Redefinition of the sexstrigatus group of Lasioglossum (Hemihalictus) Cockerell, 1897 (Hymenoptera, Apoidea, Halictidae), with a revision of Japanese species

I propose a redefinition of the sexstrigatus group of Lasioglossum (Hemihalictus) Cockerell, 1897, including a phylogenetic analysis. This group is characterised by a combination of the following 12 characteristics: male antenna short, not attaining to metasoma, male labrum with distal process and well-developed basal elevation, male head with genal process as variation, female mesepisternum reticulate-punctate on lower area, mesepisternum without tubercle in both sexes, female metasomal terga with distinct fimbriae on posterior margin, male S8 with well-developed median process, gonobase ventral arm of male genitalia connected with each other at upper ends, gonocoxite of male genitalia smooth, gonostylus of male genitalia small and simple, bud-like, and the ventral retrorse lobe of male genitalia not attaining to gonobase. The Japanese species of the sexstrigatus group are revised. Thirteen species in total are recognised, including three new species: Lasioglossum (Hemihalictus) ikudomei sp. nov., L. (H.) spectrum sp. nov., and L. (H.) subsimplicior sp. nov. Lasioglossum (Hemihalictus) perplexans (Cockerell, 1925) is synonymised under L. (H.) kiautschouense (Strand, 1910). A key to the Japanese species is provided. Bionomical data, such as flight and flower records or habitat, are reported for some species. The distributions of all species are mapped. DNA sequences including a part of the barcode region are given for L. (H.) kiautschouense, L. (H.) ohei Hirashima & Sakagami, 1966, L. (H.) speculinum (Cockerell, 1925), L. (H.) spectrum sp. nov., L. (H.) subsimplicior sp. nov., and L. (H.) taeniolellum (Vachal, 1903).

One of these, the sexstrigatus group, includes over 30 species and is diverse in eastern Asia (Pesenko 2007b;Murao et al. 2010). This group is mainly characterised by the female metasomal terga with distinct fimbriae on the lateral-apical margin and the male head with a size-linked gigantism with genal process . However, some species in the group do not necessarily share these characteristics (Murao 2017a). This group is also quite difficult to identify at the species level in Lasioglossum because identification is often based on subtle morphological differences (e.g., . A few species are known as solitary or communal Sakagami 1992), but no eusocial species are known. Some species often dominate in the Japanese bee fauna when considering the number of individuals (Ikudome 1995;Iwata 1997;Minagi et al. 2000;Negoro 2001aNegoro , 2001bMaeta et al. 2003;Gôukon 2006;Hisamatsu & Yamane 2006;Hisamatsu 2011Hisamatsu , 2017Murao, Murase & Iwata unpublished

Terminology
Terminology and style used in the description follows Murao et al. (2015b). Abbreviations used in the text are as follows: AOD = antennocular distance (shortest distance between outer margin of antennal socket and inner margin of compound eye) BL = body length (from antennal base to tip of pygidial plate) CAL = clypealveolar distance (between lower margin of antennal socket and lower margin of supraclypeus in frontal view) CPL = clypeal length (between upper and lower margins of clypeus in frontal view) EL = eye length EW = eye width (maximum length and width of the compound eye) Fn = n th antennal flagellomere FnL = length of n th flagellomere (measured along the ventral surface) FnW = width of n th flagellomere (measured from dorsal and ventral surfaces of flagellomere) GW = genal width (maximum width of the genal area when seen in lateral view) HL = head length (from top of vertex to lower margin of clypeus) HW = head width (between outer margins of compound eyes in frontal view) IAD = interantennal distance (between inner margins of antennal sockets) IOD = interocellar distance (between lateral ocelli) IS = interspace between punctures (e.g., IS 0.5 d means ½ of the diameter of a puncture) LOD = lower interorbital distance MNL = metanotal length MOD = maximum interorbital distance MPL = metapostnotal length MsW = maximum mesosomal width MtW = maximum metasomal width OCD = ocelloccipital distance (shortest distance between margins of lateral ocellus and vertex when seen in upper view) OOD = ocellocular distance (shortest distance between lateral ocellus and inner margin of compound eye) PP = punctures SCL = mesoscutellar length Sn = n th metasomal sternum SPL = scape length (a straight line from base to tip of scape) Tn = n th metasomal tergum UOD = upper interorbital distance WL = wing length (length of fore wing from the apical point to the base including tegula)

Flower records
Flower records visited by each species are based on specimen label data. The scientific names of flowering plants visited by bees are cited from Yonekura & Kajita (2003-).

