Great news! I suspect the Marmara on Cornus is something like this too... I haven't seen it in a while, but I wonder if it is active during the summer, exiting the mines in the same way... Both this one and the one on Cornus seem to like the green/new branches. I'll keep looking.

I wonder if these species have two generations, or if they overwinter as adults? In the north, all Marmara species (at least all the described ones) overwinter as larvae and continue feeding in spring, and all of the northern bark miners have a single generation, but clearly these rules don't apply everywhere!

The Gelsemium miner and the Clematis miner seem to have two generations (at least). I'll be looking for another generation on Acer negundo (I suspected there might be), and I'll look for the one on Cornus. I haven't found it in a couple of years.