ZooNotes 81: 1-14 (2015) …81… www.zoonotes.bio.uni-plovdiv.bg ISSN 1313-9916 Accepted: 18 September 2015 Уɧɢвɟɪɫɢɬɟɬɫɤɨ ɢɡɞаɬɟɥɫɬвɨ “Паɢɫɢɣ Хɢɥɟɧɞаɪɫɤɢ” Published: 15 Octoberber 2015 Plovdiv University Press “Paisii Hilendarski” 1 Biology of the blind geobiont scarab beetle genus Chaetonyx Schaum, 1862 (Scarabaeidae: Orphninae) with new distribution records of Ch. robustus Schaum, 1862 from Bulgaria DENIS GRADINAROV 1 , YANA PETROVA 1, 2 , ELENA TASHEVA- TERZIEVA 1 , ANDREY V. FROLOV 3, 4 1 Faculty of Biology, Sofia University “St. Kliment Ohridski”, 8 Dragan Tzankov Blvd., Sofia 1164, Bulgaria, e-mail: dgradinarov@abv.bg; elena.tasheva@gmail.com 2 National Genetic Laboratory, 2 Zdrave Str., Sofia, Bulgaria, e-mail: yanagradinarova@abv.bg 3 Zoological Institute, Russian Academy of Sciences, Saint-Petersburg 199034, Russia, e-mail: frolov@scarabaeoidea.com 4 Mato Grosso Federal University, Department of Biology and Zoology, Av. Fernando Corrêa da Costa, 2367, Cuiabá 78060-900, Brazil Abstract: Life cycle of the orphnine scarab beetles genus Chaetonyx was recorded for the first time based on the multiyear observations on the populations of its type species, Ch. robustus Schaum, 1862, in riverside habitats at Zemen Gorge region, South-Western Bulgaria. Our observations showed that this geobiont species is common in alluvial soils near Struma River, where it forms large colonies. At the Zemen Gorge, its preferable habitats are sparse riverside forests of Alnus glutinosa L. and Populus nigra L. neighboring grass communities. Larvae, adults and pupae were found up to 50 cm deep with most specimens inhabiting the upper soil layer from 0 to 20 cm deep. The highest recorded density was 89 adults and 581 larvae per 0.25 m 2 . Oviposition, hatching of the eggs, pupation and emergence of the new adults occur during the summer. Eggs have been found in surface soil layer in July and August, the pupae – mainly in July and August. Larvae of different instars were found in soil during all months of the study period. Adults from the new generation first occur in the beginning of August. In August, September and October adults from different generations can be found together. The main part of the adults seems to die after the reproduction period, and the common lifespan of adults seems to be about a year only. The life cycle of Ch. robustus in investigated habitat seems to be perennial and includes two years as larval stage and one as adult. Tropical Orphninae occupy a number of ecological niches but lack colonial geobiont specialists similar to Chaetonyx. Key words: Coleoptera, Orphninae, Chaetonyx robustus, biology, life cycle, insect ecology. Introduction Subfamily Orphninae is one of the poorly known groups within the hyper-diverse family Scarabaeidae. It includes 15 genera and 195 species, distributed mainly in the Afrotropical and Neotropical biogeographic regions (Paulian 1948, 1984; Frolov 2012). Habitat preferences, feeding and nesting behavior, and the life cycles are unknown for the