The most aggressive approach is to apply a light spray of a pyrethroid insecticide to the siding and eves, not bugs, wherever boxelder bugs congregate. It is not necessary to treat the bugs directly. Pyrethroid insecticides will give longer residual activity but are considerably more toxic and hazardous to apply.
Several insecticides are available for this application including cypermethrin and permethrin. Be sure to check the label for appropriate usage. You'll need a three gallon backpack sprayer, safety equipment and a ladder. Treating the maple trees on which boxelder bugs develop has not been effective. These insects are strong fliers and may be migrating from trees some distance away.
The Pest Management Store
Identification guides, reference and gardening books, etc.
, is now available that should give longer residual activity than soap while maintaining soap's safety margin. Spray areas where bugs enter buildings and congregate. No need to spray bugs directly. What I like about this new material is that you get the benefits of a residual insecticide without the usual hazards of a conventional insecticide.