The frontline of invasion: the current northern limit of the invasive range of emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), in European Russia.
Agrilus planipennis is an aggressive beetle native to Asia, which has recently invaded North America and central Russia. In European Russia, the first specimens of A. planipennis were collected in Moscow in 2003 and the Moscow Province is therefore thought to be a likely entry point to Europe. The pest spread along roads and railways and, by 2013, it was recorded in 11 provinces of Russia. The goal of this study was to clarify the current northern range limit of A. planipennis. To do this, ash (Fraxinus excelsior and F. pennsylvanica) trees were surveyed along the federal highway M10 (Russia) between Moscow and Saint Petersburg in July 2016. The condition of ash trees and presence of A. planipennis was recorded at 15 locations. We found dead ash trees with galleries of A. planipennis at six locations (56° 27.799′ N; 36° 35.383′ E to 56° 47.665′ N; 36° 03.584′ E). At the more north-western sites ash trees became infrequent and signs of A. planipennis were not observed on any ash tree. Beyond the National Park Valdayskiy (58° 00.095′ N; 33° 08.550′ E) no ash trees were observed for about 100 km. Further north in Leningrad Province, there were fragments of ash forests and many ash trees planted in parks in Saint Petersburg and its suburbs, but no signs of A. planipennis were seen. Results of this survey suggested that, for summer 2016, the north-west limit of A. planipennis was close to Tver City (about 56° 47′ N; 36° 03′ E). Further range expansion of A. planipennis may have been limited by low host density north-west of Tver City, rather than by climatic factors. However, if A. planipennis can overcome low host abundance and reach Saint Petersburg or other settlements with planted ash in Russia or abroad, it will likely cause serious damage, similar to that already observed in Moscow Province or North America.