Stenocranus Fieber, 1866

Fujinuma, Satoshi & Hayashi, Masami, 2025, Taxonomic revision of Japanese Stenocranus (Hemiptera: Fulgoromorpha: Delphacidae), Zootaxa 5706 (3), pp. 301-336 : 302-306

publication ID	https://doi.org/10.11646/zootaxa.5706.3.1
publication LSID	lsid:zoobank.org:pub:8EC89B9A-3A22-4437-AE42-DF61387992EC
persistent identifier	https://treatment.plazi.org/id/F1704704-D655-AD28-FF1A-FB70FDAC8C67
treatment provided by	Plazi
scientific name	Stenocranus Fieber, 1866
status

Treatment

Stenocranus Fieber, 1866 View in CoL

Stenocranus Fieber, 1866: 519 View in CoL . Type species: Fulgora minuta Fabricius, 1787 .

Redescription. Vertex distinctly projected anteriad beyond eyes, about 1.3–1.8× as long as wide; anterior margin angulate; lateral margins subparallel to converged anteriad; carinae distinctly ridged except median carina obsolete; submedian carinae meeting on fastigium. Frons about 2.5–3.0× as long as wide, widest near midlength, narrowed in apical 1/3; median carina usually forked in apical 1/3. Rostrum reaching or distinctly exceeding mesocoxae. Antennae terete; segment I about as long as wide; segment II about 2.3–3.8× as long as wide. Pronotum about 0.7–0.8× as long as vertex, about 1.2–1.3× as wide as head; carinae distinctly ridged; lateral carinae diverging posteriad, reaching posterior margin. Mesonotum about 2.0–2.5× as long as pronotum; carinae distinctly ridged except median carina obsolete near scutellum. Forewings distinctly exceeding abdomen, mostly subparallel, widest at apical 1/3 (near nodal line), rounded apically; ScP+R forked before CuA fork; C1 longer than C5; venation with ScP, RA and RP unbranched, MP 3-branched, CuA 4-branched (rarely 3-branched); anal veins fused in basal half of clavus, reaching wing margin before apex of clavus. Metatibiae with two lateral spines. Hind legs with spinulation: tibial apex with 5 (2 + 3) spinules, basitarsus with 7 (2 + 5) spinules, second tarsomere with 4 (rarely 5) spinules. Post-tibial spur cultrate, tectiform, shorter than basitarsus, with about 12–26 teeth on posterior margin.

Male genitalia: Pygofer triangular in lateral view, higher than wide, usually slightly produced caudad in dorsal half of caudal margin; oval in caudal view, higher than wide, angulate at lateral sides of opening for gonostyles; diaphragm broad, usually without armature. Suspensorium usually short in anterior view, narrowed to widened dorsally, with concavity. Gonostyles sinuate in lateral view; forceps-shaped in ventrocaudal view, narrow to broad, with very short to long basal angles. Aedeagus long, fine, sinuate. Phallotheca narrow to broad in lateral view, usually terminating into one or two downcurved processes; opening for aedeagus usually on left or caudal side. Anal tube rectangular in lateral view; ventral margin flat or bearing one (rarely two) pairs of processes.

Female genitalia: Pygofer nearly as long as gonoplacs in ventral view, usually mostly covered with gonoplacs. Gonocoxae VIII broad in ventral view, produced medially at base, narrowed to apices. Gonapophyses VIII slender in ventral view, nearly smooth to strongly serrated on lateroapical parts. Gonapophyses IX broad in dorsal view, dorsal margin with variously shaped teeth in apical 1/3 to 2/3. Gonoplacs usually very broad (rarely slender) in ventral view, semicircular.

Remarks. In East Asian stenocranine genera, Stenocranus can be easily distinguished from Terauchiana and Preterkelisia by its relatively short vertex, which is less than twice as long as wide. In this study, Japanese species of Stenocranus are classified into four species groups based on the investigation of male and female genitalia. Additionally, a part of current Stenocranus species should be separated as an independent genus, for which a new genus is established in this study.

In a previous investigation of the Matsumura collection, two Stenocranus species described from Japan ( Matsumura 1935a) were recognized to belong to the genus Sogata Distant ( Delphacinae ), which is similar in habitus to Stenocranus ( Fujinuma 2016) . Moreover, Stenocranus hopponis Matsumura from Taiwan may belong to Sogata , as the syntypes are similar to the holotype of Sogata nigrifrons (Muir) from Taiwan in BPBM. Furthermore, Stenocranus pacificus Kirkaldy , distributed in southern Japan, is suspected to be congeneric with Sogata or a related genus based on aedeagal morphology ( Fujinuma & Hayashi 2015) and molecular evidence ( Yashiro & Sanada-Morimura 2022). Japanese specimens are apparently identical to the holotype of S. pacificus in BPBM.

