I haven't seen any responses to Walt Spears' ([log in to unmask])
speculation:
 
"Is it possible that the bees could be infested with tracheal mites and
 that the mites could be causing a collapse in the thorax from the
 inside?"
 
Did I miss something or were there no takers?  The speculation seems
at least possible, no?
 
Aaron Morris - I think (sometimes), therefore I bee (always)!