When the hatch first begins these wet flies are more effective in taking fish than the dry fly because the emerging natural is available to the trout longer and relatively helpless. As soon as it reaches the surface, it breaks the film and is ready to fly away. Fish the wet fly imitation upstream, let it pass you, drift a while and then complete the presentation with a Leisenring lift to accurately imitate what happens to the real flies. It is during this lift that many strikes occur as the trout have focused on this habit as an identifier. When you see rises with bubbles, which are a positive indication the trout are breaking the surface film and taking the duns, then switch to the Quill Gordon classic dry fly using short, drag-free, dead drifts over sighted fish.
Some folks like to use a no-hackle version of the imitation instead of a classic pattern.
P. adoptiva is a small fellow of only 6 - 8 mm in length. A size 16 nymph is good. A Pheasant tail nymph in sizes 16 or maybe 18 is recommended. A Slate-Winged Mahogany Dun is the correct dry imitation, but I wouldn't bother with it. I have found the hatch of this fly is uncertain, not heavy, on again, off again, and does not often entice many trout to rise to the surface for it.