Use green drone frames for two reasons. Raise more drones of your favorite genetics to increase drone population for mating purposes. But perhaps more importantly, in this age of mites, use it as a tool to reduce mite population. Put these drone frames—you will always recognize them by their conspicuous off-green color—into the brood chamber. One per hive is enough. Pull the frame when the drone brood is capped and replace with another drone frame. Put the removed frame in the freezer. Repeat the cycle when the current frame is capped. Mites prefer drone brood and by doing this you will greatly reduce your mite population. But WARNING! Keep track of your timing. If those drones start emerging before you pull the frame, you have created a mite farm instead of a mite eliminator!