Effects of herbivore stress by Aphis medicaginis Koch on the Malondialdehyde contents and the activities of protective enzymes in different alfalfa varieties

The study focused on the dynamics of Malondialdehyde (MDA) contents and the activities of protective enzymes in the leaves of alfalfa varieties with various resistances to Aphis medicaginis Koch. The results showed that susceptible varieties always had higher MDA contents than resistant varieties, and the MDA contents tended to rise in both susceptible and resistant varieties in period of the varieties were pierced and sucked by aphids. Superoxide dismutase (SOD), peroxidase (POD) and phenylalanine ammonia-lyase (PAL) activities in susceptible varieties were lower than those in resistant varieties, and in both susceptible and resistant varieties the SOD and POD activities tended to rise at first and then decline, and the PAL activities rose to their peaks and then tended to remain stable. In the susceptible and resistant varieties the catalase (CAT) activities appeared to rise and decline alternatively; the PPO activities in resistant varieties were lower than those in susceptible varieties in early growth, but higher than those in susceptible varieties in later growth. It follows that infested by aphids, susceptible and resistant varieties had the MDA contents, variations of SOD, POD, PAL and PPO activities were closely correlated with their aphid resistances, hence these indexes could be used as physiological indexes for testing aphid resistance of alfalfa, whereas the relations of their CAT activities to their resistances needed to be further studied.     

棉花型和黄瓜型棉蚜(Aphis gossypii Glover)的寄主适应性及转移通道

采用寄主转接建立生命表的方法研究了棉花型和黄瓜型棉蚜对不同寄主植物的适应性,以及两寄主型棉蚜是否可通过中间桥梁寄主实现寄主互换的问题。结果表明,两寄主型棉蚜直接互换寄主后,其存活和繁殖力显著下降,表现为棉花型和黄瓜型棉蚜的净增殖率比在原寄主上分别下降980倍和12倍,平均世代寿命缩短5～12d。两寄主型棉蚜均能利用木槿植物,并且适应性没有显著差异。但是两寄主型棉蚜均不能在车前草和大叶黄杨上存活和繁殖后代。西葫芦作物对棉蚜在木槿、棉花和黄瓜寄主上的相互转移起到了重要的桥梁寄主作用。冬寄主木槿上棉蚜可通过甜瓜或西葫芦转移到黄瓜寄主上,棉花和黄瓜上棉蚜也可通西葫芦作物分别转移到黄瓜和棉花作物上,从而形成棉蚜在不同寄主植物间的相互转移通道,造成为害和病毒病的扩张。     

Physical and ant-mediated refuges from parasitism: Implications for non-target effects in biological control

A promising natural enemy for release against the Asian soybean aphid, Aphis glycines Matsumura, in North America is the aphidiine braconid wasp Binodoxys communis (Gahan). The aphid Aphis monardae Oestlund, a native of North America’s tall-grass prairies, is a non-target species that may be at risk from releases of B. communis. This paper describes ecological facets of A. monardae populations in their native habitat that could protect them from attack by this exotic biological control agent. In prairie habitats, A. monardae populations aggregate in flower heads of their host plant, Monarda fistulosa L. On this host plant, aphids are also commonly tended by four ant species, and ant-tended colonies are larger than un-attended colonies. Laboratory studies showed that parasitism rates of A. monardae by B. communis are significantly higher on vegetative M. fistulosa than on M. fistulosa flower heads. In addition, attendance of A. monardae by the ant Lasius neoniger Emery significantly decreased parasitism by B. communis. Ants attacked and killed host-seeking adult parasitoids, and preyed upon B. communis mummies. No evidence was found that B. communis reared from A. monardae are less susceptible to attack by ants than parasitoids reared from A. glycines. M. fistulosa flower heads and attendance by L. neoniger may act as refuges for A. monardae against B. communis. Our work describes spatial refuges as ecological filters that separate non-target organisms from exotic natural enemies. Implications for classical biological control of A. glycines are discussed.     

