What is the prefix for developed?

There isn't a single prefix for "developed." The word itself is already a verb and adjective, and there's no common prefix used to modify it directly.

However, depending on the context, you could use prefixes like:

* Un- (for the opposite): underdeveloped, undeveloped

* Re- (to indicate repetition): redeveloped

* Over- (to indicate excess): overdeveloped

* Under- (to indicate insufficiency): underdeveloped

The best prefix to use would depend on the specific meaning you're trying to convey.