I can only guess that it might be tentiform leaf miner. It has been years since I have seen it. How the time flies, come to think of it, it has been decades. If it is TLM , then do nothing for it and it will be cleaned up by parasites in subsequent years. Where are you in WA, give us a zone.

It's outside of Vancouver, WA - the SW part of the state. I've looked over a few places on the web searching for tentiform leaf miner... The green larvae looks familiar, but the leaf damage is WAY worse in my case - large fractions of the leaves are completely missing other than the veins. And I haven't seen any pictures on the net of the cacoon area - to compare to mine. The adult moth I saw in a couple of pictures shows a dark brown color to it, but I went & looked on my leaves, I see some very small moths with a green color, but the same shape & size. I wonder if it's a different variety of this pest?

Fauls:

Whatever you have, you might want to spray your apple trees with dormant oil a couple of times during the winter months; once early, and again just before bud break. If insects are overwintering on your trees, the oil will suffocate the eggs. Make sure you clean up fallen fruit and leaves around the trees in fall, since some insects can overwinter below the trees as well.

It would be nice to know exactly what pest you are dealing with, but even nicer to get rid of them. Oil sprays are a good routine preventive treatment for all pome fruits. It is always best to stop them before they get started.

Don Yellman, Great Falls, VA