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ŠUMARSKI LIST 9-10/2018 str. 27     <-- 27 -->        PDF

Positive correlation between the bark beetle attack density and the predator abundance has been observed. Unlike recent Swedish research (Hedgren and Schroeder, 2004), this study has disclosed high abundance of Medetera accompanied with low attack densities on felled trees. Medetera larvae turn out to be the most abundant predator off all in this context (86 %). The results suggest that their ecological impact on I. typographus populations is not present only at outbreak conditions, but also at endemic levels. High predator abundance can even result in an 80 % reduction of bark beetle populations (Weslien, 1992). Assessing the predator abundance and its impact on the size of bark beetle populations is important in determining the impact of tree removal from infested stands on the outspread of this pest (Hedgren and Schroeder, 2004).
The majority of male beetle comprised this research copulated with two females, which is compliant with some recent research (Anilla, 1971; Starzyk et al., 2000; Grodzki et al., 2014). Pursuant to the calculation made within this research the average number of females per male was 2.3, while according to Wermelinger (2004), optimal number of females per male is 3. This figure depends on host susceptibility, and it differs between wind felled (Grégoire et al., 1997) and standing killed trees (Vakula et al., 2014). When males copulate with more than two females, it comes to a significant reduction in the breeding success (Schlyter and Zhang, 1995). Contrary to the expectations, gallery systems with two maternal galleries as an evolutionary adaptation to avoid intraspecific larval competition at high attack, were the prevalent form at low attack densities.
ACKNOWLEDGMENT
Zahvala
All authors are deeply grateful to Marko Kasumović, Milan Starčević, Pere Kulaš and Mile Kasumović for their invaluable contribution to this paper regarding the fieldwork. Further on, authors are grateful to the entire Department of Forests Measurement within state-owned company “Hrvatske šume” (Croatian forests Ltd.), especially to Ivica Serdar, the chief executive, for providing insightful fieldwork information.
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