Studies On The Structures Of Insect Pest And Natural Enemy Communities In Paddy Fields Of Different Rice Types And Under Different Insecticide Treatments

An investigation was made on the structures of insect pest and natural enemy communities in paddy fields of different rice types and under different insecticide treatments based on the systematic field survey and experiment in 2002-2003. The main results were as follows:1 Structures and their dynamics of insect pest and natural enemy communities in paddy fields of different rice types 1.1 Species composition and population dynamics of each species of the communities The results of systematic investigation showed that there were 12 species of insect pests and 16 species of predatory natural enemies in early paddy field fields, 12 species of insect pests and 12 species of predatory natural enemies in middle-season paddy fields, 11 species of insect pests and 18 species of predatory natural enemies in late paddy fields. The major dominant insect pests in early paddy fields were Sogatella furcifera, Nilaparvata lugens and Cnaphalocrocis medinalis and their populations were relatively high in late development period of rice. The major dominant insect pests in both middle-season and late paddy fields were Nilaparvata lugens and Cnaphalocrocis medinalis, but their populations in late paddy fields were relatively lower than those in middle-season paddy fields. The major dominant natural enemies in paddy fields of every rice type were Erigonidium graminicola, Paederus fuscipes,Singa pygmaea and Pirata subpiraricus and their populations were rather abundant in the whole development period of rice.1.2 Spatial patterns and their dynamics of major dominant species in the communities Among the major dominant insect pests, Nilaparvata lugens was distributed mainly in the lower parts of rice plants, Sogatells furcifera was distributed mainly in the middle parts of rice plants and Cnaphalocrocis madianlis was distributed mainly in the upper parts of rice plants. All the major dominant natural enemies were distributed mainly in the middle and lower parts of rice plants. The spatial distributed patterns of dominant species of the communities had no obvious change in the temporal series.1.3 Major characteristic indices and their dynamics of the communites The total individuals of the communities were relatively few during the early and middle development periods but rose rapidly during the late development period of early rice. The total individuals of the communities changed greatly in the temporal sequence in middle-season paddy fields but were relatively stable in late paddy fields. Generally the total individuals of the communities in middle-season paddy fields were greater than those in both late and early paddy fields. The diversities of the communities were a little higher during the late development period of early rice, but were the highest during the middle development period of middle-season rice and were in rising trend with the growth and development of late rice. The principal factor affecting the diversity was species evenness of the communities in all kinds of rice types. Generally the diversities of the communities in late paddy fields were higher than those in middle-season and early paddy fields. The communities diversity indices based on species were significantly relates to those based on guilds.1.4 Cluster analysis of the communities dynamics The results of fuzzy cluster analysis showed that the general characteristics of the communities were relatively analogous from tillering stage to milk stage of early rice but changed obviously at wax stage with the sudden rise of migratory insect pest populations. The general characteristics of the communities changed obviously in temporal sequence in middle-season paddy fields but were relatively stable in late paddy fields.2 Effects of different insecticide treatments on the insect pest and natural enemy communities in paddy fields The research results showed that all 4 insecticide treatments of triazophos, shachongshuang, abamectin and Bt+imidactoprid had significant control effects on major insect pests of rice. The short perio...