Cladistic analysis
To test monophyly of the sexstrigatus group, I selected two to 16 species from each of 10 species groups of Lasioglossum (Hemihalictus) as the ingroup and two species of L. (Dialictus) as an outgroup (Appendix 1). A total of 32 morphological characters were coded using MESQUITE ver. 3.61 (Maddison & Maddison 2019) (Appendix 2). Characters are coded as '0', '1', '2' or '3' and the data matrix is shown in Appendix 3. A cladistic analysis was performed using TNT ver. 1.1 (Goloboff et al. 2008) traditional heuristic search that generated 1000 Wagner trees with random addition sequence. Symmetric resampling was performed using default settings for 1000 replicates. Unambiguous character state changes were mapped on the most parsimonious trees using WINCLADA ver. 1.00.88 (Nixon 2002).

DNA analyis
DNA extraction and PCR were conducted at the Kyushu University Museum (Fukuoka, Japan). DNA was extracted using a DNeasy Blood and Tissue kit (Qiagen, Tokyo, Japan) following the manufacture's instructions. A 707 bp including a part of DNA barcode region of the cytochrome oxidase subunit I (COI) gene fragment of mtDNA was amplified (using the primers COI_pF2 and COI_2437d), purified, and electrophoresed following the methods decribed by Murao et al. (2015c). DNA sequencing was outsourced to the FASMAC Co., Ltd (Kanagawa, Japan). The sequences analyzed in the present study are deposited in GenBank through the DNA Database of Japan (DDBJ). Appendix 4 lists the GenBank accession numbers used in the present paper. Pairwise sequence divergences within each specis of sexstrigatus group were calculated using Kimura 2-parameter distance (Kimura 1980). The analyses were conducted using MEGA5 (Tamura et al. 2011). MURAO R., Redifition and revision of the Lasioglossum sexstrigatus group in Japan revised classification that the sexstrigatus group is restricted to species sharing the characteristics of the sexstrigatus clade.  (Vachal, 1903), ♂, labrum. -C, F. L. (H.) frigidum . C. ♂, cephalic polymorphism. F. ♀, metasomal terga. -D. L. (H.) simplicior (Cockerell, 1931)

MURAO R., Redifition and revision of the Lasioglossum sexstrigatus group in Japan
The Japanese species of Hemihalictus are classified into five species groups (nitidiusculum, japonicum, semilucens, sexstrigatus, and villosulum groups). The sexstrigatus group is separated from the other four groups by the male head with genal process, the female metasomal terga generally with distinct fimbriae on posterior margin, and male S8 with developed median process.

Variation (male cephalic polymorphism)
The members of sexstrigatus group except for Lasioglossum (Hemihalictus) frigidum  display male cephalic polymorphism Ebmer et al. 1994;Murao et al. 2010). This polymorphism is caused by the allometric development of the head . The presence of a genal process is characteristic of the sexstrigatus group, but is not known from the japonicum group Ebmer et al. 1994;Murao et al. 2010). Male cephalic polymorphism with allometric variation is known to occur in various bee families such as Andrenidae Latreille, 1802, Colletidae Lepeletier, 1841, and Halictidae Thomson, 1869(summarised in Danforth et al. 2019. It also appears that such male cephalic polymorphism often occurs in communal species (Maeta 2000;Danforth et al. 2019). In the Japanese species of the sexstrigatus group, L. (H.) ohei has indeed been reported as a communal species . The other Japanese species with male cephalic polymorphism may also be communal.

Distribution
This group is distributed from the Palearctic to northern Oriental Region. It is diverse in eastern Asia.

Comments
Lasioglossum sexstrigatum was originally described as Halictus sexstrigatus by Schenck. From the scientific name '-strigatus', the original spelling was retained in accordance with Article 31.2.2 of the ICZN (International Commission on Zoological Nomenclature) Code.

Flight records
Female: April to October.
Male: June to October. The flight records of male are based on the phenological data reported by Minagi et al (2000).

Flower records
Five species in 4 families were reported as floral records in Japan by , 8 species in 5 families by Minagi et al. (2000), and 5 species in 4 families by Gôukon (2006

