If this is what you need:
(OBPs; Pelosi et al., 2006; Vogt, 2003; Vogt and Riddiford, 1981; Zhou, 2010)
You can click on the citation, go to Edit and Manage Citations, and put the text (OBPs; ) in the Prefix field (remember a space after the semicolon). This will put the text before the citations within the parenthesis.
Best wishes
Jan Ove