Abstract
Zethenia rufescentaria MOTSCHULSKY (Lepidoptera: Geometridae) is an important herbivorous pest of Japanese larch, Larix leptolepis GORDON, in Hokkaido. An outbreak of the moth occurred from 1989 to 1991 in eastern Hokkaido. About 20 parasitic insects, 1 predatory insect, and some parasitic fungi were recognized as natural enemies of the moth in the outbreak. The important observed mortality factors were starvation in the older larval stages, parasitic insects in the pupal stage, disappearance of pupae during winter (which seemed to be caused by predation by small mammals) and an entomophthoraceous disease in the larval stage. The disease is considered to be the most important factor causing the outbreak decline.
