The Influence Of Forest Belts On Population Dynamics Of Predatory Arthropods In Agroforestry System

In this paper, Gu'an County, which is situated in Langfang City, North Hebei Province, is selected as sample field. The most common arthropod natural enemies in the crop field include ladybugs, lacewings, spiders, whose biological ecology and survival strategies are studied over many years. We evaluate the status and role of forestry belts in the agroforestry ecosystem. The main conclusions are followed:1) Revealing the ecological role of forestry belts in providing the habitat and breeding surrounding for arthropod natural enemies; firstly explicit quantifying the scope and threshold of radiation scope, which is the ecological role of forestry belts for agricultural system; forestry belts are important shelters for the arthropod natural enemies to avoid the cold winter and adverse environmental factors.2) Through studying the life history and biological information of arthropods, using the quantifying form to reveal the relationship between forest, natural enemies and pests, and also the effective scope of arthropod natural enemies to prey the pests.3) Most arthropod natural enemies in certain stages of life cycle could inhibit the growth of pest population. Effective inhibition on pest population is driven by the population growth of natural enemies and moving between different crop fields.4) We propose how to maximize the protection of arthropod natural enemies in the fields, such as scientifically planning the field mode, reasonably constructing the small surroundings.After systematically studied the common arthropod species and dynamic state, we draw the following conclusions:1) In the sample fields, the lacewings, ladybugs and spiders, which are with large population and strong activities, are the common arthropod natural enemies.2) The Chrysopa formosa, Propylea japonica, Harmonia axyridis, Lycosa sinensis and Gnaphosa sinensis are the dominant species.3) The composition of dominant species in different habitats change with seasons:â‘ Before and early cultivation, the Harmonia axyridis and Coccinella septempunctata are dominant species and mainly distribute in the forestry belts;â‘¡in the mid and late period, the Propylea japonica is the dominant species and mainly distribute in the crop field;â‘¢the spiders in the time series show three periods: proliferation, peak and declineThrough contrasting the quantities of natural enemies in different habitats and spatial distribution analysis, we reveal the trends of natural enemies in habitat choice. The density of lacewings in the grass belts of crop field is non-positive correlation with the width of grass belts. The width of grass belt is approximately lm with a higher density of lacewings. This conclusion, from the view of farm planning and layout, help us to improve the field efficiency. The lacewing density in the surroundings of adjacent road shows the farther from the road the higher lacewing density. This reveals that the road environment has a significant effect on the lacewing habitat. Ladybug populations moving in different habitat patches is directly related with tree growth and harvesting crops, even in different period shows different spatial types. The spider density and species diversity in complex habitat were higher than simple habitat. The complicated degree of spider habitat is one of the important restrict factors for spider density.After studying how dose forestry belt to affect the space distribution of natural enemies, it shows that this kind of non-crop habitat, especially in the gap of planting crops, winter and population renewal process for natural enemies, provide support function to the natural enemies. It also shows that adjacently forestry belts the number of lacewings and spiders are distinctly added. The effect of forestry belt on natural enemies is differed for different forest structure. In this test, the foresty effect on lacewings is up to 20m, and the effect scope for spiders is 30m. In the early time of crop cultivation and growth, forestry belts is the most important habitat for native species, and becomes the "species pool" for the natural enemies to expand to crop fields. Forestry belt also provides important habitat for most species after harvest and in winter.The survival abilities of natural enemies to respond the interference shows that native species has the remarkable adaptability. When the spiders (Lycosa sinensis) happen to distress, its hedging strategy, hedging approach and hedging ability can effectively avoid the harm of the traditional farming activities. This part of study was done only from the side.