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PubMed1996

Analysis of amplicons containing the esterase genes responsible for insecticide resistance in the peach-potato aphid Myzus persicae (Sulzer).

The amplification of genes encoding an insecticide-detoxifying esterase (E4) in the peach-potato aphid Myzus persicae is one of the few examples where this genetic phenomenon has been shown to be involved in the response of an intact higher organism to artificial selection. Here we report quantitative and qualitative studies of the repeat units (amplicons) containing the E4 genes in a highly resistant aphid clone. Initial studies to quantify esterase sequences showed a 5-11-fold increase in resistant aphids compared with susceptible aphids, suggesting the presence of 10-22 gene copies per diploid genome. A more incisive analysis by pulsed-field gel electrophoresis confirmed the presence of about 12 copies of the E4 gene and showed them to be on about 24 kb amplicons, arranged as a tandem array of direct repeats. This, together with previous results from crossing experiments and with recent in situ hybridization studies, confirms that the E4 gene amplification in this aphid clone is heterozygous at a single locus. However, these data show that the gene amplification alone cannot account for the approx. 60 times higher levels of E4 protein and its mRNA present in this aphid clone, and therefore resistance must involve changes in both esterase gene copy number and gene expression.

Animals↗
PubMed2003

Facultative bacterial symbionts in aphids confer resistance to parasitic wasps.

Symbiotic relationships between animals and microorganisms are common in nature, yet the factors controlling the abundance and distributions of symbionts are mostly unknown. Aphids have an obligate association with the bacterium Buchnera aphidicola (the primary symbiont) that has been shown to contribute directly to aphid fitness. In addition, aphids sometimes harbor other vertically transmitted bacteria (secondary symbionts), for which few benefits of infection have been previously documented. We carried out experiments to determine the consequences of these facultative symbioses in Acyrthosiphon pisum (the pea aphid) for vulnerability of the aphid host to a hymenopteran parasitoid, Aphidius ervi, a major natural enemy in field populations. Our results show that, in a controlled genetic background, infection confers resistance to parasitoid attack by causing high mortality of developing parasitoid larvae. Compared with uninfected controls, experimentally infected aphids were as likely to be attacked by ovipositing parasitoids but less likely to support parasitoid development. This strong interaction between a symbiotic bacterium and a host natural enemy provides a mechanism for the persistence and spread of symbiotic bacteria.

Animals↗
PubMed2005

Variation in resistance to parasitism in aphids is due to symbionts not host genotype.

Natural enemies are important ecological and evolutionary forces, and heritable variation in resistance to enemies is a prerequisite for adaptive responses of populations. Such variation in resistance has been previously documented for pea aphids (Acyrthosiphon pisum) attacked by the parasitoid wasp Aphidius ervi. Although the variation was presumed to reflect genotypic differences among the aphids, another potential source of resistance to A. ervi is infection by the facultative bacterial symbiont Hamiltonella defensa. Here, we explored whether variation among symbiont isolates underlies variation among A. pisum clones in resistance to A. ervi. Although maternally transmitted, H. defensa is sometimes horizontally transferred in nature and can be experimentally established in clonal aphid lineages. We established five H. defensa isolates in a common A. pisum genetic background. All of the five isolates tested, including one originating from another aphid species, conferred resistance. Furthermore, isolates varied in levels of resistance conferred, ranging from 19% to nearly 100% resistance. In contrast, a single H. defensa isolate established in five different aphid clones conferred similar levels of resistance; that is, host genotype did not influence resistance level. These results indicate that symbiont-mediated resistance to parasitism is a general phenomenon in A. pisum and that, at least for the isolates and genotypes considered, it is the symbiont isolate that determines the level of resistance, not aphid genotype or any interaction between isolate and genotype. Thus, acquisition of a heritable symbiont appears to be a major mode of adaptation to natural enemy pressure in these insects.

Animals↗
PubMed2002

Effect of cabbage cultivars with varying levels of resistance to aphids on the performance of the parasitoid, Aphidius colemani (Hymenoptera: Braconidae).

