What citation style is mainly used in political science?
Political Scientist here. @aeismail is correct - different journals use different citation styles, as do different academic publishers. The best way around this is to use a reference manager (such as Mendeley or Papers) to not only manage your academic articles, but cite directly into your publications. These software packages are capable of formatting your citations in whichever style necessary.

With that said, my experience is that, generally, APSR's citation style is broadly accepted, with minor variation.