Studies On Population Dynamics And Spatial And Temporal Niches Of Diamondback Moth(Plutella Xylostella) In Spring Cabbage Fields

Based on asystermatic field investigation. the population dynamics of Plutella xylostella(L.) and the temporal and spatial niches of diamondback moth and the major predatory enemies in spring cabbage fields were studied in this paper. The main results were as follows:1 Population dynamics of diamondback moth in spring cabbage fieldsThe research methods of the fuzzy cluster analysis and the relationship analysis between temporal-dynamic spatial niche breadthes and population densities of diamondback moth were used to study the population dynamics of diamondback moth in order to provide basis for the scientific management of Plutella xylostella in spring cabbage fields. The research results showed that the population dynamics of Plutella xylostella in spring cabbage fields could be divided into three development periods:dot and patch occurrence period (low population density and high patchiness), expansive occurrence period (medium population density and low patchiness) and rampant occurrence period (high population density and low patchiness). The damage circumstances of diamondback moth to spring cabbage were quite complicated. Diamondback moth attacked the heart leaves of cabbage mainly in low population density and dispersed gradually to inner and outer leaves of cabbage with the growth of cabbage and the rise of its population density and led to the damage of whole cabbage plant eventually. The dot and patch occurrence period of diamondback moth population in spring cabbage fields was the critical control time.2 Spatial and temporal niches of diamondback moth and major predatory enemies in spring cabbage fieldsThe research results showed that diamondback moth had a narrow temporal niche breadth and a relative wide spatial niche breadth. This implied that the occurrence of diamondback moth had the characteristics of obvious peak-period and whole-plant damage. The temporal-dynamic spatial niche breadthes of diamondback moth had no relativity to its own population densities and this implied that the damage of diamondback moth was complicated. Among the predatory enemies, Misumenopos tricuspidata, Erigonidium graminicolum and Theridion octomaculatum had relative wide temporal and spatial niche breadthes and it meant that they had longer period of occurrence and wider range of distribution than other predatory enemies. The temporalxspatial niche overlap of the predatory enemies with Plutella xylostella was in order of Coccinella septempunctata > Misumenopos tricuspidata> Singa pygmaea> Singa sanguinea> other predatory enemies and this results showed that the above four enemies had better follow effect to diamondback moth than other predatory enemies.