Trophic relations and ecological niches of darkling beetles of the genus Nalassus Mulsant, 1854 (Coleoptera: Tenebrionidae) in the Caucasus and description of a new species from Abkhazia

Aim. To reveal mutual relations between species of the genus Nalassus in taxocenes and the division of ecological niches during cohabitation.

Material and Methods. Observations and collection of adult beetles and food objects were carried out in 2020–2022 in Dagestan, North Ossetia, Kabardino‐Balkaria,  Karachay‐Cherkessia, Krasnodar Region (Russia) and Abkhazia. The nutrition of beetles was observed directly in nature at night with headlamps, and in some cases in laboratory conditions using the test cafeteria  method.  The  number  of  beetles  per  area  was  counted  on 100 × 4 m transects. The number, sexual structure and diurnal activity (feeding, copulation) were observed with the pause of 15 to 25 minutes. We measured temperature (the range from −4 to +40°C) and humidity (the range from 0 to 100%) by loggers every 7 minutes.

Results. New localities for seven known species of Nalassus are presented. The  new  species  N. (Caucasonotus)  ritsanus  M.  Nabozhenko,  sp.  n.  is described from environs of Ritsa Lake in Abkhazia and it is compared with other Abkhazian representatives of the subgenus Caucasonotus. We revealed or added information about trophic relations for eight species of the genus; lichenophagy is typical for the majority of species; phytophagy and saprophagy were registered for Nalassus for the first time; algophagy was fixed for two species. The number, sex structure in micropopulations and ranges of air temperature and humidity during the period of imagoes activity were analyzed.

Conclusion.  The  most  important  and  perhaps  the  only  strategy  for reducing competition in the cohabitation of Nalassus in the Caucasus is a trophic specialization. An occupation of open landscapes by Caucasian Nalassus did not play a role in the subgeneric differentiation, but was partially accompanied by a transition from lichenophagy to phytophagy and saprophagy.

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