Lilac (or Ash) Borer
The Lilac borer (Podosesia syringae) is a day-flying, wasp mimic, clearwing moth. How’s that for a mouthful? Let’s break it down to figure out exactly what kind of critter this is. Lilac borers are moths, meaning they belong to the Order Lepidoptera (moths and butterflies). From the image you can clearly see that it’s also a wasp mimic, and a very good one at that. Because this moth is a clearwing (F. Sesiidae), it closely resembles the wasps it mimics and gains an advantage of reduced predation. Typically most moths are nocturnal, but the traits this moth possesses allow it to be active during the day. I think that’s covers the name explanation!
Luckily for RBG, this pest of lilacs is not a serious concern right now. The larvae are wood borers, and although some old larval holes exist in a few of the larger trunks of some of the lilac bushes in the Lilac Dell (see image), no new “boring” evidence was found.
The Lilac Dell in RBG’s Arboretum exhibits over 600 species and cultivars of common lilacs (check out #RBGpotw) – they are at their peak now and for the next week. Visit them while you can, they look spectacular, and the heady fragrance in the morning and early evening is beyond compare.