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PubMed2005

Comparison of Dn4- and Dn7-carrying spring wheat genotypes artificially infested with Russian wheat aphid (Homoptera: Aphididae) biotype 1.

Genetic resistance is a useful control strategy for managing Russian wheat aphid, Diuraphis noxia (Mordvilko), in wheat, Triticum aestivum L. In 2003, a Russian wheat aphid population (denoted as biotype 2) identified in Colorado was virulent to genotypes carrying the Dn4 Russian wheat aphid resistance gene, necessitating the rapid identification and deployment of new sources of resistance. Although the Dn7 gene had shown excellent resistance to Russian wheat aphid biotypes 1 and 2 in evaluations in the greenhouse, no information is available on the amount of protection provided by Dn7 under field conditions. The objective of this study was to compare the reaction of Dn4- and Dn7-carrying spring wheat genotypes under artificial infestation by Russian wheat aphid biotype 1 in the field. Irrigated field experiments were conducted in 2003 and 2004 in a split-split plot arrangement with six replications. The whole plot treatment was infestation level (control, 1x, and 10x Russian wheat aphids), and the subplot treatment was resistance source (Dn4- and Dn7-carrying genotypes). The sub-subplot treatment consisted of side-by-side planting of resistant and susceptible genotypes. The Dn4 subplot was significantly more damaged than the Dn7 subplot in 2003, but not in 2004. Interaction effects observed in 2004 suggested an advantage of Dn7 relative to Dn4 in terms of reduced Russian wheat aphid abundance and plant damage. Deployment of the Dn7 Russian wheat aphid resistance gene should provide protection in the field comparable with that provided by the Dn4 resistance gene for management of Russian wheat aphid biotype 1.

Animals↗
PubMed2005

Influence of aphid species and barley yellow dwarf virus on soft red winter wheat yield.

Yield loss in soft red winter wheat, Triticum aestivum L., caused by aphid-transmitted barley yellow dwarf virus (family Luteoviridae, genus Luteovirus, BYDV) was measured over a 2-yr period in central Missouri. Rhopalosiphum padi (L.) was the most common and economically important species, accounting for > 90% of the total aphids. Schizaphis graminum (Rondani), Rhopalosiphum maidis (Fitch), and Sitobion avenae (F.) made up the remainder of the aphids. Aphid numbers peaked at wheat stem elongation in 2003 with 771 R. padi per meter-row. In the 2003-2004 growing season, aphid numbers averaged seven aphids per meter-row in the fall and peaked at 18 aphids per meter-row at jointing. Wheat grain yield was reduced 17 and 13% in 2003 and 2004, respectively. Thousand kernel weights were reduced 10 and 5% in the untreated plots compared with the treated control in 2003 and 2004, respectively. Padi avenae virus was the predominate strain, accounting for 81 and 84% of the symptomatic plots that tested positive for BYDV in 2003 and 2004. Our results indicate that economic thresholds for R. padi are 16 aphids per meter-row in the fall and 164 aphids per meter-row at jointing.

Animals↗
PubMed2006

Mi-1-Mediated aphid resistance involves salicylic acid and mitogen-activated protein kinase signaling cascades.

The tomato Mi-1 gene confers resistance to root-knot nematodes (Meloidogyne spp.), potato aphids (Macrosiphum eluphorbiae), and whiteflies (Bemisia tabaci and B. tabaci biotype B). Resistance to potato aphid is developmentally regulated and is not associated with induction of a hypersensitive response. The NahG transgene that eliminates endogenous salicylic acid (SA) was used to test the role of the SA signaling pathway in the resistance mediated by Mi-1 to potato aphids. Aphids survived longer on NahG tomato plants than on wild type. However, aphid reproduction was not affected on NahG tomato. Aphid resistance in Mi-1 NahG plants was completely abolished and the phenotype was successfully rescued by application of BTH (benzo(1,2,3)-thiaiazole-7-carbothioic acid S-methyl ester), indicating that the SA signaling pathway is an important component of Mi-1-mediated aphid resistance. Using virus-induced gene silencing, one or more mitogen-activated protein kinase (MAPK) cascades required for Mi-1-mediated aphid resistance were identified. Silencing plants for MAPK kinase (LeMKK2) and MAPKs (LeMPK2 and LeMPK1, or LeMPK3) resulted in attenuation of Mi-1-mediated aphid resistance. These results further demonstrate that resistance gene-mediated signaling events against piercing-sucking insects are similar to those against other plant pathogens.

