Oxalic - how does it kill varroa

[Black Comb]

I've looked at a lot of threads but can't find an answer to the question "how does it actually kill the mite?"

I seem to remember it deforms the mouth?

Any published scientific papers on this?

Thanks in advance.

 

[boca]

OA acts as a contact acaricide. Bees don't need to ingest.
It is not the oxalate ion but the low pH which damages the mite (pH 0.9-1).

The mite loses the fine hairs from is legs which is crucial to grab to the bee and crawl on it. Possibly other damages too (not known yet).

http://apitrentine.it/dati/2008/nanetti_trento_varroa.pdf

there are some interesting pictures on page 24. Zoom in!

 

[drstitson]

Yes - AFAIK it burns off the mouthparts (and hairs).

The following two EM photos allegedly demonstrate the effect (Heilyser Tech are a canadian firm selling thymol strips and OA vaporisers).

However whilst the effect of OA may be as alleged i have serious doubts about the pictures as one will note that everything is identical apart from the missing hairs and mouthparts ie seem to be a photoshopped "spot the difference" picture. My reasons for doubt are a) the perfect realignment of the mite on it's EM grid within the vacuum chamber and b) the fact that EM specimens are either coated or impregnated with Osmium in order to provide a grounded, conductive surface. I doubt that this would allow topical treatment.

oh and c) you can even make out the ghost outline of the tip of the "proboscis" where the replacement background doesn't quite match perfectly.

 

[drstitson]

boca - great link. will have a proper read at my leisure but good to see i'm not alone in picking up the faked picture.

 

[Bee-Key-Pur]

There's nothing like a bit of gas warfare....

 

[boca]

On Nanetti's slide the first picture is labelled as "ARTEFACT!".
He must have said something about that.

 

[Winker]

i have serious doubts about the pictures .

oh and c) you can even make out the ghost outline of the tip of the "proboscis" where the replacement background doesn't quite match perfectly.

Spot on Doc it has been photoshoped. I took it into photoshop and had a close look and can 100% say its a fake.

It would have been nice to see the real before and after shots

 

[drstitson]

As i said I'm not aware of it being possible to even perform pre and post treatment scans on EM processed specimens for the reasons i gave.

 

[pbh4]

As i said I'm not aware of it being possible to even perform pre and post treatment scans on EM processed specimens for the reasons i gave.

While I agree these particular images have been photoshopped, I think you are wrong about the impossibility of doing this kind of image properly. The osmium staining is for transmission electron microscopy (TEM). This is scanning electron microscopy (SEM) so the sample does not need to be mounted on an "EM grid". It would often be put onto a black, carbon-loaded sticky pad to conduct the charge away. Biological samples are often gold-coated to conduct charge away but this is not necessary, particularly with a modern machine where the operator can chose the energy of the incident electron beam (There is a range of energies around 2 keV where the electron beam actually will discharge rather than charge the sample), or in an environmental SEM where a low water vapour pressure is used to conduct charge away. In such machines it is even possible to image living tissue.

I know all this because we have a SEM in my university research group (nano-physics) and I have put insects in for fun and obtained images easily as good as these with no special preparation (don't tell my colleagues!).

Paul

 

[chrismcd]

Both spiders and mites do not have the quality of cuticle that insects have.

You will be aware that most mites need to live in moist conditions and those spiders you find in bathtubs are desperately seeking water because they have lost too much through their cuticle and book lungs.

Then all the Hymenoptera (ie ants as well as bees) seem to have developed an ability to produce, tolerate and exploit a range of organic acids.

So, I would suggest that oxalic acid is happily tolerated by bees at a level that simple wrecks the cuticle of varroa - be it legs, mouthparts or anywhere else.

Not so much a 'mode of action' as 'gross physical damage'.

Unfortunately, I would suggest that beekeepers are closer to varroa than bees when it comes to oxalic acid tolerance - or bee stings for that matter!

I have had some nasty burns from using formic acid for preserving silage and treat oxalic acid - even the weak syrup with respect.

 

[drstitson]

Hi pbh - have to disagree about not using osmium for SEM as will "stain" any surface lipid (although of course gold typically used for sputter coating as you say).

However will happily admit that NHS path labs by definition will have ancient machines since EM has been superceded for routine diagnostic work by much simpler techniques which can use the routinely fixed histology specimens. The exceptions being renal and muscle pathology. With ever increasing centralisation of specialist services there is no place for investing in new tech in most labs. Modern research machines no doubt feature many advances which the NHS can but only dream of!!!!!

 

[Nic Rhodes]

we run several environmental SEMs, as well as installing a convention SEM into a local school. This will be used by the local beekeepers for the next microscope course I run locally but will see if we can image Varroa before and after OA treatment. It will make an interesting comaprison for the course.

