Stigmella naturnella Klimesch, 1948

van Nieukerken, Erik J., 2023, Stigmella naturnella (Klimesch, 1936) (Lepidoptera, Nepticulidae) a fast-spreading European leafminer of Betula, with a revised key to linear leafmines on Betula, Nota Lepidopterologica 46, pp. 37-82 : 37

Stigmella naturnella Klimesch

Nepticula naturnella Klimesch, 1936: 205. Lectotype ♂ (here designated), Italy: "Teriolis merid., Naturns p. Meran, el 5.10.34, J. Klimesch / Betula verr., Nept. Betula naturnella / Zucht 72/ Genital-Präparat Nro ♂ 232/ Holotypus", [larvae collected September 1934] (labels Fig. 4 ) (ZSM) [examined].

Astigmella dissona Puplesis, 1984a: 112. Holotype ♂, Russia, Primorskiy Kray, 20 km E Ussuriysk, Gornotayezhnoe, 28.v.1983, leg. R. Puplesis, genitalia slide no. AG 403 (ZIN) (synonymised by van Nieukerken et al. 2004 a: 133).

Nepticula argentifasciella " Nepticula argentifasciella Klimesch": Skala 1936: 11. Unavailable name and Junior Homonym of Nepticula argentifasciella Braun, 1912.

Stigmella naturnella Klimesch 1948: 65 [recombination, male genitalia], van Nieukerken et al. 2004 [Synonymy, European Russia]; Stonis and Rocienė 2013: 2, 3 [photographs male genitalia holotype A. dissona ].

Stigmella dissona Puplesis 1994: 58 [recombination, redescription].

Diagnosis.

Stigmella naturnella adults resemble most other Stigmella species with a fascia, pale head and white collar superficially, including other Betula miners in the S. betulicola group. Characteristic is the combination of a distinct fringe line, white fringe, rather shining fascia, and a relatively short antenna in both sexes, reaching only halfway to the fascia. The basal part of the forewing may vary from grey to black with a blue iridescence. Those with grey can be confused with S. tityrella or S. carpinella , but these have usually the last part before the fascia darker and the antennae distinctly longer, reaching the fascia. Species in the Stigmella betulicola group do not have a fringe line and the males have longer antennae. Male genitalia are very characteristic by shallow uncus, connected gnathos arms and shape and number of cornuti, female genitalia much less so, but the very long posterior apophyses are notable. For mines and larvae see below.

Description.

Male (Figs 2 , 5 ). Forewing length 1.7-2.2 mm (2.0 ± 0.2, n=6), wingspan ca. 3.9-4.8 mm. Head. Frontal tuft pale orange, collar conspicuous, cream white. Scape large, cream white. Antenna short, reaching slightly more than halfway between wing base and fascia; with 18-21 articles (19.0 ± 1.2, n=5). Thorax and forewings basal to fascia shining dark grey to almost black; a narrow silvery white fascia slightly beyond middle, usually constricted in middle; apical area contrasting darker black compared to wing base; a fringe line of black scales separates the silvery white terminal fringe. Hindwing grey. Abdomen black, no visible anal tufts.

Female (Figs 1 , 3 , 6 , 7 ). Forewing length 2.1-2.3 mm (2.2 ± 0.1, n=6), wingspan ca. 4.4-5.0 mm. Antenna very short, reaching less than halfway between wing base and fascia; with 17-18 articles (17.2 ± 0.4, n=6). Abdomen slightly tapering.

Male genitalia (Figs 9-14 ). Vinculum with narrow ventral plate; tegumen band-shaped; uncus slightly indented; gnathos with distal arms very close, appearing almost as single structure. Valvae broad, slightly acuminate. Juxta anteriorly arrow shaped, posteriorly ending in two arms. Phallus distally widened, with ca. 8-10 strong cornuti.

Female genitalia (Figs 15-17 ). Ovipositor blunt. No visible anal papillae. Tergum 8 with indented posterior margin, with central sclerotised plate, few setae along margin. Narrow posterior apophyses reaching distinctly beyond anterior apophyses in abdomen. Vestibulum folded, staining strongly with chlorazol. Ductus spermathecae not coiled. Bursa copulatrix rather long, covered with small spines and pectinations.

Biology.

Host plants. In Europe Betula pendula subsp. pendula Roth and B. pubescens Ehrh. and their hybrids, from East Asia reported from B. pendula subsp. mandshurica (Regel) Asburner & McAll. ( B. platyphylla Sukaczev) and B. dahurica Pall. (adults found on trunks, Puplesis 1984a, b). In the botanical garden of Linz, leafmines were also observed on the eastern Palearctic taxa B. pendula subsp. mandshurica and B. utilis D. Don subsp. jacquemontii (Spach) Ashburner & McAll. (see Klimesch (1990) and material examined). Much more frequently observed on B. pendula than on B. pubescens , also most literature references cite B. pendula (often under the old name B. verrucosa ), but although Baran (2013) suggested that his record from B. pubescens was a new host record, it had been recorded from B. pubescens before ( Skala 1939; Wörz 1958), records that are here partly confirmed.

Egg deposited on leaf upper- or underside, 67% were found on the underside (n=315), but the percentages differ per population, although almost always both positions occur when ten or more mines per population are examined. The egg may be deposited at any place of the leaf, but most frequently away from the midrib or large veins; the egg capsule is conspicuous and dark brown after the larva has hatched (Figs 25 , 26 ).

Leafmine (Figs 18 - 27 , 29-34 ). A linear or gallery mine with variable length and frass disposition. From the egg the mine often runs straight away, or makes a single loose bend around the egg. The mine often does not follow parts of veins or the leaf margin, but some mines do follow veins for a shorter or longer stretch. The early mine starts in the spongy parenchyma layer, often resulting in the initial part of the mine appearing green from above, outside the frass line. This arrangement is particularly frequent on Betula pubescens , but many mines do not exhibit the green appearance. Frass varying from a narrow central line to a wider band of dispersed frass; in the early part of the mine it occasionally fills its entire width. The mine may be rather contorted, only occasionally crossing itself, and rarely crossing the midrib. The exit slit is invariably on the upper side of the leaf in nature. The very few mines (2-3) where an underside slit was observed, where mines that were completed by the larva in captivity after collecting; in these cases the leaf probably did not stay in its natural position, light conditions were poor, which may explain why the larva left the mine at the leaf underside. The final larval chamber often is buckled. Mines with an upperside egg and a green part at the start are the easiest to determine as S. naturnella , see below. Total length of mine 22.0-52.9 mm (34.0 ± 7.8, n=27), width of final larval chamber 0.9-1.4 mm (1.0 ± 0.1, n=27).

Larva (Figs 23 , 24 ). The larva feeds venter upwards. Colour white to faintly pale yellow, head capsule brown; ventral nerve chord and ganglia invisible, apart from the conspicuous brown circular suboesophageal ganglion, which is a decisive diagnostic character; in actively feeding larvae the green intestine is also conspicuous.

Cocoon (Fig. 28 ). White and rather flimsy.

Life history.

Larvae have been recorded from late-May to mid-July, and again from mid-August until October, with a single record from November. It is one of the earliest Nepticulidae larvae occurring on Betula , only S. lapponica can also be found in May and early June. Larvae seem to be most abundant in August, in the autumn only single larvae are found amongst large numbers of vacated mines. Adults have been collected or observed, after hibernation, from early April to early May, and again from 25 June almost continuously to 10 October, with a single record on 3 November. Hibernating adults have been found under the bark of trees, often Platanus (Fig. 8 ), but also on oaks, in November, January, February and March in Belgium and the Netherlands (Table 1 ) and in Russia ( Ul’yanovsk) under bark of Betula on 19 April (van Nieukerken et al. 2004). Adults reared from larvae usually emerge within 2-3 weeks after collecting; in our material from the Netherlands from 17-23 days after collecting the larva (19.09 ± 2.07, n=11). Klimesch (1936, 1948) reported a pupal stage between 10-12 days, Laštůvka and Laštůvka (1991) reported 13 days between collecting and emergence; but only Sobczyk et al. (2018) reported a longer period of 32 days. Note that many of these data are from indoor rearing in the autumn, when temperatures outside, especially at night were gradually becoming lower than those inside. From these data it appears that S. naturnella has at least two generations, maybe more in some cases, but from a large part of the distribution area hardly any data are available.

Habitat and ecology

(Figs 35 , 36 ). Most localities visited by me were on sandy soil, relatively dry forests or forest margins, either dry forest with Pinus sylvestris , or other planted Pinus species, or with Quercus robur and Betula often in the undergrowth. Mines were found sometimes in Calluna heathland that was becoming overgrown with juvenile Betula trees. Betula pendula was usually the most abundant birch, but B. pubescens was also present. In the Netherlands I often heard the cricket Nemobius sylvestris (Bosc, 1792) singing in these localities; this species has a comparable habitat preference. Table 2 shows the accompanying leafminer species in 36 localities with sufficient data, most common were Stigmella sakhalinella , S. continuella and S. betulicola . In more southern localities in France, Italy and Russia, S. naturnella was the dominant species with no accompanying nepticulids, or just one ( S. sakhalinella or S. glutinosae ). Species such as Lyonetia clerkella (Linnaeus, 1758) or Agromyza alnibetulae Hendel, 1931 and some sawflies were often seen, but not consistently noted by me. Nepticulidae that prefer moister habitats and have a more northern distribution, e.g. Ectoedemia minimella , S. lapponica or S. confusella were rarely found together with S. naturnella , except on 10.x.1983 when J.J. Boomsma found S. naturnella in the Naturno area (Italy, Bolzano) together with an outbreak of hundreds of vacated mines of S. lapponica.

