Mestus morio Motschulsky, 1863 by original designation.

The genus Mestus Motschulsky is readily separated from other genera in the Delphacini of Delphacinae by the vertex with apices of submedian carinae feebly developed, by the median frontal carina distinct but feeble at base, by the post-tibial spur without teeth along posterior margin, by the caudal margin of pygofer strongly produced near base, by the pygofer with a single process on the midventral margin, and by the aedeagus with teeth subapically on both sides.

Head including eyes nearly as wide as pronotum. Vertex quadrate, anterior margin rounded, apices of submedian carinae and base of median frontal carina feebly developed. Angle of fastigium obtuse. Y-shaped carina with common stem distinct. Antennae cylindrical, short. Spinal formula of hind leg 5-7-4, post-tibial spur cultrate, concave on inner surface without teeth along posterior margin. Male pygofer in profile wider ventrally than dorsally, laterodorsal angles roundly produced, caudal margin near base strongly produced posteriorly, in posterior view the pygofer with a single process on the midventral margin, lateroventral margins not well defined. Parameres widely divergent apically. Diaphragm of pygofer broad, dorsally produced and incised in middle. Suspensorium ring-like ventrally. Aedeagus tubular, not twisted at base, subapex bearing teeth on both sides. Anal segment deeply sunk into the dorsal emargination of pygofer, caudoventral angles each produced in a spinose process.

After being established by Motschulsky (1863), the genus Mestus was subsequently studied by Melichar (1903) and Distant (1906). However, the placement of this genus was unclear and was not treated in Muir’s phylogeny of the family Delphacidae because Muir did not agree with the original description of the type species (Muir 1915). Thereafter, Muir (1917) thought Melichar had confused Anectopia mandane Kirkaldy with Mestus morio Motschulsky, just as Fennah (1973–75: 85) stated: “he [Melichar] was wrong in interpreting Anectopia mandane Kirkaldy as M. morio. Motschulsky describes M. morio as having a strong median frontal carina, and his figure shows that the tegmina are not ornamented. Anectopia mandane, by contrast, has no median carina on the frons…”. The diagnosis of the type species, especially the male genital characters, became more identifiable after the work of Fennah (1973–75), Meanwhile, Fennah reconfirmed and treated M. testaceus Motschulsky and Anectopia atrata Muir as junior synonyms of M. morio Motschulsky, respectively. This study agrees with Fennah, who suggested Anectopia atrata Muir was a junior synonym of M. morio Motschulsky because the illustrations of Anectopia atrata (see Muir 1917, Figs 22, 22a, 22b) meet the definition of the genus Mestus.

The genus Anectopia Kirkaldy was established by Kirkaldy (1907). Muir (1915) checked its type species and placed this genus in the Delphacini of Delphacinae with two species (A. mandane Kirkaldy, 1907 and A. igerna Kirkaldy, 1907) known so far. Although Anectopia lacks a redescription after its establishment, the genus Mestus studied here differs from Anectopia in the post-tibial spur not having fine teeth along the posterior margin based on the works of Kirkaldy (1907), Muir (1915) and Fennah (1973–1975).

Mestus was once placed in Araeopini of the Araeopinae by Metcalf (1943); later it was assigned to the Tropidocephalini of the Delphacinae (Fennah 1973–75). This genus is currently recognized as a member of the Delphacini within Delphacinae (Asche 1985; Yang 1989; Ding 2006). From the keys of Yang (1989) and Ding (2006), the diagnosis of this Oriental genus is rather distinct and easily distinguished from other genera in the Delphacini by the post-tibial spur cultrate, solid, without teeth along posterior margin. Particularly in the key of Yang (1989), this genus is similar to two tropidocephaline genera: Malaxa Muir and Tropidocephala Stål. However, the post-tibial spur alone is not a sufficient indicator for tribal placement and for separating Mestus from other related genera, and there are many Delphacini that lack teeth along posterior margin (e.g., all of the former Alohini), features of the male genitalia are a better indication which should be considered for these genera. Mestus bears no obvious similarities with Malaxa or Tropidocephala. Furthermore, the composition and phylogeny of the Tropidocephalini needs to be reinvestigated.

Yang (1989) described M. tungpuensis based on “coleopterous” adults in Taiwan. According to the work of Bourgoin et al. (2015), the term coleopterous is useless to describe the tegmen precisely and has little morphological value. Therefore, the members of the genus Mestus have two wing forms, brachypterous and macropterous. The macropterous form of Mestus was described by Muir (1917) from the Philippines (Anectopia atrata, a synonym of M. morio as noted above). In the Chinese fauna, only the brachypterous form has been found so far. The wing polymorphism and biogeography of this genus need to be studied further.

China (Taiwan, Yunnan), Sri Lanka, Philippines.

Brachypterous: Total length (from apex of vertex to the tip of abdomen): male (n=16) 2.40–2.75 mm, female (n=15) 2.65–2.88 mm; tegmina length: male (n=16) 1.85–1.90 mm, female (n=15) 1.88–1.98 mm.

