SEASONAL DIFFERENCE IN THE ABUNDANCE OF THE SPRUCE BEETLE (IPS-TYPOGRAPHUS JAPONICUS NIIJIMA) (COL, SCOLYTIDAE) WITHIN AND OUTSIDE FOREST IN A BIVOLTINE AREA

In Hokkaido (Japan), the spruce beetle (Ips typograpaus japonicus) kil ls standing spruce trees after selection cutting. The seasonal change in the number of beetles captured in 18-21 traps within or outside for est was analysed, with reference to a control strategy for this specie s in a bivoltine area. The number of beetles captured in traps had two peaks: one, which was small, in early June, and the other, which was a large peak, in July. However, the number of beetles captured in trap s outside the forest had only one small peak, in June. The difference between the inside and outside of the forest was caused by the differe nce in the number of newly emerged beetles captured in traps. Beetles were distributed contagiously within the forest and there was no remar kable change in distribution pattern throughout seasons. Beetles were distributed at random in June when beetle activity was high outside fo rest. Overwintered beetles must undertake long-range dispersal irrespe ctive of whether they are within or outside of forest for finding suit able breeding materials. Nevertheless, the most important point is tha t newly emerged beetles stayed inside the forest and only a few indivi duals dispersed outside the forest. This study recommends that differe nt control methods are adopted according to the seasons for the contro l of spruce beetles.