Forest@ (Dec 2010)
Large outbreaks of Ips acuminatus in Scots pine stands of the Italian Alps
Abstract
In the last years, many Scots pine (Pinus sylvestris) stands have been severely attacked by the bark beetle Ips acuminatus (Coleoptera Curculionidae Scolytinae). In the outbreak area of San Vito di Cadore (Eastern Dolomites), the number of attacked trees since 2005 and both the emergence of bark beetles and natural enemies have been assessed. The investigated forests showed dozens of easily recognizable infestation spots with size ranging from about 20-30 trees (small spots) up to 300 trees (large spots). These infested spots evolved quickly, while new ones appeared within a radius of few hundreds of meters. During the last 5 years (2006-2010) we sampled branches from small and large spots and lodged them into emergence cages: adults of I. acuminatus as well as natural enemies were collected weekly, identified and counted. At the same time, a monitoring program of the surveyed pine stands was carried out to check the enlargement of old spots and the appearance of new ones. Voltinism and phenology of I. acuminatus were investigated by pheromone traps baited with different lures (Austrian vs. Spanish lures). The effects of a sanitation felling of about 4500 infested trees, carried out by the Regional Forest Service in autumn 2007 on I. acuminatus population were also assessed. Throughout the whole sampling area I. acuminatus resulted bivoltine, with the highest density attained during the first generation. However, a part of the population still evidenced a monovoltine behaviour. The realized sanitation felling strongly reduced both breeding sites and the number of infested trees observed during the following year. Moreover the pheromone-baited traps gave useful information about changes in bark beetle population density; the trapping efficiency of Spanish lure resulted clearly higher than the Austrian one. Finally, the recorded parasitism may have a role in outbreak dynamics as it was significantly higher during the second host generation, in both small and large spots.
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