The present study covers the family Gasteruptiidae from Germany and adjacent areas, with a single genus Gasteruption. The main source of material includes specimens from Central Europe deposited in the collections of the SNSB-Zoologische Staatssammlung München, Germany (ZSM), Biologiezentrum Linz, Austria (OLL) and the private collections of Christian Schmid-Egger (CSE) and Petr Bogusch (PB). Some specimens of Central European species were collected in countries other than Germany, mainly in northern Italy, because these species are rare or even close to extinction in Central Europe and, therefore, virtually impossible to obtain from this region. Specimens from the remaining families are deposited in the ZSM or the private collection of CSE.

Specimens were identified to species level using van Achterberg and Talebi (2014) and Bogusch (2021). A complete list of voucher specimens that were treated in the present study is given in Suppl. material 1.

For DNA extraction, a single leg was removed from each specimen and sent to the Canadian Centre for DNA Barcoding (CCDB) in Guelph, Canada, for DNA extraction and barcode sequencing. DNA extraction, PCR amplification, and sequencing were conducted using standardised high-throughput protocols (Ivanova et al. 2006). The 658bp target region, starting from the 5’ end of the mitochondrial cytochrome c oxidase I (COI) gene, includes the DNA barcode region of the animal kingdom (Hebert et al. 2003). Specimens that were successfully sequenced are listed in Suppl. material 1, with sequence lengths and the number of unresolved bases. All specimen data are accessible in BOLD as a single citable dataset (dx.doi.org/10.5883/DS-GBGAST). The data include collecting locality, geographic coordinates, elevation, collector, one or more digital images, identifier, and voucher depository. Sequence data can be obtained through BOLD and include a detailed Laboratory Information Management System (LIMS) report, primer information, and access to trace files.

We only analyse Gasteruption sequences here. Sequences of remaining Hymenoptera families are not shown here, but data are available in the BOLD system. Sequence divergence statistics were calculated using the Kimura two-parameter model of sequence evolution (Kimura 1980). Barcode Index Numbers (BINs) were assigned by the BOLD system, representing globally unique identifiers for clusters of sequences that correspond closely to biological species (Ratnasingham and Hebert 2013). For BIN assignment, a minimum sequence length of 500 bp is required, and sequences between 300 and 500 bp can join an existing BIN but will not create or split BINs. BINs provide an interim taxonomic system and a way to signify Molecular Taxonomic Units (MOTUs) prior to detailed taxonomic studies including morphology. Sequences were aligned using the BOLD Aligner (amino acid-based hidden Markov models). The analyses are based on sequences with a minimum length of 500 bp and <1% ambiguous bases. Genetic distances and summary statistics were calculated using analytical tools in BOLD and are given as mean and maximum pairwise distances for intraspecific variation and as minimum pairwise distances for interspecific variations.

All Gasteruption species known from Central Europe were studied (Table 1), based on information in Bogusch (2021), except G. lugubre, a very rare species known from the European Alps and some countries in southeast Europe to Turkey. Also, we added three species occurring in southern Europe (G. dolichoderum, G. foveiceps and G. schlettereri) for better comparison with similar species, and to assist in their identification. For other Hymenoptera families, see below.

DNA barcoding allows the identification of Gasteruption to the species level or, in a few cases, to the species group level because of BIN sharing. The species that exhibited BIN sharing or BIN divergence, or that are otherwise taxonomically challenging, are discussed below.

Gasteruption jaculator (Linnaeus, 1758)

Gasteruption jaculator is widespread and common in Central Europe. The species exhibited BIN divergence, with a maximum intraspecific distance of 3.28% and separation into two different BINs. There are no morphological differences and no hint for species separation. The second BIN was also found in a single specimen from Slovakia, but generally, only a few specimens were examined. Further research is needed.

Gasteruption erythrostomum (Dahlbom, 1831)

Gasteruption erythrostomum is widespread and common in Central Europe. The species exhibited BIN divergence, with a maximum intraspecific distance of 3.39% and separation into two different BINs. There are no morphological differences and no indication of the presence of separate species. One BIN was only found in two specimens from Bavaria (Germany), whereas the other BIN is widespread in the study area.

Gasteruption foveiceps Semenov, 1892, stat. nov.

