Coptodisca juglandiella

Identification.

The original description of C. juglandiella contains little information about the habitus of the moth ("Except that it is perhaps a trifle smaller, I cannot distinguish this species in the imago from A. splendoriferella ."); it deals rather with the mine, the case and host plant (Chambers 1874). On the contrary, Clemens (1860) gives a detailed description of the adult of C. lucifluella, but this is still not sufficient for identification. Bernardo et al. (2015) redescribed this species, designated and figured its lectotype and figured also an adult specimen of C. juglandiella and gave a brief diagnosis of the latter species. We did not have the opportunity to examine the type specimen(s) of C. juglandiella . According to Miller & Hodges (1990) the majority of Chambers’ types are deposited in the Museum of Comparative Zoology (Harvard University) but a significant number are located at the National Museum of Natural History (Smithsonian Institution, Washington DC = USNM) and there are also potential but probably untraceable type specimens at The Natural History Museum (London). This species is absent from the list of Miller and Hodges (1990). We consulted the type database of USNM without result (NMNH 2020), thus the type(s) may be lost. Hungarian specimens of the two species show the diagnostic differences underlined by Bernardo et al. (2015). There is an image of an intact C. juglandiella specimen on the homepage of the Moth Photographers Group (2019) which matches the diagnosis and image of Bernardo et al. (2015, suppl. material 3). Therefore, we are confident that the identifications of Hungarian specimens as C. lucifluella and C. juglandiella are correct.

Diagnosis.

Adults of C. juglandiella (Fig. 1) are similar in external morphology to C. lucifluella (Fig. 2). However, the two species can be distinguished by wing pattern: the conspicuous black filling of C. lucifluella between the silvery grey basal area and the patch at dorsum is absent in C. juglandiella, in which the colour of this area is transitional from silvery grey (proximal edge) to yellow (distal edge). The silvery white tornal patch is narrower in C. juglandiella than in C. lucifluella . No differences in wing shape and venation were found between the two species (Figs 3, 4). In the male genitalia, we found more sensilla of the pectinifer in C. juglandiella (Fig. 5a, b) than in C. lucifluella (Fig. 6a, b), while differences between the female genitalia of the two species were not observed.

The shape of the mines is different in the two species: in C. juglandiella mines are always round, 7 mm long and 5 mm wide on average (Fig. 11), mines of C. lucifluella are rather elongate and angular (Figs 9, 10), average size 8 mm × 5 mm. The position of mines in leaflets is also different: mines of C. juglandiella are situated mostly close to the junction of the midrib and a lateral vein (Fig. 13), while the mines of C. lucifluella may occur throughout the leaflet (Fig. 12). Frass of the larva of C. juglandiella is hidden under a small area of the upperside parenchyma of the leaflet, preserved by the larva (Fig. 11), in contrast to the frass of C. lucifluella which is visible from both sides because it is dispersed in the mine and no cover is preserved (Fig. 10).

The body of the mature larva of C. juglandiella is off-white and its head, as well as the first two thoracic segments, are pale yellow (Fig. 15) while the larva of C. lucifluella is monochromatic rusty brown (Fig. 14).

We could not observe differences in the morphology of the cases or the pupae between the two species.

Morphology and recorded host plants.

Adult. External characters (Figs 1, 3). Length of forewing 1.5-1.8 mm including fringe. Head silvery grey, rest of body dark silvery grey. Basal half of forewing silvery grey; two triangular patches present at distal thirds of costa and dorsum, these patches silvery white with black border at each side. Colour of the area between the silvery grey basal field and the patch at dorsum transitional from silvery grey to yellow in proximo-distal direction. Patch of dorsum narrow (Fig. 1).

Genitalia. In the male genitalia the pectinifer has six sensilla on right valva and seven sensilla on left valva (Fig. 5a, b). Phallus with two rows of anellar spines. Female genitalia with six oviscapt teeth: a pair of large ones anteriorly, posterior ones forming a broad, slightly indented apex (Fig. 6a). Corpus bursae ovoid, apparently without either scobinations or signum (Fig. 6b).

Mine. Coptodisca juglandiella prepares blotch mines (Fig. 11) visible on both sides of the leaf. Mines are always situated between lateral veins and never traverse them. The shape of mines is always round, 7 mm long and 5 mm wide on average. Mines usually start close to the junction of the midrib and a lateral vein. This species preserves a small area of the upperside palisade parenchyma of the leaflet and hides all of its frass under this cover.

Larva. Body off-white, head and first two thoracic segments pale yellow (Fig. 15).

Case. Prepared from an oval-shaped area of the leaflet, which is severed from the leaf by chewing the epidermis on both sides around this piece (Fig. 19). Then the oval plates are attached with silk along the edges, forming an oval-shaped shield, which is somewhat more elongate than the original leaf pieces, 2.9 mm long and 1.3 mm wide (Fig. 18).

Host plants. Coptodisca juglandiella is usually found on Juglans nigra in Hungary, but we also found it on J. major and J. cinerea (new hostplant records).