Abstract
Pseudaletia separata occurred in high-larval densities, 32-180 larvae/m2 along the northwesterly part of the Japan Sea coastal areas during the mid-July in 1984 resulting in considerable losses to pasture and wheat. The percentage of parasitism on the larvae, collected from the wheat field at Oogata in Akita, by hymenopterous insects was low, 1.4%. But 42.5% of the larvae died from diseases except viruses. Moths captured in a molasses bait trap suggested that there were two waves of moth immigrations carried by cyclonic winds on June 10 and 17-18. Possible sources of the migratory populations were discussed.
