DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 3-4/2018 str. 61     <-- 61 -->        PDF

DISCUSSION
Rasprava
Which ophiostomatoid fungi are vectored by I. amitinus? – Kojim ofiostomatoidnim gljivama je I. amitinus vektor?
This study showed that I. amitinus is involved in ophiostomatoid fungi dispersal. Despite the fact that our research studies were carried out on rather small sample we found ten different ophiostomatoid fungi as well as yeast and Penicillium spp. The results were based on samples collected from one location in one breeding season of I. amitinus. Fungal species found can be compared with other investigations of the bark beetle I. amitinus in Europe (Grosmann 1931, Kirisits et al. 1998). Our findings concurred with an investigation by Kirisits et al. (1998) that was made on Norway spruce trees. Additionally, we found associations that were not previously recorded, namely those with species G. cucullata, G. fimbriisporum and O. fuscum.
Even if I. amitinus are causing more damages now then they have in the past (Jurc & Bojović 2004, Ribič 2007, Okland & Skarpaas 2008), the assemblages of ophiostomatoid fungi in this investigation showed that the associated species are not highly pathogenic, referring to the pathogenicity researches that were made with fungi species found also during this research (Repe et al. 2013, Kirisits and Offenthaler 2002, Kirisits 1998, Jankowiak and Kolarík 2010). The association of fungi was dominated by the species O. brunneo-ciliatum (Tab. 1). C. minuta was very commonly observed as well and is associated with a broad range of bark beetles as well as different host trees (Kirisits 2004). According to the pathogenicity researches, the most virulent fungal associate of bark beetles on Norway spruce is E. polonica (Repe et al. 2013 Kirisits and Offenthaler 2002, Kirisits 1998, Jankowiak and Kolarík 2010), found also during this research. However E. polonica was one of the least presented species in association with I. amitinus (Table 1), noting the fact that the sampling was undertaken at only one location and that the abundance of E. polonica could be different at other locations. Our observation of E. polonica was not as common as reported by Kirisits et al. (2000). It represented 5.9% of the associated fungi in this investigation and was found on 10.1% of all wood chips and 4.9% of bark beetles. It was not isolated not from pupae nor from larvae. Revising E. polonica abundance in prior investigations of other bark beetles on P. abies trees in Europe, the frequency of occurrence has differed considerably. It has rarely appeared as the dominant species (Solheim 1986, Kirisits 2010, Krokene & Solheim 1996) and was often not found at all or was found in moderate quantities (Jankowiak et al. 2009, Sallé et al. 2005, Giordano et al. 2013). It has been speculated that the composition of fungal associates may differ during different phases of population dynamics (Harding 1989, Solheim 1992a, Solheim 1992b, Kirisits 2004, Kirisits 2010) or over different localities in Europe (Kirisits 2004).
Wood colonization by I. amitinus – Kolonizacija drva od I. amitinus
At the beginning of bark beetle colonization, fungi were not yet present in the sapwood. Fungi penetrated into the wood slowly; an occurrence which was also presented in the research of ophiostomatoid fungi penetration in P. abies trees performed by Solheim (1992b). At the second collection time, after the bark beetles had been established in the tree, ophiostomatoid fungi were present. I. amitinus thus effectively transmitted the ophiostomatoid fungi. The most abundant species, namely, G. penicillata, was present in just 25% of wood chips out of the 158 samples taken from 18 circular sections. The complex of fungi found in wood was very similar to those found on the different beetle life stages (Table 1). The difference was that there were fewer fungi found on wood and the composition of fungi on wood differed from this on bark beetles.
At 0.5 m above the stump, few fungi were present, though there was not a strong beetle colonization either. It is known that I. amitinus prefer to colonize parts of trees with smaller dimensions (Jurc & Bojović 2004, Ribič 2007, Okland & Skarpaas 2008), consequently, beetles are more present higher up on the trunk of adult trees. Witrylak (2008) established that the most abundant I. amitinus colonization was where the habitat is more suitable for bark beetle development that is in the middle part of the stem, where the bark was 2-3 mm thick. In our research, accordingly, it was shown that the number of isolated fungi increased with the sample height. Just 9.5% of fungi was found on lowest sampling height (0.5 meters), 42.5% of fungi was found at sampling height of 6 meters and 48% of fungi on sampling height of 15 meters.
Comparison of the fungi isolated from wood and different beetle life stages – Usporedba gljiva izoliranih iz drva i različitih razvojnih faza potkornjaka
During this research, ophiostomatoid fungi were isolated from all bark beetle life stages (adult bark beetles, larvae, pupae) and wood. On adult bark beetles, the majority of ophiostomatoid fungi were found, and the smallest number was found on larvae. Considering the quantity of collected samples, the most ophiostomatoid fungi were found on pupae. This can be explained by the simple fact that feeding larvae penetrate deeper into the wood and can bore their way in front of fungi penetration. When the specimens start to pupate, thick layers of conidiophores and ascoscarps develop around them in the pupal chambers. After young specimens transform from pupae, they become inoculated with conidia and ascospores (Kirisits 2004).