Hi qB

The dead larva outside the colony may have been a drone. They do have a habit of disposing of their menfolk (and younger males) once times get tough, and losing all of your flying bees means times get tough.

Generally about three feet is the recommended distance to move a hive each day to avoid disorientating a lot of bees that have become fliers. So, a 400m move would take you until July 2011! You might get away with it in one go if you pick a time when bad weather is expected for a few days, or you engineer a major disturbance around the entrance for a while, but I've never tried that myself. Can you wait until winter to move them back?

all the best

Gavin