Animals↗
PubMed2004

Developmental regulation of Mi-mediated aphid resistance is independent of Mi-1.2 transcript levels.

Mi-1.2, a member of the intracellular, nucleotide-binding site-leucine-rich repeat family of resistance genes, confers resistance in tomato (Lycopersicon esculentum) against both root-feeding nematodes and leaf-feeding aphids. Nematode resistance is effective in all life stages of the plant; in contrast, Mi-mediated aphid resistance is developmentally regulated, and protects mature plants but not seedlings against aphid infestation. To determine if the onset of aphid resistance is regulated by Mi-1.2 transcript abundance, we compared aphid resistance and Mi-1.2 transcript levels in seedlings and flowering plants. Paired bioassays and RNase protection assays revealed that Mi-1.2 is transcribed in the leaves prior to the onset of aphid resistance, and that transcript levels are comparable in seedlings and flowering life stages. Furthermore, constitutive overexpression of Mi-1.2 in transgenic plants did not hasten the onset of aphid resistance in seedlings, or boost the level of resistance observed in flowering plants. These data demonstrate that Mi-1.2 transcript levels do not modulate the degree of aphid resistance in tomato leaves, or control the differences in regulation between aphid and nematode resistance.

Animals↗
PubMed1997

Expression and suppression of circulative aphid transmission in pea enation mosaic virus.

Pea enation mosaic virus (PEMV) is composed of two autonomously replicating virus RNAs related to the genomic RNAs of viruses in the genera Luteovirus and Umbravirus. The transmission of PEMV resembles that of its luteovirus relatives in utilizing circulative aphid transmission. However, unlike its luteovirus counterparts, PEMV can also be mechanically transmitted. Prolonged mechanical passage of PEMV can lead to the loss of aphid transmissibility, a trait that is mirrored by specific changes in the PEMV virion composition. These changes were used to examine the virus contribution to vector transmission and the mechanisms by which it is regulated. Using a local lesion isolation technique, one aphid transmissible and two aphid non-transmissible isolates of PEMV were compared. Structural analysis of a 54 kDa minor structural subunit unique to the aphid transmissible isolate demonstrated that it was a fusion of the 21 kDa virus coat protein and a 33 kDa protein encoded immediately downstream of the 21 kDa ORF, consistent with the formation of the 54 kDa subunit by translational readthrough. Genetic analyses utilizing exchanges between infectious in vitro transcripts of each isolate demonstrated that although the 33 kDa protein was non-essential for infection, its presence was mandatory for aphid transmission, and that specific changes within the 33 kDa ORF were sufficient to confer or abolish aphid transmission. This study also demonstrates that isolates of PEMV exist as mixtures of aphid transmissible and non-transmissible genotypes, and provides insight into the mechanisms used by this virus to down-regulate aphid transmission in response to a specific selection pressure.

Amino Acid Sequence↗
PubMed2002

Cauliflower mosaic virus is preferentially acquired from the phloem by its aphid vectors.

Cauliflower mosaic virus (CaMV) is transmitted in a non-circulative manner by aphids following the helper strategy. Helper proteins P2 and P3 act as a bridge between virions and the aphid cuticle. Electronic monitoring of aphid stylet activities (EPG technique), transmission tests and electron microscopy showed that CaMV is preferentially acquired from the phloem by its most common aphid vectors, Brevycorine brassicae and Myzus persicae. We also found that CaMV is semipersistently transmitted and that the rate of acquisition does not follow a typical bimodal curve. Instead, the virus could be acquired from non-phloem tissues at a low and fairly constant rate after one or more intracellular punctures within a few minutes, but the probability of acquisition rose significantly when aphids reached the phase of committed ingestion from the phloem. The acquisition rate of CaMV did not increase with increasing number of intracellular punctures, but the total duration of intracellular puncture was one of the variables selected by the stepwise logistic regression model used to fit the data that best explained acquisition of CaMV. Furthermore, aphids reaching the phloem faster had a higher probability of acquiring the virus. Our results support the hypothesis that multiple intracellular punctures of epidermal and mesophyll cells result in loading aphids with the CaMV-encoded aphid transmission factor (P2), and that aphids, in most cases, subsequently acquire CaMV particles during phloem sap ingestion. Consistently, immunoelectron microscopy showed that P3-virions are frequently found in the sieve element lumen, whereas P2 could not be detected.

