Coptodisca larvae are leaf miners on various tree species. They are tiny moths, even smaller than Heliozela and Antispila spp.; accordingly, their larval leaf mines tend to be smaller than those made by larvae of moths in those genera. Adults of all species of Coptodisca are similar in appearance, with the forewing whitish in the basal half and golden in the apical half, with two opposing white triangles at two thirds the length of the wing, and a black apical patch. Individuals of some species or populations have a greater or lesser suffusion of dark-gray scaling on the basal part of the forewing. Reliable identification to species is attained only by rearing.
Coptodisca juglandiella (Fig. 1), which feeds on black walnut, Juglans nigra (Juglandaceae), is a typical Coptodisca. It undergoes at least two generations per year in Illinois, as active leaf mines have been found in June and September. Also known from Illinois is a species that mines leaves of hop hornbeam, Ostrya virginiana (Betulaceae); several additional species are likely to occur in the state.
Figure 1. Coptodisca juglandiella. Adult, and leaf mine on black walnut, Juglans nigra (Juglandaceae).