Stelis occidentalis, n. sp

(Figs. 2, 12, 22, 32)

Diagnosis. This species, together with S. coarctatus and S. lamelliterga, form a group distinguishable from all other Nearctic Stelis by the combination of the second recurrent vein interstitial with the second traverse cubital or distal to it; body black with white lateral spots on the terga; metasoma elongate, almost cylindrical in cross section; wings entirely dark (not reddish basally); a single apical spine on the hind tibia; terga with narrow impunctate apical lamellae; and scutellum not overhanging the metanotum and propodeum. Stelis occidentalis differs from other species of the group in the long apical tibial spines of the fore and mid legs and the restriction of apical lamellae to only T1 – T3. It further differs from S. coarctatus in the absence of clear pitting medially on the subhorizontal basal shelf of the propodeum.

Description. Female. Length 5 mm, forewing length 4 mm. Black; forewing lightly stained apically in marginal cell; mandible reddish subapically; T1 – T3 with small white oval spots laterally. Pubescence white, moderate on head, mesosoma; terga sparsely pubescent, apical terga with long erect hair, sterna with moderate, uniformly distributed pubescence; legs with dense appressed hair mixed with larger erect setae. Punctation of clypeus fine, contiguous; punctures on frons, vertex, gena, mesosoma dense but not contiguous; basal zone of propodeum narrow with 4 small lateral cells, medially pitted; spiracular opening not in pit, hind surface of propodeum impunctate medially; terga shiny with small moderately dense punctures, T6 more coarsely pitted, punctures separated by shiny integument; T1 – T3 with short preapical lamellae; T4, T5 with preapical carina not overhanging margin; sterna more coarsely punctate, dull. Head slightly broader (1.1X) than long; mouthparts short, not extending beyond fossa in repose; gena slightly wider (1.1X) than eye in lateral view; eyes slightly converging below, DLID>1.0X <1.1X BLID, IOD <(0.9X) OOD> (1.1X) OPD> (1.3X) LOPD, IOD> (2.3X) LMOD; pronotal lobe weakly carinate; anterior surface of mesepisternum not concave; apical spines on fore, midtibiae long, anterior spines as long as width between spines, anterior apical spine of hindtibia long, TIB>(1.5X) BAT<(1.2X) TAR; second recurrent vein ending beyond second transverse cubital; pseudomargin of T6 with carina slightly upturned, rounded medioapically (Fig. 12); basal depression on S5 wide, incurved medially.

Male. Length 3.5 to 5 mm. As in female except: T6 with strong apical flange; T7 with prominent medioapical spine and lateral angle; S2 bowed, apical margin sharply depressed; S3 with circular basin-like median depression, apical margin of sternum with hair fringe (Fig. 22); S4 with small median comb as wide as 1/ 7X width of sternum, thick narrow hairbrush basal to comb (Fig. 32); S5 with sharp, deep V-shaped notch on apical margin; S6 rounded apically; S7 bifurcate or truncate.

Type material. Holotype female. “IDA Owyhee Co Bruneau Sand Dunes, Reared F. D. Parker“/”Rearing No. 27929B” [ex nest Ashmeadiella aridula Cockerell]. Paratypes. IDAHO, Owyhee Co: 5 Ƥ, 9 3, same data as holotype except rearing number; NEVADA, Churchill Co: 1 Ƥ, Blow Sand Mountain, 28 Jun 1980, Bechtel, Rust; 1 Ƥ, 2 3, Hazen, 3 mi W, reared, FD Parker; Elko Co: 1 Ƥ, 1 3, Wells, 10 mi E, reared, FD Parker; Humboldt Co: 1 3, Winnemucca Dunes, reared, FD Parker; Lyon Co: 1 Ƥ, Fernley Dunes, reared, FD Parker; Washoe Co: 2 Ƥ, 2 3, Nixon, reared, FD Parker; 4 Ƥ, 4 3, Nixon, 2 mi N, reared, FD Parker; 2 Ƥ, Verdi, reared, FD Parker. Holotype and paratypes deposited in BBSL.

Variation. The carina on the pronotal lobe is absent in some specimens. While presence or absence of carinae are typically fixed within species of Anthidiini, they are sometimes weak and variable in species of Stelis. Some individuals have a whitish spot on T4, rarely spots are absent on T3 and T4. A single male from the mountains of northern Utah lacks maculations entirely. Male T7 with lateral angle occasionally forming blunt tooth.

Distribution. Stelis occidentalis, as its name implies, is a western North American species, found from southern British Colombia, Canada to northern Baja California, Mexico and as far east as Idaho, Utah and New Mexico.

Biology. FDP has reared specimens of Stelis occidentalis from vertically placed trap stems and block traps placed at 29 localities in California, Arizona, Utah, Nevada, Idaho, and New Mexico. The most common host bees were species of Ashmeadiella (82%). The species and numbers of nests parasitized of Ashmeadiella were: A. gillettei Titus (11); A. aridula (9); A. bigeloviae (Cockerell) (4); A. breviceps Michener (2), A. rufipes Titus (1); A. meliloti (Cockerell) (1) and A. spp. (3). Eighteen percent of S. occidentalis specimens were reared from cells of a related megachilid genus, Hoplitis, namely H. bullifacies Michener (2), H. shoshone (Parker) (1), H. pygmaea (Timberlake) (1) and H. (Alcidamea) spp.

Etymology. The Latin occidentalis, of the west, is most appropriate for this wide ranging western North American Stelis.