Virus mediated trophic interactions between aphids and their natural enemies

Microbial endosymbionts alter the phenotype of their host which may have cascading effects at both population and community levels. However, we currently lack information on whether the effects of viruses on both host phenotypic traits and host population demography can modify interactions with upper trophic levels. To fill this gap, we investigated whether a prevalent densovirus infecting the aphid Myzus persicae (i.e. MpDNV) can modify trophic interactions between host aphids and their natural enemies (i.e. predators and parasitoids) by influencing aphid phenotypic traits (i.e. body mass and defensive behaviours), population demography (i.e. density and age-structure) and susceptibility towards both predation and parasitism. We found that the virus decreased aphid body mass but did not influence their behavioural defences. At the population level, the virus had a minor effect on aphid adult mortality whereas it strongly reduced the density of nymphs and influenced the stage structure of aphid populations. In addition, the virus enhanced the susceptibility of aphids to parasitism regardless of the parasitoid species. Predation rate on adult aphids was not influenced by the virus but ladybeetle predators strongly decreased the number of aphid nymphs, especially for uninfected ones compared to infected ones. As a result, the virus decreased predator effect on aphid populations. By reducing both aphid quality and availability, increasing their susceptibility to parasitism, and modulating predator effect on aphid populations, we highlighted that viral endosymbionts can be prevalent drivers of their host ecology as they modify their phenotypes and interspecific interactions. These virus-mediated ecological effects may have consequences on enemies foraging strategies as well as trophic webs dynamics and structure.     

CHANGES IN THE TRANSMISSIBILITY BY APHIDS OF A STRAIN OF CUCUMBER MOSAIC VIRUS

A strain of cucumber mosaic virus isolated from a spinach plant in 1946 was readily transmitted by Myzus persicae until 1955 when it lost this property, although it was still being propagated in conditions in which other strains remained transmissible. M. circumflexus also transmitted other strains but not this one. It was transmitted as readily as other strains by Aphis gossypii and Myzus ascalonicus. M. ascalonicus transmitted less frequently than Aphis gossypii. Transmission of the spinach strain by other aphids did not make it transmissible by Myzus persicae ; nor did propagation in different plant species or several passages through spinach. In 1955 the spinach strain was occasionally transmitted by M. persicae , but the cultures isolated in this way were no more readily transmissible by the aphid than was the bulk culture maintained by manual inoculation of sap, and after a few weeks all cultures ceased to be transmitted by M. persicae.     

Over-wintering of aphids,especially Myzus persicae,Sulzer, in root clamps

Mangold clamps in many districts of the British Isles were found to provide overwintering sites for Myzus persicae (Sulz.), Hyperomyzns staphyleae (Koch) and Aulacorthum solani (Kalt.). After a severe winter, when other means of overwintering are few, clamps may be the most important source of Myzus persicae. Only Myzus ascalonicus Doncaster was found in swede clamps.
Factors affecting the infestation of clamped mangolds by M. persicae were the number of aphids on the crop when lifted, the methods of topping and clamping the roots, and the temperature in the clamp. M. persicae was introduced on the leaves, and close topping was often an efficient means of control. Close topping did not control Hyperomyzus staphyleae; normally, this aphid does not seem to be a root-feeding species, but with artificially colonized mangolds it fed on both exposed roots and foliage. It is not known how this species enters the clamps. The temperature in clamps was influenced by that of the outside air and the type of cover, but changes were long-term and did not reflect diurnal variations in external air temperature. Straw, covered with soil, was the best form of cover.
In addition to harbouring Myzus persicae , mangold clamps are also important sources of sugar-beet yellows virus.     

Inheritance of L1014F and M918T sodium channel mutations associated with pyrethroid resistance in Myzus persicae

Two amino acid substitutions (L1014F and M918T) in the voltage-gated sodium channel confer target-site resistance to pyrethroid insecticides in the peach potato aphid, Myzus persicae. Pyrethroid-resistant and -susceptible M. persicae clones with various combinations of these mutations were crossed under laboratory conditions, and the genotypes of aphid progeny were analysed by direct DNA sequencing of the IIS4-S6 region of the sodium channel gene. Segregation patterns showed that in aphids heterozygous for both L1014F and M918T, both mutations were present in the same resistance allele. Despite these mutations appearing largely recessive in other pest species, such aphids exhibited strong resistance to pyrethroids in leaf-dip bioassays. These results have important implications for the spread and management of pyrethroid resistance in field populations.     