Animals↗
PubMed2004

An analysis of plant-aphid interactions by different microarray hybridization strategies.

Aphids have long been considered 'stealthy' herbivores that subvert a plant's induced defenses and manipulate its source-sink signaling, but these hypotheses are largely untested at a transcriptional level. We analysed gene expression in native tobacco plants (Nicotiana attenuata) infested with Myzus nicotianae aphids, without resorting to the use of clip-cages, with a cDNA microarray containing 240 defense-related N. attenuata genes. Using a hybridization scheme ('ratio analysis' and 'state analysis') broadly applicable in two-factor analyses, we examined how the aphids influenced source--sink relationships and determined if their feeding preference, apart from benefiting from the sink strength of young leaves, was associated with the expression of known plant defense genes. In contrast to the responses elicited by attack from tissue-feeding lepidopteran larvae and mesophyll-sucking insects, attack from phloem-feeding aphids elicited only weak responses. Similar to other herbivores, M. nicotianae feeding increased the expression of trypsin protease inhibitors (TPI), lipoxygenase, and xyloglucan-endotransglycosylase genes, and decreased small RUBISCO subunit and ubiquitin carrier protein transcripts. Aphid-specific changes included the up-regulation of glutamate synthase and the down-regulation of a germin-like protein. Aphids preferentially settled on younger leaves, which expressed more hydroperoxide lyase and TPI than did older leaves, suggesting that these genes, which mediate the synthesis of compounds reported to be toxic for aphids in other plant systems, are either not under transcriptional control or not important in this system. By identifying aphid-responsive genes, we have made a first step in identifying the 'genes that matter' in plant--aphid interactions.

Aldehyde-Lyases↗
PubMed2000

Effect of fungicide application on activity of Neozygites fresenii (Entomophthorales: Neozygitacaea) and cotton aphid (Homoptera: Aphididae) suppression.

The development of resistance in aphid populations highlights the importance of biological control as a pest management tactic. Four treatments were evaluated to determine the effects of pesticides on the population dynamics of Aphis gossypii Glover and Neozygites fresenii (Nowakowski) Batko: (1) weekly applications of the insecticide imidacloprid (Provado 1.6 F); (2) weekly applications of the fungicide chlorothalonil (Bravo 720); (3) applications of imidacloprid (Provado 1.6 F) when aphid densities exceeded 30 aphids per leaf, and (4) untreated control. Differences in aphid density among the four treatments were shown only to be significant during the 1997 growing season; however, aphid densities were greater in the chlorothalonil treatment than in the other treatments during each growing season. Percentage of N. fresenii-killed aphids was most often highest in the chlorothalonil treatment as well. The fungal epizootic caused by N. fresenii was delayed approximately 1 wk in the chlorothalonil treatment when compared with the other treatments. This delay allowed the aphids to temporarily escape suppression by the fungus and to continue to increase in density until the density-dependent effects of the epizootic overwhelmed the aphid population. N. fresenii also appeared to persist in the system when imidacloprid was in use and does appear responsible for initial aphid reductions. Treatment did not appear to have a large influence on yield outcome. Yield was variable from year to year and from location to location.

Animals↗
PubMed2001

Green peach aphid (Homoptera: Aphididae) action thresholds for controlling the spread of potato leafroll virus in Idaho.

