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Has my varroa treatment not worked?

just done what i thought was going to be a last varroa treatment of the year with apiguard. of 3 hives, 2 now (about a week after taking trays out) have very little mite drop. my flow hive however, about 20+ mites since last night. you could smell the thymol coming off during treatment, which i thought was a good sign, but i’m now wondering if i should’ve paid more attention to closing the gap in the flow super where you get at the frames. but i’m also trying to convince myself theres some way mite drop could be delayed til after treatment, eg if mites had been killed in cells that were subsequently capped & are now hatching. its a bit late here for anything other than oxalic acid, which has always struck me as just too harsh, also i don’t really know what constitutes serious mite levels now, my most recent reference book, i’ve just realised, being about 10 years out of date. anyone any thoughts…?

You really shouldn’t use thymol with a super on the hive. Is that what you are saying that you did? Anything more than 2-3% mite infestation at this time of year is not good. I would take off the super and use an oxalic acid trickle next month (November), when the bees are broodless and reliably clustered. It is really your best option for saving them, unless you can vaporize oxalic acid.

@JimM often has helpful insights into UK/Ireland concepts, so perhaps he will add something even better here.


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yes, why is that bad? i got from the instructions that you’re expected to have taken the supers off, & don’t use during a honey flow ‘in case of taste tainting’. but i’m using flow frames, so i didn’t take them off, just harvested the honey & left the frames for the bees to store their winter syrup. guess i’ve not really got a sense yet of how much they need to overwinter, but last year i fed them til they filled the super & they got off to a flying start in the spring.
how do you go about trickling oxalic acid? i’ve not used it so far but what i’ve picked up is, quite hard on the bees, kills any open brood & not effective against mites in sealed brood, hence waiting til the middle of winter. but with the random weather we get these days, who knows when or if they’ll have a broodless period over winter? unless you go in & look, & i thought it was a big no no opening hives in the cold anyway. just seems like a recipe for demoralised cold bees with a faceful of toxic fumes & a load of dead larvae to clear up. i was really hoping to’ve knocked the mites on the head now & be able to wait til spring for the next round. something i’m not understanding about oxalic? or is it just that its better than losing the whole colony?
& thanks, by the way, for the speedy reply. not what i was hoping to hear, but if thats what i’ve got to do its good to have a couple of weeks to get my head round the idea…

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So glad that you are asking questions. These things are hard to grasp sometimes. :blush:

There are several reasons for this:

  1. You can taint honey with a very strong thymol (thyme) taste
  2. Thymol is an essential oil. It is soluble in wax and could even taint any wax in the super. Even a Flow super has wax coating the cells and in the gaps between the moving sections, so that could be tainted too, flavouring your next harvest
  3. Leaving a super on increases the volume for diffusion of the thymol. While some of the thymol effect is from direct effect on bees touching it, there will be an additional effect from the vapour. If you leave a super on, you are diluting that effect

I don’t do that with Flow supers because of the tendency of my bees to put propolis (brown and sticky) in any and all gaps. This can make it difficult to impossible to open the Flow frames for harvesting during the following season. :wink:

There are lots of great videos on YouTube, if you search, you will find tons of them. There will be no open brood in your UK hive in November, and no capped brood either. If you use room temperature syrup for trickling (20°C+), then the bees will not have a hard time from it.

True for a long inspection, but if you are all set up, a trickle takes about 3 minutes, and you don’t remove any frames to do it.

Trickle has no fumes - the oxalic acid is all in solution and doesn’t “off-gas” at normal temperatures. If the syrup is relatively warm (no more than 35°C, though!), the bees won’t get cold. If you do it in November, there won’t be any larvae.

If you use oxalic acid vaporisation, the bees are also not really upset by it. I have never found dead larvae, even in late summer. I think you are hearing horror stories which are not representative of the way things usually go.

Please let us know what you decide to do. :slightly_smiling_face:


hey dawn. thanks so much, all my questions answered! so, will be looking out for the taste of thyme in next years harvest, only us eating the honey so far, so i guess thats one for me to deal with if applicable. i hadn’t really thought about the dilution caused by having supers on being a problem, if anything i was hoping it’d minimise upset to the bees if it was a bit less intense. lesson learned!
i had the same problem with the flow frames last year- had them on all season, bees weren’t using them but propolised all the gaps, then i took them off & put normal frames on for over winter. they did ok this summer though, & i was hoping now some of the gaps are waxed up there’ll be less to propolise, specially if they do use them for winter storage, which they’ve started to. well, have to see how they do next season.
i think based on your info i’ve decided to give the dreaded oxalic a go. should’ve maybe done a bit more research before dismissing it, i tend to instinctively avoid things that sound like they’re going to distress the bees…which seems to be pretty much all varroa treatments apart from the pyrethroids, which i dislike for other reasons, though i have used them.
sounds like you think vaporisation is a better option? i see my local bee supplier are selling a vaporiser at £350…& another at £35. presumably theres some difference in quality…anyway, i’ll stop being lazy at that point & go & do some research. thanks again!