Intraspecific color variation, expressed as two seasonal forms, is observed in Japanese Stenocranus planthoppers (except S. sapporensis ) distributed in temperate regions. In most species, the winter form ( Figs 1A, 1D, 1J View FIGURE 1 , 3A View FIGURE 3 ) is darker in body coloration than the summer one ( Figs 1B, 1E View FIGURE 1 , 2A View FIGURE 2 , 3B View FIGURE 3 ), whereas in a few species, the winter form is paler ( Figs 1H View FIGURE 1 , 2B, 2D View FIGURE 2 ) than the summer one ( Figs 1I View FIGURE 1 , 2C, 2E View FIGURE 2 ). The winter form occurs from September, usually overwinters as adults, and females lay eggs in the following spring. The summer form occurs from June to August. The occurrence of seasonal forms may be controlled by photoperiodic conditions, as observed in another stenocranine planthopper, T. singularis ( Kisimoto 1996, Fujinuma 2016).

Grouping of the species

Based on morphological characters of the male and female genitalia, 10 Stenocranus species can be classified into four species groups. The key characters considered for the classification are the shape of suspensorium, gonostyles, phallotheca, and gonapophyses VIII and IX.

The niisimai group

Male genitalia: Suspensorium elongated dorsally, connected with ventrobasal process of anal tube ( Figs 6A View FIGURE 6 , 9A View FIGURE 9 ); gonostyles short and broad, directed medially at apices, with long basal angles ( Fig. 6I View FIGURE 6 ); phallotheca divided into left and right parts along ventral slit, slender in lateral view, flattened laterally in apical half, with two apical processes ( Fig. 6E View FIGURE 6 ). Female genitalia: Gonapophyses VIII nearly smooth on lateroapical parts ( Fig. 7C View FIGURE 7 ); gonapophyses IX very broad in dorsal view, with row of blunt teeth in apical 2/3 ( Figs 8A, 8I View FIGURE 8 ). This group represented by a single species, S. niisimai Matsumura , feeding on Phragmites spp. ( Poaceae ).

The tamagawanus group

Male genitalia: Suspensorium short, narrowed dorsally, with shallow concavity ( Fig. 6B View FIGURE 6 ); gonostyles long, broad, directed medially at apices, with long basal angles ( Fig. 6J View FIGURE 6 ); phallotheca with ventral slit, broad in lateral view, flattened laterally in apical half, with one apical process ( Fig. 6F View FIGURE 6 ). Female genitalia: Gonapophyses VIII serrated on lateroapical parts ( Fig. 7D View FIGURE 7 ); gonapophyses IX as in niisimai group ( Figs 8B, 8J View FIGURE 8 ). This group represented by a single species, S. tamagawanus Matsumura , dependent on Phalaris arundinacea L. ( Poaceae ).

The sapporensis group

Male genitalia: Suspensorium short, widened dorsally, with deep concavity ( Fig. 6C View FIGURE 6 ); gonostyles long, narrow, directed dorsomedially at apices, with short basal angles ( Fig. 6K View FIGURE 6 ); phallotheca without ventral slit, broad in lateral view, not flattened laterally in apical half, with one apical process ( Fig. 6G View FIGURE 6 ). Female genitalia: Gonapophyses VIII as in tamagawanus group ( Figs 7E, 7F View FIGURE 7 ); gonapophyses IX moderately broad in dorsal view, with partly two rows of acute teeth in apical 1/3 ( Figs 8C–E, 8K–M View FIGURE 8 ). This group comprises four species, feeding on sedges ( Cyperaceae ).

The takasagonis group

Similar to sapporensis group in suspensorium ( Fig. 6D View FIGURE 6 ), gonostyles ( Fig. 6L View FIGURE 6 ), gonapophyses VIII and IX ( Figs 7A, 7G View FIGURE 7 , 8F, 8N View FIGURE 8 ) but differing in phallotheca with two apical processes ( Fig. 6H View FIGURE 6 ). This group comprises four species, feeding on sedges ( Cyperaceae ).