The effect of aphid resistance in plant cultivars on parasitism of Myzus persicae (Sulzer) and Brevicoryne brassicae (Linnaeus) by Aphidius colemani Viereck was investigated under laboratory conditions using three cultivars of common cabbage, Brassica oleracea var. capitata. Significantly greater aphid populations were found on cv. Derby Day (green-leaved, susceptible to both aphid species), regardless of the presence or absence of parasitoids, compared with cv. Minicole (green-leaved, partially resistant with antibiosis factors for B. brassicae) or cv. Ruby Ball (red-leaved, partially resistant with antixenosis factors for B. brassicae). Minicole had the greatest proportion of parasitized aphids and Derby Day the least. A significantly lower percentage of emerged parasitoids were recorded on Minicole for both aphid species compared with Derby Day and Ruby Ball. The implication of the results are discussed in relation to the integrated control of aphids.

Animals↗
PubMed2002

Temporal variation of RAPD-PCR phenotype composition of the grain aphid Sitobion avenae (Hemiptera: Aphididae) on wheat: the role of hydroxamic acids.

Hydroxamic acids (Hx) contained in wheat are active mutagens which play an important role in the defence of the plant against aphids. Random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) dominant markers were used to assess genetic variability in the aphid Sitobion avenae (Fabricius) in relation to hydroxamic acid levels in their host-plants. Colonies of aphids belonging to a single RAPD-PCR profile were grown on different host-plants differing in their Hx content under greenhouse conditions. The RAPD-PCR phenotypic pattern showed the appearance of two new RAPD-PCR variants after four to five generations of exposure to wheat cv. Chagual (high Hx levels), one after exposure to wheat cv. Huayún (low Hx levels), and none after exposure to oat (lacking Hx). Differential appearance of new RAPD-PCR aphid phenotypes also occurred on field-grown wheat. While the overall phenotypic 'richness' diminished during the season, the number of RAPD-PCR phenotypes decreased on cv. Huayún and increased on cv. Chagual. The preferential appearance in the field and in the greenhouse of new RAPD-PCR phenotypes of S. avenae on cv. Chagual is discussed on the basis of mutagenesis induced by hydroxamic acids and by the products of their transformation within the aphid. Aphid abundance is interpreted in terms of antixenosis and antibiosis by hydroxamic acids. The appearance on cv. Chagual of phenotypes first detected on cv. Huayún was accounted for by intercrop migrations.

Animals↗
PubMed2003

Aphids do not avoid resistance in Australian lupin (Lupinus angustifolius, L. luteus) varieties.

Laboratory bioassays and field trials were used to characterize resistance to three aphid species (Myzus persicae (Sulzer), Acyrthosiphon kondoi Shinji, Aphis craccivora (Koch) in two aphid-resistant varieties (Kalya, Tanjil) and one susceptible variety (Tallerack) of Lupinus angustifolius L., and in one resistant variety (Teo) and one susceptible variety (Wodjil) of L. luteus L. Host selection tests in the glasshouse showed that alates of all three species preferred L. luteus to L. angustifolius, but provided no evidence that alates selected susceptible varieties over resistant. These results were supported by a field trial, which showed no difference in the number of colonizing A. kondoi alates collected from the resistant and susceptible lines of each lupin species, but there were significantly more late-instar nymphs and apterous adults on the susceptible lines. In laboratory host suitability experiments, there was much greater suppression of aphid growth and survival on Teo than on Kalya and Tanjil. In field trials, the numbers of aphids were generally lower on resistant compared to susceptible lines of both lupin species with one notable exception: M. persicae numbers were not lower on the resistant variety Tanjil compared to the susceptible variety Tallerack (L. angustifolius). These results suggest that the resistance mechanisms in both lupin species do not affect the selection of hosts by colonizing aphids, but rather are affecting the growth, survival and possibly reproduction of aphids after settling.

Animals↗
PubMed1996

Structure of the dnaA region of the endosymbiont, Buchnera aphidicola, of aphid Schizaphis graminum.

