A new species of Bocchus from upper Eocene Rovno amber (Hymenoptera, Dryinidae)

A new fossil species of Dryinidae (Hymenoptera, Chrysidoidea) from upper Eocene Rovno amber (Ukraine) is described: Bocchus rex sp. nov. It is compared with two other species of Bocchus known from European amber: B. primaevus Martins & Melo from Baltic amber and B. schmalhauseni Perkovsky, Olmi, Vasilenko, Capradossi & Guglielmino from Rovno amber. A new key to the Cretaceous and Paleogene species of Bocchus is presented. The Dryininae are the most common representatives in all the amber dryinid faunas since the mid-Cretaceous. The Rovno amber fauna is an exception; possible explanations for the abundance of Bocchus species within this amber are presented.

Recently, we received two pieces of Rovno amber: one from a site in the Volyn region adjacent to the Varash district and the second most probably from the Varash district. They included specimens of Dryinidae that proved to belong to a new species, which we describe below.

Terms
The description follows the morphological terminology of Olmi et al. (2019). All measurements reported are relative, except for the total length (head to metasomal tip, without antennae and sting). Antennal proportions refer to the lengths of the relevant segments as proportions of each other, with the values rounded to the nearest whole number. The following abbreviations are used: POL, distance between the inner edges of the two lateral ocelli; OL, shortest distance between the edge of a lateral ocellus and the median ocellus; OOL, distance from the outer edge of a lateral ocellus to the compound eye; OPL, distance from the posterior edge of a lateral ocellus to the occipital carina; TL, distance from the posterior edge of the eye to the occipital carina.
The term "ADOs" (= Antennal Dorsal Organs) is used here in the sense of Riolo et al. (2016). It corresponds to the term "rhinaria" sensu Olmi (1984). According to Riolo et al. (2016), ADOs are sensory structures that might mediate the antennal responses to vibratory stimuli. As far as we know, they are usually present in the antennae of dryinid females attacking Fulgoromorpha .

Specimens
The specimens studied in this paper have been deposited in the following collections: Specimen 1: Schmalhausen Institute of Zoology (SIZK), National Academy of Sciences of Ukraine, Kiev, Ukraine. Specimen 2: State Museum of Natural History Stuttgart (SMNS), Stuttgart, Germany.

Stereomicroscopy
The multifocal photos were taken using a mirrorless Sony Alpha 6100 camera (Sony Group Corporation, Tokyo, Japan), with Canon bellows and three-way revolver for optical microscopy (Canon Inc., Tokyo, Japan). The following objectives were used: LOMO 3.7 × 0.11 (LOMO, St. Petersburg, Russia) for magnifications from 20 to 50×; Zeiss Semiplan 6.3 × 0.11 (Carl Zeiss GmbH, Jena, Germany) for magnifications from 50 to 100×. The motorized focus was managed by a Cognisys stackshot controller (Cognisys Inc., Traverse City, MI, USA). Captured images were merged into a single in-focus image by using ZereneStacker TM version 1.04 (Zerene Systems LLC, Richland, WA, USA). Images were processed with GIMP version 2.10.30 (https:// www.gimp.org).
Synchrotron X-ray phase-contrast microtomography (SR-µCT) and image processing Synchrotron X-ray microtomography (SR-µCT) (Betz et al. 2007) was performed at the UFO-I station of the Imaging Cluster at the KIT light source of Karlsruhe Institute of Technology (KIT, Karlsruhe, Germany) by using a parallel polychromatic X-ray beam produced by a 1.5 T bending magnet. Specimen 2 was glued onto a plastic pin and mounted onto the goniometer head of the sample stage for tomography. The beam was spectrally filtered with 0.5 mm aluminium with a spectrum peak around 15 keV and a full-width at half maximum bandwidth of about 10 keV. A fast indirect detector system was employed, consisting of a 13 µm LSO:Tb scintillator (Cecilia et al. 2011), diffraction limited optical microscope (Optique Peter) (Douissard et al. 2012) and a 12bit pco.dimax high-speed camera with a resolution of 2016 × 2016 pixels; 3000 projections were recorded at 70 frames per seconds and an optical magnification of 10×, resulting in an effective detector pixel size of 1.22 µm. Two separate overlapping image stacks were acquired because the specimen was larger than the field of view. Therefore, the sample was repositioned in between the imaging procedure, resulting in a certain overlap of two consecutive images. The control system concert (Vogelgesang et al. 2016) was used for automated data acquisition and online reconstruction of tomographic slices for data quality assurance. Execution of the pipelines, including online tomographic reconstruction, was performed by the UFO framework (Vogelgesang et al. 2012). Final tomographic reconstruction was carried out with tofu (Faragó et al. 2022).
The two resulting tomograms were registered and calibrated with Fiji (Schindelin et al. 2012) (https://imagej.net/Fiji) and further imported to the plugin TrakEM2 ) for stitching and cropping. Subsequently, the resulting image stack was imported to Amira version 6.0 (FEI Company, Hillsboro, OR, USA) to presegment the various cuticular and internal structures in the software's segmentation editor by manually labelling every 50 th virtual slice. These labels served as an input for automated segmentation by using the Biomedical Image Segmentation App 'Biomedisa' (Lösel et al. 2020) (https://biomedisa.org). After some minor manual corrections to the segmentation results of the 'Biomedisa' output by using Amira, we converted them into polygon meshes. We thereby applied some minor smoothing and polygon reduction to create the final 3D model (surface mesh). Diagnosis. Macropterous female of Bocchus (Figs 1a-d, 2a-c) with OOL more than three times as long as OPL (Fig. 1b); epicnemium concealed ( Fig. 1d); notauli incomplete, reaching about 0.75× length of mesoscutum (Figs 1b, 2c); fore wing with one dark transverse band (Figs 1a, 2c); petiole distinctly visible (Fig. 1a); enlarged claw (Figs 1e, f, 2d, 4a) with one long row of small teeth, in addition to one lamella; protarsomere 5 (Figs 1e, f, 2d, 4a) with distal apex broad and dark pigmented, with one preapical lamella and inner band, without bristles on inner margin.

