Genus Europiella Reuter, 1909

Europiellomorpha Duwal, in Duwal et al., 2014: 391 (n. gen.),

type species: Plagiognathus lividellus Kerzhner, 1979

[= Europiella lividella], original designation; Duwal et al., 2016: 111 (catalog). N. syn.

Diagnosis: This Holarctic genus is primarily recognized by the following characters: Small to moderate size (total length 2.1–4.7 mm); body form varying from elongate to ovoid; coloration variable from almost completely pale green or yellowish to widely dark brown; dorsum with pale or brown simple setae and silvery lanceolate setae; relatively small eyes; elongate right paramere that is obviously longer than left; and sigmoid vesica with two pointed apical blades. In Japanese species, the males are elongate and nearly parallel-sided whereas the females are short and ovoid; the immature forms are generally pale green or yellowish even in dark species (cf. Yasunaga, 2001d). Detailed generic diagnosis was provided by Schuh (2004).

Discussion. Europiella and Plagiognathus were liable to be confused with each other (e.g., Yasunaga, 1999), until Schuh (2001, 2004) suggested the definitive diagnosis for each genus. Europiella species are primarily characterized by the features mentioned above and known to be associated with herbaceous plants (mostly in Asteraceae). Japanese Plagiognathus species are recognized by the dorsal vestiture pattern (dark, simple setae only and always lacking silvery setae) and the ventral surface of the metafemur with distinctly enlarged dark spots or maculae that sometimes form two or three rows (Yasunaga, 2016).

Duwal et al. (2014) proposed a new genus Europiellomorpha Duwal to accommodate E. lividella (Kerzhner). However, the suggested generic diagnostic characters are shared by Europiella (cf. Schuh, 2004) and the present close examination on E. lividella could not recognize any apomorphy or unique character for the generic level definition (e.g., Figs. 5E, 6D, 21 M−N). Therefore, Europiellomorpha is herein regarded as a junior synonym of Europiella.

Incidentally, the identities of two closely related species in Japan, namely Europiella artemisiae (Becker, 1864) (Fig. 5A) and E. decolor (Uhler, 1893) (Fig. 5B–D), have been confused. Kerzhner (1988) reported E. decolor from seashore on Etorofu Island, Chishima Islands, and the dark, small-sized Europiella species known from all other parts of Japan was considered to match E. artemisiae (Yasunaga, 2001d). However, the present work revealed that E. artemisiae is restricted to cold temperate climatic zone (Hokkaido and Tohoku area of Honshu) whereas the populations that occur in central and southwestern Honshu, Shikoku and Kyushu represent E. decolor. Each species can be separated by the biometrics (Table 2) and genitalic structures (Figs. 4E–F; 20A–I). Although E. senjoensis (Linnavuori, 1961) (Fig. 6 E−F) is also characterized by its dark general coloration, this Artemisia -inhabiting phyline has the larger-sized body and is considered to be endemic to the central highlands of Honshu (Yasunaga, 1999; 2001d).

Yasunaga (2001d) also suspected what has been identified solely as E. miyamotoi (Kerzhner, 1988) may comprise a few sibling species similarly sharing a moderate-sized body and pale green or yellowish general coloration (cf. Figs. 5F–L, 6A–C), such as E. leucopus (Kerzhner, 1979), E. livida (Reuter, 1906) or E. gilva (Kulik, 1965) (cf. Fig. 7) known from the Russian Far East and Korean Peninsula. This study eventually verifies the occurrence of two undescribed species different from these continental elements.

As argued by Schuh (2004), Europiella contains confusable members. In Japan, some species have been often confused or misidentified as mentioned above, because of their great similarity in the external appearance and intraspecific variation in coloration and/or size. The following key would aid in unequivocal identification of Japanese congeners.

Key to Japanese species of Europiella

1. Dorsum generally pale green, pale olive green or in dry-preserved specimen often pale brown; extreme base (knee) of each base of meso- and metatibia not darkened...................................................................... 2

– Dorsum (at least pronotum) darkened or grayish brown, not tinged with green (if dorsum pale green, then bases of meso- and metatibia each with a dark knee-spot, cf. Fig. 5B); extreme base (knee) of each base of meso- and metatibia darkened or with a dark spot............................................................................................ 6

2. Ventral surface of metafemur with 3-4 dark, rounded spots (Fig. 6D)..................................... E. lividella

– Ventral surface of metafemur with numerous small dark spots.................................................. 3

3. Apical 2/3-3/4 of ventral surface of metafemur clearly spotted (Fig. 6C)............................. E. nihonica n. sp.

– Basal half of ventral surface of metafemur lacking spot or only with small faint spots............................... 4

4. Body pale or yellowish green when alive (Fig. 5J); in male vertex (interocular space) as wide as an eye in dorsal view; metafemur longer than 1.5 mm (♂)/ 1.4 mm (♀); associated with Asteraceae hosts in northern Japan ......... E. miyamotoi

– Body pale olive green when alive (Fig. 5 G−H); in male vertex wider than an eye in dorsal view; metafemur shorter than 1.4 mm in both sexes; found from Laminaceae herbs in southwestern Japan ............................... E. isodonicola n. sp.

5. Body larger, total length> 4mm (♂)/ 3.3 mm (♀); pronotum shiny fuscous (Fig. 6 E−F); mesotibia longer than basal width of pronotum; length of metatibia> 2 mm ............................................................ E. senjoensis

– Body length <3.6 mm (♂)/ 3.2 mm (♀); pronotum weakly shining, relatively matte; length of mesotibia about as long as or shorter than basal width of pronotum; length of metatibia <1.8 mm ............................................. 6

6. In male, antennal segment II as long as or longer than basal width of pronotum; in female, antennal segment III almost equal in length to head width across eyes; male vesica and female posterior wall as in Figs. 4E; 20A, D–F............ E. artemisiae

– In male, antennal segment II obviously shorter than basal width of pronotum; in female, antennal segment III shorter than head width across eyes; male vesica and female posterior wall as in Figs. 4F; 20B–C, G–I......................... E. decolor