Just because someone in the South has never seen them pupate in the hive does not mean that someone in the North hasn't. The SHB behavior could vary a lot according to the climate or temperatures at the time.
That becomes another element in the question of control. The life cycle of the SHB may well be short enough that it is able to develop survival strategies that deal with the environment they are in or develop resistance to some of the chemicals against them. I dont know how your authorities deal with "approved" chemical treatments but I do know that there are quite severe restrictions over here and at the moment trapping and management seems to be the "approved" method of control.