Overwintering of eight toothed spruce bark beetle (Ips typographus) in spruce forests of north Velebit.
A field trial was conducted in the spring of 2008 to investigate the overwintering strategy of the eight toothed spruce bark beetle (Ips typographus) on two experimental plots at different elevation zones in the northern part of the Velebit Mountain in Croatia. The core idea was to test the already described phenomenon of different hibernation niche choice within the northern dwelling populations (predominantly choosing forest litter) and southern populations (staying within their growing niche, under the spruce bark). Each experimental plot was characterized by the freshly attacked group of spruce trees (last summer - second generation of spruce bark beetle). The trial started on 19 April and ended on 9 June covering fully the flight of the first, spring generation of spruce bark beetle. The obtained results confirmed that the eight toothed spruce bark beetle does overwinter in the forest litter. The ratio between adults staying in their developmental sites (spruce bark) and those that entered forest litter varied in the two plots. In the higher plot the ratio was 50:50. The lower plot revealed a ratio of 60:40 in favour of beetles using bark instead of litter as an overwintering niche. The documented time lag between the first emergers (both bark and forest litter) and first pheromone trapped beetles illustrates the known phenomenon of the first flight phase of the spruce bark beetle - the dispersal flight.