Effects Of Elevated CO₂ On Fitness Of Brown Planthopper And Cotton Aphid,and The Mechanisms Of Their Feeding Behavior

The latest data showed that the concentration of global CO2 has incerased from 280 ppm before the industrial revolution to 404 ppm in 2016,and still keepped growing at an average of 1.8 ppm per year since 1980.Elevated CO2 could directly affect the plant growth,morphology,physiological and biochemical,then affect the herbivorous insect by"bottom-up effects".A large number of studies showed that sucking insects were the only type of insects which had a positive response to elevated CO2.What kind of response will brown planthopper(Nilaparvata lugens)and cotton aphid(Aphis gossypii)make,as the typical sucking insects,under elevated CO2?And what are the mechanisms of feeding behavior?The solution of these problems is expected to further clarify the occurrence and development tendency of the pests in agricultural production under the climate change of elevated CO2,and guide the prevention and the control of them.In this study,N.lugens and A.gossypii,as the typical sucking insects,were for our research targets.Closely combined with the actual production and the global hot academic topic of atmospheric CO2 concentration rise,this thesis studied the relationships of feeding behavior,growth and fecundity of N.lugens and A.gossypii,from insect physiology,the of insects and plant physiology and molecular biology perspective under elevated CO2 and their molecular mechanisms.Main results for this study were as follows:1.A comparative study of three methods using to fix insects for the experiments of electrical penetration graphIn the EPG experiment,the small brown planthopper(SBPH),Laodelphax striatellus(Fallen)was used as tested insect to study and compare of three commonly used fixation techniques(i.e.,the negative pressure method,anesthetization method and freezing method).The results indicated that the optimal fixation technique of SBPH L.striatellus to connect the electrical electrodes of the EPG System is the negative pressure method following by the anesthetization and freezing methods.What's more,we used the optimized negative pressure method to carry out the research on feeding behavior tests of N.lugens and A.gossypii,and feeding behavior of virus-infected L.striatellus on plant.2.Feeding behavioral response of brown planthopper,Nilaparvata lugens,(Stal),to elevated CO2As the main factor of climate change,the increase of atmospheric CO2 concentration has become a hot topic in the world.In this study,N.lugens,as the major rice pest in Asia,was used for research object.The feeding behavioral response of N.lugens to elevated CO2 and its molecular mechanisms were studied,in order to provide theoretical basis for assessing the occurrence of N.lugens under future climate change.The determined results reveal that,elevated CO2 significantly shortened the developmental duration of eggs(4.04%),nymphs(6.67%)and the lifespan of female(18.28%)to N.lugens.It meaned elevated CO2 reduced the generation period of N.lugens,which resulted in increasing the damaged risk of N.lugens.Elevated CO2 significantly reduced fresh body weight of newly emerged female adults(4.93%),but there were no effects on male adults.Elevated CO2 remarkably enhanced number of hatched eggs(22.10%)and hatching rate(8.50%)to N.lugens,which meaned elevated CO2 was beneficial to fecundity of N.lugens.Elevated CO2 significantly increased the efficiency of stylet puncturing to the 4th and 5th instar nymphs of N.lugens,and decreased the duration of P waveform up to 23.35%and 42.01%,what's more,elevated CO2 significantly enhanced the duration of phloem ingestion(N4b waveform),30.03%and 123.06%respectively.According to the RNA transcript levels of appetite genes,elevated CO2 significantly up-regulated expression of appetite genes,especially,NPF.In short,increased atmospheric CO2 could raise the risk of N.lugens damage,such as,reduced generation period,resulted of increased ingestion.3.Feeding behavioral response of cotton aphid,Aphis gossypii(Glover),to elevated CO2Effect of elevated CO2 on feeding behavior of the cotton aphid,A.gossypii(Glover),was investigated using electrical penetration graphs(EPG)on cotton,Gossypium hirsutum L.Leaf microstructures and foliar soluble constituents were also measured simultaneously to quantify the impact of foliar changes on leaf nutritional quantity and quality,owing to elevated CO2,on stylet penetration and food-quality plasticity of A.gossypii.The results indicated that significant increases in fresh body weight,fecundity and population abundances of A.gossypii were found in elevated CO2 in contrast to ambient CO2.Elevated CO2 significantly influenced the feeding behavior,as evidenced by altered EPG recordirngs,including the increased non-penetration period(walking and finding the feeding site),E2<8min(probes of sustained ingestion for less than 8 min),and 1st E2>8min(first occurrence of probes of sustained ingestion for more than 8 min),and decreased E2>8min recordings.Moreover,leaf microstructures were significantly affected by CO2 levels,with thinner upperside epidermis and thicker underside epidermis(UDE),sponge tissues(ST),and fence tissues under elevated CO2 compared to that in ambient CO2.Therefore,it is expected that A.gossypii would potentially spend more time penetrating the thicker leaf UDE and ST when the host plant is exposed to elevated CO2.Furthermore,elevated CO2 significantly enhanced foliar soluble matter,including soluble sugars(SS),free amino acids and fatty acids(FFA),and total soluble matter(TSM),which was congruent with significant increase/decrease in leaf turgor/osmotic potential.Increased leaf turgor and leaf soluble constituents favored the ingestion in A.gossypii,resulting in the increases in fresh body weight,fecundity,and population abundances under elevated CO2.These feeding behaviors and resulting population growth parameters are consistent with the significant positive correlations between aphid fresh body weight and foliar FFA/TSM,between A.gossypii fecundity and foliar SS of cotton plants,and between the time of E2<8min recordings and leaf turgor.Elevated CO2 significantly enhanced the expression of appetite gene(NPF),and led to significant up-regulation of salivary protein(SHP and COO2b).Hence,increased leaf turgor and leaf soluble constituents favored ingestion in A.gossypii,resulting in increases in fresh body weight,fecundity,and population abundances under elevated CO2,although increased leaf thickness made A.gossypii spend more time penetrating the thicker leaf underside epidermis and sponge tissues.In conclusion,elevated CO2 improved appetite of A.gossypii through increasing leaf microstructures and nutritions,and then affected the feeding behaviour of A.gossypii.To summarize,elevated CO2 could improve the fitness of sucking pests,such as,significantly shortened generation duration,fecundity,the efficiency of stylet penetration and significantly increased the duration of phloem feeding.And elevated CO2 concentration significantly increases the expression of related appetite genes.This study elucidated the responsion of the fitness of N.lugens and A.gossypii to elevated CO2 systematically.It also confirmed that the effects of their feeding behavior and their molecular mechanisms.It demonstrated the potential occurrence regular pattern of N.lugens and A.gossypii under climate change,and the rice and cotton crops may face the production safety and ecological risk under future climate change.