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PubMed2006

Effect of wind speed on the pheromone-mediated behavior of sexual morphs of the potato aphid, Macrosiphum euphorbiae (Thomas) under laboratory and field conditions.

The effect of wind on the potato aphid, Macrosiphum euphorbiae, male responsiveness to the sex pheromone, and on the calling behavior of virgin oviparae, was studied under constant wind speeds in the laboratory and in the field. A significant proportion of females called at wind speeds up to 4 m/sec, whereas male flight behavior in clean air was inhibited at velocities > 2 m/sec. However, males continued to walk over the range of wind speeds at which females called. Under constant wind velocities in a wind tunnel, males downwind of calling females oriented on the upwind edge of the release stand, and fewer individuals took flight at low constant wind speeds than in a clean air plume. In all cases, whether calling females were present or not, the males that took flight moved downwind. However, when a bridge was available, a significant proportion of males walked upwind to the pheromone source. The same orientation and walking behaviors were observed when males were placed downwind of calling females under variable wind conditions in the field. However, contrary to the laboratory results, 30% of the males tested flew upwind and landed on the source. A more detailed examination found that males orienting toward a source would walk if wind speeds were high but initiated flight in an "upwind" direction if there was a lull in wind velocity. These findings suggest that for the potato aphid, and probably for many other insect species with weak flight capacity, walking behavior is a significant component of pheromone-mediated mate location. This would permit males to continue foraging for calling females in the vicinity when wind velocities inhibit flight.

Animal Communication↗
PubMed1976

Arthropod ribosomes. Integrity of ribosomal ribonucleic acids from aphids and water fleas.

The 28 S aphid rRNA differs from those of the other insects in two points: (1) it lacks the primary nick; (2) it is larger by 0.2 - 106 daltons. The 28 S rRNA from water fleas also, like that from crayfish, is larger than those from comon insects by 0.2 - 106 daltons. These crustacean 28-S rRNAs were shown to contain the primary nick, which is probably not located in the central point. The 18-S rRNAs from aphids and water fleas had molecular weights significantly larger than 0.7 - 106, the common vaalue for the eukaryotic 18 S rRNA. It was was suggested that the 3'-terminal base sequences of these RNAs are different from the common sequences of these RNAs are different from the common sequence proposed for the 18 S rRNAA of eukaryotes. These exceptional characteristics of the rRNAs from the parthenogenetic animals may provide a probe for general functions of the rRNA in the eukaryotic ribosomes.

Animals↗
PubMed1995

Characterization of a putative 23S-5S rRNA operon of Buchnera aphidicola (endosymbiont of aphids) unlinked to the 16S rRNA-encoding gene.

Buchnera aphidicola (Ba) is an endosymbiont of the aphid Schizaphis graminum. In order to obtain information on highly expressed genes, we have chosen to study Ba genes coding for rRNAs. Previously, the single-copy rrs gene was cloned and sequenced [Munson et al., Gene 137 (1993) 171-178], and found to constitute a single transcription unit unlinked to rrl and rrf. In the present study, a 6.1-kb Ba DNA fragment containing rrl was cloned into Escherichia coli (Ec) and sequenced. Based on sequence similarity to Ec, the following genes were identified: aroE-tRNA(Glu)-rrl-rrf-cysS. AroE and CysS had 48 and 54% amino acid (aa) identity, respectively, to the corresponding Ec proteins; tRNA(Glu), rrl and rrf had 80-90% nucleotide (nt) identity with the corresponding genes of Ec rrnB. Ba tRNA(Glu)-rrl-rrs appears to be part of a single transcriptional unit; a putative promoter and a Rho-independent terminator were identified. Comparisons of sequences of aroE-rrl from endosymbionts of seven additional species of aphids indicated conservation of the -35 (TTGACT) and -10 (TGTAA/TT) promoter regions, and boxA, tRNA(Glu) and boxC. Secondary structure analysis indicated that the Ba tRNA(Glu)-rrl-rrf operon resembled the homologous region of Ec rrnB. The results of this and previous studies indicate that Ba differs from most bacteria in having the single-copy rRNA genes organized into two transcription units.

Amino Acid Sequence↗
PubMed1996

Changes in the methylation of amplified esterase DNA during loss and reselection of insecticide resistance in peach-potato aphids, Myzus persicae.

