Ehm... No: The Giant Motobug doesn't do anything in Act 3, and is only an intro for the true boss, which is not the Motobug. The Motobug appears, it breaks apart and the first boss emerges from its remnants. The only link to that Motobug could be its claws, which can be reused as the Egg-Mobile weapon.
The giant moto could also just be a random attack. He doesnt have reappear ever again or even be considered a boss in anyway.
<!--quoteo(post=268486:date=Jan 16 2009, 04:52 AM:name=Blue Cheese)--><div class='quotetop'>QUOTE (Blue Cheese @ Jan 16 2009, 04:52 AM) Something really should be done to show that it's not just an up-scaled motobug. So how about some kind of big big diesel exhaust pipe belching out black smoke, mean eyebrows, spikes and maybe mounted rocket pods? Not only would serve to differentiate from regular motobugs (aside from the size of course) but it would really look like it really would love nothing more than to freaking smear you across the ground. Someone with better pixel pushing power should try it, my lack of skillz makes me weep.[/quote] Wow, I love the suggestion! Absolutely killer!
Motobug should remain a mid-boss or something for Nack to pilot. The suggestion made by Phoebius was pretty cool bros, but the actual Motobug wouldn't make an exciting end stage boss.