Buchnera aphidicola is an intracellular prokaryote (endosymbiont) that lives in the body cavity of the aphid. Phylogenetic studies indicated that it is closely related to Escherichia coli and members of Enterobacteria. The gene order of the region containing the dnaA gene is well conserved in many bacteria. Seven genes of the endosymbiont of the aphid Schizaphis graminum, gyrB, dnaN, dnaA, rpmH, rnpA, yidD, and 60K. were found to be homologous in sequence and relative location to those of E. coli. We have further sequenced the region downstream of the 60K gene to elucidate the boundary of the conserved region, and found that one more gene, thdF, is conserved. The comparison of gene organizations of the dnaA region of the related bacteria supported the close phylogenetic relationship of B. aphidicola to E. coli. In addition, we have identified groES and groEL genes next to the thdF gene. GroEL protein was reported to be expressed at an elevated level in the endosymbionts of aphids, and is considered to play an important role in their association with the aphid host. Comparison of the structure of the groE operon with that of the endosymbiont of the aphid Acyrthosiphon pisum revealed the conservation of a sequence resembling the E. coli consensus heat shock promoter, and this sequence may be responsible for the high expression of the groEL gene in aphid endosymbionts.

Animals↗
PubMed2003

Photosynthetic responses of soybean to soybean aphid (Homoptera: Aphididae) injury.

The soybean aphid, Aphis glycines Matsumara, was discovered in the United States in the summer of 2000. Since that initial discovery, the aphid has spread across northern soybean production regions. In 2001, we examined the physiological responses of soybeans to low aphids densities (fewer than 50 aphids/leaf). In this study, we determined photosynthetic rates, leaf fluorescence responses, and photosynthetic responses to variable carbon dioxide and light levels. In addition, analyses for chlorophyll content and stable carbon isotope ratios were used to differentiate potential differences in stomatal versus mesophyll limitations to photosynthesis. We observed rate reductions of up to 50% on infested leaflets, including lealets with no apparent symptoms of aphid injury (such as chlorosis). Differences in fluorescence data indicated that photoelectron transport was not impaired. These results indicate that substantial physiological impact on soybean is possible even at low aphid densities. Also, the conventional view of aphid injury acting through reductions in chlorophyll content and light-harvesting reactions of photosynthesis is not supported by our findings in this system.

Animals↗
PubMed2003

Categories of resistance at different growth stages in halt, a winter wheat resistant to the Russian wheat aphid (Homoptera: Aphididae).

This study was designed to categorize the resistance to the Russian wheat aphid, Diuraphis noxia (Mordvilko), resistant hard red winter wheat, Halt, as compared with susceptible wheat, TAM 107, at four different growth stages. Antixenosis was expressed in Halt at growth stage Zadoks 30. Antibiosis in Halt affected fecundity, number of aphids produced per reproductive day, maximum number of nymphs produced in one day, and intrinsic rate of increase. Fecundity was lower on Halt than TAM 107, and more nymphs were produced on both varieties at growth stage 20 than 10 and 40. Fewer nymphs were produced per reproductive day and on maximum production days by aphids reared on Halt than by those reared on TAM 107. The intrinsic rate of increase of Russian wheat aphids reared on Halt was lower than aphids reared on TAM 107. Differences in plant height and plant dry weight did not occur. Chlorosis ratings showed greater damage at the earlier stages in Halt and TAM 107 and significantly more damage in TAM 107 than Halt at growth stages 10, 20, and 30. Leaf rolling occurred on infested plants of TAM 107 at growth stages 10, 20, and 30, but not growth stage 40. Halt plants did not exhibit leaf rolling. The presence of a significant level of tolerance could make Halt compatible with other integrated pest management programs. However, care should be taken with cultivars containing evidence of antixenosis or antibiosis that could cause selective pressure on the Russian wheat aphid, potentially causing biotypes to be produced.

Animals↗
PubMed2003

Tillage impacts cereal-aphid (Homoptera: Aphididae) infestations in spring small grains.

