Lasioglossum (Dialictus) obscurum (Robertson)

Gibbs, Jason, 2010, Revision of the metallic species of Lasioglossum (Dialictus) in Canada (Hymenoptera, Halictidae, Halictini) 2591, Zootaxa 2591 (1), pp. 1-382 : 215-220

Lasioglossum (Dialictus) obscurum (Robertson)

( Figures 158A–E , 159A–E )

Halictus obscurus Robertson 1892: 270 . ♀.

Lectotype. ♀ USA, Illinois, Apr. 28- May 12 [ INHS: 179,613] by W.E. LaBerge .. Examined.

Dialictus orbitatus Mitchell, 1960: 440 . ♂. [new synonymy]

Holotype. ♂ USA, North Carolina, Bluff Park , Scenic Hgwy., [Doughton Park, Blue Ridge Pkwy], 24.vi.1948 ( T. B. Mitchell); [ NCSU]. Examined.

Taxonomy. Robertson, 1902: Chloralictus obscurus , p. 249 (key); Viereck 1916: Halictus (Chloralictus) obscurus , p. 707 (key); Michener, 1951: Lasioglossum (Chloralictus) obscurum , p. 1115 (catalogue); Mitchell, 1960: Dialictus obscurus ♀, p. 376 (redescription); Krombein, 1967: Lasioglossum (Dialictus) obscurum , p. 465, L. (D.) orbitatum , p. 465 (catalogue); Hurd, 1979: Dialictus obscurum , p. 1969, D. orbitatus , p. 1969 (catalogue); Moure & Hurd, 1987: Dialictus obscurus , p. 117, D. orbitatus , p. 118 (catalogue).

Diagnosis. Females of L. obscurum can be recognised by the diagnostic combination of mesoscutal punctures sparse including the lateral portions ( Fig. 158D ), mesepisternal punctures distinct, propodeal carinae weak ( Fig. 158E ) and metasomal terga without tomentum but with very sparse apical fringes. They are superficially similar to L. nigroviride and L. tenax . Female L. nigroviride have moderately strong propodeal carinae and no fringe hairs on the metasomal terga. Female L. tenax have dense punctures on the lateral portions of the mesoscutum.

Males of L. obscurum can be recognised by the moderately elongate head (length/width ratio = 1.02– 1.05), elongate flagellomeres (length/width ratio = 1.50–1.92), imbricate postgena, polished mesoscutum due to weak microsculpture with sparse fine punctures on central disc (i=1–4d), punctate mesepisternum, apical impressed areas of the metasomal terga impunctate, and sparse plumose hairs on the apicolateral portions of S3–S5. They are similar to L. nigroviride , L. cattellae , L subversans , L. nevadense and L. tenax . Males of L. nigroviride , L. nevadense , L. knereri and L. subversans have distinctly dense plumose hairs on the metasomal sterna. Lasioglossum nevadense and L. knereri are not known to occur within the range of L. obscurum . Male L. tenax have obscure mesepisternal punctures and the punctures of the metasomal terga limited to the basal portions and the premarginal lines. Male L. cattellae are small (4.3–4.5 mm) and have strong mesoscutal and mesepisternal punctures, distinctly lineolate postgena, and moderately sparse hairs on the metasomal sterna.

Redescription. FEMALE. Length 4.88–5.86 mm; head length 1.44–1.58 mm; head width 1.49–1.66 mm; forewing length 3.78–4.70 mm.

Colouration. Head and mesosoma golden green to bluish green. Clypeus with apical half blackish brown and basal half, and supraclypeal area bronze. Antenna dark brown, flagellum with ventral surface brownish yellow. Tegula reddish brown to pale amber. Wing membrane sometimes dusky, venation and pterostigma amber. Legs brown, tarsi reddish brown. Metasoma dark brown, terga and sterna with apical margins translucent brownish yellow.

Pubescence. Dull white. Very sparse. Head and mesosoma with moderately sparse 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 (2–2.5 OD). Metasomal terga with sparse, fine setae. T2–T4 basolaterally with very sparse tomentum. T2 apicolateral and T3–T4 apical margins with very sparse fringes.

