OK then @CraBee. Very much inspired by @BeeBob's mite count work shown above - I also decided to monitor daily mite drops starting in late April following regular OA vaporising treatment. Unfortunately it's a bit off topic from the original topic based on Bayvrol treatment - but hopefully still interesting to some.
Firstly - I'm a first year beekeeper with a lot to learn
Second - this is by no means a rigorous scientific trial so please take (or don't take) from it what you will.
I have two hives located together in urban North Shore in Auckland. I took one FD honey super off each hive around mid February and then started weekly OA vaporising treatment. From 30 April - I decided to trial OA vaporising every 3 or 4 days. Also - sugar shakes on both hives in early April showed 5 and the other 6 mites. The graph below records the mite drop results following treatment.
North Hive - knocked down to a single FD brood box on 22 April, 3-4 frames of brood - with the rest honey. Queen continued to slow down on laying during the monitoring and bees now occupy only 7-8 frames.
South Hive - still two FD brood boxes - 7-8 frames of brood on 17 April. They superseded the Queen in January and she only really started slowing up on laying a couple of weeks ago - so still have 4 nice frames of brood. My last inspection a few days ago was the first sign of bee with DWV.
I have the newer Hive Dr smart bases and have been counting the mites that fall into the plastic trays that slide in underneath.
Results so far are:
Similar findings to Randy Oliver's work in that OA has a noticeable peak on both hives in the 24 hours following treatment but then the effects of OA relatively quickly reduce from 48 hours onwards.
OA has worked well at reducing mites in the North Hive (blue line) where the Queen was naturally slowing up on brood laying. The sugar shake we did early this week was zero mites. I have stopped OA treatment now but will continue to monitor mite drop every 2-3 days for a while.
On the other hand, the stronger southern hive (red line), was struggling to bring mite levels down with OA so on the 18 May - I decided to use ApiLife VAR. Yes - I know it is late in the season - however, we are in Auckland and daily temperatures are still around 19-20 degrees. Hopefully still warm enough at this stage to work? Certainly by the bees reaction during the days since the treatment went in - the smell is keeping them outside hanging around the entrance a lot longer before going in to the hive.
I will probably trial the brood break method next summer (begging in Feb?) and see what affect OA has during the 2-3 day period of having no capped brood in the hive. Perhaps creating a brood break each month in late summer/early autumn for two or three months in a row and hitting with OA vaporiser each day for 3 days in a row when there is no capped brood might get on top of them? Probably not, but worth trying - and the Queen may not appreciate be caged up for two weeks every month!
There are a lot more questions and "what ifs" raised than answers - so please excuse me if I don't have answers to queries.