2002年我国华北三代粘虫大发生的虫源分析

Analysis of source population and immigration process of Mythimna separata (Walker) caused an outbreak in North China in 2002

华北平原地区三代粘虫的大发生是一小概率事件,对其虫源问题尚无确切回答。应用HYSPLIT4.8轨迹分析平台对2002年华北平原地区三代粘虫主要迁入峰期进行轨迹回推以确定此次迁入的虫源区,同时对东北地区虫源在迁出期的去向进行了模拟;并运用GrADS气象图形软件对华北地区和东北地区迁飞期天气学背景和风场的时空分布进行了分析。结果表明:2002年华北平原地区大发生的三代粘虫主要虫源来自陕西、山西二省;东北地区虫源对本次华北平原地区的迁入无影响。

Mythimna separata （Waller） occurs almost everywhere in China and especially is one of the important pests of grain corps in north China. As the change of the farming system, M. separata population has decreased dramatically since 1980s. However, an outbreak of the third generation armyworm was seen in north China plain in 2002 abruptly, and caused a serious damage to the summer crops in five provinces in north China. In order to confirm the source areas and the migration route of the pest, the weather background during the immigration and distribution of the wind in various places at different time were analyzed and the flight pathways were traced by trajectory analysis. The re-analyzed data of global wind fields at 850hPa were provided by NOAA and ground surface rainfall records were provided by National Weather Bureau of China. Trajectory analysis was performed by using HYSPLOIT 4.8 trace analysis platform of NOAA and longitude and latitude of relevant stations were set to starting point. We set one hour before sunrise as starting time of back-trajectories and finishing time of forward-trajectories, and one hour after sunset as starting time of forward-trajectories and finishing time of back- trajectories. Generally, each migration process was analyzed for 5 successive nights. And when the route passed emigration area or marine coast, the trajectory was stopped and the flight speed of the moths was ignored. The results from trajectory analysis of the pest in north China plain area on July 22, 2002 shows that the third generation of M. separata immigrated mainly from Shannxi and Shanxi province. At 18th night July, M. separata began to emigrate from resource areas. Their flight routes were closed to the eastward trend of sub-tropical high pressure belt, the southward of mainland high pressure and the southward of cold air marching from the east side of the Qing-Tibet Plateau. After 2 nights＇ flight of 18th and 19th, immigration population entered Henan and Hebei Province. Then south-east wind and south-west wind of the later 2 days retarded the immigrants to exodus and the barrier of sinking air-flow and rainfall detained the moths in Henan and Hebei. Finally, the pest outbreak occurred in the two provinces. Among the 231 trajectories of the emigration population of M. separata in northeastern China from 15th to 25th of July shows that most of them remained in northeastern China （58.5%）, some fallen into Bohai Sea or Japanese Sea （15.2%） and the rest passed Sanjiang Plain and further to Fareast region of Russia（ 19.7% ） or migrated westward to High Mountain Zone of Great Xing＇an Mountain （5.7%）, but none could enter to the plain area of North China. The results indicate that the summer population of armyworm in northeastern China, as a victim of Pied Piper effect, could not become the source of the third generation in the plain area of northern China.