大豆蚜的生物学防治技术

大豆蚜AphisglycinesMatsumura是亚洲大豆种植区的一种主要农业害虫。近年来,大豆蚜又先后侵入北美洲和大洋州等地,对当地的大豆生产构成了潜在威胁,正成为一种世界性的农业害虫。文章对大豆蚜的分布、危害、生物学特征、天敌和防治技术等方面的研究现状进行了详细论述。     

Host plant adaptability and proteomic differences of diverse Rhopalosiphum maidis (Fitch) lineages

Corn leaf aphid Rhopalosiphum maidis (Fitch) can feed on various cereal crops and transmit viruses that may cause serious economic losses. To test the impact of both host plant species and age on R. maidis, as well as the proteomic difference of diverse populations, we first investigated the survival and reproduction of six R. maidis populations (i.e., LF, HF, GZ, DY, BJ, and MS) via a direct observation method in the laboratory on 10 and 50 cm high maize seedlings, and 10 cm high barley seedlings. Then a proteomic approach was implemented to identify the differentially expressed proteins from both aphids and endosymbionts of BJ and MS populations. Results indicated that the BJ population performed significantly better than the others on both barley and 50 cm high maize seedlings, while no population could survive on 10 cm high maize seedlings. The proteomic results demonstrated that the expression levels of myosin heavy chain (muscle isoform X12) (spot 781) and peroxidase (spot 1383) were upregulated, while ATP-dependent protease Hsp 100 (spot 2137) from Hamiltonella defensa and protein SYMBAF (spot 2703) from Serratia symbiotica were downregulated in the BJ population when compared to expression levels of the MS population. We hypothesize that the fatalness observed on 10 cm high maize seedlings may be caused by secondary metabolites that are synthesized by the seedlings and the MS population of R. maidis should be more stress-resistant than the BJ population. Our results also provide insights for understanding the interaction between host plants and aphids.     

Aphid-repellent pheromone E-β-farnesene is generated in transgenic Arabidopsis thaliana over-expressing farnesyl diphosphate synthase2

Background and Aims Plant-synthesized sesquiterpenes play a pivotal role in chemotactic interactions with insects. Biosynthesis of functionally diverse sesquiterpenes is dependent on the availability of a pool of the precursor farnesyldiphosphate (FDP). In Arabidopsis thaliana, FPS2, encoding cytosolic farnesyldiphosphate synthase, is implicated in the synthesis of cytosolic FDP, but it is not known whether enhanced levels of FDP have a commensurate effect on sesquiterpene-mediated defence responses. This study examined transgenic arabidopsis plants generated to over-express FPS2 in order to determine if any effects could be observed in the response of aphids, Myzus persicae.Methods Transgenic arabidopsis plants were generated to over-express FPS2 to produce FPS2 in either the cytosol or the chloroplasts. Morphochemical analyses of the transgenic plants were carried out to detremine growth responses of roots and shoots, and for GC-MS profiling of sesquiterpenes. Aphid response to hyrdo-distillate extracts and head-space volatiles from transgenic plants was assessed using a bioassay.Key Results Either over-expression of FPS2 in the cytosol or targetting of its translated product to chlorplasts resulted in stimulatory growth responses of transgenic arabidopsis at early and late developmental stages. GC-MS analysis of hydro-distillate extracts from aerial parts of the plants revealed biosynthesis of several novel sesquiterpenes, including E-β-farnesene, an alarm pheromone of aphids. Both entrapped volatiles and hydro-distillate extracts of the transgenic leaves triggered agitation in aphids, which was related to both time and dose of exposure.Conclusions Over-expression of FPS2 in the cytosol and targeting of its translated product to chloroplasts in arabidopsis led to synthesis of several novel sesquiterpenes, including E-β-farnesene, and induced alarm responses in M. persicae. The results suggest a potential for engineering aphid-resistant strains of arabidopsis.     

Cryptic Virulence and Avirulence Alleles Revealed by Controlled Sexual Recombination in Pea Aphids

Although aphids are worldwide crop pests, little is known about aphid effector genes underlying virulence and avirulence. Here we show that controlling the genetics of both aphid and host can reveal novel recombinant genotypes with previously undetected allelic variation in both virulence and avirulence functions. Clonal F₁ progeny populations were derived from reciprocal crosses and self-matings between two parental genotypes of pea aphid (Acyrthosiphon pisum) differing in virulence on a Medicago truncatula host carrying the RAP1 and RAP2 resistance genes. These populations showed Mendelian segregation consistent with aphid performance being controlled largely by a dominant virulence allele derived from only one parent. Altered segregation ratios on near-isogenic host genotypes differing in the region carrying RAP1 were indicative of additional heritable functions likely related to avirulence genes originating from both parents. Unexpectedly, some virulent F₁ progeny were recovered from selfing of an avirulent parent, suggesting a reservoir of cryptic alleles. Host chlorosis was associated with virulence, whereas necrotic hypersensitive-like response was not. No maternal inheritance was found for any of these characteristics, ruling out sex-linked, cytoplasmic, and endosymbiotic factors. Our results demonstrate the tractability of dissecting the genetic basis of pest-host resistance mechanisms and indicate that the annual sexual cycle in aphids may lead to frequent novel genotypes with both increased and decreased virulence. Availability of genomes for both pest and host can facilitate definition of cognate gene-for-gene relationships, potentially leading to selection of crop genotypes with multiple resistance traits.     

