Instead of throwing Pikmin at it, have a pellet fall near him. He will try to get it. Assign two Pikmin (prefably flowers) to the pellet that it is carrying. They should start a tug of war. If they get to the Onion, the Breadbug will be sucked up, losing almost all of its health. Do this once more and it will be defeated, allowing you to claim your prize (the Space Float).
David H.
Get about 70 Red Pikmin, 15 to 20 Yellow Pikmin, and no Blue Pikmin. When you reach the arena where the Bulbax is located, run around the outside of sandy area to avoid waking him up. As you run, you will find a wall. Have your Pikmin destroy the wall to enter a small place behind the sandy arena. When you arrive, split your Pikmin into groups. You will need: two groups of 35 Red Pikmin, and a group of 15 to 20 Yellow Pikmin. Then, select one Yellow Pikmin and grab a Bomb Rock that sits near the entrance to the arena. You will see it after you break down the wall. Then, lead only that Yellow Pikmin out into the arena and wake up Emperor Bulbax. When he awakens, he will look to see what woke him. You should now run back toward your other Pikmin, but do not leave the arena. When Emperor Bulbax turns around, throw the Yellow Pikmin at him. With luck, as the Emperor Bulbax opens his mouth to eat your lone Yellow Pikmin, the Pikmin will throw the Bomb Rock into his open mouth, stunning him. Next, run and grab a team of Red Pikmin. Run back into the arena and begin throwing the Red Pikmin on the Bulbax's face. When the Bulbax wakes up again, he will throw the Pikmin off him. Then, call your Pikmin back and repeat the procedure. This method allows for minimal casualties and is rather fun.
Eric M..