We only use DE. It works great for us, and we raise hundreds and hundreds of birds a year. I don't know what's more effective than instantly dead. If I have to dust, I do it at night. The next day there's not a bug to be found. I repeat five days later and five days after that. We don't, however, have a big bug problem. General cleanliness should alleviate that most of the time, but bugs are naturally out there and will on occasion show up. If we have what appears to be a parasite problem, usually in the wetter months (March-ish and October-ish), I just put a bunch of DE on their feed. Usually two or three days later, things are back to normal. On the other hand, there's no reason to run birds out of doors when there's a wet spell. If you have a wet season, as opposed to a rainy day or two, keep the birds inside and dry. Don't run birds on crappy mud.
As was pointed out, different locals have different needs. In New England, our heavy hitters are lice and Northern Fowl Mites, which comes in id-late winter. Lice are pretty easy to deal with. For mites, prevent. Clean the coops well before winter, and then if there are a few nice days in mid-winter, empty the coops again and add new shavings. Keep 'em clean and keep 'em dry. If mites come, DE and you're done, unless your place is a sty, and then there's nothing for it.
Edited to add: I remember reading once that there's a kind of mite in the South that's particularly problematic. Indeed, I believe the advise was to burn the coop down and start over. I can speak nothing to southern mites...at least for now...I'm sure climate change will change that too.
