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PubMed2005

Interactions among three species of cereal aphids simultaneously infesting wheat.

Interactions among greenbug, Schizaphis graminum (Rondani), Russian wheat aphid, Diuraphis noxia (Mordvilko), and bird cherry-oat aphid Rhopalosiphum padi (L.) were examined on wheat plants (Triticum aestivum L., cultivar TAM 107). Nymphs were released on the plants as conspecific and heterospecific pairs of either first or fourth instars and evaluated for survival, developmental time, fecundity, intra-plant movement, and affinity to plant tissues. Survival from first instar to onset of reproduction averaged 90-100% across all pair combinations. Diuraphis noxia developed faster as conspecifics than in any heterospecific combination, and faster as conspecifics feeding on the same plant tissue than on different tissues. Fecundity of S. graminum was higher for conspecifics that developed on the same plant tissue than for those feeding separately. There was evidence of amensalism (one species was harmed while the other was unaffected) in that D. noxia experienced delayed development feeding in tandem with S. graminum, and reduced fecundity with both S. graminum and R. padi. Furthermore, S. graminum nymphs had reduced survival when their mothers matured on a same plant with R. padi. Both D. noxia and R. padi changed position on the plant more often when developing with S. graminum. Survival of second generation S. graminum nymphs was reduced when this species developed and reproduced in tandem with R. padi. Preferred feeding locations were S. graminum--primary leaf, D. noxia--tertiary leaf and R. padi--stem and these were not altered in any heterospecific combinations. Heterospecific aphids had no impact on fecundity or progeny survival in any species combination when fourth instars matured and reproduced on plants not previously exposed to aphid feeding, supporting the inference that systemic, aphid-induced changes in plant physiology mediated the effects observed when first instars developed and reproduced on the same plants.

Animals↗
PubMed2006

Heterologous expression of the Mi-1.2 gene from tomato confers resistance against nematodes but not aphids in eggplant.

The Mi-1.2 gene in tomato (Solanum lycopersicum) is a member of the nucleotide-binding leucine-rich repeat (NBLRR) class of plant resistance genes, and confers resistance against root-knot nematodes (Meloidogyne spp.), the potato aphid (Macrosiphum euphorbiae), and the sweet potato whitefly (Bemisia tabaci). Mi-1.2 mediates a rapid local defensive response at the site of infection, although the signaling and defensive pathways required for resistance are largely unknown. In this study, eggplant (S. melongena) was transformed with Mi-1.2 to determine whether this gene can function in a genetic background other than tomato. Eggplants that carried Mi-1.2 displayed resistance to the root-knot nematode Meloidogyne javanica but were fully susceptible to the potato aphid, whereas a susceptible tomato line transformed with the same transgene was resistant to nematodes and aphids. This study shows that Mi-1.2 can confer nematode resistance in another Solanaceous species. It also indicates that the requirements for Mi-mediated aphid and nematode resistance differ. Potentially, aphid resistance requires additional genes that are not conserved between tomato and eggplant.

Animals↗
PubMed2001

Multiple routes to asexuality in an aphid species.

Cyclical parthenogens, including aphids, are important models for studying the evolution of sex. However, little is known about transitions to asexuality in aphids, although the mode of origin of asexual lineages has important consequences for their level of genetic diversity, ecological adaptability and the outcome of competition with their sexual relatives. Thus, we surveyed nuclear, mitochondrial and biological data obtained on cyclical and obligate parthenogens of the bird cherry-oat aphid, Rhopalosiphum padi (L), to investigate the frequency of transitions from sexuality to permanent asexuality. Many instances of asexual lineages retaining the ability to produce males are known in aphids, so particular attention was paid to the existence of occasional matings between females from sexual lineages and males produced by asexual lineages, which have the potential to produce new asexual lineages. Phylogenetic inference based on microsatellite and mitochondrial data indicates at least three independent origins of asexuality in R. padi, yielding the strongest evidence to date for multiple origins of asexuality in an aphid. Moreover, several lines of evidence demonstrate that transitions to asexuality result from two mechanisms: a complete spontaneous loss of sex and repeated gene flow from essentially asexual lineages into sexual ones.

