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PubMed1995

Inhibition of viral aphid transmission by the N-terminus of the maize dwarf mosaic virus coat protein.

Since removal of the exposed N-terminus of the coat protein of some potyviruses abolishes aphid transmission, the role of this coat protein region of maize dwarf mosaic potyvirus (MDMV) in aphid transmission was investigated. The viral cDNA encoding this region was cloned and expressed as a fusion protein in bacteria. The resulting purified N-terminus of the coat protein was used in controlled aphid transmission experiments in competition with MDMV. The results show that this region inhibits aphid transmission of MDMV, indicating a direct involvement of the N-terminal region of the coat protein in aphid transmission.

Amino Acid Sequence↗
PubMed1998

Amino acid changes in the coat protein of cucumber mosaic virus differentially affect transmission by the aphids Myzus persicae and Aphis gossypii.

Cucumber mosaic virus (CMV) transmission by two aphid species was investigated using strains of the virus with modified coat proteins. Chimeric viral RNA 3 cDNA constructs were designed with coat protein-encoding sequences from the efficiently aphid-transmitted Fny-CMV and the very poorly aphid-transmitted M-CMV. Different regions of the viral coat protein variably influenced transmission; the magnitude of effects depended on the aphid species used as vector. Five amino acid changes in the coat protein of M-CMV (positions 25, 129, 162, 168, and 214) were required to restore efficient transmission by Myzus persicae. This contrasts with previously demonstrated, more limited changes required for restoration of transmission by Aphis gossypii. A construct with modified amino acids 129, 162, and 168 was efficiently transmitted by A. gossypii, while remaining poorly transmissible by M. persicae. Transmission of Fny-CMV by single aphids of A. gossypii and M. persicae was 54.0% and 27.9%, respectively. Single coat protein amino acid changes in Fny-CMV dramatically reduced transmission by M. persicae, while showing little effect on transmission by A. gossypii.

Animals↗
PubMed1999

Faba bean necrotic yellows virus (genus Nanovirus) requires a helper factor for its aphid transmission.

Purified faba bean necrotic yellows virus (FBNYV; genus Nanovirus) alone is not transmissible by its aphid vector, Acyrthosiphon pisum, regardless of whether it is acquired from artificial diets or directly microinjected into the aphid's hemocoel. The purified virus contains all of the genetic information required for its infection cycle as it readily replicated in cowpea protoplasts and systemically infected Vicia faba seedlings that were biolistically inoculated using gold particles coated with intact virions or viral DNA. The bombarded plants not only developed the typical disease syndrome, thus indicating that FBNYV is the sole causal agent of the disease, but also served as a source from which the virus was readily acquired and transmitted by A. pisum. The defect of the purified virus in aphid transmissibility suggests that FBNYV requires a helper factor (HF) for its vector transmission that is either nonfunctional or absent in purified virus suspensions. The requirement for an HF was confirmed in complementation experiments using two distinct isolates of the virus. These experiments revealed that aphids transmitted the purified virus isolate from artificial diets only when they had fed previously on plants infected with the other FBNYV isolate. Also, microinjected FBNYV, which persisted to the same extent in A. pisum as naturally acquired virus, was transmissible when aphids had acquired the HF from infected plants. This suggests that one of the functions of the HF in the transmission process is to facilitate virus transport across the hemocoel-salivary gland interface.

Amino Acid Sequence↗
PubMed1990

What causes the aphid 28S rRNA to lack the hidden break?

In order to determine why the aphid 28S rRNA lacks the hidden break otherwise found in insects, the structure of the region of the aphid ribosomal DNA (rDNA) corresponding to the gap region, which in other insect rDNA transcripts is excised posttranscriptionally, was studied. Sequence comparison suggested that, in contradistinction to what is found in rDNA transcripts of other insects, a stem-loop structure formed in this region of the aphid rDNA transcript is not AU-rich. Nor did the loop of the aphid molecule contain the UAAU tract that can be a signal for the introduction of the hidden break, suggesting that in this particular region the aphid 28S rRNA resembles 28S rRNAs of deuterostomes, which do not contain the hidden break.

Animals↗
PubMed1996

Nucleotide sequence and presumed secondary structure of the 28S rRNA of pea aphid: implication for diversification of insect rRNA.

