Rapid Population Response of the Mediterranean Pine Engraver (Orthotomicus erosus Wollaston) Following a Severe Windthrow Event

Severe windthrow events can create highly favorable conditions for bark beetle outbreaks by generating large quantities of weakened breeding material. This study investigated the population response of the Mediterranean pine engraver, Orthotomicus erosus Wollaston, following a microburst windstorm that struck Marjan Forest Park, an urban Mediterranean Aleppo pine (Pinus halepensis Mill.) forest in Split, Croatia, in July 2025. Approximately 2,000 m3 of damaged timber remained in the forest until February 2026, enabling assessment of colonization dynamics and outbreak development. Field inspections, laboratory analyses, and pheromone trap monitoring were conducted between July 2025 and April 2026. Colonization of windthrown material began within two weeks after the disturbance, and infestation rates reached 94% of examined logs by December 2025. Most infested logs (86%) already contained emergence holes, indicating successful completion of beetle development. Pheromone traps captured a total of 131,588 individuals, with more than 88% recorded during spring 2026 and a pronounced peak occurring on 8 April 2026. The appearance of newly attacked standing trees in spring 2026 confirmed rapid population expansion from fallen material to living hosts. Results demonstrate the exceptional outbreak potential of O. erosus following extreme climatic disturbances and emphasize the importance of rapid sanitation measures and continuous monitoring in Mediterranean pine forests under climate change conditions. Delayed salvage logging after severe windthrow can rapidly trigger outbreak development of O. erosus.