Animals↗
PubMed2005

The landscape context of cereal aphid-parasitoid interactions.

Analyses at multiple spatial scales may show how important ecosystem services such as biological control are determined by processes acting on the landscape scale. We examined cereal aphid-parasitoid interactions in wheat fields in agricultural landscapes differing in structural complexity (32-100% arable land). Complex landscapes were associated with increased aphid mortality resulting from parasitism, but also with higher aphid colonization, thereby counterbalancing possible biological control by parasitoids and lastly resulting in similar aphid densities across landscapes. Thus, undisturbed perennial habitats appeared to enhance both pests and natural enemies. Analyses at multiple spatial scales (landscape sectors of 0.5-6 km diameter) showed that correlations between parasitism and percentage of arable land were significant at scales of 0.5-2 km, whereas aphid densities responded to percentage of arable land at scales of 1-6 km diameter. Hence, the higher trophic level populations appeared to be determined by smaller landscape sectors owing to dispersal limitation, showing the 'functional spatial scale' for species-specific landscape management.

Animals↗
PubMed2005

Resistance is costly: trade-offs between immunity, fecundity and survival in the pea aphid.

Parasitoids are among the most important natural enemies of insects in many environments. Acyrthosiphon pisum, the pea aphid, is a common pest of the leguminous crops in temperate regions. Pea aphids are frequently attacked by a range of endoparasitic wasps, including the common aphidiine, Aphidius ervi. Immunity to parasitoid attack is thought to involve secondary symbiotic bacteria, the presence of which is associated with the death of the parasitoid egg. It has been suggested that there is a fecundity cost of resistance, as individuals carrying the secondary symbionts associated with parasitoid resistance have fewer offspring. Supporting this hypothesis, we find a positive relationship between fecundity and susceptibility to parasitoid attack. There is also a negative relationship between fecundity and off-plant survival time (which positively correlates with resistance to parasitoid attack). Taken together, these results suggest that the aphids can either invest in defence (parasitoid resistance, increased off-plant survival time) or reproduction, and speculate that this may be mediated by changes in the aphids' endosymbiont fauna. Furthermore, there is a positive relationship between aphid size and resistance, suggesting that successful resistance to parasitoid attack may involve physical, as well as physiological, defences.

Analysis of Variance↗
PubMed1975

Polyamino acid induced aphid transmission of plant viruses.

Aphids transmitted poly-L-ornithine (PLO)-treated tobacco mosaic virus (TMV) when given acquistion and inoculation access periods as brief as 30 s and 2 min, respectively; the ability to transmit was lost within 90 min. Aphids without claws were able to transmit the virus. Transmission thus seems similar to that of nonpersistent viruses. The ratio of virus to polyamino acid, as well as the KCl concentration, markedly affected transmission. Transmission was best from mixtures which contained 250 mug/ml TMV, 2-5 MUG/ML PLO (mol. wt. 120000) and 0-6 M-KCl. A similar mixture favoured transmission when poly-L-lysine (mol. wt. 85000) was substituted for PLO, but with poly-L-lysine (mol. wt. 30 000) it was necessary to decrease the KCl to 0-3 M to obtain transmission. Less KCl (0-08 to 0-24 M) also favoured aphid transmission of PLO-treated potato virus X and tobacco rattle virus. PLO-treated TMV ultracentrifuged in the presence of, and resuspended in, 0-6 M-KCl remained aphid transmissible while PLO-treated virus in 2 M-DCl, which favours greater dissociation of the virus-PLO complex, was transmissible neither before nor after sedimentation by ultracentrifuging, and resuspension in 0-6 M-KCl. these results show that transmissibility is not due to a permanent alteration of the virus by PLO and indicate that the formation of a TMV-PLO complex is required for transmission. Sequential acquisition experiments suggest that PLO may act by binding TMV to receptor sites in aphids. However, the possibility that PLO affects the infection process was not ruled out.

Animals↗
PubMed1994

Mutations in the helper component protease gene of zucchini yellow mosaic virus affect its ability to mediate aphid transmissibility.

