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Study on Spatiotemporal Population Dynamics of Loxostege sticticalis (lepidoptera: Pyralidae) in China

Author: HuangShaoZhe
Tutor: LuoLiZhi
School: Chinese Academy of Agricultural Sciences
Course: Agricultural Entomology and Pest Control
Keywords: Loxostege sticticalis Population dynamic Spatiotemporal dynamic Geostatistics Trajectory analysis Outbreak Source relationship
CLC: S433
Type: PhD thesis
Year: 2010
Downloads: 204
Quote: 4
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Abstract


The beet webworm, Loxostege sticticalis Linneaus (Lepidoptera: Pyralidae) is one of the most destructive pests of crops and fodder plants in northern China. It survived maily in a long belt zone between 36°N-53°N and the population dynamic offen changed dramatically due to the two important life history strategies obtained by L. sticticalis: migration and diapause, adapted to the dry and cold climate in this area. Thus, understanding of the spatiotemporal dynamics was of great importance in improving the forcasting and control of beet webworm outbreaks. As the spatiotemporal dynamic were poorly understood, systematic studies were conducted to the population dynamics of beet webworm in China during 1953-2008, spatial distribution of outbreak population and affecting factors, and outbreak source relationship between China, Russian and Mongolia, using population ecology and geostatistic methods and geographic information system. The major progresses obtained were summarized as follows:Beet webworm outbreak in China was characterized with periodicity, and the outbreaks were classified as periodic eruption, while the outbreak characters were colosely related to spatial scale investigated. Basing autocorrelation and phase trajectory analysis of larvae population in national, Inner Mongolia, farming area in Inner Mongolia, Kangbao county of Hebei province, and farming area in Kangbao county of Hebei province, and adult population in Kangbao county of Hebei province, results showed that beet webworm outbreaks at national and Inner Mongolia scale were characterized with periodicity during 1953-2008, and outbreaks were classified as periodic eruption, including three outbreak periods 1953-1959, 1978-1984, 1996-2008. Beet webworm population dynamic at county level became more complicated, larvae population in farming area of Kangbao county of Hebei province were characterized with periodicity and classified as periodic eruption, while no significant autocorrelation were found in larvae population and adult population at Kangbao county of Hebei province. These results indicated that spatialtemporal population dynamic of beet webworm were closely related to spatial scales investigated, thus, discussion on spatialtemporal population dynamic of beet webworm and its monitoring and forecasting application should carried out at macro scale. Spatial population dynamics of beet webworm in China were greatly affected by environmental temperature and relative humidity, and overwintering population at northern China was one of the major sources of beet webworm outbreak at northeastern China.Environmental temperature and relative humidity could greatly affect the spatial distribution of adult population and consequent larvae population, serious outbreak of larvae happened in areas with temperature ranged 19°C-25°C and relative humidity higher than 44% during adult outbreak. The first and second generation larval population can overwintered as diapause larvae in northern China, while only the second generation larvae can overwintered as diapause larvae in northeastern China, and this was mainly because of environment variation, especially the temperature during 1 July to 20 July, serious outbreak period of the first generation larvae. Overwintering generation adults would migrate into northeastern areas and cause consequent serious outbreaks, when unfavorable environmental conditions and favorable southwest air flow happened.Beet weebworm outbreaks in China, Asia part of Russia and Mongolia were highly synchronized and wind direction by migration hight of beet webworm in the neighbouring areas favored the adults of overwintering and 1st generation migrated from eastern Siberia of Russia and eastern Mongolia into northern and northeastern China, and 1st generation adult population migrated from eastern Siberia of Russia and eastern Mongolia were responsible for the serious outbreaks of 2nd generation larvae in China in 2008. Phase analysis showed that the synchornized outbreak years between China and Mongolia, China and Far East, China and western and eastern Siberia of Russia were 4, 1, 3 and 5 years from 1978 to 1984, and 2, 4, 8 and 11 years from 1996 to 2008 by phase analysis, while synchronized nonoutbreak years between China and Mongolia, China and Far East, China and western and eastern Siberia of Russia were 9, 11, 9 and 8 years, indicating that migration taken by adult L. sticticalis were the possible cause for the synchronized outbreaks in these areas. Furthermore, the analysis of wind system by the height where the migration of adult L. sticticalis usually occur showed that possibility of northwestern wind in Haila’er (China), Chita (Russia) and Choybalsan (Mongolia) was high, which favored the adults migrate successfully from these areas to northern and northeastern China during its reproductive seasons. Finally, the larvae of the second generation infested an area of 11 million hectares at extremely high density in Northern China, although the crop damaged by the first generation larvae with low density was only 700 thousand hectares in 2008. Results of wind field and trajectory analysis showed that the source of the first-generation adults, which caused severe outbreak of second generation larvae, was tracked back to eastern Siberia of Russia, eastern Mongolia, and the boundary regions of China-Russia and China-Mongolia. All these results suggested that the outbreak source of L. sticticalis in northern China were closely related to outbreak populations in Siberia of Russia and Mongolia, via long distance windborne migration of L. sticticalis with the help of frequent northwestern wind. The results firstly reported here will greatly improve the mornitoring, forcasting and control of beet webworm population.Adult population and overwintering larvae populations of beet webworm in China belonged to the aggregated distribution, and evident spatial anisotropy were detected. Geostatistical analysis was applied to adult population and overwintering larvae population, results showed that they were charaterized with aggregated distribution and spatial anisotropy were detected. The rages of the semivariograms were 153.18-407.37 kilometers and 137.64-293.04 kilometers respectively, and the direction of major range were 63.2°, 65.5°respectively, and the nugget coefficient were 0.11, 0.45, showing that the aggregated intensity and maximum correlated range of adult population were higher than that of overwintering larvae population. Kriging prediction map also showed that the spatial distribution of overwintering larvae was similar to former reports, but the density in secondary overwintering area grew markedly. These results indicated that beet webworm populations were spatially aggregated and the main aggregation directions were southwest to northeast, and the aggregation range of adults were higher than larvae, mainly due to higher migration mobality.The major innovative discoveries in this disertation were as follows:1) Longterm population dynamic patterns of beet webworm in China were analyzed with autocorrelation and phase trajectory, results showed that population dynamic pattern were characterized with periodicity during the past 55 years, and the population dynamic pattern were found to be closely related to the spatial scale investigated. The autocorrelation level increased as the spatial scale expanded.2) As the outbreak level of beet webworm in China were proved to be closely related to the environmental temperature and relative humidity in this study, the spatial population dynamic pattern of beet webworm population in northern and northeastern China were firstly studied. Results showed that the overwintering generation adults in northern China can migrate into northeastern China with the help of favorable air flow, thus the overwintering population in northern China served as an important source area to beet webworm outbreaks in northeastern China.3) Basing on phase analysis, wind direction condition analysis and outbreak souce analysis of 1st generation adusts and 2nd generation larvae of beet webworm in China in 2008, outbreak population at Asian part of Russia and Mongolia were proved to be one of the major source areas responsible for beet webworm outbreak in China.4) Basing on geostatistical analysis of beet webowrm adults and overwintering larvae populations, the spatial distribution pattern of beet webowrm population in China was firstly proved to be aggregation, and the aggregation intensity of adults were higher than that of overwintering larvae, both their main aggregation directions were southwest to northeast.

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CLC: > Agricultural Sciences > Plant Protection > Pest and Disease Control > Plant pest and its control
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