I had an experience with feral robber bees this weekend. I reduced the entrance, then put Vicks vapor rub above the entrance, then covered with a wet sheet. Decided to leave sheet on all night and to arrow is a rain day.
My bees are 3 banded Italian these bees are 2 banded and a black butt and a large spot behind the eyes and very aggressive . I put up a screen on the hive and an inside feeder. I closed off any escapes at the top. I can't do anything else but pray.
Robbing can be the result of several reasons and once it starts, it is difficult to stop. I have reduced entrances down to nearly a half inch wide to try to stop robbing. Some causes of robbing are from leaving old comb out where the bees can find it, feeding in front of the hives or out in the open around the hives. Please don't mistake my questions for being rude, however, in your picture, that paper plate with sticks in it, sitting on that hive, is that an open bee feeding station?
Yes today I put a screen up to make do untitled the proper one for hives comes in. As far as I know the nearest hives are 10 miles from me this is why I am assuming these bees are feral as well as aggressive.