Host Adaptation Of Pea Aphids From Different Host Races

Host adaptation of insect is hot topic in the area of entomology and insect-plant interaction.Pea aphid,the type species of piercing-sucking insect,is a complex of many different host races.Preliminary study indicated that the host differentiation of pea aphid is associated with endosymbionts,strategies of metabolism of pea aphid and immune response of host plant.Many literatures have reported that pea aphids perform better on their original host plant,but mechanism is still unclear.In this dissertation,we mainly focus on illuminating the differences of host adaptation between two host races,including plant secondary substance,metabolic detoxification and feeding behavior of pea aphid.The main results were as follows:The electrical penetration technique was used to monitor the feeding behavior of two host races of pea aphid on its original or non-original host plant.When compared Pisum host race(PR)to Medicago host race(MR)on alfalfa,the PR had the fewer potential drop waveform(waveform pd)and spent more time on passive ingestion of phloem sap(waveform E2).And MR shared a similar phenomenon.From data of population dynamics,the amount of PR on alfalfa was fewer than MR,but the amount of two host races on pea had no significant difference.So MR could successfully colonize on pea after a period of acclimatization.But PR always could not adapt to alfalfa.In order to know whether maladjustment of PR was related to the plant secondary substance of alfalfa,we determined the amount of 9 plant secondary substances of alfalfa between two host races,including chlorogenic acid,protocatechuate,4-hydroxybenzoic acid,caffeic acid,syringic acid,rutoside,genistin,ferulic acid and genistein.The result show that the feeding of PR would add the amount of genistein in alfalfa,but MR was just the opposite.Other 8 plant secondary metabolites did not change significantly.To further understood the feeding efficiency and survival rate of two host races of pea aphid influenced by genistein,we used artificial diet with different concentration of genistein.The result showed that MR increased efficiency of feeding on the diet with genistein at 1ppm and 10 ppm,and the survival rate of MR on each treatment had no significant difference.When PR was on the diet with genistein at 1ppm,its feeding efficiency was improved.But the survival rate of PR on diet with genistein at 1ppm and 10 ppm were both decrease.So there existed differences between the two host races.In order to understand the difference of digestive enzyme and detoxifying enzyme between the two host races on the alfalfa,we conducted transcriptomic analysis in the entire bodies of two host races after alfalfa were infected for two weeks.Compared with MR,PR upregulated 161 genes and downregulated 37 genes.Differentially expressed gene was focus on 41 pathways,such as amino acid metabolism,carbohydrate metabolism,energy metabolism,lipid metabolism,xenobiotics biodegradation and metabolism and so on.Among upregulated genes,these included 4 genes associated with digestive enzyme and 3 genes associated with detoxifying enzyme.It can provided molecular data for digestive enzyme and detoxifying enzyme of different host races responding to different host plants.The above results showed that MR could decrease the a mount of genistein of alfalfa and need few detoxifying enzyme to overcome genistein,then MR had more nutrient and energy to grow and breed.The amount of genistein of alfalfa induced by PR was more than MR.Genistein would increase the feeding efficiency of the two host races,but decrease the survival rate of PR.PR would ingested more plant secondary substance,which lead to the upregulation of genes related to digestive enzyme and detoxifying enzyme.It is detrimental to growth,development and population fitness of PR.In conclusion,with the concept of co-evolution and insect-plant interaction,we discovered the host adaptation of piercing-sucking mouthpart,including feeding behavior,population dynamics,digestive enzyme,detoxifying enzyme of pea aphid and plant secondary substance.This study has an important theoretical significance in the sustainable control of piercing-sucking mouthpart and population differentiation.