Differential responses to verbenone in Mediterranean pine bark beetles and associated natural enemies: Implications for integrated forest management

In Mediterranean pine forests, the management of bark beetle outbreaks (Coleoptera: Curculionidae: Scolytinae) is a critical challenge. This study, conducted in coastal stands of Tuscany, evaluates the efficacy of verbenone as an anti-aggregant for a complex of bark beetles across multiple periods (2016–2019, 2022–2024, and 2025–2026). The methodology employed a dual trapping system to target different ecological niches. To monitor Ips sexdentatus, Orthotomicus erosus, and the non-aggerssive bark beetle Hylurgus ligniperda, Theysohn slot traps were used, baited with a commercial aggregation pheromone blend. Lindgren funnel traps were deployed to target Tomicus destruens, baited with host monoterpenes. To assess the repellent effect of verbenone, treatments were compared using traps baited with pheromones/monoterpenes alone versus those with added verbenone dispensers. A spatial-temporal rotation was applied, switching trap positions and treatments every control date to eliminate bias related to trap location. Results revealed highly divergent responses. Verbenone acted as a strong repellent for O. erosus and I. sexdentatus, reducing captures by 76% and 67% respectively. In contrast, H. ligniperda showed a significant attraction to verbenone, with captures increasing by 50%, likely identifying the volatile as a marker for degraded host tissue. Crucially, data from the 2025–2026 season demonstrate that verbenone fails to act as a repellent for Tomicus destruens, showing no significant reduction in captures. Regarding natural enemies, the predator Thanasimus formicarius (Coleoptera: Cleridae) was significantly inhibited by verbenone (captures reduced by 73%), while Temnochila caerulea (Coleoptera: Trogossitidae) remained neutral, its presence being more influenced by pheromone release rates than by verbenone. These findings underscore that while verbenone is effective against Ips and Orthotomicus, it is ineffective for Tomicus destruens management. A species-specific approach is therefore mandatory, as the use of verbenone may inadvertently suppress key biological control agents or be impractical towards major target pests.