Apathus citrinus Smith, 1854:385, ♂. ♂, United States (B.M.). - Lutz & Cockerell, 1920Lutz, F.E. & T.D.A. Cockerell 1920. Notes on the distribution and bibliography of North American bees of the families, Apidae, Meliponidae, Bombidae, Euglossidae, and Anthophoridae. Bull. Amer. Mus. Nat. Hist 42 (15):491-641. (distribution), 542 ( listed as synonym of Bombus laboriosus Fabricius, 1804). - As Bombus citrinus: - Owens et al., 2018Owens, B.E., L. Allain, E.C. van Gorder, J.L. Bossart & C.E. Carlton 2018. The bees (Hymenoptera: Apoidea) of Louisiana: An updated, annotated checklist. Proceedings of the Entomological Society of Washington 120 (2):272-307. (distribution). - As Psithyrus citrinus: - Dalla Torre, 1896Dalla Torre, C.G. 1896. Catalogus Hymenopterorum hucusque descriptorum systematicus et synonymicus, X. Apidae (Anthophila). Sumptibus Guilelmi Engelmann, 1-643. (distribution); Mitchell, 1962Mitchell, T.B. 1962. Bees of the Eastern United States. Volume II. Technical bulletin (North Carolina Agricultural Experiment Station) 152:1-557. (distribution); Krombein et al., 1979Krombein, K.V., P.D. Hurd, D.R. Smith & B.D. Burks 1979. Catalog of Hymenoptera in America North of Mexico. Volume 2. Apocrita (Aculeata). Smithsonian Institution Press, Washington D.C. 1199-2209. (distribution).
Apathus contiguus Cresson, 1863:112, ♂. 4 ♂♂, Conn., Penn., Del. (Coll. E. Norton, and Ent. Soc. Philad.). - Cresson, 1863Cresson, E.T. 1863. List of North American species of Bombus and Apathus. Proceedings of the Entomological Society of Philadelphia 2:83-116. (distribution); Handlirsch, 1888Handlirsch, A. 1888. Die Hummelsammlung des k. k. naturhistorischen Hofmuseums. Annalen des Naturhistorischen Museums in Wien 3:209-250.:248 ( listed as synonym of Psithyrus citrinus (Smith, 1854)); Lutz & Cockerell, 1920Lutz, F.E. & T.D.A. Cockerell 1920. Notes on the distribution and bibliography of North American bees of the families, Apidae, Meliponidae, Bombidae, Euglossidae, and Anthophoridae. Bull. Amer. Mus. Nat. Hist 42 (15):491-641. (distribution), 542 ( listed as synonym of Bombus laboriosus Fabricius, 1804); Mitchell, 1962Mitchell, T.B. 1962. Bees of the Eastern United States. Volume II. Technical bulletin (North Carolina Agricultural Experiment Station) 152:1-557.:540 ( listed as synonym of Psithyrus citrinus (Smith, 1854)); Krombein et al., 1979Krombein, K.V., P.D. Hurd, D.R. Smith & B.D. Burks 1979. Catalog of Hymenoptera in America North of Mexico. Volume 2. Apocrita (Aculeata). Smithsonian Institution Press, Washington D.C. 1199-2209.:2206 ( listed as synonym of Psithyrus citrinus (Smith, 1854)).
Psithyrus laboriosus Frison, 1921:100 - Mitchell, 1962Mitchell, T.B. 1962. Bees of the Eastern United States. Volume II. Technical bulletin (North Carolina Agricultural Experiment Station) 152:1-557.:540 ( listed as synonym of Psithyrus citrinus (Smith, 1854)).