Arbitrary green peach aphid, Myzus persicae (Sulzer), action thresholds (0, 5, 10, 20, and 40 aphids per 100 leaves) were tested in 3 yr of field experimentation to determine if they could be maintained and if they would significantly impact aphid densities and limit the incidence of potato leafroll virus (PLRV). In 1997 and 1998, significant linear relationships between thresholds and final percentage of PLRV (expressed as the percentage of tubers infected with PLRV) were observed: there was a trend toward lower PLRV incidence with decreasing action threshold in 1999. There were significant relationships between thresholds and mean number of apterous aphids in 1998 and 1999, indicating that reduction of PLRV resulted from reduced within-field spread by apterae. In almost all cases, aphid densities exceeded threshold levels from one week to the next, clearly showing that the thresholds could not be maintained. Over all experiments, four to nine seasonal applications of methamidophos were warranted by the magnitude of the threshold. Imidacloprid applied at planting to the zero aphid threshold reduced the number of methamidophos applications from nine in the insecticide-at-detection treatment to five. A revised within-field green peach aphid management plan is recommended that includes systemic insecticide applied at planting, aphid sampling every 3-4 d, and foliar insecticide application following aphid detection.

Animals↗
PubMed2005

Estimation of hymenopteran parasitism in cereal aphids by using molecular markers.

Polymerase chain reaction (PCR) primers were designed and tested for identification of immature parasitoids in small grain cereal aphids and for estimation of parasitism rates. PCR technique was evaluated for 1) greenhouse-reared greenbugs, Schizaphis graminum (Rondani), parasitized by Lysiphlebus testaceipes Cresson and 2) aphids collected from winter wheat fields in Caddo County, Oklahoma. For greenhouse samples, parasitism frequencies for greenbugs examined by PCR at 0, 24, and 48 h after removal of L. testaceipes parasitoids were compared with parasitism frequencies as determined by greenbug dissection. PCR was unable to detect parasitism in greenbugs at 0 and 24 h postparasitism, but it was able to detect parasitoids 48 h after parasitoid removal at frequencies that were not significantly different from dissected samples. Field-collected samples were analyzed by rearing 25 aphids from each sample and by comparing parasitoid frequencies of mummies developed and PCR performed on another 50 aphids. Aphid samples included corn leaf aphids, Rhopalosiphum maidis (Fitch); bird cherry-oat aphids, Rhopalosiphum padi (L.); English grain aphids, Sitobion avenae (F.); and greenbugs. Mummies were isolated until adult emergence, whereupon each parasitoid was identified to species (L. testaceipes was the only parasitoid species found). Parasitism detection frequencies for PCR also were not statistically different from parasitism frequencies of reared aphids. These results indicate that PCR is a useful tool for providing accurate estimates of parasitism rates and especially for identification of immature parasitoids to species.

Animals↗
PubMed2006

[Effects of elicitors on aphid growth and development and on specific genes expression in wheat].

This paper studied the development duration, adult weight, and mean relative growth rate (MRGR) of aphid Schizapis graminum, and the specific genes expression in wheat variety 98-10-30 (Triticum aestivum) after treated with different elicitors. The results showed that needling penetration, aphid feeding and BTH application could shorten the development duration of the aphid and decrease its adult weight, but had no significant effect on aphid MRGR. Different elicitors induced different specific genes expression in quality and quantity. The mRNA of PDF1.2 was increased significantly after aphid feeding, while there was no expression after applying BTH. Aphid feeding and BTH application increased the mRNA of BGL2, but no expression was observed in the control and after needling penetration. The induced resistance had some effects on aphid growth and development, and the response induced by aphid feeding had some similarities but significant differences to that induced by mechanical wounding and BTH application. It could be concluded that the response of aphid to elicitors was a special resistance, and there existed some overlaps or differences between it and mechanical wounding and SAR (systemic acquired resistance).

Animals↗
PubMed1999

Variability and Parasitoid Foraging Efficiency: A Case Study of Pea Aphids and Aphidius ervi.

