Monitoring And Population Dynamics Analyses Of Important Migratory Pest Insects In Northern China

China is located in the East Asian monsoon area, where many key crop pests are migrants.Irregular outbreaks of these migratory pest insects cause severe damages to crop, and therefore, threatenagricultural production and food security. There was a sudden outbreak of Proxenus lepigone a new pestinsect of maize in China in2011, and intermittent heavy occurrence of the meadow moth Loxostegesticticalis L., black cutworm Agrotis ypsilon Rottemberg, armyworm Mythimna seperata in recent years,due to the anomalies of global climate and changes in tillage practices, etc. This study aims to improvethe level of monitoring and forecasting on migratory pest insects and benefit integrated management,and also to prevent losses in agriculture and reduce many social problems caused by chemical control.In the former part, catches from aerial samples by the self-designed aerial trap and by searchlight trapwere compared, and whether the nocturnal insects could be trapped during the whole night were test onmany species based on the data of many years obtained through searchlight traps with automatictime-switches that have been deployed in Yanqing Beijing, Gongzhuling Jilin and Xilinhaote InnerMongolia, Also, the dynamics of catch sizes during the whole night and related potential effect on thetrajectory analysis were studied. Focusing on the black cutworm and armyworm, this study integratedthe data from searchlight traps with the data obtained by vertical-looking radar, included condition ofovarian development, ground and aerial meteorological data from weather station or internet, and pestinformation from the National Agro-Technical Extension and Service Centre. Then we integratedapplication of the wind field analysis, trajectory simulation and geographic information system softwaresuch as GrADS, HYSPLIT and ArcMap to analyze these data and investigate the influence of variousmeteorological factors on the population dynamics and the relationship between population fluctuationsand wind field. Also, this study explored the possibility of be migrantion of P. lepigone, and its sourceplace based on the data mentioned above. The results were as follows:1. this newly designed aerial trap for high-flying insects could function when wind speed is notstrong enough to open the tow net, and is able to prevent the catches from escaping. Aerial samplingtests showed that this aerial trap could catch many individuals from7orders such as Hemiptera,Lepidoptera, Coleoptera etc. at the height of200~400m above the ground level. For the migratory pestinsects including L. sticticalis, M. separatar, Helicoverpa armigera Hubner, that were trapped in aerialsamples, the catch sizes in searchlight trap were consistently in peaked periods, which confirmed thatsearch light trap could be a practicable tool assisting radar in identification of the high-flying targets.2. Dominant species of Orthoptera and Coleoptera only appeared in some time-sections at night,but Sympetrum Croceolum and Chrysopa formosa from Neuroptera, L. sticticalis, Pyrausta nubilalis,Hymenia recurvalis, Plutella xyllostella and many noctuids from Lepidoptera could be trapped duringthe whole night. Dynamic rhythm of catch sizes differed in different species. Distant migratory behaviorwas one of the most important factor the dynamic of specific species. When limiting the function timefor only1night, the trajectory simulation showed that the results obtained as parameterized withdifferent starting time involved more insect source place and possible landing sites, not simply thetruncated distance as generated by the traditional methods. Howerver, source places obtained by bothmethods tend to be similar with the extension of the function time. 3. In2012, the minimum temperature in Yanqing of Beijing was higher than the supercooling point(-25.35℃) of the mature larvae with cocoon. With other evidences taken into consideration, theresultsindicate that the mature larvae with cocoon of P. lepigone could therefore overwinter in YanqingBeijing. Monitoring data confirm that P. lepigone has occurred4generations per year in LuanchengHebei province and3generations per year in Yanqing Beijing. the total amount of trapped males wassignificantly higher than that of female in both sites. Nights when sex ratio of P. lepigone wassignificantly smaller than or close to1accounted for58%and30%in Yanqing and Luanchengrespectively. Variation in population sizes influences the sex ratio that changes in same trend for bothsites, that is, the sex ratios were significantly higher than1when population size rise, but close to1orsignificantly smaller than1in the the steady periods. The first generation of trapped P. lepigone adultsdid not form the normal distribution in Yanqing, and two obvious peaks appeared in the this generation.Variations in population sizes were related to the wind field at925hPa. With comprehensiveconsideration of the synchronous spurts in other light traps around Beijing, we conclude that the trappedfirst generation was composed not only the local individuals, but also the migrants or dispersers fromHebei and Tianjin，therefore, P. lepigone is a facutrative migratory species.4. Indoors feeding observation showed that there were no significantly differences in the totaldevelopment duration between sexes. Tests on potential flight ability indicated that the males are ofmore powerful flight ability. So, total development duration and flight ablilty may lead to the changes insex ratioes. In the regions where first generation occurred, temperature and precipitation in March andApril had heavy influences on the occurrence of A. ypsilon, and it seemed that higher temperature andmore rains benefit the development of A. ypsilon. In the late June, the observation with entomologicalradar confirmed that most moths of A. ypsilon generally flew below500m, ant that the biggest densitywas at height of300~400m. The observation that moths of A. ypsilon can fly during the whole nightwere approved by both radar observation and timely samples of the catches from searchlight trap.Migrants of A. ypsilon could be windborne in that every peaks in trapped moths were alwaysaccompanied with favorable wind field and velocity, furthermore, the northern cyclones frontal weatherand heavy rainfall would cause massive landing.5. In2008~2012, total trapped moths of armyworm were5105,3981,11385and50584,respectively, among which a significantly difference was identified. For armyworm, the biggest catchsizes was in2012and more than7300moths were trapped at one night which had nerver occurredbefore since this monitoring station has functioned. In conclusion, favorable weather condition were themain factors leading to the outbreak of larvae of3rd generation. Taken the relationship between catchsizes and wind fields, most of trapped moths were thought to be immigrants from surrounding regions.Therefore, appropriate weather condition for migrants in July promoted the outbreak of the3rd-generation larvae in2012. In North China, the outbreaks were mainly the result of the jointreproduction of immigrants and the local adults under the favorable environment condition and littleconcerned with adult population in Northeast China. For northeast China, the source moths of3rd-generation larvae in Northeast China were mainly from the local, because the local2nd-generationmoths in Northeast China failed to immigrate into the North China and had to stay in the natal areas ormake short southern migration due to westerly flow and rainfall in late July. The southward 2nd-generation moths in Heilongjiang mainly landed at the junction of Heilongjiang and Jilin provincesas a result of wind shear associated with heavy precipitation, lead to the serious outbreak at possiblelanding places, together with the immigrants from the North China. During the return migration seasonof3rd-generation adults, considering the influence of the terrain and monsoon in Northeast and NorthChina, we determined that only on some occasion the wind field can carry moths into North China fromNortheast China. In addition, almost all fall crops were in harvest at that time. Combining theseconsiderations together, we forecasted there was little chance for4th-generation larvae causing heavydamage to crop, which was proved to be true by the actual occurrence of4th larvae.