Studies On Population Dynamics And Temporal And Spatial Niches Of Spodoptera Litura In Autumn Cabbage Fields

Based on a systermatic field investigation,the population dynamics of Spodoptera litura(Fabricius)and the temporal and spatial niches of Spodoptera litura and the major predatory natural enemies in autumn cabbage fields were studied in this paper.The main results are as follows:1 Population dynamics of Spodoptera litura in autumn cabbage fieldsThe research results show that the population densities of Spodoptera litura in autumn cabbage fields are in trend of rise first and decline later and the population dynamics is single-peak type. The population densities of Spodoptera litura have no relativity to the aggregate degrees of population but are significant related to the rates of cabbage plants attacked by Spodoptera litura. This indicates that the occurrence of Spodoptera litura changes gradually from the dot and patch occurrence to the whole field occurrence along with the rise population.The results of fuzzy cluster analysis show the population dynamics of Spodoptera litura in autumn cabbage fields can be divided into four dynamics types: dot and patch incidence period(low population density and high patchiness), expansive or falling incidence periods(low population density and medium patchiness), peck incidence period(high population density and patchiness) and recessive incidence period(medium population density and patchiness). The incidence of Spodoptera litura population changes rapidly from the dot and patch incidence period to the peck incidence period. Therefore,the dot and patch incidence period and the expansive incidence period of Spodoptera litura in autumn cabbage fields are the critical control times.2 Spatial and temporal niches of Spodoptera litura and major predatory enemies in autumn cabbage fieldsThe research results showed that Spodoptera litura and the major predatory enemies all have narrow temporal ×spatial niche breadthes and this indicates that their populations are in uneven distribution in temporal ×spatial resource sequences. Among the major predatory enemies, Erigonidium graminicolum, Singa sanguinea, Singa pygmaea and Theridion octomaculatum have relatively great temporal ×spatial niche overlaps and this indicates that they have relatively good follow effects and great potential control effects on Spodoptera litura. In the meantime, the four predators except Singa pygmaea have relatively abundant populations.The temporal-dynamic spatial niche breadthes of Spodoptera litura have no relativity to its own population densities and this means that the damage of Spodoptera litura is complicated. On the whole, Spodoptera litura can damage the whole plants of cabbage(including heart leaves, inner leaves and outer leaves) but the outer leaves are damaged worst.