Invasions of insects and fungi is a serious problem for the existence of woody plants in the north-west of the European part of Russia. The following species of moths (Lepidoptera: Gracillariidae) that produce mines in the leaves of woody plants recently arrived into the region: Phyllonorycter issikii (feeding on lime), Cameraria ohridella (feeding on chestnut), and, likely, Acrocercops brongniardella (feeding on oak). Increasing average monthly temperatures during the growing season is a favorable factor which can promote the spread of pests and pathogens and increase their population density. The particularly warm season of 2018 had likely contributed to the noticeable increase in the population density of the invasive mining moths as well as the adventive poplar mining moth Phyllonorycter populifoliella. Invasive species of stem-boring and bark beetles as well as diseases associated with them might be particularly dangerous. Thus, Scolytus spp. (Coleoptera: Curculionidae: Scolytinae) are involved in spreading of the Dutch elm disease (caused by Ophiostoma novo-ulmi). It has been demonstrated that hybrids of Oph. novo-ulmi are spread in the region and can be highly pathogenic. Emerald ash borer Agrilus planipennis (Coleoptera: Buprestidae) is another serious potential and aggressive invader. The north-western border of its invasive range is currently in the environs of Tver city, but its arrival by highways, with transport or planting materials to the north-west of the European part of Russia is likely. The recent invasion of the ascomycete Hymenoscyphus fraxineus has already led to a noticeable deterioration of the condition of ash trees in Saint Petersburg and the Leningrad Region. The combined effect of the buprestid beetle A. planipennis and fungus H. fraxineus can have fatal consequences for ash. It is necessary to continue monitoring of the invasive species range dynamics, study of their adaptation to local conditions and the interaction of invasive insects with local and invasive woody plant pathogenic organisms.
