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PubMed2004

Effect of host defense chemicals on clonal distribution and performance of different genotypes of the cereal aphid Sitobion avenae.

Five microsatellite loci were used to study the genetic variability and population structure of Sitobion avenae (Hemiptera: Aphididae) on some of its host plants. Individuals were collected in Chile from different cultivated and wild Poaceae. Forty-four multilocus genotypes were found among the 1052 aphids analyzed, of which four represented nearly 90% of the sample. No specialist genotypes were found, although some preferred hosts endowed with chemical defenses, i.e., hydroxamic acids (Hx), while others preferred comparatively undefended hosts. Performances of some predominant and some rare genotypes were evaluated on plants differing in their Hx levels. Significant differences in performance were found among clones, the two most common genotypes showing no differences in performance among all hosts tested, and the rare genotypes showing enhanced performance on the host with highest Hx level. A hypothesis is proposed whereby the appearance of rarer genotypes is in part related to the presence of Hx.

Animals↗
PubMed2006

Chemically mediated intraguild predator avoidance by aphid parasitoids: interspecific variability in sensitivity to semiochemical trails of ladybird predators.

The avoidance responses of aphid parasitoids with varying host ranges (Aphidius eadyi, Aphidius ervi, and Praon volucre) to chemical trails deposited by intraguild predatory ladybirds, Coccinella septempunctata and Adalia bipunctata, were investigated. Females of all three parasitoid species avoided leaves previously visited by C. septempunctata or A. bipunctata adults. The avoidance responses shown by the two Aphidius species were stronger to trails of C. septempunctata than to those of A. bipunctata. However, P. volucre avoided trails of both ladybird species to a similar degree. Dose responses of these three parasitoid species to the hydrocarbons n-tricosane (C23H48), n-pentacosane (C25H52), and n-heptacosane (C27H56), which are components of the trails of both C. septempunctata and A. bipunctata, were evaluated. Dual-choice bioassays indicated the following: (1) A. eadyi showed more sensitive avoidance responses to n-tricosane than did the other two parasitoid species, (2) all three species showed similar responses to n-pentacosane across a range of doses, and (3) only P. volucre showed avoidance responses to n-heptacosane. Quantitative analyses of each hydrocarbon in the trails of the two ladybird species showed that n-pentacosane and n-heptacosane occur in significantly greater amounts in C. septempunctata trails than in those of A. bipunctata. The trails of the two species also differ qualitatively in the other hydrocarbons present.

Alkanes↗
PubMed1980

An electron microscopic study of flight muscle breakdown in an aphid Megoura viciae.

Within two days of settling to feed on a host plant degenerative changes can be detected in the flight muscles of aphids at the ultrastructural level. The thick myosin filaments and the M Lines and later the Z bands disappear leaving the thin actin filaments in the cytoplasm. The mitochondria change their configuration and become enveloped in cytosegresomes. As mitochondria become reduced in number the numbers of lysosomes and residual bodies in the cells build up. The cells then appear to become dispersed as finger-like processes protrude from them and are pinched off.

Animals↗
PubMed1987

Use of enzyme amplification in an ELISA to increase sensitivity of detection of barley yellow dwarf virus in oats and in individual vector aphids.

A new technique of alkaline phosphatase amplification in an ELISA (amplified ELISA) was used to increase the sensitivity of detection of barley yellow dwarf virus (BYDV) from oat plant sap and in individual vector aphids. Amplified ELISA differs from conventional direct double antibody sandwich ELISA (DAS-ELISA) in the enzyme substrate reaction. The bound enzyme-labelled antibody catalyzes the conversion of NADP to NAD which is then used in a secondary enzyme-mediated cyclic reaction producing a red-coloured end product. Amplified ELISA was compared with DAS-ELISA for the detection of BYDV and each assay was done with both monoclonal and polyclonal antibody reagents. Both types of antibodies detected BYDV from oat sap and amplified ELISA increased the sensitivity of detection sufficiently to allow a diagnostic test to be completed in less than 2 h using microtitre plates precoated with antibodies. However, in the amplified ELISA using polyclonal antibodies the absorbance values obtained with the healthy oat sap samples were much greater than those obtained in the DAS-ELISA, or with the monoclonal antibodies, and were too large to be acceptable for reliable diagnostic tests. Both monoclonal and polyclonal antibodies were used successfully to detect BYDV in individual virus-carrying Rhopalosiphum padi by amplified ELISA and there was little nonspecific background reaction in the control samples with either of the antibodies.

