Physiology and defense responses of wheat to the infestation of different cereal aphids

Cereal aphids are major insect pests of wheat,which cause significant damages to wheat production.Previous studies mainly focused on the resista nee of differe nt wheat varieties to one specific aphid species.However,reports on the physiology and defense responses of wheat to different cereal aphids are basically lacking.In this work,we studied the feeding behavior of three cereal aphids:the grain aphid,Sitobion avenae(Fabricius),the greenbugs,Schizaphis graminum(Ron dani),and the bird cherry-oat aphid,Rhopalosiphum padi(Linn aeus)on win ter wheat,and the physiology and defense responses of wheat to the infestation of these cereal aphids with focus on how these cereal aphids utilize divergent strategies to optimize their nutrition requirement from wheat leaves.Our results indicated that S.graminum and R.padi were better adapted to penetrating phloem tissue and to collect more nutrition than S.avenae.The harm on wheat physiology committed by S.graminum and R.padi was severer than that by S.avenae,through reducing chlorophyll concentration and interfering metabolism genes.Furthermore,cereal aphids manipulated the plant nutrition metabolism by increasing the relative concentration of major amino acids and percentage of essential amino acids.In addition,different cereal aphids triggered specific defense response in wheat.All of these results suggested that different cereal aphids utilize diverge nt strategies to cha nge the physiological and defe nse resp on ses of their host plants in order to optimize their nutriti on absorption and requireme nt.These fin dings not only exte nd our current knowledge on the insect-pla nt in teractions but also provide useful clues to develop no vel biotech no logical strategies for enhancing the resistance and toleranee of crop plants against phloem-feeding insects.

Performance and transcriptomic response of the English grain aphid, Sitobion avenae, feeding on resistant and susceptible wheat cultivars

Plant resistance against insects mainly depends on nutrient restriction and toxic metabolites, but the relative importance of nutrition and toxins remains elusive. We examined performance, nutrition ingestion, and transcriptome response of the English grain aphid, Sitobion avenae, feeding on resistant Xiaoyan 22(XY22) and susceptible Xinong 979(XN979) wheat cultivars. Aphids had lower body weight and fecundity when feeding on XY22 than on XN979, although the phloem sap of XY22 had a higher nutritive quality(in terms of amino acid:sucrose ratio). Aphids feeding on XY22 also had a lower honeydew excretion rate than those on XN979, suggesting that aphids ingested less phloem sap from XY22. The transcriptome data showed 600 differentially expressed genes(DEGs), and 11 of the top 20 KEGG pathways significantly enriched in DEGs were involved in nutrient metabolism. We found 81 DEGs associated with the metabolism of sugars, lipids, and amino acids, 59 of which were significantly downregulated in aphids feeding on XY22. In contrast, there were 18 DEGs related to detoxifying metabolism, namely eight UDP-glucuronosyltransferases, six cytochromes P450 monooxygenases, one glutathione S-transferase, two ATP-binding cassette transporters, and one major facilitator superfamily transporter;12 of these were upregulated in the aphids feeding on XY22. Our results indicated that both the quantity and quality of phloem nutrition available to aphids are critical for the growth and development of aphids, and the higher resistance of XY22 is mainly due to the reduction in phloem sap ingested by aphids, rather than toxic metabolites.

Role of TRP channels and HSPs in thermal stress response in the aphid parasitoid Aphelinus asychis(Hymenoptera:Aphelinidae)

Aphelinus asychis is an important aphid endoparasitoid.Under field and greenhouse conditions,high temperature is one of the factors limiting the application of A asychis for biological pest control.To explore the potential role of transient receptor potential(TRP)channels and heat shock proteins(HSPs)in this process,we identified 11 genes encoding TRP channels and nine genes encoding HSPs.Three proteins(AasyTRPA5,AasyPyrexia,AasyPainless)that belong to transient receptor potential ankyrin(TRPA)subfamily and nine HSPs are involved in the response to high temperature.We also investigated the survival of A asychis and the response of the identified TRP channels and HSPs to high temperature.The results showed that the maximum temperature that allowed A.asychis survival was approximately 41°C;females had higher survival rates than that of the males at 40 and 41°C.Short-term heat-shock resulted in increased expression of Amsysbsp in males,and Aasyhsp40,Aasyhsp68,Aasyhsp70-4,Aasyhsp70-5 and Aasyhsp90 were upregulated and then down regulated,whereas Aasyhsp70-3was upregulated at41°C.Moreover,Aasyhsp40and Aasyhsp90showed higherexpression levels in females,while Aasyshsp and Aasyhsp70-3 presented opposite expression patterns.At temperature above 35°C,expression of AasyPyrexia in females was significant higher than that in males,whereas AasyPainless mnd AasyTRPA5 presented higher expression in males at 40 and 41°C,respectively.Altogether,these results indicate that protect!on against thermal stress in A.asychis is coordinated by TRP channels and HSPs.These findings provide a basis for understanding the potential mechanism of A asychis in response to high temperatures.

