My bees have filled up the top box with comb, in fact, they filled the top box quite quickly. However, they don't seem to be going down into the bottom box - I have been expecting them to start drawing comb in the bottom box for a couple of weeks. the hive is real active, and seems to be doing well.

Any ideas? Do I just sit back and wait - or should I do anything to encourage them to build comb in the lower box.