We compared infestation levels of cereal aphids (Homoptera: Aphididae) in spring-seeded wheat and barley grown with and without preplant tillage for 8 site yr in eastern South Dakota. Crop residue covered approximately 25% of the soil surface with preplant tillage, whereas without preplant tillage 50% or more of surface residue was conserved. Rhopalosiphum padi (L.) comprised nearly 90% of all cereal aphids sampled, and R. maidis (Fitch), Schizaphis graminum (Rondani), and Sitobion avenae (F.) collectively comprised the remainder. R. padi routinely infested lower parts of tillers and were generally concealed by surface residue in plots with no preplant tillage. Across 7 site yr, R. padi were more abundant in plots with no preplant tillage than with preplant tillage (272.6 +/- 54.4 versus 170.1 +/- 37.2 aphid days per 25 tillers). However, in comparisons at individual site years, R. padi were greater in no-preplant tillage plots only once. For all cereal-aphid species combined, infestations were greater in plots with no preplant tillage for 1 of 8 site yr, but did not differ with tillage when compared across all site years. Cereal aphids were never more abundant in plots with preplant tillage. Our results show that conservation tillage leads to greater infestations of R. padi in spring small grains, as increased surface residue provides a favorable microhabitat for this aphid.

Agriculture↗
PubMed2004

Effect of three resistant soybean genotypes on the fecundity, mortality, and maturation of soybean aphid (Homoptera: Aphididae).

The fecundity, longevity, mortality, and maturation of the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), were characterized using three resistant soybean, Glycine max (L.) Merrill, genotypes ('Dowling', 'Jackson', and PI200538 'Sugao Zarai') and two susceptible genotypes ('Pana' and 'Loda'). Antibiosis in the resistant genotypes was demonstrated by a significant decrease in fecundity and longevity and increased mortality of A. glycines. Aphid fecundity, measured as number of offspring produced in the first 10 d by each viviparous aptera, was higher on Pana than on the resistant genotypes. Aphid longevity, the mean number of days a 1-d-old adult lived, was 7 d longer on Pana than on Dowling and Jackson. The mortality of both viviparous apterae and nymphs on resistant genotypes was significantly higher than on susceptible genotypes. A greater number of first instars survived to maturation stage (date of first reproduction) on susceptible plants than on resistant plants. None of the first instars placed on Dowling and PI200538 leaves survived to maturation. Observations of aphid behavior on leaves indicated that aphids departed from the leaves of resistant plants 8-24 h after being placed on them, whereas they remained indefinitely on leaves of susceptible cultivars and developed colonies. Reduced feeding due to ingestion of potentially toxic compounds in soybean may explain the possible mechanism of resistance to the soybean aphid.

Animals↗
PubMed2004

Identification of Russian wheat aphid (Homoptera: Aphididae) populations virulent to the Dn4 resistance gene.

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a serious worldwide pest of wheat and barley. Russian wheat aphid populations from Hungary, Russia, and Syria have previously been identified as virulent to D. noxia (Dn) 4, the gene in all Russian wheat aphid-resistant cultivars produced in Colorado. However, the virulence of Russian wheat aphid populations from central Europe, North Africa, and South America to existing Dn genes has not been assessed. Experiments with plants containing several different Dn genes demonstrated that populations from Chile, the Czech Republic, and Ethiopia are also virulent to Dn4. The Czech population was also virulent to plants containing the Dnx gene in wheat plant introduction PI220127. The Ethiopian population was also virulent to plants containing the Dny gene in the Russian wheat aphid-resistant 'Stanton' produced in Kansas. The Chilean and Ethiopian populations were unaffected by the antibiosis resistance in Dn4 plants. There were significantly more nymphs of the Chilean population on plants of Dn4 than on Dn6 plants at both 18 and 23 d postinfestation, and the Ethiopian population attained a significantly greater weight on Dn4 plants than on plants containing Dn5 or Dn6. These newly characterized virulent Russian wheat aphid populations pose a distinct threat to existing or proposed wheat cultivars possessing Dn4.

Animals↗
PubMed2005

Influence of three resistance sources in winter wheat derived from TAM 107 on yield response to Russian wheat aphid.

