The semiochemical push-and-pull technique can reduce bark beetle damage in disturbed Norway spruce forests affected by the Vaia storm

In a 2-year field study conducted in the South-Eastern Alps following a large windthrow disturbance, we tested a large-scale use of a semiochemical push-and-pull strategy to protect susceptible Norway spruce edge trees from the European spruce bark beetle, Ips typographus (Coleoptera: Curculionidae, Scolytinae). Slot traps baited with aggregation pheromones (‘pull’) and three repellent semiochemicals (‘push’) were used in both years. In 2020, 26 windthrown areas were classified into three levels of infestation risk, and each was randomly assigned to one of three experimental protocols: eight push-and-pull sites; nine trap-only sites and nine control sites. In 2021, the trials were repeated in 22 clear-cuts of infested spruce forests, applying two protocols: 16 push–pull and 6 control sites. Fifty traps and 1500 repellent dispensers were used in 2020, and 26 traps and 1500 repellent dispensers were used in 2021. The push-and-pull technique performed well in post-windthrow conditions (2020 trials), especially at high infestation risk, with significantly lower damage to forest edges when compared with untreated sites. The use of pheromone-baited traps alone was not enough to avoid colonization of forest edges, especially in high-risk sites. When the push-and-pull protocol was applied in clear-cut areas (2021 trials), the technique was less effective and did not significantly reduce the number of infested trees along the forest edge. Possible interactions with climate conditions are also discussed.