Hosts. Unknown.
Etymology. Bocchus was the name of two kings of Mauretania (the first being father-in-law to the Numidian King Jugurtha) and rex is an appropriate epithet of this nice species with its regal look.
State of preservation of paratype (= specimen 2). The head and thorax are well preserved but each have a fissure dorsally (Fig. 3c, e). The metasoma has been completely crushed (Figs 2c, 3a, c, e, g, Suppl. material 1: Video S1). Its size and form can be roughly estimated from the cavity formed in the amber. However, cavities are also present laterally between the head and the thorax (Figs 2a-c, 3a, c, e, g, i, Suppl. material 1: Video S1). Unfortunately, the resolution of the SR-µCT scan was too low to 3D-reconstruct the chelae in great detail. In the head, the partially preserved optical ganglion complex, presumably the optic lobes (= medullae), is clearly visible (Fig. 3b, d, f, h, j, Suppl. material 1: Video S1). It is the second report of optic lobe preservation for Rovno amber arthropods (cf. fig. 1 of Sukhomlyn et al. 2022). Other internal structures are partially preserved; however, it is unclear whether they belong to the optical system or different brain regions, or are partially preserved muscles of the mouthparts (Fig. 3b, d, f, h, j, Suppl. material 1: Video S1). In addition, many muscles in the thorax, the legs and, occasionally, in the metasoma are still preserved (Fig. 3b, d, f, h, j, Suppl. material 1: Video S1). However, as the depicted set of muscles is by no means complete and plays no role in species identification, it will not be discussed further here.
Remarks. After the description of Bocchus rex sp. nov., the key published by Perkovsky et al. (2020) can be modified as follows.

Key to the Cretaceous and Paleogene species of the genus Bocchus Ashmead, 1893
Female: 1 Petiole very short, almost absent (cf. fig. 4  Enlarged claw with teeth present only in the distal half of the inner margin (Fig. 4c)  Head with OOL about 62% of OPL; notauli complete, posteriorly separated (cf. fig. 9 of Perkovsky et al. 2020); protarsomere 5 with distal apex slender and not pigmented, with two bristles on inner margin (Fig. 4b)  Head with OOL about 77% of OPL (Fig. 1b); notauli incomplete, reaching about 0.80× length of mesoscutum (Figs 1b, 2c); protarsomere 5 with distal apex broad and dark pigmented, without bristles on inner margin (Fig. 4a)

Male:
Unknown. The cuticular elements in a, c, e, g, i are depicted in various shades of brown, whereas the cavity of the wasp in the amber is shown as being semi-transparent. The partially preserved optical ganglion complex is shown in blue, the potential brain regions or head muscles in purple, and the muscles (in the thorax, the legs and the metasoma) in red, whereas the cuticular elements in b, d, f, h, j are semitransparent and the cavity in the amber is omitted.

