Taxonomic study of Baeosega and its allies, with description of a new species of Nipponosega (Hymenoptera, Chrysididae, Amiseginae)

Abstract Three related genera of Asian Amiseginae, Baeosega Krombein, Nipponosega Kurzenko & Lelej, and Okinawasega Terayama are revised. The male of N. yamanei Kurzenko & Lelej and the female of O. eguchii Terayama are newly described. The following new synonymies are proposed: Baeosega humida Krombein, 1984 = B. laticeps Krombein, 1984, syn. nov.; Nipponosega yamanei Kurzenko & Lelej, 1994 = N. kantoensis Nagase, 1995, syn. nov. A new species of Nipponosega, N. lineatasp. nov. is described based on a female from Thailand. A key to genera and species of Baeosega, Nipponosega and Okinawasega is given.


Introduction
Amiseginae (Hymenoptera: Chrysididae) are egg parasitoids of stick insects (Phasmatodea) (Krombein 1983;Kimsey et al. 2013). They often show distinct sexual dimorphism: females are brachypterous; their wings are reduced to small pads reaching at most the anterior margin of the propodeum, whereas the males are macropterous.
Because brachypterous females are seldom collected in the field and their morphological characters are greatly different from males, it is difficult to make correct sex association and thus many species have been known by only one sex (Kimsey and Bohart 1991;Kimsey et al. 2016).
In the genus Nipponosega, three species are known from mainland China to Japan (Kurzenko and Lelej 1994;Nagase 1995;Xu et al. 2003). Although their males are unknown, the morphology of the female is closely related to Baeosega Krombein, 1983 and Serendibula Krombein, 1980. However, the female of Serendibula is clearly separated from Baeosega and Nipponosega by having a costate second metasomal tergite (Krombein 1983) and developed inner tooth of its claw. The monotypic genus Okinawasega was established on the basis of the male (Terayama 1999). The only known species, O. eguchii Terayama, endemic to southern Ryukyus, Japan, is apparently similar to the male of Baeosega. The genus has been insufficiently defined and thus it is difficult to distinguish it from Baeosega by the known diagnostic characters. Therefore, a comparative study of Baeosega and its allies is needed. Baeosega is known from three species from Sri Lanka (Krombein 1983) and Krombein (1983) mentioned the presence of a female of an undescribed species from Madras, southern India. In addition, Kimsey (1995) included southern Japan in its distribution, although species information was not provided. As for other related genera, the male of Baeosega is separated from Serendibula, the most similar taxon in Asia, by having longer setae on antennal flagellomeres, shorter metanotum (almost half as long as mesoscutum), and the absence of a developed inner tooth on the claw. For both genera, R1 on forewing is not indicated; however, unlike Baeosega, the distal apex of the pterostigma forms a sharp streak in Serendibula.
Although Baeosega is currently unknown outside of South Asia, the presence of Nipponosega and Okinawasega in East Asia suggests that other related taxa should be widely distributed. During the investigation of the Amiseginae fauna in Asia, several unknown females and males similar to Baeosega were found in Japan and Thailand. They provide helpful insights to understand taxonomic placement of the genera and species.

Materials and methods
Examined materials are deposited in the collections of the following institutes:
Morphological terminology follows that used by Krombein (1983) and Kimsey and Bohart (1991). The following abbreviations are used in the description:

F1-F11
flagellomere numbers; MOD anterior ocellus diameter; MS maximum length of malar space; OL distance between median ocellus and lateral ocellus; OOL distance between lateral ocellus and compound eye; OPL distance between lateral ocellus to posterior margin of vertex or occipital carina; POL distance between lateral ocelli; T1-T3 metasomal tergite numbers.
Antennal articles were measured at the point of greatest breadth and compared with the total length of the article. The length of the pronotum was measured on the midline.

