Eurystylus Stål

Yasunaga, Tomohide, Nakatani, Yukinobu & Chérot, Frédéric, 2017, Review of the mirine plant bug genus Eurystylus Stål from Japan and Taiwan (Hemiptera: Heteroptera: Miridae: Mirinae), with descriptions of two new species, a new synonymy and a new combination, Zootaxa 4227 (3), pp. 301-324 : 305-306

Genus Eurystylus Stål

Eurystylus Stål, 1871: 671 (n. gen.), type species: Eurystylus costalis Stål, 1871: 671 ( Fig. 2 F; habitus images of the holotype available on http://www2.nrm.se/en/het_nrm/c/ eurystylus _ costalis .html), monotypic; Schuh, 1995: 766 (cat.); Kerzhner & Josifov, 1999: 99 (cat.); Yasunaga, 2001: 233 (diag.); Zheng et al., 2004: 271 (diag., key to Chinese spp.); Schuh (2002– 2014) online catalog.

Diagnosis. Eurystylus is distinguished from other genera of the tribe Mirini by the following characters (whereas some of these characters are shared with the assumed related taxa, Eocalocoris Miyamoto & Yasunaga [EC], Eurystylopsis Poppius [EP], Heteropantilius Zheng & Liu [HP] or Miyamotoa Yasunaga [MY]): Body remarkably thick, box like [HP, EC, EP], generally matte or shagreened [EP]; dorsum impunctate [HP, EC, MY], with at least two types of vestiture [EP]; head weakly porrect and relatively horizontal or prognathous [HP, EC, EP, MY]; lateral margin of frons, bordering to antennal tubercle and inner margin of eye, with a fuscous, velvety mark that is usually visible even in species with darkened head ( Figs. 1 H, 2E, F); antenna, shorter than body, with segment I tumid, obviously flattened, segment II clavate (its apical part more than twice as thick as base), and segments III and IV short and filiform [HP, EC, EP, MY]; pronotum often with a pair of dark spots on disk, sometimes forming eyeshape, so-called ‘head bugs’ (as in Figs. 2 A, E; 3E); collar thickened, broader than base of antennal segment II; scutellum tumid, long, with its lateral margin length greater than basal width; each femur more or less flattened [EP]; metatibia not much longer than metafemur; male genital segment (pygophore) noticeably shortened; abdominal sterna VIII and IX in female narrow; left paramere usually strongly constricted at base of widened and flattened (often flap-like) hypophysis ( Fig. 4 ); endosoma with well-developed membranous lobes [EC, MY], with one to four lobal sclerites ( Fig. 5 , FL, ML, PL, TL); seminal duct strongly constricted distally ( Fig. 5 C); secondary gonopore thick-rimmed, with triangular or heart-shaped aperture [EC, HP, MY]; and female bursa copulatrix with a confluent ventral labiate plate [EC, EP]. The final-instar nymph is unique in having the generally pale, ovoid, thick body with several pairs of eye-like, or ocellate spots on dorsum ( Fig. 2 B–D).

Distribution. Known from the Old World, mainly subtropical and tropical zones; most species occurring in the Ethiopian and Oriental regions; only a few members known from the Australian Region and Pacific Islands.

Biology. As evidenced by many Eurystylus species that are collected on inflorescences, floral nectar and pollen are considered to be their major diets ( Yasunaga, 2001). Most congeners are presumed to be herbivorous and polyphagous. The immature forms of more than seven species (including some undetermined or undescribed ones from tropical Asia) were confirmed to inhabit inflorescences of various dicots (see Table 1). The adults of the species shown in Table 1 (except for E. jingfui ) were observed to suck on flower buds, petals and/or pedicels (cf. Fig. 1 G).

