Yes, the powder cuts their exoskeleton and they perish from dehydration. It sounds like an awful way to go, but I'll do it if that's what it takes to keep them out of my kitchen.

As for diatomaceous earth, it works best in dry places. If it gets wet they can walk right over it without issue, or it will just wash away in the rain. It's also an ingredient in toothpaste and is included in animal feed to allegedly kill parasites. The research on that seems to be propped up by those invested in selling the stuff, though, so take that with a grain of salt.

Nature is really quite incredible. This blew my mind when I saw it, and it unravels a lot of the mystery behind ant locomotion: https://i.imgur.com/7Zh6Im5.gif -- It's so simple, but it works amazingly well.