Dovresti creare un commandbuilder per il data adapter

DA = New MySqlDataAdapter(StringaSQL, Conn)
DA.Fill(DT)
Dim cmbDA As New MySqlCommandBuilder(DA)
DA.InsertCommand = cmbDA.GetInsertCommand
DA.DeleteCommand = cmbDA.GetDeleteCommand
DA.UpdateCommand = cmbDA.GetUpdateCommand

....

DA.Update(DT)