^I've seen brookies key in on Quill Gordons, March Browns, Sulphurs, Lime Sallies, Caddis, Inchworms. Everyone is correct...they are opportunists for the most part. Avoid spooking them and get a good presentation is usually money. Once in a while, you may run into a hatch and more selective trout- it happens. It also depends on how much fishing pressure your quarry see. A brookie on the Savage River tailwater will be more picky about matching the hatch (say Sulphurs) then a brookie on a freestoner where something similar in yellow will do. For Class A tribs, I try to carry patterns that mimic many different insects. Doing so cuts down on carrying too many flies while affording you max coverage for what might be flying around. The more you fish this way, the more you learn that keeping things simple really is best.