Discussion
The above-described new species is attributed to the genus Bocchus (Hymenoptera, Dryinidae, Bocchinae) because of the following characters: ocelli present; epicnemium concealed; protarsus chelate; chela with rudimentary claw. The genus Bocchus includes 103 species present in all zoogeographical regions, except for Antarctica . The hosts of Bocchus are Tropiduchidae and Caliscelidae (Hemiptera, Auchenorrhyncha) (Guglielmino et al. 2013). These two families of planthoppers are only known from the Cenozoic .
Fossil species of Bocchus are known from the Cenozoic (i.e. from Baltic and Rovno amber) as follows: B. primaevus Martins & Melo, 2019B. schmalhauseni Perkovsky, Olmi, Vasilenko, Capradossi & Guglielmino, 2020 and B. rex sp. nov. from Rovno amber, coeval of Baltic amber. Probably the hosts of the above three species were Tropiduchidae, as they are known from both Baltic and Rovno amber (Perkovsky and Bogdasarov 2009;Perkovsky et al. 2020;Olmi et al. 2022). The oldest tropiduchid is known from the lower Eocene of the Green River Formation (CO, USA) (Shcherbakov 2006). Fossil Caliscelidae are also known from the Cenozoic, but only from Dominican amber (Burdigalian, lower Miocene; 16-20 Ma) (Bourgoin et al. 2015).
The new Bocchus described here is the first hymenopteran and seventh named fossil arthropod from the Volyn Region, Ukraine (Martynov et al. 2021;Telnov et al. 2021;Legalov et al. 2022). The discovery of B. rex is indicative of the richness of Bocchus species in Rovno amber in comparison with Baltic amber: two species (29% of all dryinid species) in Rovno amber versus one (4.8% of all dryinid species) in Baltic amber. In addition, one specimen from Varash district could not be determined to the species level. This difference might be related to the climate of the Rovno amber forest being warmer than that of the Baltic amber forest (Kupryjanowicz et al. 2022;Yamamoto et al. 2022; and references therein), especially since their potential hosts (i.e. Tropiduchidae) are mainly tropical and subtropical (Bourgoin 2020).
To date, Bocchus is the most common genus of Dryinidae in Rovno amber fauna and Bocchinae is the dominant subfamily (44.4% of specimens versus 33.3% for Dryinus and Dryininae) at the specimen level. This is unusual, as Dryininae strongly dominate not only in Baltic amber, but also in Kachin (33 Dryininae species according to Olmi et al. 2022) and Dominican (ten Dryininae species versus one belonging to Bocchinae; Martins and Melo 2020) ambers, both at the specimen and species levels.
The biology of Bocchus species is poorly known so far. The species with known biology live in open environments. An even more important reason for the abundance of Bocchus is that open environments were more common in the Priabonian Ukraine than in the Baltic amber forest (Lyubarsky and Perkovsky 2012; Perkovsky 2013; Lyubarsky and Perkovsky 2019; Dietrich and Perkovsky 2020).
A comparison with the extant Bocchus species shows that their body shape is similar to the species known from European Eocene amber. The chela of B. rex and B. schmalhauseni follows the same general scheme as in the extant species. The only difference can be observed in the chela of B. primaevus and is attributable to the anomalous long and slender protarsomere 5 (Fig. 4b). A similar type of protarsomere 5 has not been found in any extant or fossil species of Bocchus. However, the significance of this anomalous chela remains unknown.
of Sciences, Moscow, Russia) for his helpful discussion of the results. We thank Elias Hamann and Marcus Zuber (both KIT) for their assistance at the beamline and Tomáš Faragó (KIT) for tomographic raw data reconstruction. We acknowledge the KIT light source for provision of instruments at their beamlines and we also thank the Institute for Beam Physics and Technology (IBPT) for operation of the storage ring, the Karlsruhe Research Accelerator (KARA). Our thanks are also extended to Oliver Betz (University of Tübingen) for his support and Theresa Jones for linguistic corrections of the manuscript. Many thanks to Eduardo G. Virla and Wesley Dondoni Colombo for their helpful comments and suggestions. We acknowledge the support of the Open Access Publishing Fund of the University of Tübingen.