Characterisation of a new virus from escarole

A new virus associated with mosaic, yellowing and necrotic symptoms in escarole has been isolated recently in southern Italy. The virus, for which the name escarole mosaic virus (EMV) is proposed, was transmissible by mechanical methods, by seeds and probably by pollen but not by Acyrthosiphon pisum, Aphis gossypii, Myzus persicae, Trialeurodes vaporariorum or Frankliniella occidentalis. The virions showed a single coat protein of about 32 kDa and eight encapsidated RNA species. Viral preparations sedimented as four components in sucrose density gradients. Electron microscopy indicated the presence of spherical particles with a diameter of 25 nm. Ultrastructural investigations on infected tissues revealed the formation of atypical inclusion bodies.     

The shallot aphis,Myzus ascalonicus Doncaster,and its behaviour as a vector of plant viruses

A new species of aphis, Myzus ascalonicus Doncaster, is briefly described, and compared with Myzus persicae Sulz., which it resembles superficially. It has been found on shallots in storage and on onions and other species of plants both in glasshouses and in the open between October and June. Its summer habits and hosts are unknown. In comparative virus transmission tests with M. persicae it was found that Myzus ascalonicus transmits dandelion yellow mosaic virus, which is not transmitted by Myzus persicae ; and also cucumber virus I, Hyoscyamus virus III and sugar-beet yellows virus, all of which are transmitted by M. persicae. Myzus ascalonicus does not transmit the viruses of potato Y severe etch, lettuce mosaic and sugar-beet mosaic which are transmitted by Myzus persicae.     

THE DETECTION OF CUCUMBER MOSAIC VIRUS IN SINGLE APHIDS

Abstract  Cucumber mosaic virus (CMV) was detected in single aphids Myzus persicae and Aphis gossy pii by dot immunobinding assay (DIBA). The DIB A procedure with the lowest detectable concentration endpoint of 0.16ng/ml of purified CMV, or 0. 32pg per sample dot of 2μI antigens, satisfied the sensitivity required for the detection of CMV in single virus-carrying aphids. The aphid extracting method of dipping the stylets dissected from aphid heads in the droplets of small volume (2–5p1) of suitable buffer not only ensured the highly concentrated Firuses fully released from the aphid stylets, but decreased the interference of non-virus materials from aphids to minimum as well, and thus overcame the two major difficulties in the detection of plant viruses in vectors. The virus-carrying rates tested by DIBA had good coincidence with the transmission rates by bioassay. Undoubtedly, such breakthroughs in the technique of detecting nonpersistent viruses in aphid vectors are of great epidemiological importance.     

Host quality of different aphid species for rearing Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae)

This study aimed to evaluate the quality of the aphid Myzus persicae (Sulzer), Lipaphis erysimi (Kaltenbach) and Brevicoryne brassicae (L.) as hosts for the parasitoid Diaeretiella rapae (McIntosh). Parasitization by D. rapae was higher on M. persicae than on L. erysimi and B. brassicae. The time of development of D. rapae from egg to mummy or egg to adult male or female were shorter on M. persicae than on L. erysimi and B. brassicae. Moreover, D. rapae showed no significant differences in the emergence rate, sex ratio and longevity when reared on the three aphid species. Myzus persicae was the largest aphid host, with B. brassicae and L. erysimi being of intermediate and of small size, respectively. Diaeretiella rapae reared on M. persicae was larger than when reared on L. erysimi and B. brassicae, and females of D. rapae were significantly larger than males on M. persicae, but males of D. rapae were larger than females when reared on L. erysimi. No difference in size was detected between males and females in parasitoids reared on B. brassicae. Among the aphid species studied, M. persicae was found to be the most suitable to D. rapae.     