Determination of the entire nucleotide sequence of the aphid 28S ribosomal RNA gene (28S rDNA) revealed that it is 4,147 bp in length with a G + C content of 60.3%. Based on the nucleotide sequence, we constructed a presumed secondary-structure model of the aphid 28S rRNA which indicated that the aphid 28S rRNA is characterized by the length and high G + C content of its variable regions. The G + C content of the aphid's variable regions was much higher than that of the entire sequence of the 28S rRNA, which formed a striking contrast to those of Drosophila with the G + C content much lower than the entire 28S molecule. In this respect, the aphid 28S rRNA somewhat resembled those of vertebrates. This is the third report of a complete large-subunit rRNA sequence from an arthropod, and the first 28S rRNA sequence for a nondipterous insect.

Animals↗
PubMed1998

Duplication of the Rdl GABA receptor subunit gene in an insecticide-resistant aphid, Myzus persicae.

Resistance to cyclodiene insecticides is associated with replacements of a single amino acid (alanine 302) in a gamma-aminobutyric acid (GABA) receptor subunit encoded by the single-copy gene Resistance to dieldrin (Rdl). Alanine 302 is predicted to reside within the second membrane-spanning region of the Rdl receptor, a region that is thought to line the integral chloride ion channel pore. In all cyclodiene-resistant insects studied to date, this same alanine residue is replaced either by a serine, or, in some resistant strains of Drosophila simulans, a glycine residue. Therefore, individuals can carry only two different Rdl alleles. In contrast, here we report the presence of up to four different Rdl-like alleles in individual clones of the green peach aphid, Myzus persicae. In addition to the wild-type copy of Rdl gene (encoding A302 or allele A), M. persicae carries three other alleles with the following amino acid replacements: A302-->Glycine (allele G), A302-->SerineTCG (allele S) and A302-->SerineAGT (allele S'). Evidence from direct nucleotide sequencing and Single Stranded Conformational Polymorphism (SSCP) analysis shows that at least three of these different Rdl alleles (i.e. A, G and S) are commonly present in individual aphids or aphid clones. Southern analysis using allele-specific probes and analysis of sequences downstream of the exon containing the resistance-associated mutation confirm the presence of two independent Rdl-like loci in M. persicae. One locus carries the susceptible alanine (A) and/or resistant glycine (G) allele while the other carries the two serine alleles (S or S'). Whereas resistance levels are correlated with the glycine replacement, the S allele was present in all aphid clones, regardless of their resistance status. These results suggest that target site insensitivity is associated with replacements at the first (A/G) but not the second (S/S') locus. Phylogenetic analysis of nucleotide sequences indicates that both putative aphid Rdl loci are monophyletic with respect to other insect Rdl genes and may have arisen through a recent gene duplication event. The implications of this duplication with respect to insecticide resistance and insect GABA receptor subunit diversity are discussed.

Alanine↗
PubMed2003

A comparative analysis of morphological and ecological characters of European aphids and lycaenids in relation to ant attendance.

Ants are a major environmental factor for many insect species. For example, aphids and lycaenids have evolved an array of associations with ants ranging from obligate myrmecophily to the avoidance of contact. Here we (1) analyze the predictive power of different ecological and morphological traits for explaining the strength of the association between ants and aphids/lycaenids and (2) contrast different taxonomic levels with respect to the variance explained by ant attendance. Data come from a literature survey including 112 species of aphids and 103 species of lycaenids from Europe. For aphids, feeding on woody plant parts is positively associated with ant attendance, while a high degree of mobility, feeding in isolation, and the possession of wings in the adult stage are negatively associated with ant attendance. In lycaenids, feeding on inflorescences and feeding on Fabaceae host plants is closely associated with ant attendance, while living in forests bears a smaller likelihood to establish mutualistic relationships. Body size always appeared to be a poor predictor for the degree of ant attendance. Overall, in both insect groups less than 10% of the variation in the ecological traits recorded is explained by the different modes of ant association. When decomposing the variance in traits explained by ant attendance at different taxonomic levels, aphids and lycaenids show contrasting results. In aphids, most variance in the degree of ant attendance is explained at the subfamily level and least at the species level. The opposite is true for lycaenids, where most variance is explained at the lowest taxonomic level. Possible mechanisms explaining these different patterns of associations with ants are suggested.