The present specimens of Gasteruption foveiceps originated from northern Italy (Aosta, Lombardy) and were formerly identified as G. nigrescens by CSE. However, a detailed examination by PB, considering the marked BIN difference in the species group, led to the discovery of different character states. Taking into account the morphological characters and synonyms of G. nigriceps, and the shape of the head and the shiny area between the antesternal and praepectal carinas (van Achterberg and Talebi 2014), the two specimens from Italy fit well with G. foveiceps. Thus, G. foveiceps is not a synonym of G. nigrescens but should be regarded as a valid species that occurs in southern Europe.

Gasteruption schlettereri Magretti, 1890, G. diversipes (Abeille de Perrin, 1879) and G. forticorne Semenov, 1892

Our original dataset includes altogether 14 specimens of this species complex, forming five clusters each with a BIN, but without a clear morphological distinction between G. schletterei, G. forticorne and G. diversipes. We cannot solve the taxonomic problems in this group with the few specimens at hand.

A single specimen of G. diversipes from Slovakia forms a cluster with specimens of Gasteruption schlettereri from northern Italy and Croatia. They most probably belong to the same species, apart from the fact that the morphological characters of both taxa are different (identified by Cornelis van Achterberg and PB).

The other cluster comprises specimens from Hungary, Slovakia and Croatia, and agrees with G. forticorne by morphology. So, G. forticorne and “G. diversipes” can be identified in Central Europe with the key of Bogusch (2021) but the second taxon still has to be checked for the correct name. The situation in southern Europe is more complicated and needs final revision. The diagnostic characters for G. forticorne, like length of malar space, or colour of genitalia in G. schlettereri males, seem to be highly variable. Currently, European specimens identified as G. schlettereri probably belong to G. diversipes and G. forticorne and the real G. schlettereri occurs in the Middle East. Our present treatment is, therefore, provisional.

Gasteruption laticeps (Tournier, 1877)

Gasteruption laticeps is widespread in Central Europe. The species exhibited BIN divergence, with a maximum intraspecific distance of 2.58% and separation into two different BINs. One BIN was recently found in eastern Central Europe and Greece (no records from Germany are available), and the other was found in southern France and the Aosta Valley in northern Italy. Probably it is a species separation in an eastern and southwestern distribution centre, as described in Myrmosa atra Panzer, 1801 or in the sibling species Smicromyrme rufipes (Fabricius, 1878) and S. frankburgeri Schmid-Egger, 2022 (Schmid-Egger and Schmidt 2021, 2022). The species group is in need of further investigation.

Gasteruption paternum Schletterer, 1889

Gasteruption paternum is a rare species occurring in Central Europe, especially in the Pannonian lowlands, recorded from the following countries: Austria, Croatia, Czech Republic, France, mainland of Greece and Crete, Hungary, Italy, Slovakia and Switzerland. In all these countries, only a few specimens were recorded in the whole history of studies on this group (Bogusch 2021). The species exhibited BIN divergence, with a maximum intraspecific distance of 5.11% and separation into two different BINs. One BIN with one specimen originating from Tyrol in Austria, the other from the Italian Alps (Piedmont). The species complex needs further research.

Gasteruption assectator (Linnaeus, 1758) aggregate

Fig. 1

Johansson and van Achterberg (2016) revised the Gasteruption assectator aggregate and resurrected two species, G. boreale and G. nigritarse, from synonymy. However, all three species remain difficult to identify by the morphology and the main morphological identification characters are continuous. Our results of the genetic barcoding showed no BIN divergence between the three taxa but some weak clustering into different clades of most (not all) examined species. This was also found in a study by Parslow et al. (2021), which also consistently recovered these species as one clade.

Figure 1. 

Male of Gasteruption assectator from Saxony (Germany). (Photo W.H. Liebig).

Additionally, specimens from higher altitudes with differently sculptured mesonotum form a separate sister group to other barcoded specimens. This situation seems to indicate the presence of a new species, as discussed by van Achterberg and Talebi (2014). Further research is needed to assess if the G. assectator aggr. includes only one highly variable species or three or more valid and different species. The use of a nuclear gene may lead to more precise results, as shown by Praz et al. (2019) in bees of the Andrena bicolor species group.

