Shield Bearers: Appearance, Territory, Damage and Life Cycle

Latin Name: Coptodisca spp.

Appearance: The larvae are elongate and gnaw circular mines in the leaves. Larvae are about a fifth of an inch long and noticeably broader behind the head. When larvae are present in foliage, they can be seen by inspecting infected leaves in a backlit environment. Adults (moths) are about a fifth of an inch long, silvery and tan, with black, brown, red, white, or mixtures of these colors.

Hosts Plants: The larvae of this species of moth feed on the leaves of apple, cottonwood, crape myrtle, oak, madrone, manzanita, mountain mahogany, poplar, Prunus species, strawberry tree, walnut, and willow trees.

Territory: Europe and North America

Damage Insect Cause: Coptodisca females penetrate the underside of a leaf to deposit their eggs. Mines are formed in the host leaves by the larvae devouring the tissue between the top and lower epidermis. In the beginning, the larvae build serpentine leaf mines, while later instars make blotch mines. When the larvae reach maturity, they rip a 0.25-inch-long disc of tissue from the leaf and utilize it to construct a cocoon. The leaf damage caused by these larvae is characterized by abandoned tunnels with tiny oval holes. Because of the high population density, leaves can develop numerous holes, and infested leaves can become partially necrotic and drop prematurely.

Life History and Habits: Overwintering occurs as adult larvae (prepupae) or pupae inside mined tissue cut from host plants by the mature larvae. Adults emerge in the spring, mate, and deposit eggs in leaf tissue. The larva eats a round to oval-shaped leaf mine surrounded by bigger veins after hatching. Each larva eats the majority of the leaf tissue in a 1/5-inch diameter or smaller area, leaving just the thin, transparent top and lower leaf epidermis.

The adult larva then cuts the remaining epidermal layers that it feeds on. It uses silk to bind the edges of the circular sections together to make a casing. The larva falls onto a silken thread and takes its cut section of the mine away, pupating within the case in bark cracks or litter on the ground. Shield bearers have one to multiple generations every year, depending on the species. The madrone shield bearer, for example, has one generation every year. According to reports, the cottonwood or poplar shield bearer has up to three generations every year.