Stigmella incognitella
Diagnosis. Hardly separable from the closely related S. perpygmaeella on external characters. S. incognitella and perpygmaeella can usually be separated from the very similar, oak-feeding species S. svenssoni by usually smaller size and less coarsely scaled forewing and S. roborella and S. ruficapitella (female) by more coarsely scaled and less shining forewings, shorter antennae and usually smaller size. The male genitalia differ from those of perpygmeella in having larger uncus, longer valvae and larger spines on vesica. The longer apophyses and pectinations on bursa separate the genitalia of incognitella from perpygmaeella.
Male. Wingspan: 5.0-6.0 mm. Head: frontal tuft ochreous to yellowish brown; collar pale ochreous; scape yellowish white; antenna three-fifths of forewing length, grey. Thorax as forewing. Forewing: unicolorous grey-brown, moderately shining; distal third more coarsely scaled, often with faint purplish sheen; terminal cilia grey brown, slightly paler at tips. Hindwings and cilia grey. Abdomen fuscous with small yellowish grey anal tufts. Female. Wingspan: 5.0-6.0 mm. Antenna half length of forewing. Abdomen with pointed ovipositor and long, pale grey anal tufts.
Male genitalia.Vinculum very long and deeply excavated, lateral lobes long, club-shaped. Uncus roughly square with broad, medial emargination and small paramedial notches. Gnathos with broad lateral arms, anterior processes small, pointed; horns and horizontal bar short, forming a V. Valva rectangular with very short, blunt distal process. Transtilla with short transverse bar and long sublateral processes. Aedeagus cylindrical, posteriorly tapering; vesica with 30-40 small spines and about 100 very small ones arranged in two groups. Manica sparsely spined. Female genitalia. Corpus bursae small, egg-shaped, at least anterior half covered with pectinations; accessory sac absent; ductus spermathecae approximately as long as corpus. Vestibulum long, strongly swollen posteriorly. Anterior apophyses long, gradually tapering, posteriores slightly shorter and slender.
Host plants: Malus spp., both wild and cultivated. Egg: on undersides of leaves. Larva: bright yellow to orange. Mine : gallery mine in the space between two veins, very short and wide; windings often confluent, forming a small blotch. Frass-line broad and irregular, frequently interrupted. Mines found late in the autumn, often in 'green islands' in yellow leaves. Cocoon: red-brown.
Eastern Denmark, southern Sweden up to Upl. and from southernmost Norway and Finland. - Central and E. Europe, N. Italy, Corsica and the British Isles.
Voltinism: in the literature stated to be bivoltine. The summer generation seems to be scarce; probably univoltine in Scandinavia. Mines from the beginning of October (Scandinavia) to beginning of December in England and C. Europe.
Description based on Johansson and Nielsen (1990)