Habitat
Lasioglossum frigidum has been collected only in coastal sand dunes. One of the collecting sites is shown in Fig. 19D.
thorax. Dorsolateral angle of pronotum obtuse; lateral surface without ridges; lateral lobe rounded. Tegula ovoid, nearly smooth. Mesoscutum (Fig. 5E) with moderately dense PP over entire surface; IS weakly tessellate over entire surface (particularly very weak on posterior area) (IS = 0.5-3 d); parapsidal line a narrow groove. Mesoscutellum with 2-4 PP on submedian area and denser PP on marginal area; IS nearly smooth on submedian area and very weakly tessellate on marginal area (IS = 2-5 d on submedian area, = 0.5-2 d on marginal area). Metanotum weakly rugulose. Mesepisternum weakly shiny, with dense shallow PP on upper area and reticulate PP on lower area; IS nearly smooth on upper area (IS = 0.5-1 d on upper area). SCL:MNL:MPL = 1:0.62:0.66. Propodeum: metapostnotum (Fig. 5F) gently inclined, with irregular sinuate ridges on anterior half in holotype and two paratypes (remaining five paratypes with short longitudinal ridges), with weak tessellation on posterior half, and nearly smooth among ridges; junction between metapostnotum and posterior surface not carinate, with weak tessellation; lateral surface weakly rugulose; posterior surface with lateral carina on lower half, without oblique carina. Coxae usual shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial European Journal of Taxonomy 763: 1-74 (2021) plate of hind leg carinate marginally. Inner hind tibial spur with slender 2-4 teeth as in Fig. 20B (n = 7). Fore wing with three submarginal cells.
abdoMen. Disc of T1 without distinct PP on medial area, and with very weak lineolation interrupted on medial area (Fig. 15B). Disc of T2 nearly smooth on anterior to medial area in holotype and two paratypes, and with weak lineolation on posterior area (anterior and posterior area with weak lineolation in four paratypes). Discs of T3-T4 with weak lineolation over entire surface. Coloration. Body black except for the following parts: mandible yellowish brown except for apically reddish brown; labrum dark yellow; pronotal lobe yellowish brown; tegula yellowish brown translucent; legs brown, without distinct yellow marks; tibial spur yellow; metasomal terga broadly yellowish brown translucent apically. Wings transparent, veins and stigma pale brown.

Male
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: lower paraocular area and pronotal dorsum to lobe sparsely tomentose. Disc of T1 with sparse hairs only on marginal area. Disc of T2-T4 with sparse short hairs over entire surface. T2-T3 with thin apical fimbriae, less distinct than in the female. thorax. Dorsolateral angle of pronotum obtuse; lateral surface without ridges; lateral lobe rounded. Tegula ovoid, nearly smooth. Mesoscutum with moderately dense PP over entire surface; IS weakly tessellate on anterior margin, nearly smooth on rest parts (IS = 1.5-3 d); parapsidal line a narrow groove. Mesoscutellum with sparse PP over entire surface; IS smooth (IS = 2.5-6 d). Metanotum weakly rugulose. Mesepisternum with moderately dense PP over entire surface; IS smooth (IS = 1-3 d). SCL:MNL:MPL = 1:0.63:0.75. Propodeum: metapostnotum weakly shiny and gently inclined, with short straight ridges occupying anterior ⅔; junction between metapostnotum and posterior surface not carinate, nearly smooth; lateral surface weakly reticulate; posterior surface nearly smooth, with lateral carina on lower ⅓, and without oblique carina. Coxae usual shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg carinate marginally. Inner hind tibial spur serrate. Fore wing with three submarginal cells.
abdoMen. Disc of T1 nearly smooth. Disc of T2-T3 with sparse fine PP; T2 weakly lineolate on apical margin; T3 weakly lioneolate on apical half. Disc of T4 weakly lineolate over entire surface. S7 with moderately long, apically rounded median process.
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: pronotum moderately densely tomentose on dorsal area and around lobe; hind trochanter, femur, and tibia mixed with plumose hairs, forming scopa. thoarx. Dorsolateral angle of pronotum obtuse; lateral surface without ridges; lateral lobe rounded. Tegula ovoid, nearly smooth. Mesoscutum (Fig. 6D) with dense PP over entire surface; IS nearly smooth on posterior area, and distinctly tessellate on the rest area (IS = 0.5-2 d); parapsidal line a narrow groove. Mesoscutellum with dense PP over entire surface, IS smooth (IS = 0.5-2 d). Metanotum weakly rugulose.
abdoMen. Disc of T1 with sparse distinct fine PP on medial area and without lineolation over entire surface (Fig. 15C). Discs of T2-T4 without lineolation over entire surface (sometimes T4 with very weak lineolation).

Male
Not examined in the present study.

Flight records
Female: May to September.
Males have been collected from July to August in Primorsky, Russian Far East (Ebmer 1996(Ebmer , 2006.

Flower records
The specimens examined in this paper were collected on the flowers of 7 species in 3 families as follows.

Habitat
This species has been collected from semi-natural grassland in western Japan. One of the collecting sites is shown in Fig. 19A.