The nucleotide sequence of the helper component protease (HC-Pro) genes of three zucchini yellow mosaic virus (ZYMV) strains has been compared with that of a helper-deficient strain of ZYMV-HC. The comparisons revealed three unique deduced amino acid differences. Two of these mutations were located in regions which are conserved in other potyviruses. The role of these mutations in aphid transmissibility was examined by exchanging DNA fragments of part of the deficient HC-Pro gene with the respective section within the gene of the infectious full-length clone of the aphid-transmissible ZYMV. The first exchange included two of the three mutations, the first coding for a change from Asp to Gly (in a non-conserved region) and the second coding for a change from Arg to Ile [within the Phe-Arg-Asp-Lys (FRNK) conserved box]. This exchange resulted in a reduced transmission (20.6% for the mutated virus compared with 57.4% in the normal ZYMV when acquired from plants and 37.2% compared with 83.1%, respectively, when acquired from membranes). The second exchange incorporated a single mutation [conferring a change from Thr to Ala within the Pro-Thr-Lys (PTK) conserved box]. This single mutation resulted in almost total loss of HC activity in aphid transmission both from plants and from membranes. The Lys residue in the conserved Lys-Ile-Thr-Cys (KITC) box, which is related to loss of HC activity in potato virus Y, tobacco vein mottling virus and in the Michigan strain of ZYMV, is unchanged in the helper-deficient ZYMV. It is therefore proposed that more than one site in HC-Pro may be functionally related to aphid transmissibility. The possible reasons for the role of these mutations in helper activity in aphid transmission of ZYMV are discussed.

Amino Acid Sequence↗
PubMed1996

Switches in the mode of transmission select for or against a poorly aphid-transmissible strain of potato virus Y with reduced helper component and virus accumulation.

A poorly aphid-transmissible potato virus Y (PVY-PAT) variant emerged after several cycles of mechanical transmission of an initially aphid-transmissible (AT) isolate. Sequence analysis of the N-terminal region of the helper component-proteinase (HC-Pro) gene revealed a Lys to Glu change at a position previously found to abolish the HC-Pro aphid transmission activity in several potyviruses. Two cycles of aphid transmission allowed the virus population to evolve towards an AT form (PVY-ATnew) where a Glu to Lys change was observed. PVY-PAT produced lower amounts of coat protein and the accumulation of its HC-Pro in infected plants decreased from 7 to 28 days post-inoculation, as compared to PVY-ATnew. RT-PCR and restriction analysis showed that the two virus populations co-existed in the PVY-AT isolate and that the AT form was counter-selected during mechanical transmission. These observations suggest that the Lys to Glu substitution leads to decreased stability of HC-Pro resulting in poor transmissions by aphids, and further strengthen the idea that HC-Pro is involved in the accumulation of potyvirus in infected plants.

Amino Acid Sequence↗
PubMed2005

Premature leaf senescence modulated by the Arabidopsis PHYTOALEXIN DEFICIENT4 gene is associated with defense against the phloem-feeding green peach aphid.

Aphids, which are phloem-feeding insects, cause extensive loss of plant productivity and are vectors of plant viruses. Aphid feeding causes changes in resource allocation in the host, resulting in an increase in flow of nutrients to the insect-infested tissue. We hypothesized that leaf senescence, which is involved in the programmed degradation of cellular components and the export of nutrients out of the senescing leaf, could be utilized by plants to limit aphid growth. Using Arabidopsis (Arabidopsis thaliana) and green peach aphid (GPA; Myzus persicae Sulzer), we found that GPA feeding induced premature chlorosis and cell death, and increased the expression of SENESCENCE ASSOCIATED GENES (SAGs), all hallmarks of leaf senescence. Hypersenescence was accompanied by enhanced resistance against GPA in the Arabidopsis constitutive expresser of PR genes5 and suppressor of SA insensitivity2 mutant plants. In contrast, resistance against GPA was compromised in the phytoalexin deficient4 (pad4) mutant plant. The PAD4 gene, which is expressed at elevated level in response to GPA feeding, modulates the GPA feeding-induced leaf senescence. In comparison to the wild-type plant, GPA feeding-induced chlorophyll loss, cell death, and SAG expression were delayed in the pad4 mutant. Although PAD4 is associated with camalexin synthesis and salicylic acid (SA) signaling, camalexin and SA signaling are not important for restricting GPA growth; growth of GPA on the camalexin-biosynthesis mutant, pad3, and the SA deficient2 and NahG plants and the SA-signaling mutant, nonexpresser of PR genes1, were comparable to that on the wild-type plant. Our results suggest that PAD4 modulates the activation of senescence in the aphid-infested leaves, which contributes to basal resistance to GPA.

