Several Evidences Revealed Migratory Locust (Locusta Migratoria L.) Migration Was A Normal State In The Eastern Monsoon Region Of China

The eastern monsoon region is the area most affected by the migratory locust Locusta migratoria,where plagues have been recorded by Chinese officials for the past 2,000 years.Longjiang(LJ)and Zhaoyuan(ZY)of Heilongjiang province are downstream of the eastern monsoon region and historically have no locust records in China.However,there was huge crop damage caused by migratory locusts in July 2009,this is the first record of locust plagues in this part of China,and the source of locust population was unrevealed.Based on degree-days(DD)model we infer that the plague derived from migrant populations,as the DD were not enough to support a full generation for locusts in LJ and ZY.To confirm our assumption and reveal the possible sources of this locust plague,we detected the locust migration by searchlight trapping and field investigation on an island in the middle of the Bohai Gulf(38°24’N,120°55’E),also we analyzed the meteorological characteristics of the eastern monsoon region.Searchlight trapping detected migratory locusts during the 13 year period 2003 to 2015.Trajectory analysis showed that individuals maintained altitude in the 600m low-level airflow,and the potential immigrant source was around the eastern Yellow River(36058’37.2"-3807’4.8" N,117°0’3.5"-118°37’48" E).Migrant locations included areas such as Huludao and Nongan,while the extreme low-level airflow from 2nd July-9th August 2008 also induced locust migration as far north as LJ and ZY.In conclusion,the low-level airflow from southern to northern China will promote locust migration,and it is likely that locust plagues in LJ and ZY in 2009 were caused by immigrant populations.We also examined vegetation structure,water levels and DD in LJ and ZY(also including Huludao,Nongan,etc.).It revealed that these regions would be suitable for locust growth and development if temperatures keep increasing.Thus,with global warming,it is possible that the migratory locust could establish colonies in north-eastern China in the future.