A study to determine yield response to the Russian wheat aphid, Diuraphis noxia (Mordvilko), was conducted during the 1997-1998 and 1998-1999 growing seasons at three eastern Colorado locations, Akron, Fort Collins, and Lamar, with three wheat lines containing either Russian wheat aphid-resistant Dn4 gene, Dn6 gene, or resistance derived from PI 222668, and TAM 107 as the susceptible control. Russian wheat aphids per tiller were greater on TAM 107 than the resistant wheat lines at the 10x infestation level at Fort Collins and Akron in 1999. Yield, seed weight, and number of seeds per spike for each wheat line were somewhat affected by Russian wheat aphid per tiller mainly at Fort Collins. The infested resistant wheat lines harbored fewer Russian wheat aphids and yielded more than the infested susceptible wheat lines. Wheat lines containing the Dn4, Dn6, and PI 222668 genes contain different levels of antibiosis or antixenosis and tolerance. Although differences existed among sites and resistance, there is a benefit to planting resistant wheat when there is a potential for Russian wheat aphid infestations.

Animals↗
PubMed1997

Genotypic variation among different phenotypes within aphid clones.

Most aphid species Hemiptera: Aphididae are parthenogenetic between periods of sexual reproduction. They are also highly polyphenic, with different adult morphs occurring in the life cycle, piz. winged, wingless, asexual and sexual. It is assumed that aphids born in a parthenogenetic clonal lineage are genetically identical regardless of the final adult form with the exception of sexual forms). Using the randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) we have found that different asexual adult phenotypes winged and wingless of some clones of two cereal aphid species (the grain aphid, Sitobion avenae (F.) and the bird-cherry aphid. Rhopalosiphum padi (L.) may be distinguished by the presence or absence of one or more RAPD-PCR bands. In three of nine clones examined, such differences were found, and Southern blotting and hybridization of the discriminating bands confirmed these to be of aphid origin, rather than due to endosymbiotic bacteria or contaminating fungi. The main 248 and 296 bp bands, in the two species respectively, were sequenced and found to be A/T rich. The smaller band showed 57% homology with white striated muscle over a stretch of 90 bp. Genomic DNA treated with dimethyl sulphoxide to remove secondary structures still showed differences in RAPD-PCR profiles between winged and wingless morphs within the unusual clones. This discovery may be widespread and therefore it is important to understand the phenomenon in relation to clonal organisms.

Animals↗
PubMed2000

Decay of mutualistic potential in aphid endosymbionts through silencing of biosynthetic loci: Buchnera of Diuraphis.

Buchnera, the primary bacterial endosymbiont of aphids, is known to provision essential amino acids lacking in the hosts' diet of plant sap. The recent discovery of silenced copies of genes for tryptophan biosynthesis (trpEG) in certain Buchnera lineages suggests a decay in symbiotic functions in some aphid species. However, neither the distribution of pseudogenes among lineages nor the impact of this gene silencing on amino-acid availability in hosts has been assessed. In Buchnera of the aphid Diuraphis noxia, tandem repeats of these pseudogenes have persisted in diverse lineages, and thpEG pseudogenes have originated at least twice within this aphid genus. Measures of amino-acid concentrations in Diuraphis species have shown that the presence of the pseudogene is associated with a decreased availability of tryptophan, indicating that gene silencing decreases nutrient provisioning by symbionts. In Buchnera of Diuraphis, rates of nonsynonymous substitutions are elevated in functional trpE copies, supporting the hypothesis that pseudogene origin and persistence reflect a reduced selection for symbiont biosynthetic contributions. The parallel evolution of trpEG pseudogenes in Buchnera of Diuraphis and certain other aphid hosts suggests that either selection at the host level is not effective or that fitness in these aphids is not limited by tryptophan availability.

Animals↗
PubMed1995

Mutational analysis of the coat protein N-terminal amino acids involved in potyvirus transmission by aphids.