Plants affect the horizontal transmission of a new densovirus infecting the green peach aphid Myzus persicae by modulating honeydew production

In a tritrophic context of plant-insect-entomopathogen,plants play important roles in modulating the interaction of insects and their pathogenic viruses.Currently,the influence of plants on the transmission of insect viruses has been mainly studied on baculoviruses and some RNA viruses,whereas the impact of plants on other insect viruses is largely unknown.Here,we identified a new densovirus infecting the green peach aphid Myzus persicae and tested whether and how host plants influence the transmission of the aphid densovirus.The complete single-stranded DNA genome of the virus,M.persicae densovirus 2,is 5727 nt and contains inverted terminal repeats.Transcription and phylogenetic analysis indicated that the virus was distinct from other a few identified aphid densoviruses.The virus abundance was detected highly in the intestinal tract of aphids,compared with the lower level of it in other tissues including head,embryo,and epidermis.Cabbage and pepper plants had no obvious effect on the vertical transmission and saliva-mediated horizontal transmission of the virus.However,the honeydew-mediated horizontal transmission among aphids highly depended on host plants(65%on cabbages versus 17%on peppers).Although the virus concentration in the honeydew produced by aphids between 2 plants was similar,the honeydew production of the infected aphids reared on peppers was dramatically reduced.Taken together,our results provide evidence that plants influence the horizontal transmission of a new densovirus in an aphid population by modulating honeydew secretion of aphids,suggesting plants may manipulate the spread of an aphid-pathogenic densovirus in nature.

Avoidance of parasitized host by female wasps of Aphidius gifuensis (Hymenoptera:Braconidae):The role of natal rearing effects and host availability?

Natal rearing experience of animals may affect their behaviors,such as habitat selection and oviposition decision.As part of the overall fitness of insect parasitoids, successful host discrimination (distinguishing parasitized hosts from unparasitized hosts) is of paramount importance.In this study we examined whether and how parasitoids' natal rearing experience would affect their host discrimination ability according to host availability.We established separate colonies ofAphidius gifuensis Ashmead by continual rearing on two hosts,Sitobion avenae E and Myzuspersicae (Suzler),and quantified self superparasitism and self superparasitism versus parasitism ratio for the four:combinations ofparasitoid colonies and host species (S.aveane and M.persicae)at four host densities (30,50,100 or 150 per plant).Results showed that self superparasitism ofM.persicae by A.gifuensis reared on S.avenae was significantly higher than by those reared on M.persicae,no matter whether the host densities were 30,50,100 or 150.Aphidius gifuensis reared on M.persicae significantly superparasitized more S.avenae than those reared on S.aveane only when host density was 30.Self superparasitism versus parasitism ratio of A.gifuensis from both colonies was always lower on natal hosts than on new hosts,and the difference was more pronounced as the host density decreased.These results suggested that natal rearing effects is important on host discrimination and oviposition decision of the parasitoid A.gifuensis.These effects promoted the parasitoid's host adaptation and made them confer greater fitness.

Bacteria abundance and diversity of different life stages of Plutella xylostella （Lepidoptera： Plutellidae）, revealed by bacteria culture-dependent and PCR-DGGE methods

Microbial abundance and diversity of different life stages （fourth instar larvae, pupae and adults） of the diamondback moth, Plutella xylostella L., collected from field and reared in laboratory, were investigated using bacteria culture-dependent method and PCR-DGGE analysis based on the sequence of bacteria 16S rRNA V3 region gene. A large quantity of bacteria was found in all life stages ofP. xylostella. Field population had higher quantity of bacteria than laboratory population, and larval gut had higher quantity than pupae and adults. Culturable bacteria differed in different life stages ofP. xylostella. Twenty-five different bacterial strains were identified in total, among them 20 strains were presented in larval gut, only 8 strains in pupae and 14 strains in adults were detected. Firmicutes bacteria, Bacillus sp., were the most dominant species in every life stage. 15 distinct bands were obtained from DGGE electrophoresis gel. The sequences blasted in GenBank database showed these bacteria belonged to six different genera. Phylogenetic analysis showed the sequences of the bacteria belonged to the Actinobacteri, Proteobacteria and Firmicutes. Serratia sp. in Proteobacteria was the most abundant species in larval gut. In pupae, unculturable bacteria were the most dominant species, and unculturable bacteria and Serratia sp. were the most dominant species in adults. Our study suggested that a combination of molecular and traditional culturing methods can be effectively used to analyze and to determine the diversity of gut microflora. These known bacteria may play important roles in development of P. xylostella.

Oviposition and survival of castor bean whitefly Trialeurodes ricini (Hemiptera: Aleyrodidae) on different host plants

Banker plant system is a new biological control method,including banker plants,alternative food and beneficials.A non-pest herbivore is particularly favored for using as an alternative host for beneficials in this system,and evaluating the potential damage caused by alternative host on the target crops is an important step(Frank,2010).So,the