Defeating the Monster

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Randy Oliver's Varroa Model
Randy Oliver’s Varroa Model

Yesterday I treated all of my hives with oxalic acid vapour using a Sublimox device plugged into a generator. The generator was a gift from a friend who I have helped out with bees over the last year. The Sublimox was a gift to myself and my bees. Research at LASI, located at my old University, scene of untold walrus frolics, shows that treating honey bees with oxalic acid vapour is as beneficial to bees as it is vile to varroa.

The best time in the UK to treat is now because the majority of hives will not be raising brood. This means that the mites cannot hide under the cappings of sealed brood cells. Of course, any honey for the beekeeper has long since been taken away, so there is no danger of contamination. We are lucky to be in a part of the world that does have a chilly Winter (although I’m sure Mike Palmer would disagree!). For a short time most colonies have a brood break, enabling very effective treatment at this time. This should result in a very low mite load going into the new year.

The importance of monitoring all hives

I am a big fan of Randy Oliver’s spreadsheet hive model which helps to show how the numbers of bees, brood and mites change over time and the impact of treatments at different times. It has taken me several attempts at tweaking the model to arrive at one which seems to accurately reflect what went on in one of my best colonies last year.

Randy has shown by performing mite checks using alcohol wash on ALL of his colonies last year – that’s over 1,000 of them – that there can be a vast range in the mite loads of colonies even in the same apiary. One colony may only show up a couple of mites from the alcohol wash whereas another in the same apiary may drop 20+ mites from a half cup of bees. The former colony is doing well, but the latter is going to crash at some point and could become a “mite bomb“; a collapsing colony that spreads its mites to surrounding colonies by various means (robbing and drifting being two possibilities).

Timing of mite treatments

My goal is to start the year with virtually no mites (less than 20) so that they can’t build up to dangerous levels before I take the honey boxes off my hives in early August. I can then perform alcohol washes to establish the mite loads in my colonies. Based on Randy’s model I would expect a mite drop of 6 to 9 mites per half cup of bees at this time. If I get a higher drop of mites (10+), then I may be experiencing mite immigration, or I may just have started off the year with more mites than I’d hoped. Either way, these hives will need to be treated with something like thymol or amitraz straight away.

If I find a drop in August of only 1 or 2 mites, then I may have found bees with some varroa tolerance, in which case I won’t treat them but will continue to monitor. Perhaps that queen is a candidate for grafting from next season. Because the “mite bomb” effect is most potent in September, I will need to do follow-up alcohol washes in September to see whether the treatment has knocked the mites down or if they are still high due to influx from outside. This will determine whether or not further action is needed in September/October (probably oxalic acid vapour at five-day intervals). 

Mite immigration in Autumn

In the Autumn there can be a sudden invasion of mites into hives, which is a big problem because (a) many people will have checked for mites and even treated earlier in the year and will assume that the hive is fine and (b) it is the time when the queen is laying “winter bees” – the bees that will ensure survival through winter and into the following spring. The exact mechanism by which mites suddenly arrive en masse from outside is the subject of an amazing research project that Randy showed me when I visited him in Grass Valley, CA this October.

He is developing a theory that the combination of heavy varroa infestation with Deformed Wing Virus (DWV), together with the behaviour and practices of beekeepers, is creating a “monster”. He suggests that whereas normally a parasite does not benefit from killing its host, this “monster” is a situation where there is an evolutionary benefit to mites/DWV causing the colony to collapse and die. The fact that mites are dispersed to other colonies in the area, and that beekeepers replace any dead colonies with new ones (normally bees with no varroa tolerance) means that the “monster” continues to prosper.

Breeding varroa tolerant bees

The long-term solution to defeating the “monster” is likely to be the widespread use of bees with a strong varroa tolerant trait. This would drastically reduce the “mite bomb” colonies as the bees would be able to somehow keep mites to a level which they can cope with, although I am not exactly sure how they would achieve this (grooming, hygienic behaviour, aversion to robbing?). For this to come about the major queen breeders would have to select for this trait, and the only way that will happen is if their customers demand it. The challenge is to breed bees which have all of the qualities that beekeepers need now, with the addition of varroa tolerance; it’s a tall order. Surely though, if you had a choice between a great queen and another great queen that also displayed varroa tolerance, the preferred option would be the latter?

We are all part of the solution

Beekeepers are part of the long-term “monster” solution because they can demand varroa tolerant bees, and try to breed for the trait themselves. Also, by being vigilant in their mite monitoring, perhaps even to the extent of checking every colony, the potential “mite bombs” can be found. These should be treated and the queen replaced before harm befalls other colonies. The most varroa tolerant bees alive will still struggle to cope with a mass invasion of mites from elsewhere, so treatment is vital when bees are succumbing to mite overload.

The idea of just leaving bees alone and letting nature take its course will not work here; the “monster” benefits from allowing colonies to collapse and die. Equally, if we just blanket treat every hive regardless of the mite load we will miss those little gems; the colonies which tolerate varroa and still make a good honey crop, have low swarming, gentle natures and so forth. It’s going to take decades to get to a place where varroa tolerance is the norm, but the sooner that beekeepers ask for this trait the sooner bee breeders will make it happen.

What do you think?

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