The nature of the amino acids in the N-terminal 'DAGX' motif of the coat protein of tobacco vein mottling virus (TVMV) that have a direct effect on aphid transmissibility of the virion were further defined by site-directed mutagenesis. In the first position of the DAGX motif, Asp or Asn are required for aphid transmissibility. In the second position, the nonpolar residue Ala, but not the nonpolar Gly or Val or the polar Thr and Ser, is compatible with transmissibility. In the third position, the small, neutral, nonpolar Gly appears to be critical; even substitution of Ala, with a minimal side-chain, drastically reduces transmissibility. Although the amino acid following the DAG sequence is not highly conserved among potyviruses, the presence of an acidic Glu or Asp residue at this position in the TVMV coat protein drastically reduces or abolishes aphid transmissibility. An attempt was made to test the hypothesis that trypsin cleavage of the N terminus is involved in the aphid inoculation process by destroying a trypsin cleavage site downstream from the DAGX motif. While the predicted decrease in transmission occurred from infected plants, there was no effect on the transmission of purified virus. Of the 23 mutations in the DAGX region of TVMV reported here and previously, only two, substitutions of Lys and Arg for Asp, had a detectable adverse effect other than on aphid transmissibility. These, and perhaps other, residues near the N terminus function in some phase of the TVMV life cycle, in addition to aphid transmission.

Amino Acid Sequence↗
PubMed2005

Aphid infestation causes different changes in carbon and nitrogen allocation in alfalfa stems as well as different inhibitions of longitudinal and radial expansion.

Alfalfa (Medicago sativa) stem elongation is strongly reduced by a pea aphid (Acyrthosiphon pisum Harris) infestation. As pea aphid is a phloem feeder that does not transmit virus or toxins, assimilate withdrawal is generally considered as the main mechanism responsible for growth reduction. Using a kinematic analysis, we investigated the spatial distributions of relative elemental growth rates of control and infested alfalfa stems. The water, carbon, and nitrogen contents per unit stem length were measured along the growth zone. Deposition rates and growth-sustaining fluxes were estimated from these patterns. Severe short-term aphid infestation (200 young adults over a 24-h period) induced a strong and synchronized reduction in rates of elongation and of water and carbon deposition. Reduced nitrogen content and associated negative nitrogen deposition rates were observed in some parts of the infested stems, especially in the apex. This suggested a mobilization of nitrogen from the apical part of the growth zone, converted from a sink tissue into a source tissue by aphids. Calculation of radial growth rates suggested that aphid infestation led to a smaller reduction in radial expansion than in elongation. Together with earlier observations of long-lasting effects of a short-term infestation, this supports the hypothesis that in addition to nutrient withdrawal, a thigmomorphogenesis-like mechanism is involved in the effect of aphid infestation on stem growth.

Animals↗
PubMed2001

Molecular responses to aphid feeding in Arabidopsis in relation to plant defense pathways.

Little is known about molecular responses in plants to phloem feeding by insects. The induction of genes associated with wound and pathogen response pathways was investigated following green peach aphid (Myzus persicae) feeding on Arabidopsis. Aphid feeding on rosette leaves induced transcription of two genes associated with salicylic acid (SA)-dependent responses to pathogens (PR-1 and BGL2) 10- and 23-fold, respectively. Induction of PR-1 and BGL2 mRNA was reduced in npr1 mutant plants, which are deficient in SA signaling. Application of the SA analog benzothiadiazole led to decreases in aphid reproduction on leaves of both wild-type plants and mutant plants deficient in responsiveness to SA, suggesting that wild-type SA-dependent responses do not influence resistance to aphids. Two-fold increases occurred in mRNA levels of PDF1.2, which encodes defensin, a peptide involved in the jasmonate (JA)-/ethylene-dependent response pathway. Transcripts encoding JA-inducible lipoxygenase (LOX2) and SA/JA-inducible Phe-ammonia lyase increased 1.5- to 2-fold. PDF1.2 and LOX2 induction by aphids did not occur in infested leaves of the JA-resistant coi1-1 mutant. Aphid feeding induced 10-fold increases in mRNA levels of a stress-related monosaccharide symporter gene, STP4. Phloem feeding on Arabidopsis leads to stimulation of response pathways associated with both pathogen infection and wounding.

Animals↗