Why is BaseController's overloaded constructor not being executed?

Question

I have a base controller which is defined as follows, but the constructor that takes the ISiteService never gets executed:

public class BaseController : Controller
{
    private ISiteService _siteService;

    public BaseController() {}

    public BaseController(ISiteService siteService)
    {
        _siteService = siteService; // this never gets hit..
    }

    protected override void Initialize(RequestContext rc)
    {
        string host = ((rc.HttpContext).Request).Url.Host; 
        Site site = _siteService.GetSiteByHost(host); // so _siteService is null...

        base.Initialize(rc);
    }
}

Can somebody tell me why this would be the case? What do I need to do to get this constructor to execute?

All controllers that implement BaseController have constructors that take various parameters supplied by StructureMap, and all those constructors are executed.

I don't know if it's relevant but this is how I'm configuring StructureMap for my dependency injection.

private void ConfigureNonOptionalDependencies()
{
    // all other dependencies are registered same as this, 
    // and the constructors all get hit
    ForRequestedType<ISiteService>()
        .TheDefaultIsConcreteType<SiteService>();
}

I'm unfamiliar with StructureMap, so I don't know if it has anything to do with this issue, or if it's more of an MVC problem. Or is it even possible for this? Thanks

edit:

also, I've tried this:

public class GroupController : BaseController
{

    private readonly IGroupService _groupService;

    private readonly ISiteService _siteService;

    public GroupController() {}

    public GroupController(
        ISiteService siteService
        ): base(siteService)
    {
        _siteService = siteService;
    }
}

Answer 1

Do your subclass constructors include a call to base ?

e.g.

public MyController(ISiteService siteService) : base(siteService)
{
    //do some MyController specific stuff
}

Answer 2

If you are already loading the controllers via structuremap, why not just eliminiate the parameterless constructor? You don't need it anymore and it is probably confusing something somewheres . . .