 

[jenkinsbrynmair]

So if as you say it doesn't actually kill the mite - is it worth treating if you have a solid floor?

 

[RoofTops]

It does kill the mites - give them a trickle of 3.2% syrup and count the mites dropping onto a varroa floor. It doesn't matter if you have solid floors other than you won't know how many have been killed and therefore be able to judge how many mites there were in to begin with. But treat them with OA and you will kill lots of mites.

 

[WI-USA-BEEK]

Interesting angle to Oxalic acid efficasy

For what its worth, here is some info from Randy olivers website here in the USA. The info below is from the following link. Additional info at this link may be of interest

http://scientificbeekeeping.com/oxalic-acid-questions-answers-and-more-questions-part-1-of-2-parts/

So, is it the acid or the oxalates that affect the mite? In European research (Nanetti, in Anonymous 1999) the efficiency of oxalic acid was compared to neutral potassium oxalate. They determined that it is the acidity, rather than the oxalate ion, that kills varroa.

We still didn’t know whether the acidity of OA killed the mite through ingestion of acidic bee “blood,” or by direct contact. Ellis and Aliano (2005) performed a clever experiment: By splitting single dequeened colonies with various dividers, and treating only one side, they found that oxalic is apparently transferred through the colony by bee body contact, rather than through trophallaxis (mouth-to-mouth transfer), and distributes well by such contact (80% kill on treated side, 65% kill on untreated).

OK, so OA spreads and kills by contact—that’s why heat vaporization (to be covered in the next installment) works well. We still don’t know how it gets into the mite’s body (no one’s proposing that mites crawl around licking the stuff up). We do know that oxalates in plants form spiky crystals that can penetrate animal tissue, similar to those of boric acid (commonly used for cockroach and ant control). Boric acid forms abrasive spikes that can penetrate the soft integument at the joints of the insect exoskeleton, and apparently desiccate the insect. It also acts as a stomach poison to ants.

Could oxalic acid work in the same manner? Heat vaporized OA does form tiny spiky crystals, as does OA evaporated from a water solution. But oxalic dissolved in sugar syrup dries to a clear, smooth, candy that shows no crystal structure (personal microscopic observations). The rub is, OA is only effective when dribbled in a sugar solution (Anon 1999), not in plain water. So go figure! We’ll leave the mode of action discussion at that…

 

[Finman]

.
I have read much about oxalic acid but I have not seen explanation why it kills.
Next question, why lactic acid and formic acid kills. But I am not ancsious to know that.

It is easy to see with eyes how oxalic syrup spreads over the bee. A bee makes cleaning movements and greeses itself with stiff acid syrup. It rubs with its all 6 legs.

Important is that lactic acid and oxalic acid are bees natural stuffs in respiration cycle. Formic acid is natural stuff in ants, wasps and bees, but in their weapons.

 

[Black Comb]

Thank you all for the replies and links.

So, no definitive answer then.

I am not interested in lactic or formic as I don't intend to use them anytime soon.

The scientific beekeeping article did say some studies had noticed a slower spring build-up when winter oxalic was used, but I suppose you have to balance this out with the fact that the ones that build up more quickly may have more mites, which will denude the colony as the summer progresses.

Choices choices.

Also, does use of H**eclean etc mean we are building up varroa resistance to oxalic? Lots of beeks that I know have started to us it, but not sure whether they are following the crowd or they are convinced it works. Too early to tell really.

 

[Finman]

Thank you all for the replies and links.

So, no definitive answer then.


The scientific beekeeping article did say some studies had noticed a slower spring build-up when winter oxalic was used,


Too early to tell really.

almost all researches say that spring build up is normal. Articles and researches have a big difference.

Oxalic trickling has been used so many years and so much that it need no evidence any more.

If you meand Randy Oliver as "scientific beekeeper", forget it. Has has done no researches about oxalic acid.

 

[Finman]

For what its worth, here is some info from Randy olivers website here in the USA.


T
We still didn’t know whether the acidity of OA killed the mite through ingestion of acidic bee “blood,” or by direct contact.

it is sure that oxalic does not make a bee poisonous to the mite. According that a larva and pupa shoud be poisonous too. There is no such systemic mite poison.

A queen eates so much food daily that it would die first.

Blood of animal pH is very stable. Bees do not suck it when you give oa-syrup to them.

 

[boca]

So, no definitive answer then.

We have the definitive answer.
The low pH damages (burns) the cuticle of the mite.
That's enough for the practical beekeeper.

... we are building up varroa resistance to oxalic?

Not before the frog develops resistance against the pressure between the asphalt and the tire.