Gasteruption hastator (Fabricius, 1804)

Fig. 2

Gasteruption hastator is a widespread species of southern Central Europe and very common in southern Europe. The species exhibited BIN divergence, with a maximum intraspecific distance of 2.63% and separation into two different BINs. One BIN with one specimen origin from Aosta Valley in northwest Italy, the other from various locations. The species needs further research and may consist of a species complex, also seen under the impression of a very long list of synonyms (van Achterberg and Talebi 2014).

Figure 2. 

Female of Gasteruption hastator from Saxony (Germany). It is the only largely red-coloured Gasteruption species in Central Europe. (Photo W.H. Liebig).

Gasteruption insidiosum Semenov, 1892

Gasteruption insidiosum is a rare species of the Middle East, reaching East Europe with its north-western part of the distribution. The specimen from Turkey forms a sister group to the group of G. erythrostomum, G. nigrescens, G. foveiceps and G. phragmiticola, while the specimen from Slovakia is also part of this group, next to G. erythrostomum. Because the specimen from Slovakia differs in several characters from true G. insidiosum from Turkey, Greece and Bulgaria, it could be a separate species or belong to some of the synonyms of this species. However, the species descriptions are incomplete and short and some of the types are unavailable, so further research is needed to decide on the identification of the specimen from Slovakia.

Figure 3. 

Female of Gasteruption minutum from Saxony (Germany) (Photo W.H. Liebig).

For the present study, 18 of the 19 of the Gasteruption species that are known to occur in Germany were analysed by DNA barcoding. In two recent DNA barcoding studies dealing with German Apiformes (bees) (Schmidt et al. 2015) and German Spheciformes (Schmid-Egger et al. 2019, 88% of the German species were covered, although the number of German species is, with 584 species in bees and 273 species in Spheciformes, much larger compared to Gasteruption. For Europe, 25 of the 26 species recorded from Central Europe (Bogusch 2021) were available for study.

The most surprising result in this study is the unexpectedly high BIN diversity, suggesting a higher-than-expected species diversity. Five species exhibited two or more BINs. BIN sharing (i.e., two or more species that share the same BIN and are not separable by DNA barcoding) occurred in four species.

We refer to the discussion in Schmid-Egger and Schmidt (2021) on how to deal with and interpret the BIN diversity and problems with a lack of clear morphological characters. The present study confirms findings from previous studies that there are more genetically (BIN) based entities than morphological taxa in any examined Hymenoptera family. Although the BIN can change as more sequences are added, we suggest, whenever possible, to include the Barcode Index Number (BIN) in any further treatment of the species with BIN diversity, including a link to the BIN or the specimens in BOLD, in case the BINs represent distinct species.

The present study provided the opportunity to deal with some rare and poorly known Hymenoptera families with a reference to the German fauna. The families treated here include six species, five of which were DNA barcoded (Table 2). Brachygaster minutus (Evaniidae) is a parasitoid of cockroach ootheca (Blattoidea), and Stephanus serrator (Stephanidae) parasitises larva of longhorn beetles (Cerambycidae). Pseudogonalos hahnii (Trigonalidae) is a hyperparasitoid larva of Ichneumonoidea and can develop only when its egg is ingested by a parasitised caterpillar of an owlet moth (Erebidae and Noctuidae). Aulacidae are koinobiont endoparasitoids of wood-boring larvae of Xiphydriidae (Hymenoptera), Cerambycidae and Buprestidae (Coleoptera). The genus Pristaulacus was revised by Turrisi (2011). Distribution of the species is insufficiently known, but it can be assumed that most or all species are widespread. The species are rarely collected, with few specimens present in museum collections.

The authors have declared that no competing interests exist.

No ethical statement was reported.

PB was supported by a Specific Research Grant from University of Hradec Králové, Nr. 2102/2023.

All three authors conducted the DNA barcoding, SS was responsible for the barcode analysis, CS and PB wrote the taxonomic part, all three authors wrote the manuscript

Stefan Schmidt https://orcid.org/0000-0001-5751-8706

Petr Bogusch https://orcid.org/0000-0002-4554-6141

All of the data that support the findings of this study are available in the main text or Supplementary Information.