| Rice leaf roller, Cnaphalocrocis medinalis Guenee, has become an important crop pest of the rice production in China due to its large area of occurrence, high frequency of outbreaks and serious damage. In a year, the populations of rice leaf roller come and go between the south and north rice-growing regions,and damage the rice plants.Their immigration and endangering is closely related to the cropping system,geographical conditions and atmospheric backgrounds, especially rice leaf roller’s long distance migrations and re-immigrations are inseparable from the favorable weather conditions.Therefore, it is meaningful to reveal the rice leaf roller’s occurrence pattern in the different growing-rice areas of China, ascertain the meteorological conditions of the typical immigration events in theory and it is valuable to the early warning and effective prevention of roce leaf roller’s catastrophes in practice. Based on the analysis and understanding for the research advances of insect (such as Cnaphalocrocis medinalis Guenee, Nilaparvata lugen (stal) and so on) migration meteorology at home and abroad, the lighting trap catches of the rice leaf roller in China during2000to2012was collected and the occurrence pattern and catastrophic immigration characteristics of rice leaf roller in the main rice-growing area of China was analyzed. From the great immigration events, a typical case of great northward migration events and a representative case of great southward migration events were screening and HYSPLIT-4, the Hybrid Single Particle Lagrangian Integrated Trajectory Model forVersion4.0, was used to the calcultions of the rice leaf roller’s migrating trajectories. Combined with the reanalyzed meteorological data of the National Center of Environmental Predicting in USA (NCEP), WRF, the Weather Research and Forecast model (WRF) for Version3.4, was used in the numerical simulations of the atmospheric backgrounds during the occurrence of the event. After the diagnosis analysis of atmospheric phyical variables, the impact of atmospheric circulation situations and dynamical fields on the immigrations of rice leaf roller was discussed. By the analysis of the correlation between the atmospheric circulation characteristic variables influencing the immigration of rice leaf roller’s populations and the immigration peak dates and the correlation between these atmospheric circulation characteristic variables and the lighting catches of the peak dates, the predictor influencing remarkablely the immigrations were screened out and the stepwise regression predicting equations for the immigration peak dates and the lighting catches of the peak dates of rice leaf roller based on the characteristic variables of atmospheric circulation were established. The results showed as follows: Firstly, the daily lighting catches of rice reaf roller in China during2000to2012was collected to analyze the immigration pattern of rice leaf roller in the main rice-growing regions of China. The great northward and southward migration events was counted and the serious occurrence areas of rice leaf roller’s catastrophic immigrations was confirmed. The results displayed:(1) the beginning dates of the immigrations occur always in the beginning of March, the period during March to August in a year is the period of the migration northward, the immigration peaks of rice leaf roller come about successively in the rice-growing regions of the south China, the southwest China, the region between the Yangtze River and the Nanling Mountain and the region between the Yangtze River and the Huaihe River. Accordingly, the period during September to November in a year is the period of the migration southward, the immigration peaks of rice leaf roller appear orderly in the rice-growing regions between the Yangtze River and the Huaihe River, the region between the Yangtze River and the Nanling Mountain and the south China and the period during the end of October to the beginning of November is the end period of rice leaf roller’s immigration.(2) If a great immigration event of rice leaf roller was difined as a process of the lighting catches of2or more plant protection stations in a day were more than500heads,37northward migration events and10southward migration events was counted.(3) The rice-growing regions between the Yangtze River and the Huaihe River was the largest probability area of the migration northward during2000to2012, the region between the Yangtze River and the Nanling Mountain situated in the next order and the landfalling probabilities of the rice-growing regions of the south China and the southwest China were small.(4) The great events and the clustered landfalling stations of migration southward were less than the migration northward and the landfalling regions of the migration southward mainly distributed in Anhui Province, Hunan Province and so on.Secondly, in order to explore the influence of atmospheric backgrounds on the rice leaf roller’s immigration and landfalling, a great event of migration northward occurred during July23rd to25th in2007and a great event of migration southward occurred during September3rd to5th in2007were screened, the Weather Research and Forecast model (WRF) for Version3.4was used in the simulations of the atmospheric backgrounds during the occurrence of the two events combined with the reanalyzed meteorological data of NCEP, and the backward migration trajectories were calculated to analyze the impact of the atmospheric backgrounds on the catastrophic immigration of rice leaf roller’s populations.The results showed as follows:(1) After the calculations of backward migration trajectories for the rice leaf roller in the screened cases, it was found that the insect sources of the rice leaf roller’s emigrating populations in the course of immigration northward included the re-emigrating populations situated in the southwest sides of the landfalled regions commonly and the migration altitudes changed from550m to850m. Similarly, the insect sources of the rice leaf roller’s immigration southward situated in the northeast sides of the landfalled regions in general and the migration altitudes changed from500m to750m. But the distribution of the immigrating trajectories in the coast regions was complicated.(2)The horizontal airflow in upper air is the main driving force of the long-distance migrations of rice leaf roller’s populations and the prevailing southerly on925hPa is favorable to the migrations northward of the rice leaf rollers. Respectively, the prevailing northerly on925hPa is favorable to the migrations southward of the rice leaf rollers. Especially, the ups and downs of three-dimensional airflow field, the change of vertical airstream strength has an important role on the rise and fall of the migration heights.(3) The subsiding airflow and rainfall are the key dynamic factors of rice leaf roller the landfalling and both of them have obvious effects on the landfalling in the event of immigration northward. The subsiding airflow was the main factor and the effect of rainfall was small in the landfalling of migration southward.(4) The immigration of rice leaf rollers was related to the temperature and the temperature requirement in the migrations northward was easily met due to the event of immigration northward occurred always in summer. The event of immigration southward appeared generally in early autumn, the temperature of appropriate migrating layers was17-19℃, and the immigration and landfalling of rice leaf roller in the migration southward were stressed by the condition of temperature.(5) As a kind of hygrotaxis pest, the suitable atmospheric moisture condition was beneficial to the long-distance migration and landfalling of rice leaf roller’s populations. In these two cases, most of the rice leaf rollers landfalled in the area of high relative humidity and the relative humidity in the landfalling areas were higher than75%.Thirdly, Taicang and Gaoyou were selected as the representative stations of typical rice-growing regions in Jiang-Huai area and the South Jiangsu, respectively. The immigration peak dates and the lighting catches on the peak dates of rice leaf roller of the two stations were analyzed and the correlation coefficents between the immigration peak date, the lighting catches on the peak dates and74atmospheric circulation indices were calculated separately. The indices associated with high correlation coeffcient and good stablity were selected as the predictors and the stepwise regression forecasting equations for the immigration peak dates and the lighting catches on the peak dates of the two stations based on the atmospheric circulation charcteristic variables were established. The results indicated as follows:(1) Many atmospheric circulation charcteristic variables had significant influence on the immigration peak dates and the lighting catches on the peak dates of rice leaf roller. Among them, the area size, strength change, location of the ridge line and north boundary of the Western Pacific subtropical high affected the immigrations of rice leaf roller’s populations and these charcteristic variables of WPSH had the positive correlation coeffcients to the immigration peak dates and the lighting catches on the peak dates. The impact of the polar vortex index and westerly circulation index was complicated. Sometimes the correlations were positive and negative were sometimes. The cold air activities and typhoons had a certain influence on the immigrations.(2) The screened predictors were used to establish the stepwise regression forecasting equations of the immigration peak dates and the lighting catches on the peak dates at the two stations and the fitting rates were high. It was found that the prediction accurracies of the immigration peak dates were higher than the lighting catches on the peak dates and the prediction effect of all equations was satisfactory in the trial forecasting during2011to2012... |
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