In the Afrotropical Region, Eurystylus oldi Poppius is frequently documented as a major pest of sorghums, Sorghum bicolor (L.) Moench ( Poaceae ) in particular, and some Eurystylus species in South Africa were documented to feed on both male and female flowers of a castor, Ricinus communis L. ( Euphorbiaceae ), causing them to shrivel and die; in some cases, entire stems die (Wheeler, 2001). In Asia, no Eurystylus member has ever been reported as an agricultural pest, even though some species actually inhabit inflorescences of economic fruit trees, and ornamental or medicinal plants (e.g., chestnuts, oranges, mangos, aralias, lilacs; Table 1). The population densities of Asian species are usually not significant, and any harmful gregarious feeding is currently not recognized.

One generation per year is assumed for Eurystylus species inhabiting temperate and colder climate zones, whereas those in tropics, subtropics or warm temperate zone appear to have a bivoltine or multivoltine life cycle.

Discussion. Eurystylus is easily separable from related genera by the flattened antennal segment I, a pair of fuscous, velvety spots at lateral corner on the frons, thicker collar, elongate scutellum, and shortened genital segments (male pygophore and female segments VIII and IX). These characters will distinguish Eurystylus from taxa possessing similar facies (e.g., tumid box-like body, clavate antennal segment II), such as Eurystylopsis known from Nepal, Taiwan and continental China, Eocalocoris from southwestern Japan, Heteropantilius from China and Taiwan, and Miyamotoa originally described from the Amami Island-Group of the Ryukyus . However, these genera equally have more smooth dorsum, cylindrical antennal segment I, nearly equilateral scutellum, and conventional mirine paramere shape, in addition to their own unique characters or autapomorphy (for further information, see Yasunaga, 1990, 1995; Yasunaga & Takai, 1994; Zheng et al., 2004). The below key equivocally distinguishes the five related genera.

Within the four genera mentioned in above generic diagnosis, Eurystylopsis is assumed to be most closely related to Eurystylus , because these two genera share seven diagnostic characters, as well as the largely matte dorsal surface, and similar coloration, vestiture pattern ( Fig. 9 A–B), and shape of the metathoracic scent efferent system ( Fig. 8 G–H). The phylogenetic relationship of Eurystylus to other mirine genera will need to be further elucidated. However the shared characters of above-mentioned genera imply that at least the four genera may be originated from a same lineage; Miyamotoa is separated from the other genera in having the reduced M-vein that represents unusual character state in the tribe Mirini .

On the other hand, a few more superficially similar taxa appear to exist in the Old World. For instance in the Australian Region, the poorly known Pseudeurystylus clavicornis Poppius, 1915 ( Fig. 9 F), the sole representative of the monotypic genus Pseudeurystylus Poppius, 1915 , also shares similar color and vestiture patterns, clavate second antennal segment, tumid body and pronotum, and thick pronotal collar. However, Pseudeurystylus can be distinguished easily from all above mentioned taxa by the four ivory-white, callose stripes on the pronotal lateral margin and propleuron, the pronotal collar thicker than the base of antennal segment II at middle but not laterally (the collar has the almost similar thickness throughout in Eurystylus ) and the pronotal callosities developed and nearly contiguous to the collar. In the Ethiopian Region where more than twelve Eurystylus species occur, Stonedahl (1995) considered the possible relationship between Eurystylus and Volumnus Stål, 1866 (including Yambio Linnavuori, 1975), mainly based on dorsal pilosity, thick and relatively short antennal segments III and IV and the presence of “a small, plate-like process on the base of maxillary plates, ventral to antennal fossae” ( Stonedahl, 1995). However, as pointed out by Stonedahl for the vestiture (op. cit.), these character states are not considered unique, being observed in other mirine genera; the genital structures of Volumnus are also different from those of Eurystylus . A relationship between Eurystylus and Volumnus appears only superficial. To demonstrate a satisfactory phylogenetic position and sister taxa of Eurystylus , comprehensive work treating all the Old World members is required.