Alkaline Phosphatase↗
PubMed1992

Detection of cauliflower mosaic virus (CaMV) in single aphids by the polymerase chain reaction (PCR).

The detection for the first time of a plant virus in a single aphid by the high sensitivity polymerase chain reaction (PCR) technology is reported. The application of PCR for the detection of viruses in their vectors will aid the understanding of the complex virus-vector relationship and therefore allow the development of new approaches for control of spread of plant virus diseases.

Animals↗
PubMed1984

Alteration with age of symbiosis of gene expression in aphid endosymbionts.

Aphid endosymbionts in vivo in young hosts synthesized almost exclusively only one protein, symbionin. The synthesis of symbionin declined with age of the host and instead the endosymbiont began to express some of its own genes which were expressed in vitro but were repressed in vivo in young host. A prolonged treatment of young host with cycloheximide brought about a physiological state similar to that in old insect. Though in the very old insect symbionin was no longer produced by its endosymbiont, the host seemed to depend almost entirely upon the gene products of the endosymbiont.

Age Factors↗
PubMed1992

Nucleotide sequence and presumed secondary structure of the internal transcribed spacers of rDNA of the pea aphid, Acyrthosiphon pisum.

1. Internal transcribed spacer (ITS) 1 and ITS 2 of rDNA of the pea aphid, Acyrthosiphon pisum consisted of 229 and 280 nucleotides, whose G+C contents were 70 and 74%, respectively. 2. Secondary structure models constructed for the ITS 1 and ITS 2 suggested that certain structural motifs have been conserved in these regions despite extensive divergence in nucleotide sequence due to species.

Animals↗
PubMed1992

Sequence analysis of a DNA fragment from Buchnera aphidicola (an endosymbiont of aphids) containing genes homologous to dnaG, rpoD, cysE, and secB.

The aphid, Schizaphis graminum, contains a prokaryotic, obligately intracellular endosymbiont, Buchnera aphidicola, which is necessary for the survival of the host. A recent study of Bu. aphidicola 16S rRNA has indicated that it is a member of the gamma-3 subdivision of the eubacterial class, Proteobacteria, which includes Escherichia coli. In order to further characterize the endosymbiont and establish its similarity to free-living eubacteria and/or organelles, we have cloned and sequenced a 4534-bp DNA fragment containing dnaG-rpoD-cysE-secB. The deduced amino acid (aa) sequence identity to the homologous E. coli proteins ranged from 47 to 80%. The close proximity of the pair, dnaG-rpoD, to the pair, cysE-secB, on the Bu. aphidicola DNA, differed from E. coli, in which these two pairs of genes are 14 min apart on the bacterial chromosome. The results of past physiological studies of the endosymbiont were consistent with the presence and function of DNA primase (DnaG), sigma factor (RpoD) and components of the secretory system (SecB). Comparison of the deduced aa sequence of Bu. aphidicola CysE (serine acetyltransferase, a key allosterically regulated enzyme in cysteine biosynthesis) with the E. coli wild-type enzyme and a mutant defective in feedback inhibition suggested that the endosymbiont CysE may not be regulated. By analogy with E. coli, the lack of feedback inhibition may lead to overproduction of cysteine by the endosymbiont. The results of this and previous investigations indicate that Bu. aphidicola has many of the properties of free-living bacteria and not of organelles.

Amino Acid Sequence↗
PubMed1992

Genetic analysis of an aphid endosymbiont DNA fragment homologous to the rnpA-rpmH-dnaA-dnaN-gyrB region of eubacteria.