Microsatellite marker analysis of peach-potato aphids (Myzus persicae, Homoptera: Aphididae) from Scottish suction traps

The peach-potato aphid Myzus persicae (Sulzer) is an important vector of plant viruses. A network of suction traps collects aerial samples of this aphid in order to monitor and help predict its spatial distribution and likely impact on virus transmission in crops. A suction trap catch is thought to be a good representation of the total aphid pool. Sensitive molecular markers have been developed that determine the genetic composition of the M. persicae population. In Scotland, UK, these were applied to field collections revealing a limited number of clones. Molecular markers are less successful when applied to specimens that have been preserved in an ethanol-based trap fluid designed to preserve morphology. An assessment of different DNA extraction and PCR techniques is presented and the most efficient are used to analyse M. persicae specimens caught in the Dundee suction trap in 2001, a year when exceptionally high numbers were caught. The results reveal that the majority of the M. persicae caught belonged to two highly insecticide resistant clones. In addition, it was possible to compare the relative frequencies of genotypes caught in the trap with those collected at insecticide treated and untreated field sites in the vicinity. These results indicate that, in addition to suction trap data, the ability to sample field sites provides valuable early warning data which have implications for pest control and virus management strategies.     

THE CORRELATION OF APHID NUMBERS WITH THE SPREAD OF LEAF ROLL AND RUGOSE MOSAIC IN POTATO CROPS

An analysis of the results of experiments in different parts of England and Wales from 1941 to 1947 on the spread of potato leaf roll and rugose mosaic showed that leaf roll spread was correlated with the number of alate Myzus persicae (Sulzer) caught on sticky traps throughout the potato-growing season; there was some correlation with the maximum count of M. persicae per 100 leaves, but this possibly results from the correlation between trapped aphids and the number per 100 leaves. Spread of rugose mosaic (potato virus Y) was correlated to a lesser degree with number of M, persicae , perhaps because other aphid species are often vectors. With both diseases higher correlations were obtained when the infected plants were dispersed among the healthy crop than when they were placed together in a row. It is concluded that it is possible to predict the average health of potato stocks in the following year from average trap data; further work may enable the health of individual stocks to be predicted.     

Effects of aphid alarm pheromone derivatives and related compounds on non- and semi-persistent plant virus transmission by Myzus persicae

A derivative, prepared from the aphid alarm pheromone (E)-β-farnesene and the saturated straight 14-carbon chain dialkyl ester of acetylene dicarboxylic acid, was the most active compound tested for inhibiting acquisition by the aphid Myzus persicae of the non-persistently transmitted potato virus Y (PVY). Derivatives lacking, or with shorter, or branched or partially-unsaturated carbon side-chains were less active. The one derivative tested also inhibited inoculation of PVY, and acquisition of beet mosaic virus (also non-persistent) and the semi-persistent beet yellows virus. However, it had no obvious effect on aphid probing behaviour; related compounds lacking the (E)-β-farnesene moiety also inhibited acquisition of PVY.     

Myzus persicae (green peach aphid) salivary components induce defence responses in Arabidopsis thaliana

Myzus persicae (green peach aphid) feeding on Arabidopsis thaliana induces a defence response, quantified as reduced aphid progeny production, in infested leaves but not in other parts of the plant. Similarly, infiltration of aphid saliva into Arabidopsis leaves causes only a local increase in aphid resistance. Further characterization of the defence-eliciting salivary components indicates that Arabidopsis recognizes a proteinaceous elicitor with a size between 3 and 10 kD. Genetic analysis using well-characterized Arabidopsis mutants shows that saliva-induced resistance against M. persicae is independent of the known defence signalling pathways involving salicylic acid, jasmonate and ethylene. Among 78 Arabidopsis genes that were induced by aphid saliva infiltration, 52 had been identified previously as aphid-induced, but few are responsive to the well-known plant defence signalling molecules salicylic acid and jasmonate. Quantitative PCR analyses confirm expression of saliva-induced genes. In particular, expression of a set of O -methyltransferases, which may be involved in the synthesis of aphid-repellent glucosinolates, was significantly up-regulated by both M. persicae feeding and treatment with aphid saliva. However, this did not correlate with increased production of 4-methoxyindol-3-ylmethylglucosinolate, suggesting that aphid salivary components trigger an Arabidopsis defence response that is independent of this aphid-deterrent glucosinolate.     

