Those pesky mites

DWV symptoms

DWV symptoms

If you haven’t yet treated your colonies to reduce Varroa levels before the winter arrives it may well be too late. High Varroa levels are known to result in the transmission of virulent strains of deformed wing virus (DWV). These replicate to very high levels and reduce the lifespan of bees. If this happens to the ‘winter bees’ raised in late summer/early autumn there’s a significant chance that the colony will die during the winter.

Mite levels in most of my colonies have been very low this year. Partly due to thorough Varroa management in the 2015/16 winter (the only thing I can take credit for), partly due to the relative sparsity of beekeepers in Fife, partly due to the late Spring and consequent slow build-up of colonies and partly due to an extended mid-season brood break when requeening. Most colonies yielded only a small number of mites (<50) during and after a 3 x 5 day treatment regime (to be discussed in detail in a later post) by sublimation.

Infested arrivals

The low mite drop definitely wasn’t due to operator error or vaporiser malfunction. At the same time I treated a swarm that had moved into a bait hive in early June …

Out, damn'd mite ...

Out, damn’d mite …

This is ~20% of the Varroa tray. Have a guess at the number of mites in this view only. Click on the image to read the full legend which includes the mite count.

The image above was taken on the 18th of September, a day or two after starting the second round of 3 x 5 day treatments. The colony really was riddled. When a colony swarms 35% of the mites in the colony leave with the swarm (or, in this case, arrives with it). For this reason the swarm was treated for mites shortly after it arrived in June. It did have a reasonably high mite load but subsequently built up very quickly and didn’t experience the mid-season brood break my other colonies benefitted from.

The colony now has an acceptable mite drop (<1 per day). Similar colonies are still rearing brood – I’ve not checked this one, but they are bringing in some pollen from somewhere – so there’s a possibility the majority of the remaining mites are tucked away in sealed cells. I’ll keep a close eye on this colony through the next few weeks and will be treating again midwinter to further reduce the parasite burden.

Treat ’em right

If you are treating this late in the season make sure you use a miticide that is appropriate for the conditions. Apiguard (a thymol-containing treatment) is almost certainly unsuitable unless you’re living in southern France as it needs a temperature of 15°C to be effective. MAQS has a recommended temperature minimum of 10°C which may be achievable.

Hard chemicals such as Apivar and Apistan can be used at lower temperatures but there’s little point in treating with Apistan unless you’re certain all your mites are sensitive. They almost certainly are not as Apistan/Bayvarol resistance is very widespread in the UK mite population. Just because you get an increased mite drop in the presence of Apistan does not mean treatment has been effective. Perhaps all you’ve done is killed the sensitive mites in the population, leaving the remainder untroubled. This is what’s known as a bad idea … both for your bees next season and for your neighbours.

 I’m posting this now due to the large number of searches for, and visits to, pages on use of Apiguard or other Varroa treatments. These are currently running second to ‘fondant‘ in one form or another.

12 thoughts on “Those pesky mites

  1. calum

    5 * 2ml/frame treatments of Formic acid 60% was my autumn treatment From august to Sept as weather allowed every 7-10 days

    1. David Post author

      Interesting. Is that trickled, sprayed or what Calum? With a 7-10 day interval I assume you have some evidence that formic acid remains active for at least some of the intervening period? If not, surely there’s a possibility that a mite will emerge from a capped cell and re-enter another between treatments. I can’t remember the average time a mite remains outside capped cells, but have a vague recollection it was 8 days on average.

    1. David Post author

      No … if you’re using Api-Bioxal take care with the caramelised glucose in the vaporiser. Since your colony will also almost certainly still have brood present you’ll need to use repeat treatments to get the mites that escape because they’re in capped cells. Current evidence from no less an authority than ‘Hivemaker’ on the suggests that 3 treatments at 5 day intervals is effective. I have a post on this in preparation.

  2. calum

    Evaporated, it is applied to a 100mm*100mm Vileda type cleaning sponge mat. Needs above 18°C to evaporate effectively and low air humidity (>60% if I remember). It damages the mouthpieces of the mites (kills them) on bees, the repeats are so that emerging bees are treated too (at least 3 cycles cover this) the extras I do cover reinvasion too. I try to treat ideally 5-7 times.

    1. David Post author

      Thanks Calum … always interesting to see how others cope with the little blighters. We’d struggle in Scotland to have the necessary temperatures, though I suspect the temperature in the hive exceeds 18°C most of the time.

  3. calum

    Yes you might be better off with the Italian method (or a version of it).
    They have an enclosure for 2 frames surrounded by queen excluder material.
    The queen is placed in the box, and “trapped” there till all other brood has emerged.
    The hive is then treated (probably oxalic acid sublimation would be most reliable for Scotland).
    Following that the queen is released, and the 2 frames of by now sealed brood is destoryed, or collected and treated separately on emergance and used to build up nucs.

    1. David Post author

      I’ve got one of those brood trapping frames but mine (from Thorne’s) only encloses a single frame which may be insufficient. I’ve always thought a shook swarm coupled with a timely burst of oxalic acid/Api-Bioxal vapour, assuming it’s warm enough etc. to draw comb, would provide them with a great start to the season. Conditions this season were not suitable for this but I achieved a brood break by getting the timing of my queen rearing completely wrong 🙁

  4. calum

    just reading up on an alternative method.
    The queen is kept in your single frame cage for 6 weeks. Every 7-10 days the frame is replaced with a frame with foundation. The frames of open brood are placed in the colony, removed and destroyed once the cells have been sealed. This is carried out in May-June. This is equal to 2 Varroa reproduction cycles so there should be a hugely reduced population of mites in theory.
    For me reinvasion will always be an issue using this method. But for wet climates probably better than some other methods.

    1. David Post author

      Hi Calum
      I can see how that works but I’d also be concerned about the impact it would have on colony size – and hence nectar gathering capacity – in the relatively short season we have here in Scotland. This season (which may well not be typical – I’ve only recently moved here) I didn’t properly inspect a colony until early May and the final full inspection was late August/early September … effectively only ~5 months. Many of my colonies were waiting for queens to mate in June, when it rained a lot, and the consequent brood break really weakened the colonies meaning I missed much of the summer flow. D’oh!
      Next season I’ll be better prepared. Famous last words. I intend to stagger queen replacement when needed, do more vertical splits and keep my production colonies together. I should add that Varroa levels are generally very low in my bees and, even when I lived in the warmer Midlands, I’ve rarely had DWV problems. Despite the relatively poor season (my worst in absolute terms of honey yield) I’ve got enough to sell through the winter, I’ve finished the season with more colonies than I started and I’m reasonably content they’re going into the winter healthy and with ample stores.

  5. calum

    the other alternative would be the heat treatments of colonies.
    Austria is giving beekeeping clubs there money for the equipment – it is VERY expensive.
    The whole hive is heated in a controlled way to something like 38°C (dont hold me to that figure) for a set time.
    Kills varroa, but not the bees and brood, though odviously they are stressed by it but Varroa free.
    Not very practical if you have many colonies I fear.

    1. David Post author

      It won’t be long until someone designs and advertises a ‘jacket’ of some sort to add to the hive with a heating element to achieve this. My honey warming cabinet quickly achieves this temperature, with an internal fan to get the warm air circulating well. Until then I’d agree that this isn’t practical.

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