Abstract
A large number of adult male diamondback moths (DBM) were caught by pheromone traps from April to November in and around Morioka City (39°42'N) over 5 consecutive years (1983 to 1987). the numbers caught showed two peaks; one in May to early June (I) and the other in July (II). Oviposition started in May and egg density increased from the end of May to early June in cabbage fields planted in April. the numbers of newly emerged adults which developed in these fields planted in April. the numbers of newly emerged adults which developed in these fields increased from the end of June to early July. the second peak of DBM caught by the traps in July (II) could be explained by this increase of newly emerged adults. Although living DBM larvae and pupae were commonly observed in the Chinese cabbage and rape fields in autumn, none were found in the following spring. thus, it was concluded that the first peak of DBM adults in spring (I) around Morioka City had not hibernated locally but were migrants from the southern part of Japan where this insect can survive over winter.