Color. General color of male dark brown (Figs 1, 2). Vertex, frons and genae blackish brown (Figs 1, 5, 6). Eyes grayish black (Figs 1, 2, 5, 6). Antennae pale brown (Figs 1, 2, 5, 6). Pronotum, mesonotum, tegmina and abdomen dark brown (Figs 1, 2, 5); in some specimens the posterior margin of pronotum and scutellum brown. Postclypeus blackish-brown except apex and median carina yellow (Fig. 6). Longitudinal veins of forewing speckled with black brown granules (Figs 1, 2, 19). Legs yellowish brown except fore- and middle coxae brown, apices of spines on tibiae and tarsi of hind legs black (Figs 4, 7). General color of female beige (Fig. 3). Tegmina semitransparent (Fig. 3). Ovipositor brown to blackish brown.

Structure. Vertex at about 1.32 times as broad as long in midline, slightly narrower at apex than at base (about 0.97: 1), anterior margin rounded, slightly projecting in front of eyes, lateral margins concave in dorsal view, submedian carinae originating from near 1/3 base of lateral carinae and feeble at apex (Figs 1, 5). Y-shaped carina with lateral arms faint, basal compartment shallowly concave, wider at base than greatest length (about 1.95:1) (Fig. 5). Fastigium rounded (Fig. 2). Frons longer in midline than maximum width about 1.61:1, widest at level of ocelli, lateral carinae slightly convex medially, median carina feeble at base (Fig. 6). Postclypeus wider at base than frons at apex (about 1.16:1), post- and anteclypeus together approximately 0.89× the length of frons (Fig. 6). Rostrum almost reaching meso-trochanters. Antennae terete, apex reaching to near the middle of postclypeus, scape longer than wide at apex (about 1.51:1), pedicle nearly twice the length of scape (Fig. 6).

Pronotum in midline slightly shorter than length of vertex (about 0.85:1), lateral carinae slightly curved, not reaching posterior margin of pronotum (Figs 1, 5), Mesonotum medially ca. 1.14 times longer than vertex and pronotum together, lateral carina almost straight, reaching posterior margin, median carina obscure before apex of scutellum (Figs 1, 5). Tegmina almost reaching or slightly surpassing apex of abdomen, longer than widest part about 2.48:1, widest near middle (Figs 1–3, 19). Spination of apex of hind leg 5 (3+2) (tibia), 7(5+2) (basitarsus) and 4 (2nd tarsomere) (Figs 4, 7). Hind tibiae 0.93–1.07 mm long, bearing 2 lateral teeth, post-tibial spur (0.33–0.38 mm) about 0.76× length of metabasitarsus, without identifiable teeth along posterior margin (Figs 4, 7).

Male genitalia. Pygofer in profile wider ventrally than dorsally, dorsolateral angle roundly produced, caudoventral margin near base with a well-developed, subquadrangular process, reaching the same level as medioventral process in profile (Fig. 9); in posterior view pygofer subquadrate, lateroventral margins excavated, medioventral process simple, spine-like in ventral view (Figs 8, 10, 11). Suspensorium ventrally ring-like, dorsally broad (Fig. 16). Dorsal margin of diaphragm produced, incised and membranous medially, in profile surpassing end of pygofer (Figs 9, 10). Parameres reaching the level of anal segment, sinuate, convergent at bases and then divergent distally, apices narrowed and strongly curved laterad, in posterior view each has a small tooth medially along inner margin (Figs 8, 9, 12, 17). Aedeagus moderate, in profile broadened dorsally in basal 1/3, ventral margin almost straight medially, at apex has a membranous tag on ventral side; in dorsocaudal view the aedeagus armed with approximately ten teeth circling the apical orifice, another bigger tooth, if present, shifted basally on the dorsal side (Figs 12–15). Male anal segment collar-shaped, laterocaudal margin with a long spinous process, overlapped near bases (Figs 8, 9, 12, 18).

Holotype. ♂ (brachypterous, NWAFU), China, Yunnan Province, Weixi County, 13-VIII-2010, coll. Meng Zhang. Paratypes. 15♂♂, 15♀♀ (brachypterous, NWAFU), same data as holotype.

This specific name alludes to the two overlapped processes near bases of the anal segment.

Unknown.

Mestus cruciatus sp. n. differs from M. tungpuensis Yang in having the caudoventral protrusion of pygofer near base well developed, extending to the same level as apex of medioventral process in profile; the aedeagus broadened dorsally in basal 1/3, ventral margin in profile almost straight medially. It differs from M. morio Motschulsky in having the medioventral process of pygofer simple, not widening in basal third; the inner margin of parameres each with tooth medially in posterior view. Furthermore, the new species differs from both species in having the lateroventral processes of male anal segment overlapped near bases.

Yunnan Province (in southwest China).