| Summary: | In 2019, the bark beetle <i>Ips amitinus</i> (native to central Europe) was identified in south-western Siberia at a distance exceeding 2500 km east of its previously known easternmost location in the European part of Russia. In Siberia, its invasive populations are characterised by high abundance and harmfulness. Here, <i>I. amitinus</i> accomplishes primary attacks on standing vital trees of <i>Pinus sibirica</i> with a lethal outcome. This invasion has already resulted in massive dieback in stands of pine over a large geographic territory. By, 2021, the invaded area was estimated to cover at least 31,200 km<sup>2</sup>. The objectives of this study were to investigate fungi associated with/vectored by <i>I. amitinus</i> in its invasive area in south-western Siberia and wood decay fungi that cause root and butt rots to <i>P. sibirica</i>. This led to the following conclusions: (i) DNA analysis of sixty adult beetles of <i>Ips amitinus</i> collected from <i>P. sibirica</i> in south-west Siberia revealed the presence of 143 fungal taxa; (ii) species richness was significantly higher in beetles collected from dead branches than from (more recently infested) dying branches; (iii) fungal communities were >90% dominated by yeasts, among which the most common were <i>Nakazawaea holstii</i>, <i>Kuraishia molischiana</i>, and <i>N. ambrosiae</i>; (iv) entomopathogenic <i>Beauveria bassiana s.l.</i> was the most common fungus isolated from dead/mycosed beetles of <i>I. amitinus</i>, followed by <i>Lophium arboricola</i> and four <i>Ophiostoma</i> spp.; and (v) <i>Heterobasidion parviporum</i> was the most common decay fungus detected, which was causing heart rot in stems of <i>P. sibirica</i>.
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