Adaptation, Physiological↗
PubMed2002

Amino acid substitutions within the Cys-rich domain of the tobacco etch potyvirus HC-Pro result in loss of transmissibility by aphids.

We examined the role of several amino acid residues located at the N-terminus of the tobacco etch potyvirus (TEV) helper component-proteinase (HC-Pro) in virus transmissibility by aphids. Site-directed mutagenesis resulted in changes affecting amino acids that appear highly conserved among a number of potyviruses. The TEV HC-Pro amino acid residues Gly343, Val345, Ala346, Ile348, Pro355, Lys358, and Ile359 were arranged within a Cys-rich domain in a region dispensable for TEV infectivity. Two HC-Pro mutants (TEV-P355R and -K358N) exhibited a drastically reduced rate of aphid transmission whereas other mutants (TEV-G343D, -V345E, -A346H, -I348D, and -P355L) were completely unable to be aphid transmitted. In contrast, the I359M mutation had no effect on aphid transmissibility of TEV. This lack of transmissibility did not appear to be due to large differences in the amounts of both coat protein (CP) and HC-Pro in infected tobacco plants. Our results indicated that these amino acid residues likely play a highly conserved role in aphid transmission among potyviruses.

Amino Acid Sequence↗
PubMed2006

Epicuticular factors involved in host recognition for the aphid parasitoid Aphidius rhopalosiphi.

In insect parasitoids, fitness is dependent on the host finding and recognition abilities of the female. Host recognition cues have been described for various host-parasitoid systems, but are still under investigation in aphid parasitoids. Our study aimed to clarify the respective role of physical and chemical cues in recognition of the aphid cuticle. Shed aphid exuviae were used as an elicitor in order to avoid any influence of color, movement, or volatiles present in a living aphid. We assessed the effect of chemical and heat treatments on the texture of the cuticle by using scanning electron microscopy and tested the recognition of treated cuticles by the parasitoid. We showed that recognition cues of the cuticle can be removed chemically (using combined treatments with n-hexane and methanol). Moreover, heat treatment destroyed the physical texture of the cuticle without significantly reducing parasitoid recognition. In a second step, we showed that epicuticular extracts deposited on pieces of paper triggered female attack behavior. First results concerning the chemical composition of the active extract are presented. This study shows that chemical compounds extractable by organic solvents mediate cuticle recognition by aphid parasitoids.

Animals↗
PubMed2005

Systemic response to aphid infestation by Myzus persicae in the phloem of Apium graveolens.

Little is known about the molecular processes involved in the phloem response to aphid feeding. We investigated molecular responses to aphid feeding on celery (Apium graveolenscv. Dulce) plants infested with the aphid Myzus persicae, as a means of identifying changes in phloem function. We used celery as our model species as it is easy to separate the phloem from the surrounding tissues in the petioles of mature leaves of this species. We generated a total of 1187 expressed sequence tags (ESTs), corresponding to 891 non-redundant genes. We analysed these ESTs in silico after cDNA macroarray hybridisation. Aphid feeding led to significant increase in RNA accumulation for 126 different genes. Different patterns of deregulation were observed, including transitory or stable induction 3 or 7 days after infestation. The genes affected belonged to various functional categories and were induced systemically in the phloem after infestation. In particular, genes involved in cell wall modification, water transport, vitamin biosynthesis, photosynthesis, carbon assimilation and nitrogen and carbon mobilisation were up-regulated in the phloem. Further analysis of the response in the phloem or xylem suggested that a component of the response was developed more specifically in the phloem. However, this component was different from the stress responses in the phloem driven by pathogen infection. Our results indicate that the phloem is actively involved in multiple adjustments, recruiting metabolic pathways and in structural changes far from aphid feeding sites. However, they also suggest that the phloem displays specific mechanisms that may not be induced in other tissues.

Animals↗
PubMed1983

Aphid transmission and a polypeptide are specified by a defined region of the cauliflower mosaic virus genome.