Diagnosis
Females are similar to L. (H.) simplicior but separated from them by the head slightly longer than wide or nearly as long as wide (HL / HW ratio 1.01 ± 0.02), IS of mesoscutum nearly smooth on posterior margin, and metasomal terga with silky dull luster. In contrast, in L. (H.) simplicior, the head wider than long (HL / HW ratio 0.97 ± 0.03), IS of mesoscutum with distinct tessellation over entire surface, and metasomal terga with enamel-like luster as in most species of Lasioglossum.

Flight period
Female: April to November.
Male: July to September. The flight records of males are based on the paratypes collected or reared from the nest .

Flower records
The specimens examined in this paper were collected on the flowers of 50 species in 19 families as follows.

Habitat
This species has been collected mainly from the mountain of western Japan. One of the collecting sites is shown in Fig. 19A. Sakagami et al. (1966) and Sakagami (1992) reported on the biology of this species as univoltine and communal, with nest structure type Ia of Sakagami & Michener (1962). (Cockerell, 1931

Diagnosis
Females are similar to L. (H.) ohei, but separated from them by the head wider than long (HL / HW ratio 0.97 ± 0.03), IS of mesoscutum with distinct tessellation over entire surface, and metasomal terga with enamel-like luster. In contrast, in L. (H.) ohei, the head is slightly longer than wide or nearly as long as wide (HL / HW ratio 1.01 ± 0.02), IS of mesoscutum nearly smooth on posterior margin, and metasomal terga with silky dull luster.  Coloration. Body black except for the following parts: mandible reddish brown apically; flagellum blackish brown ventrally; tegula yellowish brown translucent; tibial spur yellow; metasomal terga broadly yellowish brown translucent apically. Wings transparent, veins and stigma yellowish brown.
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: pronotum moderately densely tomentose on dorsal area and around lobe; hind trochanter, femur, and tibia mixed with plumose hairs, forming scopa. Coloration. Body black except for the following parts: mandible yellow except for apically reddish; labrum and lower half of clypeus yellow; flagellum yellowish brown ventrally; tegula yellowish brown translucent; tibiae basally and apically yellow; tibial spur yellow; tarsi yellow; metasomal terga broadly yellowish brown translucent apically. Wings transparent, veins and stigma pale yellowish brown.
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: lower paraocular area sparsely tomentose.  (2021) posterior margin; junction between metapostnotum and posterior surface not carinate and nearly smooth; lateral surface weakly rugulose; posterior surface with lateral carina on lower half, without oblique carina. Coxae usual shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg carinate marginally. Inner hind tibial spur serrate. Fore wing with three submarginal cells. MURAO R., Redifition and revision of the Lasioglossum sexstrigatus group in Japan abdoMen. Disc of T1 with sparse fine PP and without lineolation. Disc of T2-T3 with denser PP than T1; T2 without lineolation, and T3 posteriorly with weak lineolation. T4 with weak lineolation over entire surface. S7 with moderately long, apically rounded median process.

Flight period
Female: late May to early October.
Male: late May to middle October.

Comments
The type locality of this species is Shanghai in China, so it is not surprising that L. simplicior is also distributed on the Japanese mainland. Interestingly, Japanese specimens matching the holotype were found only on the Izu Islands and not on the Japanese mainland. In the future, it may be worth while to verify whether the population of the Izu Islands indeed represents L. simplicior, after comparison of the genes of both the continental and Izu Islands populations. This species has been recorded from Japan (Takahashi & Sakagami 1993;Goubara et al. 2004;Fukasawa & Miyano 2010). However, these records were excluded from the Japanese bee fauna because of the need to re-examine them (Tadauchi & Murao 2014;Murao 2020). In the present study, the distribution of this species in Japan was reconfirmed by comparing with the type specimen.  Figs 9, 15F, 18D, 20E

Diagnosis
Females are similar to L. (H.) ikudomei sp. nov. but are separated from them by the supraclypeal area dimly shiny (IS distinctly tessellate), the PP on the mesoscutum denser (IS = 2 d in maximum) (Fig. 9E), and the lineolation of T1 more clear. In contrast, in L. (H.) ikudomei sp. nov., the supraclypeal area is more shiny (IS weakly tessellate), the PP on the mesoscutum sparser (IS = 3 d in maximum) (Fig. 5E), and T1 with very weak lineolation.  Coloration. Body black except for the following parts: mandible reddish brown apically; F4-F10 yellowish brown ventrally; tegula yellowish brown translucent; tibial spur yellow; metasomal terga narrowly yellowish brown translucent apically. Wings transparent, veins and stigma blackish brown.

