Taxonomic revision of the East Asian genus Scleropteroides Colonnelli, 1979 (Coleoptera, Curculionidae, Ceutorhynchinae)

Abstract The genus Scleropteroides Colonnelli, 1979 (Ceutorhynchinae: Scleropterini) was revised on the basis of detailed morphological observations. The genus was redefined to include three species from East Asia: S. hypocrita (Hustache, 1916) is redescribed and recorded from northeastern China and northern Korea for the first time; S. horridulus (Voss, 1958) is redescribed with new records from southern Korea; S. insularis Voss, 1971 was moved from synonymy with S. hypocrita to that with S. horridulus (syn. n.), and S. longiprocessus Huang & Yoshitake, sp. n. is described as new, sympatric with S. hypocrita in Japan. All the species are associated with woody Rubus species (Rosaceae). A key to species, habitus photographs, illustrations of important characters, and distribution maps are provided for each species.

External structures were observed under a Leica MZ95 stereoscopic microscope. Measurements of body parts are defined and abbreviated as follows: LB = body length, from the apex of the pronotum to the apices of elytra; LR = rostrum length, from a lateral view; WP = maximum width of pronotum; LP = pronotum length, from the base to the apex along the midline; WE = maximum width of elytra; and LE = length of elytra, from the base of humeri to the apex of elytra. All measurements are in millimeters. Habitus photographs were taken using a Nikon Coolpix995 digital camera attached to a Nikon SMZ1500 stereoscopic microscope. To examine terminalia, the specimens were macerated in hot water and dissected under a stereoscopic microscope. The abdomen was removed from the body and then cleaned in hot 10% KOH solution for 5-10 min. Terminalia were extracted from the abdomen and mounted on slides with glycerol (male) or pure water (female), examined using a Nikon Eclipse 55i optical microscope, and illustrated in detail using a camera lucida. Scale bars were calibrated using a Nikon objective micrometer. Details of some external structures were observed with a scanning electron microscope (Hitachi 3000-N). Plant nomenclature follows Yonekura and Kajita (2003). Distribution maps  are based on records of S. hypocrita from Korea (Hong et al. 1999, 2000, Korotyaev and Hong 2004) and all the specimens examined in this study. Verbatim label data indicated by quotation marks are provided for the holotypes. Label breaks are indicated by a slash ("/").
Elytra  subcordate, nearly as long as wide, widest just behind humeri; suture evidently bent leftward; interval I of right elytron slightly broader than that of left elytron; all intervals subequal in width and height, nearly three times as wide as striae, each with row of more or less small and acute squamate granules; striae less marked, nearly naked, lacking conspicuous scales or hair, finely punctured; each puncture round, separated by distance more than three times as long as its diameter. Hind wings (Fig. 19) well-developed.
Underside. Prosternum coarsely and moderately densely punctured; mesoventrite densely and finely punctured; metaventrite with dense medium-sized punctures on disc and with sparser and coarser punctures on sides; lateral pieces of meso-and metasterna sparsely coarsely punctured. Rostral channel (Fig. 13) long, extending far beyond level between posterior margins of mesocoxal cavities, with dense minute punctures; mesoventral receptacle deep, laterally costate; costae short, subparallel; metaventral receptacle very deep, terminating in steep wall and Ushaped margin; lateral walls of meso-and metaventral receptacles interrupted by inner margins of mesocoxae; metaventrite more or less prominent ventrally along apico-lateral margin of metaventral receptacle. Metendosternite as in Fig. 14. Venter coarsely and more or less densely punctured; ventrites III and IV nearly polished on disc, with only transverse row of coarse and sparse punctures; ventrite V with subtriangular median concavity along basal margin; concavity faintly sulcate along midline. Tergum as in Figs 20-21; tergite VII with pair of minute setiferous plectral tubercles near base.
Pygidium transverse-pentagonal, flattened, very coarsely and reticulately punctured; bottom of each puncture opaque due to dense minute punctations; upper flange arcuate downward on each side.
Female. Rostrum (Figs 24-25) slightly more slender. Antennae inserted just behind middle of the rostrum. Tibiae simple, not mucronate on all legs. Ventrites I and II moderately inflated, sparsely punctured, lacking prominence. Ventrite V simple or only with longitudinal median sulcus, lacking concavity. Pygidium smaller, sectorial, mainly covered with hair-like scales. Otherwise as in male.