Distribution

(Figs 37 , 38 ). Central and West Europe: Austria (throughout), Belgium (new record: north-western part), Croatia (new record: Brodsko-Posavska), Czechia (Bohemia and Moravia), France (new record: Sarthe, Savoie), Germany ( Baden-Württemberg, Bayern, Brandenburg, Nordrhein-Westfalen [new record], Saarland [new record], Sachsen), Hungary, Italy (Bolzano, Torino [new record], Trento), the Netherlands (new record: southern two thirds), Poland, Slovakia, Switzerland (Graubunden, Valais), Ukraine (new record: Chernikhiv Oblast), Russia, from European part to Primorye (van Nieukerken and Sinev 2019, 2022) and Japan, Honshu ( Hirano 2013). For further details, references and history see below.

DNA barcodes

(Fig. 39 ). DNA barcode data are available for a total of 35 specimens across the distribution area between the Netherlands and Japan. All fall within Barcode Identification Number BOLD:AAV8372, with an average distance of 0.72% and a maximum distance of 1.63%. The nearest neighbour, with 5.9% distance, is the North American Stigmella nigriverticella (Chambers, 1875), in the Stigmella saginella group. However, barcodes of the closely related Eastern Palaearctic species S. mirabella Puplesis, 1984 are still unknown. There is some geographical pattern visible in the NJ tree (Fig. 39 , see also the haplotype network given on the BIN page, http://www.boldsystems.org/index.php/Public_BarcodeCluster?clusteruri=BOLD:AAV8372). All Dutch, French and western German DNA barcodes belong to the same cluster, together with some Austrian records, whereas the remaining Austrian records and one from Germany, Sachsen, group with an Italian and several Russian records. DNA barcodes, especially those from easternmost Russia, Primorsky Kray, show most variation, but it should be noted that these DNA barcodes were on average a bit shorter than the others (total length 510-618 base pairs). However for the region covered by the missing base pairs, the other sequences show only variability in three sites.

Nomenclature and lectotype designation.

Klimesch originally intended to name the species " Nepticula argentifasciella ", as can be seen on some of his original mines in the collection Wörz, examined by me. However, he had crossed out that name on the herbarium sheets and replaced it by " Nepticula naturnella ", presumably having realised that N. argentifasciella was a homonym of the North American Nepticula argentifasciella Braun, 1912 (now Stigmella argentifasciella ). The name, however, entered the literature as a nomen nudum, as it was cited by Skala (1937).

Nepticula naturnella was described from an unspecified number of specimens, without selecting a holotype. I designate as lectotype the male that bears Klimesch’s dissection number 232 (labels see Fig. 4 ).

Remarks.

Stigmella naturnella was placed in the Stigmella lapponica group by van Nieukerken (1986a) on the basis of the gnathos shape, which was later shown to be a homoplasious character ( Doorenweerd et al. 2016). Puplesis (1984a, b) based his genus Astigmella Puplesis, 1984 on the synonym A. dissona . He separated that genus from Stigmella by the shorter Cu vein in the forewing and the characteristic genitalia. Astigmella was later synonymised with Stigmella (van Nieukerken 1986a). Currently S. naturnella is considered to form a separate species group with the East Palearctic S. mirabella (Puplesis, 1984), falling within the large “Non-Core” Stigmella clade, partly on the basis of unpublished molecular data. The Nepticula naturnella group is close to some Asiatic Ficus mining species, and relatively close to the S. ulmivora and S. saginella groups.

Material examined.

23 ♂ 11 ♀ 1 sex unknown, cocoons. B. = Betula . All in RMNH, unless otherwise mentioned.

Austria • 1 ♂; Nordtirol , Fliess; 25 Jun. 2008; 47.117°N, 10.632°E; alt. 1000 m; P. Skou & D. Nilsson leg.; Genitalia slide: JCK8488; ZMUC .

Germany • 1 ♂; Saarland, Fraulautern , TrÜbpl.; 49.325°N, 6.7854°E; 04 Sep. 2020; A. Werno leg.; Genitalia slide: EvN5341; RMNH.INS.25341; Werno, A., personal collection . • 1 ♀; Sachsen, Königswartha, Deichgebiet ; 51.3193°N, 14.3527°E; 01 Jul. 2020; A. Werno leg.; Genitalia slide: EvN5342; RMNH.INS.25342; Werno, A., personal collection .

Hungary • 1 ♀; Veszprem, Uzsa, Nyires ; 46.897°N, 17.333°E; 27 Aug. 1968; J. Szöcs leg.; B. pubescens ; emerged 13 Sep. 1968; Genitalia slide: VU1874; HNHM .

Japan • 1 ♀; Honshu, Nagano ken, Yamagata-mura, Karasawa ; 36.158°N, 137.846°E; 13 Jun. 2009; Nagao Hirano leg.; B. pendula subsp. mandshurica ; emerged 25 Jun. 2009; EventId: Host-2733; Genitalia slide: EvN4747; RMNH.INS.24747 .

Netherlands - Gelderland • 1 ♂ 2 ♀, 2 cocoons (plus exuviae); Wekerom, De Valouwe, Immenkampweg; 52.08977°N, 5.71459°E; 16 Sep. 2020; EvN leg.; B. pendula ; emerged 04 Oct. 2020; EventId: EvN no 2020062-1K; Genitalia slide: EvN5268; RMNH.INS.25268, RMNH.INS.17206-17208 . • 2 ♂ 1 ♀, 4 cocoons (plus exuviae); Wekerom, Wekeromse Zand, near Hoge Valksedijk; 52.09188°N, 5.67616°E; 16 Sep. 2020; EvN leg.; B. pendula ; emerged 03-04 Oct. 2020; EventId: EvN no 2020063-1K; RMNH.INS.17209-17212. • 1 ♂; Wolfheze, Wolfhezerbos, Oude Kloosterweg; 51.997°N, 5.79882°E; 07 Oct. 2020; EvN leg.; B. pendula ; emerged 25 Oct. 2020; EventId: EvN no 2020100-1K; RMNH.INS.17215. - Limburg • 1 ♀; Leudal, Sint Elisabeth, Roggelse Beek valley ; 51.25462°N, 5.93057°E; 21 Sep. 2020; EvN leg.; B. pendula ; emerged 08 Oct. 2020; EventId: EvN no 2020071-1K; RMNH.INS.17213 . - Noord-Brabant • 1 ♀; Goirle, Gorp en Roovert - Noord; 51.50795°N, 5.07473°E; 30 Sep. 2020; EvN leg.; B. pendula ; emerged 20 Oct. 2020; EventId: EvN no 2020082-1K; RMNH.INS.17214 . - Utrecht • 1 ♀; Soest, Hees, Wieksloterweg, Heitje; 52.15885°N, 5.27867°E; 23 Aug. 2021; EvN leg.; B. pubescens ; emerged 13 Sep. 2021; EventId: EvN no 2021123-K; RMNH.INS.17451 . • 1 ♀, 2 cocoons (plus exuviae); Soest, Korte Duinen S. edge; 52.15107°N, 5.32399°E; 10 Sep. 2020; EvN leg.; B. pendula ; emerged 01 Oct. 2020; EventId: EvN no 2020056-1K; RMNH.INS.17204-17205. • 1 ♀; Soest, Korte Duinen S. edge; 52.15112°N, 5.32402°E; 23 Aug. 2021; EvN leg.; B. pubescens ; emerged 11 Sep. 2021; EventId: EvN no 2021121-1K; RMNH.INS.17448. • 1 ♀; same locality data; B. pendula ; emerged 11 Sep. 2021; EventId: EvN no 2021122-1K; RMNH.INS.17449 .

Russia - Primorsky Krai • 1 ♂ ; 20 km E Ussurijsk, GTS [Gornotayezhnoye, Mountain taiga station]; 43.692°N, 132.164°E; 02 Aug. 1982; R. Puplesis leg.; Genitalia slide: JCK8123 . - Samara Oblast • 1 ♂ ; Zhiguli , Bakhilova Polyana, S.; 53.4°N, 49.07°E; 04 May. 1992; S.A. Sachkov leg.; Genitalia slide: EvN3303; Zolotuhin, V., personal collection . - Ulyanovsk Oblast • 6 ♂; Ul’yanovsk N., Pobeda forest Park ; 54.37°N, 48.42°E; 19 Apr. 1995; V. Isajevy leg.; under trunks of B. pendula ; Genitalia slide: EvN3302; RMNH.INS.23302 . • 7 ♂; same data; Zolotuhin, V., personal collection .

