I returned the following year (July 16, 2013) to the same American Elm (Ulmus americana) sapling, looking for more adults, but none were present. However, I did notice many drooping and/or severed branch tips. Just proximal to the cuts, there were clear signs of stem borers at work (small holes, some packed with frass/sawdust). I tried to gently peel back the bark on one of the stems, but accidentally killed a cerambycid larva in doing so. Impossible to prove, but perhaps the tree was infested with Oberea praelonga? Hopefully, I will be able to rear some adults from these same branches. (Addendum: Unfortunately, I was not successful with that either!)