This time last year, I wrote about some drooping Ohio buckeye leaves I had just found in Ohio, which I later determined to be caused by Zeiraphera claypoleana, the “buckeye petiole borer.” Commenting on my original post, Moni Hayne mentioned finding some leaf mines on Ohio buckeye in Iowa, and I encouraged her to post them on BugGuide.net. She did, and it is clear from her photos that the miner is an agromyzid fly. The problem is, no agromyzids are known to mine buckeye or anything related to it. Before long, two other Iowans, John Pearson and MJ Hatfield, had posted photos of similar mines. Here is one of John’s:
These gradually widening, linear mines are easily distinguishable from the two other mines that have been documented on buckeye, both of which are made by moths in the family Gracillariidae. Cameraria aesculisella makes an elongate blotch, pupating within the mine, whereas this agromyzid exits to pupate. The mine is very similar to that of its close relative, C. guttifinitella, on poison ivy:
In Illinois, Terry Harrison has reared a moth from Ohio buckeye that is indistinguishable from Caloptilia negundella, which feeds on boxelder. As with most Caloptilia species, C. negundella makes a small blotch mine on the underside of a leaf, then abandons it and feeds in a conical roll at the tip of the leaf:
Based on what I have seen so far, the fly larvae are only active in May. In addition to the Iowa sightings, this photo by Jason Dombroskie from Ontario appears to show the same mines, likewise in May. I was already planning to send out a plea for people to keep an eye out for these mines this month, when today a fourth Iowan, Aaron Brees, sent me photos of two examples he has found in the past week. So I figured I’d better put the word out now: if there is any buckeye near you, please take a look in the next week or so and collect any linear leaf mines you find (with larvae still inside them)! If you find any, place the leaves in a ziploc-type bag or a collecting vial right away; this will prevent the leaves from wilting, and they should last long enough for the larvae to complete their development. Then get in touch with me, and we can discuss what to do next.
If you do go out to inspect some buckeyes, here’s something else to look for: at least two BugGuide contributors have photographed sawfly larvae in the genus Dimorphopteryx feeding on buckeye, but this is not a known host for this or any other sawfly genus. They have been found in Lousiana in mid-May, and in Ohio in late June (so they may not show up until after the agromyzid leafminers are gone). The larvae have the general look of the ones below, which were feeding on oak and chestnut.