Effects Of Drought Stress On Ecological Fitness And Physiological Characteristics Of Brown Planthopper, Nilaparvata Lugens Stal

Brown planthopper (BPH), Nilaparvata lungens (Stal), characterized by its monsoon migration and r-strategy life pattern, is one of the most important rice insect pests in Asia rice growing countries. With the changes of the cultivation system, the adaption of high-yield rice varieties, the improvement of fertilizer and water conditions and intensive application of chemical pesticides since the initiation of green revolution from1960s, BPH has become a serious ecomonical insect pests of rice in China. With the global climate change, the extreme weather such as floods and droughts kept to happen frequently. The extreme weather may affect the dynamics of BPH population in paddy field. This thesis explored the effects of drought stress simulated by different concentrations (0,5%,10%,15%and20%) of Polyethylene Glycol (PEG)6000on the feeding behavior and oviposition performances, survival, development and reproduction of BPH, population dynamics and morphological charateristics of yeast-like symbiote (YLS) and the activities of protective and detoxification enzymes in BPH feeding on three rice varieties TN1(susceptible), IR36(with resistant gene bph2), Hanyou3(drought-tolerant) in laboratory. The main results are showed as follows:1. In the choice test, the percentage of BPH female adult on rice plants stressed with different concentrations of PEG6000decreased significantly with the increase of stress degree (P<0.001), whereas no marked difference in the percentage of BPH nymph was found on rice plants with different stress degree (P=0.093). The number of eggs laid within72h was negatively correlated with the concentration of PEG6000on TN1and IR36(P=0.001and P=0.008, respectively). On the rice plants of IR36and Hanyou3, BPH nymph tended to move from upper-middle to basal part of leaf sheath when the PEG6000concentration increased, however, it didn't happen on TN1. The amount of honeydew secreted by BHP female adult within48h reduced on TN1and Hanyou3with the increasing of the concentration of PEG6000, and they were very low and no significant difference on rice plants of IR36treated with different concentrations of PEG6000.2. The effects of drought stress on nymphal duration of BPH were different among three tested rice varieties. On IR36, the nymphal duration of female BPH were obviously prolonged with the increasing of the concentrations of PEG6000, whereas no marked difference was recorded in nymphal duration of female BPH on TN1and Hanyou3, and in male BPH on all three tested rice varieties among different concentrations of PEG6000. The nymph survival rates on on TN1treated with15%and20%PEG6000solution were54.17%and54.67%, which were23%and22%lower than the treatment with5%PEG6000solution, respectively. While on Hanyou3and IR36, the survival rates of BPH nymph decreased markedly with elevated PEG6000concentration. The lowest survival rates with66%and22%, respectively, were found on Hanyou3and IR36with20%PEG6000. The survival rate on IR36was obviously lower than those TN1and Hanyou3. The weights of newly emerged BPH female adults were negatively correlated with the concentrations of PEG6000. No significant difference in weight of BPH female adult on IR36was found among the concentrations of PEG6000. The lowest weights of newly emerged BPH female adults both on TN1and IR36with20%PEG6000was1.67mg, which were significantly lower than that on control. The duration of BPH egg was prolonged significantly with the increasing of PGE6000concentration. The marked longer egg durations on TN1and IR36with20%PEG6000were9.09and9.35days respectively. The similar trend was found on Hanyou3, but no significant differences among different PEG6000concentrations. The female longevity of BPH adult and the number of BPH egg laid on all three tested rice varieties were decreased significantly with the increasing of the concentration of PEG6000, while no significant differences in ratio of female BPH, the percentage of brachypterous adult, and the hatchability of BPH egg were recorded among different PEG6000concentrations.3. The number of yeast-like symbiote (YLS) in BPH female adult on all three tested rice varieties was obviously reduced with the increasing of concentration of PEG6000, except that there was no significant difference among treatments of different PEG6000concentration on IR36. And it was markedly lower on Hanyou3stressed with10%,15%,20%PEG6000than that on control plants. The length of YLS was influenced significantly by the concentrations of PEG6000and rice varieties, while no marked difference was found on the width and ratio of length and width of YLS.4. The activity of POD in BPH on the same rice variety increased with the increasing concentration of PEG6000, while the activities of SOD and CAT increased obviously with the increasing of PEG6000on all three tested rice varieties. In addition, the activity of GST in BPH feeding on all three tested rice varieties stressed with20%PEG6000was markedly higher than that under control except that on Hanyou3treated with15%PGE6000. The activities of EST in BPH on TN1and IR36stressed with PGE6000were significantly higher than that on untreated rice when the concentration of PEG6000was above10%, however, the concentration of PEG6000must be above15%on Hanyou3.