Effects Of Simulated Global Warming On Interactions Between Winter Wheat-Wheat Aphid-Natural Enemies

With the increasing emission of greenhouse gas and human activity,the global climate will be gradually warming,and China is one of most serious countries in climate warming.The main features of gloal warming include the change of temperature parameter,such as increased mean temperature,more extreme high temperature and the different warming degree among different geographic regions.Wheat aphid is the most serious pests on wheat,belong to sucking insects,can cause seriously damage to wheat yield and quality,not only by directly feeding wheat plant juice,but also secreting honeydew causing gray mold to affect the photosynthesis of wheat.In the context of global warming,insects could be bound to have a profound response to climate change,which has become a current hightlight for research.In this paper,by analysising the impacts of climate warming on winter wheat,wheat aphids,and natural enemies in wheat ecosystem at different regions in China,the aim is to understand warming how to influence the population dynamic of wheat aphids,and the results provide the theoretical foundation for wheat pests monitor and control strategies.In this study,there were four aspects for investigation:1)analysis of the history data,2)field experiments of trans-regional field simulating climate warming,3)life table of Sitobion avenae,and 4)effect of environmental temperature variations on flight and locomotory behavior of Harmonia axyridis.The comprehensive analysis was conducted to understand the impacts of climate warming on the occurrence and development of wheat aphids in wheat field system.The main results were as follows:The stepwise regression analysis was used to explore the correlation of aphid abundance?Y?and weather data?X₁:maximum temperature,X₂:mean temperature,X₃:minimum temperature?,and reaults showed significant positive correlation between aphid abundance and average temperature?10 April to31 May?and regression equation:Y=0.17862X₂+0.08331,R₂=0.5250.Sample cluster analysis was used for the meteorologic data during 16 years from 1979 to 1997,and the data could be divided into three categories.The average temperature of the three different categories were 18.00±0.14?,16.96±0.19?,15.83±0.23?,respectively.Temperature gradients were constructed from historical meteorological data;One-way GLM was used to analysis the average temperature and aphid abundance from different categories,following with Duncan multiple comparison.The results showed that average temperature of different categories was significantly different,and the aphid abundance significantly increased with warming.To further explore the ecological mechanism of wheat aphid inceased significantly with warming,trans-regional field elevated temperature experiments were conducted at Langfang?Hebei Province?,Yuanyang?Henan Province?,Wuhan?Hubei Province?.The investigated data were including,for wheat:the time of growth period,biomass,thousand grain weight?TGW?,for wheat aphids:the population dynamic of S.avenae and R.padi,for natural enemies,the number of mummies and the abundance of lady beetles.The results showed warming advanced the growth period from turning green to mature by9-12d,7d,4d at Langfang,Yuanyang,Wuhan,respectively.Warming significantly increased above-ground biomass of wheat from Langfang and Yuanyang,but not at Wuhan.The abundance of S.avenae at Langfang and Yuanyang was affected by warming,but not at Wuhan,and the abundance of R.padi at Langfang was significantly increased by warming,but not at Yuanyang and Wuhan.Warming significantly decreased the rate of parasitism at Langfang and Yuanyang,and the abundance of lady beetles at Langfang,but not at Yuanyang,neither no significant effect on the rate of parasitism and the number of lady beetles at Wuhan.The results showed that the wheat ecosystem at different regions had different responses to warming,and compare with lower latitude areas,the wheat ecosystem from the middle to high latitude areas were more susceptibal response to warming.The biomass and TGW of wheat increasesd significantly with warming,and counteract the negative effects of wheat aphid on yield loss,so warming did't decrease the wheat yield.Therefore,global warming not only directly influence the abundance of wheat aphids,but also could strengthen bottom-up positive regulation on wheat growth and decrease top-down control of natural enemies to increase the abundance of aphids.To understand the effect of warming on the parameters of wheat aphids,in natural condition,a life table of S.avenae was established.The results showed that warning significantly increased aphid's fecunicity,decreased the duration of nymphs and increased the duration of reproduction,significantly increased the net rate of fecundity and intrinsic rate,significant decreased population doubling time and average generation cycle,but had no significant effect on winged type of S.avenae.The results indicated that elevated temperature in the field could directly contribute to the development of population of S.avenae.In order to uncover the effect of temperature on the flight and movement behavior of ladybeetle.The H.axyridis in fight and search behavior were investigated with the flight mill and insect behavior recording device under different temperature treatments?i.e.three in constant temperature conditions?15??25??35??,continuously liner temperature variation from 15?to 35?,and continuously jumping alternation temperature variation among 15?-25?-35?in the lab?.The results indicated that flight parameters,including frequency,total flight distance,accumulative flight duration and average flight speed of H.axyridis were all significantly higher at 15?than other constant temperature.Furthermore,the walking parameters,including frequency,total walking distance,average walking speed and direction change frequency of H.axyridis were all higher at 35?than others.Under the treatment of continuously jumping alternation temperature,the lady beetles were significantly higher performance of both flight and searching ability than both treatments of continuously linear temperature variation and constant normal temperature?25??treatment.The research demonstrated that H.axyridis tends to flight more at lower temperature and showed superb walking/searching ability at higher temperature.Through historical data analysis and trans-regional field warming experiments,we know that climate warming significantly increased the abundance of wheat aphid in field.A preliminary ecological mechanism was uncovered that warming could not only directly impact wheat aphids,but also changing the relative proportion and function of the related ecological factors in wheat field,caused from bottom to top effect of wheat-aphids and top-down effect of natural enemies-aphids.On the one hand,wheat was infested by higher population of wheat aphids to decrease yield,but on the other hand,warming significantly increased the biomass and TGW of wheat,So warming did't decreased the wheat yield.The result implied that the control index of wheat aphids should be broaden under global warming.At the time,the responses of wheat field systems to climate warming in different geographical areas are different,and in comparision with lower latitudes,the wheat ecosystem from the middle-high latitudes response to warming greater.