Spruce bark beetles ( Ips typographus, Pityogenes chalcographus, Col.: Scolytidae) in the Dinaric mountain forests of Slovenia: Monitoring and modeling

In this paper, we analyze the phenology of spruce bark beetles ( Ips typographus and Pityogenes chalcographus) in the Dinaric mountain forests of southwestern Slovenia. The study of I. typographus took place from 1986 to 2000, while that of P. chalcographus took place from 1993 to 2000 in an area characterized as a Dinaric Fir-Beech forest community ( Abieti- Fagetum dinaricum) on the Karst plateau (447–751 m above sea level). On the studied area Norway spruce ( Picea abies) has been planted between 60 and 90 years ago on approximately 1000 ha. Frequent catastrophic weather conditions are characteristic for this area, followed by an increased trophic capacity of the forest for the various bark beetle species. The population density of spruce bark beetles was monitored at five locations at varying exposures using commercial pheromones (Pheroprax ® and Chalcoprax ®) in traps under the trade name Theysohn. Both species studied ( I. typographus and P. chalcographus) have a relatively high abundance and have two main generations per year; both species may also produce two sister generations. Data on some environmental factors as well as data on bark beetle catches have been collected and then analyzed to model the dependence of spruce bark beetle catches on the environmental factors. The machine learning methodology of liner regression as well as model tree induction was used for this purpose. The following attributes were used to analyze the occurrence of both species of bark beetle: position (NW, NE, W, E, N and S), age of pheromone, number of days since last monitoring, average monthly temperature, monthly precipitation, month and previous number of bark beetles. There was a strong correlation between a high population density of I. typograpus and Northeast (NE) and position and a high density of populations of P. chalcographus and West (W) and North (N) positions.