Surface sculpture. Face imbricate, punctation fine. Clypeus polished, punctation moderately sparse (i=1– 3d). Supraclypeal area with punctation irregularly spaced (i=1–3d). Lower paraocular area punctation dense (i≤d). Antennocular area punctation moderately dense (i=1–1.5d). Upper paraocular area and frons punctatereticulate. Ocellocular area punctate (i≤d). Gena lineolate. Postgena imbricate. Mesoscutum imbricate, submedial portion polished, punctation fine, moderately sparse between parapsidal lines (i=1–4d) and laterad of parapsidal lines (i=1–2d), dense on anterolateral portions (i≤d). Mesoscutellum polished, submedial punctation sparse (i=2–5d). Axilla punctate. Metanotum imbricate. Preëpisternum rugulose. Hypoepimeral area imbricate-punctate (i=1–1.5d). Mesepisternum imbricate, weakly polished, distinctly punctate (i≤d), more widely spaced on ventral portion (i=1–3d). Metepisternum with dorsal third rugoso-striate, ventral portion imbricate. Metapostnotum incompletely longitudinally striate, posterior margin imbricate. Propodeum with dorsolateral slope and lateral and posterior surfaces imbricate. Metasomal terga coriarious. T1 dorsal surface obscurely, sparsely punctate. T2–T4 punctation on basal halves close (i=1–2d), apical half obscurely punctate (except along premarginal line).

Structure. Head wide (length/width ratio = 0.95–0.97). Eyes convergent below (UOD/LOD ratio = 1.18– 1.20). Clypeus 2/3 below suborbital tangent, apicolateral margins 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 3–4 teeth. Metapostnotum truncate (MMR ratio = 1.21–1.40), posterior margin weakly angled onto posterior surface. Propodeum with oblique carina obscure, lateral carina weak, not reaching dorsal margin.

MALE. Similar to female except for the usual secondary sexual characters and as follows. Length 5.43– 5.92 mm; head length 1.54–1.61 mm; head width 1.51–1.54 mm; forewing length 4.39–4.58 mm.

Colouration. Flagellum with ventral surface pale brownish yellow. Tegula reddish brown. Wing membrane subhyaline, venation and pterostigma reddish brown to pale brownish yellow. Tarsi tan to brownish yellow.

Pubescence. Paraocular area with subappressed tomentum obscuring surface. Clypeus with scattered tomentum not obscuring surface. S3 apical half and S4–S5 lateral portions with dense, erect plumose hairs (1– 2 OD).

Surface sculpture. Mesoscutum polished to imbricate, punctation denser laterad of parapsidal lines (i≤d). Mesepisternum polished, weakly imbricate with distinct punctation (i=1–1.5d). Metapostnotum with coarse rugae, apical margin rounded onto posterior surface. Propodeum with dorsolateral slope and posterior surface of propodeum rugose, lateral surface rugulose. Metasomal terga polished except margins weakly coriarious. T2–T4 punctation on basal portions moderately dense (i=1–2d), apical impressed areas impunctate.

Structure. Head elongate (length/width ratio = 1.02–1.05). Eyes strongly convergent below (UOD/LOD ratio = 1.39–1.58). Antennal sockets distant (IAD/OAD> 1.4). Frontal line carinate, ending 2 OD below median ocellus. Pedicel less than F1. F2 length 1.57–1.69X F1. F2–F10 elongate (length/width ratio = 1.50– 1.92). Metapostnotum moderately elongate (MMR ratio = 1.17–1.20), posterior margin sharply angled onto posterior surface.

Terminalia . S7 with median lobe columnar, apex rounded ( Fig. 159D ). S8 with apicomedial margin weakly convex ( Fig. 159D ). Genitalia as in Fig. 159D–E . Gonobase with ventral arms widely separated. Gonostylus small, dorsal setae elongate. Retrorse lobe narrow, weakly attenuated apically.

Range. Ontario, south to North Carolina, west to Wisconsin, Missouri ( Fig. 160 ).

