Mesoscale Analysis On Source Areas And Landing Mechanisms Of Sogatella Furcifera(Horvath) Migration In Hunan Province

In recent years, the continuous outbreaks of white-backed planthopper, Sogatella furcifera (Horvath) (WBPH) have caused heavy losses in rice industry of China. Hunan province is a major rice producing area of China and a part of the main round-rout of rice planthoppers migrating throughout China, moreover, it is prone area and the main breeding area of WBPH. At present, there was little study on mesoscale source areas of WBPH in different patial and temporal conditions,while the regional landing mechanisms of WBPH in Hunan had no detailed conclusion yet. Therefore, it’s extremely urgent to realize detailed offsite forecast by making the mesoscale source areas and landing mechanisms of the early immigrant WBPH in Hunan province clear. In this study, we showed the distribution of definite mesoscale source areas of WBPH in Hunan from 2000 to 2012 and focused on its migration processes with multifactorial dynamic space-time analysis.We obtained the following results:1. The migration rules of the early immigrant WBPH in Hunan from 2000 to 2012In this part, we studied the migration rules of the early immigrant WBPH of 5 sites in Hunan province in 13 years. The results were as follows:(1) The average first appearance time of northern Hunan was 10d-20d later than southern Hunan;(2) the first appearance time from 2000 to 2005 delaied within 35d, but brought forward after 2006, e.g. the first appearance time of these five sites in 2007 in which WBPH had an national outbreak were 10d-25d earlier than the average first appearance time of 13 years. (3) The landing areas of early immigrant WBPH primarily along Wuling mountainous region in western Hunan, Xuefeng mountainous region in southern Hunan and eastern end of Xiang-Gui Corridor. (4)In April, both of the South China Sea and southeast asia effected by Subtropical high prevail southwest monsoon.Due to the location of southeastern Hunan and obstruction of Nanling mountains, the landing of WBPH in southeastern Hunan has a much smaller amount and a fewer occurrence than that in southwestern Hunan.2. The mesoscale source areas of WBPH in Hunan provinceIn this part, we showed definite mesoscale source areas of migrant WBPH during March to June in Hunan from 2000 to 2012 with the Weather Research and Forecast (WRF) model and three-dimensional trajectory analysis program, then made relevance analysis on relationship between the monthly temperature from January to March in source areas separately and first appearance time and quantity of light-trap catches.We obtained the following results:(1) Geographical distributions of source areas of early immigrant WBPH in Hunan of 13 years had obvious difference. WBPH immigrated to western Hunan mainly from northern Vietnam and southwestern Guangxi, while to southeastern or middle Hunan located in southern Guangdong and southeastern Guangxi. (2) The main source area of southern Hunan in March was southeastern Yunnan, at the same time, some immigrant WBPH were from northern Laos and northern Vietnam. In April, the immigrant WBPH almost started their flight from southwestern Guangxi, followed from northern Vietnam, meanwhile, southern Yunnan and northern Laos contributed a few WBPH. In May, southern Guangxi was still the main source area of WBPH, southern Guangdong and northern Vietnam were follwed. In June, the growing WBPH population immigrate to Hunan had extended its regional source areas into northern Guangxi, northern Guangdong and southern Guizhou.3. Landing mechanisms of early immigrant WBPH in Hunan provinceIn this part, we conducted analysis of dynamic atmospheric circulation and of its spatial and temporal process with the high-resolution WRF model output meteorology data, finally determined the landing mechanisms of early immigrant WBPH, especially the whole immigration progress during late April and early May in 2012 combing with variously topographic features of Hunan. We obtained the following results:(1) WBPH from source areas are carried towards north by the south Low Level Jet, then clustered and forced to land by downdrafts, low temperature barrier and precipitation which caused by frontal cyclone, shear line and strong updraft. (2) Terrain is a main factor in frequently forcing massive WBPH to land in western Hunan. It’s owing to the roller caused by mountain blocking and friction, mountain breeze and ravine wind between two valleys that immigrating events of WBPH most occur in valleys and on the windward side of mountains.