Fauna of leaf beetles (Coleoptera, Chrysomelidae) of isolated Volga Islands and mechanisms of their secondary settlement

The following paper deals with the study that was carried out during 1974–2016 in natural and laboratory conditions in the Samara Region. The authors studied the features of adults leaf beetles survival as a result of the Volga river flood spill, flooding of the isolated island systems as well as migratory processes of insects. Over a 12-year period of field research, 11 entomologists, using 2 traditional and 6 author’s methods, have collected 29 species of Chrysomelidae beetles on 11 large Volga Islands (3 of which are periodically flooded) and 20 large, regularly flooded shallows and braids. It is established that the fauna of the Islands’ leaf beetles is very close to the fauna of adjacent coasts by genesis. The authors analyze the origin and relief of typical Islands, the level of flood waters, the duration of flooding of the Volga river floodplain near Samarskaya Luka, the mechanisms of survival of beetles by adapting them to the conditions of habitats or features of their migrations, with the secondary settlement of island systems. It is established that, in addition to the active flight and autonomous navigation to the Islands, beetles use available «boats» – «rafts from vegetable flood sludge», small and fairly large floating objects (from branches and boards to river vessels). It is established that migrations occur annually, completely regardless of the island beetles-predecessors population wintering success.