Lasioglossum sexstrigatus (Schenck, 1869)

Murao, Ryuki, 2021, Redefinition of the sexstrigatus group of Lasioglossum (Hemihalictus) Cockerell, 1897 (Hymenoptera, Apoidea, Halictidae), with a revision of Japanese species, European Journal of Taxonomy 763, pp. 1-74 : 7-11

The sexstrigatus group

Diagnosis

Species of the sexstrigatus group are characterized by a combination of the following characters: 1) male antenna short, not reaching metasoma ( Fig. 2A ); 2) male labrum with well-developed basal elevation ( Fig. 2B ) (except for Lasioglossum (Hemihalictus) ohei Hirashima & Sakagami, 1966 ); 3) male labrum with distal process ( Fig. 2B ); 4) male head with genal process as variation ( Fig. 2C–D ); 5) female mesepisternum reticulate-punctate on lower area ( Fig. 2E ); 6) mesepisternum without tubercle in both sexes; 7) female metasomal terga with distinct fimbriae on posterior margin ( Fig. 2F ) (except for L. (H.) sphecodicolor Sakagami & Tadauchi, 1995 ); 8) male S8 with well-developed (over S7) median process ( Fig. 3A ); 9) gonobase ventral arms of male genitalia connected with each other at upper ends ( Fig. 3C ); 10) gonocoxite of male genitalia smooth ( Fig. 3B–D ); 11) gonostylus of male genitalia small and simple, bud-like ( Fig. 3B–C ); and 12) the ventral retrorse lobe of male genitalia not reaching gonobase ( Fig. 3B–C ).

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 Sakagami & Ebmer, 1996 display male cephalic polymorphism ( Sakagami et al. 1966; Ebmer et al. 1994; Sakagami & Ebmer 1996; Murao et al. 2010). This polymorphism is caused by the allometric development of the head ( Sakagami et al. 1966). The presence of a genal process is characteristic of the sexstrigatus group, but is not known from the japonicum group ( Sakagami et al. 1966; Ebmer et al. 1994; Sakagami & Tadauchi 1995; 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 ( Sakagami et al. 1966). 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.

Species included in Japan

1) L. amamiense Ebmer & Sakagami, 1994

2) L. frigidum Sakagami & Ebmer, 1996

3) L. ikudomei sp. nov.

4) L. kiautschouense ( Strand, 1910)

5) L. ohei Hirashima & Sakagami, 1966

6) L. simplicior ( Cockerell, 1931)

7) L. smilodon Ebmer & Sakagami, 1994

8) L. spectrum sp. nov.

9) L. speculinum ( Cockerell, 1925)

10) L. sphecodicolor Sakagami & Tadauchi, 1995

11) L. subsimplicior sp. nov.

12) L. tadauchii Murao, 2012

13) L. taeniolellum ( Vachal, 1903)

The following 10 species were included as members of the sexstrigatus group sensu Sakagami & Ebmer (1996), Pesenko (2007a), and Murao et al. (2010) in Japan ( Ebmer et al. 1994; Pesenko 2007b; Murao et al. 2010): 1) Lasioglossum (Hemihalictus) bicornutum Murao, 2010 , 2) L. (H.) canaliculatum Murao, 2010 , 3) L. (H.) donanense Murao, 2010, 4) L. (H.) japonicum (Dalla Torre, 1896) , 5) L. (H.) kankauchare (Strand, 1914), 6) L. (H.) latifacies Murao, 2010, 7) L. (H.) silivicolum Murao, 2010, 8) L. (H.) urumaense Murao, 2020, 9) L. (H.) yonaguniense Murao, 2010, and 10) L. (H.) zipangu Ebmer & Sakagami, 1994 . As stated above, these species, except for L. (H.) bicornutum , L. (H.) kankauchare, L. (H.) latifacies, and L. (H.) silvicolum, form a separate clade as the japonicum group ( Fig. 1 ). Both L. (H.) latifacies and L. (H.) silvicolum are included in the japonicum group because males (undescribed) of both species share a non-homoplasious syapomorphy of this group (Murao unpublished). The Japanese specimens of L. (H.) kankauchare recorded by Blüthgen (1925, as Halictus kankaucharis ) have been preserved in ZMHB. I visited ZMHB in 2012 to examine the bee specimens from the Oriental Region. At that time, I also examined the Japanese specimens of L. (H.) kankauchare. As a result, the Japanese specimens of L. (H.) kankauchare recorded by Blüthgen (1925) proved to be a misidentification of L. (H.) japonicum .

Comments on non-Japanese species excluded from the sexstrigatus group

Lasioglossum (Hemihalictus) micante ( Michener, 1993) endemic in Taiwan belongs to the sexstrigatus group sensu Sakagami & Ebmer (1996), Pesenko (2007a) and Murao et al. (2010) ( Michener 1993). According to Michener (1993), a male (holotype) of L. (H.) micante (female unknown) lacks both the genal process of the head and the median process of S8. This species probably belongs to a different species group in the sexstrigatus group. However, since only a male of this species is known, future taxonomic studies of the genus Lasioglossum in Taiwan will be necessary.

Figures

Fig. 2. A, E. Lasioglossum (Hemihalictus) sexstrigatus (Schenck, 1869). A. ♂, lateral habitus. E. ♀, mesepisternum. — B. L. (H.) taeniolellum (Vachal, 1903), ♂, labrum. — C, F. L. (H.) frigidum Sakagami & Ebmer, 1996. C. ♂, cephalic polymorphism. F. ♀, metasomal terga. — D. L. (H.) simplicior (Cockerell, 1931), ♂, cephalic polymorphism. Scale bars: A = 2 mm; B = 0.2 mm; C, E = 0.5 mm; D, F = 1 mm.

Fig. 3. Lasioglossum (Hemihalictus) sexstrigatus (Schenck, 1869), ♂. A. S7–S8. B. Genitalia in lateral view. C. Genitalia in ventral view. D. Genitalia in dorsal view. Scale bars: 0.1 mm.

Fig. 1. A most parsimonious tree resulting from analysis of the matrix in Appendix 3. Black circles indicate non-homoplacious changes, white circles indicate homoplasious change. For characters and character states see Appendix 2.