Some Hosts and Properties of a Potyvirus Infecting Vanilla fragrans (Orchidaceae) in the Kingdom of Tonga

Abstract A potyvirus was isolated from Vanilla fragrans exhibiting leaf distortion, chlorotic and necrotic lesions and vine die-back. The virus can be propagated in Nicotiana clevelandii and N. benthamiana and induces local lesions in Chenopodium amaranticolor and C. quinoa. The flexuous particles have a mean length of 765 nm, pinwheel inclusions are found in systemically infected N. benthamiana leaves and SDS-polyacrylamide gel electrophoresis indicates a single polypeptide of M 32.7 × 10³. The virus is transmissible from N. clevelandii to N. clevelandii by the aphid species Myzus persicae and Aphis gossypii. A polyclonal antiserum raised to the Tongan potyvirus failed to react, with the potyvirus associated with mosaic symptoms of V. tahitensis in French Polynesia and ISEM failed to detect any close relationship to 22 other potyviruses.     

桃蚜不同蚜型DNA多态性的RAPD研究

采用RAPD方法,对全周期桃蚜的有翅产雌性母蚜、无翅性母蚜、雄蚜、卵、干母、干雌、有翅迁移蚜等蚜型的DNA遗传多态性进行了分析。结果表明：卵的DNA多态性最大,性蚜次之,孤雌生殖蚜最小;卵与其它蚜型之间在遗传上具最大差异,其中与孤雌生蚜的差异大于与性蚜的;干母、干雌和迁移蚜之间的遗传关系最近。     

Microsatellite variation in cyclically parthenogenetic populations of Myzus persicae in south-eastern Australia

We examined the population structure of the introduced aphid, Myzus persicae collected mainly from its primary host, Prunus persica, in south-east Australia. Myzus persicae has been present in Australia since at least 1893. Samples were collected in the spring of 1998 from two mainland and three Tasmanian localities and isofemale lines were established in the laboratory. The reproductive mode (life cycle), karyotype and 17-locus microsatellite genotype of each clone were determined. All populations showed significant population differentiation (F(ST) 0.058-0.202) even over small geographic distances (<50 km). All clones were karyotypically normal except for a subset of clones from one site that was exposed to the carbamate insecticide, Pirimor, the week prior to sampling. Those clones were heterozygous for an autosomal 1,3 translocation frequently associated in M. persicae with insecticide resistance. In contrast to other loci and despite being on different chromosomes, loci myz2(A) and M55(A) showed general and significant linkage disequilibrium. These loci may be affected by epistatic selection. We discuss the observed high clonal diversity, moderate but significant population differentiation, general conformance to Hardy-Weinberg equilibria and low linkage disequilibria with particular focus on the global population biology of M. persicae.     

Azadirachta indica metabolites interfere with the host-endosymbiont relationship and inhibit the transmission of potato leafroll virus by Myzus persicae

The effects of neem (Azadirachta indica A. Juss) seed kernel extracts (NSKE) and azadirachtin on the ability of Myzus persicae (Sulz.) to transmit potato leafroll luteovirus (PLRV) was studied. Moreover, it was investigated whether treatments with these compounds would exert an effect on larval growth and mortality, and on the aphid intracellular symbionts. Endosymbiotic bacteria play an essential role in the performance of aphids, and in luteovirus transmission by aphids. NSKE and azadirachtin were offered to one-day-old M. persicae nymphs via a membrane feeding system. The neem metabolites displayed a 100% mortality at doses higher than 2560 ppm. At intermediate doses, ranging between 320 and 2560 ppm, larval growth and mortality were affected in a dose-dependent manner. The transmission of PLRV by M. persicae was inhibited by 55–90%. The endosymbiont population of the aphid was clearly affected by a treatment with neem metabolites as the release of their most abundant protein, Buchnera GroEL, into the haemocoel of the aphid was inhibited. Moreover, morphological aberrations on the bacterial endosymbionts were observed in aphids which fed on 2560 ppm of azadirachtin. At doses lower than 160 ppm of NSKE or azadirachtin, the endosymbiont population of M. persicae, and mortality, growth and feeding behaviour were similar to that of the untreated groups of aphids. However, PLRV transmission was still inhibited by 40–70%. The possible targets of the neem metabolites in the aphid are discussed.     

