(Figures 132, 133)
Halictus hemimelas Cockerell, 1901: 285. Ƥ.
Holotype. Ƥ USA, [New Mexico], top of the Las Vegas range, 29.vi. 1901, (Cockerell); [NMNH: 12073].
Taxonomy. Michener, 1951: Lasioglossum (Chloralictus) hemimelas, p. 1114 (catalogue); Moure and Hurd, 1987: Dialictus hemimelas, p. 103 (catalogue).
Diagnosis. Female L. hemimelas can be recognised by the following diagnostic combination: T 1 anterior surface with evenly distributed erect hairs but acarinarial fan completely absent (Fig. 133), metapostnotal rugae nearly reaching posterior margin (Fig. 133), and T 2 apical impressed area impunctate. They are most similar to L. versans and L. ruidosense (Cockerell), both of which have the metapostnotal rugae short not reaching more than 2 / 3 distance to posterior margin.
Male unknown.
Redescription. FEMALE. Length 5.80–6.16 mm; head length 1.80 mm; head width 1.66 mm; forewing length 4.21–4.27 mm.
Colouration. Head and mesosoma faintly bluish green, nearly brown on parts of face and propodeum. Clypeus with apical half blackish brown, basal half, and supraclypeal area bronze. Antenna dark brown, flagellum with ventral surface brown to reddish brown. Tegula dark reddish brown. Wing membrane subhyaline, venation and pterostigma reddish brown. Legs dark brown, medio- and distitarsi reddish brown. Metasoma dark brown, terga and sterna with marginal areas reddish brown.
Pubescence. Dull white. Sparse. Head and mesosoma with moderately dense woolly hairs (1–1.5 OD), longest on genal beard, metanotum, and mesopleuron (2–2.5 OD). Lower paraocular area and gena without subappressed tomentum. Propodeum with moderately dense plumose hairs on lateral and posterior surfaces (1.5–2 OD). Metasomal terga with sparse, fine hairs. T 1 acarinarial fan absent, declivitous surface with sparse, erect hairs (1.5 OD). T 2 –T 4 with dense tomentum basolaterally. T 4 apical margins with very sparse fringe.
Surface sculpture. Face imbricate, punctation fine. Clypeus with apical half polished, punctation moderately sparse (i= 1–2 d). Supraclypeal area with punctation sparse (i= 1–4 d). Lower paraocular and antennocular areas with punctation moderately sparse, shallow (i= 1–2 d). Upper paraocular area, frons, and ocellocular area reticulate-punctate. Gena lineolate. Postgena imbricate. Mesoscutum tessellate-imbricate, punctation fine and shallow, moderately dense between parapsidal lines (i= 1–1.5 d), dense laterad of parapsidal line (i≤d), contiguous on anterolateral portion. Mesoscutellum polished, weakly imbricate, submedial punctation moderately dense (i= 1–3 d). Axilla punctate. Metanotum reticulatepunctate. Preëpisternum weakly rugulose. Hypoepimeral area ruguloso-imbricate. Mesepisternum granular-imbricate, obscurely punctate ventrally. Metepisternum with dorsal third rugoso-carinulate, ventral portion imbricate. Metapostnotum with fine anastomosing rugae, not extending much more than ¾ distance to posterior margin, posterior half weakly imbricate. Propodeum with dorsolateral slope weakly imbricate, lateral surface imbricate-tessellate, posterior surface tessellate. Metasomal terga polished except apical impressed areas weakly coriarious, punctation on basal halves distinct (i= 1.5–2 d), T 1 –T 2 apical impressed areas impunctate, T 3 –T 4 apical impressed areas impunctate anterolaterally.
Structure. Head elongate (length/width ratio = 0.99–1.09). Eyes convergent below (UOD/LOD ratio = 1.19). Clypeus 3 / 4 below suborbital tangent, apicolateral margins strongly convergent. Antennal sockets close (IAD/OAD <0.5). Frontal line carinate, ending 2 OD below median ocellus. Gena narrower than eye. Inner metatibial spur pectinate with 3 branches. Metapostnotum moderately elongate (MMR ratio = 1.23), posterior margin rounded onto posterior surface. Propodeum with oblique carina virtually absent, lateral carina weak, reaching less than halfway to dorsal margin.
MALE. Unknown
Range. New Mexico, possibly Colorado, Wisconsin (Fig. 131). USA: NM, CO, WI?.
Additional material examined. USA: COLORADO: 1 Ƥ Rio Grande, the south fork, N 37 ° 33 ʹ W 106 ° 47 ʹ, 9250 ft., 18–19.vi. 1919; [AMNH]; WISCONSIN: 1 Ƥ Oconto Co., Sunrise Lake Rd., N 45 ˚ 13.4571 ʹ W 88 ˚ 27.5446 ʹ, 24.v. 2005 (A. Wolf); [PCYU].
DNA Barcode. Available. Single sequence.
Comments. Rare. Lasioglossum hemimelas has not been recorded from the eastern USA except for a single specimen from Wisconsin (see Wolf & Ascher 2009). The Wisconsin specimen has been DNA barcoded and is distinct from L. versans. The Wisconsin specimen is disjunct from the species’ type locality. This is a member of the L. ruidosense species-group (defined below), which contains only three nominal species but may be much more diverse (J. Gibbs unpublished data). Populations of the L. ruidosense species-group, such as those at the type locality of L. hemimelas are typically limited to high elevations in the south-western USA or high latitudes, ranging to the arctic. Such high altitude populations may be isolated to such an extent that they warrant being considered distinct species. It is possible that the Wisconsin specimen, although matching the diagnostic characters of L. hemimelas, will prove not to be conspecific. The Wisconsin specimen has a shorter head (length/width ratio = 0.99) than the holotype and the name is applied to the Wisconsin specimen with some uncertainty.