Family Chrysididae Latreille, 1802 Subfamily Amiseginae Mocsáry, 1889
Key to the genera and species of Baeosega and its allies Based on the key to genera of Amiseginae provided by Kimsey and Bohart (1991 Diagnosis. The female of Baeosega is superficially similar to Nipponosega and Okinawasega. However, the occipital carina is developed and reaching lower gena in Nipponosega (absent in Baeosega) and the deep malar sulcus is present in Okinawasega (only faintly indicated in Baeosega). The male is very similar to Okinawasega. The longer setae on flagellum and remarkably long R1 of the forewing are useful characters distinguishing Okinawasega from Baeosega. Compared to the above two genera, the male of Nipponosega has the pronotum short. The pronotum of Baeosega and Okinawasega is as long as or longer than mesoscutum but it is shorter in Nipponosega. Compared to genera found in South Asia, Baeosega is most similar to Serendibula. In the female of Baeosega, the metasomal T2 is lacking fine longitudinal carinae whereas T2 of Serendibula is covered with fine carinae. The male of Baeosega can be distinguished from Serendibula by having longer setae on antennal flagellomeres, the shorter metanotum, almost half as long as mesoscutellum (metanotum is longer, almost as long as mesoscutellum in Serendibula) and the tubular distal apex of pterostigma (very sharp in Serendibula). The inner tooth of tarsal claw is minute and indistinct in both female and male of Baeosega, whereas the inner tooth is distinctively large in Serendibula. Description. Female. Clypeal apex not thickened; malar sulcus absent or indicated as faint track; scapal basin shallow, cross-ridged, median longitudinal carina absent; occipital carina absent, at most posterior margin of vertex forming corner behind ocellar triangle; eye setose; flagellum fusiform, intermediate segments broader than long, and with ventral surface flattened. Mesosoma slender, dorsum more or less punctate; pronotum with median groove and shallow pit before lateral lobe, 1.0-1.4 × as long as combined length of mesoscutum, mesoscutellum and metanotum; mesoscutum with notauli; parapsides lacking; posterolateral corner of mesoscutum not lobate; micropterous ( Fig. 1A, B), forewing pads extending to posterior margin of mesoscutellum; mesopleuron with omaulus, without scrobal sulcus; metanotum triangular and small, ca. 2/3 as long as mesoscutellum; propodeum with long dorsal surface and a pair of recumbent teeth present, meeting or almost meeting together, dorsal posterolateral angles bluntly angulate, lateral and posterior surfaces abruptly declivous. Hind coxa with dorsobasal carina; tarsal claws with a minute inner tooth. Metasoma smooth, shagreened or weakly granulated, without longitudinally striate area.

Hosts. Unknown.
Remarks. According to Krombein (1983), the female of Baeosega has no malar groove. However, a trace of a groove is present from the lower margin of the eye to the mandibular base. A minute inner tooth is also present in the claws of both female and male, but the size of tooth is remarkably small compared to Serendibula. Krombein, 1983 Figures 1A, 3, 4 Baeosega humida Krombein, 1983: 46  Distribution. Sri Lanka (Central Province, Kandy District).

Baeosega humida
Remarks. According to Krombein (1983), the slender proportion of the head and mesosoma of Baeosega laticeps Krombein is the important diagnostic character separating it from B. humida Krombein. However, the body proportion can be variable to some extent. This variation is probably caused by the different shape of the host egg. Because there is no significant difference except for the proportion (slightly compressed laterally or not), B. laticeps is considered to be a junior subjective synonym of B. humida. Krombein, 1983 Figures 1B, C, 5, 6 Baeosega torrida Krombein, 1983: 44, holotype ♀ by original designation. Type locality: Angunakolapelessa, Uva District, Southern Province, Sri Lanka.   8C); eye setose; flagellum fusiform, intermediate segments broader than long, and with ventral surface flattened. Mesosoma slender, punctate or longitudinally striate; pronotum with median groove and shallow pit before lateral lobe, as long as combined length of mesoscutum, mesoscutellum and metanotum; mesoscutum with notauli and without parapsides; posterolateral corner of mesoscutum not lobate; micropterous (Figs 1D, 2A), forewing pads extending to posterior margin of mesoscutellum; mesopleuron with omaulus; scrobal sulcus lacking; metanotum triangular, longer than mesoscutellum; propodeum with long dorsal surface and a pair of recumbent teeth present, almost meeting together, dorsal posterolateral angles bluntly angulate, lateral surfaces abruptly declivous and posterior surface rounded. Hind coxa with dorsobasal carina; tarsal claws without inner tooth. Metasoma smooth.
Diagnosis. Nipponosega kurzenkoi is closely related to N. yamanei from Japan. It can be distinguished from N. yamanei by the fully testaceous mesopleuron, whereas it is blackish in N. yamanei ( Fig. 2A). Also, the frons is wider than in N. yamanei. The maximum interocular distance (measured at the lower end of the face) is 1.2 × longer than the width of frons (1.5-2.0 in N. yamanei). Other diagnostic characters are as follows: body length 3.0 mm; head black, smooth with scattered punctures; lateral ocelli well separated from the inner margin of eye; mesosoma largely testaceous with mesoscutum and mesoscutellum black; pronotum smooth with scattered punctures; legs yellow; metasoma dark brown. Male is unknown.