Insecticide resistance in peach-potato aphids, Myzus persicae, results from the amplification of genes encoding an esterase that hydrolyses and sequesters insecticides. Resistance is normally stable, but highly resistant aphid clones sometimes lose resistance when insecticidal selection pressure is removed. This loss of resistance, termed reversion, arises from a loss of elevated esterase enzyme through transcriptional control, i.e. without loss of the amplified esterase DNA sequences. We have shown that loss of the elevated enzyme occurred simultaneously with loss of methylation at CCGG sites in the amplified DNA sequences. During reselection of resistance in these revertant clones, enzyme levels increased, but there was no corresponding return of methylation to DNA sequences. Thus, although DNA methylation is closely correlated with expression of the amplified esterase genes during reversion, it may not be a factor in the reverse process.

Animals↗
PubMed2004

The serotonergic system is involved in feeding inhibition by pymetrozine. Comparative studies on a locust (Locusta migratoria) and an aphid (Myzus persicae).

Pymetrozine inhibits feeding in aphids immediately after application without producing visible neurotoxic effects, as previously reported. In the present work, Locusta migratoria, though not a plant-sucking insect, was found to respond to pymetrozine by displaying unique symptoms, which were lifting and stretching of the hindlegs, in addition to inhibition of feeding. In locust, pymetrozine enhanced spontaneous spike discharge of the metathoracic and suboesophageal ganglia in situ at nanomolar concentrations. Similarly, pymetrozine increased the spontaneous rhythmic contractions of the isolated foregut with maximal effects also in the nanomolar range. The actions of pymetrozine were counteracted by biogenic amine receptor antagonists and mimicked by serotonin, not by dopamine and octopamine. Moreover, pymetrozine and serotonin strongly potentiated the effects of each other. Pymetrozine was inactive at all neurotransmitter receptors present on isolated locust neuronal somata, and at all other examined neuronal sites. In Myzus persicae, electrical penetration graph experiments revealed that serotonin, like pymetrozine, inhibited stylet penetration, and strongly enhanced the action of pymetrozine, comparable to the locust. Amine receptor antagonists were not specifically active in the aphid. We conclude from the present results that pymetrozine acts via a novel mechanism that is linked to the signalling pathway of serotonin.

Animals↗
PubMed2004

Comparative analysis of two genomic regions among four strains of Buchnera aphidicola, primary endosymbiont of aphids.

Preliminary analysis of two selected genomic regions of Buchnera aphidicola BCc, the primary endosymbiont of the cedar aphid Cinara cedri, has revealed a number of interesting features when compared with the corresponding homologous regions of the three B. aphidicola genomes previously sequenced, that are associated with different aphid species. Both regions exhibit a significant reduction in length and gene number in B. aphidicola BCc, as it could be expected since it possess the smallest bacterial genome. However, the observed genome reduction is not even in both regions, as it appears to be dependent on the nature of their gene content. The region fpr-trxA, that contains mainly metabolic genes, has lost almost half of its genes (45.6%) and has reduced 52.9% its length. The reductive process in the region rrl-aroK, that contains mainly ribosomal protein genes, is less dramatic, since it has lost 9.3% of genes and has reduced 15.5% of its length. Length reduction is mainly due to the loss of protein-coding genes, not to the shortening of ORFs or intergenic regions. In both regions, G+C content is about 4% lower in BCc than in the other B. aphidicola strains. However, when only conserved genes and intergenic regions of the four B. aphidicola strains are compared, the G+C reduction is higher in the fpr-trxA region.

Animals↗
PubMed2006

Genome reduction of the aphid endosymbiont Buchnera aphidicola in a recent evolutionary time scale.

Genome reduction, a typical feature of symbiotic bacteria, was analyzed in the last stages of evolution of Buchnera aphidicola, the primary aphid endosymbiont, in two neutrally evolving regions: the pseudogene cmk and an intergenic region. These two regions were examined in endosymbionts from several lineages of their aphid host Rhopalosiphum padi, and different species of the same genus, whose divergence times ranged from 0.62 to 19.51 million years. Estimates of nucleotide substitution rates were between 4.3 and 6.7x10(-9) substitution/site/year, with G or C nucleotides being substituted around four times more frequently than A or T. Two different types of indel events were detected, of which many were small (1-10 nt) but one was large (about 200 nucleotides). With respect to the large one and considering the proportion and size of the deletions and insertions, the reduction rate was 1.3x10(-8) lost nucleotides/site/year. We propose a stepwise scenario for the last stages of evolution in B. aphidicola: together with a very slow and gradual degradation, considerable indels would punctually emerge. The only restriction to large deletion fixation is that the lost fragment does not contain essential genes.

Animals↗
PubMed2004

Mutations in acetylcholinesterase associated with insecticide resistance in the cotton aphid, Aphis gossypii Glover.

