Diagnosis. See S. minusculella.
Male. Wingspan: 3.9-4.7 mm. Head: frontal tuft ferruginous to reddish; collar bronzy fuscous; scape yellowish white; antenna approximately half as long as forewing. Forewing: shiny copper-brown, sometimes with faint purple tinge near base and in distal part; terminal cilia concolorous. Hindwing: pale grey brown; without androconial scales. Abdomen fuscous with metallic reflections. Female. Wingspan: 4.0-4.7 mm. Similar to male. Male genitalia. Vinculum with widely separated very small and triangular lateral corners, emargination shallow. Uncus with widely separated distinct latero-posterior protuberances. Gnathos with short transverse bar and short horns. Valva with long distal process and pointed inner lobe; distal process extending much further posteriorly than uncus, inner lobe extending nearly as far as uncus. Aedeagus approximately as long as genital capsule. Cornuti oval to triangular. Female genitalia. Bursa copulatrix very small, approximately one-third length of abdomen. Accessory sac very small and almost round; reticulate field small and indistinct. Ductus spermathecae distinctly longer than bursa copulatrix.
Host plants: Malus sylvestris and Pyrus communis. Egg: on leaf underside or upperside. Larva: green. Mine : starts as a slender gallery, with thin linear frass, often following a vein or leaf- margin; widens later, convolutions often so contorted as to form false blotch; frass usually narrow linear throughout, occasionally narrow and contorted in parts. Often several mines occur in the same leaf. Mines on Malus sometimes very similar to those of S. malella, but malella has a yellow larva; vacated mines cannot be identified with certainty. The other Pyrus-feeding species often have coiled frass which is always wider than in desperatella. Cocoon: bright orange-red.
Not in Scandinavia and Finland. - Widely distributed but local and very rare in western Europe and England, more common in the mountains of C. Europe. Not found in The Netherlands and Belgium. Western USSR and central Italy (Schoorl et al., 1985).
Voltinism: incompletely known, records contradictory. Larvae known from end of August until beginning of October (Emmet, 1976), but Borkowski (1969) reported two generations from the Polish Sudeten, with larvae in June/July and August/September.
Description based on Johansson and Nielsen (1990)