湖南白背飞虱前期迁入种群中小尺度虫源地及降落机制

湖南是白背飞虱(Sogatella furcifera(Horváth))南北往返的必经之路和主害区。明确白背飞虱前期(至5月20日)迁入种群的中小尺度虫源地和降落机制,对实现精细化异地预测至关重要。择出2012年湖南稻区白背飞虱前期迁入种群的上灯峰日,用新一代中尺度数值预报模式WRF(Weather Rsearch and Forecast)做三维轨迹分析,明确虫源地分布,并对其迁飞过程进行多因素的时空动态分析。结果表明:(1)2012年湘西白背飞虱迁入虫源主要来自越南北部、广西西南部,少量来自广西东南部与广东南部。湘东南、湘中迁入虫源主要来自广东南部、广西东南部,少部分来自海南。此外,每年4月下旬与5月上旬我国南部盛行西南气流,湘东南位置偏东,加之南岭山脉的阻挡,该区迁入峰次与迁入量较湘西较少。(2)低空急流为白背飞虱的北迁提供了运载气流,锋面气旋与切变线等天气尺度系统以及强烈上升气流带来的降水、低温屏障与下沉气流是湖南稻区白背飞虱集中迫降的3个直接因素;(3)白背飞虱前期迁入种群在湖南的主要落点基本沿湘西武陵山区至湘南雪峰山区一带以及"湘桂走廊"东端分布,地形是导致湘西降虫发生频率高、迁入量大的主要因素。由于山体阻塞与地面摩擦形成的小型垂直环流、夜间山风的作用及山谷间的峡谷风可导致白背飞虱的集中降落,较大的灯诱峰次主要位于谷地或者是山体的迎风坡。

Mesoscale source areas and landing mechanisms of the early immigrant white-backed planthopper Sogatella furcifera (Horváth) in Hunan Province, China

Recently, continuous outbreaks of the white-backed planthopper (WBPH) Sogatella furcifera (Horváth) have caused heavy rice yield losses in China. Hunan Province is a hotspot in principal migration pathways, and consequently, the main infestation area for the rice planthopper species; therefore, significant economic damage caused by WBPH outbreaks in this province will directly threaten food security in China. Therefore, a better understanding of the source areas and landing mechanisms of immigrant planthoppers in a mesoscale region such as Hunan Province would be essential for an accurate and detailed offsite forecast based on the hopper occurrence status in the source area. A trajectory analysis method based on atmospheric conditions has been developed for the quantitative simulation of population movements and distributions over a range of temporal and spatial scales. Meanwhile, the Weather Research and Forecasting (WRF) model can not only improve the precision and accuracy of trajectory calculation by providing a meteorological background with high spatial and temporal resolution, but also describe and interpret the WBPH migratory mesoscale process by analyzing atmospheric parameters with its advanced numerical technique. In this study, weather datasets on peak days of light-trap catches of the early immigrant WBPHs in Hunan Province during late April and early May of 2012 were selected to conduct a three-dimensional trajectory analysis and a multifactor spatio-temporal dynamic analysis to simulate the migration processes with the WRF model. The following results were derived from the analysis: (1) From April to May 2012, immigrant populations of WBPH in western Hunan were mainly from northern Vietnam and southwestern Guangxi and partly from southeastern Guangxi and southern Guangdong. Source areas of WBPHs that immigrated to southeastern or central Hunan were traced back to southeastern Guangxi and southern Guangdong and partly to Hainan. In late April and early May, source areas of migrant WBPHs were relatively different between western and eastern Hunan. A prevailing southwest monsoon and obstruction by the Nanling Mountains ensured that fewer early immigrant WBPHs landed in southeastern Hunan than in southwestern Hunan. (2) The source populations of WBPH were carried by the southwest low level jet and then clustered and forced to land by downdrafts, a low temperature barrier, and precipitation, which was caused by a frontal cyclone, shear line, or strong updraft, with the application of a three-dimensional trajectory analysis and meteorological modeling. (3) The landing areas of the early immigrant WBPHs were primarily along the Wuling mountainous region in western Hunan, the Xuefeng mountainous region in southern Hunan, and the eastern end of the Xiang-Gui Corridor. Terrain-forced flows (winds modified or channeled by the underlying complex terrain) are associated with mountainous terrain. Thus, terrain was believed to be a main factor that forced massive numbers of WBPHs to land and immigrate frequently into western Hunan. Most of the immigration events and insect convergence occurred in valleys and on the windward side of mountains owing to the vortex effect caused by mountain blocking and friction, mountain breezes, and ravine winds in a valley.