| Description: |
Plagiognathus Fieber, 1858 Diagnosis. East Asian congeners of Plagiognathus are recognized by the following combination of characters: Body elongate and subparallel-sided (♂)/ elongate-ovoid (♀), small to moderate in size (total length 2.9–4.5 mm); coloration variable (Figs 1–2); dorsum generally shining, with uniformly distributed, dark, simple setae, lacking silvery or wooly recumbent setae; vesica always with two apical blades (cf. Figs 6, 8B–C, 9D–F); sclerotized rings large, contiguous to each other mesally (Fig. 7); and posterior wall of bursae simple (cf. Figs 8E–F, 9H–I). As suggested by Schuh (2001), this large Holarctic genus is defined principally by the form of the male genitalia, such as twisted, often sigmoid vesica with two apical blades and rather slender, lanceolate right paramere. Some species of Plagiognathus exhibit great similarity in external appearance to certain members of Europiella Reuter, 1909; however, Europiella is distinct in having both silvery and simple setae on dorsum, right paramere remarkably widened and often squared, vesica apically with membranous area, and sclerotized ring small and narrow-rimmed (e.g., Schuh et al. 1995; Yasunaga 2022). Further diagnostic characters and a redescription for Plagionathus were provided by Schuh (2001). Discussion Plagiognathus forms one of the largest genera among the plant bug subfamily Phylinae and is known to comprise more than 120 described species; of these about 80 % are Nearctic elements (Schuh 2001, 2002 – 2013; Aukema 2018). Nonetheless, more than a few species appear to be wrongly placed in Plagiognathus and require further verification by dissecting the male genitalia (Schuh 2001). For eastern Asia, six congeners were reported by Yasunaga (2001), in addition to P. obscuriceps (Stål, 1858) occurring in northern Russian Far East and eastern Siberia and associated with Salix spp. (Salicaceae) (Kerzhner 1988). In Japan and adjacent regions, the fauna of Plagiognathus species has previously been the subject of several recent works, and ... |