Animals↗
PubMed1990

Chimeric tomato plants show that aphid resistance and triacylglucose production are epidermal autonomous characters.

Graft chimeras were generated using Lycopersicon pennellii and L. esculentum to determine the contribution of the three meristem layers (L1, L2, and L3) to trichome density, sugar ester production, and aphid resistance. Sugar esters, in the form of triacylglucoses, have been implicated in the aphid resistance of pennellii. One chimera possessed the epidermal layer (L1) of pennellii and the internal tissues (L2 and L3) of the aphid-susceptible esculentum. The second chimera had both the L1 and L2 of pennellii and the L3 of esculentum. Type IV trichome densities did not differ significantly among the chimeras and pennellii. Both chimeras accumulated sugar esters with similar sugar and fatty acid composition as pennellii. The concentration of epicuticular sugar ester on the chimeras was also comparable with that of pennellii. Leaf cage and feeding studies demonstrated that both chimeras are as resistant to aphids as is pennellii. The resistance could be reduced similarly on all three types of plants by removal of the type IV trichome exudate. These results indicate that the presence and density of the type IV trichomes and the amount and type of sugar esters produced are features determined by the genotype of the epidermis. These epidermal features are sufficient to account for the aphid resistance observed in pennellii.

Animals↗
PubMed1987

Honeydew of aphids as a source of sugar for Phlebotomus ariasi.

Wild-caught Phlebotomus ariasi Tonnoir, starved until their sugar meals had been digested, were caged for 24 h with plants or plants infested with aphids and then tested for fructose, a constituent of plant sap. No evidence was found that the flies took sap directly from nine types of plants present in their habitat. About two-thirds of flies caged with oak (Quercus ilex L.) infested with an aphid [Lachnus roboris (L.)] and about a fifth kept with leaves of the french bean (Phaseolus vulgaris L.) infested with an aphid took honeydew. Experiments with three other aphid species gave negative results. Of sandflies caught in an oak tree infested with aphids, half of the females and three-quarters of the males contained fructose. Tests on females caught in a house and grouped according to state of engorgement showed that, having taken blood, the females stop taking sugar until the bloodmeal is completely digested. It is predicted that honeydews are important in the development of Leishmania infantum Nicolle in the gut of P. ariasi.

Animals↗
PubMed2006

Functional genomics of Buchnera and the ecology of aphid hosts.

In many animal groups, mutualistic bacterial symbionts play a central role in host ecology, by provisioning rare nutrients and thus enabling specialization on restricted diets. Among such symbionts, genomic studies are most advanced for Buchnera, the obligate symbiont of aphids, which feed on phloem sap. The contents of the highly reduced Buchnera genomes have verified its role in aphid nutrition. Comparisons of Buchnera gene sets indicate ongoing, irreversible gene losses that are expected to affect aphid nutritional needs. Furthermore, almost all regulatory genes have been eliminated, raising the question of whether and how gene expression responds to environmental change. Microarray studies on genome-wide expression indicate that Buchnera has evolved some constitutive changes in gene expression: homologues of heat stress genes have elevated transcript levels in Buchnera (relative to other bacteria) even in the absence of stress. Additionally, the microarray results indicate that responses to heat stress and to amino acid availability are both few and modest. Observed responses are consistent with control by the few ancestral regulators retained in the genome. Initial studies on the role of host genes in mediating the symbiosis reveal distinctive expression patterns in host cells harbouring Buchnera. In the near future, a complete genome of pea aphid will accelerate progress in understanding the functional integration of aphid and Buchnera genomes. Although information for other insect symbioses is relatively limited, studies on symbionts of carpenter ants and tsetse flies indicate many similarities to Buchnera.

