Spatial Niche Of Rice Arthropod Community And Predation Of Spider To Planthopper In Rice Field

The thesis reviewed the research progress on structure and function of rice arthropod community. Based on the previous researches, day and seasonal variation of spatial niche of rice arthropod community, effects of application of two insecticides at different time (morning and afternoon) in a day on survival rate and predation function of spiders, and predation number of planthoppers by spiders per day in natural rice field were studied, combined with the biocontrol practice of insect pest. The results were as follows:Spatial niche of spiders in rice field varied with season. The spatial niche breadth of wolf spiders gradually became large from July to September; that of Tetragnathidae was the smallest in middle August; Micryphantidae was the largest in later July; it was the largest in later August to early September for Theridiidae. Population size of spiders was an important factor affecting the spatial niche breadth. The spatial niche of spiders in different time (morning, 6 clock; noon, 12 clock and afternoon, 6 clock) in a day showed regularity of obvious daytime change. Spatial niche of wolf spiders was the largest in the noon, which of Micryphantidae was almost constant. That of Tetragnathidae in the afternoon was larger than that in the morning during July to August, but inversely during September. Spatial niche breadth in the morning during July to August was the largest for Theridiidae, inversely for Saltidae. Similarity indices of inter-species of spider community were also calculated in this paper. The effects of two insecticides spraying at different time (morning and afternoon) on survival rate and predation function of spider community varied with spiders, the effect of bisultap spraying in the morning on mortality rate and decrease of predation function for spider group was less than that in the afternoon, and inversely for methamidophos.Predation number of field spider group to planthoppers per day was also studied by pulse sample and killing planthoppers by dichlorvos and predation effects on functional response of spider at laboratory and in semi-field (cage rice in pot) were compared in this paper. The result showed that average consumptive number to planthoppers per day per spider in rice field was 0.669 per hill. That number was significant less than that at laboratory and in semi-field. Data analysis from pulse sample indicated the relationship between predation percentages (Y) and planthopper density (X) per hill was fitted by aparabola, the equation was as following:Y=0.27241+O.002996x-0.000136x2 ?.139445From that equation, it was confirmed that the predation percentage of predators at low and high density of planthopper was lower than that at the middle (about 10 planthoppers per hill). Analysis also showed the relationship between the predation number of spider group and two dominant spiders, Micryphantidae and Lycosidae, was fitted by binary linear regression, but their regression coefficients were negative. That indicated the predation number decreased with increase of the spider density, which bad been confirmed by multi-predator coexistence system and field cage experiments.