The study of occurrence dynamics of the migratory population of oriental armyworm Mythimna separata(Walker)in Liaoning

To investigate the occurrence dynamics of armyworm,Mythimna separata(Walker),in Shenyang and Xiuyan districts,we monitored the moth of armyworm using the giant light beam to trap the population migrating across Shenyang with the aid of vertical-pointing searchlight-traps from 2017 to 2018.Based on the meteorological data,we analyzed the appearance period,peak date of armyworm moth and its composition of the migratory population.Our study aims to be used for reference in armyworm disaster prevention and allopatry forecast.We conclude that there are two major peak periods of armyworm in Liaoning Province,and the first generation of armyworm is totally immigrant population,and the second generation of armyworm emigrates with the upward airflow.Shenyang and Xiuyan districts both locate on the armyworm migratory flight route and their return.The first appearance of armyworm moth was recorded on 11 th May,and peak duration was from late May to early June.The first generation of immigrant armyworm moth was from mid-May to early June.We also monitored that the second generation peak duration was held from early July to early August.The third generation was totally irregular,from mid-August to mid-September.The first generation of immigrant armyworm moth in Xiuyan district was held from late May to early June,the migrant period was from mid July to mid August.Rainfall and other meteorological activities are the major cause of outbreak for the third generation of armyworm.The rampant infestation is an integrated outcome of two pest sources in fused reproduction,one source is local emigrant population which hindered by meteorological factors,and the other source is sequential immigrant populations from Northern China to Liaoning districts.