Holotype
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: pronotal dorsum to lobe and metanotum densely tomentose; hind trochanter, femur, and tibia mixed with plumose hairs, forming scopa. Disc of T1 without short hairs. Discs of T2-T4 with moderately dense short hairs over entire surface.  (2021) Propodeum: metapostnotum (Fig. 9F) dimly shiny and gently inclined, with straight ridges occupying anterior half, and distinctly tessellate on posterior half; junction between metapostnotum and posterior surface not carinate, distinctly tessellate; lateral surface distinctly tessellate; posterior surface with lateral carina on lower half, without oblique carina. Coxae usual shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg carinate marginally. Inner hind tibial spur pectinate, with 3-4 teeth as in Fig. 20E (n = 4). Fore wing with three submarginal cells.
abdoMen. Disc of T1 without distinct PP and with weak lineolation over entire surface (Fig. 15F). Disc of T2 weakly lineolate on anterior and posterior area, and nearly smooth on medial area. Discs of T3-T4 with weak lineolation over entire surface. Coloration. Body black except for the following parts: lower half or margin dark yellow; mandible reddish brown; labrum dark yellow; pedicel and F1 yellowish brown ventrally; tegula yellowish brown translucent; tibial spur yellow; tarsi yellowish brown or brown; metasomal terga narrowly yellowish brown translucent apically. Wings transparent, veins and stigma blackish brown.

Male
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: pronotal dorsum to lobe and metanotum sparsely tomentose. Disc of T1 with sparse short hairs. Discs of T2-T4 with moderately dense short hairs over entire surface. T2-T3 with thin apical fimbriae, not clear in female. thoarx. Dorsolateral angle of pronotum obtuse; lateral surface without ridges; lateral lobe rounded. Tegula ovoid, nearly smooth. Mesoscutum with dense PP over entire surface; IS weakly tessellate on anterior half, nearly smooth on posterior half (IS = 0.5-2 d); parapsidal line a narrow groove. Mesoscutellum with sparser PP over entire surface; IS smooth (IS = 1-4 d). Metanotum weakly rugulose. Mesepisternum with moderately dense shallow PP on upper area and weak reticulate PP on lower area; IS smooth. SCL:MNL:MPL = 1:0.53:0.72. Propodeum: metapostnotum weakly shiny and gently inclined, with short straight ridges occupying anterior half and weakly tessellate on posterior half; junction between metapostnotum and posterior surface not carinate, weakly tessellate; lateral surface distinctly tessellate; posterior surface with lateral carina on lower half, without oblique carina. Coxae MURAO R., Redifition and revision of the Lasioglossum sexstrigatus group in Japan usual shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg carinate marginally. Inner hind tibial spur serrate. Fore wing with three submarginal cells.
abdoMen. Disc of T1-T3 with fine sparse PP. Disc of T1 basally weakly lineolate or smooth (paratype and 1 ♂ lineolate, but 1 ♂ not lineolate). Disc of T2-T3 weakly lineolate on anterior and posterior areas, and nearly smooth on medial area. Discs of T4 with weak lineolation over entire surface. S7 with moderately long, apically rounded median process.
Genitalia. Gonobase flat at bottom, ventral arms connected with each other at upper ends; gonocoxite smooth; ventral retrorse lobe tongue-like, moderately long but not reaching gonobase, with sparse short hairs ventrally.

Flight period
Female: April to October.
Male: August to October. The flight records of male are based on the collecting data of the original description .

Diagnosis
Females are similar to L. (H.) epicinctus but are separated from them by the frons with sparse hairs (not mixed with tomentose hairs) and the ridges of the metapostnotum long (nearly reaching posterior margin as in Fig. 10F). In contrast, in L. (H.) epicinctus, the frons is mixed with dense whitish tomentose hairs and the ridges of the metapostnotum are short (only present on basal area).

Etymology
The specific name is derived from 'Obake', meaning 'ghost' in Japanese. This species has been called "Obake-chibi-kohanabachi" in Japanese, hence its scientific name.    Coloration. Body black except for the following parts: mandible reddish brown apically; F4-F10 brown (holotype) or yellowish brown ventrally; tegula yellowish brown translucent; tibial spur yellow; metasomal terga broadly yellowish brown translucent apically. Wings transparent, veins and stigma brown.
abdoMen. Disc of T1 with weak lineolation on basal and apical areas (not overlapping in puncture zone on medial area) (Fig. 16A), and with sparse fine PP on medial area. Disc of T2 with weak lineolation on basal and apical area, and without lineolation on medial area. T3-T4 weakly lineolate over entire surface. Coloration. Body black except for the following parts: lower half of clypeus yellow; mandible yellow except for apically reddish; labrum yellow; F1 yellowish brown or brown ventrally; pronotal lobe yellowish brown; tegula yellow translucent; tibiae basally and apically yellow; tibial spur yellow; tarsi yellow; metasomal terga broadly yellowish brown translucent apically. Wings transparent, veins and stigma pale brown.

