Adult locust leafminers are beetles that are approximately 6 mm long. Adult beetles are the overwintering life stage, often found sheltered beneath the leaf litter nearby host trees. When temperatures warm in the spring, adult beetles emerge from their winter locations and begin feeding on newly developing host plant leaves. Adult females deposit their eggs which are flat and oval in shape on the underside of host plant leaves. Eggs overlap and are cemented together with excrement. Following hatch, the larvae enter the tissues between the top and bottom layer of the leaf, creating a mine as they feed. Mines grow in size as the larvae grow in size and feed. This species preferentially mines the tips of host plant leaflets. Mines are irregular blotches in shape, containing larvae that when fully grown appear flattened and yellowish-white in color. Larvae have black heads, legs, and a black anal shield. Pupation occurs within the mines in the host plant leaves. Beetles will emerge from the pupal cases, at which point the adult beetles will skeletonize the undersides of the host plant leaves. In parts of its range, such as southern Ohio, a second generation of locust leafminers occurs. A second species of leafmining insect (Sumitrosis rosea) occurs in locust and may be found in the same trees as Odontota dorsalis.
Foliage of black locust are impacted by the larvae and adult beetles. Larvae create a blotch-shaped leaf mine. Adults will skeletonize the undersides of the host plant leaflets. In high populations the entire tree's foliage can appear fire-swept by late summer. If a tree grows two sets of leaves during a single season, the locust leafminer is capable of damaging both. If this happens during multiple seasons, the tree will perish.
Monitor for adult beetle emergence as new foliage develops in the spring. Flip leaves over and search for egg masses. Damage from this insect may not be noticed until leaves appear scorched or browned by mid-summer.
Proper planting and practices that maintain tree vigor can help individual trees withstand defoliation if it occurs. This can include adequate watering during drought periods.
Several wasp parasitoids of the locust leafminer are reported. Trichogramma odontotae, Spilochalcis odontotae, and Closterocerus tricinctus are three notable species. In the southern portion of the locust leafminer's range, the wheel bug Arilus cristatus is a common predator of the larvae while they are still inside the leaf tissue. Another predator in the Miridae, Lopidea robinae is also known.
Abamectin (NL)
Acephate (NL)
Azadirachtin (NL)
Beauveria bassiana (NL)
Bifenthrin (NL)
Clothianidin (NL)
Cyantraniliprole (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)
Malathion(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.