Biological note. Adults of this common species were collected from Rubus idaeus L. subsp. melanolasius Focke f. concolor (Kom.) Ohwi in Korea (Korotyaev and Hong 2004). In addition, we collected a number of adults at several localities in the southern Korean Peninsula, mainly from R. crataegifolius Bunge with flower buds and Rubus pungens Camb. var. oldhamii (Miq.) Maxim. with flowers. In Japan, adults have been collected on many occasions from Rubus species, such as R. crataegifolius, R. microphyllus, and R. trifidus. In Toyosawa-rindou, Iwate, Honshu (Fig. 135), a number of adults (Fig. 138) were found on R. crataegifolius (Fig. 136) and observed feeding on the leaves and flowers of the plant (Fig. 137).
Biological note. In several localities in Honshu, a number of adults of this species were found on Rubus palmatus Thunb. var. coptophyllus (A.Gray) Kuntze ex Koidz. In addition, adults of this species were collected mostly from Rubus palmatus Thunb. and rarely from R. crataegifolius Bunge on Mt. Kusenbuyama, Kyushu. Diagnosis. This species differs from S. hypocrita on the basis of the following characters: subapical part of the prothorax strongly constricted (Fig. 38); elytra with strongly prominent humeri, straightly convergent toward the subapical calli (Fig. 39); scales in a row on the elytral intervals erect, much longer than the width of each interval (Fig. 39); male metaventrite more strongly prominent ventrally along the apico-lateral margin of the metaventral receptacle; male ventrite I with no prominence; apical projection of the penis truncate at the apex (Figs 91,101,111,114,117,120,and 123); basal part of the endophallus with a pair of weakly falcate sclerites (Figs 90, 100); female sternite VIII with apically divergent arms (Figs 97, 107); bursa copulatrix usually without minute coniform spicules (Figs 95, 105 Vestiture. Clavate scales long and erect on head, basal 2/3 of rostrum, and pronotum. Hair-like scales long and semierect on apical 1/3 of rostrum. Scales on elytral intervals (Fig. 39) erect, long, 1.3-1.5 × as long as interval width. Clavate scales on tibiae erect.
Biological note. A number of adults were collected from Rubus croceacanthus H.Lév. growing along the edge of an evergreen broad-leaved forest at the foot of Mt. Yuwandake, Amami-Oshima Island.
Comment. In the study, we could not examine the holotype of Rhytidosomus insularis Voss, which should be preserved in ELKU, but K. Morimoto (pers. comm., 2005) had examined it and confirmed its taxonomic identity. Also, our examination of a long series of Scleropteroides specimens from the type locality, Amami-Oshima Island, revealed that only one species of this genus occurs on the island.

Systematic position and definition of the genus
Scleropteroides was established as a genus allied to Scleropterus in the tribe Scleropterini (Colonnelli 1979). This placement was followed by subsequent authors (Alonso-Zarazaga and Lyal 1999, Hong et al.1999, Yoshitake et al. 2004, Colonnelli 2004, Korotyaev and Hong 2004, except by Morimoto (1989) who placed it in the tribe Ceutorhynchini. This is not unexpected as Scleropterini has never been clearly defined (Schultze 1902, Reitter 1913, Wagner 1937) and the morphological distinction between Scleropterini and Ceutorhynchini is still unclear because of inconsistencies in character states defining the two tribes (Colonnelli 1984(Colonnelli , 2004. In addition, a recent molecular phylogenetic study (Kato et al. 2006) did not support the monophyly of either Ceutorhynchini or Scleropterini, although it supported a close relationship between Scleropteroides and Scleropterus. Here we follow the recent tribal classification by Colonnelli (2004) for convenience, although we acknowledge it is in need of revision.
Morphologically, Scleropteroides is close to Scleropterus in sharing a rounded apex of the antennal scape, a six-segmented antennal funicle, a pronotum with neither tubercules nor prominences, elytral intervals bearing small and acute squamate granules usually in a row, a rostral channel extending to the metaventrite, and appendiculate claws. In addition, the close affinity between the two genera is emphasized by similarities in structures of the male and female genitalia.
The most apparent differences between the two genera are the structure of the hind wings (character 7) and associated characters (3, 6, and 8). Apart from these differences associated with hind-wing reduction in Scleropterus, however, Scleropteroides clearly differs from Scleropterus in having a pronotum lacking a sulcus, even elytral intervals, dentate femora, and simple protibiae. Additionally, Scleropteroides can also be distinguished from Scleropterus by the meso-and metatibiae lacking mucrones in females.

