Once again...............my point, and that of Rene Harrop..............is that in heavily fished areas, with catch and release, trout become very cautious about taking the fishers' offerings. To allow one to be MORE successful in such water, new designs of flies, taking into account what we now know about the stages of insects and what they look like and how they behave, new flies have been developed.
This is not to say that old styles and old patterns will not catch fish. But, usually, the fisher is looking for his/her best chance of taking a rising trout. It is for such fishers, in such heavily fished waters that these flies he has designed and tied are for. It is an attempt to give the fisher a better chance of fooling the fish. These flies and the designs of them are not developed and tied to fool naive trout.
Here's one I caught on the Ranch I caught on a Green Drake emerged pattern of Rene's:
The area just above The Ranch a day or two before the Ranch opened.