Natural enemies in Ips typographus trapping programs: evidence from monitoring and mass-trapping in the Italian Alps

Following large-scale disturbances such as the 2018 Vaia storm in the Italian Alps, trapping programs using aggregation pheromones have been widely implemented against the European spruce bark beetle, Ips typographus (Coleoptera: Curculionidae: Scolytinae), although potential side effects on non-target insects remain debated. Because predators and parasitoids provide key ecosystem services through natural regulation of bark beetle populations, quantifying their occurrence in trapping programs is particularly relevant. In 2024, we assessed non-target captures in operational I. typographus pheromone traps in the Alta Badia valley (South Tyrol, Italy), comparing single monitoring traps with dry collection to mass-trapping stations using three-trap cross configurations with preservative liquid. All by-catch was collected and morphologically identified. Total by-catch amounted to 16,362 individuals (5.71% of sampled catches). Natural enemies represented 7,640 specimens (46.69% of by-catch), a proportion comparable to that of non-target bark beetles (46.67%). The non-target proportion (excluding bark beetles) was significantly higher in mass-trapping than in monitoring (4.15% vs. 1.00%). Importantly, parasitoids were repeatedly captured: Tomicobia seitneri (Hymenoptera: Pteromalidae) dominated the natural enemy assemblage (6,784 individuals; 88.80%), while Ropalophorus clavicornis (Hymenoptera: Braconidae) was also detected (299 individuals; 3.91%). Scaling up to the valley-wide program suggests that ~47,898 natural enemies may have been captured by mass-traps over the study period. Our findings provide quantitative evidence that I. typographus mass-trapping programs can interact strongly with the natural enemy complex, including parasitoids, highlighting a necessity to incorporate the conservation of biological control agents into large-scale trapping strategies. For example, at our lowest-altitude site, a spring flight peak occurred with very few non-target captures, suggesting that site- and season-specific timing may offer a potential strategy to maintain biological control services while meeting management objectives. Author biography: Dr. Tiziana Panzavolta is an Associate Professor in the Department of Agriculture, Food, Environment, and Forestry at the University of Florence. Her research focuses on