Old timers tell of how mean bees get when they are on a buckwheat flow. For some reason, buckwheat flowers only yield nectar in the morning. So, if you open up hives during the afternoon, they are ready to sting on cue.
You could say that having the sweet stuff stop in the middle of a perfectly nice day just puts the in a very bad mood. Do bees have moods? Most beekeepers will tell you that they do.
Is there a scientific explanation for moods? I suppose there is, chemical imbalance and all that. Feeding sugar to bees seems to put them into a good mood, and that is just like a drug that makes you feel better.
Perhaps they get withdrawal symptoms when their sweet stuff is cut off abruptly. Sure seems that way to us.