Patterns, drivers and detectability of infestation symptoms following attacks by the European spruce bark beetle

Abstract Recent outbreaks of the European spruce bark beetle ( Ips typographus ) in Norway Picea abies forests Central Europe highlight importance timely detection and sanitation infested trees for pest management efficacy. This study provides novel quantitative evidence on manifestation infestation symptoms their visual detectability, to guide accelerated, optimized terrestrial monitoring, as well establishing benchmarks potential alternative (e.g. sensor-based) monitoring approaches. We employed bi-weekly, individual tree-level assessments 85 hectares spruce-dominated unmanaged forest over a 2-year period south-western Germany (detecting total 1,176 trees). By applying decision tree-type models, we quantified predictive power observed correlation with environmental factors time. Terrestrial accuracy timeliness were high, suggestive being sufficient suppress I. outbreak propagation by subsequent felling. Among six studied symptoms, boring dust occurred most frequently (in 82% correctly detected infestations) is suitable detection. Total symptom abundance was best explained two site parameters (slope, Standardized Precipitation-Evapotranspiration-Index) population density, while it widely independent tree Though varied time among trees, patterns clearly identified. For instance, infestations spring critical be detected, increasing crown discoloration defoliation facilitated late summer autumn. Findings further imply that hibernation would optimally already felling applied before November.