| In recent years, global environmental change, especially the rise in atmospheric CO2concentration, has been an item of great concern for the scientific community. Elevated atmospheric CO2concentration can enhance crop photosynthesis, and change allocation of photo synthatic production;it can also alter composition of carbon-based secondary defense chemicals.Therefore, nitrogen nutrition and resistance of plants will be influenced by elevated CO2. In addition, the rise of CO2concentration can induce globle warming, which is of much importance for insect biology. So a study of effects of both elevated CO2and temperature at the same time oninsect pests should be encouraged, which would advance our understanding of influnce of climate change on agriculture. However, few empirical studies of insects address this issue by consideration of both climate factors.In this thesis study, we, using Mythimna separata (Walker) as the model system, imposed treatments of both CO2and temperature to examine its development, reproduction, some physiological traits, and food utilization efficiency of larvae in incubators. The main results and conclusions obtained from this study were summarized below.1. Effects of elevated CO2and temperature on development and fecundity of Mo separata across successive generations. To estimate effects of climate change on biology of Mythimna separata (Walker) of the economic pest on grain crops, experiments were made in growth chambers, where two levels of CO2(390μL/L and780μL/L) and two levels of temperature (20℃and25℃) were manipulated in the factorial design, to observe development fecundity across six consecutive generations. Three-way ANOVA results showed that temperature, CO2, generation, and their two-way interactions exerted statistically significant effects on larval and pupal duration. In the rising temperature, elevated CO2constricted larval duration of the2nd,3rd, and6th generation by13.0%,10.5%, and24.1%, respectively, and reduced pupal duration of the3rd and6th generation by19.2%and17.9%, respectively; but increased pupal duration of the2nd generation by1.42%. It also reduced pupal body weight of the2nd,3rd, and6th generation by21.3%,0.4%, and15.9%, respectively; decreased fecundity of the3rd generation by40.5%, but increased fecundity of the6th generation by6.2folds. In the lower temperature, elevated CO2extended larval duration of the1st and2nd generation by25.8%and40.9%, respectively; but contracted larval duration of the3rd and6th generation by9.9%and10.3%, respectively. It also extended pupal duration of the1st and2nd generation by32.0%, and25.4%, respectively; but decreased pupal duration of the3rd and6th generation by10.1%and14.2%, respectively. The study suggest that with elevated CO2and temperature M. separate would be negatively impacted after a few generations of acclimation.2. Effects of elevated CO2and temperature on larval food consumption and food utilization of M. separata across successive generations. To assess infuence of elevated CO2and temperature on larval food consumption and nutrition utilization, experiments were conducted in growth chambers by using a factorial design for both CO2(two levels:390μL/L and780μL/L) and temperature (two levels:20℃and25℃). Food intake and digestion were measured across six successive generations of M. separata larvae. Three-way ANOVA showed significant influences of CO2, temperature, generation, and their interaction on some of food digestion indices. Elevated CO2had statistically significant impacts on approximate digestibility (AD) and efficiency of conversion of ingested food (ECI). Rising temperature exerted significant influence on all growth and food utilization indices examined. Generation affected all food utilization indices examined. In20℃, elevated CO2increased AD of the1st and3rd generation larvae by33.1%and12.5%, respectively, but decreased relative consumption rate of the2nd generation larvae; increased the relative growth rate (RGR) by1.1times and the efficiency of conversion of digested food (ECD) of the6th generation larvae by83.9%. In25℃, elevated CO2decreased RGR of the2nd and6th generation by58.6%and41.0%, respectively; decreased AD of the2nd generation larvae by24.8%, and ECD and ECI of the6th generation larvae by38.9%and30.5%, respectively. The results suggested that elevated CO2have positive effects on food consumption and utilization in lower temperature, but negative influence in higher temperature.3. Effects of elevated CO2on physiological property of M. separata across successive generations. To examine influence of elevated CO2on protection enzymes and energy accumulation after a few generations in M. separate, larval survival, the enzyme activity, and energy reserves were measured on the7th generation. The results showed that larval survival of the7th generation was increased (after4th instar) under elevated CO2, compared to that under ambient CO2; the protective enzyme activity and protein content in mature larvae were not affected; triglyceride content and body dry weight was decreased, but body water content increased in adults, under elevated CO2. The study suggested that elevated CO2reduced energy reserves of adults, which can have negative influence on flight ability for migration.4. Effects of elevated CO2on food selection of M. separata. To assess preferences of M. separate larvae for wheat plants grown under elevated CO2, non-choice and choice trials were made to observe selection between wheat leaves from elevated CO2(780μL/L) and ambient CO2(390μL/L) treatments. In both choice and non-choice trials, the3rd and4th instar larvae exhibited more selection for leaves from the ambient than elevated CO2, with more consumption of leaves by75%and35.7%respectively in choice test, and26.74%and30.72%, respectively in non-choice test; but the6th instar larvae did not show significant food selection. The study suggested that intermediate instar larvae favor wheat leaves grown under the ambient CO2, but mature larvae did not exhibit such favor. |
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