Abstract
Japanese pine sawyer, Monochamus alternatus, females were allowed to lay eggs at weekly intervals into fresh Pinus densiflora logs during the oviposition seasons of 1979 to 1981. Fine and coarse-meshed cages were used to isolate some logs from the beetles' natural enemies. Others were uncaged. Many univoltine and a few semivoltine adults emerged from the logs. Variations in the survival rate from egg to adult were significantly explained by the presence of the natural enemies and the initial density of the sawyer, but not by the oviposition time. The density-dependent mortality was found during the period from egg to adult stage and was caused by intraspecific competitions. The natural enemies, possibly small insects able to pass through the coarse-meshed cages, were density-independent mortality factors, lowering the level of the survival rate. These experiments were conducted in the Ishikawa Forest Experiment Station Arboretum which consisted of deciduous and evergreen trees.
