Harmfulness of xylophagous insects for silver birch (Betula pendula Roth.) in the left-bank forest-steppe of Ukraine
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The aim of the research was to determine the rate of the damage of xylophagous insects for silver birch (Betula pendula Roth.) stands in the Left Bank Forest-steppe of Ukraine. Evaluation of physiological harmfulness considered a health condition of inhabited trees, features of maturating feeding and pathogens vectoring for the cases of so-called ‘provoked aggressiveness’ and its absence. Evaluation of technical harmfulness considered a location and depth of larval galleries and pupal chambers, colonized sapwood surface, and stem part. Evaluation of general harmfulness considered physiological harmfulness, technical harmfulness and generation number. Among 22 xylophagous insect species, 4 species were widespread (Agrilus viridis (Linnaeus, 1758), Xylotrechus rusticus (Linnaeus, 1758), Xyleborinus saxeseni (Ratzeburg, 1837), and Xyleborinus attenuatus (Blandford, 1894)); 3 species were common, 6 species were rare and 9 species were single. The highest physiological harmfulness is expected for Tremex fuscicornis (Fabricius, 1787) and Tremex magus (Fabricius, 1787), Сhrysobothris affinis (Fabricius, 1774), Agrilus viridis (Linnaeus, 1758), Xylotrechus rusticus, and bark beetles. The highest technical harmfulness is expected for wood wasps – Tremex spp., jewel beetles Dicerca furcata (Thunberg, 1787) and Dicerca alni (Fischer von Waldheim, 1824), longhorn beetle Xylotrechus rusticus, and xylomycetophages – Xyleborinus sp. All widespread species are evaluated by a wide range of physiological harmfulness. Three of them (all except Agrilus viridis) are evaluated by highly technical harmfulness and from moderate to highly general harmfulness. Among the species having a common occurrence, Tremex fuscicornis can be highly harmful only in the case of tree weakening by negative factors, another two species can be non-harmful, and Xiphydria longicollis (Geoffroy, 1785) can be low harmful in the case of tree weakening by negative factors. Among the rare species, Scolytus ratzeburgi Janson, 1856 can be low or moderately harmful and Tremex magus can be low or highly harmful depending on the presence or absence of other negative factors. Among single species, Zeuzera pyrina (Linnaeus, 1761) can be moderately harmful because it colonizes almost healthy trees. The rest three species can be moderately harmful in the case of tree weakening by negative factors.
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