I use any yellow dubbing. Sometimes I use Yellow Ice Dubbing, Yellow SLF or even Superfine. I also mix up the Ice Dubbing with the other two to give it a little trigger of sorts. I use either a copper, or brown glass bead. The rib is either brown krystal flash or copper. I tie the flies on a size 18 2499spbl.
The main thing is that the imitation has a yellowish body and a barker head. If you do not like beads you can dub the head.