True bugs (Heteroptera) of relict elm groves in the lower reaches of the Selenga River (Republic of Buryatia)

At present, a comprehensive study of refugia is becoming more and more urgent. One of the most interesting refugia of the nemoral biota in Baikal Siberia is the groves (or small forests) of the Japanese elm that grow in the lower reaches of the Selenga River (Republic of Buryatia). Different researchers consider the Japanese elm as a separate species Ulmus japonica (Rehd.) Sarg. or as a variety of Ulmus davidiana Planch. var. japonica (Rehder) Nakai. It is a relict species for Siberia, the main area of which extends to the east of Zabaykalskiy Kray. The communities formed by the Japanese elm are poorly understood according to many components. There is little information on the entomofauna of elm forests, in particular, on the fauna of true bugs (Heteroptera). The objectives of this research were inventory of terrestrial Heteroptera of elm groves; identification of the main plant communities, as habitats of insects; comparison of Heteroptera groups from different plant communities; detection of rare species for the Baikal region. We collected the material in Pribaykalskiy district of Buryatia in elm groves near the settlements Mostovka, Talovka, Yugovo, and Ilinka in 2014-2016. The list comprised several species, known from literature, collected from the Japanese elm in the vicinity of Tataurovo village (See Fig. 1). To collect insects, we used standard entomological methods: using an insect sweep net, shaking trees and shrubs, examining plant litter, and soil traps. Thus, we collected approximately 2300 specimens of bugs in the main plant associations. We determined the species of the specimens according to Vinokurov NN and Kanyukova EV (1995), as well as using the reference insect collection of the Zoological Institute, Russian Academy of Sciences (Saint Petersburg). The geographic distribution of species is based on the data from Hemiptera Catalogue of the Asian part of Russia and the Palearctic (2013). Information on the habitats of insects is presented as a longitudinal component and is given in accordance with KB Gorodkov's classification (1984). To determine the similarity of faunas belonging to different plant communities, we used the Chekanovsky-Serensen index; calculations and construction of the dendrogram were performed with the PAST software version 3.17 using the Paired group algorithm. To study the structure of the vegetation cover, we used standard geobotanical methods and methods of geographic information system and geobotanical vegetation mapping. The names of flora species are given according to SK Cherepanov (1995). As a result, we found five basic plant associations, in which true bugs were collected: 1). Elm bush (Padus avium Mill., Crataegus sanguinea Pall., C. dahurica Koehne ex C.K. Schneid., Salix schwerinii E.L. Wolf, Rosa davurica Pall., Rosa acicularis Lindl., Ribes spicatum E. Robson, Swida alba (L.) Opiz)-grass (Anemonastrum crinitum (Juz.) Holub, Urtica dioica L., Thalictrum minus L., Equisetum arvense L., Carex sp., Agrimonia pilosa Ledeb., Poa sibirica Roshev. etc.) forest. 2). Forb (Lappula squarrosa (Retz.) Dumort., Silene amoena L., Papaver nudicaule L. etc.)-thyme (Thymus ssp.)-gramineous (Agrimonia pilosa) steppes. 3). Forb (Medicago falcata L., Mentha arvensis L., Achillea millefolium L., Plantago media L., Trifolium repens L. etc.)-gramineous (Poa sibirica, Alopecuruspratensis L. etc.) meadows. 4). Poplar forb (Equisetum arvense, Cirsium setosum, Vicia cracca L.)- gramineous (Poa sibirica) groves. 5). Willow (Salix viminalis L., S. rorida Laksch.) communities with poorly developed grass cover (Carex spp., Equisetum arvense, Calamagrostis epigeios (L.) Roth. etc.). In these plant associations, 88 species of Heteroptera from 14 families and 58 genera were collected (See Table 1). In terms of the number, the following species dominate: Miridae, Lygaeidae, and Pentatomidae. According to the type of geographical distribution, species with wide ranges (Trans-Eurasian, Transpalaearctic, Holarctic, and European-Siberian) predominate. The greatest number of species of true bugs was collected in meadows and elm groves; these communities are most diverse in composition of vegetation and are favorable for the habitation of many insect species. Some meadow plant species come under the canopy of elms. Steppes (26 species), willow and poplar communities (16 species each) have more specific conditions and a narrower species composition of plants. A comparison of Heteroptera species lists from different plant associations was carried out. The calculations established relatively low values (less than 0.5) of the Chekanovsky-Serensen index, which range from 0.1 between willow and steppe communities to 0.45 between elm forests and meadows. Such rates indicate a fairly distinct delineation of groups of true bugs in different plant associations (See Table 2 and Fig. 2). The most similar groups are bugs of elm forests and meadows (0.45), because many species of meadow vegetation occur under canopy of elms. However, the similarity index is not very high (0.45), which indicates the essential specificity of each association. A part of species of true bugs only lives in the Japanese elm, or prefers this species to other trees and shrubs. For example, the predatory plant bug Deraeocoris olivaceus was noted in the studied territory only on elms, whereas in their absence it also lives on other trees. The widely spread shield bug Pentatoma rufipes is also common in many deciduous trees, but in the studied territory it prefers the Japanese elm, in which it occurs in large numbers. The plant bug Psallus ulmi feeds on the species of the genus Ulmus, so it was only noted in elm forests among the studied plant associations. Willow communities include many hygrophilic and hygromesophilic insects, which live, mainly, on sedges and willows, therefore these communities are most distinct from others in the species composition of Heteroptera. Six species of true bugs are identified from the list (See Table 1), which are rare for Baikal Siberia: Phytocoris nowickyi Fieber, 1870, Pilophorus mongolicus Kerzhner, 1984, Megalocoleus molliculus (Fallen, 1807), Bathysolen nubilus (Fallen, 1807), Spathocera lobata (Herrich-Schaeffer , 1840), and Sehirus morio (Linnaeus, 1758). Among them, one species, Sehirus morio, from the family Cydnidae was first indicated for the Republic of Buryatia. The paper contains 2 Figures, 2 Tables and 15 References.

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