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Japanagromyza viridula (formerly Agromyza viridula)

 Damage from the oak shothole leafminer. Photo: Tawny Simisky
Scientific Name: 
Japanagromyza viridula (formerly Agromyza viridula)
Common Name: 
Oak Shothole Leafminer
Growing Degree Days (GDD's): 
None available at this time.
Host Plant(s) Common Name (Scientific Name): 
Oak (Quercus spp.)
Insect Description: 

The oak shothole leafminer is considered native to the United States, although very little is known about this species and other agromyzid leaf miners. It is reportedly found throughout the eastern U.S. from Maine to Georgia, and likely the entire eastern half of the United States. Adult female flies are active when red and white oak buds are just opening and until the newly developing leaves are approximately 5 cm (~2") in length. Females create damage to the leaves with their ovipositors, which allows them to drink host plant fluids from the leaf. Occasionally, the female will also lay an egg in the leaf. The eggs hatch and mining from the larvae of the oak shothole leafminer is reported to occur in the second week of June in Maine, while in Ohio there are reports that the blotch mines created by this insect are most evident in early to mid-May in that state. Reportedly, fully grown larvae emerge from their mines to drop to the soil to pupate. Johnson and Lyon (1991) states that although adults are present the following spring, they may also reappear later in the same season “if a second flush of growth takes place or water sprouts (epicormic shoots) develop”. The oak shothole leafminer is not usually considered a significant pest of oak, and the damage it causes typically does not have a significant impact on the overall health of the tree. However, in a 1967 paper detailing observations from the 1960’s in Maine, there is a question about the economic importance of this species on ornamental oaks. In 1964, an “abundance of neat, prominent holes in foliage of ornamental red and white oaks (Quercus borealis var. maxima and Q. alba) in southern Maine” was observed. This was again observed in 1965. The cause, at the time determined to be Japanagromyza viridula, was identified by the State Entomologist with the Maine Forest Service and partners in the USDA. Their observations stated that many more “punctures” are made by the female for feeding than for oviposition (egg laying) and this is a common pattern of flies in this family. This might explain why the damage from the feeding adult females seems so extensive, whereas the mines from the feeding larvae of this insect are not present in the same proportion and may even be difficult to find.

In 1965 in Maine, the first discovery of adult flies was made in mid-June on red oak sprouts. Feeding punctures from female flies was described as numerous, while egg laying was relatively rare. “Mines were of a blotch type.” Larvae emerged from their mines before pupating. Not much is known about the life cycle or its timing during the season for this insect. This 1967 paper suggests that multiple hosts may occur for the flies, although that is not certain either. Based on what occurred in Maine in 1964 and 1965, the authors suggest that the injury caused by the peculiar feeding habits of these flies may be economically important on ornamental oaks. At the time, ornamental white and red oaks were widely affected by the shot-hole injury in much of southern Maine. However, only circumstantial evidence was available to suggest that, under certain conditions, the emergence of agromyzid flies and the co-occurring appearance of juvenile foliage of oak may allow extensive attack. Following the widespread activity of this insect in 1965, “the infestation expected in the spring of 1966 did not materialize for some unknown reason” (LaBonte and Lipovsky, 1967).

Damage to Host: 

The damage caused by the activity of the adult female oak shothole leafminer is characteristic of this fly species. Females create holes in the leaves when they are no more than 4.5 cm (~1 3/4") long. This damage is caused by the adult female fly feeding. Because the fly’s mouthparts are unable to pierce the newly developing leaf tissue, it uses its ovipositor to cause enough damage such that any fluids leaking from the leaf can then be lapped up. The female fly will move the ovipositor in side-to-side and circular motions, creating initial injury that is no more than 0.7 mm (~3/100") at its widest point on the tiny, newly developing leaves. The area injured by this action soon turns brown and dries, eventually forming a small disk. This disk of necrotic tissue often remains conspicuously attached to the expanding hole formed in the leaf. As the leaves grow in size, the damage from these flies enlarges, and the holes are described to be approximately six times the size of the original injury created by the tiny flies, who are themselves about 3 mm (~1/10") in length. Occasionally, the female fly will lay an egg in the leaf tissue. This feeding activity results in fully expanded leaves that appear tattered and full of holes, very early in the season. This can be shocking to property owners, as the flies themselves are so small they go unnoticed. Additionally, as was seen in 2019 in Massachusetts, damage to the leaves of oak from this insect can appear more severe in cases where oak anthracnose (Apiognomonia errabunda) is also present in the same tree. This fungal leaf disease can cause the leaves of white oak to become dry, papery, and gray-colored or the leaves become blackened and wilted.


As oak leaves expand in the spring, look for tiny holes or tatters in the leaves. The adult oak shothole leafminer flies themselves may not be visible due to their tiny size. Because feeding damage occurs so early, management of this insect may be very difficult to time. Thankfully, the oak shothole leafminer rarely causes damage to its host that impacts tree health, so management is rarely necessary. This species is also typically found in low populations, and may go completely unnoticed. On occasion, outbreaks occur for a couple of years prior to collapse. The feeding damage from this insect may be confused for that of Lepidopteran caterpillars that chew leaves early in the season prior to leaf expansion. (For example, spongy moth - Lymantria dispar - or winter moth - Operophtera brumata.) The main difference between the damage from the early season feeding caterpillars and the oak shothole leafmining fly is the necrotic tab of tissue (the tiny, circular tab) that remains in the center of the hole in the leaf. That sign, along with leaf mines, will differentiate the damage for this species (Johnson and Lyon, 1991). Note that later on in the season, the necrotic tabs of tissue may fall from the leaf - making it difficult to identify damage caused by this insect.

Cultural Management: 

No effective cultural management options are understood for this species at this time.

Natural Enemies & Biological Control: 

As discussed above, following the widespread activity of this insect in 1965 in Maine, “the infestation expected in the spring of 1966 did not materialize for some unknown reason” (LaBonte and Lipovsky, 1967). This historical record, along with observations in 2019 and subsequent years in Massachusetts, seems indicative of a population collapse potentially caused by natural enemies of this insect. There could be biotic (or abiotic) explanations for the collapse of the oak shothole leafminer populations, or more likely some combination of the two. At this time, the natural enemies of this species are not understood.

Chemical Management: 

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Bifenthrin (NL)

Carbaryl (L)

Clothianidin (NL)

Cyantraniliprole (NL)

Cyromazine (NL)

Diflubenzuron (N)

Dinotefuran (NL)

Emamectin benzoate (L)

Fenpropathrin (NL)

Flonicamid+cyclaniliprole (N)

Gamma-cyhalothrin (adults) (L)

Horticultural oil (L)

Imidacloprid (L)

Insecticidal soap (NL)

Lambda-cyhalothrin (adults) (L)


Neem oil (NL)

Permethrin (L)

Pyrethrin+sulfur (NL)

Spinosad (NL)


Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), diflubenzuron (soil drench), dinotefuran (soil drench), emamectin benzoate (injection), imidacloprid (soil drench), and neem oil (soil drench).

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: .