Spatial distribution of hibernating adults of eight-toothed spruce bark beetle (I. typographus L.) and double-spined bark beetle (I. duplicatus C. R. Sahlb.)

Field research was conducted in selected pine−spruce stands of the Oleśnica Śląska Forest District (SW Poland), where in 2004 intensive mortality of trees infested by I. typographus and I. duplicatus was observed. The results show that most I. typographus beetles hibernated under the bark of sample trees (71.2%). Most I. duplicatus beetles hibernated in forest litter and soil (90.5%). In the litter and soil samples, the largest number of hibernating beetles (of both species) were observed in the close neighborhood of tree stems, within the radius of up to l m (96.2% and 94.0% respectively). The estimated number of beetles hibernating in the forest litter and soil under the canopy of a single sample tree was 383 and 61, respectively. In bark samples I. typographus hibernated only as adult (imago)