid in sugar syrup and trickle it on the bees in Winter, but I have heard several horror stories about winter losses, mainly on smaller colonies, and the vapour is meant to be kinder to the bees and equally unkind to mites. See video by Richard Noel:

Go forth and stop your mites from multiplying.

[main image copyright Bayer]

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