Roger Sonnenberg questions whether oil/sugar patties can or should be left on during the flow or taken off. Roger, Sue Coby at Ohio State did some work a couple of years ago and compared the effects of tracheal mite control with just spring and fall oil/sugar patties and continual treatment. Her conclusion was that just spring and fall treatment was not at all effective, but very good results were obtained with continual treatment. I think the general conclusion is that continual treatment does not adversely contaminate, as both products (oil and sugar) are foods we consume every day. I personally use continual treatment. That said, I have observed (as have others) that the bees store the granulated sugar in cells and cap it with liquid honey. If you extracting honey, I suggest you look carefully to see if sugar crystals are in your jars. This might be a particular danger if you extract frames from the brood nest. Presumably, they will either be strained/filtered out or liquefied by heating, but I suggest you be certain. I personally raise only comb honey and have never observed any sugar crystals in the combs. Lloyd [log in to unmask] Owner, Ross Rounds the finest in comb honey production.