Two acetylcholinesterase genes, Ace1 and Ace2, have been fully cloned and sequenced from both organophosphate-resistant and susceptible clones of cotton aphid. Comparison of both nucleic acid and deduced amino acid sequences revealed considerable nucleotide polymorphisms. Further study found that two mutations occurred consistently in all resistant aphids. The mutation F139L in Ace2 corresponding to F115S in Drosophila acetylcholinesterase might reduce the enzyme sensitivity and result in insecticide resistance. The other mutation A302S in Ace1 abutting the conserved catalytic triad might affect the activity and insecticide sensitivity of the enzyme. Phylogenetic analysis showed that insect acetylcholinesterases fall into two subgroups, of which Ace1 is the paralogous gene whereas Ace2 is the orthologous gene of Drosophila AChE. Both subgroups contain resistance-associated AChE genes. To avoid confusion in the future work, a nomenclature of insect AChE is also suggested in the paper.

Acetylcholinesterase↗
PubMed2004

Annotated expressed sequence tags for studies of the regulation of reproductive modes in aphids.

The damaging effect of aphids to crops is largely determined by the spectacular rate of increase of populational expansion due to their parthenogenetic generations. Despite this, the molecular processes triggering the transition between the parthenogenetic and sexual phases between their annual life cycle have received little attention. Here, we describe a collection of genes from the cereal aphid Rhopalosiphum padi expressed during the switch from parthenogenetic to sexual reproduction. After cDNA cloning and sequencing, 726 expressed sequence tags (EST) were annotated. The R. padi EST collection contained a substantial number (139) of bacterial endosymbiont sequences. The majority of R. padi cDNAs encoded either unknown proteins (56%) or housekeeping polypeptides (38%). The large proportion of sequences without similarities in the databases is related to both their small size and their high GC content, corresponding probably to the presence of 5'-unstranslated regions. Fifteen genes involved in developmental and differentiation events were identified by similarity to known genes. Some of these may be useful candidates for markers of the early steps of sexual differentiation.

Amino Acid Sequence↗
PubMed2006

Proteomics in Myzus persicae: effect of aphid host plant switch.

Chemical ecology is the study of how particular chemicals are involved in interactions of organisms with each other and with their surroundings. In order to reduce insect attack, plants have evolved a variety of defence mechanisms, both constitutive and inducible, while insects have evolved strategies to overcome these plant defences (such as detoxification enzymes). A major determinant of the influence of evolutionary arms races is the strategy of the insect: generalist insect herbivores, such as Myzus persicae aphid, need more complex adaptive mechanisms since they need to respond to a large array of different plant defensive chemicals. Here we studied the chemical ecology of M. persicae associated with different plant species, from Brassicaceae and Solanaceae families. To identify the involved adaptation systems to cope with the plant secondary substances and to assess the differential expression of these systems, a proteomic approach was developed. A non-restrictive approach was developed to identify all the potential adaptation systems toward the secondary metabolites from host plants. The complex protein mixtures were separated by two-dimensional electrophoresis methods and the related spots of proteins significantly varying were selected and identified by mass spectrometry (ESI MS/MS) coupled with data bank investigations. Fourteen aphid proteins were found to vary according to host plant switch; ten of them were down regulated (proteins involved in glycolysis, TCA cycle, protein and lipid synthesis) while four others were overexpressed (mainly related to the cytoskeleton). These techniques are very reliable to describe the proteome from organisms such as insects in response to particular environmental change such as host plant species of herbivores.

Adaptation, Physiological↗
PubMed2026

MicroRNA-driven regulatory networks in aphid ecological adaptation: integrating stress tolerance, dispersal plasticity, and population expansion.

Aphids (Hemiptera: Aphididae) are important agricultural pests and exhibit strong ecological adaptability, allowing them to persist under stress, disperse to new habitats, and rapidly increase population size. Recent advances in functional genomics have identified microRNAs (miRNAs) as key post-transcriptional regulators involved in these processes, yet their roles have remained fragmented across studies. Here, we synthesize current evidence into a "three-stage framework", encompassing population maintenance under stress, dispersal to new habitats, and population expansion upon establishment. We highlight how miRNAs regulate detoxification pathways (e.g., P450s, UGTs, ABC transporters), mediate interactions with host plants and symbionts, and integrate hormonal signaling networks including insulin, juvenile hormone, and ecdysteroid pathways. This framework identifies candidate miRNAs, target genes, and signaling pathways that may recur across different ecological contexts, including stress responses, dispersal-related plasticity, and reproductive regulation. However, direct evidence demonstrating that candidate shared miRNA regulators coordinate multiple life-history stages remains limited and requires further experimental validation. We critically evaluate the strength of functional evidence, distinguishing experimentally validated miRNA-target interactions from prediction- or expression-based associations. Finally, we discuss emerging applications of miRNA-based pest control, including artificial miRNAs, RNAi technologies, and nanocarrier delivery systems. By linking molecular mechanisms with ecological outcomes, this review provides a synthesis and highlights miRNAs as important regulators of aphid adaptation and candidate targets for sustainable management strategies.

Aphids↗
PubMed2003

Reproductive response of generalist and specialist aphid morphs with the same genotype to plant secondary compounds and amino acids.

Many studies have paid particular attention to the role of either secondary plant compounds or amino acids as determinants of host-plant range in phytophagous insects. Here we examine the relative importance of both of these classes of compound in host acceptance by generalist and specialist morphs of the black bean aphid, Aphis fabae, that are morphologically similar and genetically identical. Eleven secondary plant compounds and six amino acids with known biological activity in aphids are presented to insects within an artificial membrane system as single compounds, mixtures of same-class compounds and combined mixtures of the two classes of compound. It is found that 1) when specific single secondary compounds and amino acids are presented to generalist and specialist morphs of A. fabae, differential responses are exclusively consistent with plant-use strategy for amino acids but not for secondary compounds, 2) neither secondary compound nor amino acid mixtures give reproductive responses entirely consistent with plant range, but the response to secondary compounds is broadly consistent with plant range whereas the response to amino acids is not, 3) when secondary compounds and amino acid mixtures are combined, the response to secondary compounds generally dominates that to amino acids. Some scenarios of plant-range determination by secondary plant compounds and amino acids, suggested by results, are discussed.

Amino Acids↗
PubMed2004

Cold shock injury and ecological costs of rapid cold hardening in the grain aphid Sitobion avenae (Hemiptera: Aphididae).

The ability of first instar nymphs and newly moulted pre-reproductive adults of the grain aphid S. avenae to rapidly cold harden was investigated. When nymphs reared at 20 degrees C were transferred directly to -8 degrees C for 3 h, there was 18% survival. This exposure was selected as the discriminating temperature. Maximum increases in survival were achieved by acclimating nymphs for 2 h at 0 degrees C and adults for 3 h at 0 degrees C, resulting in survival of 83% and 68%, respectively. Cooling nymphs from 10 to 0 degrees C at different rates (1, 0.1 and 0.05 degrees C min(-1)) also increased cold hardiness, with the slowest rate of 0.05 degrees C min(-1) conferring the highest survival following exposure to the discriminating temperature. Adult aphids also expressed a rapid cold hardening response but to a lesser extent, with survival increasing from 16% to 68% following 3 h at 0 degrees C. There were no 'ecological costs' associated with rapid cold hardening in terms of development, longevity or fecundity. The data support the hypothesis that rapid cold hardening can be induced during the cooling phase of natural diurnal temperature cycles, allowing insects to track daily changes in environmental temperatures.

Acclimatization↗
PubMed2004

Binding of the insecticidal lectin Concanavalin A in pea aphid, Acyrthosiphon pisum (Harris) and induced effects on the structure of midgut epithelial cells.

Concanavalin A (lectin from Canavalia ensiformis L., ConA) has previously been shown to act as a feeding inhibitor for Acyrthosiphon pisum, the pea aphid. In the present study a range of histochemical and biochemical techniques were used to elucidate the target tissues and binding sites of the lectin in the aphid. Diet uptake was evaluated using a radioactive tracer (14C-methylated inulin) and demonstrated that adults were capable of ingesting high quantities of the toxin (approx. 1 microg over a 48 h period). Electophoretic analysis and enzyme-linked immuno-sorbent assay of honeydew samples confirmed these results and further demonstrated that only small levels of ConA were excreted. Histofluorescence and immunolocalisation studies on nymphs revealed that the stomach was the primary target for ConA. At concentrations up to 400 microg ml(-1), lectin binding only occurred in the stomach region, however, at high concentrations (800 microg ml(-1)) the whole digestive tract was stained, although there was no evidence of binding in either the oesophagus or rectum. In addition to binding, there was evidence to suggest that ConA was also causing systemic effects in that the lectin appeared to cross the intestinal epithelial barrier. Immunohistochemical and electron microscopy studies revealed that ConA induced severe cellular swelling of the epithelial cells, accompanied by hypersecretion and a progressive detachment of the apical membrane; however, the striated border itself did not appear to be directly affected. Furthermore, there was no lysis of the epithelium, nor loss of integrity of the epithelial cells themselves. Our results suggest that ConA interacts with glycosylated receptors at the surface of the stomach epithelial cells, interfering with normal metabolism and cell function, resulting in a rapid feedback response on feeding behaviour. Whilst our results provide a much greater understanding regarding the modes of action of ConA in insects, they suggest that different lectins, including other mannose binding lectins, have different modes of action at the cellular levels, and thus generalizations should be treated with caution.

