The pine bark beetle Ips acuminatus: an ecological perspective on life-history traits promoting outbreaks

The bark beetle Ips acuminatus is an important pest in pine-dominated forests of Eurasia. Recently, the frequency of I. acuminatus outbreaks and mortality of host trees have increased, most likely as a result of climate change-related alterations in environmental conditions. Therefore, detailed information on the species’ natural history is essential to understand its potential to damage forests and to apply sustainable management measures. We provide a comprehensive overview on the life history of I. acuminatus, focusing on traits that might explain outbreaks and the ability to cause tree mortality. We review its importance for European forestry, outbreak behavior, host plant usage, reproductive biology, temperature-dependent development, diapause and overwintering behavior, and interactions with fungi, bacteria, nematodes and other arthropods. Interestingly, I. acuminatus has a strong nutritional dependency on the fungus Ophiostoma macrosporum, underlined by the presence of a prominent oral mycetangium, a spore-carrying organ, in females, which is not known for other Ips species. Moreover, I. acuminatus can reproduce sexually and asexually (pseudogamy). Additionally, information on the species’ evolutionary past provides valuable insights into the origin of certain traits. We present a phylogeny of the genus Ips and examine selected life-history traits in an evolutionary context. Together with its sister species Ips chinensis, I. acuminatus forms a separate clade within Ips. The ancestor of Ips bark beetles originated about 20 million years ago and was a pine-colonizing species inhabiting the Holarctic. Finally, open fields of research are identified to guide future work on this ecologically and economically important pine bark beetle.