As soon I was done watching the molting spider yesterday, I turned around and saw this unusual pattern on a black cherry leaf:
On close inspection, I saw (as you can plainly see at this level of magnification) that this pattern was caused by the feeding of a sawfly larva. I immediately thought of a description by Harrison G. Dyar* that has long puzzled me. In his notes about Schizocerus prunivorus (now Argidae: Sterictiphora prunivora), he writes that the egg is inserted “in a pyriform slit under the lower epidermis at the middle of one edge of the leaf; laid singly. The larva hatches and eats a curious winding slit down into the leaf; later this reaches the edge.” The host plants he lists for this species are pin cherry (Prunus pensylvanica), black cherry (P. serotina), and shadbush (Amelanchier canadensis). He provides no illustration of the “curious winding slit,” so we are left to imagine what this looks like. Needham et al. (1928)** seem to have interpreted this as a description of a leaf mine, since they include it in their discussion of leaf-mining sawflies. More recent literature, however, states that Schizocerella pilicornis, which mines in purslane, is the only leaf-mining argid sawfly. So I’ve been waiting to see something that I would call a “curious winding slit” in a cherry leaf, and this seems like a good candidate. I’ll see if I can raise this larva to adulthood to confirm my suspicion.
* Dyar, Harrison G. 1897. On the larvae of certain saw flies. Journal of the New York Entomological Society 5(1):18-30.
** Needham, James G., Stuart W. Frost, and Beatrice H. Tothill. 1928. Leaf-mining Insects. The Williams & Wilkins Company, Baltimore.