Drone are not the brightest bees. I usually harvest in the Fall, and drone population is decreased then, so I never had much of a problem with them. Drones are very light sensitive, so if you but an escape board on top with either shims or a vent box, I bet the light would coax them out. In fact, come to think of it, I use a night light on top of an escape board to expedite clearing of bees from stacks of supers. One night and they are empty, perhaps that is why I never noticed the drones lingering behind. :roll: