Occurrence Patterns And Numerical Simulations Of Nilaparvata Lugens In Southwestern Of China

The outbreak of brown planthopper(BPH),Nilaparvata lugens(Stal)threatens directly the safety of rice production in our country.The southwest rice-growing region is the first station where the foreign insect source enters the domestic rice region because of its special geographical location.However,the complicated topography and the lack of historical observation data make it difficult to have the systematic study on the migration path of BPH in the southwestern rice region,and most of the research on the insect pests of the brown planthopper is based on the simulation results of the HYSPLIT online computing platform.As compared to HYSPLIT,the WRF-F1exPart model can better analyze the migration process of brown planthoppers and trace the source of insects,this id because the FlexPart model has included more realistic parameters for convection,surface stress,and various terrain parameters.Thus,based on the data of BPH in 38 years observed from plant protection monitoring stations in southwest China,the temporal and spatial distribution of BPH migrations was analyzed and a series of cases were selected,then the Flexible Particle Dispersion(Flexpart)model driven by the Weather Research and Forecast Model(WRF)outputs was used to simulate the early immigration peaks observed at these cases.This study has an important theoretical value and practical significance in determine the sources of BPH at the time of their early immigration into the rice-planting areas of Southwestern China.The main conclusions are as follows:1.The occurrence years of severe and moderate severe BPH were mainly concentrated in 1980s,and the probability of this was over 31%.The beginning dates of BPH were related to the geographical location of the observation stations.It occurred between April 10th and May 20th each year in the northeast region,while mainly concentrated around April 10th in the south region.As for the ending dates of BPH,it mainly varied between mid of October and late November before 2007,and appeared around September 17th after 2007.2.In recent years,the source areas of early immigration of BPH in Yunnan Province were investigated were mainly from Myanmar,partly from Laos and Thailand,a few from Vietnam,and very few from Bangladesh.The landing of BPH was mainly driven by the southwest airflow,the low-temperature barrier,vertical motions and weak rainfall which were associated with the Indo-Burma low pressure system,while relative humidity field had limited impact on the landing of BPH.3.In order to research the sensitivity of the terrain to the immigration of BPH in the simulation by WRF model,the migratory process of BPH in different altitude terrain conditions was surveyed.The results indicated that:with the change of terrain height,the migration trajectory of BPH will change obviously.In addition,when the altitude was zero,the move distance of BPH presented longer than that with topographic barrier,and the pest source was significantly different.This is because with the terrain height decreased,the temperature decreased,the vertical air flow disturbance weakened,the wind direction changed and the wind velocity increased,as a result,the speed of the brown planthopper migration accelerated and the distance to move was longer,and the insect source area changed finally.