Distribution and abundance of the alien Xylosandrus germanus and other ambrosia beetles (Coleoptera: Curculionidae, Scolytinae) in different forest stands in central Slovenia.
The East Asian ambrosia beetle (Xylosandrus germanus - Blandford 1894) is an invasive species that has become successfully established in Europe and North America. In Slovenia, X. germanus was first recorded in 2000 in the western part of the country, and since 2008 the species has also been identified in other parts of Slovenia. The first economic damage was recorded in 2016 after a massive attack on recently felled logs of different tree species, spurring research into this non-native invasive species. To examine the distribution and abundance of X. germanus compared to other ambrosia beetles and to determine voltinism and the flight period of the species in our climatic conditions, we deployed 19 ethanol-baited traps from March to November 2017 in oak-, beech- and fir-dominated forest stands in central Slovenia. To verify the vertical distribution of X. germanus, traps were installed at altitudes ranging from 303 m to 941 m a.s.l. Furthermore, the impact of the ice storm that hit Slovenia in 2014 on the abundance of X. germanus was also studied. Non-native X. germanus represented 71.8% of the total catch and was significantly more abundant than the other five most common species: Xyleborinus saxesenii (20.0%), Xyleborus monographus (3.6%), Anisandrus dispar (2.5%), Trypodendron domesticum (1.2%) and Trypodendron signatum (0.6%). X. germanus was most abundant in beech-dominated stands, but the differences between forest types were not significant. The species was found along the entire altitudinal gradient. Our results indicate that the swarming of X. germanus in lowland forests may already occur by the middle of March. Maximum flying activity was observed in May and early June in forests below 600 m a.s.l. and at the end of May and in June in forests above 700 m a.s.l. Only one generation per year was observed. The ice storm positively affected the abundance of X. germanus, especially in areas where sanitary logging was delayed. Xyleborinus attenuatus was detected for the first time in Slovenia.