On the diatomaceous earth note: it works on all and any carapace insects. They just have to get covered in it, and they shrivel up and die. I bought some to deal with a cockroach problem, and then also used it on my plants to treat spider mites. It’s also a nutritional supplement, and completely nontoxic. The only risk is that you can’t be breathing it in or face respiratory issues.
How well it works for fleas I can’t say, given their jumping ability. For cockroaches I just laid down lines on the floor (think salt lines to ward off demons on Supernatural) so that they had to walk through it to get into my cupboards. For the spider mites I just dunked the plants’ leaves in a pile of it, and sprinkled it over the pots until they looked like they had experienced a localized snowfalls.
For flea treatment on pets, my boss suggests rubbing it into their fur. However the vast majority of a flea problem isn’t on the pets themselves, but in your carpet and upholstery. Revolution works by poisoning the pets’ blood so that the fleas die when they try to feed, but also doesn’t address the environmental population, which is why you’re supposed to spray your house.
You can use the diatomaceous earth on your house for fleas but white powder doesn’t typically mix with upholstery very well, and it has to be in sufficient quantities that they get more than their gross little feet covered.
My store sells 500g tubs for $12.99 CAD. If you’re looking for your own and can’t find this brand, just keep in mind that it has to be food-grade in order to be effective against insects.