As everyone is aware, the pile on in a small area by large numbers of bees and wasps of unknown origin is exactly the activity of robber bees. The thought that an individual beek can control the spread of anything seems illogical and especially so when taking into account swarming and or feral bees. The goal imo is to develop colonies with good resistance and maintain hygiene practice equal to that which we would like of our bees. I am probably fortunate in not being surrounded by large numbers of kept colonies. When I know I will be breaking down a hive and having a good sort out I know that it will leave them exposed enough to attract robbers, My way of distraction is to place pebbles in a tray and pour syrup onto it, the tray being about 40ft away from where I am working. ?Thus far it seems to have worked a treat. When I observe the comings and goings it is quite easy to distinguish the foreigners via their differing arrival and dispatch routes from that taken by my girls. It does give an indicator who else is on your patch. As for aggression when feeding, I have never observed that. Again, I accept that my location is fortunate.