Taken from:
R. M. Bohart and L. S. Kimsey. 1982. A Synopsis of the Chrysididae in America North of Mexico.
Pseudomalus janus (Haldeman)
Hedychrum janus Haldeman 1844:53. Neotype female, Mt. MacIntire, New York (Cornell).
Elampus coruscans Norton 1879:234. Lectotype female. Canada (ANSP).
Omalus corruscans Aaron 1885:214. In error.
Omalus semicircularis Aaron 1885:215. Lectotype male, Colorado (ANSP). New synonym.
Discussion: The identity of janus was settled by Bohart and Campos (1960:242). Externally the best features are the green to green blue mesopleuron and usually obtuse apical notch of T-III. The forefemur is unusually broad and sharp edged, especially in the female (fig. 74). Among our four species of Pseudomalus the male genitalia of Janus is distinctive since the cuspis projects posteriorly only a little farther than the digitus (fig. 91). Modal body length is 5.0 mm. Krombein (1979:1223) considered semicircularis as a distinct species. After reexamination of the type, we place it under janus.
Hosts: Pemphredon concolor Say, P. confertim W. Fox (as errans Rohwi) (Krombein 1979:1223).
Material examined: 74 males including type of semicircularis, 108 females including neotype of janus and lectotype of coruscans.
Distribution: widespread and from coast to coast in U.S. and southern Canada. Most specimens have been collected in the Transition and Canadian Life Zones.
Subgenus Pseudomalus Ashmead
Pseudomalus Ashmead 1902:229. Generotype: Omalus semicircularis Aaron 1885 (janus Haldemann 1844), monotypic.
Discussion: Our four species of this subgenus are medium small and all have a characteristic clump of large punctures posteromedially on the scutum (fig. 61) and the pubescence on the abdomen is unusually long. The notauli are complete and end posteriorly in a large pit. The metanotum is broadly rounded.
Key to subgenus Pseudomalus
1. Tergal color reddish or greenish to golden, strongly contrasting with thoracic coloration
..auratus (Linnaeus)
Tergal color blue, green or purple, not contrasting with thoracic coloration
. 2
2. Scutum swollen anteriorly on either side of notauli, appearing trilobate in anterior view (fig. 73); area between notauli and parapsidal lines polished with small evenly distributed punctures
trilobatus Bohart and Campos
Scutum not swollen on either side of notauli; area between notauli and parapsidal lines often with fine striations or scratches, or irregularly and coarsely punctate
...3
3. Mesopleuron generally bluish to purple, T-III with acute apical notch (fig. 85), female forefemur about three times as long as broad (fig. 75)
..purpuratus (Provancher)
Mesopleuron predominantly green or greenish blue, T-III usually with obtuse apical notch, female forefemur about 2.5 times as long as broad (fig. 74)
...janus (Haldeman)
Genus Omalus Panzer
Diagnosis: forewing medial vein strongly arched (fig. 59), median and submedian cells practically asetose, RS stub at least as long as stigma and extending beyond it apicad; tarsal claws with two to five subsidiary teeth (figs. 68-72), forefemur partly to strongly carinate beneath but not angled; mesopleuron simple; T-III nearly always with an apicomedial notch.
Discussion: As presently constituted, Omalus in North America contains three subgenera and 17 species. This compares with more than 100 species worldwide. Nine of the U.S. species are found only west of the 100th meridian.
For the most part Omalus are medium to small wasps which as far as known parasitize relatively small aphid-storing pemphredonine wasps. Most of the latter are twig nesters and several have been reared from old bee burrows in rose canes. Transport of roses by ship in the 16th and 17th centuries may have been the route by which auratus and possibly aeneus reached our eastern shores.
Specimens of Omalus are fairly often taken by wasp collectors, and we have examined 4, 600. Bohart and Campos (1960) revised North American species of the genus and clarified the relationship to Elampus. Both genera have a practically asetose median cell and a strongly arched median vein. Also, two species of Omalus have the Elampus-like features of projecting metanotum and a membrane in the truncation of T-III. A critical difference in Elampus is the long genal fringe in males and short setiform fringe in females. Omalus of both sexes have the genal fringe rather short and sparse. Furthermore, the association of scutal punctures with the notauli in the Elampus-like forms points to Omalus (Diplorrhos).
Sex recognition in Omalus is difficult unless male genitalia or the female sting are visible. Other identifying features of males are the more evenly concave S-Ill toward the apex and the shorter more rotund T-III. Also, males tend to be darker than females but this character is not dependable.
Key to subgenera of Omalus
1. Scutal punctures clumped along notauli, leaving extensive lateral and medial impunctate areas (fig. 65); metanotum usually angulate in lateral view (fig. 77)
..Diplorrhos Aaron p. 42
Scutal punctures not particularly clumped along notauli, either scattered randomly or clumped posteriorly between notauli, occasionally almost impunctate
..2
2. Scutum with large shallow punctures clumped posteriorly between notauli (fig. 61); tarsal claws with three to six subsidiary teeth (fig. 69)
Pseudomalus Ashmead p.40
Scutum almost impunctate or with evenly scattered small punctures (fig. 62); tarsal
claws usually with two subsidiary teeth (figs. 68, 70)
Omalus s. s. Panzer p.37
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