General ⇒ natbib and apa: how to get different and's?

[O.Langner]

I'm still struggling with implementing apa citations really correctly with tex. I use natbib and a selfmade style for bibtex. The problem, I couldn't resolve yet is, how to use different and's for citations in parenthesis and textual citations:

Example: (Langner & Bowers, 2008) vs. Langner and Bowers (2008)

Currently I only see the chance to define one thing for this by putting a \bbland-command into the custom babelbst.tex file. To get this clear: I already do not get, whether this is a natbib or bibtex issue. Where does natbib grab the symbol or text for 'and' from?

Thankful for suggestions!
Oliver