Q:

Insert primary key from one table into another based on user input from a form

I have a form with an asp:DropDownList that populates its contents from the Item_Description column in the Item table.
I would like to allow users to select an item from the drop-down list, and when the form is submitted, insert the ItemID value for the selected item into the Orders table using C#/T-SQL.
I could theoretically accomplish this with some lengthy if/else statements, but this seems too simple to require so much code.
I am able to update other tables by assigning asp:Textbox values to parameters and inserting them upon submission. I just can't seem to figure out how to pass the ItemID to the Orders table when a user selects a related item from the list.
P.S. I have already established a connection to my database, protected against SQL injection, etc.
Drop-down list:
ID="ddlItems"
Code for tables:
CREATE TABLE Item
(
    ItemID int primary key,
    Item_Description varchar(255)
); 

CREATE TABLE Orders
(
    OrderID int primary key,
    Order_Item varchar(255)
);

Code-behind method for Submit button click event:
protected void Submit_Click(object sender, EventArgs e)
{
    SqlConnection conn;
    SqlCommand comm;
    SqlDataReader reader;
    conn = new SqlConnection("Server=*omitted*");
    comm = new SqlCommand("INSERT INTO Orders VALUES @ItemID;", conn);

    comm.Parameters.Add("@ItemID", System.Data.SqlDbType.Int);
    comm.Parameters["@ItemID"].Value = <<<This is where I need help>>>;

    try
    {
        conn.Open();
        reader = comm.ExecuteReader();
        reader.Close();
    }
    catch
    {
        results.Text = "Error adding data. ";
    }
    finally
    {
        // Close the connection
        conn.Close();
        results.Text = "Added data.";
    }
}

Drop-down List binding:
<asp:DropDOwnList ID="ddlItems" runat="server" AutoPostBack="True" AppendDataBoundItems="True" DataSourceID="SqlDataSource1" DataTextField="Item_Description" DataValueField="Item_Description">
<asp:ListItem Value=""></asp:ListItem>
<asp:DropDownList>

A:

I am assuming that you are binding your drop downlist with the Item table.
So follow this approach.

Query would be (For binding drop downlist data from item table) 
select * from item
In C#
ddlItems.DataSource = "your data table in which you are taking result of above query";
ddlItems.DataBind();

(I think you already have done the above steps)

Now just add two attribute to your drop down list in source like this.
<asp:DropDownList ID="ddlItems" runat="server" DataTextField="Item_Description"   DataValueField="ItemID " >

Now you can directly access the id for selected item in drop down from c# code 
comm.Parameters["@ItemID"].Value=  ddlItems.SelectedItem.Value;

Edit
Now looking at your edited question you just need to change DataValueField="ItemID" only :)