When a parasitoid is searching for hosts, not all hosts are equally likely to be attacked. This variability in attack probability may affect the parasitoid functional response. Using a collection of experiments, we quantified the functional response of Aphidius ervi (Hymenoptera: Braconidae), an insect parasitoid of the pea aphid Acyrthosiphon pisum (Homoptera: Aphididae). We measured variability in the number of hosts attacked by a foraging parasitoid both among plants and within plants. At the first scale, A. ervi, searching among plants containing different numbers of aphids, showed both aphid-density-dependent and aphid-density-independent variability in the number of aphids attacked per plant. Within plants, A. ervi selectively attacked second and third instar aphids relative to other instars. Furthermore, there was variability in the susceptibility of attack among aphids independent of instar. Variability in attack rates among aphids both among and within plants decreased parasitoid foraging efficiency, with the greatest decrease caused by among-plant variability. Furthermore, the decrease in foraging efficiency was greatest when the average number of aphids per plant was low, thereby transforming a strong Type II functional response into one approaching Type I.

host‐parasitoid interactions↗
PubMed2000

Cucumber mosaic virus mutants with altered physical properties and defective in aphid vector transmission.

Two mutant strains of cucumber mosaic virus (CMV) were investigated with respect to virion stability and molecular determinants of aphid vector transmission. The mutant 2A1-MT-60x, derived from the mechanically passaged wild type 2A1-AT, is poorly transmissible by the aphid Aphis gossypii and not transmissible by the aphid Myzus persicae, whereas the wild type virus is transmissible by both aphid species. The mutant phenotype was shown to be conferred by a single encoded amino acid change of alanine to threonine at position 162 of the coat protein (CP). Modifying the mutant CP gene to encode the wild type sequence (alanine) at position 162 restored aphid transmission. To test for a correspondence between changes in the physical stability of virions and defects in aphid transmission, a urea disruption assay was developed. Virions of aphid-transmissible strains 2A1-AT and CMV-Fny were stable with treatments of up to between 3 and 4 M urea. In this assay mutant viruses 2A1-MT-60x and CMV-M were less stable, as they were completely disrupted at urea concentrations of 2 and 1 M urea, respectively. The mutant 2A1-MT-60x also accumulated at a reduced level in infected squash relative to the wild type virus. These studies suggest that a primary factor in the loss of aphid transmissibility of some strains of CMV is a reduction in virion stability.

Amino Acid Substitution↗
PubMed1992

Viruses of the Potyviridae with non-aphid vectors.

The large majority of members of the family Potyviridae are aphid-transmitted. However, 17 viruses whose vectors are unknown have been classified as members of the genus Potyvirus. Loss of aphid transmissibility has been observed in some strains of several potyviruses. There are currently 11 members of the Potyviridae whose vectors are not aphids. These viruses with non-aphid vectors exhibit most of the characteristics of the family. Viruses of the Potyviridae induce cytoplasmic cylindrical inclusions in their hosts whether their vectors are aphids, non-aphids, or are unknown. The virus genome produces the inclusion protein and thus the viruses have related inclusion body gene sequences. Non-aphid-transmitted viruses of the Potyviridae also are serologically related to aphid-transmitted potyviruses.

Animals↗
PubMed2004

Aphid effects on rhizosphere microorganisms and microfauna depend more on barley growth phase than on soil fertilization.

This paper gives the first reports on aphid effects on rhizosphere organisms as influenced by soil nutrient status and plant development. Barley plants grown in pots fertilized with N but without P (N), with N and P (NP), or not fertilized (0) were sampled in the early growth phase (day 25), 1 week before and 1 week after spike emergence. Aphids were added 16 days before sampling was carried out. In a separate experiment belowground respiration was measured on N and NP fertilized plant-soil systems with aphid treatments comparable to the first experiment. Aphids reduced numbers of rhizosphere bacteria and fungal feeding nematodes 1 week before spike emergence. Before spike emergence, aphids reduced belowground respiration in NP treatments. These findings strongly indicate that aphids reduced allocation of photoassimilates to roots and deposition of root exudates in the growth phase of the plant. Contrary to this, 1 week after spike emergence numbers of bacteria, fungal feeding nematodes and Protozoa were higher in rhizospheres of plants subjected to aphids probably because aphids enhanced root mortality and root decomposition. Protozoa and bacterial feeding nematodes were stimulated at different experimental conditions with nematodes being the dominant bacterial grazers at N fertilization and Protozoa in the NP treatment before spike emergence.

Analysis of Variance↗
PubMed2006

Mutualism in a community context: the positive feedback between an ant-aphid mutualism and a gall-making midge.

