Studies on biological control of the diamondback moth.

对甘蓝小菜蛾及其寄生性天敌在露地（O-field）和9mm网（N-field）两种甘蓝田中的种群动态进行了连续6年的研究。在春、夏两季，白色蝶对甘蓝的危害很大，N田的甘蓝受到保护。共10%的甘蓝植物饲养在田间进行了检查，每个月两次抽样。采集小菜蛾三、四龄幼虫、蛹及茧蜂茧，室内饲养，观察寄生蜂羽化情况。春季至夏季DBM密度很低。DBM种群密度从2 ~ 3月开始呈上升趋势，4 ~ 5月达到高峰。在O-和N-田中DBM的最高密度分别为80和100株/株。两种寄生蜂，茧蜂，Cotesia plutellae，和姬蜂，Diadromus subtilicornis被认为是优势。菜蛾绒茧蜂和潜叶蚤的最大平均密度分别为30头/株和25头/株。寄生蜂对小菜蛾的寄生率以5 ~ 6月最高，菜蛾茧蜂为50-75%，拟分角姬小蜂为80-90%。然而，他们未能调节DBM人口在4月初，因为缺乏同步的生活史与主机高峰丰度。建议在早春大量释放拟寄生蜂，以有效地控制该季节的DBM种群。

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.