Study About Predation On Rice Planthoppers And Ecological Mechanism Of Natural Regulation By Generalist Predators In Rice Ecosystem

Rice planthoppers have been the most serious pests threatening rice production in Asia since the 1960s.There are numerous natural enemies in paddy ecosystem,which have great potential for controlling rice planthoppers.Therefore,it is crucial to understand the relationships between biodiversity and ecological function in rice ecosystem as well as interactions among planthoppers and predators.Predators are effective biological control agents in rice ecosystems,but the comparative study of predations among main predator species under field conditions have not been fully explored since lack of practical methodology.In this study,field experiment and molecular gut-content analysis based on PCR,as well as metabarcoding,were used to explore the predations on Sogatella furcifera(Horvath)and Nilaparvata lugens Stal by the generalist spider predators and the mechanism of diet switch for five major predator species in rice ecosystem.The results are shown as follows:(1)A series of field experiments using the same research protocol were carried out to compare the community structures between tropical(Philippines)and subtropical(China)rice ecosystems in 2011-2012 and to explore the ecological mechanisms related to frequent outbreaks in subtropical rice ecosystem.The results showed that planthopper populations in subtropical area could be characterized as the higher population growth rate and higher peak density.The average growth rate in subtropical area was significantly higher than that in tropical area.The higher realized fecundity in subtropical area indicated that the higher growth rates and higher peak densities were mainly related to the poor natural regulating forces in subtropical area.Our results showed that resistant variety could significantly reduce the peak density in subtropical areas.(2)More than 3000 spiders of dominant species were collected from subtropical rice ecosystems to compare their predations on S.furcifera and N.lugens using DNA based gut content analysis.The positive rates for all spider taxa were closely related to prey densities,as well as their behaviors and niches.The relationships of positive rates to prey planthopper densities for Pardosa pseudoannulata(Boes.et Str.),Coleosoma octomaculata(Boes.et Str.),Tetragnatha maxillosa Thorell and Ummeliata insecticeps(Boes.et Str.)in field conditions could be described with type ? functional response.Quantitative comparisons of predations among the 4 spider species confirmed that P.pseudoannulata and C.octomaculata were more rapacious than U.insecticeps and T.maxillosa in field conditions.The comparison of ratio of spider to the planthoppers and positive rates between fields revealed that biological control by spiders could be effectively integrated with variety resistance.The generalist spiders could follow up planthopper populations in time and assemblages of spiders cooperated with variety resistance could effectively suppress planthopper populations.(3)In this study,arthropods(including herbivores,predators,parasitoids and neutral insects)from rice paddies in Zhejiang province were collected using the suction sampling,basin trapping or net sweeps.Total genomic DNAs were extracted from 131 key species in all samples for DNA barcoding using the mitochondrial cytochrome oxidase I gene COI amplification.Based on these sequences,a DNA barcode library was established.The 131 species in the library could be classified into 2 Classes,10 Orders,53 Families and 108 genera.The average interspecies K2P genetic distance was 0.304,the minimum distance was 0.004,the maximum distance was 0.474.The average intraspecies K2P genetic distance was 0.004,The minimum distance was 0.000,and the maximum distance was 0.033.(4)Based on the DNA reference library,NCBI and the references,a pair of degenerate primers was developed for amplification of the major arthropods in rice ecosystem.87%of arthropod species could be amplificated by the minibarcode primers and the average luminance of the bands by agarose gel electrophoresis is 2.7 pieces of"+",which indicate that the degenerate primers are suitable for the following-up research work.(5)Using Next-Generation Sequencing approaches,the prey spectrum and diet switch mechanisms for the 5 main predators including P.pseudoannulata,C.octomaculata,T.maxillosa,U.insecticeps and Cyrtorhinus lividipennis were studied.The results showed that P.pseudoannulata has much stronger intraguild predation,but T.maxillosaand C.lividipennis have stronger predation on rice planthoppers.All the results indicated that the application of new technology related to molecular biology could help us to understand the roles and mechanism of generalist predators for pest management in field conditions in further.