The genus Omalus Panzer, 1801 (Hymenoptera, Chrysididae) from China, with descriptions of four new species

Abstract The Chinese species of the genus Omalus Panzer, 1801 are revised and keyed for the first time. Eight species are recorded, of which four are new to science and one is new to China: Omalus aeneus (Fabricius, 1787), Omalus berezovskii (Semenov-Tian-Shanskij, 1932), Omalus potanini (Semenov-Tian-Shanskij, 1932), Omalus imbecillus (Mocsáry, 1889) (new to China), Omalus helanshanus sp. n., Omalus probiaccinctus sp. n., Omalus pseudoimbecillus sp. n., and Omalus tibetanus sp. n.


Introduction
The genus Omalus Panzer, 1801 belongs to the chrysidid tribe Elampini (Chrysidinae). This genus is differently interpreted by different authors, and the complex history of this genus was summarised by Rosa (2006). In this study, we follow the system used for Fauna Europaea (Rosa and Soon 2013), which is slightly altered according to the system of Kimsey and Bohart (1991).

Materials and methods
All specimens were examined and described under a stereomicroscope (Olympus SZ61). All photos were taken with a digital camera (CoolSNAP) attached to a Zeiss Stemi 2000-CS stereomicroscope. Images were processed using Image-Pro Plus software.
Morphological terminology follows Kimsey and Bohart (1991). Abbreviations used in the descriptions are as follows: F-I, F-II, F-III, etc. = flagellum I, flagellum II, flagellum III and so on; L/W = relative length to width; MOD = midocellar diameter; MS = malar space, the shortest distance between the base of the mandible and the margin of the compound eyes; Notaulic pit = the pit on the posterior margin of mesoscutum where notauli originate; PD = puncture diameter; T-I, T-II, T-III, etc. = metasomal tergum I, tergum II, tergum III and so on.
Colouration. Head and mesosoma mostly metallic bluish-purple, with face, mesopleuron and metapleuron metallic green. Antenna black, with scapes and pedicel metallic greenish-blue. Tegula metallic green, with apex brown. Leg metallic bluish-purple, with tarsus brown. Metasoma metallic blue with purple reflections, with T-II blackish dorsally.
Colouration. Head and mesosoma mostly metallic bluish-purple, with distinct or faint metallic green reflections on mesopleuron, metanotum, metapleuron, and propodeum. Antenna black, with scape and pedicel metallic green. Tegula purple, with apex brownish. Leg metallic bluish-purple, with tarsus brown. Metasoma metallic bluishpurple, with some metallic green reflections.
Colouration. Face metallic green. Head and mesosoma metallic blue, with purple reflections on vertex, median pronotum, and mesoscutum. Antenna black, with scape and pedicel metallic greenish-blue. Tegula metallic blue. Leg metallic greenish-blue, with tarsus brown. Metasoma purple, with metallic blue.
Biology. Unknown. Collected in July and August (Semenov-Tian-Shanskij 1932;Kimsey and Bohart 1991). Diagnosis. Omalus probiaccinctus sp. n. is related to O. biaccinctus based on the similar and peculiar punctures on the mesoscutum, which is unique in the West Palaearctic species. However, Omalus probiaccinctus sp. n. can be separated from the latter by having the body mostly metallic greenish-blue (body dark metallic blue or green, black medially on mesoscutum, metanotum, propodeum and metasoma in O. biaccinctus); tarsal claw with four teeth (three in O. biaccinctus); apex of T-III with faint median notch (apex of T-III with distinct, deep median notch in O. biaccinctus).
Male. Unknown. Distribution. China (Guizhou). Biology. Unknown. Collected in June. Etymology. The name probiaccinctus is derived from the Latin preposition proand the chrysidid name biaccinctus. Diagnosis. Omalus pseudoimbecillus sp. n. is similar to O. imbecillus based on the colouration, polished mesoscutum, and oval metasoma. However, it can be distinguished from the latter by having the tegula transparent brownish, with faint metallic reflections anteriorly (fully metallic blue in O. imbecillus); mesopleuron with striae between punctures (without striae in O. imbecillus); propodeal angle distinct and stout (indistinct in O. imbecillus).
Male. Unknown. Distribution. China (Tibet). Biology. Unknown. Collected in June. Etymology. The species is named after the type locality.