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RESULTS REZULTATI Historical records of the Birch bark beetle in Croatia – Povijesni pronalasci brezovog potkornjaka bjelikara u Hrvatskoj The Birch bark beetle was first recorded in Croatia between 1891 and 1906 in Duboka close to Pleternica (Koča, 1900; Koča, 1906). An additional observation of the bark beetle was made in Skrad in 1913 (Trédl, 1915b; Langhoffer, 1915). Depoli (1940) reports the possible presence of the Birch bark beetle in Skrad in the 1930’s, but detailed information regarding the impacts on forest stands or research conducted on the bark beetle is lacking. None of the museum specimens of this bark beetle were collected from Croatia, they originate from neighboring countries. Therefore, 103 years have passed since this species was last recorded in Croatia. Specimens of the Birch bark beetle are in two collections held within CNHM: Spaić & Pfeffer beetle collection (1. Wingelmüller, Butschowitz, Czech Republic, South Moravian Region; Inv. No 2251; 2. Württemberg (Württemberg), Germany; Inv. No 2252) and in the Novak insect collection (CNHM) a specimen of the Birch bark beetle exists, but without the description of the location, only with the name of the collector – “Josef Klimesch”. In Hensch’s entomological collection at the Faculty of Forestry, University of Zagreb specimens of the Birch bark beetle originate from Vojvodina, Serbia (“Ruma, Slavonija”). Current records of the Birch bark beetle in Croatia – Trenutni pronalasci brezovog potkornjaka bjelikara u Hrvatskoj Silver birch tree logs (containing Birch bark beetles) were collected in Striježevica, on November 23rd, 2016. On November 24th, 2016 logs were collected from Jankovac and July 3rd, 2017 logs were collected from Ravna Gora. At two other locations (Orljavac and Sošice) signs of attack from Birch bark beetles were observed (Figure 3, Table 1). In total, 55 specimens (18 males, 37 females) were collected from field collected Silver birch logs. Also, specimens of the longhorn beetle Saperda scalaris L. (1758) (Coleoptera: Cerambycide) and an insect parasitoid Dendrosoter protuberans Nees (1834) (Hymenoptera: Braconidae) emerged from logs. DISCUSSION AND CONCLUSIONS RASPRAVA I ZAKLJUČCI Faunistic studies of bark beetles in Estonia, Finland, Russia (Voolma et al., 2004, Mandelshtam & Khairetdinov, 2017) and Slovakia (Kollár et al., 2009) regularly record the presence of Birch bark beetle. Although the Birch bark beetle is distributed throughout Europe, Siberia, Korea, Japan and China (Pfeffer, 1995; Vigna Taglianti et al., 1999; Alonso-Zarazaga et al., 2016) it is rarely recorded in Croatia. The primary reason for few recorded occurrences in Croatia is that Silver birch is minor component of forest stands with a wood stock of only 0.10 % and of little economic importance (Hrvatske šume d.o.o., 2017), which relates to southern edge of its distribution area in Europe (Kovačić & Nikolić, 2005; Hynynen et al., 2009). Climate change effects on Silver birch have been researched in Finland (Briceno-Elizondo et al., 2006; Garcia-Gonzalo et al., 2007), and found that this tree species may increase in abundance at its northern range. This tree species will likely suffer and decline in abundance at its southern ranges as temperatures increase, but what will happen in Croatia requires further research. This bark beetle is the only Scolytus species to colonize and kill birch (Linnakoski et al., 2009). Throughout its range, the Birch bark beetle colonizes a number of birch species: B. pubescens (Ehrh.), B. pendula (Roth), B. raddeana (Trautv.), B. dahurica (Pall.), B. ermanii (Cham.), B. platyphylla (Sukatschev) and B. costata (Trautv.) (Pfeffer, 1995; Zúbrik et al., 2013). Since the last known record in Croatia was before 103 years ago (Trédl, 1915b; Langhoffer, 1915), we can conclude that this species in Croatia has a low population density in forests, although Silver birch trees can also be found in city parks and private gardens (Karavla, 2006), where so far the Birch bark beetle has gone unnoticed. Impacts of this beetle may be minimal (Linnakoski et al., 2008; Linnakoski et al., 2009) but research on this bark beetle should not be neglected since it represents valuable part of entomofauna in Croatia. Research about the Birch bark beetle in other regions and their relationship with ophiostomatoid fungi have so far confirmed significant connection with the tree fungus Ophiostoma karelicum (Linnakoski et al., 2008; Linnakoski et al., 2009; Jankowiak, 2011). According to Linnakoski et al. (2008; 2009,) Ophiostoma karelicum pathogenic role combined with Birch bark beetle remains unclear. Similar bark beetle-fungal associations, but with far more visible impact on forest stands, can be seen with Dutch elm disease (pathogen Ophiostoma novo-ulmi) which is also transferred by Scolytus bark beetles (Moser et al., 2010) and Sudden wilt disease in Mango (pathogen Ceratocystis manginecans) transmitted by the bark beetle Hypocryphalus mangifera Stebbing (1914) (Al Adawi et al., 2012). Further research about Birch bark beetle in Croatia should target fungal relationships in order to see which species of ophiostomatoid fungi are present and possibly to clarify its role on the southern edge of Silver birch distribution area. Phoretic mites also play an important role in bark beetle ecology and interactions between bark beetles, phoretic mites and ophiostomatoid fungi range from mutualism, commensalism to antagonism (Klepzig et al., 2001; Hofstetter et al., 2006, Moser et al., 2010). Phoretic mites are |