Buchnera aphidicola is a Gram- eubacterium with a DNA G+C content of 28-30 mol%. This organism is an obligate intracellular symbiont of aphids. To determine its similarity to or difference from other eubacteria, a 4.9-kb DNA fragment from B. aphidicola containing the gene homologous to Escherichia coli dnaA (a gene involved in the initiation of chromosome replication) was cloned into E. coli and sequenced. The order of genes on this fragment, 60K-10K-rnpA-rpmH-dnaA-dnaN-gyrB, was similar to that found in other eubacteria. The sole difference was the absence of recF between dnaN and gyrB. The deduced amino acid sequence of these proteins resembled those of E. coli by a 41 to 83% identity. Except for E. coli, in all the eubacteria so far examined, dnaA is preceded by multiple 9-nucleotide repeats known as a DnaA boxes. No DnaA boxes were detected in the endosymbiont DNA. The possibility that this observation is a consequence of the low G+C content of this DNA fragment (14 mol% G+C) is unlikely since in Mycoplasma capricolum this fragment (19 mol% G+C) has eight DnaA boxes (Fujita et al., 1992). The presence of the sequence, GATC, recognized by the Dam methyl-transferase system, only within six regions coding for proteins suggests that methylation is not a factor in the regulation of the initiation of endosymbiont chromosome replication.

Amino Acid Sequence↗
PubMed2005

Evidence for multiple origins of identical insecticide resistance mutations in the aphid Myzus persicae.

The peach-potato aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) has developed resistance to pyrethroid insecticides as a result of a mechanism conferring reduced nervous system sensitivity, termed knockdown resistance (kdr). This reduced sensitivity is caused by two mutations, L1014F (kdr) and M918T (super-kdr), in the para-type voltage gated sodium channel. Kdr mutations in M. persicae are found in field populations world-wide. In order to investigate whether this situation is due to the mutations arising independently in different populations or by single mutation events that have spread by migration, regions flanking these mutations were sequenced from different geographical areas. The DNA sequences produced, which included a 1 kb intron, were found to be highly conserved. Several different haplotypes were identified containing kdr and super-kdr. Whilst these results could indicate either multiple independent origins of both mutations or recombination following a single origin, given the short timescale of resistance development, multiple independent origins of kdr and super-kdr are the most plausible interpretation.

Amino Acid Substitution↗
PubMed2004

Electrophysiological characterisation of olfactory sensilla in the black bean aphid, Aphis fabae.

Electrophysiological responses of three different olfactory sensilla (proximal primary rhinaria (PPR), distal primary rhinaria (DPR) and secondary rhinaria (SR)) to the sex pheromone components, nepetalactol, nepetalactone, and a plant volatile, (E)-2-hexenal, were investigated in four different morphs of the black bean aphid, Aphis fabae Scopoli. The DC responses recorded directly from the antennal sensilla and termed electrosensillograms (ESGs) were generally much larger (up to 14 mV) than electroantennogram (EAG) responses (up to 2.5 mV). Characteristic morph-specific response profiles to these compounds were observed in each type of rhinarium and response waveforms were different between (E)-2-hexenal and the sex pheromone components. (E)-2-Hexenal elicited the largest responses at PPR, while nepetalactol and nepetalactone elicited the largest responses at SR in gynoparae and males. Nepetalactol and nepetalactone also showed significant activities on DPR and PPR in all morphs. In contrast, (E)-2-hexenal had almost no activity on SR. However, almost all of the SR investigated in males and gynoparae were sensitive to both nepetalactol and nepetalactone. A small sub-set of male SR responded mainly to nepetalactol. SR of winged virginoparae did not respond to the sex pheromone compounds. Paraffin oil (the solvent control) also elicited significant responses at PPR in virginoparae but not in other morphs. In a further experiment, SR of winged virginoparae showed no response to 30 other plant volatile compounds or the alarm pheromone component, (E)-beta-farnesene. Nepetalactol and nepetalactone had similar dose-response profiles in the SR of gynoparae. The results indicate that SR in males and gynoparae are highly specialised to detect sex pheromone compounds, while the DPR and PPR are relatively broadly tuned to both plant volatiles and sex pheromone components. The presence of SR in winged virginoparae that are not responsive to sex pheromone components, alarm pheromone, or any of the plant volatile compounds tested may indicate a possible role of these sensilla to detect, as yet, unknown compound(s) with a high specificity. The present study also suggests that PPR may play a role in detecting paraffin-related compounds such as cuticular hydrocarbons of plants.

Animals↗
PubMed2005

Evidence for trichromacy in the green peach aphid, Myzus persicae (Sulz.) (Hemiptera: Aphididae).