Male
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: paraocular area, pronotal dorsum to lobe thinly tomentose. Metasomal terga with sparse, simple and short hairs over entire surface. thorax. Dorsolateral angle of pronotum obtuse; lateral surface without ridges; lateral lobe rounded. Tegula ovoid, nearly smooth. Mesoscutum with dense PP over entire surface; IS smooth except for anteriorly weakly tessellate (IS = 0.5-2 d); parapsidal line a narrow groove. Mesoscutellum with moderately dense PP over entire surface; IS smooth (IS = 0.5-4 d). Metanotum weakly rugulose. Mesepisternum with dense PP over entire surface; IS smooth (IS = 0.5-1 d). SCL:MNL:MPL = 1:0.49:0.68. Propodeum: metapostnotum shiny and gently inclined, with short straight ridges occupying anterior half or anterior ⅔, weakly tessellate or nearly smooth on posterior half or posterior ⅓; junction between metapostnotum and posterior surface not carinate, weakly tessellate or nearly smooth; lateral surface weakly rugulose and distinctly tessellated; posterior surface with lateral carina on lower half, without oblique carina. Coxae normal shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg weakly carinate marginally. Inner hind tibial spur serrate. Fore wing with three submarginal cells.
abdoMen. Disc of T1 without distinct PP and tessellation. Disc of T2-T4 with moderately dense fine PP, T2 without lineolation, T3-T4 with weak lineolation on apical margin. S7 with moderately long, apically rounded median process.

Variation
Disc of T1 lineolate only on basal area (Fig. 16B) in the specimens (not type series) collected from Hokkaido (northern Japan).

Flight period
Female: April to Novemver.
Males are collected from June to August based on 46 male specimens in the late Dr Sakagami's collection (MNHAH). These specimens were collected from the nest of this species (identified as L. (H.) pallilomum (Strand, 1914)).

Flower records
The specimens examined in this paper were collected on the flowers of 61 species in 30 families as follows. Acanthaceae: Justicia hayatae Yamam. Amaranthaceae: Achyranthes bidentata Blume var.

Habitat
This species has been collected from various environments such as cultivated or urban areas in the lowlands, seaside, mountain areas, and semi-natural grassland. The type locality is shown in Fig. 19B.

Diagnosis
Females are separated from other members of the sexstrigatus group occurring in Japan by a combination of the following character states: head relatively longer than wide (length / width ratio 1.07); metasoma entirely black; metasomal terga with white fimbriae on latero-apical margins; and disc of T1 basally to medially with distinct lineolation (Fig. 16C) (Murao 2017a).

Material examined
Holotype RUSSIA -Siberia • ♀; Preobrageniya Bay; 12 Jul.; USNM. PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: pronotal dorsum to lobe and metanotum densely tomentose; hind trochanter, femur, and tibia mixed with plumose hairs, forming scopa. Disc of T1 with sparse short hairs on medial and posterior areas. Discs of T2-T4 with moderately dense short hairs over entire surface.  (Fig. 11E) weakly shiny and gently inclined, with nearly straight ridges reaching posterior area; junction between metapostnotum and posterior surface not carinate, weakly tessellate; lateral surface weakly rugulose; posterior surface with lateral carina on lower half, without oblique carina. Coxae normal shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg carinate marginally. Inner hind tibial spur with 3-4 slender teeth as in Fig. 20G (n = 6). Fore wing with three submarginal cells.

Other material
abdoMen. Disc of T1 with moderately dense distinct PP on medial area and with lineolation on anterior and medial areas (lineolation reaching punctate zone on medial area, but interrupted on submedial patch) (Fig. 16C). Disc of T2-T3 nearly smooth on medial area, and very weakly lineolate on remaining part. Disc of T4 with very weak lineolation over entire surface.

Male
Not examined in the present study.

Variation
Disc of T1 distinctly lineolate over entire surface in three specimens collected from Hachijo Is., Japan.

Flight period
Female: June to September.
Males have been collected from July to August in the Korean Peninsula (Ebmer 1978b).

Diagnosis
Females are similar to L. (H.) eidmanni (Blüthgen, 1930). According to , this species is only separated from L. (H.) eidmanni by the metasomal terga without distinct apical fimbriae. In contrast, in L. (H.) eidmanni, the metasomal terga have more or less dense and welldeveloped apical fimbriae.

Flight period
Female: April to October.
Male: August to October. The flight records of male are based on the collection data of the original description of this species .

Diagnosis
Females are similar to L. (H.) simplicior but are separated from them by the lineolation of T1 interrupted in part (Fig. 16E). In contrast, in L. (H.) simplicior, the lineolation of T1 is present across the entire surface (Fig. 15E).

