Influence of insects on the diversity of fungi in decaying spruce wood in managed and natural forests

Insects are known to disseminate fungal propagules to decaying wood. Their effect on the diversity of the decomposer mycota is so far unexplored. Sixteen Norway spruces ( Picea abies) were felled and cut into 50 cm long bolts which were placed in four managed and four natural stands in southern Finland. The bolts were covered with net cages to prevent insect access. Half of the net cages were opened during each spring for 3 weeks. After 28–30 months, the bolts were investigated for insect marks, dry weight loss, and a batch of them was taken for fungal isolations. The fungal isolates were first divided into morphologically distinguishable taxonomic genera or species and further into operational chemotaxonomical units (OCTUs) by their combined fatty acid and sterol profiles (FAST-profiles). The number of insect marks (holes and gnawings) found on the bolts after 28–30 months varied from 0 to 6400/m 2 depending on the site and on whether the net cage was opened during spring or not. The bolts were attacked mainly by two bark beetle species, Trypodendron lineatum and Hylurgops palliatus. Boring and gnawing marks of these beetles were significantly more common on bolts in managed than in natural sites. Bolt dry weight loss correlated positively ( r=0.461, P