Temporal and spatial variation of Xylosandrus germanus (Coleoptera: Curculionidae: Scolytinae) captures in lowland forests: Positive effect of tree species diversity on the abundance of an invasive ambrosia beetle

Invasive ambrosia beetles, such as the black stem borer (Xylosandrus germanus), pose serious ecological and economic threats to various natural, semi-natural and artificial ecosystems with suitable host plants. This study investigates the temporal and spatial variation in X. germanus abundance within lowland, mostly oak-dominated forests of the West Carpathians, focusing on the influence of tree species diversity, altitude, and forest stand age. Our findings reveal a strong positive correlation between tree diversity and X. germanus abundance, suggesting that diverse forests provide favourable conditions for beetle establishment. Altitude also exhibited a significant positive effect, likely due to increasing humidity and more suitable microclimatic conditions at higher elevations. In contrast, forest age had a small but significant negative effect, potentially due to reduced availability of stressed host trees in older stands. Beetle activity peaked in early to mid-June, in agreement with previous observations of phenology of this species in Central Europe. These findings contribute to our understanding of the ecological factors shaping X. germanus populations and provide valuable insights for forest management strategies aimed at mitigating the spread of invasive ambrosia beetles.