Material examined
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: pronotal dorsum to lobe and metanotum moderately densely tomentose; hind trochanter, femur, and tibia mixed with plumose hairs, forming scopa. Disc of T1 with sparse short hairs on medial area. Discs of T2-T4 with moderately dense short hairs over entire surface. thoirax. Dorsolateral angle of pronotum obtuse; lateral surface without ridges; lateral lobe rounded. Tegula ovoid, nearly smooth. Mesoscutum (Fig. 13D) with dense PP over entire surface; IS distinctly tessellate nearly over entire surface (but weakly tessellate on posterior margin) (IS = 0.5-2 d); parapsidal line a narrow groove. Mesoscutellum with moderately dense PP over entire surface; IS weakly tessellate over entire surface (IS = 0.5-3 d in paratypes). Metanotum weakly rugulose. Mesepisternum with reticulate PP on upper area and weak rugulae on lower area. SCL:MNL:MPL = 1:0.58:0.67. Propodeum: metapostnotum (Fig. 13E) weakly shiny and gently inclined, with straight ridges reaching to near posterior margin; junction between metapostnotum and posterior surface not carinate, weakly tessellate; lateral surface weakly rugulose and distinctly tessellate; posterior surface with lateral carina on lower half, without oblique carina. Coxae normal shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg carinate marginally. Inner hind tibial spur with 3-4 slender teeth (n = 27). Fore wing with three submarginal cells.
abdoMen. Disc of T1 with weak lineolation interrupted on medial area (Fig. 16E), and with sparse fine PP on medial area; submedian patch distinct and nearly smooth. Disc of T2-T3 with very weak lineolation on apical half, and without lineolation on basal half. T4 very weakly lineolate over entire surface.

Male
Unknown.

Habitat
This species has been collected mainly from mountainous areas in western Japan. One of the collecting sites in Japan is shown in Fig. 19A. Murao, 2012 Fig. 18D Lasioglossum (

Diagnosis
Females are similar to L. (H.) taeniolellum. According to , this species is separated from L. (H.) taeniolellum by the postgena having distinct lineolation over entire surface, the distal process of labrum without lateral projection (Murao 2012: fig. 5), and T1 with short hairs and fine PP on disc : fig. 7). In contrast, in L. (H.) taeniolellum, the lineolation on postgena does not reach the apical margin, the distal process of labrum with horn-like lateral projection (Fig. 14D), and T1 nearly smooth. Male unknown.

Flight records
Female: April to October.

Flower records
Two species in two families were reported as floral records by .

Habitat
This species has been collected from around subtropical forests in mountainous area . It may prefer humid environments.

Diagnosis
Females are similar to L. (H.) tadauchii, but are separated from them by the lineolation on postgena not reaching the apical margin, the distal process of the labrum with a horn-like lateral projection (Fig. 14D), and T1 nearly smooth. In contrast, in L. (H.) tadauchii, the postgena have a distinct lineolation across the entire surface, the distal process of the labrum is without a lateral projection (Murao 2012: fig. 5), and T1 has short hairs and fine PP on the disc (Murao 2012: fig. 7).

