Bark borer Semanotus japonicus (Col., Cerambycidae) utilization of Japanese cedar Cryptomeria japonica: a delicate balance between a primary and secondary insect

The bark borer, Semanotus japonicus (Col., Cerambycidae), attacks living Ja panese cedar, Cryptomeria japonica, with newly hatched larvae mainly feedin g within the inner bark of the trunk. To understand how S. japonicus is aff ected by host nutrition and resin flow, newly hatched larvae were introduce d into stressed cedar trees. Stress was induced by either heavy pruning, st em cutting (i.e. removing the side branches and top of tree), or girdling. Larval mortality due to resin flow in the 'heavy pruning treatment' and the 'stem cutting treatment' tended to be lower than that in the untreated con trol cedar trees where all larvae were drowned by resin flow. Parasitism to the larval stage was observed in the stem-cutting trees, not in living tre es, suggesting that S. japonicus may avoid parasitism in living cedar trees because few volatiles are produced. In the 'stem-girdling treatment', alth ough more than 90% of the introduced larvae died due to poor nutrition belo w the girdle, 7.8% of the larvae above the girdle reached the adult stage. The live body weight of the adults collected from above the girdle was simi lar to those taken from naturally infested cedar trees. These results sugge st that S. japonicus requires adequate host nutrition but that larvae are d efenceless against high resin flow. Thus, S. japonicus seems to be in a tra nsition state between being primary or secondary with respect to its attack behavior on living cedar trees.