Switzerland • 1 ♂; Graubunden, GR, Trimmis, Hag ; 46.9124°N, 9.560464°E; alt. 560 m; 13 Jul. 2005; A. Kopp leg.; Genitalia slide: AK5.095; Kopp, A., personal collection .

Ukraine • 1 ♂; Chernihiv Oblast, Korop ; 51.58°N, 32.98°E; 24-31 Jul. 2009; K.E. Lundsten & Bo Wikström leg.; Genitalia slide: EvN5196; RMNH.INS.25196 .

Larvae and leafmines (in collection). B. = Betula . All in RMNH, unless otherwise mentioned.

Austria • 3 mines; Oberösterreich, Linz-Bauernberg, Botanischer Garten ; 48.297°N, 14.277°E; 13.vi.1976; J. Klimesch leg.; Betula jacquemontii [= B. utilis subsp. jacquemontii ]; RMNH.INS.47930 .

Croatia • 10 mines; Brodsko-Posavska, Nova Gradiska , in town; 45.254°N, 17.387°E; 17 Oct. 1983; van Nieukerken & Boomsma leg.; B. pendula ; EventId: VU no 83505-H; ZMA.INS.MIG.11575 .

Czechia • 2 mines; Bohemia centr., Prague; 50.12208°N, 14.49573°E; 16 Sep. 2010; V. Lanta leg.; B. pendula ; RMNH.INS.45394. • 3 mines (photo examined); Moravia, Kotojedy, Obora; 49.264°N, 17.402°E; 30 Aug. 1961; H. Zavřel leg.; B. pendula ; BMNH(E)425547; NHMUK .

France - Sarthe • 1 larva (slide, DNA barcoded), 7 mines; Le Mans , Arche de la Nature , Bois de Changé; 47.9885°N, 0.2604°E; alt. 85 m; 07 Oct. 2017; EvN & S. Richter leg.; B. pendula ; EventId: EvN no 2017146-2M/H; RMNH.INS.31042(.P), RMNH.INS.44072, RMNH.INS.44073. • 1 larva (ethanol, tissue collection), 5 mines; same locality data; B. pubescens ; EventId: EvN no 2017147-1H/M; RMNH.INS.31044, RMNH.INS.44075, RMNH.INS.44077. • 11 mines; Le Mans, Arche de la Nature, Bois de Changé; 47.9888°N, 0.25835°E; alt. 83 m; 07 Oct. 2017; EvN & S. Richter leg.; B. pendula ; EventId: EvN no 2017150-3H; RMNH.INS.44085. - Savoie • 4 mines; Avrieux, along D215; 45.22262°N, 6.72683°E; alt. 1375 m; 24 Sep. 2018; EvN leg.; B. pendula ; EventId: EvN no 2018158-4H; RMNH.INS.46341. • 11 mines; Saint-Martin-d’Arc, Les Fontaines; 45.20722°N, 6.46972°E; alt. 900 m; 21-24 Aug. 2017; M. Kozlov & V. Zverev leg.; B. pendula ; ecological sample 50; RMNH.INS.46127 .

Germany - Baden-Württemberg • 4 mines; Badenweiler, Sophienruhe ; 47.7977°N, 7.6749°E; 28 Sep. 2001; AC & WN Ellis leg.; B. pendula ; ZMA.INS.MIG.07497. • 4 mines; Stuttgart, Willdpark; 48.77°N, 9.1°E; 01 Sep. 1935; Wörz leg.; B. pubescens ; SMNS. • 2 mines; Zuffenhausen, Lemberg; 48.82°N, 9.14°E; [no date]; Wörz leg.; B. pendula ; SMNS . - Nordrhein-Westfalen • 4 mines; Wegberg, Forst Meinweg ; 51.15875°N, 6.19451°E; 23 Sep. 2021; EvN leg.; B. pubescens ; EventId: EvN no 2021152-3H; RMNH.INS.48753 . - Sachsen • 1 mine; Pirna, Copitz, Camping ; 50.98168°N, 13.92177°E; alt. 120 m; 28 Jul. 2014; EvN leg.; B. pendula ; EventId: EvN no 2014067-3H; RMNH.INS.47934 .

Italy - Bolzano • 4 mines (on 2 sheets); Südtirol, Naturno bei Meran, 46.656°N, 11.00200°E; "Ende 09.34, imagines e.l. A.10.34, Ende 06.35, imagines e.l. A.7.34 [recte 35]"; J. Klimesch leg.; B. pendula [ Betula verrucosa ]; SMNS (coll. Wörz). • 22 mines; Naturno, 3 km SE, N. slope; 46.62964°N, 11.02486°E; alt. 1000 m; 10 Oct. 1983; J.J. Boomsma leg.; B. pendula ; EventId: VU no. 83437; RMNH.INS.46938. • 2 mines; Naturno, N. slope; 46.62987°N, 11.01181°E; alt. 800 m; 10 Oct. 1983; J.J. Boomsma leg.; B. pendula ; EventId: VU no. 83433; RMNH.INS.46937. • 3 larvae, mines; Naturno, near Canal; 46.63°N, 11.025°E; 24 Jun. 1985; J.J. Boomsma leg.; B. ; RMNH.INS.12248. • 10 mines; Völlan, 2 km S Lana; 46.59373°N, 11.15197°E; alt. 670 m; 10 Jul. 2005; EvN leg.; B. pendula ; EventId: EvN no 2005064-H; RMNH.INS.41069. - Torino • 4 larvae (ethanol, tissue collection, DNA barcoded), 55 mines; Issiglio, along SP61; 45.44865°N, 7.73024°E; alt. 750 m; 02 Oct. 2018; EvN leg.; B. pendula ; EventId: EvN no 2018242-1M/H; slide: RMNH.INS.31263-31266, RMNH.INS.46501-46502. • 10 mines; Valle del Chisone , Perosa Argentina, rivervalley N of city; 44.96208°N, 7.18461°E; alt. 627 m; 30 Sep. 2018; EvN leg.; B. pendula ; EventId: EvN no 2018230-H; RMNH.INS.46487. • 11 mines; Valperga, Sacro Monte di Belmonte ; 45.36688°N, 7.63067°E; alt. 685 m; 01 Oct. 2018; EvN leg.; B. pendula ; EventId: EvN no 2018238-1H; RMNH.INS.46497 .