The green peach aphid, Myzus persicae (Hemiptera: Aphididae) is an important phytophagous pest of greenhouse and field crops. In the host finding process visual cues are of paramount importance. In order to contribute to the understanding of the perception of visual stimuli in this species, we measured the electroretinogram of alate female summer migrants of M. persicae. The spectral sensitivity was measured in 10nm steps under both dark and light adaptation from 320 to 640 nm. The dark adapted spectral sensitivity curve showed one maximum in the green region around 530 nm and a distinct shoulder between 500 and 510 nm. In presence of adapting light, a secondary blue-green peak (490 nm) and a third peak in the near UV (330-340 nm) were observed. From these results we conclude that M. persicae has three spectral types of photoreceptors.

Animals↗
PubMed2006

Within-species variability of the response to 20-hydroxyecdysone in peach-potato aphid (Myzus persicae Sulzer).

Phytoecdysteroids have been proposed as new tools for controlling crop pests because of their endocrine disruption and deterrent effects on insects and nematodes. There is increasing evidence of variability between taxa in sensitivity to phytoecdysteroids, but the genetic variability of this sensitivity within species is unknown. However, knowledge about this intraspecies variability is required for predicting evolution of the pest's response to new control methods. We assessed the variability of the response of the aphid Myzus persicae Sulzer, a major agricultural pest, to 20-hydroxyecdysone (20E). We determined the number of nymphs produced by six clones of M. persicae exposed to various concentrations of 20E and the capacity of these clones to detect 20E in choice experiments. High concentrations of 20E significantly decreased the number of nymphs produced for two clones and both increases and decreases in the number of offspring were detected at low concentrations. Two clones significantly avoided food with 20E, while one significantly preferred it, suggesting that 20E does not always act as a deterrent in this species. We conclude that genetic variability in the response to 20E exists in natural populations of M. persicae. The consequences of this finding on the sustainability of control methods using 20E are discussed.

Animals↗
PubMed2006

Direct effects of snowdrop lectin (GNA) on larvae of three aphid predators and fate of GNA after ingestion.

Plants genetically modified to express Galanthus nivalis agglutinin (GNA) have been found to confer partial resistance to homopteran pests. Laboratory experiments were conducted to investigate direct effects of GNA on larvae of three species of aphid predators that differ in their feeding and digestive physiology, i.e. Chrysoperla carnea, Adalia bipunctata and Coccinella septempunctata. Longevity of all three predator species was directly affected by GNA, when they were fed a sucrose solution containing 1% GNA. However, a difference in sensitivity towards GNA was observed when comparing the first and last larval stage of the three species. In vitro studies revealed that gut enzymes from none of the three species were able to break down GNA. In vivo feed-chase studies demonstrated accumulation of GNA in the larvae. After the larvae had been transferred to a diet devoid of GNA, the protein stayed present in the body of C. carnea, but decreased over time in both ladybirds. Binding studies showed that GNA binds to glycoproteins that can be found in the guts of larvae of all three predator species. Immunoassay by Western blotting of haemolymph samples only occasionally showed the presence of GNA. Fluorescence microscopy confirmed GNA accumulation in the midgut of C. carnea larvae. Implications of these findings for non-target risk assessment of GNA-transgenic crops are discussed.

Animals↗
PubMed2005

The reactive oxygen species are involved in resistance responses of wheat to the Russian wheat aphid.

The effect of Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), infestation on the hydrogen peroxide (H(2)O(2)) content and NADPH oxidase (EC 1.6.3.1) activity was studied in the resistant (cv. Tugela DN) and near-isogenic susceptible (cv. Tugela) wheat (Triticum aestivum L.). The objective of this study was to investigate the involvement of the reactive oxygen species (ROS) during the resistance responses against the RWA. Infestation significantly induced an early accumulation of the H(2)O(2) and increase of NADPH oxidase activity to higher levels in the resistant than susceptible plants. Results of inhibitory studies using diphenylene iodonium (DPI), a suicide inhibitor of NADPH oxidase, strongly suggested a possible signalling role for H(2)O(2) during RWA resistance response by activation of downstream defence enzymes [intercellular peroxidase (EC 1.11.1.7) and beta-1,3-glucanase (EC 3.2.1.39)].

