Omalus aeneus (Fabricius, 1787)

Paukkunen, Juho, Berg, Alexander, Soon, Villu, Odegaard, Frode & Rosa, Paolo, 2015, An illustrated key to the cuckoo wasps (Hymenoptera, Chrysididae) of the Nordic and Baltic countries, with description of a new species, ZooKeys 548, pp. 1-116 : 12-13

Taxon classification Animalia Hymenoptera Chrysididae

Omalus aeneus (Fabricius, 1787) Figs 18, 19, 22, 23

Chrysis aenea Fabricius, 1787: 284.

Omalus aeneus : Panzer 1801: 13.

Diagnosis.

Length 3-6 mm. The species resembles closely Omalus puncticollis , but usually has only very small punctures and short pubescence on the mesoscutum (Figs 18, 22), sparser and finer punctation on the pronotum (Figs 18, 22), and a shallower apical notch on T3 (Fig. 23). Some specimens have relatively coarse punctation medially on the pronotum and mesoscutum, but compared to Omalus puncticollis their pubescence is shorter, flagellomeres are longer, and the apical notch of T3 is shallower. In the female, the body is completely deep blue, violet or green (Fig. 18), whereas in the male it is dorsally black and laterally with green or blue reflections.

Distribution.

Denmark, Estonia, Finland, Latvia, Lithuania, Norway, Sweden. Common. - Trans-Palearctic/Holarctic: from western Europe and northern Africa to Japan, China and Taiwan. Possibly accidentally introduced to North America ( Kimsey and Bohart 1991) and Australia ( Krombein 1979).

Biology.

Habitat: forest margins and clearings, semi-open sandy areas. Adults are often observed on sun-exposed leaves of trees and bushes, and they are attracted to honeydew of aphids. Occasionally they are also found on flowers of Apiaceae and Euphorbiaceae ( Trautmann 1927, Hoop 1971, Linsenmaier 1997). Flight period: June to August. Host: Passaloecus corniger Shuckard, Passaloecus eremita Kohl, Passaloecus gracilis (Curtis), Passaloecus singularis Dahlbom, Passaloecus turionum Dahlbom, Pemphredon lethifer (Shuckard), Pemphredon lugubris (Fabricius) and Psenulus pallipes (Panzer) ( Crabronidae ) ( Barbey and Ferriere 1923, Strumia 1997, Gathmann and Tscharntke 1999, our own obs.). The species has been reared from old resin-galls of Retinea resinella ( Tortricidae ) containing host nests. Females oviposit in live aphids and do not enter the host nest (our own obs.). A similar behaviour has been observed in Omalus biaccinctus ( Winterhagen 2015).

Remarks.

Mitochondrial DNA studies indicate that the Nordic and Baltic specimens of Omalus aeneus belong to at least five genetically distinct lineages (excl. Omalus puncticollis ), and several other lineages have been found in other countries ( Paukkunen et al. 2014). It is very likely that more than one species is involved.