Mestus Motschulsky, 1863

Ren, Feng-juan, Xie, Qi & Qin, Dao-zheng, 2015, Mestuscruciatus, a new delphacid species from southwest China with some remarks on the genus (Hemiptera, Fulgoromorpha, Delphacidae), ZooKeys 545, pp. 67-74 : 68-69

Taxon classification Animalia Hemiptera Delphacidae

Genus Mestus Motschulsky, 1863

Mestus Motschulsky, 1863: 111; Distant 1906: 489; Fennah 1973-75: 85; Yang 1989: 161; Ding 2006: 396.

Type species:

Mestus morio Motschulsky, 1863 by original designation.

Diagnosis.

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.

Description.

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.

Remarks.

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 Del phacidae 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 Mestus morio . Motschulsky describes Mestus 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 Mestus testaceus Motschulsky and Anectopia atrata Muir as junior synonyms of Mestus morio Motschulsky, respectively. This study agrees with Fennah, who suggested Anectopia atrata Muir was a junior synonym of Mestus 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 ( Anectopia mandane Kirkaldy, 1907 and Anectopia 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 Mestus 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 Mestus 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.

Distribution.

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