Extracted from Rightmyer, M. 2008. A review of the cleptoparasitic bee genus Triepeolus (Hymenoptera: Apidae).—Part I Zootaxa: 1710
Description.—Length ca. 9.5–13 mm; ITW 1.8–2.8 mm. Integument black, with dark reddish brown to orange on basal half of mandible, part or entire labrum, and F1, sometimes on apical margin of clypeus, scape,
and pronotal lobe; orange on tegula and legs (except basally on coxae and spurs); dorsum of mesosoma and metasoma with bands of pale yellow setae. Clypeus with faint midline and faint large punctures. Paramedian band long, clearly separated from other pale setae on mesoscutum. Scutellum moderately bigibbous; axillar spine triangular, surpassing scutellum midpoint, with apical point directed inwardly. Mesepisternum with very short, sparse, erect, simple setae; with dense, white, branched setae on upper third (lacking or sparse on
hypoepimeron) and sometimes along margins ventrally; entire ventral half or medioventral area asetose or covered with sparse, brown, branched setae; with contiguous, minute punctures. T1 discal patch transversely ovate, with BTB and ATB not or little interrupted medially; T2 LLB forming acute angle with ATB. Female: Pseudopygidial area semicircular to subtriangular with large amount of basal and lateral shining silvery setae, mostly enclosing median region of coarse setae; shining setae mediobasally often with slight notch; T5 lateral white setae extending basally, surrounding on either side a black median band basal to pseudopygidial area; S2–S4 with white setae (sometimes faint) at apex; S5 slightly downcurved at apex. Male: Unknown.
Comments.—This species is similar to T. circumculus; the two can be differentiated by the pseudopygidial area, in which the basal shining setae is less distinctly differentiated from the apical coarse setae in T. occidentalis; the mesepisternum, which is more densely punctate in T. occidentalis; and by the axillar spine, which is more robust in T. occidentalis.
Distribution.—USA: Colorado, Idaho, Kansas, North Dakota.
Host Records.—Melissodes mizeae Cockerell [= Melissodes (Eumelissodes) menuachus Cresson]?
(Hicks, 1926, two females observed entering and spending time in nests of host).
Floral Records.—Grindelia squarrosa (Pursh) Dunal.
Seasonal Records.—21 August to October (day unspecified).
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