Oxalic acid puzzle?

[Nirakaro]

Right, it's a small colony that I hived from a swarm six weeks ago, they seem happy enough, on six or seven top bars, though they haven't expanded much since I got them. I thought I should treat for varroa, so I vaporised a gram of oxalic acid in the bottom of the hive, then removed the vaporiser and stuck in a sheet of greased white card to see what fell onto it. Twenty-four hours later, I see no tiny dead mites: what does this mean? Does it mean for example, that they're good varroa-hygienic bees, not infested with varroa?
What I did see though, in the middle of the card, is a sprinkling of crystalline white powder, that looks suspiciously like oxalic acid (and no, I didn't taste it to check!) What does this mean? The vaporised acid condensed on the comb, and the bees didn't like the taste so took it off and dumped it? Or what?

 

[Murox]

You should assume, as you did, that varroa are present. Assuming your vaping was good no obvious mite drop is a bonus from a small recently hived swarm. A six week old swarm colony isn't very likely to have loads/many mites, and you said its not developed much so minimal egg laying. I don't think it means that you have stumbled upon vsh bees. The vaporisation into a gaseous state only lasts for a second or two, it then becomes a fine white powder, which you may see when you vape initially. The powder goes everywhere in the hive and the bees groom themselves and everything else so you end up with a small pile of 'dust' caught on your sticky card.

 

[jenkinsbrynmair]

freshly hived swarm, so hasn't had that much time to draw comb then (assuming the queen was mated) get brood laid. once the first brood develops into the larval stage, any mites hitching a ride on the bees will have swiftly moved into the cells to breed before they were sealed.
OA doesn't penetrate into sealed brood so the mites are probably still in there waiting to emerge and cause havoc with the other bees. There's a good chance that's what has happened in this case. You need to do a cycle of three vapes spaced one every five days to see what then turns up.

 

[drex]

I believe that maximum mite drop only occurs after a few days, something like 5

 

[Erichalfbee]

I believe that maximum mite drop only occurs after a few days, something like 5

No. 24 hours sees over 90% of the phoretic mites drop.

 

[drex]

Thanks Dani, I was not thinking. I believe what I said applies to Apiguard etc.

 

[ericbeaumont]

though they haven't expanded much since I got them

Was there a nectar flow in August? If not, and you didn't feed, the queen may have reduced laying or gone off entirely.

Pretty dry down here and plenty of attempts at robbing. Now the ivy is open that's stopped, and now there's income, your queen may accelerate.