Netherlands - Gelderland • 1 mine; Ede, Edese Heide, Koeweg; 52.05867°N, 5.69665°E; 16 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020064-2H; RMNH.INS.48336. • 6 mines; Ede, Planken Wambuis, Mosselse Pad; 52.07214°N, 5.7576°E; 16 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020058-2H; RMNH.INS.48308. • 3 mines; Ugchelen, Leesterheide, t Leesten; 52.16887°N, 5.90794°E; 07 Oct. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020097-1H; RMNH.INS.48432. • 1 mine; same locality data; B. pubescens ; EventId: EvN no 2020098-1H; RMNH.INS.48437. • 3 larvae (ethanol, tissue collection, DNA barcoded, slide), 22 mines; Wekerom, De Valouwe, Immenkampweg; 52.08977°N, 5.71459°E; 16 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020062-1H/K/M; RMNH.INS.31449-31450, RMNH.INS. 48317-48319. • 10 mines (larvae reared); Wekerom, Wekeromse Zand, near Hoge Valksedijk; 52.09188°N, 5.67616°E; 16 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020063-1H/K; RMNH.INS. 48327-48328. • 4 mines (larva reared); Wolfheze, Wolfhezerbos, Oude Kloosterweg; 51.997°N, 5.79882°E; 07 Oct. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020100-1H/K; RMNH.INS.48445-48446. - Limburg • 1 mine; Epen, Onderste Bos; 50.7657°N, 5.89338°E; 20 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020067-2H; RMNH.INS.48342. • 1 mine; Epen, Geuldal, Cottessen; 50.76232°N, 5.93053°E; 20 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020068-2H; RMNH.INS.48346. • 1 larva (DNA barcoded, slide), 6 mines; Leudal, Nunhem - Sint Ursula, Zelsterbeek valley; 51.25424°N, 5.9512°E; 21 Sep. 2020; EvN leg.; B. pubescens ; EventId: EvN no 2020073-1H/M; RMNH.INS.31460, RMNH.INS.48359-48360. • 5 mines; same locality data; B. pendula ; EventId: EvN no 2020072-1H; RMNH.INS.48357. • 1 larva, 10 mines; Leudal, Sint Elisabeth, 2 km E Heythuysen; 51.24649°N, 5.92678°E; 21 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020070-1H/M; RMNH.INS.31458, RMNH.INS. 48350-48351. • 4 mines (larva reared); Leudal, Sint Elisabeth, Roggelse Beek valley; 51.25462°N, 5.93057°E; 21 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020071-1H/K; RMNH.INS. 48354-48355. - Noord-Brabant • 14 mines (2 larvae reared); Goirle, Gorp en Roovert - Noord; 51.50795°N, 5.07473°E; 30 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020082-1H/K; RMNH.INS. 48381-48382. • 2 larvae (ethanol, tissue collection, DNA barcoded, slide), 22 mines (3 larvae reared); Goirle, Gorp en Roovert - Noord; 51.50512°N, 5.08499°E; 30 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020083-1H/K/M; RMNH.INS.31465-31466, RMNH.INS. 48389-48391. • 22 mines; Goirle, Regte Heide; 51.52008°N, 5.03386°E; 30 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020081-1H; RMNH.INS.48377. • 9 mines; Leende, Leenderbos, Parking Strijperpad; 51.35075°N, 5.51628°E; 19 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020065-1H; RMNH.INS.48337. • 10 mines; Tilburg, Kaaistoep Oost; 51.54092°N, 5.02876°E; 30 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020079-1H; RMNH.INS.48370. • 4 mines; Tilburg, Wilhelminakanaal, East banks; 51.52175°N, 5.14482°E; 30 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020084-1H; RMNH.INS.48398. • 2 mines; same locality data; B. pubescens ; EventId: EvN no 2020085-1H; RMNH.INS.48402. • 2 mines; Tilburg, De Sijsten, Heidebaan; 51.54111°N, 5.00389°E; 30 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020080-1H; RMNH.INS.48375. - Overijssel • 4 mines; Lemele, Lemelerberg; 52.46178°N, 6.39946°E; 3 Aug. 2022; EvN leg.; B. pendula ; EventId: EvN no 2022005-1H; RMNH.INS.48842. - Utrecht • 13 mines (rearing failed); Leersum, Dartheide; 52.02°N, 5.4083°E; 25 Sep. 2020; Ben van As leg.; B. pendula ; EventId: EvN no 2020087-K/H; RMNH.INS.48407. • 1 mine; Leusden, Den Treek, Hazenwater; 52.12511°N, 5.37929°E; 10 Sep. 2020; EvN leg.; B. pubescens ; EventId: EvN no 2020052-5H; RMNH.INS.48278. • 5 mines; Leusden, Den Treek-Henschoten, t Waswater; 52.11789°N, 5.37407°E; 10 Sep. 2020; EvN leg.; B. pubescens ; EventId: EvN no 2020054-1H; RMNH.INS.48281. • 19 mines; Soest, Korte Duinen S.; 52.15137°N, 5.3261°E; 04 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020046-1H; RMNH.INS.48250. • 2 mines; Soest, Korte Duinen S.; 52.15131°N, 5.32578°E; 04 Sep. 2020; EvN leg.; B. pubescens ; EventId: EvN no 2020047-4H; RMNH.INS.48259. • 1 larva (ethanol, tissue collection), 49 mines; Soest, Korte Duinen S.; 52.15122°N, 5.32729°E; 10 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020055-1H/M; RMNH.INS.31444, RMNH.INS. 48288, 48290. • 10 mines; Soest, Korte Duinen S.; 52.15131°N, 5.32675°E; 23 Aug. 2021; EvN leg.; B. pendula ; EventId: EvN no 2021120-1H/K; RMNH.INS.48692-48693. • 3 larvae (ethanol, tissue collection, DNA barcoded, slide), 25 mines (larvae reared); Soest, Korte Duinen S. edge; 52.15107°N, 5.32399°E; 10 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020056-1H/K/M; RMNH.INS.31441-31443, RMNH.INS.48297-48299. • 13 mines; Soest, Korte Duinen S. edge; 52.15112°N, 5.32402°E; 23 Aug. 2021; EvN leg.; B. pubescens ; EventId: EvN no 2021121-1H/K; RMNH.INS.48696- RMNH.INS.48697. • 9 mines; Soest, Korte Duinen S. edge; 52.15112°N, 5.32402°E; 23 Aug. 2021; EvN leg.; B. pendula ; EventId: EvN no 2021122-1H/K; RMNH.INS.48699-48700. • 1 larva (DNA barcoded, slide), 8 mines; Soest, Lange Duinen E.; 52.15116°N, 5.30074°E; 04 Sep. 2020; EvN leg.; B. pendula ; EventId: EvN no 2020049-1H/M; RMNH.INS.31436, RMNH.INS.48264-48265. • 1 larva, 1 mine; Soest, Lange Duinen S.; 52.14687°N, 5.28791°E; 23 Aug. 2021; EvN leg.; B. pubescens ; EventId: EvN no 2021130-M/H; RMNH.INS.31659, RMNH.INS.48713. • 1 mine; Soest, Op Hees, W border; 52.15582°N, 5.25182°E; 23 Aug. 2021; EvN leg.; B. pendula ; EventId: EvN no 2021125-H; RMNH.INS.48705. • 3 mines; Soest, Op Hees, W border; 52.15582°N, 5.25182°E; 23 Aug. 2021; EvN leg.; B. pubescens ; EventId: EvN no 2021126-1H; RMNH.INS.48706. • 6 mines; Soest, Op Hees/ Willem Arntzbos; 52.15152°N, 5.25401°E; 23 Aug. 2021; EvN leg.; B. pubescens ; EventId: EvN no 2021127-H/K; RMNH.INS.48708- RMNH.INS.48709. • 2 mines; Soest, Hees, Wieksloterweg, Heitje; 52.15885°N, 5.27867°E; 23 Aug. 2021; EvN leg.; B. pubescens ; EventId: EvN no 2021123-K; RMNH.INS.48704. • 5 mines; Soest, Soesterberg, nr Wildwissel, along railway; 52.14528°N, 5.26222°E; 23 Aug. 2021; EvN leg.; B. pubescens ; EventId: EvN no 2021128-H/K; RMNH.INS.48710-48711.

Poland • 5 mines; Mazowieckie, Walendów; 52.08816°N, 20.8445°E; 16 Sep. 2010; V. Lanta leg.; B. pendula ; RMNH.INS.45444 .

Russia- Irkutsk Oblast • 1 larva (DNA barcoded, slide), 2 mines; Tulun; 54.60111°N, 100.64°E; alt. 510 m; 22 Aug. 2009; V. Chepinoga leg.; B. pendula subsp. Betula pendula mandshurica ; EventId: Kozlov-3-leaf1; RMNH.INS.29880, RMNH.INS.46693. - Kaluga Oblast • 1 mine; Kondrovo Distr., Gorbenki; 54.6589°N, 35.9385°E; 13 Aug. 2013; L.V. Bolshakov leg.; B. pendula ; RMNH.INS.45634. - Krasnoyarsk Krai • 1 larva (DNA barcoded, slide); village Tanzybei, foothill of Sayan Mts ; 53.1199°N, 92.9672°E; 17 Jun. 2017; N. Kirichenko leg.; B. pendula ; EventId: NK-13-17; RMNH.INS.31140. - Lipetsk Oblast • 1 mine; Krasnoe Distr. , Jablonovo; 52.8318°N, 38.9817°E; 11 Aug. 2014; L.V. Bolshakov leg.; B. pendula ; RMNH.INS.47960. • 2 mines; Krasnoe Distr. , Leski; 52.8729°N, 38.97°E; 15 Jul. 2013; L.V. Bolshakov leg.; B. pendula ; RMNH.INS.45783. • 1 larva (DNA barcoded, slide), 61 mines; Usman Distr. , Usman; 51.983°N, 39.783°E; alt. 165 m; 28 Jul. 2017; V. Zverev leg.; B. pendula ; RMNH.INS.31160, RMNH.INS.44331, RMNH.INS.44341, RMNH.INS.45010. • 46 mines; same locality data; B. pubescens ; RMNH.INS. 44337-44338. - Moscow Oblast • 1 mine; Serpukhov, Svinenki; 54.9°N, 37.8°E; alt. 130 m; 16 Sep. 2009; M. Brynskikh leg.; B. pendula ; RMNH.INS.46670. - Novosibirsk Oblast • 1 larva (DNA barcoded, slide); Novosibirsk, Central Siberian botanical garden; 54.82°N, 83.10389°E; alt. 155 m; 10 Jul. 2012; N. Kirichenko leg.; B. pendula ; EventId: CD13121; RMNH.INS.30247. • 7 mines; same locality data; 14 Sep. 2013; N. Kirichenko leg.; B. pendula ; EventId: NK# 68_12; RMNH.INS.40809, 40810. - Sverdlovsk Oblast • 1 mine; Revda; 56.8075°N, 59.3625°E; alt. 375 m; 15 Aug. 2009; E. Belskaya leg.; B. pubescens ; RMNH.INS.46719. - Tula Oblast • 2 mines; Kurkino Distr. , Danilovka; 53.5926°N, 38.5499°E; 26 Jul. 2006; L.V. Bolshakov leg.; B. pendula ; RMNH.INS.45931. • 1 mine; Kurkino Distr. , Vodyanoe Pole; 53.6176°N, 38.5766°E; 17 Jul. 2009; L.V. Bolshakov leg.; B. pendula ; RMNH.INS.45973. • 2 mines; Leninski Distr. , Inshinsky, 10 km W. Tula; 54.1436°N, 37.4738°E; 26 Sep. 2009; L.V. Bolshakov leg.; B. pendula ; RMNH.INS.45976. • 1 mine; Shchyokino Distr. , Yasnaya Polyana, 14 km S Tula; 54.0893°N, 57.5101°E; 01 Aug. 2009; L.V. Bolshakov leg.; B. pendula ; RMNH.INS.46010. - Ulyanovsk Oblast • 6 mines; Surskoe Distr. , 10 km WNW vill. Lava; 54.55°N, 46.883°E; 07 Jul. 2019; V. Zolotuhin leg.; B. pubescens ; EventId: VZ19_13- Betula pubescens ; RMNH.INS.46845. • 1 mine; Ulyanovsk city; 54.3°N, 48.38°E; 09 Sep. 2002; students Uljanovsk State Pedag. Univ. leg.; B. pendula ; RMNH.INS.27861. • 1 larva (DNA barcoded, slide), 82 mines; Ulyanovsk city S., Vinnovka forest-park; 54.27°N, 48.03°E; Jul.- Aug. 2002; A. Mistchenko leg.; B. pendula ; slide: EvN3566; RMNH.INS.23566, RMNH.INS.27857-27860. • 4 mines; Ulyanovsk Oblast, Ulyanovsk city S., Vinnovka forest-park; 54.27°N, 48.03°E; 21 Sep. 2002; A. Mistchenko leg.; B. pendula ; RMNH.INS.27862, RMNH.INS.27866 [the latter was misidentified as S. betulicola by van Nieukerken et al. 2004). • 1 mine; Ulyanovsk city S., Vinnovka forest-park; 54.27°N, 48.03°E; 30 Sep. 2002; A. Mistchenko leg.; B. pendula ; RMNH.INS.27863. - Voronezh Oblast • 1 larva (DNA barcoded, slide), 3 mines; Voronezh; 51.583°N, 39.167°E; alt. 150 m; 28 Aug. 2017; V. Zverev leg.; B. pubescens ; RMNH.INS.31325, RMNH.INS.46142.

