Western Tentiform Leafminer: Appearance, Territory, Damage and Life Cycle

Latin Name: Phyllonorycter Elmaella Appearance: Adult moths are around 0.12 inch in length. The wings are golden bronze with white bands, and they are draped over the body like a roof. On the undersides of leaves, flat, transparent eggs are laid. The larvae’s appearance changes as they go through five instars, depending on their age. Young larvae are cream-colored and lack legs. Older instars have legs, are cream-colored, and are around 0.12 inch in length. Mature larvae are yellow in color and about 0.18 inch long. Hosts Plants: Western tentiform leafminer predominantly targets apple and crabapple; if these are utilized as pollinators, they may be extensively affected. It can attack pears; however, this has been quite rare in Washington. It also destroys sweet and tart cherries and has been particularly damaging to the former crop in some areas. Territory: Europe and North America Damage Insect Cause: When the larvae hatch, they nibble through the leaf tissue, forming a mine through the egg cover. The first three instars feed on spongy mesophyll, forming a mine under the leaf surfaces, often along leaf veins. As the pupa develops, mines on the underside of the leaf expand in size. Mines may be observed around the summits of the leaves, and the last two instars feed on various leaf tissues up to the skin. Because of the webbing produced in the mine, the leaves appear mottled, peaked, or tentiform. Under the epidermis, the green color is gone, leaving white patches. When exceptionally large infestations are present and produce significant foliar damage to destroy limbs or blooming branches, the damage is primarily foliar and only a problem with fruit set. Adults of the first generation deposit their eggs mostly on early stem leaves and flower clusters. When adults emerge from pupation, they break through the surface of the leaf, revealing a mine. Pupal casing is still present in the mine. Adults lay eggs on the underside of leaves three to four times per year. Life History and Habits: This insect spends the winter as a pupa in leaf litter. The adults appear early in the season and deposit eggs on the undersides of leaves at the pink stage of flower bud development. Eggs are transparent and flat. The first three larval instars feed on spongy soft tissue inside the leaves, causing blotches to appear solely on the underside of the leaves. Later instars emerge between early and mid-May. These feed on the upper surface of the leaf beneath the epidermis, creating silken webs to connect the mine, giving it the distinctive “tentiform” look. The larvae then pupate within the leaf. Every year, three to four generations overlap.