Relationships among species
Our extensive and detailed examination of a large number of specimens revealed that Scleropteroides comprises three East Asian species -S. hypocrita, S. horridulus, and S. longiprocessus. They are very similar in general appearance, as well as in general structures of male and female terminalia, but can be distinguished clearly by several consistent, taxonomically important morphological differences as shown in the following lines.
Scleropteroides hypocrita is characterized mainly by a moderately constricted prothorax in the subapical part (Fig. 34), gently convergent elytra toward the subapical calli (Fig. 35), moderately prominent humeri (Fig. 35), and elytral intervals with a row of semirecumbent scales that are evidently shorter than the interval width (Fig. 35). In addition, the species is also distinguished by sexual structures in males, such as a slightly widened rostrum in the apical half (Fig. 22), metaventrite that is weakly prominent along the apico-lateral margin of the metaventral receptacle, ventrite I bearing a median prominence along the apical margin, the penis with a blunt apical projection that is rounded at the apex (Figs 41,51,61), and a pair of plate-like sclerites on the basal part of the endophallus (Figs 40,50,60). In females, the arms of sternite VIII are apically arcuate (Figs 47,57,67) and the posterior part of the bursa copulatrix is densely covered with minute coniform spicules (Figs 45,55,65). The length of scales in a row on the elytral intervals is variable, from 0.4 to 0.8 times as long as the interval width, mostly ranging from 0.5 to 0.6 times as long. We examined specimens from various localities in detail, but no significant geographical variation was observed in the external or genital structures of either sex. Colonnelli (2004) synonymized S. insularis with S. hypocrita in his world catalog of the subfamily Ceutorhynchinae; however, he gave no explanation for this taxonomic treatment. Our study revealed that S. insularis is actually identical with S. horridulus. Scleropteroides horridulus shows remarkable morphological differences from S. hypocrita in the strongly constricted subapical part of the prothorax (Fig. 38), straightly convergent elytra toward the subapical calli (Fig. 39), strongly prominent humeri (Fig. 39), erect scales on elytral intervals that are much longer than the interval width ( Fig. 39), and ventrite I lacking a median prominence. In addition, S. horridulus clearly differs from S. hypocrita in having the following male sexual traits: metaventrite more strongly prominent ventrally along the apico-lateral margin of the metaventral receptacle, apical projection of the penis truncate at the apex (Figs 91,101,111,114,117,120,123), and paired sclerites in the basal part of the endophallus weakly falcate (Figs  95, 105). Furthermore, S. horridulus has apically divergent arms on sternite VIII in females (Figs 97, 107). We consider S. horridulus a valid species despite of Colonnelli's (2004) synonymy of S. insularis with S. hypocrita. This species shows geographical variation in female genital structure. In specimens from continental China and Korea, the bursa copulatrix is densely armed with minute spicules in the posterior part (Fig. 105), whereas it is unarmed in specimens from Taiwan and the Nansei Islands (Fig. 95). This may suggest the presence of a cryptic species because structures of the bursa copulatrix are usually conservative and not variable within a species.
Scleropteroides longiprocessus shows character states intermediate between S. hypocrita and S. horridulus in having a strong constriction in the subapical part of the prothorax (Fig. 36), strongly prominent humeral calli (Fig. 37), and elytral intervals with semierect scales, each of which is nearly as long as the interval width (Fig. 37). This species was previously confused with S. hypocrita due to their close resemblance in general appearance and the lack of a detailed morphological examination. However, S. longiprocessus differs from S. hypocrita by having a stouter rostrum (Fig. 26), more rapidly convergent elytra toward the subapical calli (Fig. 37), and ventrite I lacking a median prominence. Moreover, S. longiprocessus is distinguished by male sexual traits, such as a metaventrite that is more prominent ventrally along the apico-lateral margin of the metaventral receptacle, an elongate projection at the apex of the penis (Figs 71, 81), and the paired falcate sclerites in the basal part of the endophallus (Figs 70, 80). With regard to female sexual traits in S. longiprocessus, the arms of sternite VIII are apically divergent (Figs 77,87) and the bursa copulatrix lacks spicules (Figs 75,85). This species shows non-geographical intraspecific variation in the length of scales on the elytral intervals. Most specimens examined had scales slightly longer than the interval width, but some specimens bore stouter scales that were slightly shorter than the interval width.
