Lasioglossum forbesii (Robertson 1890)

Lasioglossum forbesii (Robertson)

Halictus Forbesii Robertson, 1890:315 [female, male].

Halictus forbesii.—Robertson, 1894 [emendation, flower records].—Cockerell, 1897:163 [flower and locality records]; 1898c:51 [taxonomic notes]; 1906:294 [locality record].—Graenicher, 1907 [flower records]; 1909 [flower records].—Cresson, 1928:60 [lectotype designation].

Lasioglossum forbesii.—Robertson, 1902:247 [key].—Michener, 1951:1106 [Nearctic catalog].—Evans, 1955:47 [predator, Philanthus sanbornii Cresson].—Mitchell, 1960:342 [redescription, key].—Knerer and Atwood, 1962:163 [nest, locality and flower records]; 1967:104 [conopid parasitoid].—Hurd, 1979:1957 [Nearctic catalog].

Curtisapis forbesii.—Robertson, 1918:91 [taxonomic notes]; 1929 [flower records].

Halictus forbesi.—Michener, 1951:1106.—Hurd, 1979: 1957 [lapsus calami].

TYPE MATERIAL.—The female lectotype of Halictus forbesii, designated by E.T. Cresson (1928), is deposited in the Academy of Natural Sciences at Philadelphia. The specimen is in excellent condition and is labeled

Robertson S.[outhern] Illinois/LectoTYPE 4257 [red label]/Halictus Forbesii Rob.[ertson] [handwritten].

I have not examined the other three females and two males from Robertson's original series; they are presumably also in Philadelphia.

DISTRIBUTION (Figure 406).—Although Lasioglossum forbesii is partly sympatric with L. acuminatum and L. paraforbesii it has the most southern distribution among species of the forbesii group. It is found from New York to Wisconsin and south to Oklahoma, Arkansas, and North Carolina.

DIAGNOSIS.—The hair fringe that surrounds the glabrous central area of the acarinarium on the anterior surface of tergum I is distinctively formed in L. forbesii. The elongate fringe hairs extend laterally on the tergal surface and form an extensive and thick hair patch with a distinctly transverse dorsal margin (Figure 408). The dorsal opening of the acarinarial hair fringe is extremely narrow, much more so than that of L. paraforbesii (Figure 409). The acarinarium of L. acuminatum, the other species in the forbesii group, is uniquely arrow-shaped (Figure 407). Other characters helpful in recognizing L. forbesii are the short head (Figure 425, length/width ratio x = 0.89, n = 20; head longer in L. paraforbesii, Figure 434, x = 0.92, n = 20) and the sharply-edged, posterolateral edges of the dorsal propodeal surface (this was mentioned in Robertson's original description).

Among forbesii group males (see above diagnosis of the forbesii group) the males of L. forbesii cannot reliably be separated from those of L. paraforbesii. Lasioglossum forbesii males have wider heads than those of the latter species (Figure 426, length/width ratio x = 0.90, n = 20; compare with Figure 435, x = 0.93, n = 20) but this character is at best difficult to work with. The extremely elongate mandibles of L. acuminatum males (Figure 411) will differentiate them from the above species.

DESCRIPTION.—FEMALE: (1) Length 7.0–9.4 mm (x = 8.5, n = 20); (2) wing length 2.1–2.8 mm (x = 2.5, n = 20); (3) abdominal width 2.4–3.1 mm (x = 2.7, n = 20).

Structure: (4) Head short (Figure 425; length/width ratio 0.83–0.96, x = 0.89, n = 20). (7) Supraclypeal area evenly rounded, (8) moderately protuberant. (9) Clypeus projecting approximately 0.64 of its length below lower margin of eyes; (11) surface without median longitudinal sulcation. (14) Distance between lateral ocelli subequal to distance between lateral ocellus and eye. (23) Flagellomere 1 slightly shorter than 2 along dorsal surface. Labrum as in Figure 427; (27) distal keel moderately narrow as seen in frontal view, lateral edges slightly bowed; (28) distal lateral projections weakly developed, rounded; (29) some fimbrial setae bluntly rounded.

(32) Pronotal lateral angle broadly obtuse; (33) pronotal lateral ridge incomplete, interrupted by oblique lateral sulcus; (34) lower portion of lateral ridge sharply edged. (35) Mesoscutal lip weakly bilobed, (36) moderately elevated from pronotum. (40) Dorsal surface of propodeum about 0.82 the length of scutellum and about 1.6 times the length of metanotum, (41) slightly depressed centrally, (42) posterior margin broadly rounded; (43) propodeal triangle moderately well defined, evident medially as a V-shaped elevation with sharply-edged lateral rims, fading towards metanotum; (44) lateral carinae extending at most half the length of posterior surface. (45) Tibial spur similar to Figure 46.

(46) Lateral edge of metasomal tergum II moderately sinuate.

Sculpture: (47) Face shiny, (48) punctures moderately dense below ocelli, separated by at most their width, becoming less dense near antennae. (51) Supraclypeal area weakly granulate, (51) uniformly punctate, punctures separated by 1–2 times their width. (53) Clypeus polished; (54) punctures separated by their width basally, becoming less dense apically and apicolaterally. (56) Mesoscutum moderately shiny; (57) punctation as in Figure 430, punctures separated by their width or less laterally and anteriorly, less dense centrally, punctures 1–4 times their width apart. (58) Scutellum very sparsely punctate adjacent to median line, punctures 2–3 times their width apart. (63) Dorsal surface of propodeum (Figure 429) ruguloso-striate laterally, rugulose medially; (64) surface alveolated. (65) Metasomal tergum I moderately shiny; (66) punctation fine, dense, punctures slightly less than their width apart.

