Mass Reproduction of Polygraphus proximus Blandford in Fir Forests of Siberia Infected with Root and Stem Pathogens: Monitoring, Patterns, and Biological Control

Abstract

Conifer decline (Abies sibirica Ledeb. stands) as a result of complex biotic effects on the territory of Krasnoyarsk krai by 2018 reached an area of 541 400 ha; the potential area of further death of A. sibirica is up to 10 million ha. The main reason is the phytopathogenic fungi Armillaria mellea s.l. and Heterobasidion annosum s.l. combined with bark beetle Polygraphus proximus. Trees affected by root pathogens are centers of forest dieback, from which pathological outbreaks spread, including the effects of P. proximus and its phytopathogenic mycoassociates. Neonectria fuckeliana (C. Booth) Castl & Rossman is among the concomitant pathogens in the scale of the lesion, which causes a resin flow that is similar to the effects of P. proximus attack. The phytopathogenicity of pure cultures of the dominant root pathogens of Armillaria borealis Marxm. & Korhonen and Heterobasidion annosum (Fr.) Bref., as well as the stem pathogen of N. fuckeliana, has been confirmed by a series of experiments in vitro. Promising natural agents for the regulation of P. proximus abundance are highly virulent aboriginal strains of Beauveria bassiana (Bals.–Criv.) Vuill., resulting in maximum insect death (up to 100%) for 7–11 days and retaining activity in the temperature range of 16–24 ± 1°C.