Studies On Dynamics Of Arthropod Communities With Several Insecticide Treatments In Rice Fields Along The Yangtze River

An investigation was made on the structures of arthropod communities and population dynamics of major insect pests and enemies based on the systematic fields' survey and experiment in rice fields along the Yangtze River in which year or from July 4 to September 5. Study on the temporal dynamics of characteristics of arthropod communities in rice fields by analyzing guilds and nutrition classes. The effects of different substitutes for high-toxic insecticides on the structures of arthropod communities in rice fields were studied. The main results were as follows:1 Structures and their dynamics of insect pest and enemy communities in rice fields along the Yangtze River1.1 Species composition and population dynamics of each species of the communities in rice fields along the Yangtze RiverThe results of systematic investigation showed that there were 12 species of insect pests, 10 species of predatory natural enemies and 3 species of neutral arthropods. The major dominant insect pests were Cnaphalocrocis medinalis, Nilaparvata lugens, Sogatella furcifera, Laodelphax striatellus and Stenchaetothrips biformis. The major dominant natural enemies were Erigonidium graminicola, Singa pygmaea, Theridion octomaculatum, Pirata subpiraticus and Misumenops tricuspidatus. Their populations were rather abundant in whole development stage of rice plant.1.2 Nutritional structures of arthropod communities in rice fields along the Yangtze RiverBasal species of arthropod communities, approximately 90%, occupied dominant effect. Insect pests occupied dominant status in arthropod communities in rice fields along the Yangtze River. The population of intermediate species and top species of arthropod communities had considerable control effect on basal species although the number was relatively small, which approximately occupied 10% of total individuals of arthropod. The top species acted as beneficial supplementary effect.1.3 Major characteristic indices and their dynamics of the communities in rice fields along the Yangtze RiverThe total individuals of communities were relatively few during early development stage but rose rapidly during middle and late development stages of rice, which changed rather obvious in whole development stage of rice plant. The principal factor affecting the diversity was species evenness of the communities in all kinds of rice types. Generally the diversities of the communities were higher during middle and late stages than that in early period. The communities diversity indices based on species were significantly relates to those based on guilds.1.4 The dominant induces of insect pests and natural enemies in rice fields along Yangtze RiverThe dominant induces of arthropod communities in rice fields along the Yangtze River reflected distribution characteristics and roles in the communities of dominant insect pests and natural enemies in course of time. The dominant status was the population of Cnaphalocrocis medinalis in July, but Nilaparvata lugens in August.1.5 Cluster analysis of the community dynamicsThe results of fuzzy cluster analysis showed that the communities were divided into 3 types, which included former tillering stage, from later tillering stage to former tassel stage and wax stage, and from latter tassel stage to milk stage of rice. Characteristics of the communities changed obviously at wax stage with the sudden rise of migratory insect pest populations.2 Effects of different insecticide treatments on the insect pest and natural enemy communities in rice fieldsThe research results showed that all 5 insecticide treatments of 50% Methamidophos,40%Chlorpyrifos, 16% Aver-pyridaphenthione, 20%Mab-chlorpyrifos, and 3.5% Mab-Fipronil had significant control effects on major insect pests of rice. The control effects on insect pests of 20%Mab-chlorpyrifos and 3.5% Mab-Fipronil treatments were higher than 40% Chlorpyrifos and 16% Aver-pyridaphenthione treatments and effect on natural enemies were relatively little, which were propitious to protect natural enemies and could keep continuable control effect to insect pests in rice fields. The control effect of 50% Methamidophos treatment on insect pests was the best among 5 insecticides, but also had the best effect on natural enemies. Based on the general evaluation of effect on arthropod communities, the treatment of 3.5% Mab-Fipronil was the most optimal among given insecticides because of rather longer controlling period and less effect on natural enemies.3 Similarites of insect pest and natural enemy communities at different development stages of rice under different insecticide treatmentsThe similarity analysis results showed that there were rather obvious differences among five plots under different insecticide treatments after 2 weeks. The community characteristics in 20%Mab-chlorpyrifos treatment plot was most similar to that in 3.5% Mab-Fipronil treatment plot, and 40% Chlorpyrifos to 16% Aver-pyridaphenthione secondly. These four insecticide treatments plot all had significant difference with 50% Methamidophos treatment plot, due to attribute of different insecticides and different effects on insect pests and natural enemies.