THE EARLY STAGES OF FUNGAL INVASION IN NORWAY SPRUCE INFESTED BY THE BARK BEETLE IPS-TYPOGRAPHUS

Healthy Norway spruce trees infested by the bark beetle Ips typographu s were investigated weekly for 10 weeks to examine the early stages in fungal invasion. The study was performed in southeastern Norway durin g an epidemic period. The fungal association consisted of Ophiostoma s pecies and an undescribed Graphium species, which invaded the sapwood in an obvious succession. The pathogenic species Ophiostoma polonicum was the first invader of both phloem and sapwood and was always in the leading edge of fungal penetration into sapwood. Ophiostoma bicolor f ollowed 0. polonicum in the sapwood invasion. These species were succe ssively replaced by Graphium sp. 1, Ophiostoma penicillatum and Ophios toma ainoae. Ophiostoma penicillatum seems to be more adapted to colon izing the phloem than the sapwood. The earliest invaders were the spec ies most frequently carried by the beetles.