Silencing the expression of the salivary sheath protein causes transgenerational feeding suppression in the aphid Sitobion avenae

Aphids produce gel saliva during feeding which forms a sheath around the stylet as it penetrates through the apoplast. The sheath is required for the sustained ingestion of phloem sap from sieve elements and is thought to form when the structural sheath protein (SHP) is cross‐linked by intermolecular disulphide bridges. We investigated the possibility of controlling aphid infestation by host‐induced gene silencing (HIGS) targeting shp expression in the grain aphid Sitobion avenae. When aphids were fed on transgenic barley expressing shp double‐stranded RNA (shp‐dsRNA), they produced significantly lower levels of shp mRNA compared to aphids feeding on wild‐type plants, suggesting that the transfer of inhibitory RNA from the plant to the insect was successful. shp expression remained low when aphids were transferred from transgenic plants and fed for 1 or 2 weeks, respectively, on wild‐type plants, confirming that silencing had a prolonged impact. Reduced shp expression correlated with a decline in growth, reproduction and survival rates. Remarkably, morphological and physiological aberrations such as winged adults and delayed maturation were maintained over seven aphid generations feeding on wild‐type plants. Targeting shp expression therefore appears to cause strong transgenerational effects on feeding, development and survival in S. avenae, suggesting that the HIGS technology has a realistic potential for the control of aphid pests in agriculture.     

Quantitative trait loci mapping of phenotypic plasticity and genotype-environment interactions in plant and insect performance

Community genetic studies generally ignore the plasticity of the functional traits through which the effect is passed from individuals to the associated community. However, the ability of organisms to be phenotypically plastic allows them to rapidly adapt to changing environments and plasticity is commonly observed across all taxa. Owing to the fitness benefits of phenotypic plasticity, evolutionary biologists are interested in its genetic basis, which could explain how phenotypic plasticity is involved in the evolution of species interactions. Two current ideas exist: (i) phenotypic plasticity is caused by environmentally sensitive loci associated with a phenotype; (ii) phenotypic plasticity is caused by regulatory genes that simply influence the plasticity of a phenotype. Here, we designed a quantitative trait loci (QTL) mapping experiment to locate QTL on the barley genome associated with barley performance when the environment varies in the presence of aphids, and the composition of the rhizosphere. We simultaneously mapped aphid performance across variable rhizosphere environments. We mapped main effects, QTL × environment interaction (QTL×E), and phenotypic plasticity (measured as the difference in mean trait values) for barley and aphid performance onto the barley genome using an interval mapping procedure. We found that QTL associated with phenotypic plasticity were co-located with main effect QTL and QTL×E. We also located phenotypic plasticity QTL that were located separately from main effect QTL. These results support both of the current ideas of how phenotypic plasticity is genetically based and provide an initial insight into the functional genetic basis of how phenotypically plastic traits may still be important sources of community genetic effects.     

How the insect immune system interacts with an obligate symbiotic bacterium

The animal immune system provides defence against microbial infection, and the evolution of certain animal–microbial symbioses is predicted to involve adaptive changes in the host immune system to accommodate the microbial partner. For example, the reduced humoral immune system in the pea aphid Acyrthosiphon pisum, including an apparently non-functional immune deficiency (IMD) signalling pathway and absence of peptidoglycan recognition proteins (PGRPs), has been suggested to be an adaptation for the symbiosis with the bacterium Buchnera aphidicola. To investigate this hypothesis, the interaction between Buchnera and non-host cells, specifically cultured Drosophila S2 cells, was investigated. Microarray analysis of the gene expression pattern in S2 cells indicated that Buchnera triggered an immune response, including upregulated expression of genes for antimicrobial peptides via the IMD pathway with the PGRP-LC as receptor. Buchnera cells were readily taken up by S2 cells, but were subsequently eliminated over 1–2 days. These data suggest that Buchnera induces in non-host cells a defensive immune response that is deficient in its host. They support the proposed contribution of the Buchnera symbiosis to the evolution of the apparently reduced immune function in the aphid host.