Mestus cruciatus, a new delphacid species from southwest China with some remarks on the genus (Hemiptera, Fulgoromorpha, Delphacidae)

Abstract A new delphacid (Hemiptera, Fulgoromorpha, Delphacidae) species, Mestus cruciatus sp. n. is described based on specimens from Yunnan Province, China. Habitus photos and illustrations of male genitalia are provided. The Mestus species and phylogenetic arrangement of this genus is discussed. A key to the species of Mestus is also provided.


Introduction
The Oriental planthopper genus Mestus was established by Motschulsky (1863) with Mestus morio as the type species from Sri Lanka. It is a small genus in the Delphacini of Delphacinae with two species currently recognized, M. morio Motschulsky and M. tungpuensis Yang (Motschulsky 1863;Metcalf 1943;Fennah 1973-75;Yang 1989). It is distributed in Sri Lanka, the Philippines and south China (Taiwan). Recent identification of material in the collections of NWAFU has led to the discovery of a new species of this genus from Yunnan Province (southwest China) and it is described here.

Materials and methods
The specimens examined in this study including type material are deposited in the Entomological Museum, Northwest A&F University, Yangling, Shaanxi, China (NWA-FU). The genital segments of the examined specimens were macerated in 10% KOH and drawn from preparations in glycerin jelly with the aid of a light microscope. Line diagrams were drawn using an OLYMPUS PM-10AD microscope. Photographs were taken with an automontage QIMAGING Retiga 4000R digital camera (CCD) stereozoom microscope. The terminology in this paper follows that of Ding (2006). Measurements of the body length were from the apex of the vertex to the posterior tip of the abdomen. All measurements are in millimeters (mm).

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, posttibial 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 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 andA. 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 posttibial 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.
Etymology. This specific name alludes to the two overlapped processes near bases of the anal segment.
Host plant. Unknown. Discussion. 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.