Varroa resistance to Pyrethroids (Yorkshire)

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Queen Bee
Dec 14, 2008
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East Yorkshire
Hive Type
Number of Hives

I am starting this new thread which developed from the following one.

I have just administered Oxalic acid to my hives and monitored (after 24hrs) about 100 - 200 mite drop.

This is despite following the beebase information that my area does not have pyrethroid resistant mites.

Throughout the year I also followed a IPM with the use of open mesh floors drone culling and sugar dusting.

Also my local association is still selling to its members the Bavarol strips (which I used at the end of September).

I am in no way worried about my hives, they are very strong, and also now the oxalic acid will have helped.

One possible problem might have been the Septemeber warm spell.

How have other members faired? Have you used OA, did you do a count?

Are you in an area which is listed as Ok to use Pyrethroids?

So varroa has had 8 or 9 weeks to increase numbers. This is about 6 varroa lifecycles and they can double their numbers each lifecycle. So a total drop of 100 doesn't sound too bad. But if it's 100 day after day that would be a worry.

Thanks Chris
Hi Jim

Your Oxalic trickle has just given you the best answer you could wish for.

Bayvoral saw it's best days years ago and Apistan shortly after although until recently we used Apistan and a late Oxalic to good effect.

Keep up the IPM with an early Aug Thymol type treatment backed up with a Winter Oxalic and your bees should be in good shape.

Longer Autumns/collapsing hives can all increase mite numbers in your hives, Oxalic is great belt and braces and gives you a clean a start for the following year as you can get.

As to your assoc and bee base, don't depend on them:confused: they have only just figured out how to use some treatmnts like Oxalic and have only recently given info on how to use it.

Regards Ian
Thanks Ian for the vote of confidence.

You think you are doing everything correctly and then see this (large) mite drop.

But from what you have said and Chris's above info, providing tomorrows board is relatively clean, things look OK, and I should be going into 2009 with strong clean (ish) hives.


I have just administered Oxalic acid to my hives and monitored (after 24hrs) about 100 - 200 mite drop.


Trickling affects during next 3 weeks.

Finnish beekeeping specialist Ari Seppälä calculated from Finnish
varroa trickling research following lag time :

cure ---- rate of all falled
1 week ---- 54 %
2 week ---- 20 %
3 week -----13 %
4 week ------8 %
5 week ------5 %

A finnish researcher Seppo Korpela has calculated during many years mites' drop

year 2000 altogether 34468 falled mites

1-2 weeks 96%
3-4. weeks 2,4 %

v. 2004 ... 10730 mites:

1-2 weeks 98 %
3-4 weeks 2 %

Y 2005.... 12270 mites

1-2 weeks 96 %
3-4 weeks 4 %
That was my thought Hivemaker.

Its so damned mild down here on the Hampshire coast I am sure if I pulled a few frames I would find a little brood.
That is assuming they are broodless Jim.

Possibly not even way up North where I am. LOL, So you soft southerens will now be adding your supers I guess!

So what can we do, if there is brood all the way through "winter"?
Yes get them supers on,start queen rearing next week. haha. and not so much of the soft.

Seriously though, there is not a lot we can do,short of removing brood,and i'm not doing that trick,better to do as your doing, monitoring the mites and if they need it give them a treatment in spring before adding the supers,and the rest you know,do as you allready have been this year.
I could not bring myself, to either break open the hive at this time of year, or take away brood. Just does not seam right! But then again, I might have said a few years ago does not seam right to be adding oxalic acid to my hives!

I will monitor and as Hivemaker says treat in spring. Oxalic acid ????

I now have 2 very nice empty bottles from my purchased Oxalic acid treatment.

I will now venture to make my own solution as per the recipe on this this forum.
If you want to know, do the have brood, put in-out digitaln thermometer into cluster.

It there are brood, temp is 32C.
It there are no brood, temp is 23C.

When you disturb the colony in winter, temp may rise to 42C.


But I do not look their brood. If they have during winter, they will starve before January. No mites either...
No Jim, not oxalic acid again, thymol, or formic,but the formic is not as easy to use,there are different methods. Just a short treatment ,will knock out a large proportion of mites,but only if needed obviously,then your other IPM .
Calm down, Calm down!

No one have seen that Jim has brood. Could we suppose that he has not. Who knows better than Jim. If you cannot sleep at night, open the hive and look if it has brood.

You loose nothing compared to these all advices. You will surely loose your hives if you do what this gang gets into their mind.

If some one say sometging in internet, you go into panic. Internet is not healthy place.
Hi Jim

Sounds like you are doing just fine, I am in sunny Surrey/Berks and pulled a few frames at the Weekend on some nuc's and no brood. Although I would not be so confident about some of the large hives. BUT DON'T WORRY TO MUCH!!!!!!!!!!!!!!!!!!!

You can and they do in some of the milder parts of E.U remove small areas of brood.

Brood is not so much affected by temp but rather the availability of pollen and season/daylight IMO

Regards Ian