Study On The Community Structure And Population Dynamics Of Migratory Insects Across The Bohai Strait

Long-distance migration plays a key role in the sudden outbreaks of crop pests and plant diseases, which has become a bottleneck problem in the sustainable development of agriculture in China. Bohai Strait is the major pathway for the seasonal northward and backward migration of many insect species in northern China. To clarify the annually and seasonal fluctuations of the community structure and population dynamics of insects migration across the sea, is the theoretical and practical foundation to understand the disaster mechanism of crop pests and to improve the ability of early-warning system. System monitoring of different insect species migration across the sea were carried out by means of the entomological radar, searchlight trapping, ovarian dissection, trajectory analysis, etc., on a small isolated island located in the center of Bohai Strait during 2003-2013, and the main results were summarized as follows.1. Species composition and community structure of insects migration across the Bohai Strait was clarified preliminarily, and a total of 119 insect species, which belong to 9 orders and 36 families, were trapped from April to October 2003-2013. The subcommunity of crop pests including 100 species belong to 26 families, and the subcommunity of natural enemies including 19 species. Lepidoptera is the predominant group, while Odonata and Coleoptera is the subdominant group of the total group. Homoptera, Neuroptera, Diptera, Orthoptera, Hemiptera, and Hymenoptera in the subordinate group. According to the index of occurrence, seven species was considered to be the constant species, and 30 species was considered to be the accessory species, while 82 species was considered to be the accidental species of the total community.2. Five migration periods were divided by Fisher’s optimal segmentation method. The number of species and biomass was significantly correlated to months, i.e. the numbers were monotonic increasing with the increase of the date in the northward migration period, while monotonic decreasing with the increase of the date in the backward migration period. There was no significant monthly difference in the index of evenness, dominance, and dominant concentration of the whole community, which showed that the species composition and community structure was relatively stable during all periods when insects migration across the Bohai Strait.3. The variation on the number of species and biomass was significantly correlated to that of air temperature, relative humidity, precipitation, front activation, and etc.4. The biomass of 33 species of backward migration insects increased more than 10 times compared to the northward migration, and 49 species of the backward migration insects increased 1-10 times compared to the northward migration, which showed that the pole-ward migration to high-latitude by the prevailing southwest winds in spring and summer, brought significantly ecological and reproductive benefits to the population.5. Significant annually and seasonal accompanying migration between natural enemies and crop pests exist in all migration periods. The annually total number of species and biomass of natural enemies was significantly negatively correlated to that of crop pests, which showed that the interaction between the two populations is undoubtedly of important ecological and behavioral significance. The temporal niche of lacewings and ladybugs was significantly overlapped to that of Lepidopteran insects, and their biomass significantly correlated with each other, which showed that there exist the phenomena of accompanying migration between lacewings/ladybugs and Lepidopteran insects.6. Firstly confirmed that A. lucorum, A. lepigone, M. crassisigna are long-distance insect species in field environment both at home and abroad. The vast majority of A. lucorum adults flying at airspeeds 0.5-2.5 m/s and at altitudes < 150 m above ground level, and A. lucorum adults had downwind displacement rather than randomly by heading toward their seasonally favorable directions. More than 90% of tested A. lepigone and M. crassisigna moths originated from C3 plants were significantly higher than that from C4 plants in all generations, suggesting that maize fields are not the main host sites for these pest species.7. Firstly confirmed that seasonal migration of C. medinalis, S. litura, P. xylostella, S. exigua between their overwinterring region and summer breeding region is a regular ecological phenomenon rather than an accidental event, which provides foundation of studies on poleward expansion of insect species under current global warming scenarios.8. The proportion of vergin females and sexually immature individuals of M. crassisigna was significantly higher than that of mated females and sexually matured individuals, which suggests that the onset of migration this species exhibits is initiated mainly by sexually immature females, which is termed the ‘oogenesis-flight syndrome’. However, the other 6 species showed the opposite results in at least one migration period or one month, which provides a beneficial supplement for the ‘oogenesis-flight syndrome’ theory.9. Air temperature plays a key role in the layer concentration when C. medinalis migration across the Bohai Strait. Most of the emigrating populations took off at dusk along with the strong updraft airflow in the emigrating region, with an “area density” peaking at 0.5h later; C. medinalis could ascend to the altitudes of up to 600 m above ground level, with maximum volume density always occurred at the temperature inversion layer, however, in nights with a much higher temperature range, multiple layering was common and most of which were located at the altitude where the temperature was ±2℃ degrees deviated to the maximum temperature, while, it is safely to say that 22 ℃ was the most suitable temperature for migratory C. medinalis layering, while, in altitudes where temperature was lower than 16℃, there was almost no C. medinalis distributed in such low temperature.10. Analysis of the track direction of the targets registered on the PPI showed that C. medinalis moths were heading toward the downwind direction, rather than being displaced randomly. The included angle between displacement direction and wind direction was much higher when wind speed was relatively lower(0-5.66m/s), and the displacement direction of C. medinalis in such conditions mainly determined by the seasonal preference directions. With the wind speed increasing(5.66-11.32m/s), the included angle decreased, and the displacement direction was determined by both the seasonal preference direction and wind direction. When wind speed higher than 11.32 m/s, the included angle was the smallest, and the displacement direction of C. medinalis was dominantly determined by wind direction.11. The volume density of C. medinalis was significantly correlated to temperature variation, precipitation, wind speed, pressure variation and front activation. Based on the open Web GIS and radar monitoring technology, the monitoring system for prediction and forecast of C. medinalis around Bohai Gulf was designed and developed, to reflect the population dynamics of this insect species comprehensively and intuitively, as well as to advance the accuracy and time-effectiveness of the early warning system on other migratory insect species. All of the software for building this system is free and open, and it has many advantages, such as user-friendly, easy to use, maintain and update, lowly demand for user’s software and hardware, and etc. The results show that this system is useful for regional precaution and macro decision-making for crop pests.