Animals↗
PubMed2004

How many soldiers are optimal for an aphid colony?

A number of aphid species produce sterile soldiers that defend their colony-mates against predators. How many soldiers should a colony produce? Assuming logistic growth of the aphid colony, we can theoretically deduce that soldiers will be produced until the marginal defensive efficacy of a soldier diminishes to rm/K, a ratio of two exogenous variables of the logistic equation, which are the maximum intrinsic rate of increase and carrying capacity. This conclusion holds true irrespective of the number of founders. As the number of founders increases, the entire colony size becomes larger, thus decreasing the percentage of soldiers. In case of multiple founders, each clone will produce the same number of reproductives that remain on the hostplant.

Animals↗
PubMed1999

A solvent-free, rapid and simple virus RNA-release method for potato leafroll virus detection in aphids and plants by reverse transcription polymerase chain reaction.

A one-step, rapid and economical method for potato leafroll virus (PLRV) RNA release that is applicable to the use on a microcentrifuge scale is described. Discs (3-6 mm diameter) from leaves, petioles, stems, and tubers of potato plants were incubated in microcentrifuge tubes with detergent solution. The supernatants were used directly for reverse transcription (RT) and polymerase chain reaction (PCR). Of the seven nonionic detergents of the TritonX series evaluated, Triton X405R was the most effective, although X-405 and X-1OOR were also effective in releasing PLRV RNA. Application of the detergent method for detecting PLRV in greenhouse-grown potato organs (leaves, petioles, stems, tubers) and in field-grown tubers was demonstrated and compared to the multi-step phenol method. When individual aphids, Myzus persicae, were ground in 20 microl of detergent solution and supernatants were used for RT-PCR, virus was detected in single aphids in undiluted solutions and up to a dilution of 1:4. The concentration of PLRV RNA released by the detergent method was substantially lower than that released by the phenol method. However, the detergent method was sensitive enough to detect PLRV from potato leaves, petioles, and stems 2 weeks after graft inoculation. The detergent method was rapid and economical, and has potential for large-scale application. The extracts survived over 37 days at room temperature, thus making it possible to mail extracts from remote areas lacking specialised RT-PCR facilities to a central laboratory for PLRV testing.

Animals↗
PubMed2000

Barrier crops as a cultural control measure of non-persistently transmitted aphid-borne viruses.

Barrier crops have been used since the early 1950s as a cultural control strategy for reducing the spread of non-persistently transmitted aphid-borne viruses. Since then, this strategy has been investigated by several authors, resulting in a wide range of divergent conclusions on its effectiveness. In a series of field and laboratory experiments carried out in central Spain during 1995-1998, we investigated the efficacy and mode of action of various barrier crops for reducing the spread of Potato virus Y and Cucumber mosaic virus in pepper. The barriers acted as natural 'sinks' for non-persistent viruses and did not reduce the number of aphids landing in the protected crop, as suggested by some authors. There was a significant reduction in virus spread and an increase in yield in two of the four years of trials. Such differences in the effectiveness of the barrier crop strategy show that its efficacy depends on a series of factors such as the kind of virus spread pattern (monocyclic or polycyclic), the height of the barrier crop at the time of maximum risk of infection and the extent of competition between the barrier and the protected crop. Moreover, the barrier crop should not host any potential insect pest or pathogen able to damage the protected crop. It is concluded that use of barrier crops can be an effective crop management strategy to protect against virus infection, but only under specific circumstances.

Animals↗
PubMed1998

Characterization of a monoclonal antibody recognizing a DAG-containing epitope conserved in aphid transmissible potyviruses: evidence that the DAG motif is in a defined conformation.

Two viral proteins, the helper component-protease and the coat protein, are required for the non-persistent aphid transmission of potyviruses. In the potyvirus coat protein, the tripeptide aspartate-alanine-glycine (DAG) has often been shown to be involved. A monoclonal antibody, raised against a synthetic decapeptide containing the DAG tripeptide, reacted with the peptide as well as with isolates of soybean mosaic, tobacco etch and tobacco vein mottling potyviruses. Experiments indicate that the monoclonal antibody recognizes a conformational rather than a sequential epitope. The data support the suggestion that the DAG region plays a structural role to determine a coat protein-helper component-protease conformation that influences aphid transmission.

Amino Acid Sequence↗