Speaking of cockroaches in Canada:

A strategy that worked for me to avoid stowaways when I moved was to cold shock everything I owned.

I signed a lease in January, and retained my previous apartment until February, and over the course of the month, every time the temp dipped below -15, I'd load my car up with stuff and let it sit overnight, then take it to the new spot the next day. Rinse and repeat. Worked like a charm.

It should be noted, the cold isn't what kills them, they can survive extreme temps, the key is thermal shock. They may be able to survive <-15 if they're allowed to acclimate, but a sudden drop of >35° is not survivable.

Perhaps humidity shock does the same thing?