Overwintering Migration of the Double-Spined Spruce Bark Beetle Ips duplicatus (Sahlberg, 1836) (Coleoptera; Curculionidae)

The double-spined bark beetle, Ips duplicatus, is an example of a species whose economic importance has increased in many European countries over the past decade. Many aspects of its life cycle remain unknown, complicating its management. I. duplicatus adults overwinter in forest litter, which makes the removal of infested trees during winter ineffective. Therefore, this study focuses on the mechanisms and timing of I. duplicatus overwintering migration into the forest litter. Only 2.2% of adult I. duplicatus overwintered under the bark of spruce logs stored outdoors from August 2016 to March 2017. In all, 94.4% of the beetles emerged and burrowed in forest litter. Migration began in late August, peaked in mid-September, and lasted until mid-October. At that time, forest litter collected at the base of an infested tree contained an average of 154.7 +/- 23.9 I. duplicatus. Catches of migrating adults on glue stripes proved that the beetles walked down the trunk on days when the average daily temperature reached 10-15 degrees C. Based on the results, we suggest that trees infested with I. duplicatus that have completed their development into adults should be removed no later than September. Sanitation cutting in the following months is not effective against this pest.