Animals↗
PubMed2003

An amino acid substitution on the second acetylcholinesterase in the pirimicarb-resistant strains of the peach potato aphid, Myzus persicae.

cDNAs encoding two acetylcholinesterases (AChEs) were isolated from the peach potato aphid, Myzus persicae. MpAChE1 was orthologous and MpAChE2 was paralogous with the ace of Drosophila melanogaster. The deduced amino acid sequence of MpAChE1 cDNA was identical between the pirimicarb susceptible and resistant strains. However, a single amino acid substitution of Ser431Phe on MpAchE2 was found in the pirimicarb resistant strains. This substitution was located in the acyl pocket of the enzyme and was thought to alter the ligand specificity.

Acetylcholinesterase↗
PubMed2003

Midgut adaptation and digestive enzyme distribution in a phloem feeding insect, the pea aphid Acyrthosiphon pisum.

Transmission electron micrographs of the pea aphid midgut revealed that its anterior region has cells with an apical complex network of lamellae (apical lamellae) instead of the usual regularly-arranged microvilli. These apical lamellae are linked to one another by trabeculae. Modified perimicrovillar membranes (MPM) are associated with the lamellae and project into the lumen. Trabeculae and MPM become less conspicuous along the midgut. The most active A. pisum digestive enzymes are membrane-bound. An aminopeptidase (APN) is described elsewhere. An alpha-glucosidase (alpha-Glu) has a molecular mass of 72 kDa, pH optimum 6.0 and catalyzes in vitro transglycosylations in the presence of an excess of the substrate sucrose. There is a major cysteine proteinase activity (CP) on protein substrates that has a molecular mass of 40 kDa, pH optimum 5.5, is inhibited by E-64 and chymostatin and is activated by EDTA+cysteine. The enzyme is more active against carbobenzoxy-Phe-Arg-4-methylcoumarin-7-amide (ZFRMCA) than against ZRRMCA. These features identify the purified CP as a cathepsin-L-like cysteine proteinase. Most CP is found in the anterior midgut, whereas alpha-Glu and APN predominate in the posterior midgut. With the aid of antibodies, alpha-Glu and CP were immunolocalized in cell vesicles and MPM, whereas APN was localized in vesicles, apical lamellae and MPM. The data suggest that the anterior midgut is structurally reinforced to resist osmotic pressures and that the transglycosylating alpha-Glu, together with CP and APN are bound to MPM, thus being both distributed over a large surface and prevented from excretion with honeydew. alpha-Glu frees glucose from sucrose without increasing the osmolarity, and CP and APN may process toxins or other proteins occasionally present in phloem.

Aminopeptidases↗
PubMed2003

Decision making by generalist and specialist aphids with the same genotype.

One idea to explain the high incidence of specialisation in phytophagous insects is that their nervous systems are simple and unable to efficiently recognise multiple host plants. Here this 'neural limitations' hypothesis is tested using a generalist (the summer winged virginopara) and specialist (the autumn gynopara) morph of a single clone of the black bean aphid, Aphis fabae, that are almost identical morphologically and have the same genotype. Electrical monitoring of stylet behaviour and non-invasive behavioural observations are used to compare initial plant recognition, first reproduction, 'first registered phloem contact' and 'phloem acceptance' of the generalist and specialist on their specific host plants (generalist--herbaceous hosts, Beta vulgaris, Papaver dubium, Rumex obtusifolius, Vicia faba; specialist--woody host, Euonymus europaeus) and on the same host (E. europaeus). Additional analyses of behaviour over the first few minutes of plant contact are carried out for three mutual non-host plants: Euonymus alatus, Prunus padus and Brassica pekinensis. Few examples are found where the host-selection behaviour of the specialist on its host plant is more efficient than the generalist across its hosts and there is little difference in the behaviour of the different forms on the same host. Indeed there are several instances where the generalist is behaviourally more efficient than the specialist. These include absolute time to first reproduction by the generalist on various herbaceous hosts and the same host, E. europaeus, absolute time to first registered phloem contact by the generalist on P. dubium, and incidence of phloem acceptance by the generalist on several of its herbaceous hosts. Rejection of non-hosts is carried out more efficiently by the specialist gynopara on P. padus and B. pekinensis but not on E. alatus. For generalist and specialist morphs of the same A. fabae genotype, therefore, broad host range does not appear to be associated with a reduced ability to make plant-use decisions.

Animals↗