Animal Feed↗
PubMed2001

Secondary intracellular symbiotic bacteria in aphids of the genus Yamatocallis (Homoptera: Aphididae: Drepanosiphinae).

A novel secondary intracellular symbiotic bacterium from aphids of the genus Yamatocallis (subfamily Drepanosiphinae) was characterized by using molecular phylogenetic analysis, in situ hybridization, and diagnostic PCR detection. In the aphid tissues, this bacterium (tentatively designated YSMS [Yamatocallis secondary mycetocyte symbiont]) was found specifically in large cells surrounded by primary mycetocytes harboring Buchnera cells. Of nine drepanosiphine aphids examined, YSMS was detected in only two species of the same genus, Yamatocallis tokyoensis and Yamatocallis hirayamae. In natural populations of these aphids, YSMS was present in 100% of the individuals. Phylogenetic analysis based on 16S ribosomal DNA (rDNA) sequences demonstrated that YSMS of Y. tokyoensis and Y. hirayamae constitute a distinct and isolated clade in the gamma subdivision of the class Proteobacteria. No 16S rDNA sequences of secondary endosymbionts characterized so far from other aphids showed phylogenetic affinity to YSMS. Based on these results, I suggest that YSMS was acquired by an ancestor of the genus Yamatocallis and has been conserved throughout the evolution of the lineage. By using the nucleotide substitution rate for 16S rDNA of Buchnera spp., the time of acquisition of YSMS was estimated to be about 13 to 26 million years ago, in the Miocene epoch of the Tertiary period.

Animals↗
PubMed2005

Rickettsia symbiont in the pea aphid Acyrthosiphon pisum: novel cellular tropism, effect on host fitness, and interaction with the essential symbiont Buchnera.

In natural populations of the pea aphid Acyrthosiphon pisum, a facultative bacterial symbiont of the genus Rickettsia has been detected at considerable infection frequencies worldwide. We investigated the effects of the Rickettsia symbiont on the host aphid and also on the coexisting essential symbiont Buchnera. In situ hybridization revealed that the Rickettsia symbiont was specifically localized in two types of host cells specialized for endosymbiosis: secondary mycetocytes and sheath cells. Electron microscopy identified bacterial rods, about 2 mum long and 0.5 mum thick, in sheath cells of Rickettsia-infected aphids. Virus-like particles were sometimes observed in association with the bacterial cells. By an antibiotic treatment, we generated Rickettsia-infected and Rickettsia-eliminated aphid strains with an identical genetic background. Comparison of these strains revealed that Rickettsia infection negatively affected some components of the host fitness. Quantitative PCR analysis of the bacterial population dynamics identified a remarkable interaction between the coexisting symbionts: Buchnera population was significantly suppressed in the presence of Rickettsia, particularly at the young adult stage, when the aphid most actively reproduces. On the basis of these results, we discussed the possible mechanisms that enable the prevalence of Rickettsia infection in natural host populations in spite of the negative fitness effects observed in the laboratory.

Animals↗
PubMed2006

Host plant selection by aphids: behavioral, evolutionary, and applied perspectives.

As phloem feeders and major vectors of plant viruses, aphids are important pests of agricultural and horticultural crops worldwide. The processes of aphid settling and reproduction on plants therefore have a direct economic impact, and a better understanding of these events may lead to improved management strategies. Aphids are also important model organisms in the analysis of population differentiation and speciation in animals, and new ideas on plant utilization influence our understanding of the mechanisms generating biological diversity. Recent research suggests that the dominant cues controlling plant preference and initiation of reproduction are detected early during the stylet penetration process, well before the nutrient supply (phloem) is contacted. Aphids regularly puncture cells along the stylet pathway and ingest cytosolic samples, and the cues stimulating settling and parturition likely are metabolites present in peripheral (nonvascular) plant cells. We discuss these findings and their implications for aphid evolution and management.

Animals↗
PubMed2003

Luteovirus-aphid interactions.