Distribution. China (Zhejiang).
Remarks. Although the body color could be variable to some extent, no specimen of N. yamanei with completely testaceous mesopleuron has been found; a closely related species showing different distribution. The morphology of N. kurzenkoi should be evaluated in more detail to discuss their identification. However, diagnostic characters shown above do not overlap with those of N. yamanei. In the original description of N. kurzenkoi Xu et al., 2003, the evaluation of POD is different from the POD (= POL herein) used in Nagase (1995). The POD sensu Xu et al. (2003) is correspond to OOL herein. Diagnosis. Nipponosega lineata sp. nov. is readily distinguished from other Nipponosega species by the longitudinally costate pronotum (Fig. 7D). Other characters useful to distinguish from other species are as follows: body length 2.8 mm; head black, punctate with interspaces smooth, posterior margin of vertex longitudinally costate (Fig. 7D); maximum interocular distance 2.9 × longer than width of frons; lateral ocelli almost touching the inner margin of eye; malar sulcus indicated as a faint track (Fig. 7C); outer orbit of eye with a row of punctures; occipital carina present (Fig. 7B, D), reaching lower gena; antenna blackish with scape and F1 testaceous; mesosoma reddish but dorsum largely black; mesoscutum and mesoscutellum punctate; legs brownish; metasoma dark brown, smooth. Male is unknown.
Distribution. Thailand (Tak Province). Etymology. The specific name derives from the Latin word lineata, referring to the presence of striae on the pronotum.
Remarks. The holotype was collected from the leaf litter.    Diagnosis. In the genus Nipponosega, N. yamanei Kurzenko & Lelej is the only species known by both female and male. The female is similar to N. kurzenkoi in China. They can be distinguished by the body coloration and the width of frons. The mesopleuron is blackish in N. yamanei ( Fig. 2A), whereas it is fully testaceous in N. kurzenkoi. The frons is narrower, the maximum interocular distance is 1.5-2.0 × longer than the width of frons in full face view (1.2 in N. kurzenkoi). Other diagnostic characters of the female are as follows: body length 2.5-3.9 mm; head black, smooth with scattered punctures; posterior ocelli well separated from the inner margin of eye; pronotum reddish, smooth with scattered punctures; mesoscutum, mesoscutellum, anterior part of mesepisternum and often propodeum black; legs yellow; metasoma dark brown. The body length of the male is 3.2-3.8 mm. The male of other species of Nipponosega is unknown. Compared to other genera found in Japan, the male of N. yamanei can be distinguished by the head without occipital carina and impunctate welt; the body black, without metallic reflection; and the forewing with R1 thick, not clearly separated from pterostigma.
Metasoma faintly coriaceous, sparsely covered with setae; length of setae 2 MOD. Color. Head black. Antenna basally testaceous, F2-F10 dark brown, sometimes dorsal half of F2 testaceous. Mandible testaceous with reddish teeth. Mesosoma with prothorax, posterior half of mesopleuron and lateral surface of propodeum reddish to light brownish, remainder of mesothorax, metanotum and dorsal to posterior surface of propodeum brownish to blackish; dorsum of pronotum blackish in the female from Mt. Takanawa (Ehime Pref.); metanotum and propodeum sometimes paler especially in smaller specimens. Tegulae and wings testaceous to brown. Legs testaceous, sometimes femora and tibiae brownish. Metasoma brown to dark brown, rarely blackish, usually anterior surface of T1 and sterna paler.
Distribution. Japan (Honshu; Shikoku; Kyushu; Tsushima Isl.; Yakushima Isl.). Hosts. Diapheromeridae: Micadina phluctainoides (Rehn, 1904). Remarks. Although ocelli and head proportions of the female have been considered useful for species classification (Nagase 1995), they actually show great variation. The holotypes of N. yamanei (Fig. 8B) and N. kantoensis (Fig. 8D) are examples of the two extremes and intermediate females are more frequently found. This makes it difficult to distinguish between the two types. Males of N. yamanei were only obtained by Malaise traps and occasionally they were collected together with Cladobethylus japonicus Kimsey, 1997. The males of both species have been unknown; however, the morphological characters of the trapped males were close to those of Baeosega. As Cladobethylus is a genus showing little sexual dimorphism (Kimsey 2019), they are considered as Nipponosega. Compared to the abundance of the female, the male of N. yamanei is rarely collected. Some females were found above the ground surface (1 m or more) (Nagase 1995;Tomura 2020), but in fact they are more likely on the ground floor or in the leaf litter. Multiple females were obtained in Malaise traps, suggesting that females actively walk around the forest floor and climb understory vegetation. Females were observed to carry the host eggs for oviposition (Y. Hisasue, personal communication).
Diagnosis. General characters of Okinawasega are similar to those of Baeosega and Nipponosega; however, there are some distinctive differences, e.g., the deep malar sulcus in the female, the elongated linear R1 in the male. For more details, see the diagnosis of Baeosega. Description. Female. Clypeal apex not thickened; malar sulcus present (Fig. 10D); scapal basin shallow, cross-ridged, median longitudinal carina present; occipital carina absent but posterior margin of vertex forming distinct corner behind ocellar triangle; eye setose; flagellum fusiform, intermediate segments broader than long, and with ventral surface flattened. Mesosoma slender, punctate by dense punctures; pronotum with median groove and shallow pit before lateral lobe, as long as combined length of mesoscutum, mesoscutellum and metanotum; mesoscutum with notauli and without parapsides; posterolateral corner of mesoscutum not lobate; micropterous (Fig. 2C), forewing pads extending to posterior margin of mesoscutellum; mesopleuron with omaulus, without scrobal sulcus; metanotum triangular and small, slightly shorter than mesoscutellum; propodeum with long dorsal surface and a pair of recumbent teeth present, almost meeting together, dorsal posterolateral angles bluntly angulate, lateral and posterior surfaces abruptly declivous. Hind coxa with dorsobasal carina; tarsal claws without inner tooth. Metasoma smooth.
Color. Head, mesosoma and metasoma black but lateral surface of T1 brown, S1 dark brown. Antenna black but scape dark brown, pedicel and F1 brown. Mandible pale brown with apex black. Maxillary and labial palpi brown. Tegula and wings dark brown. Coxae and trochanters testaceous; remainder of fore and middle legs brown; remainder of hind leg dark brown.
Distribution. Japan: Yaeyama Islands, Southern Ryukyus (Ishigaki Isl., Iriomote Isl.) Remarks. No species in Baeosega-related genera are known from Ishigaki-jima and Iriomote-jima except for the male of Okinawasega eguchii Terayama. The newly found female was clearly related to Baeosega, and was therefore assigned to Okinawasega. Compared to males, females are seldom collected. The females actively walk on the ground surface and sometimes leap a small distance.

