Diatomaceous Earth seems to be about the only thing that will kill boxelder bugs, too. I was up to my arse in those earlier this year. They kept getting “lost” and invading the house by the dozens! I did some sealing up of my exterior and put DE around outside in my stony borders. It took a week to have the desired effect, but I really think it has helped. I almost never see them inside now, and the masses outside have been decimated. Good stuff.
Just be sure you use the “food grade” stuff or some that is labeled for garden use, and not the DE that is used in pool filter media. The pool filter variety of DE is heat-treated, causing it to lose its efficacy (its microscopic sharp edges which cut the bugs and cause them to dehydrate and die).
See post 66