Leafminers are so named because they tunnel between the upper and lower epidermis to feed on the leaf mesophyll. Leafmining is a lifestyle that's unrelated to taxonomy. The feeding habit is practiced by insects belonging to the orders Hymenoptera (sawflies), Coleoptera (beetles), Lepidoptera (moths), and Diptera (flies).
The Boxwood Leafminer (Monarthropalpus flavus) confines its leafmining activity to its namesake host and is one of the most obvious leafmining flies found in Ohio. It was once the most significant boxwood pest in Ohio; however, Box Tree Moth (BTM) (Cydalima perspectalis) has largely stolen its thunder.
Oddly, boxwood leafminer belongs to the “gall midge” family Cecidomyiidae. Most dipteran leafminers belong to the “leafmining fly” family, Agromyzidae. I posted a BYGL Alert on boxwood leafminer on April 24, 2026, titled, Boxwood Leafminer Adults are on the Wing. You can read the Alert by clicking this hotlink: https://bygl.osu.edu/node/2621
Buckeye Leafminer Fly
I first came across this leafmining fly in 2013 on wild buckeyes (Aesculus spp.) in a park near my home in Butler County, OH. However, the culprit was unknown; it had never been classified by science. All that I could determine was that the fly most likely belonged to the dipteran leafmining family, Agromyzidae.
The previously unknown leafmining fly on buckeye became known to science with a 2019 paper published in the journal Zootaxa, in which this leafmining agromizid fly, along with 11 others, was described and given a scientific name. The leafminer that I had found in southwest Ohio, and the subject of this Alert, was named Phytomyza aesculi.
There’s evidence that buckeye leafmining fly females use their sharp ovipositors (ovi = egg) to puncture the upper leaf surface so they can feed on the exuding sap. Of course, they also use their ovipositors to insert eggs between the upper and lower leaf surfaces.
Once the eggs hatch, the resulting early instar buckeye leafmining fly maggots produce snaking (serpentine) leaf mines. As the maggots mature, the mines become wider; sometimes ballooning into blotch mines. Leaves may be infested with only a single maggot that produces a meandering leafmine, or several maggots that produce coalescing leafmines.
The fly appears to have only one generation per season. I've only found P. aesculi on wild buckeyes. I've never observed the leafminer on buckeyes in landscapes or on horsechestnuts. The Entomological Society of America has not yet assigned a common name to the new scientific name, so as with past BYGL Alerts on this leafminer, I will continue to call it the "buckeye leafmining fly."
Damage by the buckeye leafminer fly on large trees is usually simply an oddity, affecting a few leaves. However, damage to small, understory trees can be significant, affecting multiple leaves. However, I’m not aware of any research quantifying impacts on forest ecosystems.
Native Holly Leafminer
Our native holly leafminer (Phytomyza ilicicola, family Agromyzidae) focuses on American holly (Ilex opaca) and associated cultivars. The flies emerge in the spring to target the tender, newly expanding leaves. The flies are doomed if they emerge after the leaves fully expand and become hardened.
As with the buckeye leafminer fly, the holly leafminer females use their sharp ovipositors to puncture leaves to release sap. They then use their lapping mouthparts to gulp the nutrient-rich sap droplets.
The female puncture wounds were once called “spine spot” and erroneously blamed on the sharp leaf spines piercing neighboring leaves in high winds. However, it would require hurricane-force winds to whip around the stiffly attached leaves. Thus, spine spot falls into the category of possible, but not probable.
Of course, the females also use their ovipositors to insert eggs into the leaves. The resulting maggots follow the same leafmining patterns described with the buckeye leafmining fly. Thin, snaking, serpentine mines eventually expand into blotch mines.
Leafmining progresses throughout the growing season and ceases the following spring when the maggots pupate. New adults emerge with the expansion of new leaves.
Damage by the native holly leafminer can cause leaves to become discolored and drop prematurely. However, the impact is mainly aesthetic on landscape holies. It seldom rises to a level that produces significant harm to overall plant health. Also, populations tend to rise and fall dramatically from year to year owing to impacts from natural enemies, particularly parasitoid wasps. Thus, control measures aren’t required.
However, leafmining activity in nursery production is a different matter, especially on trees tagged for sale. According to Hong and Day (2026), adult activity can be suppressed with topical sprays applied as new leaves are expanding, using products with the active ingredients cyromazine, lambda-cyhalothrin, permethrin, and the biorational insecticide, spinosad.
Leafmining maggots can be suppressed with applications of systemic products with the active ingredients acephate, dinotefuran, imidacloprid, and the insect growth regulator insecticide, cyromazine. Applications should be made after egg hatch, which usually occurs sometime in June in Ohio. An imidacloprid application can be made earlier since it takes time for the less soluble insecticide to disperse throughout the plant.
Finally, our native holly leafminer should not be confused with the non-native Holly Leafminer (P. ilicis) that targets non-native Christmas holly (I. aquifolium) and its cultivars as well as associated hybrids. The holly leafminer has the same lifecycle as our native leafminer. However, aside from targeting different hosts, the holly leafminer maggots skip the serpentine leafmining phase to produce blotch mines.
Selected References
Eber, S. (2004). Bottom‐up density regulation in the holly leaf‐miner Phytomyza ilicis. Journal of Animal Ecology, 73(5), 948-958.
https://doi.org/10.1111/j.0021-8790.2004.00867.x
Eiseman, C. S., & Lonsdale, O. (2019). New State and Host Records for Agromyzidae (Diptera) in the United States, with the Description of Ten New Species. Zootaxa, 4661(1), 1–39.
https://doi.org/10.11646/zootaxa.4661.1.1
Hong, C., Day, E., (Content Coordinators). (2026). Horticulture & Forest Crops 2026 Pest Management Guide, Virginia Cooperative Extension Publication 456-017.
https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-017/ENTO-635.pdf
Marino, P. C., & Cornell, H. V. (1992). Adult movement of the native holly leafminer, Phytomyza ilicicola Loew (Diptera: Agromyzidae): consequences for host choice within and between habitats. Oecologia, 92(1), 76-82.
https://www.jstor.org/stable/4220130
Marino, P. C., & Cornell, H. V. (1993). Adult feeding and oviposition of Phytomyza ilicicola (Diptera: Agromyzidae) in response to leaf and tree phenology. Environmental Entomology, 22(6), 1294-1301.
https://doi.org/10.1093/ee/22.6.1294
