In an hour and 15 minutes we'll finally see who is behind the name Big Bug. My money is on Stinkfly.
Ball Weevil - Larger than an average bug, but too small in comparison to Ben's other bug-like aliens to be given the name "Big Bug".
Big Chill - Yes, he is similar to a large insect, but his most symbolic attribute is his ice abilities, so Big Chill will most likely be given an ice related name.
Crashhopper - I can't think of a definitive reason as to why he wouldn't be Big Bug, so Crashhopper is understandable.
Nanomech - Isn't Nanomech smaller than most insects?
Upgrade - A bug is another term for a virus, so wouldn't this name better fit Malware if he were one of Ben's aliens? The point of Upgrade is to improve machinery to meet his requirements, not to destabilize them.