SUCCESS OF SPRUCE BEETLE ATTACKS IN PRUNED AND UNPRUNED BOLES OF LUTZ SPRUCE IN SOUTH-CENTRAL ALASKA

Pruning live branches from different heights and sides on the boles of long-crowned Lutz spruce (Picea x lutzii Little) baited with frontalin reduced successful spruce beetle (Dendroctonus rufipennis Kby) attacks in pruned sections of most trees. The benefits of pruning seemed to be primarily from increased temperature and light intensity resulting from greater exposure and insolation on pruned boles, but physiological changes in the host such as improved moisture status, although not measured, should not be disregarded. Pruning had little protective effect on rapidly growing bole sections because those sections were already resistant to successful spruce beetle attack. The effect of pruning on successful beetle attack was presumably conservative because baited trees were used. Removing the lower live branches from Lutz spruce reduced successful spruce beetle attacks on warm sites in south-central Alaska, and this method should be tested on cold sites.