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Let’s see what @JimM thinks, if he has time to answer. For my hives in the UK, I would use OAV (oxalic acid vaporisation) once the hive is broodless. You can even do an accelerated mite drop count 24 hours after that (try the forum search tool at the top right - it has been discussed many times) and see whether you need to repeat the treatment. I would buy a good vaporiser though, they vary a lot. I use a Swiss-made Varrox, and have been very happy with it. :wink:

I agree with everything that Dawn said except that the broodless period might be early december more than november, but its makes little difference.

I have a question for the OP though. Did you give the full apiguard treatment, ie two trays of thymol for 2 weeks each and leaving the last tray in the hive until its all removed by the bees? You mentioned a drop of 20 mites a week after the treatment stopped. What was the mite drop like during the treatment. I wouldn’'t conclude that the treatment didn’t work on the information so far.
However many beekeepers, myself included, have a treatment regime that comprises thymol in august/september followed by oxalic in december and this seems to work very well.
Oxalic dribbling is very easy and takes no more than a couple of minutes per hive and really does work.
Yes, most sublimation gear is expensive and you have to add facemasks on top of that. For three hives, i would try dribbling first and if you get good results consider moving to sublimation in the future. There are some less expensive devices available such as the gasvap. If treating in december, I would do all the hives at the same time.


Just to add that the reason to use oxalic in a broodless period is not because it kills larvae; it doesn’t. Its because the oxalic won’t penetrate sealed cells so varroa in a cell with a larva will not be killed.

Some people use OA in the brood period too to deal with heavy infections. In this case the vaping is repeated every 5 days until no more varroa drop. The reason is to catch varroa that emerge from brood cells as they are uncapped.


Very nice explanations, @JimM. Thank you so much for taking the time to post and provide your experience too. Great teamwork! :blush:

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There are beekeepers on this forum who have used this oxalic acid method for treating varroa mites. It’s simplicity and effectiveness in many areas of the world has greatly improved the success and enjoyment of beekeeping for them…including myself. Randy Oliver’s research has been indispensable and he has evaluated many products for varroa mite control…


Thank you for adding this @Doug1. I bang this drum so often, I hesitate to do it again. I love the sponges, not sure how good they would be in the UK at this time of year though. Great idea to try out for the UK next year. I am going to try some Hopguard 3 within the next year or so. Can’t hurt to rotate treatments a bit, as Randy implies. :blush:

By the way, Happy Thanksgiving (for Canada)! :wink:

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well! thanks guys. specially interesting, the idea of slowing mites down by stopping them reentering brood cells. i wasn’t sure from that article whether the implication was that the treatment might be fostering resistant behaviour? seems like it might, having a constant population of mites to practice on…
i’m afraid i did cut my thymol treatment a bit short. very bad i know, its been a bit of a steep learning curve this year, i didn’t think i had much of a mite problem, & also was aware i’d left it a bit late for winter prep. plus, having left supers on, i also found the apiguard trays didn’t fit between them & the brood box, so i made some division boards with cut out bits for them, which i wanted to get out before winter in case they interfere with clustering…& so on. so i left the first tray in for 2 weeks, then changed to the second but took that out after 2 weeks too. same result both times, 2 colonies had removed most of the apiguard but left a residue of crystals, other one had removed it all (this wasn’t the colony i’m worried about).
i was similarly slack about mite counts, just been pulling the trays out every couple of days for a look. but 2 of the 3 didn’t have much drop throughout really, whereas the one i’m concerned about seemed to have a fair bit. these, if its relevant, are our original colony, still headed by last years queen, they’ve swarmed twice this year, being seperated from all brood both times. last one was late july, & i think their numbers have been down a bit since.

It’s an essential drum to be banging! And I feel the same way when reposting photos etc. but there always seems to be a new crowd asking questions on this wonderful forum. And what makes no sense to the novice at one point in time can later be comprehensible when the right set of circumstances present themselves. Your contributions to this forum Dawn_SD are invaluable!

Thankfully my experience with the mangement of the varroa mite has evolved to quite a simple task…but it takes a bit of experience to get there. If only I had a forum like this to ask for advice when I first encountered the mite!

