Influences Of Agricultural Landscape Context On Population Densities Of Chilo Suppressalis And Chromatomyia Horticola In Rice-rape Cropping System

As one part of ecology, the focus of landscape science is the relationship between creatures in a specific surrounding and its living environment. The purpose of this thesis is mainly focus on the changes of pests and its parasitoid enemies in different landscape factors in different time and the influence of landscape composition working on pests' population density. We chose different landscape contexts in Northern Jiangxi where have various landscape compositions, including Nanchang city, Jiujiang city and Yichun city. In winter, much attention were paid in the occurrence of oil leaf miner Chromatomyia horticola during rape flowering and what landscape factors impact on pest population density. In summer, rice stem borer Chilo suppressalis as experimental subjects were been investigated in different landscape backgrounds. We also estimated the damage of C. suppressalis by calculated the dead heart rate and the loss of production in different areas in paddy filed. In the same time, the dynamics of parasitoids were been included and dominant species of rice stem borer were been identified.1. Relationship between agricultural landscape composition and population density of Chromatomyia horticola during oil seed reap bloomAgricultural landscapes impact the ecosystem services of biological control and pollination, but they may also affect the density of pests. In order to understand the effect of different agricultural landscape backgrounds on population density of the oilseed rape leaf miner C. horticola, surveys were done at three times during rape flowering at 18 sites in different landscape contexts in Northern Jiangxi. Generalized linear models with a negative binomial error distribution were used to analyze the relationship between leaf miner density and landscape composition. The results show that during the initial flowering stage, full-blossom period and flower preliminary final, the population of C. horticola shown similar trend. Serious damage occurred during full-bloom, and the density of leaf miners differed substantially among different sites. Landscape variables correlated with densities of C. horticola. Grassland and forest area near the surveyed fields had a significant positive correlation with pest density, whereas arable land area in mid-range scales(1 000 m radius) had a negative correlation with C. horticola. Contrary to expectation, these results indicate that landscapes with more arable land had lower prevalence of the rape leaf miner. Further work is needed to corroborate and explain these findings. The current paper should be a case study for the analysis of ecosystem services, also may provide reference materials for ecological control of C. horticola.2. The occurrence and damage of rice stem borer Chilo suppressalis in different landscape contextsPeriodical outbreak of pests population density in different landscape contexts in different time have not been understood. In order to understand the relationship between rice stem borer C. suppressalis and landscape context, we chose a series of experimental sites with different landscape backgrounds. Linear regression analyses were used to analyze the relationship between rice stem borer density and the proportion of cultivated land and nature land. One of the results show that the number of overwinter generation of C. suppressalis have a positive correlation with the proportion of cultivated land. In the same time, the damage caused by C. suppressalis in early season rice has correlation with the occurrence of C. suppressalis. The results also show that C. suppressalis have a highly significant positive correlation with the proportion of cultivated land and a negative correlation with the proportion of nature land. The damage varied in different time at two separated years. The study of the loss of production indicated that the use of pesticide can help to reduce the damage caused by pests, but we cannot ignore the ecosystem services of biological control provided by landscape contexts. The current paper can be a case study to analyze the relationship between landscape contexts and pests population and may also provide some ideas in control stem borer.3. The occurrence regularity of rice stem borer's parasitical enemies in different times and identification of dominant parasitoidsParasitoids can provide ecosystem services of biological control for paddy filed. In order to understand the rule of parasitoids and make clear the dominant species, the eggs of rice stem borer C. suppressalis were placed on experimental paddy fields and were recovered after two days in the field. The results show that inter-temporal wasps are the dominant parasitoids in May. Egg parasitism was dominantly appeared in July and there was not found a parasitoid wasp in September. The average of inter-temporal parasitism rates was 0.92%,the highest rate was 7.19%, the lowest rate was 0 and egg parasitism rates were 5.94%, the highest rate was 43.89%, the lowest rate was 0. By the molecular identification of the dominant species of parasitoids, we found that egg parasitoid wasps including six species of Trichogramma and two kinds of inter-temporal wasps named Aphelinus kurdjumovi and Zele deceptpr. These results make it clear of the occurrence dominant parasitoid species in different times and provide reference materials to a further application of parasitoids in paddy filed.