Itachi's genjutsu can work vs Bee believe it or not. Remember Itachi's genjutsu is a lot different then a normal genjutsu. His genjustu alters time so 1 second can equal 1 day in time. His tsukuyomi will defeat Bee before the 8 tails would even notice he was in a genjutsu. YES it is a fact. If you remember he used it vs Kakashi and a split second=3 days in his tsukuyomi. Also he caught Naruto in a genjutsu while Naruto was with Chiyo,Sakura and Kakashi and they didn't even realize he was in one. He was able to have a conversation with Naruto in the genjutsu while in real time only a few seconds have passed.