Infection of young turnip leaves with an aphid-transmissible isolate, Cabb B-JI, of cauliflower mosaic virus (CaMV) causes synthesis of an Mr 18 000 polypeptide (p18) which co-purifies with virus inclusion bodies. This polypeptide is not detectable in leaves infected with either of two aphid non-transmissible isolates. Campbell and CM4-184. Construction in vitro, of hybrid genomes between Cabb B-JI and Campbell isolates demonstrates that aphid transmissibility and presence of p18 is dependent on the small genome fragment from the BstEII site to the XhoI site. A deletion made in this fragment within open reading frame (ORF) II causes loss of aphid transmissibility and also terminates production of p18. We conclude that aphid transmissibility and the presence of p18 are related to the expression of ORF II of the CaMV genome.

Animals↗
PubMed2005

Impact of the entomopathogenic fungus Verticillium lecanii on development of an aphid parasitoid, Aphidius colemani.

The parasitoid Aphidius colemani developed normally (approximately 90% adult emergence) when its cotton aphid (Aphis gossypii) host was treated with Verticillum lecanii conidia 5 or 7 days after parasitization. Fungus exposure 1 day before or up to 3 days after parasitization, however, reduced A. colemani emergence from 0 to 10%. Also, numbers of spores and mycelial fragments in aphid homogenates were much higher in aphids exposed to the fungus up to 3 days after parasitization than in aphids treated after 5 or 7 days. Our results suggest that the parasitoid and fungus may be used together for aphid biocontrol as long as fungus applications are timed to allow late-instar development of the parasitoid.

Animals↗
PubMed2005

Mass harvesting of the entomopathogenic fungus, Neozygites fresenii, from natural field epizootics in the cotton aphid, Aphis gossypii.

Epizootics caused by insect pathogens sometimes occur over wide areas and result in millions of infected insects. Naturally infected insects can be considered a natural resource for harvesting insect pathogens. We developed methods to mass harvest the fungal pathogen Neozygites fresenii (Entomophthorales: Neozygitaceae) from epizootics in Aphis gossypii (Homoptera: Aphididae) in a commercial cotton field in Arkansas. A total of 30,722 aphids infected with N. fresenii in the mature hyphal body or early conidiophore stages were harvested, dried, and frozen. Three desiccants were compared: silica gel, dry rock salt, and wet rock salt. Silica gel was the superior material because it more rapidly and thoroughly dried cotton leaves and aphids. Using this method a mean of 193.4 infected aphids could be harvested per hour from cotton leaves dried over silica gel. The quality of harvested infected aphids was high and resulted in a mean of 70.4% sporulation from infected aphids harvested from the silica gel desiccant.

Animals↗
PubMed2006

Factors affecting transmission of fungal pathogens of aphids.

Fungal pathogens are the most important pathogens of aphids (Homoptera: Aphididae), and epizootics, particularly those caused by Entomophthorales (Zygomycota), are frequently observed and often rapidly reduce aphid populations. Fungi in the Hypocreales (Ascomycota) are less commonly found infecting aphids but can be important. The transmission of aphid fungal pathogens is affected by many factors, including: host biology and structure, pathogen characteristics, host-plant characteristics, and environmental factors. This paper is an overview of selected factors affecting transmission of aphid pathogens.

Animals↗
PubMed2004

Evaluation of a simple membrane-based nucleic acid preparation protocol for RT-PCR detection of potato viruses from aphid and plant tissues.

A rapid and simple protocol for preparing viral RNA from aphids (Myzus persicae) and potato (Solanum tuberosum L.) tissue (leaves, sprouts, and tubers) for reverse transcription-polymerase chain reaction (RT-PCR) was developed. The four-step method involves: (1) preparing plant crude sap or aphid macerates in a buffered detergent (Triton XL-80N) solution; (2) immobilizing clarified sap on a nitrocellulose membrane; (3) performing reverse transcription using eluted water extract from cut-out spot from membrane; and (4) amplifying cDNA through PCR. The entire procedure from tissue grinding to RT-PCR can be completed within 6h. The protocol was applied successfully for the detection of individual potato viruses: carlavirus Potato virus S (PVS), potexvirus Potato virus X (PVX), potyvirus Potato virus Y (PVY), and polerovirus Potato leafroll virus (PLRV). PLRV was also detected from individual viruliferous aphids or composites of viruliferous and healthy aphids. PVY and PLRV were detected from extracts immobilized on nitrocellulose membranes, stored for more than 65-273 days at room temperature (25 degrees C). The protocol was companed with the 'long protocols' involving enzyme and phenol extraction for aphids or sodium sulfite and phenol extraction for tubers. The simplified protocol was found comparable in sensitivity to these long procedures, and is especially suitable for those regions where specialized PCR laboratories are only available in centralized locations. Viral RNA immobilized membranes can be mailed out for detection by RT-PCR to these centralized laboratories from remote areas of the country.

