Behavior And Molecular Mechanism Of The Interaction Between The Pea Aphid And Aphidius Gifuensis

The aphid endoparasitoid,Aphidius gifuensis is one of the most important aphid natural enemies and has been successfully used to control Myzys persicae and other aphid species.Olfaction and gustation play critical roles during the host-location search process of insects.A.gifuensis is able to detect its target hosts by plant volatiles,aphid alarm pheromone and cuticle hydrocarbons effectively during the parasitic process.Based on the recognition,A.gifuensis used different oviposition strategy,which could increase their parasitism efficiency.In this study,we analyzed the molecular mechanism of the recognition and regulation of A.gifuensis on the pea aphid,Acyrthosiphon pisum Harris,based on insect behavior assays,transcriptome and metabolism analyses.1 Key factors that influence the parasitic preference of A.gufensis on A.pisumA.gifuensis preferentially attack second and third instar nymph.Meanwhile,the parasitism capacities on the second and third instar nymphs were also higher than on other instars.Parasitic response of A.gifuensis on the red and green A.pisum morphs show that no color preference was observed in A.gifuensis;however,the parasitic capacity of A.gifuensis on the green A.pisum morph was significantly higher than the red A.pisum morph.The red A.pisum showed greater defensive capabilities,such as escaping,kickings and dropping from host plants.Based on the comparative transcriptome results,we found the expression of gene that involved in the alarm pheromone production in the red A.pisum morph was higher that in green A.pisum morph,while no significant difference was observed in immune response genes.Furthermore,we also analyzed the preference of A.gifuensis on aphid alarm pheromone,E-?-farnesene,and cuticle hydrocarbons.Insect behavior assays showed significant attractive activity of E-?-farnesene,whereas no preference was observed on cuticle hydrocarbons.2 Identification and expression analysis of chemosensory genes in the aphid endoparasitoid A.gifuensisUsing a bioinformatics screen,we identified 100 chemosensory genes including 13 odorant-binding proteins,5 chemosensory proteins 62 odorant receptors,15 gustatory receptors,23 ionotropic receptors and 107 odorant-degrading enzymes(one aldehyde oxidase(AOX),four alcohol dehydrogenases(ADs),eight UDP-glucuronosyltransferases(UGTs),45 cytochrome P450(P450s),nine glutathione S-transferases(GSTs)and 40 carboxylesterases(CCEs))from the sex-specific antennal transcriptome.In addition,combining with the demonstrated functions of chemosensory genes in other insects,the sex-,tissue-,and host-specific expression profile of chemosensory genes potentially revealed the candidate physiological functions.3 Effects of the parasitism of A.gifuensis on aphid nutrition regulation and its potential mechanismsThe analyses of A.gifuensis parasitism on nutrition metabolism of A.pisum showed that parasitism induced dramatic change on the nutrition composition of A.pisum.At 120 h,the proportion of the essential amino acids in parasitized A.pisum was significantly higher than that in health A.pisum.Content of Arg,Met,His,and Ile in parasitized A.pisum were significantly higher than health A.pisum,whereas the content of Asp,Gly,Ala,Glu,and Ser in parasitized A.pisum were significantly lower than health A.pisum.Besides the amino acid,we also found A.gifuensis parasitism influenced the composition of solube sugars,while no influence on the content of total solube sugars.At 120 h,the content of lipid in protein parasitized A.pisum was significantly higher than in healthy A.pisum,while no difference at other time point.Furthermore,A.gifuensis parasitism has no impact on the content of protein.In addition,we analyzed the potential mechanism of how A.gifuensis parasitism influences the nutrition metabolism in A.pisum.Based on the transcriptome and qPCR data,we found that at early parasitism time point(24h and 48h),A.gifuensis parasitism did not influence the expression in A.pisum;while at late time point(120h),A.gifuensis parasitism changed more genes expression.In relation to nutrition metabolism,major of these changed genes showed higher expression in parasitized A.pisum.Furthermore,we also characterized the effects of parasitism on the immune responses in A.pisum.At early parasitism time point(24h and 48h),A.gifuensis parasitism did not influence the expression in A.pisum;while at the late time point(120h),A.gifuensis parasitism changed more genes expression.Major of these changed genes were involved in the immune response including alarm pheromone synthesis genes and prophenoloxidases.4 Identification of the venom proteins from A.gifuensisTo ensure a successful parasitism,parasitic wasps always inject venom proteins into host to overcome the host immune system to help their eggs hatch and growth.In this study,we identified the venom proteins from A.gifuensis by transcriptome.The most abundant venom proteins(top ten)were: c31810_g1(gamma glutamyl transpeptidase),c37137_g18(calcium-transporting ATPase sarcoplasmic/endoplasmic reticulum),c30563_g3(serine protease 52),c31096_g1(gamma glutamyl transpeptidase),c18357_g1(odonrant-binding protein 10),c30894_g1(calreticulin),35614_g1(odonrant-binding protein 3),c37137_g2(calcium-transporting ATPase sarcoplasmic/endoplasmic reticulum),c10661_g1(chymotrypsin),and c32571_g2(enolase).The most abundance venom protein: c31810_g1 showed very high similarity with Aphidius ervi gamma glutamyl transpeptidase,which is involved in the apoptosis in the ovaries.Furthermore,both of the c31810_g1 and c31096_g1 were predominately expressed in the venom of A.gifuensis.In addition,we also found a calreticulin,which is also highly expressed in venom.Calreticulin from A.gifuensis was similar to the calreticulin from Pteromalus puparum.In this work,behavior,metabolism and transcriptome method were used to help us understand the molecular mechanism of the interaction beween the pea aphid and A.gifuensis.Our results laid a primary foundation of the understanding of the triple interaction of plant-pest-nature enemies.Futhermore,these results also promote the release strategy of natural enemies.In addition,these identified chemosensory genes provide valuble information for scientist to develop new insecticide and find more attractive compound for natural enemies.