Discussion
The discovery of previously unknown sexes of Nipponosega and Okinawasega revealed that the male morphology of the two genera and Baeosega is rather conservative, even though females show clear differences. Males share following features: the absence of the occipital carina; mesopleuron without omaulus and scrobal sulcus; the relatively shorter metanotum, which is 0.5-0.7 × as long as mesoscutellum; the tarsal claw without large inner tooth, at most one small tooth. As for the posterior margin of the head in females, an indistinct occipital carina is sometimes present behind the ocellar triangle in Baeosega and Okinawasega. However, the structure is not clearly cariniform. It is observed only as faintly suppressed posterior margin (Fig. 3C). The distinct occipital carina is present only in the female of Nipponosega (Figs 7D, 8C). In males, some genera have the forewing with R1 distinguishable from the distal part of pterostigma (e.g., Imasega Krombein and Mahinda Krombein). This linear extension of R1 is not indicated in Baeosega (Fig. 4B) and Nipponosega (Fig. 9D) but a long linear R1 is clearly indicated in Okinawasega (Fig. 11D). While further research is required, the R1 condition can be a diagnostic character of amisegine genera (Krombein 1983;Kimsey and Bohart 1991).
In B. humida and N. yamanei, the body proportions of females can vary within a species. Although only a few records on the host of Amiseginae are available, the adult body size of egg parasitoids is usually affected by the host, for example, the size and age of the host egg (Da Rocha et al. 2007). Additionally, discontinuous differences can be observed in egg parasitoids if they attack different host eggs, as is known in Scelionidae (Arakawa et al. 2004;Abram et al. 2016;Botch and Delfosse 2018). Further studies on their host and their life history will provide a clearer picture of the background of the host-dependent variation.