Members of the Luteoviridae are transmitted by aphids in a circulative, nonpropagative manner that requires the virus to be acquired through gut tissue into the aphid hemocoel and then exit through salivary tissues. This process is aphid species-specific and involves specific recognition of the virus by unidentified components on the membranes of gut and salivary tissues. Transport through the tissues is an endocytosis/exocytosis process. Both structural proteins of the virus are involved in the transmission process, with multiple protein domains regulating the movement and survival of the virus in the aphid and plant. Here we review what is known about the genetic, cellular, and molecular mechanisms regulating these complex and specific virus-aphid interactions.

Animals↗
PubMed2006

Dispersal strategies of phytophagous insects at a local scale: adaptive potential of aphids in an agricultural environment.

BACKGROUND: The spread of agriculture greatly modified the selective pressures exerted by plants on phytophagous insects, by providing these insects with a high-level resource, structured in time and space. The life history, behavioural and physiological traits of some insect species may have evolved in response to these changes, allowing them to crowd on crops and to become agricultural pests. Dispersal, which is one of these traits, is a key concept in evolutionary biology but has been over-simplified in most theoretical studies. We evaluated the impact of the local-scale dispersal strategy of phytophagous insects on their fitness, using an individual-based model to simulate population dynamics and dispersal between leaves and plants, by walking and flying, of the aphid Aphis gossypii, a major agricultural pest, in a melon field. We compared the optimal values for dispersal parameters in the model with the corresponding observed values in experimental trials. RESULTS: We show that the rates of walking and flying disperser production on leaves were the most important traits determining the fitness criteria, whereas dispersal distance and the clustering of flying dispersers on the target plant had no effect. We further show that the effect of dispersal parameters on aphid fitness depended strongly on plant characteristics. CONCLUSION: Parameters defining the dispersal strategies of aphids at a local scale are key components of the fitness of these insects and may thus be essential in the adaptation to agricultural environments that are structured in space and time. Moreover, the fact that the effect of dispersal parameters on aphid fitness depends strongly on plant characteristics suggests that traits defining aphid dispersal strategies may be a cornerstone of host-plant specialization.

Adaptation, Physiological↗
PubMed2001

Oxidative responses of resistant and susceptible cereal leaves to symptomatic and nonsymptomatic cereal aphid (Hemiptera: Aphididae) feeding.

The impact of the leaf-chlorosis-eliciting Russian wheat aphid, Diuraphis noxia (Mordvilko), and the nonchlorosis-eliciting bird cherry-oat aphid, Rhopalosiphum padi (L.), feeding on D. noxia-susceptible and -resistant cereals was examined during the period (i.e., 3, 6, and 9 d after aphid infestation) that leaf chlorosis developed. After aphid number, leaf rolling and chlorosis ratings, and fresh leaf weight were recorded on each sampling date, total protein content, peroxidase, catalase, and polyphenol oxidase activities of each plant sample were determined spectrophotometrically. Although R. padi and D. noxia feeding caused significant increase of total protein content in comparison with the control cereal leaves, the difference in total protein content between R. padi and D. noxia-infested leaves was not significant. Although R. padi-feeding did not elicit any changes of peroxidase specific activity in any of the four cereals in comparison with the control leaves, D. noxia feeding elicited greater increases of peroxidase specific activity only on resistant 'Halt' wheat (Triticum aestivum L.) and susceptible 'Morex' barley (Hordeum vulgare L.), but not on susceptible 'Arapahoe' and resistant 'Border' oat (Avena sativa L.). D. noxia-feeding elicited a ninefold increase in peroxidase specific activity on Morex barley and a threefold on Halt wheat 9 d after the initial infestation in comparison with control leaves. Furthermore, D. noxia feeding did not elicit any differential changes of catalase and polyphenol oxidase activities in comparison with either R. padi feeding or control leaves. The findings suggest that D. noxia feeding probably results in oxidative stress in plants. Moderate increase of peroxidase activity (approximately threefold) in resistant Halt compared with susceptible Arapahoe wheat might have contributed to its resistance to D. noxia, whereas the ninefold peroxidase activity increase may have possibly contributed to barley's susceptibility. Different enzymatic responses in wheat, barley, and oat to D. noxia and R. padi feeding indicate the cereals have different mechanisms of aphid resistance.

Animals↗