Stigmella malella, Stigmella
Diagnosis. Externally very similar to S. freyella. See that species. Male genitalia: combination of shape of the gnathos, semi-circular emarginate vinculum and long row of cornuti distinguish malella from all other species. The female genitalia are somewhat similar to the other species of the malella group, but bursa copulatrix is longer and most of the pectinations are moderately long.
Male. Wingspan: 4.5-5.1 mm. Head: frontal tuft ochreous to orange, sometimes mixed with ferruginous; scape and collar yellowish white; antenna approximately half to distinctly longer than half length of forewing. Thorax concolorous with base of forewing. Forewing: area proximal to fascia dark fuscous and faintly shining, sometimes appearing coarsely scaled; fascia slightly beyond middle of forewing, silvery white and narrow to very narrow, often constricted at midlength; distal to fascia faintly shining dark fuscous, usually appearing coarsely scaled, with distinct cilia-line; terminal cilia distinctly paler, silvery grey. Hindwing: greyish brown. Abdomen fuscous; with very short, fuscous anal tufts. Female. Wingspan: 4.6-5.5 mm. Antenna less than half length of wing. Abdomen without anal tufts. Otherwise similar to male.
Male genitalia. Vinculum long, anterior extension deeply emarginate, corners pointed. Uncus distinctly bilobed; lobes triangular, margins well sclerotized. Tegumen narrower than uncus, rounded in middle. Gnathos with broad, arch-like central element; horns slender and short; anterior processes strong. Valva with arcuate distal process; inner lobe rounded. Transtilla without sublateral processes, forming short horizontal bar. Aedeagus slightly shorter than genital capsule; vesica with small to large spines in roughly two patches; anterior patch with generally smaller spines than apical patch; vesica partly with minute pectinations.
Female genitalia. Bursa copulatrix approximately three- quarters length of abdomen. Accessory sac small or appearing absent. Reticulate field small and indistinct. Vestibulum approximately half as long as corpus bursae. Corpus bursae oval, asymmetrical; corpus completely covered with pectinations; anterior part with some scale-like pectinations, posterior part with longer and narrower pectinations. Apophyses posteriores and anteriores of subequal length, slender. Ductus spermathecae convoluted four to five times, vesicle membranous.
Host plant: Malus spp. and occasionally Prunus spp. Egg: on underside of leaf, often near a rib. Larva: pale yellow to yellow. Mine : in Sweden usually found in the most shaded parts of wild apple trees, extremely variable; commences as a narrow, winding gallery which broadens into a wide gallery or becomes a false blotch mine from close-set winding gallery; frass often in a thin midline. In thicker, more sunexposed leaves, the mine is shorter and straighter with a broader frass line. It is frequently not possible to separate the vacated mine of malella from those of S. magdalenae and S. desperatella. Cocoon: red-brown.
In eastern Denmark, in Sweden up to Sdm. Not recorded from Norway and in Finland only from Al. - Widely distributed in Europe from Ireland to Italy.
Voltinism: two generations per year. Mines found from mid-July to late September. S. malella is regarded as a pest on apple in southern Austria, northern Italy and The Netherlands. Pest status is also reported from Pakistan (Bradley, pers. comm. to EJvN).
Description based on Johansson and Nielsen (1990)