Life-history traits promoting outbreaks of the pine bark beetle Ips acuminatus (Coleoptera: Curculionidae, Scolytinae) in the south-eastern Alps

The pine bark beetle Ips acuminatus has recently increased frequency and intensity of outbreaks in Pinus sylvestris stands in the Alps. During a 3-year period, we investigated life-history traits of the species that may have adaptive value. In the south-eastern Alps, I. acuminatus becomes active in early spring when the air temperature reaches 14A degrees C, suggesting the presence of a local population adapted to low temperature. Such an early emergence allows the complete development of a second generation, even if only a portion of the population is truly bivoltine. As a consequence, there are two main attack periods, the first in early spring and the second in summer, resulting in different trees being colonised each time. Irrespective of the generation, a large part of the beetles leaves the breeding substrate before hibernation, and this is interpreted as an escape from natural enemies associated with the bark. These findings suggest that the populations of I. acuminatus of the south-eastern Alps may benefit from climate warming as they have more opportunities to complete the second generation and to escape from mortality factors associated with a long permanence in the bark. In addition, the extended period of tree colonisation offers more possibilities to locate suitable hosts and to build up outbreak densities.