A new monitoring index for ecological vulnerability and its application in the Yellow River Basin,China from 2000 to 2022

The ecological environment of the Yellow River Basin has become more fragile under the combined action of natural and manmade activities.However,the change mechanisms of ecological vulnerability in different sub-regions and periods vary,and the reasons for this variability are yet to be explained.Thus,in this study,we proposed a new remote sensing ecological vulnerability index by considering moisture,heat,greenness,dryness,land degradation,and social economy indicators and then analyzed and disclosed the spatial and temporal change patterns of ecological vulnerability of the Yellow River Basin,China from 2000 to 2022 and its driving mechanisms.The results showed that the newly proposed remote sensing ecological vulnerability index had a high accuracy,at 86.36%,which indicated a higher applicability in the Yellow River Basin.From 2000 to 2022,the average remote sensing ecological vulnerability index of the Yellow River Basin was 1.03,denoting moderate vulnerability level.The intensive vulnerability area was the most widely distributed,which was mostly located in the northern part of Shaanxi Province and the eastern part of Shanxi Province.From 2000 to 2022,the ecological vulnerability in the Yellow showed an overall stable trend,while that of the central and eastern regions showed an obvious trend of improvement.The gravity center of ecological vulnerability migrated southwest,indicating that the aggravation of ecological vulnerability in the southwestern regions was more severe than in the northeastern regions of the basin.The dominant single factor of changes in ecological vulnerability shifted from normalized difference vegetation index(NDVI)to temperature from 2000 to 2022,and the interaction factors shifted from temperature∩NDVI to temperature∩precipitation,which indicated that the global climate change exerted a more significant impact on regional ecosystems.The above results could provide decision support for the ecological protection and restoration of the Yellow River Basin.

Case study on the first immigration of fall armyworm,Spodoptera frugiperda invading into China

The fall armyworm(FAW),Spodoptera frugiperda is one of the most damaging crop pests,and it has become major threat to the food security of many countries.In order to monitor possible invasion of this pest into China,a searchlight trap was established in March 2018 in western Yunnan Province,China,where it has served as the"first station"for many pests that have migrated from Myanmar to China.A number of suspected FAW moths were captured and identified by DNA sequencing.The results showed that the FAW moth was first captured on December 11 and formed its first immigration peak in mid-December 2018.DNA detection revealed that the early invading FAW population was the"corn-strain".The field survey indicated that the pest mainly colonized corn in Pu’er,Dehong and Baoshan areas.Migration trajectory simulation implied that the moths might have mainly come from the eastern area in the mid-latitude region of Myanmar(20-25°N,94-100°E).This case study confirmed the first immigration of FAW into China,and will be helpful for guiding monitoring and management work to control this pest.

Windborne migration routes of newly-emerged fall armyworm from Qinling Mountains-Huaihe River region,China

The fall armyworm(FAW,Lepidoptera:Noctuidae),Spodoptera frugiperda(J.E.Smith),invaded China in mid-December 2018;since then,it has become a great threat to Chinese agricultural production.Qinling Mountains-Huaihe River region(QM-HRR)is the transitional zone between northern and southern China,an important region for both corn and wheat production.Based on the actual occurrence of QM-HRR invaded by FAW in 2019,daily mean surface air temperature and nocturnal wind conditions at 925 hPa were examined,and migratory routes of FAW moths originated in QM-HRR were modeled by a forward-trajectory-analysis approach.The results indicated that migratory activities of FAW adults emerged in QM-HRR were initiated from late June.The moths from western QM-HRR,where has complex topographic terrain,mainly flied to Ningxia and Inner Mongolia before mid September.However,FAW moths from the eastern QM-HRR primarily engaged in high-altitude northward transport assisted by the prevailing southerly winds before mid August,and the North China Plain was identified as the main destination of FAW.Meanwhile,the migration trajectories of FAW moths had a possibility to reach the Northeast China Plain.From mid August,FAW moths in eastern QM-HRR largely migrated southward and returned to the Yangtze River Valley.This study provides detailed information on the occurrence and migration routes of FAW moths from QM-HRR and will be helpful for early warning and development of integrated pest management strategies for the control of this exotic insect pest.

Migration of invasive Spodoptera frugiperda(Lepidoptera:Noctuidae)across the Bohai Sea in northern China

