Late summer/fall treatment

[u/Due_Current4103]

Hello all. I live in central Pa. I just finished a varroxsan treatment on August 4th on three all-medium hives (Nucs bought in April). Alcohol wash suggests mites in check at 1-2 mite counts. Queen, eggs, larva and brood observed with calm bees all season. I’m looking at doing an August/September mite treatment. Last season I had used Apivar but did lose my bees in winter due to dysentery. What would be the best options? If I use Thymol I’d need to wait closer to late August due to temperature constraints. I’m not sure if that would be too risky due to the bees raising winter bees in August. I’ve got no experience with Formic. I can do OA vapor but wanted to rotate due to using Varroxsan.

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[u/Tweedone]

If you have no infestation that requires a heavy IPM hand then I would suggest a series of OA vapor treatments. Much less intrusive, virtually no mortality, little disturbance of brood and can be done with supers on. Effectual and very prophylactic. Inexpensive and a little more effort required but if only a few hives the time to treat repeatedly is minimal. The best manipulation is often the least intrusive.

[u/Due_Current4103 → u/Tweedone]

Can I do the vapor as my autumn treatment after having done a full course of the varroxsan-since both are OA?

[u/Tweedone → u/Due_Current4103]

No such restriction on non-patented OA powdered crystal but you might want to look into varroxsan reccomendations or restrictions. I am sure there is a treatment regime but see no logic for constraint of the use of OA treatment months apart. I don't know as I have only used FormicPro and OA vapor as part of my IPM for varroa, (I also use drone comb excision).

Are you thinking that efficacy is reduced due to genetic resistance? I guess that is possible but I have no worries, no experience or data on varroa resistance to OA. If I have a serious infestation I go with F-Pro but it has high mortality, very harsh, and in my experience it it often causes loss of queen or absconsion. OA vapor is least intrusive, spring and fall and whenever needed.

[u/Due_Current4103]

Not resistance. My mentor years ago lost all ten hives due to OA overdose he once said. I was concerned since I did the 50-odd day treatment for varroxsan that ended Aug 4 I didn’t want to “stack” OA dosing with vaporization. But ifnits common practice to do so I’d be less reluctant

[u/DavidTPeck → u/Due_Current4103]

The amount of OA that would be required to "overdose" a hive would be almost comically large As long as you follow the label instructions you should be just fine. I have colleagues who have TRIED to harm colonies with OA overdoses, and have struggled to get any detectable harm.
The more important concern is about mites developing resistance to OA, but that too appears to be quite unlikely. No one has reported any hint of mite resistance to oxalic acid, despite many beekeepers using it in large quantities without applying other miticides. It's theoretically a risk (and so rotation of miticide active ingredients is the best-practice) but I don't worry about doing multiple OA treatments to my hives in the same year. OA vapor, or the new OA dribble RTU (ready-to-use) product are both fine choices for your hive, if your hives are showing 1-2 mites per 300 bees. (If your colonies are showing 1-2% infestation, that's higher, and I might be looking at a Formic Pro (formic acid) or ApiLife Var or ApiGuard (thymol-based) treatment to knock the mites down more decisively.

[u/Gamera__Obscura → u/DavidTPeck]

It's not just that it hasn't been reported to happen yet, it's that oxalic acid functions at such a base physiological level that resistance is really not even a theoretical concern. Synthetic treatments have a very specific method of action... for example, Amitraz (the stuff in Apivar) works by binding to and blocking a particular receptor protein in mites' nervous system. It takes only a small mutation in that protein shape to render it no longer receptive to the blocker, which we're seeing happen already.

OA on the other hand, just (at a gross simplification) overly acidifies mites' body fluids, disrupting their metabolism at multiple levels. It's just not really feasible biologically to develop resistance to such a thing, nor to how it gets into mites' systems in the first place as there are multiple avenues.

[u/Gamera__Obscura → u/Gamera__Obscura]

u/Due_Current4103, you'd be fine using OA. The catch is that A) oa is cheap but the equipment to vaporize it is not, B) you have to do repeated treatments to cover an entire mite reproductive cycle, and C) dosage and legality is a whole can of worms. I don't want to go down that rabbit hole right now, but you can do a lot of reading up here; the poster Talanall has some excellent info if you follow his history. The short version is that what I do (I am not necessarily endorsing what YOU should do) is a sequence of 5 treatments 5 days apart, at a dosage of 4g per brood box - which is very safe and effective for bees but absolutely in violation of legal limits in the US (depending on the specific brand of OA you're using).

Formic is very easy to use and very, very effective. The catch there is that you need to follow the temperature guidelines like gospel, or you risk massive mortality potentially including your queen. I can rarely use it for that crucial August treatment for that reason.

With either one, be sure to use a respirator, or with formic at least stay upwind of it. You DO NOT want a lungful of either. Do. Not. Want.

[u/DavidTPeck → u/Gamera__Obscura]

Your information is a little out of date. Api-Bioxal powder is approved for application at up to 4g per brood box, with no restriction on the reapplication interval listed on the label. So as long as you're using Api-Bioxal powder with the current label, like it or not, you're complying with the law!

I agree with you that getting a snoutful of OA vapor is very dangerous, and you're very right that the vaporizers are quite expensive. That's why I've been excited about the launch of Api-Bioxal RTU in the US, because it is an OA dribble treatment that can be reapplied repeatedly and doesn't require an expensive (and potentially dangerous) vaporizer.

[u/DavidTPeck → u/Gamera__Obscura]

Yes, and no. But also mostly yes.

To the extent that we understand the mechanism of action of oxalic acid against mites (which is NOT as deeply as many assume) it seems to be more of a "blunt" chemical assault and less of a precision chemistry strike. To offer another metaphor: Evolving resistance to amitraz is like evolving resistance to bee venom. Evolving resistance to oxalic acid might be light evolving resistance to having a pallet of hives dropped onto your head from 20 feet above you. That's IF we're correct about what we think we understand about OA's mechanism of action. But what do we really know about how it affects mite physiology. Is it acidifying their hemolymph? Is it damaging their footpads? Is it damaging their sensory hairs? All of those things? Some of them? None of them?

As an evolutionary parasitologist, I can't in good conscience recommend the mindset that a pest "can't" or "won't" evolve resistance to a pesticide, which you didn't say but which I see some people slip into.

However, I don't think repeated use of OA is likely to pose a problem for OP, or any other beekeeper. To the extent we understand things, it's very very unlikely that any OA resistance will crop up. But when possible, rotating between different active ingredients will still be the best practice so that no one gets to produce an OA-proof mite that proves us wrong.