Introduction

The Lepidoptera fauna of Mongolia is of considerable interest to zoologists. Entomologists from different countries (former Soviet Union, Hungary, Russia etc.) have been studying the insect fauna (including Lepidoptera) of Mongolia for many years. Some groups of Mongolian lepidopterans were studied relatively well, namely Papilionoidea (Tshikolovets et al. 2009; Yakovlev, 2012), Sphingidae (Derzhavets, 1977; Yakovlev et al. 2015), Zygaenidae (Efetov et al. 2012), Cossidae (Yakovlev, 2004, 2015), Notodontidae (Morozov et al. 2016; Schintlmeister, 2008) and Pterophoridae (Ustjuzhanin & Kovtunovich, 2008). Nevertheless, the knowledge about other taxonomic groups (e. g. Geometridae, Noctuidae, Alucitidae) remains insufficient. The recent publications illustrate this well (Knyazev et al. 2020; Ustjuzhanin et al. 2016).

Our research considers the west part of Mongolia, Mongolian Altai in particular, which is still poorly known. The Mongolian Altai is a mountain system in Mongolia and China which stretches approximately 1000 km from the northwest to the southeast. The mountain system of the Mongolian Altai reaches uplands of the Altai Republic (Russia) in the north, borders with deserts and semi-deserts of Dzhungaria and Gobi towards the south and west, and semi-deserts of the Great Lakes Depression in the northeastern area of the system. Mongolian Altai reaches an altitude of 4362 m (Mountain Munkh-Khajrkhan-Ula) and consists of several parallel ridges. Southwestern slopes receive more precipitation than northeastern ones, and they consist of richer forest-meadow landscapes (with spruce and larch prevailing in forests), changing into steppes in lowlands and alpine meadows. Steppes and semi-deserts dominate on northeastern slopes, while semi-deserts prevail between the mountains (Kamelin, 2005; Yakovlev et al. 2015).

The Mongolian Altai is a significant frontier in the distribution of insects: a number of studies have shown that insect fauna of the southwestern (Dzhungarian) slopes of Mongolian Altai differs markedly from those of the northeastern slopes. This conclusion is based on the distribution of Orthoptera (Sergeev, 1986), Coleoptera (Kryzhanovskij, 2002), Lepidoptera (Yakovlev, 2011, 2012, 2015). The main ridge of the Mongolian Altai divides the biota of the Altai Mountain region into two biological provinces: Altai-Dzhungarian (western) and Western Mongolian (eastern) (Yakovlev, 2012).

In June 2022 the authors of this article made a trip to the south of Mongolian Altai (Figure 1). The main goals of this expedition were to study the Lepidoptera fauna in south-western (Dzhungarian) macroslope of Mongolian Altai and Dzhungarian Gobi, the less studied and rather rich in biodiversity southern parts of Khovd and Gov’-Altai Aimags (Yakovlev, 2012; Yakovlev & Dubatolov 2013a, b).

The present paper is devoted to Geometridae recorded by us during this travel. Although Mongolia is one of the largest countries, little is known about its moth fauna, and there is no comprehensive review of species richness, diversity, and distribution patterns of geometrid moths in the country. A fairly complete historical review of the study of geometrid moths in Mongolia was given by Enkhtur and co-authors (2020). Only a few works deal with the geometrid moths of the Mongolian Altai (Vasilenko, 2004, 2006).

Here we provide the list of Geometridae recorded in 11 localities of W Mongolia (Table 1), including the species new for Mongolia.