regarding passing querysting from user control

 Hi,
i am using a search user control having a drop down list , i would like to pass either query string or drop down list selected value to the user control code behind in order to display a panel containing datalist. 
 User Control Front Code :
  
<asp:TableCell>
<asp:DropDownList ID="manufacturer" runat="server" CssClass="quicksearchdropdown" ></asp:DropDownList>
</asp:TableCell>
<asp:TableCell>
<asp:DropDownList ID="network" runat="server" CssClass="quicksearchdropdown"></asp:DropDownList>
</asp:TableCell>
<asp:TableCell>
<asp:DropDownList ID="freegift" runat="server" Cs ...