The fall armyworm(FAW),Spodoptera frugiperda(J.E.Smith),is an important agricultural pest with a strong migratory ability.While the species is native to the Americas,it has recently invaded China,ravaging crops in many provinces(autonomous regions,municipalities).Its long-distance migration,which is critical to understand for pest management programs,has been well studied in its native region.In other regions however,the moth’s migration patterns have not yet been characterized.Here,the migratory behavior of FAW populations in China was studied on an isolated island located in the center of the Bohai Strait from spring to autumn 2019,the year in which FAW first reached this region,by using searchlight trapping,stable carbon isotopes and trajectory simulation.The main results were summarized as follows:(i)The number of FAW moths caught by searchlight trapping provided direct evidence that the species migrated across the Bohai Sea.(ii)Species identification was confirmed by both morphology and molecular methods,and only the"corn-strain"that preferentially infests maize and sorghum was found in the collections.(iii)Stable carbon isotope measurements showed that up to 95.07%of captured moths displayed the C4 isotope signature,thus providing additional evidence that this species is a migrant as there are no major C4 plants at the trapping site.(iv)Backward trajectory analysis indicated that the pest now threatens to expand its range into the agriculturally important region of Northeast China,and thus authorities in this region should be vigilant to the threat posed by this species.Together,these findings add to our knowledge concerning the occurrence of FAW in northern China,and will help us to develop sustainable and effective monitoring,forecasting,and pest management strategies.

Analysis on the migration of first-generation Mythimna separata(Walker) in China in 2013

Mythimna separata（Walker） is an important pest which can cause serious damages to cereal crops. In the past two decades, several heavy outbreaks have taken place in northern China. In order to develop a fine-scale method of forecasting outbreaks, population data were collected in northern China using searchlight traps and ground light traps. A background weather pattern analysis and trajectory analysis were performed via the Weather Research and Forecast（WRF） and FLEXPART models. Our results showed that heavy migration of first-generation M. separata appeared in northern China in 2013. In Yanqing District, Beijing, the cumulative number of captured adults in searchlight traps was around 250000 and the daily maximum for trapped moths was 86000. During the peak period, the majority of M. separata moths arrived after 00：00 every night. The sex ratio（female：male） at each monitoring site was greater than 1 and greatly fluctuated with population dynamics. During the migration peak, prevailing downdraft winds benefited M. separata moths to land passively. Trajectory simulation showed that immigrants were from Anhui, Jiangsu and Hubei provinces and most of them could continue to fly into the northeastern regions of China. These results provide technical support for fine-scale forecasting of the outbreak of M. separata at meso-and micro-scale.

Lagrangian-based spatial-temporal topological study on the evolution and migration of coherent structures in wall turbulence

In this work,we study the development,evolution,and migration of turbulent coherent structures in the turbulent boundary layer at Reτ=630 using time-resolved particle image velocimetry(TR-PIV).Multiple techniques,including multi-scale analysis,conditional averaging,cross-correlation,and spatial-temporal topological analysis are applied to extract the evolution principle,migration trajectory,and convection velocity vector of the targeted coherent structures from a Lagrangian perspective.The spanwise vortex structures with larger scale and intensity at a certain wall-normal height y were the main focus of the present study.In the statistical sense,spanwise vortex structures move away from the wall with the shape changing from a bulge to an ellipse,and finally to a circle.Two straight lines emerge from the mean transfer trajectory curve of the spanwise vortex,in which the horizontal one is located at the viscous sublayer(y^(+)<10),the other is a logarithmic straight line existing in the range of 50<y^(+)<120,and the inclination angle of the tangential migration path is fixed at around 12°.The streamwise convection velocity U_(c)of scaled spanwise vortex structures satisfies U_(c)/U_(∞)=0.5-0.6 below y=0.03δ(i.e.,U^(+)_(c)=11-13 undery^(+)=20).In particular,in the region of 50<y^(+)<120,the velocity growth curves of U_(c)and wall-normal convection velocity V_(c)follow the log-law distribution very well,and the slopes are consistent with that of the log-law region of the turbulent boundary layer.Our observations provide microscopic evidences of the logarithmic-linear distribution of the migration trajectory of spanwise vortex structures.

Overseas immigration of fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), invading Korea and Japan in 2019

The fall armyworm(FAW),Spodoptera frugiperda(J.E.Smith),spread rapidly in Africa and Asia recently,causing huge economic losses in crop production.Fall armyworm caterpillars were first detected in South Korea and Japan in June 2019.Here,the migration timing and path for FAW into the countries were estimated by a trajectory simulation approach implementing the insect's flight behavior.The result showed that FAWs found in both South Korea and Japan were estimated to have come from eastern China by crossing the Yellow Sea or the East China Sea in 10–36 h in three series of migrations.In the first series,FAW moths that arrived on Jeju Island during 22–24 May were estimated to be from Zhejiang,Anhui and Fujian Provinces after 1–2 nights’flights.In the second series,it was estimated that FAW moths landed in southern Korea and Kyushu region of Japan simultaneously or successively during 5–9 June,and these moths mostly came from Guangdong and Fujian Provinces.The FAW moths in the third series were estimated to have immigrated from Taiwan Province onto Okinawa Islands during 19–24 June.During these migrations,southwesterly low-level jets extending from eastern China to southern Korea and/or Japan were observed in the northwestern periphery of the western Pacific Subtropical High.These results,for the first time,suggested that the overseas FAW immigrants invading Korea and Japan came from eastern and southern China.This study is helpful for future monitoring,early warning and the source control of this pest in the two countries.