中国稻纵卷叶螟发生特点及北迁的大气背景

稻纵卷叶螟因其发生面积大、暴发频率高、致害程度重而成为我国水稻生产上的重要害虫。为了阐明大气背景对其北迁重大过程的影响,利用2000—2012年中国稻纵卷叶螟灯诱数据分析了我国水稻主产区稻纵卷叶螟迁入的主要特征;选取2007年7月下旬的一次重大北迁过程作为典型个例,运用中尺度天气研究和预报模式WRF,结合NCEP气象再分析资料,模拟了这一过程的大气背景,推算了稻纵卷叶螟的迁飞轨迹,并分析了大气背景对稻纵卷叶螟灾变性迁入的影响。研究表明:(1)这13年中,我国稻纵卷叶螟的迁入大多在3月初始见,3—8月为北迁期,从南到北先后在华南、西南、江岭、江淮稻区出现迁入峰;9—11月为南迁期,从北到南先后迁入江淮、江岭、华南稻区并出现相应的迁入峰,10月底至11月初为终见期。(2)北迁个例中各站逆推轨迹分析显示:包括再迁飞在内的不同时段虫源地基本上位于降虫区的西南方,迁飞高度都变化于550—850 m之间,但在沿海地区降落的稻纵卷叶螟迁飞轨迹是复杂的。(3)水平气流是稻纵卷叶螟远距离北迁的主要运载动力,925 h Pa上南方稻区一致的偏南气流对稻纵卷叶螟北迁极为有利;三维流场的起伏、特别是垂直气流的强弱变化对迁飞高度的变化起重要的作用。(4)下沉气流和降水是稻纵卷叶螟降落的关键动力因素,两者都对降虫有明显影响。(5)在这一北迁过程中,稻纵卷叶螟种群多降落在相对湿度大的区域,降虫区的相对湿度均在75%以上。

Migration pattern of rice leaf roller and impact of atmospheric conditions on a heavy migration event in China

Rice leaf roller, Cnaphalocrocis medinalis Guenee, is one of the most important crop pests in China due to its large area of occurrence, high frequency of outbreaks and serious damage to rice yields. In this paper, the lighting trap observational data of rice leaf rollers from 2000 to 2012 were analyzed to assess the impacts of atmospheric conditions on the migration and landfall of rice leaf roller. We have identified the main features of rice leaf roller''s migration in the main rice-growing areas of China and presented a detailed analysis on a typical migration event occurred in late July, 2007 and verified the assessment result. By means of the Hybrid Single Particle Lagrangian Integrated Trojectory Model for Version 4.0 (HYSPLIT-4), a software of calculating particle trajectory in the air, the backward migration trajectories of the rice leaf roller landfalled the rice growing regions in the the Yangtze River Valley were calculated and the Weather Research and Forecast model (WRF) ''s simulations on the atmospheric backgrounds in this event combined with the reanalysis data of the National Ceter of Environmental Predicting (NCEP) were used to assess the impacts of weather conditions on the catastrophic migrations of rice leaf roller. Several important findings are obtained from this study. First, during the studying period from 2000 to 2012, the migration of rice leaf roller started at the beginning of March in a year, the period during March to August was the period of prevailing migration northward in which the populations immigrate into the south China, the southwest China, the regions between the Nanling Mountain and the Yangtze River and the valley regions between the Yangtze River and the Huaihe River in China successively and emerge a series of immigration peaks. During the period from September to November each year, the southward migration is the reversed processes in the above regions. The rice leaf roller migrated backward to the valley region between the Yangtze River and the Huaihe River, the regions between the Nanling Mountain and the Yangtze River and South China in turn. Second, the backward trajectories calculations of rice leaf roller''s migration northward included the beginning and re-emigrating populations in the selected event indicated that the sources of the rice leaf roller''s populations were situated at the southwest parts of the landfall regions and the migration altitudes varied from 550 m to 850 m above ground level. As a comparison, the migrating trajectories in the coastal regions were more complicated than the other regions. Third, the horizontal wind is the main driving force for the long-distance migration of rice leaf roller''s populations and the prevailing southerly at 925 hPa height is favorable for the migration northward. Three-dimensional windfield, especially the strong vertical airstream plays a dominant role in the up and down of the migration heights. Fourth, the downward flow and rainfall are the two key dynamic factors for the landfall of the rice leaf rollers. Fifth, as a kind of hygrotaxis pest, the suitable atmospheric moisture condition is beneficial to the long-distance migration and landfalling of rice leaf roller''s populations. In this event, most of the rice leaf rollers landfalled in the areas of the relative humidity higher than 75%.