Additionally, S. longiprocessus resembles S. horridulus in having straightly convergent elytra toward the subapical calli (Figs 37, 39), a metaventrite that is moderately prominent ventrally along the apico-lateral margin of the metaventral receptacle in males, ventrite I lacking a median prominence in both sexes, and the apically divergent arms of female sternite VIII (Figs 77, 87, 97, 107). However, S. longiprocessus is easily distinguished from S. horridulus by the more strongly widened rostrum in males (Fig. 26), the pronotum with subparallel sides in the basal half and a weaker subapical constriction, less-developed elytral humeri, less erect and shorter scales on the elytral intervals (Fig. 37), a penis with a slender apical projection that is rounded at the apex (Figs 71, 81), narrower sclerites in the basal part of the endophallus (Figs 70, 80), and an unarmed bursa copulatrix (Figs 75, 85).
The affinity of the three Scleropteroides species is still uncertain and a phylogenetic analysis of the genus is necessary to clarify their relationships.

Host plant associations
Rubus is a cosmopolitan genus and contains an estimated 900-1000 species worldwide (Thompson 1997). Rubus are shrubs or subshrubs, deciduous, rarely evergreen or semievergreen, and sometimes perennial creeping dwarf herbs (Lu and Boufford 2003). To date, 249 Rubus species have been recorded from China (including Taiwan), Korea, and Japan (Lu and Boufford 2003, KPNI 2008, Yonekura and Kajita 2003. In East Asia, Rubus species constitute the understory of open woodlands, especially in and around clearings and margins. They also occur in more open, sunny locations along forest roads and along rivers. Presently, ecological information on Scleropteroides weevils is limited and their host plant associations are not clear (Table 2). However, the available data indicate that Scleropteroides weevils are associated with woody Rubus species belonging to the subgenus Idaeobatus and growing in and around woodlands at least in the adult stage because adults were collected from Rubus shrubs and observed feeding on leaves and flowers of the plants on many occasions. With regard to adult feeding habits, S. hypocrita widely utilizes at least four Rubus species (R. crataegifolius, R. idaeus subsp. melanolasius f. concolor, R. microphyllus, and R. trifidus) in Korea and Japan, whereas S. longiprocessus was observed feeding on R. palmatus in Honshu and Kyushu, and S. horridulus on R. croceacanthus in the Ryukyus. In two localities in Toyota City, Honshu, Japan, adults of S. hypocrita and S. longiprocessus were found separately on R. microphyllus and R. palmatus var. coptophyllus, respectively (K. Izawa, pers. comm., 2014). Similarly, on Mt. Kusenbuyama, Kyushu, Japan, adults of S. hypocrita and S. longiprocessus were collected separately on R. crataegifolius and R. palmatus, respectively, except a few individuals of S. longiprocessus collected simultaneously with S. hypocrita on R. crataegifolius. These observations suggest that Scleropteroides species might show some differences in host use in localities where they occur sympatrically. As mentioned above, S. hypocrita is sympatric with S. longiprocessus in Japan and with S. horridulus in South Korea (Table 1). Further studies are needed to explore the host plant range of each Scleropteroides species, especially in sympatric localities.
Generally, each species in the subfamily Ceutorhynchinae utilizes the same host plant in the adult and larval stages (e.g., Hoffmann 1954, Jordheuil 1963, Dieckmann 1972. Therefore, Scleropteroides weevils would be suspected to be associated with Rubus species in their larval stage. Scleropteroides adults appear before and during the flowering season of Rubus and were frequently found on reproductive organs of the plants. Further surveys focusing on larval food sources are necessary to elucidate the host plant associations of Scleropteroides weevils.

Distribution and biogeography
The distribution of Scleropteroides is limited to East Asia (Figs 133-134), in contrast to Scleropterus, which is widely distributed from Central Europe through Central Asia to East Asia (Colonnelli 2004). Scleropteroides hypocrita is distributed in northeast China, North and South Korea, and Japan (Fig. 133), whereas S. longiprocessus is restricted to Japan (Fig. 134). The two species occur sympatrically in many localities in Japan (Table 1). Further, S. horridulus is distributed from Fujian through Taiwan to the Nansei Islands and in South Korea (Figs 133-134). This species is sympatric with S. hypocrita at least in the Korean Peninsula (Table 1), but the distributional boundary of the two species is still unclear in continental China.
Currently, a considerable gap still remains in the distribution of Scleropteroides, especially in continental China and the Korean Peninsula. In addition, this genus has never been recorded from the southern part of the Russian Far East. Since the distribution of Scleropteroides strongly suggests its occurrence in these regions, further surveys are necessary to elucidate the range of the genus and that of each species.