Slovakia • 2 mines; Zapadoslovensky Kraj , Sekule, 6 km SW Kúty; 48.614°N, 17.009°E; 04 Oct. 1992; EvN leg.; B. pendula ; EventId: EvN no 92075; RMNH.INS.48289 .

Leafmine diagnostics

Although most leafmines occurring on Betula in Europe can be identified from the leafmine pattern and larval characters with several sources ( Hering 1957; Pitkin et al. 2019; Edmunds 2022; Ellis 2022), identification of linear or corridor mines is still a challenge, especially now, since S. naturnella appears to have become widespread, while the two Stigmella species normally found on Alnus have been recorded on Betula several times in more southern parts of Europe. To assist identification, diagnostic notes are provided for all Stigmella species occurring on Betula in Europe followed by an identification key.

Identification is easiest for either completed, vacated mines, in fresh condition (or dried when fresh), or mines with active larvae in their final instar. Old and withered mines should preferably be left on the tree, only with experience can they sometimes be distinguished. Moreover, mines with dead or parasitised larvae may be more difficult or even impossible to identify, as are mines containing young larvae. It is important to check whether the position of the egg is on the leaf upper- or underside as it is for the position of the exit slit where the larva has left the mine. These characters can only be seen effectively with magnification, at least a loupe in the field is necessary or a stereo microscope in the laboratory. For photographic recording detailed images are needed, and especially photos with back lighting, which shows frass and larva better.

Larvae of Nepticulidae usually are situated in their mines with the ventral side at the leaf upperside, but all species belonging to "Core Stigmella " ( Doorenweerd et al. 2016: 279) have the dorsum upwards. This character, often overlooked, is helpful in separating the species belonging to core Stigmella (here S. continuella , S. lapponica , S. confusella and S. tristis ) from the rest. The larval head capsule, especially in the final instar, is longer at the dorsal side than at the ventral side (high magnification needed; see e.g. Gustafsson and van Nieukerken 1990), dorsally the paired brains may be visible (e.g. Fig. 69 ), no other ganglia, whereas in species with venter upwards often the ventral nerve chord is visible (e.g. Fig. 41 ), but this may be obsolete, and in S. naturnella only the suboesophageal ganglion is visible (Figs 23 , 24 ).

Stigmella naturnella (Klimesch, 1936) (Figs 18 - 27 , 29-34 ). Egg: on leaf under- or upperside, usually away from major veins, rarely against a vein, more often in the area near the margin. Exit: leaf upperside. Larva: venter upwards, pale whitish, with distinct brown circular suboesophageal ganglion, but no other ventral ganglia visible. Early mine: starts directly away from egg, sometimes with single bend around egg; early mine often appearing green as larva eats only sponge parenchyma. Later mine: rather variable, rarely very straight, but sometimes with straight parts; frass often rather narrow, but can be much wider and forming clumps.

Occurrence: usually on mature trees, occasionally on juvenile trees, rarely more than one or two mines per leaf. Prefers dryer habitats in open forests and Betula pendula , but can be found in many other habitats as well. Larvae of second generation occur from August, often in low numbers.

Note: mines with upperside egg and/or green early part are easy to recognise, vacated mines without these characters may be difficult to separate especially from those of S. confusella , but mine of S. naturnella is usually narrower (final larval chamber 0.9-1.4 mm wide) and shorter (length 22-53 mm, small overlap with S. confusella ) and frass appears more broken. Some isolated mines may be unidentifiable, so studying a series of mines is best for a certain identification.

Stigmella betulicola (Stainton, 1856) (Figs 40-44 ). Egg: on leaf underside, against a major vein. Exit: leaf underside. Larva: venter upwards, deeply yellow, with chain of ventral ganglia clearly visible. Early mine: starts contorted with close coils in a very confined area (Fig. 42 ), never green. Later mine: rather variable, frass width variable, between 1/3 and 3/4 mine width, sometimes filling early mine completely, mine rather long or shorter in thicker leaves.

Occurrence: most frequent on low growth, seedlings, juvenile trees, often gregarious with many mines on one leaf.

Note: mines of S. luteella are often mistaken for S. betulicola when the green part of the mine is absent. The larger contorted part and small differences in frass deposition may help if no larva is present, but some mines remain unidentifiable. Mines of S. glutinosae may be very similar to S. betulicola , but do not have coils at the start of the mine.

Stigmella luteella (Stainton, 1857) (Figs 45-52 ). Egg: on leaf underside (rarely on upperside), against a major vein. Exit: leaf underside. Larva: venter upwards, pale yellow, ventral ganglia hardly or not visible. Early mine: starts with a distinctly contorted part (Fig. 52 ), area larger than in Stigmella betulicola ; frequently the early part of the mine is in the spongy parenchyma and therefore appearing green from above. Later mine: rather variable, frass either in a very thin line or the line is broader (up to 3/4 the width of the mine) and the frass line is broken, mine rather long, shorter in thicker leaves; sides of mine often scalloped.

Occurrence: usually on mature trees, occurring later in the season than most Stigmella species, frequently found still feeding in green islands in fallen leaves in October-November. Rarely gregarious.

Note: mines of S. luteella are often mistaken for S. betulicola when the green part of the mine is absent, especially in northern Europe. The larger contorted part and small differences in frass deposition may help identification if no larva is present, but some mines will remain unidentifiable.

Stigmella glutinosae (Stainton, 1858) (Figs 53-57 ). Egg: usually on leaf underside, against a major vein, in some cases on upperside (about 20% of 51 mines examined, but all upperside eggs were in one sample). Exit: usually leaf underside, in some cases on upperside. Larva: venter upwards, pale yellow, ventral ganglia hardly or not visible. Early mine: runs straight away from egg. Later mine: rather variable, frass either in a very thin line, or a broader line with frass dispersed, and width up to 2/3 of the mine, mine rather short, total length 23.2-41.4 mm (34.5 ± 6.4, 6), final larval chamber 1.0-1.4 mm wide.

Occurrence: when on Betula often on seedlings and juvenile trees, but also on mature trees. Occasionally gregarious (Fig. 53 ). More frequent on Alnus , but in southern parts of Russia and in France several times recorded on Betula , proven by rearing and DNA barcodes. Some leafmines from Germany (Fig. 57 ) and the Netherlands probably also belong to Stigmella glutinosae , but independent confirmation is lacking.

Note: mines of S. glutinosae may resemble those of Stigmella naturnella , but the egg position on a vein and larval exit on underside usually separate the two, as does the green early mine in many Stigmella naturnella . Some mines remain unidentifiable. Some of the mines from Ulyanovsk figured as S. naturnella by van Nieukerken et al. (2004: fig. 10) fit S. glutinosae better, suggesting that the mine sample was a mixture of the two. It is highly likely that the leafmine reported as S. confusella from Ukraine, the Crimea by Navickaitė et al. (2014) also belongs to S. glutinosae .

Stigmella alnetella (Stainton, 1858) (Figs 58 , 59 ). Only two mines on Betula are available that are proven by DNA barcodes, to be from S. alnetella . Egg: on leaf underside, against a major vein. Exit: leaf underside. Larva: venter upwards, pale yellow, ventral ganglia hardly or not visible. Early mine: slightly coiled. Later mine: with frass coiled, in a rather broad line in both the mines examined. Probably more variable, as in the leafmines on Alnus .

