its a simple solution
First in user control create a delegate above Page_Load() method
public delegate void OnSelectedIndexchanged();
public event OnSelectedindexchanged Setactionname;
then in your dropdown selected index change add following line
if (Setactionname!= null)
Setactionname();
then go to your ASPX page and
UsercontrolName.Setactionname+= this.Mehtodnameonlocalpage;
create a function in your aspx code behind page and do what u need to do like
private void SetSelectedActor()
{
}