Redescription
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: pronotal dorsum to lobe and metanotum moderately densely tomentose; posterior surface of propodeum sparsely tomentose; hind trochanter, femur, and tibia mixed with plumose hairs, forming scopa. Disc of T1 without short hairs on medial area. Discs of T2-T4 with moderately dense short hairs over entire surface. MURAO R., Redifition and revision of the Lasioglossum sexstrigatus group in Japan thorax. Dorsolateral angle of pronotum obtuse; lateral surface without ridges; lateral lobe rounded. Tegula ovoid, nearly smooth. Mesoscutum (Fig. 14E) with dense PP over entire surface; IS distinctly tessellate over entire surface (IS = 0.5-2 d); parapsidal line a narrow groove. Mesoscutellum with sparse PP on submedian area and denser PP on marginal area; IS nearly smooth over entire surface (IS = 1-3 d on submedian area, and 0.5-1 d on marginal area). Metanotum weakly rugulose. Mesepisternum with reticulate PP over entire surface. SCL:MNL:MPL = 1:0.56:0.71. Propodeum: metapostnotum (Fig. 14F) weakly shiny and gently inclined, with short straight ridges occupying only anterior half, with weak tessellation on posterior half; junction between metapostnotum and posterior surface not carinate, weakly tessellate; lateral surface weakly rugulose and distinctly tessellate; posterior surface with lateral carina on lower half, without oblique carina. Coxae normal shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg carinate marginally. Inner hind tibial spur with 2-5 slender teeth as in Fig. 20I (n = 13). Fore wing with three submarginal cells.
abdoMen. Disc of T1 nearly smooth over entire surface (Fig. 16F). Disc of T2 very weakly lineolate in part (only anterior or both anterior and posterior area). T3-T4 very weakly lineolate over entire surface. Coloration. Body black except for the following parts: lower half of clypeus yellow; mandible except for apically and labrum yellow; mandible apically reddish; all flagellar segments yellowish brown ventrally; pronotal lobe yellow or yellowish brown; tegula yellow translucent; tibiae basally and apically yellow; tibial spur yellow; tarsi yellow; metasomal terga broadly yellowish brown translucent apically. Wings transparent, veins and stigma yellowish brown.
PubesCenCe. Body hairs whitish, and covered with erect and sparse straight or fine branched hairs except for the following parts: lower paraocular area, supraclypeal area, pronotal dorsum to lobe and metanotum thinly tomentose. Metasomal terga with sparse, simple and short hairs over entire surface. thorax. Dorsolateral angle of pronotum obtuse; lateral surface without ridges; lateral lobe rounded. Tegula ovoid, nearly smooth. Mesoscutum with dense PP over entire surface; IS smooth except for anteriorly weakly tessellate (IS = 0.5-2 d); parapsidal line a narrow groove. Mesoscutellum with sparse PP over entire surface; IS smooth (IS = 1-5 d). Metanotum weakly rugulose. Mesepisternum with moderately dense PP over entire surface; IS smooth (IS = 1-3 d). SCL:MNL:MPL = 1:0.49:0.68. Propodeum: metapostnotum shiny and gently inclined, with short straight ridges occupying only European Journal of Taxonomy 763: 1-74 (2021) anterior half, weakly tessellate or nearly smooth on posterior half; junction between metapostnotum and posterior surface not carinate, weakly tessellate or nearly smooth; lateral surface weakly rugulose and distinctly tessellate; posterior surface with lateral carina on lower half, without oblique carina. Coxae normal shape, without tubercle. Fore trochanter narrow, longer than wide. Basitibial plate of hind leg weakly carinate marginally. Inner hind tibial spur without tooth. Fore wing with three submarginal cells.
abdoMen. Disc of T1 without distinct PP and tessellation. Disc of T2-T4 with sparse fine PP, T2 without lineolation, T3 with weak lineolation on apical half, and T4 with weak lineolate over entire surface. S7 with moderately long, apically truncate or rounded median process.

Flight period
Female: April to December.

Comments
This unknown species has been identified as Lasioglossum (Hemihalictus) sexstrigatus (Schenck, 1869) in Japan. According to DNA analysis in the present study, the pair-wise sequence divergence between Japanese and European specimens was quite clear (7.3-7.9% between L. sexstrigatus and L. sp. in Table 1). Morphologically, females of this species are slightly different from L. (H.) sexstrigatus as the mesoscutum has a weak tessellation over the entire surface (in contrast, in L. (H.) sexstrigatus, the mesoscutum is nearly smooth on the posterior half).

Discussion
The morphological differences among species of the sexstrigatus group often depend on subtle characteristics such as the sculpture of the mesoscutum or T1 and the length of metapostnotal ridges, etc., as described in the diagnosis of each species and the above Key. These characteristics are useful only in female specimens. Generally, in Lasioglossum, the interspecific differences are clearer in males than in the female, particularly using male genitalia. However, the interspecific differences in males of the sexstrigatus group is unclear even when comparing male genitalia. In addition, it is even more difficult to identify the species, owing to the male cephalic polymorphism. Among the European Lasioglossum, L. (H.) pleurospeculum Herrmann, 2001, L. (H.) sabulosum (Warncke, 1986), and L. (H.) sexstrigatus belong to the sexstrigatus group (Herrmann & Doczkal 1999;Herrmann 2001). According to Herrmann & Doczkal (1999) and Herrmann (2001), the tooth of the inner hind tibial spur in females is one of the useful characters that distinguishes L. However, for the Japanese species, there is no interspecific difference in the female inner hind tibial spur (Fig. 20). In the present study, I examined part of the DNA barcoding region of the cytochrome oxidase subunit I gene of mitochondrial DNA gene for some species of the sexstrigatus group. The interspecies sequence divergences were larger than intraspecies divergences as in Table 1. Thus, DNA barcodes are quite useful in judging the interspecific differences in the sexstrigatus group. The sexstrigatus group is diverse in eastern Asia, and its diversity is unclear in the Oriental Region. Accumulation and utilisation of DNA data will be a very effective tool in the progress of taxonomic study of the sexstrigatus group in the Oriental Region.