Kudos to Flowhive and their dedicated staff for providing this knowledge platform… :sparkling_heart:

Thanks…another great feast with the family here. Have avoided Cholecystitis so far :smile:…going for a big walk today. But the leftovers…mmm…and the ubiquitous homemade pumpkin pie…mmm…


Actually, looking at this i think you are probably worrying too much. The hives got a full four week dose and its clear that they bees removed the crystals. This action is what seems to distribute the thymol and kills the mites. You also got a considerable mite drop during treatment. With some treatments, vaping for example, its quite normal to see a mite drop several days after the treatments ends.
However its clear to me that the hive was heavily infested, and that you killed a lot of mites and that the hive must now be in a better condition than previously. Unless there are other issues i think you can leave things until December and dribble OA then.
By the way there are no resistance issues with either thymol or oxalic acid. Same applies to formic acid, but that has a reputation of being more severe on the bees. Resistance is certainly an issue with the pharma type products.

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thanks. i’ll keep watching the situation, & do an OA treatment over winter as advised. its early to say, but i think that mite drop has slowed a bit now.
so all the thymol being removed is good? i was slightly concerned that one of my hives obviously hated it so much they’d got rid straight away, i thought it’d need to be there for a bit for the vapour to circulate. one of the smaller colonies this, by the way. they were a bit fidgety before treatment & they’ve been even more so since. very few mites dropping out of there now though.

i was actually talking about resistance to mites by the the bees rather than resistance to the treatment by the mites. there was an article in the BBKA mag the other day talking about mite resistant behaviour being able to arise naturally in populations of A. mellifera given the right conditions, wondered if mites hanging around & not hiding in cells might be one of those conditions. glad to hear about the lack of mite resistance to the ‘natural’ treatments though, its the likelihood of resistance arising that puts me off things like apistan…mostly.
just a quick wonder about formic acid too, i’ve only just clocked it as a potential treatment, & liked the idea of being able to treat sealed brood. but if its harder on the bees, & can penetrate sealed cells, surely that means its going to affect the brood too, & you’d expect them, with their soft little bodies & no exoskeleton, to be more susceptible to pretty much anything wouldn’t you?
what i was starting to think was, in the middle of summer you do sometimes find whole frames of just sealed brood, & if you could take them out, wipe out their mite population & put them back you could make a huge dent in the mites without hardly bothering the bees at all. probably not a good idea for all sorts of reasons though…

another development i’m a bit puzzled by. just had a look on the floor of that hive, similar number of mites again, but based on an encounter yesterday i fetched them out into a pot & had a bit closer look, & about half of them were still alive. i’ve heard them described as being both fast & slow moving, all the ones i’ve ever seen alive before were in trays during treatment, & very much not at their best. these started slow, but with a bit of jostling about in the warm soon got quite sprightly.
so whats going on there? i took the thymol out 10 days ago, but something is still making apparently healthy mites drop out of the hive & sit there on the floor til, presumably, i reactivate them either by removing from the hive atmosphere or warming them up.

Yes, That’s my understanding of the mode of action, the bees try to remove the thymol and in doing so distribute it around the hive. You will sometimes see thymol crystals outside the entrance to the hive during treatment.
Another point which i didn’t ask you about was the ambient temperature during treatment. It should have been 15C or over but i think you would have been ok there.

Yes, my understanding of resistance is that its not that the mites have less effect on the resistant bees (after all its hard to be resistant to something which would effectively eat and makes a mess of your liver), but rather that the bees develop behaviours that limit the growth of mite numbers, so-called hygenic behaviour. The bees examine sealed larval cells and open those containing varroa larvae. Some strains of bees are more prone to do this than others and it can be bred for. However like much breeding, there are positives and negatives.

Treatments like this have been tried, eg confining the queen to particular frames and then discarding the brood as all the varroa should have moved into these cells; Discarding frames of drone brood which disproportionately attract varroa; even taking out frames and heat treating them (raising temperature by 2 or 3 degrees will kill varroa but not the bees, but none of them seem to be worth the hassle.

Actually the comment in your final post does concern me. Large numbers of live varroa after treatment is not good. More often you have dead varroa falling as bees tidy up after treatments but your experience suggests that there are reasonable numbers still alive in the hive. It could also be that the queen has reduced laying considerably and the varroa have not enough cells to enter and thus fall, but that is just speculation on my part.

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didn’t get so far as to use an actual thermometer, but i was pretty sure it was above 15 most of the daytime. might’ve dropped below a few days though, & probably a fair bit at night. i was going by the mite drop & the smell of thyme mostly, but i wonder, if there were times when the thymol concentration was lower, if mites might’ve come out of hatching cells, got a less than fatal dose & then gone into another cell? i’m getting fluctuation in the daily drop now, down to 4 one day, back in double figures the next. no more still alive so far though. i don’t actually know what thymol does to the mites, maybe a low dose could have lingering effects?
it’d make sense for queenie to be slowing down, shes a couple of years old & swarmed twice this year, sort of hoping they’ll supersede over the winter, otherwise i’m going to have to deal with her next spring. they’ve been suprisingly active lately as well for the time of year, & i’ve noticed before that lots of activity tends to result in more mite drop.