If there is no insulation in the wall then there's not many reasons for them to be in that wall void as the insulation would provide an area to nest. They may travel behind the wall voids but the main nest will not be behind it. They will most likely be using the studs as a food source and traveling up the sides of the studs. You will not foam the entire void, rather you will drill a hole close to the top of the ceiling/stud on either side of the stud. Once the holes are in place on each side, inject the foam into each hole for 5-10 seconds, allowing the foam to expand but slide down the sides of the studs where they would travel. If you are seeing them along the baseboard areas, drill holes every 8-10 inches apart across the area between studs, about an inch or 2 above the baseboard. Use the same injection rate for each hole and let dry. The Termidor Foam has some residual for about a month after it dissipates so if any are missed in the initial application the rest of the colony should be affected.
You can kill the termites yourself! The easiest and most efficient way would be to use Termidor Foam.