Occurrence: both mines on Betula were on mature trees. Common on Alnus , the two larvae barcoded from Betula were from Italy; reared once in Sweden ( Johansson and Nielsen 1990).

Note: Considering the difficulty of separating mines of S. alnetella from those of Stigmella glutinosae on Alnus , we expect to experience the same difficulty on Betula . The two mines examined resemble somewhat those of S. sakhalinella , but distinguishing features are: egg on vein, early mine with narrow linear frass and exit on leaf underside. These two Italian mines were found amongst a large number of vacated mines resembling those of S. glutinosae , that could belong to either species, but are tentatively identified as S. glutinosae .

Stigmella sakhalinella Puplesis, 1984 (in older European literature under the name S. distinguenda auct.) (Figs 60-63 ). Egg: usually on leaf underside, but in several cases on leaf upperside, most frequently near leaf margin, but other positions over the whole leaf have been observed. Exit: leaf upperside. Larva: venter upwards, dark yellow, ventral ganglia clearly visible. Early mine: starts rather contorted, filled with dark frass. Later mine: usually somewhat contorted, or following leaf margin, frass black, coiled, usually almost filling width of mine, leaving narrow borders; occasionally the frass line is narrower, but still coiled (Fig. 61 ).

Occurrence: usually on mature trees, but also on juvenile trees, occasionally gregarious.

Note: mine unmistakeable, although S. alnetella when rarely on Betula has some resemblance in the second part of the mine. Young mines sometimes confused with S. betulicola .

Stigmella confusella (Wood & Walsingham, 1894) (Figs 64-69 ). Egg: on leaf underside, usually close to a vein. Exit: leaf upperside. Larva: dorsum upwards, greenish whitish, the bilobed brain clearly visible from upper side, differing from the (ventral) circular suboesophageal ganglion in S. naturnella , no other ganglia visible from above. Mine: often with long straight stretches, following veins partly, occasionally partly more contorted (as in Figs 64 , 65 ), especially at start; overall the mine has an angular appearance; frass throughout in a narrow central line, often continuous, only partly broken in later part of mine.

Occurrence: usually on mature trees, rarely with more than two mines per leaf. Prefers B. pubescens in moist habitats. Univoltine, usually occurring later than S. lapponica.

Note: mine most similar to S. lapponica , but the early frass of that species always separates the two. Less typical mines may be confused with S. naturnella , but the species are not often found together and S. confusella has a considerably longer mine: 41-91 mm (68.9 mm ± 15.6, n=12), with only a small overlap with S. naturnella . Also, the final larval chamber is wider: 1.3-2.0 mm (1.6 ± 0.2, n=12), and usually straight, whereas that of S. naturnella is often buckled. However, some unfinished mines (without distinct larval remains) in areas where both species occur may be inseparable. Vacated mines of Lyonetia clerkella are sometimes mistaken for S. confusella , especially where photographs are used for determination, but the extreme length of the mine, its sinuous condition and the absence of a visible egg are diagnostic.

Stigmella lapponica (Wocke, 1862) (Figs 70-72 ). Egg: on leaf underside, usually close to a vein. Exit: leaf upperside. Larva: dorsum upwards, greenish whitish, the bilobed brain clearly visible from upper side, differing from the circular suboesophageal ganglion in S. naturnella , no other ganglia visible from above. Early mine (made by first 3 instars) filled entirely with green or brown frass, in last instar frass arranged in a narrow central line, often continuous, only partly broken in later part of mine. Mine: often with long straight stretches, partly following veins, occasionally rather more contorted, the mine has an angular appearance.

Occurrence: usually on mature trees, rarely with more than two mines per leaf. Prefers B. pubescens in moist habitats, occurs earlier than S. confusella , univoltine.

Note: unmistakeable by the aberrant early frass. In Nordic mines (northern Fennoscandia, Russia) the frass in the early part differs still from the second part, but often less conspicuously than in more southern populations. Otherwise the same diagnostic characters as in S. confusella apply.

Stigmella continuella (Stainton, 1856) (Figs 73 , 74 ). Egg: on leaf underside, almost always on midrib. Exit: leaf upperside. Larva: dorsum upwards, yellow, but in mine often appearing green, no ganglia visible from upper side. Early mine a narrow gallery, much contorted in a zigzag fashion, with windings usually lying against each other, in some cases the windings more separate; earliest part sometimes with narrow linear frass for about 1 mm, later filled with brown frass, early mine forming a distinct brown spot on the leaf, and the leaf tissue between the windings turning brown; later mine a long and rather broad gallery, may follow veins and sometimes angular, filled with green frass pellets, often coiled, arranged in zigzags, frass green when fresh and then almost inseparable from green tissue of leaf, later turning brown.

Occurrence: regularly on seedlings and juvenile trees, but also on mature trees, sometimes with more than two mines per leaf. No host preference, in various habitats, but common in heathland.

Note: unmistakeable from the brown blot at the start and the green frass, which completely fills the mine.

Other linear miners on Betula

Stigmella tristis (Wocke, 1862) is an arctic species, confined to Betula nana and unlikely to occur sympatrically with S. naturnella. It is the only other Betula mining Stigmella species with the egg on leaf upperside ( Johansson and Nielsen 1990).

Mines of Lyonetia clerkella are often confused with Stigmella mines. The extremely long and narrow mines run through the leaves independent of the veins or leaf margins; frass deposited as a broken, central line of variable width. There is no eggshell on the leaf, but an oviposition scar, the larva is very long, with conspicuously constricted segments and distinct legs, visible from the leaf upperside as six black dots. Vacated mines have a very long final chamber without frass. Often on young leaves, seedlings, juvenile trees. Apart from Betula also common on Rosaceae trees.

Bucculatrix demaryella (Duponchel, 1840). Regularly confused with young mines of Stigmella species, usually S. luteella. Egg on leaf underside. Mine is usually short (up to 1 cm), but may be considerably longer in thinner leaves, always starting on the midrib or a larger vein, in a vein angle; usually with blackish frass in a broad line or filling the mine. Larva leaves the mine early, later feeding externally, causing windows on leaf underside. Larval chamber relatively long, three times as long as wide, often bent. The presence of small silken moulting cocoons of young larvae on the leaf are a sign of Bucculatrix mines.

Other linear mines are rather different and easier to identify with online keys ( Ellis 2022), e.g. the dipteran Agromyza alnibetulae , the weevil Anoplus plantaris ( Naezén, 1794). The early linear mines of Eriocrania sparrmannella (Bosc, 1791), E. salopiella (Stainton, 1854) and Phylloporia bistrigella (Haworth, 1828) are sometimes confused with Stigmella mines before the blotch part is formed.

Key to mines of Stigmella on Betula in Europe

1	Mine almost completely filled with dispersed frass in distinct coils ( “zigzag”), sometimes leaving narrow white margins (Figs 58-63 , 73 , 74 )	2
-	Mine with frass in a central line of variable thickness, at least in second half of mine, may be broken, and filling up to two thirds of mine width, but never in coils	4
2	Frass in fresh mines green, filling the width of the mine, rendering it almost invisible, later frass turning brown. Early mine narrow brown and much contorted, forming a brown blot (Figs 73 , 74 ). Egg always underside, usually on or near midrib. Larva with dorsum upwards, no ganglia visible	S. continuella
-	Frass in fresh mines brown to black, usually leaving narrow white margins. Early mine usually blackish, with few or no coils. Egg position variable, usually underside, sometimes upperside. Larva with venter upwards	3
3	Egg away from midrib, anywhere in leaf, often near margin. Exit slit on leaf upperside. Larva deep yellow with conspicuous chain of ganglia visible (Figs 60-63 )	S. sakhalinella
-	Egg against midrib or another major vein. Exit slit usually on leaf underside. Larva pale yellow, ganglia not or hardly visible. Rare on Betula (Figs 58 , 59 )	S. alnetella
4	Early mine completely filled with green or sometimes brown frass, later mine angular with narrow central line of frass, the change in frass deposition is abrupt, complete mine long (Figs 70-72 ). Exit slit on leaf upperside, egg on underside. Larva with dorsum upwards	S. lapponica
-	Early mine may be filled with frass, but without abrupt change between early and later parts of mine, or with narrow frass line. Mine length, exit slit and egg position variable	5
5	Egg on leaf upperside	6
-	Egg on leaf underside	8
6	Leafmine on Betula nana in northern Europe, mine rather short	S. tristis
-	Leafmine on other species of Betula , mine rather long	7
7	Egg anywhere on leaf, but usually away from major veins. Early mine often on underside, appearing green. Exit slit on leaf upperside. Larva pale whitish, with distinct circular suboesophageal ganglion, but no other ventral ganglia visible	S. naturnella
-	Egg against midrib or another major vein. Early mine never green. Exit slit usually on leaf underside. Larva pale yellow, ganglia not or hardly visible, but prothorax with square brown plate. Occasionally on Betula , common in some places (Figs 53-57 )	S. glutinosae
8	Early mine contorted in a small area. Egg against midrib or another major vein. Exit slit on leaf underside. Larva with venter upwards	9
-	Early mine running away from egg, not contorted, sometimes with a bend around it. Egg position variable. Exit slit variable. Larva with venter or dorsum upwards	10
9	Early mine usually conspicuously contorted, and often appearing green. Sides of mine often scalloped, scallops usually free of frass. Larva pale yellow, without visible ganglia. Usually on trees, not on seedlings (Figs 45-52 )	S. luteella
-	Early mine briefly tightly contorted, never green. Sides of mine rather straight. Larva deep yellow with conspicuous chain of ganglia. Mines often gregarious on seedlings or saplings, rarely on trees (Figs 40-44 )	S. betulicola
10	Egg usually away from major veins. Early part of mine may be green or not. Mine not very long (length 22-53 mm), not particularly angular, frass central, of variable thickness; width of final larval chamber 0.9-1.4 mm. Exit slit on upperside. Larva with venter upwards, pale whitish, with distinct circular suboesophageal ganglion, but no other ventral ganglia visible	S. naturnella
-	Egg against midrib or another major vein. Early mine never green. Mine rather short (23-41 mm), somewhat angular; width of final larval chamber 1.0-1.4 mm. Exit slit on leaf underside, exceptionally on upperside. Larva with venter upwards, pale yellow, ganglia not or hardly visible, prothorax with square brown plate. Occasionally on Betula , common in some places (Figs 53-57 )	S. glutinosae
-	Egg usually close to a vein. Early mine never green. Mine very long (41-91 mm), usually distinctly angular, with long parts following veins; width of final larval chamber 1.3-2.0 mm. Exit slit on leaf upperside. Larva with dorsum upwards, greenish whitish, the bilobed brain clearly visible from upper side (Figs 64-69 )	S. confusella

