I catch wild trout on Powerbait micronymphs on a dead stick in winter. Not sure if it's the scent, the flavor, or the wiggly legs that draws the strike, but I do suspect it's the flavor that keeps the bait in their mouth long enough for me to get a hookset. They seem to work on it for a long time, like real bait. When they aren't fresh, you don't get all the strikes, and they don't hold on long at all. The wild trout I catch with them are mostly browns in lakes. Haven't tried them in streams. I note also that I have more success with them than I do with completely artifical lures, like kasty's and other jigs and spoons without bait.
Even so, there are problems with enforcement of this law. Anglers pretty much have to self police. It is often understood that certain regulations are not easily enforced, and the thinking is that most anglers will obey the ban voluntarily, and the few that ignore it will be few enough in number not to cause a big problem. I talked to a warden friend of mine and he acknowledged that they find bait and bait containers at Parvin (artificials only), but that they find a heck of a lot more at nearby Dowdy (bait allowed). My observation, fishing up there a lot, is that the artifical lures only reg at Parvin basically served to insure that fishing pressure there is a lot lower than at Dowdy. In some cases, that is really the goal. Set the regulation so people will voluntarily choose to fish there less often.