Responses Of Biological Characteristics Of Nilaparvata Lugens（Stal） To Elevated CO₂Concentration And Temperature

With the increase in human activities and large-scale use of fossil fuel, atmospheric CO2concentration has increased from a pre-industrial value of about280ppm to379ppm in2005, and is predicted to rise to540-970ppm by the end of this century. At the same time, the greenhouse effect caused by increase of CO2concentration will lead to global warming. According to statistics, the surface temperature has increased by0.3-0.6℃by the end of the last century and is expected to rise by1.0-3.5℃by2100.Being one of the key meteorological factors affecting insect’s biological characteristics, changes in environment temperature directly affect the level of the insect’s metabolic rate, growth, development, survival, reproduction and behavior. Within a certain temperature range, increased temperature can enhance the activity of the enzymes and hormones, and accelerate the speed of biochemical reactions, which speeds up the rate of development. Outside the optimum temperature, the opposite results are exprected. Therefore, the temperature is one of the most important factors in determining insect population dynamics. Elevated carbon dioxide (CO2) affects directly plant physiological and biochemical processes, i.e., accelerate the photosynthetic rate, stimulates plant growth, increases the biomass of above-ground parts, enhances crop yields and increases the C:N ratio of most plant species. The changes induced by elevated CO2can alter the production of primary and secondary metabolites, and indirectly affect the fitness of herbivorous insects, and the growth and development of natural enemies by tritrophic interactions. Numerous researches indicate that the effects of elevated CO2on insects are mainly indirect, mediated by host plants’chemical composition and nutritional status. Therefore understanding the effects of elevated CO2or temperature on herbivorous insects will provide theoretical basis for monitoring and forecasting the dynamics of insect population in the context of global climate change.In these experiments, the effects of elevated CO2or temperature on growth, development, fecundity of the brown planthopper were examined in closed-dynamic CO2chamber (CDCC). The main results are as follows.1. At constant temperatures,19,22.25.28.31, and34℃, biological characteristics of the brown planthopper were determined.(1) Durations of egg and different stadiums of nymph were the shortest at28℃. and prolonged at other temperatures. At eahc of the temperatures, duration of the5th instas was the longest. Eggs laid at34℃did not hatch, suggesting that34℃is the highest inhibiting temperature fo the brown planthopper.(2) Nymphal durations were different at different temperatures with regard to wing form and gender; nymphs molted as brachypterous females developed longer than those molted as brachypterous and macropterous males at all temperatures with exception of22℃. There were no macropterous females in the emerged offspring adults.(3) The longevity of brachypterous females was significantly different between the temperature levels, extended with the decreases of the temperature. Brachypterous female adults lived for about22.5d at19℃, and only13.5 d at34℃. The survival rates at different temperatures ranked as25>22>28>19>31℃; high mortality occurred in young nymphs at low temperatures and in old nymphs. at high temperatures.(4) Pre-oviposition period ranked from the long to the short was19>31>22>25>28℃, and period of peak oviposition,22>25>28>31>19℃. Fecundity of individual female was the highest at28℃(256eggs/female), and decreased with the increase or decrease of temperature; the lowest fecundity occurred at19℃(108eggs/female), only42%of that at28℃.(5) The developmental threshold temperatures of egg.1-5th instars and the whole generation were7.9,15.3,13.6,12.9.12.5,9.1, and13.3℃, respectively; and their effective accumulated temperatures were161.2,23.2,33.6.32.8.35.5.80.1, and180.5day·degree. respectively.2. The effects of CO2concentration on the biological characteristics of rice plants and fitness of the brown planthopper were measured in closed-dynamic CO2chamber (CDCC) with CO2set at750ppm (eCO2) and360ppm (aCO2). The results indicated:(1) Forty-five day old rice plants at aCO2and eCO2showed no difference in leaf length, leaf area, number of tillers, height and diameter of the primary stem, but leaves of rice plants were wider at aCO2than at eCO2.(2) The root dry weight was not different between CO2levels, However, fresh weight and dry weight of above-ground parts were bigger at aCO2than at eCO2.(3) The macropterous females of the brown planthopper showed no preference in host selection for rice plants cultured at different CO2concentrations within48h of exposure. Among the females landing on rice plants,59%and49%selected plants cultured at aCO2at24h and48h, respectively. The females also exhibited no preference in oviposition on rice plants grown at different CO2concentrations. After exposure for48h, the macropterous females deposited57.2eggs per plant at aCO2and58.9eggs per plant at eCO2.(4) Honeydew excretion, which reflects the feeding amount of planthopper, was23.6and19.4mg per three brachypterous females within24h at aCO2and, respectively. The consumption in eCO2decrease by9.7%.The difference was not significant; Weight of the offspring brachyptery was not different between aCO2and eCO2, brachypterous female weighed about2.5mg and brachypterous male weighed about1.3mg. However, macropterous male was heavier at eCO2(1.5mg) than at aCO2(1.3mg);(5) Duration of brachypterous female nymphs or brachypterous male nymphs did not differ, but that of macropterous male nymphs differed significantly between the CO2levels. Eggs hatched in about7.6d and nymph stage lasted for12to14d at either aCO2or eCO2, no difference in egg and nymph stage duration was detected between the CO2levels, Brachypterous female adults lived for about14to15d, there was no difference between the CO2levels.(6) Fecundity tests showed that When the Fl generation brachypterous females emerging at aCO2and eCO2were confined with rice plants cultured at their originating CO2concentrations, no matter the Fecundity one female or the Fecundity one female one day, the aCO2females deposited more eggs at aCO2than the eCO2females at eCO2, which epresents-deerese of42.9%and40.21%respectively, with the increase of CO2concentration. The trend of Fecundity is present downward Parabola.(7) We measured C and N contents in rice stems and the concentrations of17free amino acids in rice stem, rice sap flow and planthopper honeydew samples. At eCO2, both C and N contents in rice stems increased as compared with those at aCO2, However, C/N ratio of rice stems decreased significantly. In rice stem, Lys, Met, Leu, Lys and Pro were down-regulated in rice stems at eCO2, but there was no significant difference in the total content of16free amino acids (Thr could not be detected due to overlap of peaks) between CO2treatments; In rice sap flow, Pro concentration was not affected by CO2treatments and the other15free amino acids were all up-regulated, the total content of16free amino acids (Thr could not be detected due to overlap of peaks) was significantly higher in sap flow collected from plants grown at eCO2than from plants at aCO2. In honeydew, total concentration of the other16free amino acids (Met could not be detected due to overlap of peaks) was significantly higher in planthoppers fed on plants exposed to eCO2than that at aCO2. The contents of Ser, Lys, Arg and Pro in honeydew were not different between CO2treatments, Gly was down-regulated and the other11free amino acids were up-regulated in planthoppers fed on plants exposed to eCO2.