History of distribution and spread of Stigmella naturnella

The original specimens were collected in 1934 and 1935 around the villages of Naturno and Stava in South Tyrol (Italy, prov. Bolzano), where the mines were reported as common, but with few larvae ( Klimesch 1936). A few years later Joseph Klimesch collected the species in the Trento region ( Klimesch 1948, 1951). Here we report that the species was still common in the Naturno area in 1983 and 1985 (collected by J.J. Boomsma), and in Bolzano province in 2005. Hugo Skala, who was in contact with Klimesch, soon reported more records of this species from Austria, Germany and Czechia ( Skala 1937, 1939), but all were based on leafmines alone, without confirmation from reared specimens, which made Klimesch (1948) reluctant to accept these records. The oldest of these records were leafmines collected by Albert Wörz from the Stuttgart area, Württemberg, Germany, in 1935. Later Wörz (1958) repeated these records in detail. Wörz cited Klimesch’s opinion on these mines as “höchstwahrscheinlich” ("most likely"). Buhr (1940a, b) reported leafmines of this species, all identified by Skala, from various places in Germany, especially Berlin (botanical garden) and Mecklenburg. These old records have never been re-evaluated after the original publications. Hering (1957) did not cite them, but the Stuttgart records were cited in the German checklists, albeit with doubts in the second edition ( Gaedike and Heinicke 1999; Gaedike et al. 2017). I have been able to study most of these leafmines; the majority of Buhr’s leafmines from Berlin are still available in his leafmine collection (Herbarium Hausknecht, Jena) and Wörz’s leafmines are available in his collection in Stuttgart. Buhr’s mines were re-identified by me as belonging to respectively Stigmella cf glutinosae and S. luteella , but Wörz’s leafmines (six in total) from the Willdpark in Stuttgart and Lemberg were indeed correctly identified as S. naturnella .

The old record from Czechia in 1937, from Mladé Buky (Jungbuch) ( Skala 1939; Haase 1942), also identified by Skala, was given a question mark by Haase and the remark hier muß das Zuchtergebnis erst volle Gewißheit bringen [here must the rearing results provide certainty]. The identity of this record therefore remains uncertain, but is not impossible that it is of S. naturnella .

The only other old record that has been confirmed was from Austria, Linz, Bauernberg (Botanical Garden), from mines collected by Skala in 1936 ( Skala 1937). Two of his leafmines are housed in the collection of Rebel in the Vienna Museum, of which detailed published photographs show enough detail to consider them as correctly identified ( Lödl and Gaal-Haszler 2010) (although it is unfortunate that no photos with back lightning were made); Klimesch (1990) found the species here again in the 1970s, and we have some duplicate mines in RMNH. Karl Burmann also found the species in Innsbruck in 1940 ( Hartig 1964), and again in 1950 and 1960. For these we have no confirmations, but they are probably correct.

After the early findings, very little information became available for S. naturnella for many years. An unpublished record shows that it was present in Czechia, Moravia in 1961, mines collected by H. Zavřel, present in the Hering Herbarium (NHMUK). The next published record was from Hungary in 1968 ( Szőcs 1971, 1973), so far the only Hungarian record. It took 20 years for the next published records to be made from Czechia and Slovakia ( Laštůvka and Laštůvka 1991; Laštůvka et al. 1992), although the species had meanwhile been found again in 1982 in Austria, in Vorarlberg (https://www.gbif.org/occurrence/99543229). I found leafmines of the species in 1983 in Croatia, but at that time I did not recognise them and identified these as S. betulicola .

Meanwhile, the species was discovered as Astigmella dissona in Far East Russia in the early 1980s ( Puplesis 1984a, b). Only much later was it shown that S. naturnella is the same species, although the synonymy was already suggested by van Nieukerken (1986b). It was subsequently also found in European Russia, with the earliest record from 1992 (van Nieukerken et al. 2004, 2023 in prep).

More records were published from Austria and Czechia ( Huemer 1996; Huemer and Wieser 1996; Liška et al. 2000; Laštůvka and Marek 2002; Šefrová 2005; Šumpich 2011, 2017; Wieser 2012), the first record in Switzerland was in 2005 ( Kopp 2010) and we here report the first record from Ukraine in 2009.

Up to the early 2000s, most records were within a limited area, Alpine valleys and warmer areas in southern Germany, Czechia, Slovakia and Hungary, and further east throughout Russia ( Dubatolov 2007; Bolshakov et al. 2008; van Nieukerken and Sinev 2019; van Nieukerken et al. 2023 in prep). My new recordings of the species in the western Alps of France and Piemonte in 2018 still largely fit this picture. Surprising new records, however, have come from much farther northwards, first from Poland in 2010 (new record of mines from Walendów) and 2011 ( Baran 2013), then Germany, Sachsen in 2014 (new record of mines from Pirna), in the Oberlausitz in 2015 and 2017 and in Bavaria in 2017 and 2018 ( Guggemoos et al. 2018; Segerer et al. 2019). It was earlier found again in Baden-Württemberg by Willem Ellis and mistaken for S. luteella as shown by leafmines in RMNH, collected 28 September 2001 (Fig. 32 ). In October 2017 I found many leafmines in Central France near Le Mans (Sarthe), a first record for that country; in 2018 independently Mikhail Kozlov and I collected mines in the French Alps, in Savoie.

The earliest indications for an expansion into Belgium and the Netherlands are online observations from 2017, in March and April Guus Dekker observed adults in the Netherlands, Noord-Brabant (Table 1 ), in August larvae and mines were observed in Belgium, Limburg, Zwarte Beek - Bakel by Carina van Steenwinkel, originally identified as S. confusella (https://waarnemingen.be/observation/142508204/, see also Ellis 2022) and in October in the Netherlands, Noord-Brabant, near Ossendrecht, originally identified as S. luteella. The identity of these and subsequent online records as S. naturnella was first recognised by me in autumn 2020. In 2018 and 2019 most records were still from Belgium, but in 2020 S. naturnella appeared to be common in the southern half of the Netherlands, where it was recorded in the provinces Limburg, Noord-Brabant, Utrecht, Noord-Holland (only area near Hilversum) and Gelderland, the Veluwe. In the last province I was unable to find any mines of S. naturnella in the Veluwe area north of highway A1 (four sites visited in 2020), whereas it was common in southern parts of the Veluwe, a sandy area of forests, heathlands and sand dunes. Yet in the area around Leiden and Wassenaar (Zuid-Holland) S. naturnella was still absent. The online observations fit this pattern. In 2021 the species was observed more northernly in the province of Flevoland (https://waarneming.nl/observation/228044436/), confirmed again in 2022. In 2022 it was also found in the coastal dunes of Zeeland (Schouwen) and the northernmost records come from the province of Overijssel. More northern records along the coast (Noord-Holland) remain uncertain, these are vacated mines that also may belong to S. glutinosae. In Belgium observations originate from the following provinces: Antwerpen, Brussel, Hainaut, Limburg, Oost-Vlaanderen, Vlaams-Brabant and West-Vlaanderen.

Rechecking mines of other Betula feeding Stigmella in the rich leafmine collections of RMNH did not reveal any older misidentified mines of S. naturnella in the Netherlands.

In 2020 S. naturnella was also found in Saarland, and in 2021 and 2022 in Nordrhein-Westfalen in Germany, near Hövelhof.

Figures

Figure 1. Stigmella naturnella, live female, The Netherlands, Rijssen, emerged 14. x. 2022 (photo Gerwin van de Maat).

