New species and an image key to the wingless Cryptorhynchinae of the Caucasus (Coleoptera: Curculionidae: Tylodina) - a hypothesis on the spread of forest and open land species in the Western Palaearctic

Three new species from the Caucasus, Caucasusacalles subglobosus Stüben sp. nov., Caucasusacalles circularis Stüben sp. nov. and Acalles krasnodarensis Stüben sp. nov., are described from the Cuacasus (Georgia, Armenia and Russia) and are distinguished from related species based on morphological and molecular data. The new taxa are included in a phylogram and a CO1 distance matrix is given including the closest species from the Caucasus and the Eastern Mediterranean region.

A pictorial key to all 21 Caucasian wingless cryptorhynchine species known so far is presented. The striking decline in species diversity among the Cryptorhynchinae from west to east—from the Iberian Peninsula to Italy, Greece, Turkey and finally to the Caucasus —and from south to north is probably due to the displacement of the forest species that still dominated during the Miocene. After migration across the Strait of Gibraltar, this displacement seems to be the result of drier habitat conditions, the reduction of forest areas in the south-western Mediterranean region and the increase of open landscapes during the Pliocene.