I just got some great pictures from one of great Extension Agents, Mark Danieley, this week
of some pretty messed up ash trees in a parking lot. They have sawdust (frass) accumulated on the ground around their trunks and in clumps on the bark. Of course the first thought was whether the tree was infested with emerald ash borer. Mark noted however that the holes were round not D-shaped. Turns out the trees are infested with banded ash clearwing larvae. As the larvae feed they periodically shove frass out of their galleries to keep them clear. This time of year the larvae are getting very big and thus feeding heavily. Adults will emerge soon. Thus, the holes in the pictures are from last year when adults emerged front he same trees. That is why they did not have characteristic pupal casings sticking out of the holes.