New and little-known bees of the genus Epeolus Latreille, 1802 (Hymenoptera, Apidae, Nomadinae) from Mongolia

A review of nine species of the bee genus Epeolus Latreille, 1802 (Hymenoptera: Apidae, Nomadinae) currently known from Mongolia is given. Two new species, E. leleji sp. nov. and E. mongolicus sp. nov. are described. The following five known species are newly recorded from Mongolia: E. alpinus Friese, 1893, E. cruciger (Panzer, 1799), E. melectiformis Yasumatsu, 1938, E. nudiventris Bischoff, 1930, and E. ruficornis Morawitz, 1875. A lectotype is designated for Epeolus tarsalis Morawitz, 1874.


Introduction
Mongolia is a large, landlocked country in eastern Central Asia, covering 1,564,100 km². Politically, Mongolia is divided into 21 provinces named "aimags" in addition to the capital, Ulaanbaatar (Fig. 1). This territory, as part of the Central Asian region, is an important centre of bee diversity in the Palaearctic (Michener 1979).
In recent years, significant progress has been made towards a better knowledge of the Mongolian species of some genera: Colletes Latreille, 1802 (Kuhlmann andProshchalykin 2013;Proshchalykin and Kuhlmann 2015), Hylaeus Fabricius, 1793 (Colletidae) (Dathe and Proshchalykin 2016), and Sphecodes Latreille, 1804 (Halictidae) (Astafurova and Proshchalykin 2015;Astafurova et al. 2015). In total, 348 bee species are currently known from Mongolia (Ascher and Pickering 2021). However, taxonomic information about most Mongolian genera is still fragmentary. We begin here with a reference to the genus Epeolus Latreille, 1802. The genus Epeolus includes 109 species spread across much of the globe: they occur throughout the Holarctic zone, from the west coast of the United States and eastwards to Europe and as far as Japan. About 65 species are known from North and Central America, about 35 from the Palaearctic region, of which 17 species are found in Europe (Michener 2007;Onuferko 2018;Bogusch and Hadrava 2018). The Epeolus fauna of Mongolia is particularly under-recorded. Only two species, Epeolus tarsalis Morawitz, 1874 and E. variegatus (Linnaeus, 1758), have been recorded from this country, though without precise localities (Friese 1895).
In the present paper, based on a comprehensive study of specimens deposited in various collections, we report seven additional species, with two species described as new and five species recorded from Mongolia for the first time, resulting in a total number of nine Epeolus species known from this country. In addition, we designate a lectotype for Epeolus tarsalis Morawitz, 1874 in order to clarify the status and diagnosis of type specimens.
A key to Mongolian Epeolus has not been included in this paper, it is forthcoming in a subsequent publication uniting this and the Eastern Palaearctic fauna due to their extensive species sharing and the need for some additional work in these regions.

Materials and methods
The results presented in this paper are based on 277 specimens collected in Mongolia and currently housed in the Zoological Institute, Russian Academy of Sciences (St. Peters burg, Russia, ZISP); Oberösterreichisches Landesmuseum, Biologiezentrum (Linz, Austria, OLBL) and the personal collection of Maximilian Schwarz (Ansfelden, Austria, PCMS).
The taxonomy, synonymy and distribution of species follow those of Friese (1895), Levchenko et al. (2017) and Bogusch and Hadrava (2018). Morphological terminology follows that of Engel (2001) and Michener (2007). The density of integumental punctures is described using the following formula: puncture diameter (in μm) / ratio of distance between punctures to average puncture diameter, e.g., 15-20 μm / 0.5-1.5. Abbreviations F, T, and S are used for flagellomere, metasomal tergum and metasomal sternum respectively. The species are listed alphabetically. The records are first sorted alphabetically according to the aimags, and then chronologically according to the locality. Hard brackets are used when certain data are added to specimen label Specimens were studied with an Olympus SZ51 stereomicroscope and photographs taken with a combination of a stereomicroscope (Olympus SZX10) and digital camera (Olympus OM-D). Final images are stacked composites using Helicon Focus 6. All images were post-processed for contrast and brightness using Adobe Photoshop.
New distributional records are noted with an asterisk (*). Diagnosis. This species differs from other Palaearctic species of the genus by having forewings with two submarginal cells (versus three cells in other species, except E. bischoffi Mavromoustakis, 1954) ( Fig. 2A, B). The new species are clearly distinguished from E. bischoffi by lack of long black dense hair on the whole body, position of labral teeth closer to apical margin, the reddish female mesosoma (black in E. bischoffi) and many other characters.

Epeolus melectiformis Yasumatsu, 1938
Epeolus melectiformis Yasumatsu, 1938: 224, ♀, ♂ (type locality: Ookawa-mura, Tosa, Shikoku, Japan).  Diagnosis. This species is clearly distinguished from other Palaearctic species by red metasoma with spectacular bright copper-reddish (Fig. 5A, B) or gold-yellowish (Fig. 5C) tomentum entirely covering terga and well-developed on head and mesosoma. Unlike other Palaearctic species, the new species does not possess contrast col-oration of pubescence, forming light spots or bands. The species is structurally closest to E. alpinus and E. cruciger, since it also belongs to E. cruciger species group, and especially resembles E. alpinus in having long setae on vertex and labrum with almost straight apical margin (slightly curved).
Male. Unknown. Etymology. The specific epithet is named after the country of origin. Distribution. Mongolia (Bulgan, Zavkhan).

Epeolus nudiventris Bischoff, 1930
Epeolus nudiventris Bischoff, 1930: 14 Unlike other Epeolini, all Epeolus species are so far known as cleptoparasites of species of Colletes (Colletidae). The Mongolian fauna includes 38 Colletes species, of which more than a half are found only in Mongolia or adjacent territories of China, Kazakhstan and Siberia (Russia) (Proshchalykin 2017). Although Colletes are found in all aimags of Mongolia, the fauna of the steppe and desert zones is the richest one. Most Colletes species prefer open landscapes with dry and well-warmed soils suitable for nesting. In addition, some Colletes are oligolectic, visiting a limited taxonomic range of flowering plants. It is obvious that the biodiversity of cleptoparasites is associated with their hosts. In this regard, Mongolia, like the rest of Central Asian territories, is very promising for the study of the genus Epeolus. It is quite certain that new records for regional faunas and species that are new to science will be found during further studies.