Effects Of Atmospheric Low Temperature Stress On The Initial Immigration Of Nilaparvata Lugens(St?l) In China In A Year

Brown planthopper(BPH),Nilaparvata lugens(St?l)is a major rice pest with special characteristics of feeding,long-range migration,and catastrophic infesting.The low temperature environment of the atmosphere can effectively stress the migration process of N.lugens,causing the populations to land intensively in some areas in the certain space-time conditions.The low-temperature stress would almost interact with other meteorological elements(such as wind,vertical airflow,and relative humidity fields)together acts on the landing process of N.lugens,which induced the drop of N.lugens' migrating populations occurred mostly on the initial immigration to the north or the terminal immigration to the south during the year.In the past,it was reported that some cases studies of N.lugens migration combined with atmospheric background fields was used to comprehensively analyze its landing mechanism at home and abroad.However,there were few studies on the statistical characteristics of the effects of atmospheric low temperature stress on N.lugens migration and its mechanism during the N.lugens' landing process.Based on the light catch data of N.lugens during the period from 2000 to 2017,in this paper,the HYSPLIT model was used to simulate the initial immigration processes of N.lugens into the Southwest China and the South China in a year,reveal the temporal and spatial pattern of the initial migration of N.lugens in the two rice areas.The characteristics of the atmospheric temperature field during the initial migrations were also analyzed statistically.The differences in the effects of low temperature stress on N.lugens in the two rice regions and the initial migration periods in different years were compared.The typical cases were selected from the initial migration processes affected by the low temperature of the atmosphere,and the meteorological data was used to analyze the mechanisms of the effect of low temperature stress on the immigration of N.lugens under different conditions.The results of the study will lay a theoretical foundation for the further study of the migration mechanism of N.lugens under the trend of global warming and provide a reference for early warning and rice production safety of N.lugens in China.The main findings were as follows:1.Based on the analysis of the statistical characteristics of the onset and peak days of the first immigration of N.lugens in the South China and the southwest China during 2000-2017 and the influence of atmospheric temperature field on the initial immigration processes,the following conclusions were obtained:(1)In recent years,the initial immigration of N.lugens into China was earlier than before,and the initial migration into the rice paddies in South China was earlier than that in the Southwest rice paddies.The early onset of the southwest rice area may be related to the temperature rise in its prevalent migration layer in March,while the early onset of the South China rice area may be related to the northward shift of N.lugens population over winter.(2)In the southwest rice region,the first migration of N.lugens in the year was mainly came from Myanmar,and the initial source of overseas pests that migrated in the South China ricegrowing region during the year mainly came from central and northern parts of Vietnam and Laos.(3)The study on the temperature distribution in the prevailing migratory layer showed that the probability of the occurrence of low temperature barrier is about 54.4% during the initial migration of brown planthopper in the year,and the average low temperature intensity and the average cooling range of the moving night are 13.45? and 1.88? respectively.Among them,the low temperature stress was more significant in South China(the probability of occurrence was 58.3%,the average intensity was 13.18?),and more significant in the initial stage(the probability of occurrence was 70.6%,the average intensity was 12.53?)Research on the temperature distribution in the prevalent migratory layer showed that the probability of low temperature barrier occurred during the initial immigrations of N.lugens was about 54.4%.The average low temperature stress intensity was 13.45? and the average cooling range was 1.88?.Among them,the low temperature stress was more significant in South China(the occurrence probability was 58.3%,the average intensity was 13.18?),and more obvious in the immigration beginning dates(the occurrence probability was 70.6%,the average intensity was 12.53?).2.A typical case study of the effects of low atmospheric temperature on the immigration of N.lugens under different weather backgrounds indicated that:(1)The effects of low temperature stress on the population of BPH are mainly reflected in two aspects: First,the low temperature stress caused by cold air forces the population of BPH migrating to the north to reduce the migration height and select the appropriate temperature field,and finally to land on the south side of the "cold wall",at the same time,the downdraft in the cold area dynamically forces the population to land.Second,the flow field around the pest reduction area changes after being disturbed by the cold air group,and BPH The population of louse lost the effective flow field suitable for northward migration,leading to the end of a migration process.(2)The intermittent low mountains in the South China cannot effectively prevent the invasion of northern cold air and the northward migration of N.lugens populations.Therefore,the effect of low atmospheric temperature on the northward migration of N.lugens was more significant;while the Southwest China rice-growing region had a more significant barrier effect;It was because of its high-altitude terrain that forces the pest-carrying airstream moving northward.The topographical stress and the low-temperature stress of the upper layer caused the population to fall.Therefore,the low-temperature stress was relatively weak.