In the query for the listbox, you can make it filter by a value on the form. Make sure your form is open. Then in the query for your listbox, on the field you want to filter by. Right-click in the "criteria" section and click "build". The expression builder pops up. in the box on the bottom left of the builder click "forms", then "loaded forms" then the form you are filtering by. Then in the middle box will be a display of all controls on the form. Double click on the control that you want to use as a filter, then Click OK. Then save your query.