A healthy, overwintered colony of midnight (hybrid) bees swarmed on April
6th and 9th.  A careful inspection on the 9th revealed several empty queen
cells, a couple maturing queen cells, and some capped brood.  An inspection
today (April 23rd) yielded no brood in any stages of development and all
queen cells empty.
 
Has this colony become queenless or is there still time for a virgin to mate
and lay?  Do I need to introduce a young, mated queen to this colony?  Or do
I just need patience?
 
Help, please.