Stigmella alnetella (Stainton, 1856)
Diagnosis. S. alnetella is easily separated from all other species of the betulicola group by its metallic shining forewings, and from the Betula-feeding S. continuella by its dark collar (continuella has the yellowish white collar). In the male genitalia the two horn-like processes from the uncus are characteristic. The prominent sinuous structure in segment VIII separates the female genitalia of alnetella from those of all other species.
Male. Wingspan: 3.9-4.5 mm. Head: frontal tuft ferruginous; collar dark bronzy fuscous; scape shining yellowish white, usually edged with silvery to metallic grey; antenna longer than half length of forewing. Forewing: area proximal to fascia metallic dark brown to almost black, dorsum coppery brown to golden; fascia postmedial, shining silvery; distal to fascia dark purple fuscous; terminal cilia of same colour as distal part of wing, tipped silvery grey at apex. Hindwing grey with silvery-tipped cilia at apex. Abdomen dark fuscous.
Female. Wingspan: 4.3-4.8 mm. Head: scape yellowish white, without grey edge; antenna approximately half length of forewing. Otherwise similar to male.
Male genitalia. Vinculum with V-shaped emargination. Uncus with posterior corners produced into distinctly pointed processes. Gnathos with long horns. Tegumen broad, margin dentate. Valva with distal half narrow. Transtilla bilobed, ventral arms absent. Aedeagus small. Female genitalia. Corpus bursae almost completely covered with prominent pectinations. Segment VIII with prominent, strongly sclerotized, sinuous structure.
Host plants: Alnus glutinosa, A. viridis and A. cordata, occasionally also on Betula. Egg: on lower surface of leaf, close to a rib. Larva: pale yellow without distinct spot on prothorax; with green intestine and pale brownish head. Mine: a long slender gallery towards margin of leaf, frequently following a vein or the margin of the leaf. Frass throughout as a thin central line occupying approximately one-third width of mine. Mines of both alnetella and S. glutinosae very similar and it is not possible to separate the vacated mines. Cocoon: pale brown.
Widely distributed in Denmark and Fennoscandia up to about 52` northern latitude. - The range includes England and Scotland in the west, western USSR in the east and Corsica, Italy and the Caucasus in the USSR to the south.
Voltinism: two generations per year in south and central Europe; only one generation known from Scandinavia. S. alnetella seems to be the rarest of the Alnus-feeding nepticulids in Scandinavia.
Description based on Johansson and Nielsen (1990)
