Oxalic acid sublimation frequency

[Hivemaker.]

Efficacy of Vaporization

Radetzki, Thomas. Vaporisation of oxalic acid in a field trial with 1’509 colonies

Radetzki found that mite kill takes place in the first week, and tapers off for the next two weeks. “Without brood one vaporizer treatment is more than 95% effective

 

[Arfermo]

So ... the ideal situation would be when there is no brood present and the temperature outside is less than 5 degrees so that few bees are flying .. but - you really don't want the bees to be clustered as the treatment works by the OA being spread throughout the hive and the bees (and phoretic mites) coming into contact with the sublimated OA. If they are clustered then the treatment will not be as effective.=QUOTE]

My view over quite a few years of sublimation is that if one puts the pan with crystals in right below where the cluster is most likely to be, that will result in the convected heat and fogged oxalic disturbing the cluster enough to ensure most if not all get a dose. In any case the particles are everywhere else and any bees doing a shift on the outside of the cluster and feeding on the stores will get treated too. Don't see any problems - the drop rate from sublimation has been proved to be around 95% and probably some more anyway. I have no doubts that sublimation is the most effective method imo and beats trickling by some margin especially when weather is cold as one doesn't need to open the hive either.

 

[tresallier]

 

[mbc]

Radetzki found that mite kill takes place in the first week, and tapers off for the next two weeks. “Without brood one vaporizer treatment is more than 95% effective

The questions I cant find the answers to are;
- does the treatment continue to kill mites which emerge post treatment?
- for how long is it effective on newly emerging mites and what percentage of these will it kill?
presumably on a downwards sloping sliding scale on the time axis after treatment

Observation would suggest that it is not very effective on newly emerging mites post treatment, and that the length of time quoted in the mite drops over a fortnight is merely showing the mites initially poisoned taking time to die.

 

[Hivemaker.]

The questions I cant find the answers to are;
- does the treatment continue to kill mites which emerge post treatment?

Yes effectively for five days, then it tapers off to almost nothing.

The recommended dose for colonies with brood is three or four doses seven days apart, however i found out that this is not effective enough, and treated 7, 6, 5 4, 3, 2 days apart to find out the most effective which is 5.


Most mites are killed in the first 48 hours, around 95/98%, if a second dose is given the following day there is no more big mite kill, just a slow drop for the next five days, then it almost stops, this would indicate these are mainly the mites which are coming out with emerging brood over these five days when the oxalic is still effective, as the initial big kill has already taken place.

 

[wessexmario]

I've been looking at the temperatures required for oxalic acid, above 157C it sublimes to vapour, but if it goes above 190C then it instead turns to formic acid and CO2.

Of course too much CO2 is no good for any living animal,
I understand that formic acid has been used in lower concentrations against varroa, but does neat formic acid have a detrimental effect on bees?

Do we need to ensure that when vaporising oxalic acid, the temperature is kept below 190C ?

 

[Hivemaker.]

I've been looking at the temperatures required for oxalic acid, above 157C it sublimes to vapour, but if it goes above 190C then it instead turns to formic acid and CO2.

And two grams of oxalic vapourizes almost instantly at the lower temperature, so the chances of it ever reaching a temperature to turn to formic before it sublimates off are almost none existent, unless it is a larger amount in a semi sealed vessel like a pressure cooker type setup.

 

[Curley]

Mario, I am not an expert on using this as a miticide but guess that as the oxalic acid sublimes then it will rise as a vapour away from the heat source and over heating will be avoided. (In the same way that steam (as measured at the kettle spout) won't exceed 100C - even though steam can be heated beyond this temperature in a sealed vessel.
To get the effect you are worried about would, I think, involve heating the vapour in a sealed vessel or possibly having a sufficient mass/compaction of the compound to trap vapour next to the heat source.

Sorry HM - you beat me to it!

 

[wessexmario]

I've been thinking about heating devices to do the job, considering things like a blow lamp, soldering iron or a diesel glow plug to provide the heat, but all can easily reach temperatures well over 190C, and a glow plug could reach a much higher temperature very quickly, especially given the small mass being heated.
Another consideration for a device is that a sealed apparatus is safer for the beekeeper, but as you say an increase in pressure will also affect state change temperatures.