Figure 37. Distribution records of Stigmella naturnella in Europe and western Siberia.

Figure 38. Global distribution records of Stigmella naturnella, from France to Japan (Honshu). Grid interval 20 degrees.

Figure 39. Neighbor Joining tree of partial COI sequences (DNA barcodes) of Stigmella naturnella, under the KP 2 model. The labels provide data on Sample Id, Host (if known), Collection date, Country, Province.

Figures 2 - 4. Stigmella naturnella 2. male, The Netherlands, Wolfheze, RMNH. INS. 17215 l; 3. female, Goirle, The Netherlands, RMNH. INS. 17214; 4. Lectotype labels (photo Andreas Segerer). Scale bar: 1 mm (2, 3).

Figures 5 - 8. Stigmella naturnella, live adults 5. Male, 4. x. 2020, Netherlands, Wekerom, RMNH. INS. 25268; 6, 7. Female, 1. x. 2020, Netherlands, Soest RMNH. INS. 17204; 8. Hibernating adult under bark of Platanus, Belgium, Antwerp, 6. ii. 2020 (photo Stijn Baeten), https: // waarnemingen. be / observation / 185190974 /. Scale bars: 1 mm.

Figures 9 - 14. Stigmella naturnella, male genitalia, ventral aspect. 9, 10. Slide EvN 5268; 11, 12. Slide EvN 5341; 13. Genitalia without valvae and phallus, slide EvN 3302; 14. Phallus, slide EvN 3303. Scale bars: 100 µm (9 - 12 top left, 13, 14 top right).

Figures 15 - 17. Stigmella naturnella, female genitalia, ventral aspect 15. Bursa copulatrix, slide VU 1874; 16, 17. Abdominal tip, respectively more ventrally and more dorsally in focus, slide EvN 5342. Scale bar: 200 µm (16, 17).

Figures 23 - 28. Stigmella naturnella, biological details, all on Betula pendula 23. Larva, detail of Fig. 18; 24. Larva, detail of Fig. 21; 25. Early part of leafmine, with upperside egg, Wekerom, data as Fig. 18; 26. Early part of leafmine from underside, with underside egg; Italy, Naturno, 1935, coll. Woerz; 27. Final part of mine with exit slit on leaf upperside; Soest, Korte Duinen, 23 Aug. 2021, EvN no 2021120; 28. Cocoon, Wekerom, data as Fig. 18. Scale bars: 1 mm.

Figures 18 - 22. Stigmella naturnella, occupied leafmines, seen from above, with dark field illumination; all from The Netherlands 18, 19, 22. Wekerom, De Valouwe, 16 Sep. 2020, Betula pendula, EvN no 2020062 - 1; 20. Goirle, Gorp en Roovert, 30 Sep. 2020, B. pendula, EvN no 2020083 - 1; 21. Soest, Korte Duinen, 23 Aug. 2021, B. pubescens, EvN no 2021121. Scale bars: 5 mm (all but 21 on same scale), arrows point at egg position (upper- or underside of leaf).

Figures 29 - 34. Stigmella naturnella, vacated leafmines, dried samples 29. Italy, Naturno, Jun. 1935, Betula pendula, coll. Woerz; 30. Italy, Naturno, Sep. 1934, B. pendula, coll. Woerz; 31. Germany, Stuttgart, Willdpark, Sep. 1935, B. pubescens, coll. Woerz; 32. Germany, Badenweiler, Sep. 2001, B. pendula, ZMA. INS. MIG. 07497; 33. Russia, Voronezh, Aug. 2017, unfinished mines, one larva barcoded, B. pubescens, RMNH. INS. 46142; 34. Netherlands, Wekerom, De Valouwe, Sep. 2020, Betula pendula, EvN no 2020062 - 1. Scale bar: 5 mm (all on same scale).

Figures 35, 36. Habitat of Stigmella naturnella 35 (top). The Netherlands, Goirle, Gorp en Roovert - Noord, 30 Sep. 2020, EventId: EvN no 2020083, many mines of S. naturnella on Betula pendula shrub; 36 (bottom). Germany (NRW), Hoevelhof, NSG Moosheide, 19 Aug. 2021, in 2021 only one mine on B. pendula (photo Dieter Robrecht).

Figures 64 - 69. Stigmella confusella, leafmines 64. Occupied mine, Netherlands, Leidschendam, 11 Aug. 2013, Betula pubescens, EvN no 2013098 - 3; 65. Occupied mine, dried with larva (barcoded), Russia, St. Petersburg, 1 Jul. 2016, Betula sp., RMNH. INS. 31461; 66. Vacated mine, Netherlands, Goirle, 12 Sep. 1982, B. pubescens, VU no 82417; 67. Vacated mine, Norway, Stryn, Kjenndalen, 28 Jul. 2000, Betula sp., EvN no 2000115 - 1 H; 68. Vacated mine, Finland, Harjavalta, 14 Sep. 2009, B. pendula 69. Detail larva of Fig. 64. Scale bars: 5 mm.

Figures 40 - 44. Stigmella betulicola, leafmines 40. 7 vacated mines, France, Le Mans, 7 Oct. 2017, Betula pubescens, 7 adults emerged Mar. 2018, EvN no. 2017150 - K; 41 - 44. Occupied mines, The Netherlands, Goirle, 30 Sep. 2020, B. pendula, EvN no. 2020083 - 2; 41. Detail of larva; 42. Details of coiled mine start. Scale bars: 1 mm (to 41 and 42); 5 mm (43 and 44 on same scale).

Figures 45 - 52. Stigmella luteella, leafmines 45 - 47. 2 Occupied mines and one vacated mine, The Netherlands, Ede, 16 Sep. 2020, Betula pubescens, EvN no 2020058 - 1 K; 48. Vacated mine, The Netherlands, Wekerom, 16 Sep. 2020, B. pendula, EvN no 2020062 - 2; 49. Vacated mine, Germany, Hamburg, 28 Sep. 1932, B. utilis, published as Nepticula naturnella by Buhr (1940 b: 229); 50. detail of larva in Fig. 45; 51. mine with dead larva, barcoded, Russia, Karelia Rep., Nadvoitsy, 26 Aug. 2012, B. pubescens, RMNH. INS. 29973; 52. data as Fig. 48, early part of mine and egg, leaf underside. Scale bars: 5 mm (45 - 49, 51); 1 mm (52); no scale for 50.

Figures 53 - 57. Stigmella glutinosae, leafmines on Betula, confirmed by DNA barcoding, except 57. 53. France, Le Mans, 7 Oct. 2017, B. pubescens, 6 mines, 4 ♂ 1 ♀ emerged, left mine, near cross, incomplete, larva taken for barcoding, EvN no 2017150 - 3 K / M; 54. France, Villeneuve-sur-Cher, 30 Jul. 2009, larva taken from mine, B. pendula, EvN no 2009039 - M; 55. Russia, Voronezh, 28. viii. 2017, B. pendula, dried mines with larvae, larva taken from right mine, RMNH. INS. 31158; 56. Russia, Lipetsk Obl., Osman, 28 Aug. 2017, B. pendula, RMNH. INS. 31159; 57. Vacated mine, Germany, Berlin, Botanischer Garten, 17 Aug. 1936, B. papyrifera (as B. excelsa), published as Nepticula naturnella by Buhr (1940 b: 229). Scale bars: 5 mm (55 - 57 on same scale).

Figures 58 - 63. 58, 59. Stigmella alnetella, vacated leafmines on Betula, confirmed by DNA barcoding, Italy, Roma, Manziano, 17 Sep. 2005, B. pendula, EvN no 2005115 - 3 M 60 - 63. Stigmella sakhalinella, leafmines. 60. Occupied mine, Netherlands, Soest, 23 Aug. 2021, B. pendula, EvN no 2021122 - 2 K; 61. Occupied mine, Netherlands, Wassenaar, 10 Oct. 2018, B. pubescens, EvN no 2018263 - 2; 62. Vacated mine, Netherlands, Wassenaar, Meijendel, 11 Oct. 2007, B. pubescens, EvN no 2007122 - 1 M; 63. Vacated mine, Finland, Helsinki, Ojakkala, 1 Sep. 2017, B. pendula, RMNH. INS. 44352. Scale bars: 5 mm (58 & 59, 60 & 61 and 62 & 63 each on same scale).

Figures 70 - 74. Stigmella lapponica, leafmines 70. Occupied mine, England, Copley, North Dean wood, 7 Jun. 2018, B. pubescens, photo Charlie Streets; 71. Occupied mine, Netherlands, Noordhollands Duinreservaat, 15 Jun. 2018, Betula spec., photo Wouter Bol; 72. Vacated mine, Portugal, NP Gerez, 7 Jul. 1980, B. pubescens. 73, 74. Stigmella continuella 73. Vacated and occupied mine (larva arrowed), Netherlands, Afferden, 24 Sep. 2008, B. pubescens, EvN no 2008107 - 1 K; 74. Occupied mine, Netherlands, Wekerom, 16 Sep. 2020, B. pendula, EvN no 2020062 - 4 K. Scale bars: 5 mm; no scales available for Figs 70 - 72.