A Mass Reproduction Outbreak and Estimation of the Spreading Risks for the Small Spruce Bark Beetle in Cedar Pine Forests of the Tomsk Region

The results of studying the mass reproduction outbreak of a new invasive pest of the Siberian pine (Pinus s-ibirica Du Tour), the small spruce bark beetle (Ips amitinus (Eichh.)), observed in Siberia for the first time, are presented in this paper. The studies were carried out in the south-eastern part of Western Siberia, within the Tomsk region, in pine forests damaged by an invasive bark beetle. It is shown that the occurrence of the outbreak was provoked by favourable weather conditions of recent decades and the abundance of trees, weakened for various reasons, in the recipient ecosystems of the invasion, among which the outbreak of the Siberian moth in 2016–2018 was of great importance. The small spruce bark beetle population dynamics in new habitats was compared with the native area in Europe, and certain peculiarities were revealed: an increase in the populations’ numbers level, a narrowing of trophic specialisation up to a regional monophagy, a decrease in the role of an interspecific competition due to the displacement of local stem dendrophagous species by the invader, the simultaneous existence of outbreak foci in different development stages and the correlation between their characteristics, the species composition of the forest stands and the weakening factors. An original method for assessing the spreading risk for an outbreak of the small spruce bark beetle breeding in the Tomsk region under the influence of a complex of factors that contribute to an increase in its number has been proposed and implemented at the forestries level.