Recent changes in the distribution of carboxylesterase genes and associated chromosomal rearrangements in Greek populations of the tobacco aphid Myzus persicae nicotianae

We present data on the frequency of amplified E4 and FE4 carboxylesterase genes in Myzus persicae s.l. clones collected during the years 2002–2007 and 2012 in Greece. Most clones were of the tobacco aphid, Myzus persicae nicotianae. Samples from 2012 were genotyped with microsatellite DNA markers and a number of them were karyotyped. Aphid clones with amplified FE4 genes predominated in all years, whereas E4 was present in only 3.5% of all samples and always occurred in clones with FE4. Most of the clones examined showed high carboxylesterase activity levels (R2 resistant category). The results showed marked changes in the frequencies of the two carboxylesterase genes in the tobacco aphid populations compared to published data that were collected in Greece in the mid 1990s, when E4 was recorded on its own in 20% of all samples and in 32% of samples from tobacco. A parallel change in karyotype was also observed because the A1,3 translocation, which had a worldwide association with amplified E4 genes in the 1990s, was not detected in the clones analyzed in 2012. Possible causes for these changes are discussed, although selection as a result of pest management practices appears to be the major one. Novel chromosomal rearrangements were also found in M. persicae nicotianae clones. These rearrangements could be a result of clastogenic effects of nicotine, which could persist because of the holocentric nature of aphid chromosomes. The results are discussed in relation to rapid evolution events that have taken place in the tobacco aphid in Greece during the last two decades. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 455–470.     

Volatiles from potato plants infected with potato leafroll virus attract and arrest the virus vector, Myzus persicae (Homoptera: Aphididae)

The influence of viral disease symptoms on the behaviour of virus vectors has implications for disease epidemiology. Here we show that previously reported preferential colonization of potatoes infected by potato leafroll virus (genus Polerovirus) (luteovirus) (PLRV) by alatae of Myzus persicae, the principal aphid vector of PLRV, is influenced by volatile emissions from PLRV-infected plants. First, in our bioassays both differential immigration and emigration were involved in preferential colonization by aphids of PLRV-infected plants. Second, M. persicae apterae aggregated preferentially, on screening above leaflets of PLRV-infected potatoes as compared with leaflets from uninfected plants, or from plants infected with potato virus X (PVX) or potato virus Y (PVY). Third, the aphids aggregated preferentially on screening over leaflet models treated with volatiles collected from PLRV-infected plants as compared with those collected from uninfected plants. The specific cues eliciting the aphid responses were not determined, but differences between headspace volatiles of infected and uninfected plants suggest possible ones.     

Resistance of potato cultivars to Myzus persicae (Sulz.) (Hemiptera: Aphididae)

Aphids are the most important vectors of viruses infecting potato (Solanum tuberosum). We focused on the response of the aphid vector Myzus persicae (Sulzer) to five commercial potatocultivars: ágata, Jaette Bintje, Mondial, Monalisa and Santè, by traditional antibiosis and antixenosis tests and by the EPG (Electrical Penetration Graph) technique, as a step forward to the design of effective management practices. Our aim was to identify plant factors involved in resistance of these cultivars against M. persicae, both at the surface and in deeper plant tissues. Results from the antixenosis test confirmed a strong preference of M. persicae for the Mondial cultivar. The antibiosis study indicated a lower population development of the aphid in 'Monalisa' when compared to 'ágata' and 'Jaette Bintje'. EPG assays indicated that 'Santè' inhibited the initial feeding process of M. persicae, whereas 'Monalisa' showed a physical-type of resistance as demonstrated by a very high number of short probes. The cultivar Mondial showed average values for all EPG variables analyzed. The behavior in 'Jaette Bintje' indicated this cultivar was an ideal host for aphid feeding and reproduction. Together, the EPG data revealed the existence of pre and post-phloematics factors in the cultivars under study, which have important implications on the efficiency of transmission and spread of virus in potato by M. persicae.