Coloration: (71) Wing membrane pale yellowish brown.

Vestiture: (74) Pubescence of head white. (75) Pubescence of thorax white; (76) mesoscutal hairs moderately sparse and plumose. (77) Hind tibial hairs concolorous, yellowish brown. (78) Anterior hairs of metasomal tergum I and (76) basal hair bands of terga II-IV white. (80) Acarinarium present (Figure 408), a very small circular, glabrous area surrounded laterally and dorsally by elongate fringe hairs, dorsal fringe hairs forming a straight-edged acarinarial border; opening of acarinarium extremely narrow, width of opening approximately one-third the width of lateral fringe hairs as seen in dorsal view.

MALE: Similar to female except as follows: (1) length 6.7–8.6 mm (x = 7.5, n = 20); (2) wing length 1.9–2.3 mm (x = 2.0, n = 20); (3) abdominal width 1.7–2.1 mm (x = 1.9, n = 20). (4) Head as in Figure 426 (length/width ratio 0.85–0.95, x = 0.88, n = 20). (5) Gena subequal to eye in width, (6) moderately produced posteriorly. (10) Clypeal surface shallowly depressed ventrally. Labrum as in Figure 428; (24) distal process weakly developed, slightly projecting but not acutely pointed as in L. acuminatum and L. paraforbesii; (25) basal area depressed medially; (26) basal lateral depressions absent. (30) Mandible short, just reaching opposing clypeal angle. (53) Clypeus polished; (54) punctures well formed and dense basally, very fine and scattered over apical two-thirds. (68) Clypeal maculation present (Figure 426). (69) Flagellum pale yellowish orange ventrally, contrasting with dark dorsum. (72) Tarsi yellow to yellowish orange. ventrally, contrasting with dark dorsum. (72) Tarsi yellow to yellowish orange.

Vestiture: Sternal vestiture as in Figures 416, 417; (82) hairs on sternum IV erect, elongate, becoming shorter laterally; (83) sternum V with some inconspicuous erect hairs but without noticeable hair patterns or lobes.

Terminalia: Sterna VII-VIII as in Figure 431; (85) sternum VIII with elongate, slender median process, slightly broader apically than along stem. Genitalia similar to Figures 419–422; (86) gonobase moderately elongate; (87) gonostylus elongate, moderately slender, tapering to acute apex (Figure 432, more slender than that of L. acuminatum)., (89) retrorse membranous lobe extremely slender; (90) volsella with prominent lateral lobe.

FLIGHT RECORDS (Figure 433).—Females of L. forbesii have been collected from late March (one female from southern Illinois and the other from Raleigh, North Carolina) through September, with a peak in late April. Males have been taken from June to August, with one record from late October (Black Mountains, North Carolina).

FLOWER RECORDS.—Females (45): Rosaceae 29%; Leguminosae 16%; Salicaceae 13%. Males (9): Leguminosae 50%. Total: 54 in 14 families, 20 genera as follows:

*Amorpha 3(1) Apocynum 1, Ceanothus 1, 2; Cercis 1; Claytonia 2; Galax 1; Houstonia 1; Hydrangea 1; Koellia 1; *Melilotus 6(1), 4; *Prunus 4(2); Rhamnus 3; *Rhus 4(3); *Rubus 7(7); Salix 6; *Senecio 1(1); Spirea 2; Taraxacum 1; Thaspium 1; Vitex 1.

SPECIMENS EXAMINED.—196(147, 49).

UNITED STATES. ARKANSAS: Cleburne Co.; Marion Co. DISTRICT OF COLUMBIA. ILLIONOIS: Champaign Co.: Urbana. INDIANA: Posey Co.: Mt. Vernon, 2 mi E, 5 mi S; Tippecanoe Co. KANSAS: Anderson Co.: Garnett; Dickinson Co.; Douglas Co.; Miami Co.; Pottawatomie Co.: Little Gobi Desert; Riley Co.: Manhattan, Marlatt. MICHIGAN: Clinton Co.: Grand Ledge; Ingham Co.: East Lansing. MISSOURI: Boone Co.: Columbia; Dallas Co.: Buffalo; Franklin Co.: Missouri Botanical Garden Arboretum (Gray Summit); Greene Co.: Atherton, Willard; Howell Co.: Willow Springs; St. Louis Co.: St. Louis; Shannon Co.: Round springs. NEBRASKA: Lancaster Co.: Lincoln. NEW JERSEY: Burlington Co.: Medford Lakes. NEW YORK: Rensselaer Co.: Brainard; Suffolk Co.: Fire Island. NORTH CAROLINA: Allegheny Co.: Scenic Highway; Avery Co.: Grandfather Mt.; Macon Co.: Highlands; McDowell Co.: Marion; Wake Co.: Raleigh. OHIO: Clark Co.: Springfield; Franklin Co.: Columbus; Highland Co.; Hocking Co.; Ottawa Co.: Put-In-Bay; Ross Co. OKLAHOMA: Payne Co.: Stillwater, 3 mi E. PENNSYLVANIA: Fayette Co.: Uniontown; Westmoreland Co. VIRGINIA: Arlington Co.: Glencarlyn; Fairfax Co.: Falls Church; Montgomery Co.: Blacksburg. WEST VIRGINIA: Randolph Co.: Cheat Mt. WISCONSIN: Crawford Co.: Gays Mills; Dane Co.: Belleville, Eagle Heights; Lafayette Co.; Waushara Co.: Wild Rose.