[justinl]

I had a pretty good outbreak of photosynthetic FW and my Halichoeres chrysus took care of them pretty good. I've heard they will clean up AEFW too so I gues they aren't too species specific about their FW prey. H. melanurus and H. iridis are supposed to be very good at this as well. Don't know about red bugs.

this is just me speculating now, but I also firmly believe that it is the smaller specimens who are most likely to eat such small prey; Many adult fish in general do something called resource partitioning. That is, the adults eat different prey than their juvenile forms so as not to compete for food with them and reduce their survival. It is a common behavioral strategy and I would not be surprised to see wrasses exhibiting this.

edit: also, you should not feed the tank much. If you stuff the fish full of easy to obtain prepared foods, there won't be any need for it to expend energy hunting for live food.