Elm Leafminer: Appearance, Territory, Damage and Life Cycle

Latin Name: Kaliofenusa Ulmi Sundevall

Appearance: Adults are little, stout-bodied black wasps around 3.5 mm long that can be seen sitting on foliage. The larvae are creamy colored, flattened, and have a dark brown head. They grow within blotchy leaf mines.

Hosts Plants: American elm, Camperdown elm, English elm, Scotch elm, and Siberian elm

Territory: The elm leafminer is most likely an invasive bug that arrived in North America on imported elms.  This leafminer can now be found throughout eastern Canada and the northeastern United States, all the way west to the Lake States.

Damage Insect Cause: They begin eating on the leaf’s top and below surfaces, forming brown blotch-like mines. When many larvae mine a single leaf, the mines typically join together, hollowing down the whole leaf. These leaves will wither, die, and fall to the ground over time. Holes are left in a leaf if it is only half mined. The insect hibernates as a larva in a brown paper-like cocoon found in the earth throughout the winter. Pupation takes place in the spring. Adults emerge in early May and are visible until the first week of June. The adults are little four-winged sawflies belonging to the ichneumonids, chalcids, ants, bees, and wasp’s insect order.

Life History and Habits: Winter is spent in a cocoon in the soil near an afflicted elm tree as a fully developed larval. Adults arrive immediately after fresh elm leaves emerge, usually lying on the leaves, and pupation happens in late winter. Females inject eggs into the leaf’s core’s upper surface, causing a dark oviposition wound. The larvae construct meandering leafmines between the leaf surfaces, which become blotchy as the larva grows and the mine spreads. The larvae grow to full size in 3-4 weeks after the eggs hatch, then cut through the bottom of the leaf and fall to the ground. They dig into the earth and create a small chamber before creating a protective cocoon around themselves. Only one generation is born each year.