At the end of June, Julia and I visited Marci and Jim Hess and explored some of their remnant and restored prairie in Lafayette County, Wisconsin. We were of course focusing on collecting leafminers, and I spotted something unusual on a cup plant leaf that I decided to collect even though it turned out not to be a leaf mine. Cup plant (Asteraceae: Silphium perfoliatum) gets its name from the way opposing petioles are fused at the base, forming a “cup” that catches rainwater:
These brown patches at the edge of one of the leaves looked like they could be mines of a casebearer moth larva (Coleophoridae: Coleophora)…
…but flipping the leaf over revealed that they were actually “window feeding,” the work of a caterpillar feeding on the lower leaf surface under the protection of some webbing it had spun.
The white object to the left looked to me like the cocoon of a metalmark moth (Choreutidae). I’m only familiar with a few species, and wasn’t sure if one was known to feed on cup plant.
On July 7, my hunch proved to be correct when the gorgeous adult moth emerged:
Knowing the host plant, I was quickly able to identify it as Tebenna silphiella, which has been given the common name of “Rosinweed Moth” because apparently rosinweed (Silphium integrifolium) is (was) its only known host. The Latin name, which allows for the possibility of it eating other Silphium species, turns out to be more appropriate.