The large and distinctive chalcidoid wasp Leptoomus janzeni Gibson, 2008, originally described from late Eocene Baltic amber, is newly recorded from coeval Rovno amber (Ukraine) based on a single well-preserved female specimen. Only 66 species of Rovno hymenopterans (49%) are also known from Baltic amber. High resolution photomicrographs and measurements of the specimen are given. Some character states of the new specimen, such as a green metallic coloration, a bare and flat prepectus, location and number of multiporous plate sensillae on the flagellum, sclerotized spur vein of the hind wing, and two metatibial spur are reported in this species for the first time.

Baltic amber, Eocene, prepectus, spur vein, Ukraine

Chalcidoidea (Hymenoptera) are currently divided into 23 extant families (Heraty et al. 2013; Janšta et al. 2018). Members of the families Cynipencyrtidae, Encyrtidae, Eupelmidae (except male Eupelminae), and Tanaostigmatidae share an enlarged, convex mesopleuron (acropleuron sensu Gibson 1986) and several other correlated adaptations hypothesized to enhance jumping ability (Gibson 1986). It has sometimes been suggested that these taxa constitute a monophyletic group based on this enlarged mesopleuron (Trjapitzin 1968, 1989; LaSalle 1987). However, Gibson (1989) did not find any putative synapomorphies for the group as he defined it, and the morphological analysis of Heraty et al. (2013) retrieved the group as a monophyletic only if Oodera Westwood (Pteromalidae: Cleonyminae) was included. The combined morphological-molecular results of Heraty et al. (2013) did not retrieve this group as monophyletic, nor did the transcriptome-based phylogenies of Peters et al. (2018) and Zhang et al. (2020), suggesting that adaptations for jumping evolved independently.

Here, we report a large and well-preserved female from Rovno amber that we treat as conspecific with Leptoomus janzeni Gibson, 2008 (Chalcidoidea), originally described from Baltic amber. Gibson (2008) did a detailed analysis of the morphology of L. janzeni and compared it with that of Cynipencyrtus Ishii, 1928 (Cynipencyrtidae), Encyrtidae, Eupelmidae, and Tanaostigmatidae. This suggested that Leptoomus is likely in or near Clade E, sensu Heraty et al. (2013), the chalcid “jumpers” with an enlarged acropleuron. Gibson (2008, p. 24) proposed: “until evolutionary relationships of the treated taxa are established more confidently by such studies it seems prudent to classify L. janzeni along with Cynipencyrtus in Tanaostigmatidae”. Members of Tanaostigmatidae are distinguished in particular by an enlarged, bulbous prepectus projecting anteriorly beside the pronotum that resembles the prepectal structure of L. janzeni (Figs 1B, C, 2A: pre).

Ukrainian Rovno amber (Priabonian stage, 33.9–37.8 Mya) is the southern coeval of Baltic amber, from which L. janzeni was described. The amber containing the specimen of L. janzeni was found at the village of Velyki Telkovichi (Vladimirets Distr., Rovno Region, Ukraine) and is housed at the Schmalhausen Institute of Zoology of the National Academy of Sciences of Ukraine, Kiev (SIZK). The localities and composition of the Rovno amber fauna were recently characterized in a series of reviews by Perkovsky et al. (2010), Jałoszyński and Perkovsky (2016), Perkovsky (2016, 2018) and Martynova et al. (2019). Including Ektopicercus punctatus Simutnik (Simutnik and Perkovsky 2020), and L. janzeni, 135 species of Hymenoptera are now known from Rovno amber, with 66 (49%) in common with Baltic amber (Radchenko and Perkovsky 2020; this paper).

Nearly all studied Rovno amber inclusions from Rovno Region were collected from Klesov and the Horyn River Basin (Perkovsky et al. 2010; Perkovsky 2017) except new collections from the more western basins of the Styr and Stokhod rivers and especially the Veselukha River floodplain between them (Lyubarsky and Perkovsky 2020). These new collections (mostly from Voronki and Velyki Telkovichi) revealed a number of new species of beetles, neuropterans and snakeflies (Jałoszyński and Perkovsky 2019; Legalov et al. 2019; Colombo et al. 2020; Perkovsky and Makarkin 2019, 2020; Makarkin and Perkovsky 2020; Lyubarsky and Perkovsky 2020; Radchenko and Khomych 2020; Perkovsky et al. 2020) as well as new mosses and liverworts (Mamontov et al. 2020 and references therein), including the first named amber Sphagnum from Velyki Telkovichi and some species previously recorded from Baltic amber (Perkovsky and Olmi 2018; Martynova et al. 2019; Mamontov et al. 2020) or from Baltic and Bitterfeld ambers (Radchenko and Perkovsky 2018, 2020).

Photographs were taken using a Leica Z16 APO stereomicroscope with a Leica DFC 450 camera and processed with LAS V3.8 software. To improve imaging, we applied sucrose syrup of approximately the same refractive index as the amber and placed a glass coverslip on top; after photography, the syrup was removed using warm water. Some images were then enhanced (brightness and contrast only) using Adobe Photoshop.

Terminology and abbreviations follow Gibson (1997), Noyes et al. (1997), and Heraty et al. (2013). The following abbreviations are used in the text and illustrations:

OOL minimum distance between an eye margin and the adjacent posterior ocellus;

POL minimum distance between the posterior ocelli;

OCL minimum distance between a posterior ocellus and the occipital margin;

LOL minimum distance between the anterior ocellus and a posterior ocellus;

F1, F2, etc. funicular segments 1, 2, etc.;

mps multiporous plate sensilla;

mspl mesopleuron;

pre prepectus;

spv spur vein.

The set of morphological features possessed by L. janzeni places the taxon in the “jumpers” Clade E sensu Heraty et al. (2013). As previously shown by Gibson (2008), L. janzeni appears to be close to Tanaostigmatidae. To establish the position of L. janzeni on the chalcidoid tree, further research is needed with additional fossil and molecular data.

We are grateful to Gary A.P. Gibson (Canadian National Collection of Insects, Arachnids and Nematodes, Agriculture and Agri-Food Canada) for confirming the correctness of the determination of the L. janzeni and valuable comments; Anatoly P. Vlaskin (SIZK) for cutting and polishing the sample, Bruce Archibald (Simon Fraser University, Burnaby, Canada) for editing of the English. The authors are thankful to the editor Petr Janšta and to an anonymous reviewer for corrections. The study was supported by the National Research Foundation of Ukraine grant “Leading and Young Scientists Research Support” (registration number 2020.02 / 0369) for the first author.