Studies on biological control of the diamondback moth.

对小菜蛾及其寄生蜂在露天栽培田(O田)和覆盖9 mm网目甘蓝田(N田)的种群动态进行了6年的研究。在春夏季节，N地的甘蓝受到白蝶的保护，白蝶对甘蓝的危害很大。在每个月两次的抽样中，总共检查了10%的田间种植的甘蓝植株。采集小蜂的3龄、4龄幼虫、4龄幼虫和蚕茧，在实验室饲养，观察寄生蜂的出现情况。在春季到夏季，胸木密度很低。林木种群密度从2、3月份开始呈上升趋势，并在4~5月份达到峰值。O田和N田的最高密度分别为80株和100株。两种寄生蜂--菜绒茧蜂(Cotesia Plutellae)和稻纵卷叶蜂(Diadromus Subtilicornis)--为优势种。最大平均密度分别为30只/株和25只/株。小蜂对DBM的寄生率在5~6月最高，菜青虫的寄生率为50%~75%，枯草杆菌的寄生率为80%~90%。然而，它们未能在4月初调节DBM种群，因为它们的生活史与寄主峰值丰度缺乏同步。建议在初春大规模释放该寄生蜂，以有效地控制该季节的小蜂种群。

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.