What is a drone layer?

Answer 1

When a queen lays an egg she chooses whether or not to ferilize it from her store of sperm in the spermetheca. If the egg is fertilized the developing bee will be female (queen or worker) and if not it will be male (drone). If the queen runs out of sperm, either through age or because she was not properly mated in the first place, she cannot fertilize the eggs so is only capable of producing unfertilized drone eggs.
A variation of this is the laying worker. If a colony becomes queenless for any reason and the workers don't succeed in raising another queen to replace her, the lack of 'queen substance' (pheromones from the queen) will cause the workers' ovaries to start developing. Eventually some will start laying eggs but because workers never mate these eggs cannot be fertilized and the result is more drones.