So if I undestand correctly Apinor on every visit you spray 4-5 ml upon opening the colony. A bit more if needed. I assume that might be the case when you start pulling frames out. How many times do you visit a colony in a year 10-20 times? Then when they are broodless you use lactic again and completely spray the bees frame by frame? Others with more colonies could use oxalic, either drizzle or vaporization. This you have been doing for 19 years? I also assume that 85-90% of your colonies are alive and relatively well come spring.