Although mutualisms are widespread and often described in natural history accounts, their ecological influences on other community members remain largely unexplored. Many of these influences are likely a result of indirect effects. In this field study, we investigated the indirect effects of an ant-aphid mutualism on the abundance, survival rates and parasitism rates of a co-occurring herbivore. Rabdophaga salicisbrassicoides (Diptera: Cecidomyiidae) induces rosette galls on the developing shoots of Salix exigua trees, and populations can reach outbreak densities (up to 1,000 galls/stem) in central Washington State (USA). Ant-tended aphids feed on these same stems and often feed on gall tissue. In this study we used a combination of manipulative experiments and observational surveys to test the hypothesis that the abundances of aphids, ants, and galls have positive and reciprocal effects on one another, in a manner that would create a positive feedback loop in population growth. In addition, we examined whether the combined presence of ants and aphids reduces parasitism rates for the gallers. In support of the positive feedback loop hypothesis, aphids enjoyed higher population growth rates in the presence of ants and galls, the presence of ants and aphids resulted in increased abundance of galls, and the abundances of ants, aphids and galls were all positively correlated with one another. However, the mechanism underlying the positive effect of ants and aphids on galler density remains unknown, as the mutualism did not affect parasitism rates. More broadly, this study demonstrates that mutualisms can have significant and complex indirect effects on community and population ecology.

Analysis of Variance↗
PubMed1998

Potyvirus aphid transmission requires helper component and homologous coat protein for maximal efficiency.

Aphid transmission of potyviruses depends on the presence of specific sequence domains in two virus encoded proteins, the coat protein (CP) and helper component-proteinase (HC-Pro). Aphid transmissable peanut stripe virus (PStV), like most potyviruses, has an Asp-Ala-Gly (DAG) motif in the amino-terminal part of the CP. Peanut Mottle Virus (PeMoV) was determined to be highly aphid transmissible but has a unique Asp-Ala-Ala-Ala (DAAA) motif. To determine if the DAAA motif could functionally replace the DAG motif in PStV, mutations were made in a full-length cDNA clone of PStV. All of the mutations in the CP DAG motif abolished aphid transmissibility of PStV but did not affect virus infectivity. The aphid transmissibility of the PStV-DAAA mutant was partially restored by feeding aphids an artificial diet containing purified virus and PeMoV HC-Pro. The PStV-DAAA virus was poorly transmitted by aphids in vitro with HC-Pro purified from PStV or tobacco vein mottling virus (TVMV) infected plants. These experiments support the theory that specific HC-Pro/CP interactions are required for efficient aphid transmission. Based upon the sequence comparisons of 16 potyviral HC-Pro proteins several conserved motifs and striking differences have been identified. PeMoV was determined to have an Ala-Ser-Cys (ASC) HC-Pro motif instead of a highly conserved Cys-Cys-Cys (CCC) motif. We have predicted that this CCC motif could play an important role in the specific interaction between the HC-Pro and the CP DAG motif.

Amino Acid Sequence↗
PubMed1996

Detection of stylet-borne and circulative potato viruses in aphids by duplex reverse transcription polymerase chain reaction.

A reverse transcription polymerase chain reaction (RT-PCR) assay was designed to amplify stylet-borne potato virus Yo (PVYo) in aphids using primers located in the viral capsid gene. A 480 bp long product was detected in aphids exposed to PVYo-infected potato plants. Approximately 40% of Myzus persicae and 15% of Aphis nasturtii exposed briefly to PVYo-infected plants acquired the virus. This rate of acquisition by both species of aphids was typical of our earlier observation of the virus transmission tests. No significant difference in virus detection was observed whether the aphids were tested immediately after exposure to virus sources or stored for up to 45 days in ethanol at room temperature. The addition of a second pair to primers located in the capsid gene of circulative potato leafroll virus (PLRV) allowed simultaneous amplification of two viruses (duplex RT-PCR) in single aphids. Acquisition of PVYo by the aphids already viruliferous with PLRV was significantly reduced, compared to aphids not carrying PLRV. Duplex RT-PCR for PVYo and PLRV could be applied to analyze aphids collected from the field to ascertain the relative presence of both viruses in a single test.

Animals↗