|Budget Amount *help
¥1,500,000 (Direct Cost : ¥1,500,000)
Fiscal Year 2005 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 2004 : ¥200,000 (Direct Cost : ¥200,000)
Fiscal Year 2003 : ¥900,000 (Direct Cost : ¥900,000)
Population dynamics of the diamondback moth (DBM) and its parasitoids were studied for 6 years in the two cabbage fields, open culture field (O-field) and one covered with insect screen (9mm mesh) (N-field). The cabbage in N field was protected from the white butterflies which severely attack the plants in the spring to summer seasons. Total of 10% of cabbage plants reared in the fields were examined in each sampling of two per month. Third and fourth instars larvae and pupae of DBM and also Braconid cocoon were collected, and reared in the laboratory to check the emergence of parasitoids. DBM densities were very low in spring to summer seasons. The DBM population densities began an upward trend from February or March, and built towards to peak in April-May. The highest densities of the DBM were 80 and 100 per plant in the O- and N- fields, respectively. Two species of parasitoids, Braconid, Cotesia plutellae, and Ichneumonid, Diadromus subtilicornis were recognized as dominant. The maximum mean densities of C.plutellae and D.subtilicornis were 30 and 25 per plant, respectively. The highest percentage parasitism of DBM by the parasitoids was observed in May-June, 50-75% for C.plutellae and 80-90% for D.subtilicornis. They, however, failed to regulate the DBM population in early April, because of lack of synchronization of their life cycle with host peak abundance. A mass release of the parasitoids in the early spring was suggested to control effectively the DBM population in the season.