The pic is approx 2 inches by 3 inches with about 100 mites on a bottom board. The white stuff is diatomaceous earth. This photo taken 24 hrs after treatment with Oxalic acid vapor: one gram per 10 frame langstrof deep. The total mite drop was very high, my guess 800-1000 mites on bottom board. This was a non-hygenic hive, obvious from the pic. My hygenic hives might have 40-60 total mite drop.
With above in mind, your question regarding mite drop is highly dependent on:
1. the hygenic qualities of the hive
2. previous treatments
3. mite virulence or reproduction as one may define.
4. time of year.
5. Hive stress:
Dearth
Disease
Error by beekeeper
Beetles
Pesticides and such
6. Hive density: recent swarm, or split, robbing
7. Percent, number of cells of capped brood.
The fewer mites the better in all cases. Health to your bees.
Cheers
Add: I have not posted much lately, been very busy with stuff. Just want to say happy healthy holidays to all my BeeMaster friends, in US, across the pond and down under.