While i can’t comment on the question regarding mites, I definitely do find water has mixed in with the oil in the first of the 4 sections of the white tray after a heavy rain.
When the wax droppings, pollen and everything else drops into the water, it definitely starts to grow mould. I think it’s fairly common with heavy rains and some leakage in the front entrance of the hive.
Generally though, it’s never progressed too far by the time I do my monthly change of vegetable oil in the trays.
It could be a leak from rain, but it definitely could be condensation at this time of year in your climate. I would consider putting some insulation in the hive roof, and even insulation around the outside of the hive.
You don’t say how may oxalic acid vapor (OAV) treatments you gave. The normal course is 3 treatments at 5 to 6 day intervals. If the bees are clustered, you may be able to get away with just one treatment.
So now to answer your question properly. What you have discovered is what is known in the UK as an “accelerated mite drop” count. The accurate way to do it is clean the tray, treat with OAV, replace the tray and then count the number of mites on the tray exactly 24 hours after the last treatment. If you count more than 50 mites, you definitely should treat again.
In your situation, I would treat again, and do the count at 24 hours.
Interesting. I even had to look up some of the terms. Never used Oxalic Acid vapour or other forms.
What I have learnt is many prefer to administer the vapour through a top bee entrance. Also that the kit and treatment is very cheap and no wastage. I open a pack of Bayvarol and waste half.
As a result of my reading I am already making 8 top boards with 3mm mesh for summer ventilation which I can reduce or more likely remove in winter. The wooden mesh frame frame will include a closeable top entrance which will also be just wide and deep enough to get the oxalic vapour spoon into top of hive. The entrance depth will be strictly 3/8th inch.
That is a tragedy then! It is one of the few organic Varroa treatments available. It has very low toxicity to bees and oxalic acid is found naturally in nectar and honey. Also, because it works via a chemical erosion method on mites, there has been no reported resistance to it so far. In fact, one large bee research institute in Argentina used it continuously (and nothing else) for 15 years with no decrease in effectiveness or signs of mite resistance.
It is optimally used on a broodless hive, as it requires direct contact with the mites and doesn’t penetrate brood caps. When it sublimes the vapor is hotter than ambient air and rises rapidly through the hive, so really it is best to use a passive OAV crucible in the lowest part of the hive. If you have a fan-driven model, you can use any entrance.