Animals↗
PubMed2005

A simple wax-embedding method for isolation of aphid hemolymph for detection of luteoviruses in the hemocoel.

A protocol for isolating hemolymph from viruliferous aphids has been developed. This method uses warm melted wax to immobilize the aphid. Following removal of a hind leg, the hemolymph can be collected readily. Flushing with RNase-free water allows for collection of sufficient hemolymph for RNA extraction from individual aphids. The extracted RNA was successfully used for detection of barley yellow dwarf virus (BYDV) and pea enation mosaic virus (PEMV) from individual viruliferous Rhopalosiphum padi and Acyrthosiphon pisum aphids, respectively. A TaqMan real-time RT-PCR protocol for quantitation of PEMV in the hemolymph of individual aphids was developed. The wax-embedding hemolymph collection technique provides a useful tool for studying molecular interactions between persistent and circulative plant viruses and their insect vectors.

Animals↗
PubMed2003

Extraordinary proliferation of microorganisms in aposymbiotic pea aphids, Acyrthosiphon pisum.

Aposymbiotic pea aphids, which were deprived of their intracellular symbiotic bacterium, Buchnera, exhibit growth retardation and no fecundity. High performance liquid chromatographic (HPLC) analysis revealed that these aposymbiotic aphids, when reared on broad bean plants, accumulated a large amount of histamine. To assess the possibility of extraordinary proliferation of microorganisms other than Buchnera, we enumerated eubacteria and fungi in aphids using the real-time quantitative PCR method that targets genes encoding small-subunit rRNAs. The result showed that these microorganisms were extremely abundant in the aposymbiotic aphids reared on plants. Microbial communities in aposymbiotic aphids were further profiled by phylogenetic analysis of small-subunit rDNAs. Of 172 nonchimeric sequences of fungal 18S rDNAs, 138 (80.2%) belonged to the phylum Ascomycota. Among them, 21 clustered within a monophyletic group consisting of insect-pathogenic fungi and yeast-like symbionts of homopteran insects. Thirty-one (18.0%), two (1.2%), and one (0.6%) clones were clustered within the Basidiomycota, Zygomycota, and Oomycota, respectively. Of 167 nonchimeric sequences of eubacterial 16S rDNAs, 84 (50.3%) belonged to the gamma-subdivision of Proteobacteria to which most primary endosymbionts of insects and prolific histamine producers belong. Forty (24.0%), 25 (15.0%), 10 (6.0%), and five (3.0%) clones were clustered within alpha-Proteobacteria, Cytophaga-Flavobacterium-Bacteroides (CFB) group, Actinobacteria, and beta-Proteobacteria, respectively. Three had no phylogenetic association with known taxonomic divisions. None of the sequences studied in this study coincided exactly with those deposited in GenBank.

Animals↗
PubMed2003

Aphid sex pheromones: from discovery to commercial production.

This review charts the progress made with aphid sex pheromone chemistry, from initial identification of cyclopentanoid nepetalactones, for example (4aS,7S,7aR)-nepetalactone (1). and (1R,4aS,7S,7aR)-nepetalactol (2). to commercial production from a renewable non-food crop, the catmint, Nepeta cataria (Lamiaceae). The availability of aphid sex pheromone components is now facilitating the development of new aphid pest control strategies, incorporating the use of other semiochemicals, particularly in the manipulation of populations of aphid parasitoids and aphid predators such as lacewings, which can utilise the nepetalactones and closely related molecules to locate their hosts and prey. This is the first example of a plant resource being developed as a feedstock for the production of a commercially valuable insect pheromone. The development of a plant-based production route highlights the tremendous potential that higher plants offer as cheap and renewable resources for the production of insect semiochemicals, through the wide array of secondary metabolites that they can generate.

Animals↗