Rising temperatures explain past immigration of the thermophilic oak-inhabiting beetle Coraebus florentinus (Coleoptera: Buprestidae) in south-west Germany

Global warming enables the immigration of species previously absent from a given region. Coraebus florentinus (Coleoptera: Buprestidae) is a beetle with a Mediterranean distribution that has expanded its northern range margin northwards within the last 30 years. It develops in branches and shoots of oak (Quercus spp.) and is considered a pest in Mediterranean countries. By modelling the current spatial distribution of C. florentinus using three independent modelling approaches (generalised linear models, boosted regression trees, maximum entropy modelling) we identified abiotic factors which explain its current spatial distribution (1991-1999) in south-west Germany and reconstructed its immigration into Germany since 1950. All modelling approaches suggest that monthly maximum temperatures determined the range margin of the species in south-west Germany from 1991 to 1999. Occurrence probabilities increased exponentially with mean maximum temperatures higher than 10 A degrees C in March and 22 A degrees C in June. Mean precipitation in May also seems to be important for the species occurrence, particularly in regions where oaks grow on poor sandy soil; however, this generally plays a minor role. All of these environmental conditions are linked to higher reproduction of C. florentinus on oaks in warm and dry habitats, as reported from southern Europe. We show that climatic conditions for the beetle have improved significantly in south-west Germany since 1950, which is most likely the reason for the northward shift of its range margin. Our modelling results suggest a further range expansion of the beetle in Central Europe.