In Japan and Taiwan, three species, Eurystylus coelestialium , E. luteus , and E. sauteri , have been reported. However, our attempts to identify the specimens from these areas revealed that the Japanese and Taiwanese populations which have been assigned to E. luteus should belong to E. sauteri , and all previous records of E. sauteri from SW Japan and Taiwan were incorrect (see below Discussion for E. ryukyus and E. sauteri ). Judging from the overall similarities (as in Figs. 3 A–G, 4B–I) and distribution patterns ( Fig. 7 ), it is highly probable that luteus (described by Hsiao from Anhui, China in 1941) and sauteri (by Poppius from Taiwan in 1915) are conspecific. The holotype of luteus is unfortunately female, but the male endosomal illustrations based on Chinese materials ( Zheng & Chen, 1991; Zheng et al., 2004) doubtlessly coincide with those found in Japan and Taiwan ( Fig. 4 D–I). We therefore refrain from using luteus for relevant Japanese and Taiwanese specimens, to avoid further taxonomic confusion.

Figures

FIGURE 1. Habitus images of Eurystylus species. A. Male adult from Chitwan, Nepal, identical to E. jingfui n. sp. B – C. E. ryukyus n. sp., female on Fraxinus griffithii. D. E. sauteri, female on Solidago canadensis, with Taylorilygus apicalis (Fieber) (upper) and Nysius plebeius Distant (middle). E – G. Ditto, male (E, G) and female (F) on Ligustorum japonicum. H, Ditto, head (velvety spots arrowed).

FIGURE 2. Habitus images of adult females and final-instar nymph (B – D) of Eurystylus species. A – B. E. coelestialium (image courtesy of M. Takai). C. E. sauteri Poppius. D. E. ryukyus n. sp. E. E. burmanicus from Chitwan, Nepal. F. E. costalis from Kathmandu Valley, Nepal.

FIGURE 3. Habitus images of dry-preserved specimens for E. sauteri (A – D), E. ryukyus n. sp. (E – G) and E. jingfui n. sp. (H – K).

FIGURE 4. Pygophore (A), left paramere (B, D, F, H, J) and right paramere (C, E, G, I, K) of Eurystylus species. A – C. E. ryukyus n. sp. D – I. E. sauteri. J – K. E. jingfui n. sp.

FIGURE 5. Endosoma and adjacent structures of Eurystylus species. A – C. E. ryukyus n. sp. D – G. E. sauteri Poppius. H. E. jingfui n. sp. I – J. E. coelestialium. Scale bars 0.2 mm.

FIGURE 7. Map showing the distributions of three closely related Eurystylus species; records (provincial levels) in continental China based upon Zheng et al. (2004).

FIGURE 8. Habitus images of dry-preserved specimens. A. Eurystylus coelestialium, lectotype male (upper) and paralectotype female mounted together (in 1998, MZHF). B. Male det. as E. luteus by Josifov from Pyongyang, North Korea (MZHF). C. E. sauteri, holotype female. D. Eurystylomorpha crassicornis, holotype male (Taiwan). E – F. Ditto, females in dorsal (E) and ventral (F) view. G. Ditto, scent efferent system. H. Eurystylopsis clavicornis, female from Kirtipur, Nepal (ventral view). I. Ditto, male. Scale bars 2 mm. Images (C & D) courtesy of J. F. Tsai and NMNS.

FIGURE 9. Habitus images of Eurystylopsis species (Nepal) & type specimens of E. harmandi (E) & Pseudeurystylus clavicornis (F). A. E. clavicornis in Kirtipur, Nepal (same individual of Fig. 8 G). B. E. clavicornis, female (= Fig. 8 H). C – D. Live individual probably corresponding to E. harmandi from Langtang Himal. E. E. harmandi, syntype female from India (Dardjiling) (MNHN). F. Pseudeurystylus clavicornis, holotype male from Australia (Sydney) (MZHF). Scale bars for (E & F) 1 mm.