We have written a number of BYGL reports over the past several years on the springtime occurrence of leafmining damage on wild Ohio buckeyes caused by an unidentified leafmining fly in Ohio. During this week's BYGL online diagnostic inservice yesterday, Curtis Young (OSU Extension, Van Wert County) reported that he is seeing a return of the damage in northwest Ohio. Likewise, I have seen the damage in the southwest part of the state.
Leafminers create mines by consuming the tissue sandwiched between the upper and lower leaf surfaces. Leafminers may belong to a number of insect orders including Lepidoptera (moths), Coleoptera (beetles), Hymenoptera (sawflies) and Diptera (flies). One of the most notorious leafminers is the Horsechestnut Leafminer (Cameraria ohridella) which is a leafmining moth (family Gracillariidae) that is wreaking havoc on its namesake host in Europe. However, this leafminer has not been found in North America.
Opening the mines of our leafminer on buckeyes will reveal tiny light green fly larvae (maggots). The fly is most likely a member of the family Agromyzidae (leafmining flies). However, last season Dave Shetlar (OSU Entomology, "Bug Doc") consulted a synopsis of North American agromyzid leafminers, but could not find a reference to a leafmining fly that feeds on buckeye.
Thus far, I've only found this leafminer on wild Ohio buckeyes. I've never observed it on buckeyes in landscapes or on horsechestnuts. Since I cannot provide a scientific name or approved common name, I will refer to the fly as the "buckeye leafmining fly."
Buckeye leafmining fly maggots produce snaking (serpentine) leaf mines along the edges of the leaf or within the boundaries of the leaf veins. As the maggots mature, the mines simply become wider; they do not balloon into blotch mines. Leaves may be infested with only a single maggot that produces a meandering serpentine mine across much of the leaf or several maggots that produce parallel mines bounded by leaf veins. Like other agromyzids, females appear to use their sharp ovipositors to pierce the upper leaf surface so they can feed on the exuding sap. This produces tiny spot-like holes in the leaf surface; a symptom shared with other agromyzids such as the Native Holly Leafminer (Phytomyza ilicicola).
Seeking the true identify of this leafmining fly revealed a cautionary note. A Google search using the keywords "Aesculus leafminer" pointed me in the direction of the horsechestnut leafminer; however, this moth has not been found in North America. I also found reports of an "Aesculus leafminer" occurring on Ohio buckeyes in the upper Midwest. Presumably, since the reports describe serpentine leafmines, not the blotchy mines produced by the European moth, the reports were based on observing either the leafmining fly we are reporting or some other agromyzid.