Additional material examined. CANADA: ONTARIO: 1♀ Pt. Pelee, 7.vi.1961 (G. Knerer) ; USA: ILLI- NOIS: 1♀ Fermilab , 8.viii.2003 (D. Huie) ; MARYLAND: 1♀ Anne Arundel Co., N39.02727 W076.6669, 24–25.vii.2003 ( R. Jackowski); 1♀ Montgomery Co. , N38.97 W077.1565, 24.vi.2006 (S.W. Droege); [ PCYU] ; MICHIGAN: 1♀ Filmore Twp. , 29.vii.2004 (J. Tuell); [ ARC] ; MISSOURI: 1♀ Linn Co., Pershing S.P., Locust Crk. , 12.vii.2000 (Arduser) ; NEW HAMPSHIRE: 1♂ Meredith , 26.viii.1960 ( R. A. Morse); [ PCYU] ; NEW YORK: 6♀ Wayne Co., Endress, Sodus Pt , 19.v.2009 (M.G. Park); [ CUIC]; 1♀ Worchester Co. , Ossining , Clemmons Garden , 21.vii.2005 (E. Fetridge); [ PCYU] ; NORTH CAROLINA: 1♀ Great Smoky Mountain N.P., Cataloochee , N35.62813 W083.09997, 6.viii.2006 (J. Gibbs); [ GSNP]; PENNSYLVA- NIA: 1♀ Montgomery Co., MapleA, N40.194 W075.369, 7.vii.2004 (L. Kurtz) ; TENNESSEE: 1♀ HWY 321, nr Gatlinburg , N35.75988 W083.3615, 8.viii.2006 (J. Gibbs) ; VERMONT: 1♂ Lamoille Co., 4.5 mi NE Hyde Park , 28.vii.2006 (M.F. Veit) ; VIRGINIA: 1♀ Frederick Co., N39.1928 W078.4197, 27.v.2005 (S.W. Droege); 1♀ KOA, 15 km N of Harrisonburg , N38.534 W078.704, 6.vi.2005 (A. Zayed) ; WEST VIRGINIA:

1♀ Hampshire Co., N39.2479 W078.5267, 6–8.viii.2006 (Students) ; 1♀ Hampshire Co., N39.2489 W078.5256, 30.vii.2005 [ PCYU] .

Floral records. ANACARDIACEAE : Rhus , APIACEAE : Chaerophyllum procumbens , Osmorhiza longistylis , ASTERACEAE : Boltonia asteroides , Coreopsis palmata , Heliopsis helianthoides , Pseudognaphalium obtusifolium , Rudbeckia , Symphyotrichum pilosum pilosum , S. ericoides ericoides , BRASSICACEAE : Arabis shortii , A. laevigata , Barbarea , CAPRIFOLIACEAE : Symphoricarpos orbiculatus , CARYOPHYLLACEAE : Stellaria media , CORNACEAE : Cornus florida , FABACEAE : Melilotus , Robinia , HYDROPHYLLACEAE : Ellisia nyctelea , Hydrophyllum , LAMIACEAE : Stachys , LILIACEAE : Maianthemum racemosum , M. stellatum , ONAGRACEAE : Circaea lutetiana , POLEMONIACEAE : Polemonium reptans , POLYGONACEAE : Fagopyrum , PORTULACACEAE : Claytonia virginica , RANUNCULACEAE : Aquilegia , Enemion biternatum , Ranunculus recurvatus , R. hispidus nitidus , ROSACEAE : Aruncus , Prunus persica , Spiraea , RUBI- ACEAE: Galium aparine , SCROPHULARIACEAE : Lindernia dubia .

Additional floral records for an Eastern Kansas species tentatively identified as this species are as follows. ANACARDIACEAE : Rhus aromatica , R. glabra , ASTERACEAE : Echinacea purpurea , Rudbeckia , BRAS- SICACEAE: Erysimum repandum , FABACEAE : Amorpha canescens , A. fruticosa , Dalea , Medicago sativa , Melilotus officinalis , Robinia pseudoacacia , HIPPOCASTANACEAE : Aesculus glabra glabra , LAMI-

ACEAE: Monarda fistulosa , M. f. fistulosa mollis , LILIACEAE : Camassia scilloides , RHAMNACEAE : Ceanothus herbaceus , ROSACEAE : Crataegus , Fragaria virginiana , Malus pumila , Prunus serotina , Zizia aurea , SALICACEAE : Salix .

Biology. Reinhard 1924: (predator); Evans & Lin, 1959: (predator); Michener, 1966: (life history, nest architecture, floral relationships, as obscurus ?).

Comments. Uncommon.

Michener (1966) considered the species called L. obscurus ? as very similar to L. versatum . These species are easily separable which suggests that the species studied by Michener may not have been L. obscurum .

Figures

FIGURE 158. Lasioglossum obscurum (Robertson). Female (A) lateral habitus; (B) dorsal habitus; (C) face; (D) mesoscutum; (E) metapostnotum. Scale bars, A–C = 1 mm.

FIGURE 159. Lasioglossum obscurum (Robertson). Male (A) lateral habitus; (B) dorsal habitus; (C) face; (D) ventral view of genital capsule, S7, S8; (E) dorsal view of genital capsule. Scale bars, A–C = 1 mm, E = 0.5 mm.

FIGURE 160. Distribution of Lasioglossum obscurum (dark grey) and L. occidentale (light grey).