Stratification and seasonal dynamics of the weevil (Coleoptera, Curculionoidea) assemblages in the Northern Caspian semidesert

In 2003-2004, 102 species of five weevil families were found in the steppe and desert associations of the Caspian semidesert (Dzhanybek Station). Representatives of Curculionidae predominated. The majority of the commonest weevil species were most abundant (20) in the steppe associations, only 6 species were found in the steppe ones. The composition of the weevil community sharply changes during spring and summer. The greatest species richness (86 species) is observed in spring. Most of the species dominating in the herbage, both in the steppe and desert communities, are steppe polyphagous broad-nosed weevils with the daytime activity (Euidosomus acuminatus, Omias verruca, O. rotundatus, Phyllobius brevis); their majority are ephemeral species with short adult life. The soil surface layer is dominated by Temnorhinus strabus, Humeromima nitida, Mesagroicus poriventris, Archaeophloeus inermis, and Trachyphloeus amplithorax. In summer, 53 species of weevils are recorded; their numbers on the soil surface sharply drop, all abundant species being restricted to the herbage layer. Ecological characteristics of the steppe and desert weevil assemblages considerably change, and distinctions between these two types of assemblages increase. The correspondence between the characteristics of the vegetation and the dominant species composition is most evident in summer. Weevils feeding on intensely vegetating Medicago romanica (Stenopterapion tenue, Sitona spp., and Tychius spp.) achieve high densities in the steppe herbage; the core of the desert assemblages is formed by species associated with dominating chenopods (Metadonus anceps) and wormwoods (Ptochus porcellus) characterized by late and prolonged vegetation period.