Mediterranean Transformation of Central European Insect Fauna (Hymenoptera, Diptera, Lepidoptera), Non-native Species and Mediterranean Influx

The Central European fauna, in the last decades, has been undergoing a strong transformation due to four main factors: the retreat of species that require cool and wet habitats, the proliferation of species that thrive in warm and dry conditions, the northward migration of Mediterranean species, and the gradual establishment of species with tropical origins. In this study, we detail the changes in the orders Hymenoptera, Diptera, and Lepidoptera, and analyze the establishment of non native insects and the northward migration of Mediterranean species. The transformation towards a Mediterranean-type fauna is prominently indicated by the population increase of xerothermic Aculeata, bee flies (Bombyliidae), and horse flies (Tabanidae). Additionally, groups that require cool and wet ecological conditions, particularly hoverflies (Syrphidae), but also sawflies (Tenthredinidae) and tachinid flies (Tachinidae), have shown notable decline. In nocturnal moths, we observe a decrease in species richness in certain areas, as well as frequent outbreaks in populations of some less climate-sensitive species. Some species of butterflies are less sensitive to the current extent of climate change, exhibiting significant population growth under protected conditions. However, most of the previously sporadic and rare butterfly species have proven to be climate-sensitive, unable to achieve significant population growth even under strict nature conservation. In recent decades, the influx from Mediterranean regions and the establishment of tropical non native insect species have turned into exponential rate. We have reviewed the presence of alien species, recording 803 alien insect species in our region, 298 of them have arrived in the past quarter-century, with a significant proportion (54%) originating from tropical and Mediterranean regions.