This is a serious problem. I would call your local County Extension Office, as just spraying them once isn’t going to break their reproductive cycle.
In the interim, I would read labels on pesticides at the DIY stores & buy a hose-attachment sprayer.
I looked it up at the County Extension Office as you suggested an found out that there is a lot of work involved. No easy spray fixes and they live through the winter snow. They say you can cut down your box trees if you want. I don't know if the trees I have are box trees, but I'm not going to cut my trees. I have too just maintain as much as possible by raking leaves and burning them and spray, I have animals so I have to be careful with that too.
What does your pest control use?
They probably will tell you it’s “proprietary”. If you want to use a spreader, there’s pesticide granules.
Once again, I would read labels at HD, Lowe’s & Menards.
Boxelder bugs don't die unless the poison has direct contact with them. We have them all winter in my area where even subzero temps doesn't kill them off. A perimeter spray such as ortho home defense helps keep them on the outside of the house. They are harmless
Mix dish soap and water in a spray bottle & spray directly on them. This does kill them. Also, I have vacuumed them if they are inside the house