I'm happy with the physics, it's the biological effect of formic acid I'm really after ?

 

[user 6228]

I've been thinking about heating devices to do the job, considering things like a blow lamp, soldering iron or a diesel glow plug to provide the heat, but all can easily reach temperatures well over 190C, and a glow plug could reach a much higher temperature very quickly, especially given the small mass being heated.
Another consideration for a device is that a sealed apparatus is safer for the beekeeper, but as you say an increase in pressure will also affect state change temperatures.

I'm happy with the physics, it's the biological effect of formic acid I'm really after ?

the glowplug device can easily be made temperature controlled

 

[pargyle]

Yes effectively for five days, then it tapers off to almost nothing.

The recommended dose for colonies with brood is three or four doses seven days apart, however i found out that this is not effective enough, and treated 7, 6, 5 4, 3, 2 days apart to find out the most effective which is 5.


Most mites are killed in the first 48 hours, around 95/98%, if a second dose is given the following day there is no more big mite kill, just a slow drop for the next five days, then it almost stops, this would indicate these are mainly the mites which are coming out with emerging brood over these five days when the oxalic is still effective, as the initial big kill has already taken place.

Thanks Pete ... Looks like the practical solution has trumped the theoretical one ... five day intervals x 3 treatments sounds like the optimum - would you reduce the 2 gms to 1gm for second and third treatments ?

 

[mbc]

Thanks Pete ...

+1

 

[Gilberdyke John]

Yes effectively for five days, then it tapers off to almost nothing.

The recommended dose for colonies with brood is three or four doses seven days apart, however i found out that this is not effective enough, and treated 7, 6, 5 4, 3, 2 days apart to find out the most effective which is 5.


Most mites are killed in the first 48 hours, around 95/98%, if a second dose is given the following day there is no more big mite kill, just a slow drop for the next five days, then it almost stops, this would indicate these are mainly the mites which are coming out with emerging brood over these five days when the oxalic is still effective, as the initial big kill has already taken place.

This is a bit of massively valuable information. Thanks Hivemaker should there be a sticky post covering the method, dosage and the efficacy of OA vapourisation?

 

[alanf]

Yes effectively for five days, then it tapers off to almost nothing.

The recommended dose for colonies with brood is three or four doses seven days apart, however i found out that this is not effective enough, and treated 7, 6, 5 4, 3, 2 days apart to find out the most effective which is 5.

Interesting practical trials.

Most mites are killed in the first 48 hours, around 95/98%, if a second dose is given the following day there is no more big mite kill, just a slow drop for the next five days, then it almost stops...

Is this the "next day" after the first treatment , or the "next day" after 48 hours? Just trying to clarify.

 

[user 3509]

How much Oxalic acid would you use in a vaporiser if you have a brood and a half?

 

[tresallier]

Interesting practical trials.Is this the "next day" after the first treatment , or the "next day" after 48 hours? Just trying to clarify.

The next day in the chosen cycle. ie day five

 

[midnight sun]

How much Oxalic acid would you use in a vaporiser if you have a brood and a half?

If the dose is 1 gram for a std national deep (8 7/8 inches), if you are talking about sublimation, then I would say that 1.5 grams would be ok and wouldn't overdose as a 'brood and a half' is one and a half times the volume. (close enough).
If you read Hivemakers thread, he has used various multiples of the standard dose with no ill affect.
hope that helps

 

[oliver90owner]

With a solid spread around the hive, the most likely downside, after effect on the bees, is the residual oxalic in the hive and potentially in any honey if simple common sense is not followed. While oxalic acid is a natural constiuent of honey, vastly raised levels may attract the attention of TS, were your honey tested.....

 

[Bee Bumble]

How much Oxalic acid would you use in a vaporiser if you have a brood and a half?

Two grammes.

 

[REDWOOD]

Interesting reading, thanks everyone of their input, I now know how much and how often to vaporise