Evolution Trend For Population Dynamics And Damage Loss Of Agrotis Ipsilon(Lepidoptera: Noctuidae) In China

The black cutworm Agrotis ipsilon(Hufnagel)(Lepidoptera:Noctuidae)is a cosmopolitan polyphagous insect pest.As an obligate migrant and under-ground herbivore,A.ipsilon could break out unexpectedly somewhere,causing enormous yield loss.As other migratory insect pests of great agricultural and economic importance,the population dynamics of A.ipsilon were influenced by crop-planting patterns,climatic environment and control measures.Thus,the evolution trends of its population dynamics and corresponding damage and loss need to be explored,in order to reveal regional catastrophe regulations and develop integrated management strategies.Here,we monitored dynamics of both the high-altitude migrants of 23 sites during 2014-2017 and the ground-level populations of 15 sites over 1991-2017 in China,and also summarized dynamics of annual loss caused by cutworms on major crops in China during 2008-2017,as well as damage patterns of A.ipsilon in severe occurrence regions,indicating profound conclusions as follows:1.The high-altitude migrants of A.ipsilon demonstrated frequently large-scale migration annually,with seasonal peaks indicating spatio-temporal clustering across China.The spring migration patterns of A.ipsilon were: in March and April,migrated from South China to coastal Zhejiang and Jiangsu and then southern part of North China in eastern-orientation,or to the south of the lower reaches of the Yangtze river,Jianghuai region,and then southern part of North China in middle-orientation,or to Southwest China in western-orientation;in May,continuously migrated to middle and northern part of North China and then Northeast China in northeastern-orientation,or to Northwest China in northwestern-orientation.2.Given the occurrence ecological regionalization of A.ipsilon in China,the ground-level populations in Huang-Huai region and North China could be partially explained by high-altitude immigration from South China.Occurrence areas for A.ipsilon were delineated into 5 ecological parts on the basis of mid-winter isotherms(January isotherms of 10℃,4℃,0℃ and-6℃)from south to north in China.In Huang-Huai region and North China,across four different occurrence areas of II,III,IV and V,ground-level populations and high-altitude migrants of A.ipsilon captures exhibited clear positive linear regressions(P< 0.01).Across the wide range from 31.6°N to 41.2°N,the key occurrence date of A.ipsilon adults postponed toward higher latitude: as latitude elevates 1°,the appearance date,first peak date and main peak date of overwintering adults and the main peak date of first generation adults postpone 2.61 d,3.72 d,3.58 d and 1.26 d,respectively.The daily capture rate of the main peak of overwintering generation adults,mean larval density,plant damage rate and plant mortality rate showed significant differences among 15 observation sites,topped by Fenyang,Jinyuan and Yanhu in Shanxi province,indicating highest severity in these sites.3.Progressive increases in ambient temperature drove extensive northern-expansion of overwintering and migration area,and remarkable earlier phenological responses of A.ipsilon in China.From 1991 to 2017,systematic records of corresponding 10°C,4°C and 0°C January isotherms showed how the northernmost borders of area I,II and III for A.ipsilon probably moved northward by 154.31 ± 7.83 km,232.38 ± 15.05 km and 58.66 ± 21.38 km(i.e.,1.40°,2.11° and 0.50°N),respectively.High-altitude migrants of A.ipsilon were captured in Fujin(Heilongjiang)in late May 2015-2017,thus indicating that the northern limit of its migration has reached the border of Northeast China and moved northward by 702 km(i.e.,6.38°N).Over a 27-year time period,the first peak date,main peak date of overwintering generation adults and the main peak date of the first-generation adults of A.ipsilon showed a respective 15.35-,17.05-and 7.87-day advancement in the Huang-Huai region and North China,accompany with significant increases of averaged DMAT in corresponding periods by 2.31 ℃,2.01 ℃ and 0.51℃.4.Recently,occurrence area of cutworms and its actual loss rose up in China,causing increasing economic loss of agricultural products and enormous input of insecticides.During 2008-2017,occurrence area,control area,actual yield loss and recovered yield loss of cutworms were 2.51163 million ha,3.05381 million ha,0.1419 million ton and 0.5397 million ton,respectively,on eight main host crops in China.Given annual insecticides input for cutworms control evaluated as 273 million RMB,economic loss of agricultural products cost 289 million RMB,and recovered economic loss cost 1.099 billion RMB.There were two different damage patterns of A.ipsilon,characterized as Abruptly Breakout Pattern(FY)and Stably Occur Pattern(YH).For FY Pattern,the occurrence ratio was below 25% normally,but once outbreak,the severe occurrence ratio could surpass 70%,causing 50% yield loss at least;For YH Pattern in contrast,the occurrence ratio was above 80% annually,but the severe occurrence ratio was always below 25%.Here,we provided clear evidences for routine large-scale and long-distance migration of A.ipsilon in East Asia,illustrated three migrate routes and quantitative resource relationships of A.ipsilon during spring migrating procedures from main overwintering areas into main occurrence areas,and demonstrated spatio-temporal characteristics of latitude-depending phenology and regional difference in population abundance of A.ipsilon,based on ecological distribution in China,thus indicating theory basis,predicting methods and numerical models for allopatric forecasting of A.ipsilon.We first put forward climate-triggered migratory alteration of A.ipsilon in China,characterized as northern-expanded overwintering and migration area and advanced immigrating peaks,proposing references for extreme long-term forecasting of major migratory insect pests of agricultural importance.We also concluded increasing trends of damage and loss caused by cutworms and its economic importance in China,demonstrated different damage patterns of A.ipsilon in serve occurrence regions,improving integrated pests management and regional control strategy.