Effect of the Four-Eyed Fir Bark Beetle Invasion on the Species Composition and Structure of the Siberian Fir Stem Pest Complex

In the region of a Polygraphus proximus invasion, we have studied the patterns of stem dendrophages consortia (simple structural systems in biocenosis that combine autotrophic and heterotrophic organisms based on topical and trophic relations), the core of which is the host tree Abies sibirica ledeb. The analysis is carried out on 4835 trees from 46 sample plots in the dark coniferous fir forests of Tomsk oblast according to the following indicators: the vital state of trees and stands; the taxonomic composition of insects, their occurrence, abundance, and ecological characteristics; and participation in the formation of xylophages communities at different host-tree weakening stages. On the fir trees with P. proximus , 21 species of stem dendrophages are identified. In all studied stands, the four-eyed fir bark beetle is absolutely dominant. Monochamus urussovi Fisch. is a permanent inhabitant of the stands damaged by the alien bark beetle. A direct dependence of the species coincidence degree with the disturbance of forest stands and their taxation indicators is revealed ( r s = 0.6). The species richness of the population consortia of fir has an average dependence on the forest density and capacity ( r s = 0.4). The ability of abundant species of stem dendrophages to selectively colonize fir trees at a different stage of resistance decline and reveal the features of pre- and postinvasive consortia is determined for the first time. In a multispecies group, P. proximus acts as an initiator of the succession of stem inhabitants, determining the composition of individual consortia, the sequence of colonization of the plant by species of dendrophages in accordance with the degree of weakening of the host tree, and the ability of insects to use the forage substrate. It is found that the number of the main aboriginal physiological pests of fir is at a low level, and they populate weakened trees following the attacks of an alien bark beetle or drying out for other reasons. The transformation of the indigenous stem dendrophage complex as a result of the invasion of the four-eyed fir bark beetle is an example of a rapid consortiogenesis leading to ecological and evolutionary changes in ecosystems.